Antimicrobial Susceptibility of Haemophilus parainfluenzae

Fifty random clinical isolates of Haemophilus parainfluenzae were tested for their susceptibility to 10 antibiotics by a microtiter broth dilution method. Three of the strains tested were resistant to ampicillin, whereas eight were resistant to tetracycline. All strains tested were susceptible to chloramphenicol, kanamycin, gentamicin, cephalothin, and colistin. The ranges of minimal inhibitory concentrations for the three remaining antibiotics were: 0.5 to >/=128 mug of penicillin G per ml, 0.03 to 4 mug of carbenicillin per ml, and 1 to 16 mug of erythromycin per ml. Elevated minimal inhibitory concentrations for penicillin and carbenicillin were noted for the three ampicillin-resistant strains. Tests for beta-lactamase production demonstrated the presence of this enzyme in each of the three ampicillin-resistant strains.     

Antibiotic Susceptibility of Clinical Isolates of Listeria monocytogenes

A broth microdilution method was used to measure the minimal inhibitory concentrations (MICs) of the antibiotics most often recommended for treatment of listeriosis. The MICs of ampicillin, penicillin, erythromycin, and tetracycline for 175 strains of Listeria monocytogenes were below the approximate MIC breakpoint for susceptible strains as recommended by the National Committee on Clinical Laboratory Standards. Inhibition diameters for 125 strains were measured by the standardized disk method (National Committee on Clinical Laboratory Standards) and compared with the appropriate MIC values. By both methods, strains were susceptible to the above four antibiotics, except for three strains, which were intermediate in susceptibility to penicillin by the disk method. Since the minimal bactericidal concentrations for ampicillin and penicillin significantly exceeded the MICs for these antibiotics, 45 strains were evaluated with ampicillin (5 mug/ml) and gentamicin (1 mug/ml) to compare the synergistic bactericidal effect of the two used in combination and singly. An increased kill of 100-fold was observed with the antibiotics combined in 19 strains after 4 to 6 h and in 40 strains after 24 h. A comparison of results with microdilution in Trypticase soy broth and agar dilution in Mueller-Hinton agar revealed that MICs for gentamicin, kanamycin, and streptomycin were strongly influenced by the media used. The MICs were consistently lower in Mueller-Hinton agar.     

Antimicrobial Susceptibility of Haemophilus ducreyi

The susceptibility of 19 isolates of Haemophilus ducreyi from a recent chancroid outbreak and four reference strains was determined in vitro to 13 antimicrobial agents. The rabbit intradermal test for virulence was positive for all of the local isolates, but not for the reference strains. The "nonvirulent" reference strains were inhibited by lower minimum inhibitory concentrations (MICs) of most agents tested. For the virulent isolates, the range of MICs (in micrograms per milliliter) of the following were: of vancomycin, 8 to 128; of polymyxin, 32 to 128; of cloxacillin, 32 to 64; of tetracycline, 0.5 to 32; of cephalothin, 4 to 8; of doxycycline, 0.25 to 8; and of kanamycin, 1 to 8. Three strains were resistant to penicillin and ampicillin (MIC >/= 128 mug/ml), and these three strains produced beta-lactamase. The remainder were susceptible to 4 mug/ml. All strains were susceptible to rifampin (MIC 相似文献   

Susceptibility of Haemophilus influenzae Type b to Cefatrizine, Ampicillin, and Chloramphenicol

The susceptibility of 269 isolates of Haemophilus influenzae type b to cefatrizine (BL-S640), ampicillin, and chloramphenicol was evaluated by disk diffusion susceptibility tests, using a modified Bauer-Kirby method. Broth dilution susceptibility tests were performed on 88 of these isolates, including all isolates resistant by disk to cefatrizine or ampicillin. Six of the isolates were resistant by disk to cefatrizine (zone size, <16 mm), four were resistant to ampicillin (zone size, <19 mm), and none were resistant to chloramphenicol (zone size, <17 mm). Only two of the six isolates of H. influenzae that were resistant to cefatrizine by disk were resistant to more than 4 mug of drug per ml. The four organisms resistant to ampicillin on disk were resistant, when tested by the broth method, to >128 mug/ml. These four ampicillin-resistant H. influenzae were susceptible to <4 mug of cefatrizine per ml. The two isolates resistant to >4 mug of cefatrizine per ml were susceptible to 0.5 and 2 mug of ampicillin, respectively, per ml. The activity of cefatrizine appears to be comparable in vitro to ampicillin against H. influenzae.     

Susceptibility of Haemophilus influenzae Isolates from Blood and Cerebrospinal Fluid to Ampicillin, Chloramphenicol, and Trimethoprim-Sulfamethoxazole

Susceptibility to ampicillin and chloramphenicol in vitro has been determined for Haemophilus influenzae strains isolated from blood and/or cerebrospinal fluid cultures of patients admitted to two Atlanta hospitals from 1 January 1974 to 31 March 1975. Since the appearance of ampicillin-resistant strains of this organism in early 1974, chloramphenicol has been used in these hospitals as initial therapy for severe infection due to H. influenzae. Strains from five of 94 patients were resistant to ampicillin (minimum inhibitory concentration [MIC] >/= 12.5 mug/ml), but all strains were susceptible to chloramphenicol (MIC < 2 mug/ml). The first 35 strains studied, including three resistant to ampicillin, were also tested for in vitro susceptibility to trimethoprim-sulfamethoxazole; all were highly susceptible (MIC 相似文献   

Antibiotic Susceptibility of Haemophilus vaginalis (Corynebacterium vaginale) to 21 Antibiotics

A total of 56 strains of Haemophilus vaginalis were tested for their in vitro susceptibility to 21 antimicrobial agents by an agar dilution method. All strains were inhibited by 1 mug or less of penicillin, ampicillin, carbenicillin, and vancomycin per ml. The cephalosporins were less active; 4 mug of cefazolin per ml, 16 mug of cephalothin per ml, or 128 mug of cephalexin per ml was required to inhibit all strains. Kanamycin, gentamicin, tobramycin, and neomycin were relatively inactive against H. vaginalis. All strains were inhibited by 4 mug of streptomycin per ml and 2 mug of chloramphenicol per ml. Only 57% of the strains were inhibited by 4 mug of tetracycline per ml, whereas 43% were inhibited by 16 to 64 mug/ml. The combination sulfamethoxazole/trimethoprim was relatively inactive against H. vaginalis. All strains tested exhibited minimal inhibitory concentrations of >/=128 mug when tested against colistin, nalidixic acid, and sulfadiazine. Erythromycin and clindamycin were the most active of the antibiotics tested; for all strains the minimal inhibitory concentrations were 相似文献   

Comparative Susceptibility of Haemophilus Species to Cefaclor, Cefamandole, and Five Other Cephalosporins and Ampicillin, Chloramphenicol, and Tetracycline

The minimal inhibitory concentration of cefaclor, cephalexin, cephradine, cefamandole, cephalothin, cephapirin, cefazolin, ampicillin, chloramphenicol, and tetracycline for inhibition of 198 freshly isolated clinical strains of Haemophilus species (23 H. influenzae type b, 157 H. influenzae non-type b, 14 H. parainfluenzae, and 4 H. aphrophilus) was determined simultaneously by a slightly modified WHO-ICS agar dilution method. Nine strains were resistant to ampicillin. There was no correlation between ampicillin resistance and minimal inhibitory concentration of other antibiotics. All strains were susceptible to chloramphenicol, and all except five were susceptible to tetracycline. Cefaclor was the most active oral cephalosporin, and cefamandole was the most active parenteral cephalosporin. Among the seven cephalosporins tested, cefamandole was the most effective compound. All but two strains were inhibited by cefamandole at 2 mug or less per ml.     

Susceptibility of Haemophilus ducreyi to ampicillin and sulbactam in vitro.

The MICs of ampicillin, ampicillin plus sulbactam in equal proportions, and a range of ampicillin concentrations with a constant 0.5 micrograms/ml concentration of sulbactam were determined for 66 strains of Haemophilus ducreyi by an agar dilution technique with standardized inocula prepared by ultrasonication. Fifty-five strains were susceptible to ampicillin alone (MIC range, 0.06 to 1 microgram/ml). The MICs for the 11 resistant strains were (micrograms per milliliter): range, 8 to greater than 16; MIC for 50% of the strains tested (MIC50), greater than 16; MIC90, greater than 16; 8 of them produced beta-lactamase. In the presence of an equal concentration of sulbactam, the MICs for ampicillin-resistant strains were lowered to (micrograms per milliliter): range, 0.125 to 2; MIC50, 0.25; MIC90, 1. In the presence of a fixed 0.5-micrograms/ml concentration of sulbactam, the MICs for the resistant strains were (micrograms per milliliter): range, 0.125 to 2; MIC50, 0.125; MIC90, 0.25. Sulbactam-ampicillin appears to be suitable for the treatment of H. ducreyi infections, especially those caused by ampicillin-resistant strains.     

Microdilution Technique for Antimicrobial Susceptibility Testing of Anaerobic Bacteria

A microdilution technique using commercially available media and materials was developed and used to determine the minimal inhibitory concentrations (MICs) of clindamycin, chloramphenicol, tetracycline, minocycline, ampicillin, carbenicillin, cephalothin, and gentamicin for 101 anaerobic isolates. Representative strains of Bacteroides, Clostridium, Fusobacterium, Peptococcus, and Peptostreptococcus were tested. The use of Schaedler broth at pH 7.2, an inoculum of 10(5) to 10(7) colony-forming units per ml, and incubation at 35 C in an anaerobic glove box with an atmosphere of 80% nitrogen, 10% hydrogen, and 10% carbon dioxide resulted in good growth and easily interpretable results. After 48 h of incubation, 97% of strains tested were inhibited by 3.1 mug or less of clindamycin per ml and 98% were inhibited by 12.5 mug or less of chloramphenicol per ml. Tetracycline and minocycline inhibited 81 and 88% of strains tested in concentrations of 1.6 mug or less per ml and 1.6 mug or less per ml, respectively. Ampicillin inhibited all strains other than B. fragilis in concentrations of 3.1 mug or less per ml. Excluding certain strains of Bacteroides and Clostridium, carbenicillin in concentrations of 12.5 mug or less per ml and cephalothin in concentrations of 6.2 mug or less per ml inhibited all strains tested. Gentamicin was inactive although some strains of anaerobic cocci and Bacteroides were inhibited by 3.1 mug or less per ml. After 18 to 24 h of incubation, eight of the 101 strains had not grown sufficiently for MICs to be determined; for the 93 strains which had grown sufficiently, 93% of 744 MICs were the same or one concentration lower than the 48-h MICs.     

Susceptibility of Pathogenic Actinomycetes to Antimicrobial Compounds

Current interest in antimicrobial susceptibility testing of anaerobic pathogens and recent recognition that actinomycetes other than Actinomyces israelii may cause actinomycosis in man prompted this in vitro survey of 74 strains of actinomycetes, representing seven species. Minimum inhibitory concentrations (MICs) for 24 antimicrobials were determined by inhibition of gross colonial enlargement in semisolid antibiotic agar after incubation at 37 C for 48 h under anaerobic conditions. Erythromycin and rifampin were the most active drugs in vitro (MICs of 0.008 to 0.25 mug/ml), although a small number of non-israelii strains were conspicuously more resistant to the latter (MICs >0.5 mug/ml). Penicillin G, cephaloridine, minocycline, and clindamycin were also very active in vitro (MICs of 0.03 to 1.0 mug/ml); for a few non-israelii strains the MICs of clindamycin were 2.0 to 8.0 mug/ml. MICs of cephalothin, ampicillin, lincomycin, tetracycline, doxycycline, and chloramphenicol were well within a therapeutic range for all strains of A. israelii and most other species, although the MIC of lincomycin against a few non-israelii strains and of tetracycline and doxycycline against the majority of these strains was 2.0 to 8.0 mug/ml. Oxacillin, dicloxacillin, and cephalexin were less active in vitro, particularly against strains other than A. israelii. Most non-israelii species were not suppressed by 125 mug of metronidazole per ml, which concentration inhibited all strains of A. israelii; otherwise, there were no antimicrobial susceptibility differences among the species tested. Aminoglycoside activity was negligible.     

Antibacterial Activity of Apalcillin (PC-904) Against Gram-Negative Bacilli, Especially Ampicillin-, Carbenicillin-, and Gentamicin-Resistant Clinical Isolates

Apalcillin (PC-904) is active against carbenicillin- and ampicillin-resistant strains of gram-negative bacilli. Among Pseudomonas aeruginosa strains highly resistant to carbenicillin (>/=3,200 mug/ml), half of them were susceptible to PC-904 at a concentration of 50 to 1,600 mug/ml. The minimal inhibitory concentration of PC-904 against P. aeruginosa strains resistant to carbenicillin (400 to 1,600 mug/ml) ranged from 3.1 to 25 mug/ml. Ampicillin- and carbenicillin-resistant Enterobacteriaceae strains were similarly susceptible to PC-904. However, drug resistance to PC-904 was already apparent among some strains of P. aeruginosa, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, P. vulgaris, and P. morganii, recently isolated in Japan; i.e., 4, 35, 32, 4, 6, and 14% of strains isolated were resistant. PC-904 was more active, on the other hand, than ampicillin and carbenicillin against antibiotic-susceptible Enterobacteriaceae and also showed high activity against most species of Pseudomonadaceae, especially P. cepacia and P. aeruginosa. The minimum inhibitory concentrations of PC-904 were greatly affected by inoculum size when the organisms tested were strains producing large amounts of beta-lactamase.     

Activities of newer beta-lactam antibiotics against ampicillin, chloramphenicol, or multiply-resistant Haemophilus influenzae

The susceptibilities of singly or multiply-resistant clinical isolates of Haemophilus influenzae were determined by agar dilution to aztreonam, imipenem, and six third-generation cephalosporins. These included selected isolates that were resistant to ampicillin only, chloramphenicol only, and four isolates that were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. All of the isolates were highly susceptible to these newer beta-lactam antibiotics. Isolates resistant to trimethoprim-sulfamethoxazole and/or chloramphenicol had susceptibilities similar to those of strains resistant only to ampicillin. Ceftriaxone, ceftizoxime, and cefotaxime were the most active of the study antibiotics (MIC90 = 0.004-0.016 micrograms/ml), and were also bactericidal at concentrations no more than twice the minimum inhibitory concentration (MIC). Minimum inhibitory concentrations of cefoperazone increased dramatically with only a 10-fold increase in inoculum size of beta-lactamase producing strains, while MICs of the other new agents were not significantly affected by elevation of the inoculum. These new antibiotics appear to be promising candidates for therapy of infections due to resistant H. influenzae.     

Neisseria gonorrhoeae strains isolated in Hong Kong: in vitro susceptibility to 13 antibiotics.

Fifty-five Neisseria gonorrhoeae strains isolated in Hong Kong over a period of 6 months were tested for their in vitro susceptibility to 13 antimicrobial agents by the agar dilution method. Six strains were beta-lactamase producing. In addition, five beta-lactamase strains from Singapore were tested. Among the non-beta-lactamase-producing strains, 34 (62%) had intermediate resistance to penicillin, with minimal inhibitory concentrations (MICs) ranging from 0.125 to 0.5 microgram/ml, and 15 strains were fully susceptible to penicillin (MICs, 0.015 to 0.06 microgram/ml). The MICs of penicillin for all beta-lactamase-producing strains were 2 microgram/ml, and the strains were resistant to ampicillin. Although a direct correlation between the MICs for resistance to penicillin and the other antibiotics tested was not observed, the gonococci isolated in Hong Kong were notably more resistant to tetracycline and streptomycin than has been reported elsewhere, with 78% of strains requiring for inhibition an MIC of tetracycline of greater than 2 microgram/ml and 51% of the isolates requiring an MIC of streptomycin of greater than 128 microgram/ml. All strains were susceptible to spectinomycin and kanamycin as well as to sulfamethoxazole-trimethoprim (ratio, 19:1). Among the cephalosporins, the order of effectiveness was cefuroxime, cefamandole, and cefoxitin. The older generation of cephalosporins, cephradine and cephalexin, was the least effective: 45 and 37% of the strains, respectively, required for inhibition MICs of greater than or equal to 8 microgram/ml. Cefotaxime, a new parenteral cephalosporin, was the most active; the median MIC was at least 10-fold lower than that of cefuroxime.     

In Vitro Susceptibility of Haemophilus influenzae to Trimethoprim-Sulfamethoxazole

Thirty-four strains of Haemophilus influenzae (20 ampicillin sensitive and 14 ampicillin resistant), mostly type b isolates from cerebrospinal fluid or blood, were tested for susceptibility to a combination of trimethoprim-sulfamethoxazole (TMP-SMZ) in a ratio of 1 part TMP to 19 parts SMZ. All strains were very susceptible to the TMP-SMZ combination, with minimal inhibitory concentrations ranging from 0.007-0.14 to 0.06-1.18 mug of TMP-SMZ per ml. There was little difference in the susceptibility of the ampicillin-sensitive and ampicillin-resistant strains to TMP-SMZ.     

Synergism of Carbenicillin and Gentamicin Against Enterococci

Carbenicillin and gentamicin were tested for synergism against 25 strains of enterococci by two different methods. Killing curves were determined by doing serial colony counts of broth cultures containing the antibiotics separately and in combination. The combination was synergistic for all 25 strains with 75 and 4 mug of carbenicillin and gentamicin per ml, respectively. Reducing the concentrations to 50 and 3 mug of the antibiotics per ml with four strains significantly reduced the rate of killing of the combination. Synergism was also studied by constructing isobolograms, by using the standard two-dimensional broth dilution checker-board technique, and by measuring the end points both for minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs). Synergism was present for all 25 strains when bactericidal end points (MBCs) were evaluated, but was present for only 7 of the 25 strains when MICs were used to construct isobolograms. The time and effort involved were roughly the same for killing curves and for isobolograms, and it was concluded that neither had a distinct advantage over the other.     

In Vitro Sensitivity of Salmonella to Ten Antimicrobial Agents Including Sulfamethoxazole and Trimethoprim, Alone and in Combination

The activities of trimethoprim (TMP) and sulfamethoxazole (SMZ), alone and in combination (SMZ-TMP), and of the following antibiotics were tested against 115 clinical isolates of nontyphoid Salmonella species: tobramycin, gentamicin, ampicillin, amoxicillin, neomycin, kanamycin, chloramphenicol, and tetracycline. The methods of disk diffusion, microtiter broth dilution, and agar dilution were employed for all single antimicrobial agents as well as for SMZ-TMP studies. Growth curves were performed in broth. SMZ-TMP, TMP, gentamicin, tobramycin, and neomycin were the most active drugs in vitro. All strains were inhibited by 100 mug of SMZ per ml was required for at least 10% of strains. SMZ and TMP in a ratio of 10:0.5, respectively, inhibited all isolates and were synergistic for 105 strains. All strains inhibited by the combination of 10:0.5 SMZ-TMP had a zone diameter of >/=22 mm by using a combination disk containing 1.25 mug of TMP and 23.75 mug of SMZ. Seven isolates were resistant to >100 mug/ml of ampicillin or amoxicillin; all isolates were sensitive to chloramphenicol at 相似文献   

In Vitro Susceptibility of Pseudomonas cepacia and Pseudomonas maltophilia to Trimethoprim and Trimethoprim-Sulfamethoxazole

Our earlier studies had shown that the two pseudomonads, Pseudomonas cepacia and Pseudomonas maltophilia, were organisms that were highly resistant to most antibiotics. The present study was undertaken to determine the susceptibility of these bacteria to trimethoprim and the trimethoprim-sulfamethoxazole combination which has been used with apparent success in treating infections caused by these pseudomonads. All 51 strains of P. cepacia were inhibited by 2 mug or less of trimethoprim per ml, whereas all 45 of the P. maltophilia were resistant to greater than 32 mug/ml. When the P. maltophilia was tested against trimethoprim-sulfamethoxazole, two strains were resistant and one only moderately resistant, but all other strains were susceptible. All P. cepacia strains were also susceptible with an average zone of inhibition significantly larger than for P. maltophilia (P < 0.005). These in vitro studies support recent case study reports of successful therapy using the trimethoprim-sulfamethoxazole combination.     

In Vitro Activity of Spectinomycin Against Recent Urinary Tract Isolates

The susceptibilities to spectinomycin of 303 recent urinary tract isolates were determined and compared to the susceptibilities of those strains to ampicillin, tetracycline, and gentamicin. Based on minimal inhibitory concentrations, 84% of Escherichia coli, Klebsiella, and Enterobacter, 31% of other Enterobacteriaceae, 7% of Staphylococcus aureus and Streptococcus (including enterococci), and 0% of Pseudomonas aeruginosa were susceptible to concentrations of spectinomycin that are easily surpassed in serum (相似文献   

Beta-Lactamase Production and Resistance to Beta-Lactam Antibiotics in Nocardia

Although ampicillin has been suggested as a useful agent for the treatment of nocardiosis in man, little is known regarding the presence of beta-lactamase in Nocardia or its possible role in determining resistance to ampicillin and the other beta-lactam antibiotics. We have evaluated 55 isolates of Nocardia for susceptibility to five beta-lactam antibiotics and for the presence of beta-lactamase. Nocardia were resistant to penicillin G, cloxacillin, and cefazolin, but 27 and 62% were susceptible to 3.1 and 25 mug of ampicillin per ml, respectively. Almost 90% of these ampicillin-susceptible or intermediate strains were also susceptible to carbenicillin. The combination of ampicillin and cloxacillin was synergistic against many ampicillin-resistant strains. Beta-lactamase was detected in 89% of Nocardia isolates when intact cells were used and in six of six strains after cell fractionation. This beta-lactamase was most active against penicillin G and ampicillin, with lesser activity against carbenicillin and cephaloridine. These studies suggest that beta-lactamase may be present in all clinical isolates of Nocardia and that mechanisms of antimicrobial resistance other than or in addition to beta-lactamase are responsible for resistance of Nocardia to ampicillin and carbenicillin.     

Isolation and Characterization of Multiply Antibiotic-Resistant Clostridium perfringens Strains from Porcine Feces

Multiply antibiotic-resistant strains of Clostridium perfringens were isolated from porcine feces. Strains that were resistant to tetracycline, erythromycin, clindamycin, and lincomycin were isolated, but no penicillin- or chloramphenicol-resistant strains were obtained. Typical minimal inhibitory concentrations for resistant strains were 16 to 64 mug of tetracycline per ml, 64 to >128 mug of erythromycin per ml, >/=128 mug of lincomycin per ml, and 16 to 128 mug of clindamycin per ml. Resistance to erythromycin was always associated with resistance to lincomycin and clindamycin. Minimal inhibitory concentrations were determined for 258 strains from six farms that used antibiotics in their feeds and 240 strains from five farms that did not use antibiotics. The results show that 77.9 and 22.7% of the strains from the former farms were resistant to tetracycline and erythromycin-clindamycin-lincomycin, respectively. The comparable data from the latter farms were 25.0 and 0.8%, respectively. Agarose gel electrophoresis failed to reveal a plasmid band that was common to the resistant strains but absent in the susceptible strains. Attempts to transfer tetracycline, erythromycin, and clindamycin resistance from one strain, CW459, were not successful. Antibiotic-susceptible mutants were not isolated from this strain, despite the use of a variety of curing agents.