Antibacterial activity of aztreonam: a synthetic monobactam. A comparative study with thirteen other antibiotics

The in vitro activity of aztreoman (SQ 26, 776), a new monocyclic beta-lactam antimicrobial agent, was determined against 1720 bacteria, all clinical isolates, and compared with that of thirteen beta-lactam and aminoglycoside antibiotics. Aztreonam inhibited 90% of Citrobacter diversus, Citrobacter freundii, Enterobacter agglomerans, E. coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus morganii, Proteus rettgeri, Proteus vulgaris and Salmonella sp. by less than or equal to 0.4 micrograms ml-1. This activity was superior to moxalactam, piperacillin, cefamandole, cefoperazone, cefoxitin, cefsulodin, ceftazidime and aminoglycoside antibiotics. Aztreonam was as active as moxalactam against Enterobacter aerogenes, Enterobacter cloacae and Shigella species. Pseudomonas aeruginosa strains resistant to moxalactam, piperacillin, cefamandole, cefoperazone, cefotaxime, cefoxitin, cefsulodin and ceftazidime were inhibited by aztreonam 50% by 6.3 micrograms ml-1 and 90% by 16 micrograms ml-1. Aztreonam was as active as ceftazidime against Serratia marcescens, all strains were inhibited by 3.1 micrograms ml-1 and 90% by 1.6 micrograms ml-1. There was no major difference between MBC and MIC values of aztreonam and the effect of inoculum size upon MIC values was observed at 10(7) CFU.     

Antibiotic activity and synergism of ceftazidime and netilmicin against gram-negative pathogenic bacteria

The in vitro activity of ceftazidime and netilmicin against gram-negative bacteria often causing hospital infections was evaluated and furthermore synergistic effects of these antibiotics were studied. Ceftazidime was as active as netilmicin against Enterobacteriaceae, e.g. Enterobacter, Klebsiella, Morganella inhibiting 90% of these strains at concentrations from 0.5 to 4 micrograms/ml. Ceftazidime was the most effective agent against Pseudomonas aeruginosa, being even more active than cefsulodin, with a mean minimal inhibitory concentration (MIC) of 4.57 micrograms/ml (median 2.0 micrograms/ml), also inhibiting cefoperazone- and cefsulodin-resistant Pseudomonas. There was at most a two-fold difference in either MIC or minimal bactericidal concentration (MBC). In all genera tested an increase of the inoculum size from 10(4) to 5 X 10(6) colony forming units had minimal effects upon the MIC or MBC of ceftazidime and there was no decrease of the MIC in the presence of clavulanic acid or sulbactam. When ceftazidime and netilmicin were combined synergism was observed against all strains tested.     

In vitro activity of aztreonam, cefuroxime and ceftazidime against gram-negative rods isolated from hospital patients with urinary tract infection

The in vitro activity of aztreonam, cefuroxime and ceftazidime was determined against 2,372 Gram-negative rods (including Pseudomonas spp.) isolated from hospital patients with urinary tract infections during 1985. Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique in Mueller-Hinton agar. The inoculum used was approximately 10(5) colony forming units (cfu) contained in 10 microliter Mueller-Hinton broth, which was applied to the surface of the agar plates using a multipoint inoculator. Following inoculation plates were incubated aerobically at 37 degrees C for 18 h. The MIC of each antimicrobial for each organism examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum. The minimum concentration required to inhibit the growth of 90% (MIC90) of the bacterial isolates in each genus or species examined was also determined. In general the antibacterial spectrum of aztreonam was comparable to that of ceftazidime and superior to that of cefuroxime. Against Escherichia coli, which accounted for 72% of the isolates examined, aztreonam (MIC90 less than or equal to 0.25 microgram/ml) was slightly more active than ceftazidime (MIC90 0.5 microgram/ml) and considerably more active than cefuroxime (MIC90 8 micrograms/ml). Aztreonam was active against Pseudomonas spp. (MIC90 16 micrograms/ml), although somewhat less so than ceftazidime (MIC90 4 micrograms/ml). Cefuroxime showed low activity against this genus (MIC90 greater than 128 micrograms/ml).     

Clinical study of cefpodoxime proxetil dry syrup for skin and soft tissue infections in the field of pediatrics

Concurrently with administering a newly developed cephem derivative antibiotic (CEP), cefpodoxime proxetil (CPDX-PR, CS-807) dry syrup, to children with skin and soft tissue infections, activities of 7 drugs against a group of microorganisms were tested. The drugs tested included 4 drugs of the cephem group, R-3746, a Na-salt form of CPDX, cefaclor (CCL), cephalexin (CEX) and cefadroxil (CDX), and 3 drugs of the penicillin group, ampicillin (ABPC), methicillin (DMPPC) and cloxacillin (MCIPC). The bacterial strains tested were 71 strains of Staphylococcus aureus and 1 strain of Streptococcus pyogenes, all isolated from the above cases of pediatric infections. Inoculum sizes used in these tests were 10(6) and 10(8) cfu/ml. Ages of children in those cases to which the drug was administered ranged from 2 months to 15 years. A total of 66 cases were treated, including 60 cases of impetigo, 5 cases of subcutaneous abscess and 1 case of phlegmon. The drug was administered for an average of 6 days with a daily average dose level of 9.4 mg/kg divided into 3 doses except 1 case where a twice daily dose regimen was used. Clinical and bacteriological effects were examined, and the occurrence of adverse reactions and abnormal laboratory test results were recorded. The results of these tests are summarized below. 1. The activity test for R-3746 (Na-salt of CPDX) against 71 strains of S. aureus performed at an inoculum level of 10(8) cfu/ml showed 2 peaks of MIC values, one in a range of 1.56 to 6.25 micrograms/ml and the other higher than 100 micrograms/ml. The most prevalent MIC value was 3.13 micrograms/ml with MIC against 51 strains or 71.8% of the strains tested showing this value, and MIC values of 25 micrograms/ml or higher were obtained for 13 strains or 18.3% of the strains tested. The MIC80 was 6.25 micrograms/ml. Thus, R-3746 showed an antibacterial activity slightly weaker than MCIPC and DMPPC but similar to CCL, CEX and CDX. MIC values obtained at an inoculum level of 10(6) cfu/ml also had 2 peaks, one in a range of 1.56 to 3.13 micrograms/ml and the other higher than 25 micrograms/ml. Strains against which R-3746 had the MIC value of 3.13 micrograms/ml were the most numerous with 47 strains or 66.2%, and strains against which the MIC value of higher than 25 micrograms/ml was obtained were next with 13 strains or 18.3%.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antimycoplasmal activities of ofloxacin and commonly used antimicrobial agents on Mycoplasma gallisepticum

In vitro activities of ofloxacin (OFLX), a new quinolone derivative, against 29 strains of Mycoplasma gallisepticum was compared with those of 4 commonly used antimicrobial agents, doxycycline (DOXY), tylosin (TS), spectinomycin (SPCM) and thiamphenicol (TP). Antimycoplasmal activities of the drugs were evaluated on the MIC (final MIC) and MPC (minimum mycoplasmacidal concentration) values which were determined by a broth dilution procedure. The following results were obtained. 1. The MIC90s of OFLX and DOXY were both 0.20 micrograms/ml. The MICs of TS were distributed through a wide range (less than or equal to 0.006 - 0.78 micrograms/ml), and its MIC90 was 0.78 micrograms/ml. Of 29 M. gallisepticum strains, 27.6% were recognized as TS-resistant. The MIC90 values of SPCM and TP were 1.56 micrograms/ml and 3.13 micrograms/ml, respectively. The MIC90 of OFLX was equal to that of DOXY and 4- to 16-fold smaller than the values of the other 3 antibiotics. 2. The MPC of OFLX was the lowest among the antibiotics tested, its MPC90 value was 0.39 micrograms/ml and was followed by DOXY (1.56 micrograms/ml). The MPCs of TS were distributed in a wide range (0.012 - 3.13 micrograms/ml), and its MPC90 was 3.13 micrograms/ml. The MPC90 values of SPCM and TP were both 6.25 micrograms/ml. Therefore, the mycoplasmacidal activity of OFLX evaluated with MPC90 values was 4- to 16-fold greater than those of the other 4 antibiotics.     

In vitro activity of HR 756, a new cephalosporin compound.

The in vitro activity of HR 756, a new cephalosporin, has been determined against recent clinical isolates and compared with that of other beta-lactam antibiotics. The geometric means of the minimum inhibitory concentrations (MIC) for different isolates of Escherichia coli (100 isolates), Klebsiella pneumoniae (84), Pseudomonas aeruginosa (121), Proteus mirabilis (52), indole-positive Proteus species (9), Salmonella species (19), Staphylococcus aureus penicillin-sensitive (29) and penicillin-resistant (39) were: 0.095, 0.124, 11.1, 0.095, 0.0107, 0.078, 1 and 0.95 mcg/ml, respectively. Its activity was affected by rise in inoculum against S. aureus and P. aeruginosa but not against K. pneumoniae and E. coli. Bactericidal activity was determined by membrane filtration method. HR 756 was found to be bactericidal to E. coli, K. pneumoniae, P. aeruginosa and Proteus species. Although the MICs of the tested S. aureus strains were 1 mcg/ml, 5 mcg/ml of HR 756 failed to kill 99% of the inoculum within 24 hours.     

Clinical laboratory approach for estimating effective administrative dose of tobramycin. Reevaluation of in vitro MIC break points of disk susceptibility test

The reliability of the tobramycin (TOB) disc susceptibility test in estimating approximate values of MICs was studied using various clinical isolates totaling 261 strains and using Showa discs (8 mm diameter containing 30 micrograms of TOB) and Difco discs (6 mm diameter containing 10 micrograms of TOB). Clinical significance of a 4 category system for the interpretation of the disc tests, which is widely used in Japan, and that of a 3 category system used in USA and Europe, were also evaluated to determine which system would be more suitable for the evaluation of proper dose levels of administration. Furthermore, the evaluation was made using these discs with respect to the in vitro MIC break points for therapeutic use of antibiotics proposed by the British Society for Antimicrobial Chemotherapy (J. Antimicr. Chemoth. 21:701-710, 1988). The results obtained with the disc method were compared with MICs determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The results of the TOB disc susceptibility test either with Showa or Difco discs were well correlated with MICs, showing the reliability of the disc method to estimate approximate values of MICs. Break points in MIC values proposed for the classification of bacteria into the 4 categories of susceptibility are () MIC less than or equal to 2 micrograms/ml, (++) MIC greater than 2-10 micrograms/ml, (+) MIC greater than 10-50 micrograms/ml, (-) MIC greater than 50 micrograms/ml. Those proposed in the 3 categories of susceptibility are Sensitive (S) MIC less than or equal to 4 micrograms/ml, Intermediate (I) MIC greater than 4-8 micrograms/ml, Resistance (R) MIC greater than 8 micrograms/ml. In the 4 category classification system of the Showa disc susceptibility test, 16 out of 261 strains (6.1%) tested showed false positive results and 7 (2.7%) did false negative results. If the classification was modified as follows: ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml, false positive results were markedly reduced. Only 6 out of 261 strains (2.3%) showed false positive results, and 7 (2.7%) did false negative results. With Difco disc, in the 4 category interpretation system, 8 out of 261 strains (3.1%) tested showed false positive and 35 (13.4%) did false negative results. No inhibitory zones were observed against a majority of strains with MIC greater than 25 micrograms/ml, thus unable to assess (+) susceptibility.(ABSTRACT TRUNCATED AT 400 WORDS)     

Piperacillin (T-1220), a new semisynthetic penicillin: in vitro antimicrobial activity comparison with carbenicillin, ticarcillin, ampicillin, cephalothin, cefamandole and cefoxitin

Piperacillin (T-1220) is a new semisynthetic penicillin with an unusually broad spectrum of antimicrobial activity. In vitro comparisons of this drug with 6 other beta-lactam antimicrobics (ticarcillin, carbenicillin, ampicillin, cephalothin, cefamandole and cefoxitin) were conducted. These included minimal inhibitory concentrations (MIC) against 394 bacterial isolates, the minimal lethal concentrations (MLC) against 79 of those, as well as the effect of inoculum size on the MIC and MLC of the drugs. Piperacillin had significantly greater activity than did the other penicillins against Pseudomonas species and Klebsiella pneumoniae. Against P. aeruginosa piperacillin was 8- and 16-fold more active than ticarcillin and carbenicillin, respectively. The MLC of piperacillin rarely differed from the MIC by more than one log2 dilutions except against P. aeruginosa in which the MLC was 4-fold greater or more than the MIC of 45% of isolates tested. Ticarcillin, carbenicillin and cefoxitin showed minimal inoculum size effects. Cefamandole results showed the greatest inoculum size variation with 55% and 37% of isolates showing an 8-fold increase in MIC and MLC respectively by increasing inoculum from 10(5) to 10(7) CFU/ml. Piperacillin was intermediately effected having 25% of strains greater than 8-fold increase in MIC.     

Clinical laboratory approach to estimating the effective administration dose of imipenem/cilastatin. Evaluation of the disk susceptibility test and its interpretation system

In vitro activities of imipenem/cilastatin (IPM/CS) against 413 clinical isolates were studied through the evaluation of MICs and the results of disk susceptibility tests. The MICs were determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The MIC80s of imipenem (IPM) against Staphylococcus aureus and Staphylococcus epidermidis were 25 and 1.56 micrograms/ml, respectively, showing a bimodal MIC distribution. However, the distribution of MICs against other bacteria studied was of monomodal pattern. Group A Streptococcus, Enterococcus faecalis were inhibited by IPM at dose levels less than 0.025 and 6.25 micrograms/ml, respectively. IPM inhibited Escherichia coli at 0.20 microgram/ml, Klebsiella pneumoniae at 0.39 microgram/ml, Pseudomonas aeruginosa at 3.13 micrograms/ml except one strain showed a MIC of 25 micrograms/ml, Serratia spp. at 3.13 micrograms/ml except one with MIC greater than 100 micrograms/ml, Citrobacter freundii at 0.78 microgram/ml and Enterobacter spp. at 0.39 microgram/ml. Indole (-) Proteus and indole (+) Proteus were inhibited by this drug at levels of 3.13 and 1.56 micrograms/ml, respectively. The reliability of the IPM disk diffusion susceptibility test in quantitative estimation of antimicrobial activities was well demonstrated using commercialized 8 mm diameter Showa disks containing 30 micrograms antibiotic and also disks containing 1-30 micrograms prepared in this laboratory. For the interpretation of the Showa disk susceptibility test, a 4 category system was used. In the 4 category system for Showa IPM disk the following classification of inhibitory zone diameters has been proposed; ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml. The results of the test using Showa 30 micrograms disk against various clinical isolates were accurately classified into the 4 groups, showing false positive 8 out of 304 strains (2.6%) and false negative 1 of 304 strains (0.3%). With Showa 30 micrograms disks subclassification of strains with MIC less than 3 micrograms/ml cannot be achieved. In this study, however, the differentiation of strains with MICs less than 1 microgram/ml was made with disks containing 5-10 micrograms, which afforded to set MIC break points at 1 and 3 micrograms/ml. According to current concepts on pharmacokinetics for antibiotics including the penetration of drugs into tissues and inflammatory fluids, serum protein binding of drugs appears to be one of the important determinants of drug distribution in the body. Only free, unbound drug molecules can readily pass through capillary pores into tissue fluids except in the hepato-biliary system.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vitro susceptibilities of causative organisms isolated from patients with primary respiratory tract infections to BRL 25000 (clavulanic acid/amoxicillin)

The in vitro susceptibilities of various causative organisms recently isolated from patients with primary respiratory tract infections to BRL 25000 (a formulation of amoxicillin, 2 parts, and potassium clavulanate, 1 part), amoxicillin (AMPC), cefaclor (CCL), cephalexin (CEX), cefadroxil (CDX) and cefroxadine (CXD) were determined. beta-Lactamase producing strains were detected by nitrocefin chromogenic method and PCG acidometric method. The frequency of isolation of beta-lactamase production in strains of S. aureus, H. influenzae, B. catarrhalis and K. pneumoniae was 92%, 18%, 36% and 98%, respectively. Against S. aureus strains with MIC values to AMPC of less than or equal to 100 micrograms/ml and CEX of less than or equal to 25 micrograms/ml BRL 25000 showed MIC values in the range 0.39-6.25 micrograms/ml with inocula of 10(6) CFU/ml, while BRL 25000 required 12.5-100 micrograms/ml of concentrations for inhibition of the strains with MIC values to AMPC of greater than 100 micrograms/ml and CEX of greater than or equal to 25 micrograms/ml. Against S. pyogenes and S. pneumoniae BRL 25000 showed MIC values in the range less than 0.024-0.10 micrograms/ml with inocula of 10(6) CFU/ml, which is much more active than CCL, CEX, CDX and CXD and slight less active than AMPC. Against H. influenzae and B. catarrhalis BRL 25000 showed MIC values in the range 0.20-6.25 micrograms/ml with inocula of 10(6) CFU/ml, which showed most potent activity among the agents tested. The activity of BRL 25000 against K. pneumoniae was approximately equal to that of CCL and superior to that of AMPC, CEX, CDX and CXD.     

Evaluation of in vitro antimicrobial activity of cefazolin alone and in combination with cefmetazole or flomoxef using agar dilution method and disk diffusion method]

Antimicrobial activities of cefazolin (CEZ) against 251 strains of various clinical isolates obtained during 1989 and 1990 were determined using the Mueller-Hinton agar dilution method at an inoculum level 10(6) CFU/ml. The reliability of the disk susceptility test was also studied using Mueller-Hinton agar and various disks at inoculum levels of 10(3-4) CFU/cm2 in estimating approximate values of MICs. In addition, antimicrobial activities of CEZ and cefmetazole (CMZ) or flomoxef (FMOX) in combination were investigated against methicillin-sensitive and -resistant Staphylococcus aureus (MSSA and MRSA) using the checkerboard agar dilution MIC method and the disk diffusion test either with the disks contained CEZ, CMZ, and FMOX alone, or CEZ, and CMZ or FMOX in combination. In this study, the MICs of CEZ against S. aureus were distributed with the 3 peak values at 0.39 microgram/ml, 3.13 micrograms/ml and > 100 micrograms/ml. MICs against MSSA were 0.39 microgram/ml to 0.78 microgram/ml, whereas those against MRSA were greater than 0.78 microgram/ml. MICs against majority of strains of Enterococcus faecalis were 25 micrograms/ml. Over 90% of strains of Escherichia coli and Klebsiella pneumoniae were inhibited at the level of 3.13 micrograms/ml. About 60% of isolates of indole negative Proteus spp. were inhibited at the levels of less than 3.13 micrograms/ml and 100% at 6.25 micrograms/ml, but MICs against indole positive Proteus spp., Serratia spp. and Pseudomonas aeruginosa were over 100 micrograms/ml. The antimicrobial activities of CEZ against these clinical isolates were not significantly different compared to those reported about 15-20 years ago, except for S. aureus. Highly resistant strains of S. aureus to CEZ were more prevalent in this study. The inhibitory zones obtained with the disk test were compared with MICs. The results of CEZ disk susceptibility test with 30 micrograms disk (Showa) or 10 micrograms disk (prepared in this laboratory) were well correlated with MICs (r = -0.837 and -0.814, respectively), showing the reliavility of the disk method in estimating approximate values of MICs. In the 4 category classification system currently used in Japan, break points in MIC values proposed are () MIC < or = 3 micrograms/ml, (++) > 3-15 micrograms/ml, (+) > 15-60 micrograms/ml, (-) > 60 micrograms/ml. The results obtained with 30 micrograms disks showed false positive in 7.7% and false negative in 6.8% of the samples. The disk results with E. faecalis showed a higher ratio of false positive results.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antimicrobial susceptibility of Pseudomonas aeruginosa isolated in Fukushima Prefecture

We investigated the susceptibility of Pseudomonas aeruginosa (isolated from the sputum of patients with respiratory infection in 4 medical institutions in Fukushima Prefecture) to 8 beta-lactam antibiotics including three carbapenems and relationships among MICs of antibiotics tested. The MIC90 values for a total of 216 strains were 6.25 micrograms/ml for meropenem, 12.5 micrograms/ml for imipenem and ceftazidime, 25 micrograms/ml for panipenem and cefsulodin, 50 micrograms/ml for cefpirome and over than 200 micrograms/ml for cefoperazone and piperacillin. The frequency of resistance of these strains to each antibiotic was as follows: The resistant strains were 19 (8.8%) for meropenem, 34 (15.7%) for imipenem and ceftazidime, 50 (23.1%) for cefsulodin, 72 (33.3%) for panipenem, 76 (35.2%) for piperacillin and 90 (41.7%) for cefpirome. Eighteen strains (18.3%) of 19 meropenem resitant straisn were resistant to imipenem and panipenem, but 16 strains of the 34 imipenem-resistant strains and 54 strains of the 72 panipenem-resistant strains were susceptible to meropenem. In investigation of isolation of multi-resistant Pseudomonas aeruginosa, the susceptibility of strains tested to 7 antibiotics except cefoperazone was as follows: The strains susceptible to all the 7 antibiotics were 92 strains (42.6%), and 33 strains (15.2%) were resistant to 2 antibiotics, 31 strains (14.4%) were resistant to 1 antibiotic, 21 strains (9.7%) were resistant to 3 antibiotics, 13 strains (6.0%) were resistant to 5 antibiotics, 9 (4.2%) were resistant to 4 and 7 antibiotics, and 8 strains (3.7%) were reistant to 6 antibiotics. Since the emergence of these multi-resistant strains is closely related to frequent use of antibiotics for nosocomial infections, special attention should be paid to the antimicrobial susceptibility of Pseudomonas aeruginosa and the situation of antibiotic resistant strains.     

Clinical laboratory approach in estimating the effective dosage of cefamandole

Reliability of the cefamandole (CMD) disc susceptibility test in estimating approximate values of MICs was studied using various clinical isolates totaling 246 strains with Showa discs (8 mm diameter containing 30 micrograms of CMD). Clinical significance of a 4 category system for the interpretation of the CMD disc tests, which is normally used in Japan, was also evaluated to determine whether this system would be suitable or not for the evaluation of a proper dose of administration. The results obtained with the disc method were compared with MICs determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The results of the CMD disc susceptibility test were well correlated with MICs, showing the reliability of the disc method to estimate approximate values of MICs. Break points in MIC values proposed for the classification of bacteria into 4 categories of susceptibility are () MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml. Only 4 (1.6%) out the 246 strains tested showed false positive results and 11 (4.5%) showed false negative results, showing the excellent reliability of this test. In this study, approximately 90% of strains of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolated from clinical materials randomly were inhibited by CMD at concentrations less than 3.13 micrograms/ml. Proteus vulgaris and Enterobacter aerogenes were sensitive to CMD at 67 and 69% of strains, respectively, at concentrations below 6.25 micrograms/ml. CMD was not active against Pseudomonas aeruginosa, Serratia marcescens and Enterococcus faecalis. About 90% of Staphylococcus aureus were inhibited at dose levels smaller than 6.25 micrograms/ml and 70% of the strains at levels less than 3.13 micrograms/ml. Susceptibilities to 15 micrograms/ml CMD of highly methicillin-resistant strains (MIC greater than 30 micrograms/ml) of S. aureus were examined. Ten of 12 strains examined were found susceptible to CMD, but only 6 of the 12 to cefmetazole. Imipenem/cilastatin was effective to 5 of the 12 strains at levels lower than 3 micrograms/ml and to one at a level less than 15 micrograms/ml. Minocycline was effective against 11 strains at concentrations below 2 micrograms/ml.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antimicrobial susceptibility of clinical isolates of Enterobacteriaceae producing complex beta-lactamase patterns including extended-spectrum enzymes

The antimicrobial susceptibility of 103 clinical isolates of Enterobacteriaceae to 11 antibiotics, was investigated, using a conventional inoculum size (5 x 10(5) CFU) and a higher inoculum size (5 x 10(8) CFU). All the isolates produced complex beta-lactamase patterns, including an extended-spectrum beta-lactamase (ESBL) of the TEM- or SHV-type plus other enzymes (a TEM-type or an SHV-type non-ESBL and/or a class C enzyme). The following repertoire of ESBLs was produced by the isolates: TEM-15, TEM-19, TEM-26, TEM-52, TEM-72, TEM-87, TEM-92, SHV-2a, SHV-5 and SHV-12, as assessed by sequencing. Production of the other enzymes was showed by analytical isoelectric focusing. Overall, meropenem was the most active agent and less influenced by inoculum size, while other beta-lactams showed a lower activity and a significant inoculum size effect. In conclusion, from its in vitro performance, meropenem could be considered as the last resource drug against strains producing complex beta-lactamase patterns including an ESBL.     

In vitro antimicrobial activity of cefpirome, a new cephalosporin with a broad antimicrobial spectrum

The in vitro activity of cefpirome (HR 810), a new cephalosporin antibiotic having a 2,3-cyclopentenopyridine group in the 3-position side chain, was compared with in vitro activities of 5 other cephalosporins. HR 810 showed a broad spectrum of antimicrobial activity against Gram-positive and Gram-negative bacteria when tested using 71 standard strains and 876 clinical isolates. HR 810 inhibited 70% of the clinically isolated Staphylococcus aureus and Staphylococcus epidermidis strains when used at 0.59-0.84 microgram/ml, 2- to 25-fold lower than values of reference antibiotics, and the compound was also highly effective against Enterococcus faecalis which is relatively resistant to most of the existing cephem antibiotics. The activity of HR 810 against Enterobacteriaceae members (11 species), based on its minimal inhibitory concentrations inhibiting 90% of bacterial growth (MIC90S), was the highest among the cephalosporins used. Especially against Enterobacter species and Citrobacter freundii, the MIC90S of the compound were 4- to 64-fold lower than the values of the other antibiotics. Against Pseudomonas aeruginosa, HR 810 was as active as cefoperazone, an antipseudomonal agent. The minimal bactericidal concentrations (MBCs) of HR 810 were equal to or only 2-fold greater than the MICs for most of 12 standard strains tested. The compound markedly decreased viable bacterial counts at its MICs, thus showing strong bactericidal activities. The in vitro activity of HR 810 was not affected by pH or human serum content of agar media, but the activity against Gram-negative bacteria was lowered as the inoculum size increased.     

The comparative activity of twelve 4-quinolone antimicrobials against gram-positive and gram-negative anaerobes

The minimal inhibitory concentrations (MICs) of twelve 4-quinolone antimicrobials were determined for the Bacteroides fragilis group (50), Bacteroides melaninogenicus (20), Bacteroides bivius (10), Fusobacterium spp. (10), anaerobic Gram-positive cocci (50) and Clostridium spp. (20). MICs were determined using an agar dilution technique in Mueller-Hinton agar supplemented with 10% lysed horse blood. The inoculum used was approximately 10(4) colony-forming units, contained in 10 microliter of Mueller-Hinton broth, which was applied to the agar plates using a multipoint inoculator. Following inoculation, plates were incubated at 37 degrees C for 48 h in an anaerobic atmosphere. The MIC of each antimicrobial for each isolate examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum. The minimum concentrations required to inhibit the growth of 50% (MIC50) and 90% (MIC90) of the organism examined were also determined. All of the more recently synthesised 4-quinolones showed increased activity against the anaerobic bacteria used in this study. Ciprofloxacin and ofloxacin were the most active compounds examined (Bacteroides fragilis group MIC90 ciprofloxacin 4 micrograms/ml; ofloxacin 4 microgram/ml; Bacteroides melaninogenicus MIC90 ciprofloxacin 2 micrograms/ml, ofloxacin 2 micrograms/ml; Bacteroides bivius MIC90 ciprofloxacin 16 micrograms/ml, ofloxacin 32 micrograms/ml; Fusobacterium spp. MIC90 ciprofloxacin 2 micrograms/ml, ofloxacin 4 micrograms/ml; Clostridium spp. MIC90 ciprofloxacin 1 microgram/ml, ofloxacin 1 microgram/ml and anaerobic Gram-positive cocci MIC90 ciprofloxacin 4 micrograms/ml, ofloxacin 4 micrograms/ml).     

Antimicrobial activity of prenylflavanones

Among two flavanones [YS01, YS02] and eight prenylflavanones [YS03-YS10], preliminary screening with fifteen test bacterial strains showed that YS06 was the most active agent. YS06 exhibited highly significant antimicrobial action when tested against 228 bacterial strains comprising two Gram-positive and six Gram-negative genera. The in vitro susceptibility test was carried out by determining the minimum inhibitory concentration (MIC) of YS06 by agar dilution technique. Twenty-two out of fifty strains of Staphylococcus aureus were inhibited at 25 to 50 micrograms/mL of the agent. YS06 also inhibited strains of Salmonella, Shigella and a few strains of Escherichia coli strains were also highly sensitive to YS06, while Kleibsiella spp. and Pseudomonas aeruginosa were much less sensitive. In in vivo study, YS06 offered significant protection (p < 0.001 according to chi-square test) to Swiss albino mice (challenged with 50 minimum lethal dose (MLD, virulent bacterium) at concentrations of 160 and 80 micrograms/mouse.     

Clinical laboratory approach for estimating effective administrative dose of cephalothin. Reevaluation of MIC break points in 4 category system of disc susceptibility test

The reliability of the cephalothin (CET) disc susceptibility test in estimating approximate values of MICs was studied using various clinical isolates totaling 248 strains and using Showa discs (8 mm diameter containing 30 micrograms of CET) and Difco discs (6 mm diameter containing 30 micrograms of CET). Clinical significance of a 4 category system for the interpretation of the CET disc tests, which is widely used in Japan, was reevaluated to determine whether this system would be suitable or not for the evaluation of proper dose levels of administration. The results obtained with the disc methods were compared with MICs determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The results of the CET disc susceptibility test were well correlated with MICs, showing the reliability of the disc method to estimate approximate values of MICs. Break points in MIC values proposed for the classification of bacteria into 4 categories of susceptibility are ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml. With the Showa disc susceptibility test, 15 out of the 248 strains (6.0%) tested showed false positive results and 6 strains (2.4%) showed false negative results. With the Difco disc test, 18 out of the 248 strains (7.3%) tested showed false positive results and 6 (2.4%) showed false negative results. Excluding Enterococcus faecalis from the test, results because better in the quantitative estimation of MICs, resulting false positive rates of 3.2% (Showa), and 4.4% (Difco). A 3 category system of the interpretation of disc test is generally used in the USA and Europe. MIC break points proposed for the classification of the CET test are sensitive, MIC less than or equal to 8 micrograms/ml, and resistance, MIC greater than or equal to 32 micrograms/ml. With the Showa disc susceptibility test, 14 out of the 248 strains (5.6%) tested showed false positive results and 6 strains (2.4%) showed false negative results. With the Difco disc test 7 out of the 248 strains (2.8%) showed false positive results and 21 strains (8.5%) showed false negative results. In this study, MIC70S of CET against Staphylococcus aureus and Staphylococcus epidermidis were 1.56 and 0.78 micrograms/ml, respectively. CET was not so effective against Gram-negative rods except Klebsiella pneumoniae, Proteus mirabilis and Escherichia coli. MIC70S against K. pneumoniae, P. mirabilis, and E. coli were 6.25, 3.13, and 3.13 micrograms/ml, respectively.     

Clinical laboratory approach for estimating effective administrative dose of cefuzonam. Evaluation of disc susceptibility test and its interpretation system

In vitro activities of cefuzonam (CZON) against 273 clinical isolates were studied through the evaluation of MIC's and the results of disc susceptibility test. The MIC's were determined using the agar dilution method at an inoculum level of 10(6)CFU/ml. The MIC80's of CZON against Streptococcus pneumoniae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Haemophilus influenzae and Citrobacter spp. were less than 0.20 microgram/ml. The MIC80's against Serratia marcescens and Enterobacter aerogenes were both 6.25 micrograms/ml, and that against Pseudomonas aeruginosa was 100 micrograms/ml. The MIC80's against Staphy-lococcus epidermidis were 25 and 6.25 micrograms/ml, respectively. Approximately 70% of strains of S. aureus were inhibited at concentrations less than 1.56 microgram/ml. For the interpretation of the CZON Showa 30 micrograms disc susceptibility test a 4 category system was used. In the 4 category system for Showa disc containing CZON, the following classification inhibitory zone diameters has been proposed: ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC less than 60 micrograms/ml. Reliability of the CZON disc tests in estimating approximate MIC values was studied using Showa 30 micrograms discs and discs prepared in this laboratory containing 1-10 micrograms CZON. A good negative correlation was observed between inhibitory zone diameters and MIC's, showing the reliability of the disc method. The results of the test using Showa 30 micrograms disc against various clinical isolates were accurately classified into the 4 groups except those against P. aeruginosa. Some strains of P. aeuruginosa showed false positive results, exhibiting relatively larger inhibitory zone diameters compared with MIC's against these organisms. As CZON is not effective against P. aeruginosa a much better overall correlation between MIC's and the disc test would result when P. aeruginosa was excluded. With Showa 30 micrograms discs of various cephalosporins, sub-classification of strains with MIC less than 3 micrograms/ml cannot be achieved. In this study, however, it was demonstrated that differentiation of strains with MIC's less than 0.5-1.56 micrograms/ml was possible when discs containing 1-10 micrograms of CZON were used. According to recent concepts on pharmacokinetics for antibiotics including penetration of drugs into tissues and inflammatory fluids, serum protein binding of drugs appears to be one of the important determinants of drug distribution in the body.(ABSTRACT TRUNCATED AT 400 WORDS)     

Clinical laboratory approach for estimating effective administrative dose of cefoperazone. Evaluation of disc susceptibility test and its interpretation system

To interpret of the cefoperazone (CPZ) disc susceptibility test, a 4 category system is used in Japan, but a 3 category system is used in the U.S.A. and Europe. In the 4 category interpretation system of Showa CPZ disc the following classification is used: ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3 approximately 15 micrograms/ml, (+) MIC greater than 15 approximately 60 micrograms/ml, (-) MIC greater than 60 micrograms/ml. In the 3 category system the classification used is as follows: susceptible MIC less than or equal to 16 micrograms/ml, moderately susceptible MIC greater than 16 approximately 32 micrograms/ml, resistant MIC greater than 32 micrograms/ml, or susceptible MIC less than or equal to 32 micrograms/ml, moderately susceptible MIC greater than 32 approximately 64 micrograms/ml, resistant MIC greater than 64 micrograms/ml, depending on dose levels, 1 or 2 g. Reliability of the CPZ disc susceptibility test in estimating approximate MICs by classifying the test results into 4 categories was studied using discs containing 1, 2, 5, 10, 30 and 75 micrograms. The MICs were determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. A good negative correlation was observed between inhibitory zone diameters and MICs, showing reliability of the test using these discs. The results obtained with discs containing 30 or 75 micrograms of CPZ were well categorized into the 4 groups mentioned above. Some strains of Pseudomonas aeruginosa and Enterococcus faecalis, however, showed false positive results. When different break points of inhibitory zone diameters than those used for other bacteria were used for P. aeruginosa, and E. faecalis was excluded from the test, an excellent correlations were obtained. With 30 or 75 micrograms discs, it was unable to subclassify strains against which MICs of CPZ were below 3 micrograms/ml. However, with discs containing 1 to 10 micrograms, it was possible to separate the strains against which MICs were less than 0.5 microgram/ml. The fact that most frequent values of MICs of CPZ against Escherichia coli, Klebsiella pneumoniae, Proteus spp., Haemophilus influenzae, Streptococcus pyogenes etc. were less than 0.5 microgram/ml supports the usefulness of low dose discs. According to recently ongoing concepts on the pharmacokinetics of antibiotics and their penetration into tissues and inflammatory fluids, serum protein binding appear to be one of the important determinants of drug distribution in the body. Only free, unbound drug molecules can readily pass through capillary pores into tissue fluids except into hepatic biliary system.(ABSTRACT TRUNCATED AT 400 WORDS)