Susceptibility of Staphylococcus species and subspecies to teicoplanin.

Twenty-four Staphylococcus species and their subspecies were examined for their susceptibilities to teicoplanin by disk diffusion (30-micrograms disk) and agar dilution for the determination of MICs. Moderately susceptible and resistant clinical strains were further tested for their susceptibilities to oxacillin and vancomycin. Teicoplanin resistance was not observed in the reference strains of the various Staphylococcus species isolated from healthy volunteers or animals. However, the novobiocin-resistant species Staphylococcus saprophyticus, Staphylococcus cohnii, Staphylococcus xylosus, Staphylococcus arlettae, Staphylococcus kloosii, and Staphylococcus gallinarum were less susceptible to teicoplanin (MIC, 2 to 8 micrograms/ml) than most of the novobiocin-susceptible species were (MIC, 0.5 to 4 micrograms/ml). Clinical isolates of coagulase-negative species were generally less susceptible to teicoplanin than were reference strains. Seven percent of the Staphylococcus epidermidis clinical strains were moderately susceptible (MIC, 16 micrograms/ml) to teicoplanin. Of these strains, 70% were oxacillin resistant. For Staphylococcus haemolyticus strains, 11% were resistant (MIC, greater than 16 micrograms/ml) and 21% were moderately susceptible to teicoplanin. Of these strains, 95% were oxacillin resistant, No strains of S. epidermidis or S. haemolyticus were intermediate or resistant to vancomycin. Teicoplanin appears to be less active in vitro against oxacillin-resistant S. haemolyticus. However, teicoplanin is an effective antimicrobial agent against many Staphylococcus species.     

The prevalence of staphylococcal resistance to penicillinase-resistant penicillins. A retrospective and prospective national surveillance trial of isolates from 40 medical centers

In a retrospective survey of resistance to penicillinase-resistant penicillins (PRPs) in 152,076 clinical staphylococcal strains isolated in 40 United States Hospitals in 1985 and 1986, rates of resistance to oxacillin were found to be 11 and 13%, respectively, among Staphylococcus aureus isolates. The rates were approximately four times higher among coagulase-negative staphylococcal strains. In a prospective study of 1,408 wound or bacteremia isolates from the participant hospitals, oxacillin and methicillin agar screening, disk diffusion, and broth microdilution testing were conducted at a single reference laboratory. These tests yielded PRP resistance rates of 15% among S. aureus, 75% among S. epidermidis, and 48% among other coagulase-negative strains. No major changes in the distribution of resistance rates among hospitals or by hospital type were observed. Dilution susceptibility testing of several antimicrobial agents against PRP-resistant isolates and species-matched susceptible isolates from the same hospital showed that teicoplanin and vancomycin were the most active drugs (100% of S. aureus isolates were susceptible). Teicoplanin and vancomycin disk diffusion testing of all PRP-resistant staphylococcal strains also showed that these isolates were susceptible to the glycopeptides. However, agar dilution screening and broth microdilution tests revealed that several coagulase-negative strains, predominantly S. haemolyticus, had teicoplanin MICs greater than or equal to 8 micrograms/ml. S. haemolyticus isolates represented a very small number of the total stains tested. Teicoplanin and vancomycin were also the most active drugs when tested against older (1962-82) clinical PRP-resistant S. aureus strains from the reference laboratory collection. The methods found to be superior in detecting PRP-resistant strains were the oxacillin 6 micrograms/ml agar screening test in 4% NaCl-supplemented Mueller-Hinton agar and the 1 microgram oxacillin disk test. By reference laboratory standards, participant laboratories were incorrect in only 2.3% of species identifications and 4.5% of oxacillin-susceptibility determinations, indicating acceptable contemporary agreement and accuracy.     

Susceptibility of Staphylococcus species and subspecies to fleroxacin.

Twenty-four Staphylococcus species or subspecies were examined for their susceptibilities to the fluoroquinolone fleroxacin (Ro 23-6240) by disk diffusion (5-micrograms disk) and by agar dilution for the determination of MICs. Resistant strains were further tested for their susceptibilities to oxacillin and the fluoroquinolone ciprofloxacin. Reference strains of the novobiocin-resistant species (Staphylococcus saprophyticus, Staphylococcus cohnii, Staphylococcus xylosus, Staphylococcus arlettae, and Staphylococcus gallinarum) had an intrinsic intermediate susceptibility (MIC, 4 micrograms/ml) to fleroxacin. Fleroxacin resistance was not observed in the reference strains of the novobiocin-susceptible species (MIC, 0.5 to 2.0 micrograms/ml). Clinical isolates of coagulase-negative species were generally less susceptible to fleroxacin than were reference strains. Seven percent of the Staphylococcus epidermidis clinical strains were resistant (MIC, greater than or equal to 8 micrograms/ml) to fleroxacin. Of these strains, 77% were resistant to oxacillin and 50% were resistant to ciprofloxacin. Thirty-four percent of the Staphylococcus haemolyticus clinical strains were resistant to fleroxacin, and 9% had intermediate susceptibility. Of the resistant strains, 95% were resistant to oxacillin and 77% were resistant to ciprofloxacin, while 23% had intermediate susceptibility to ciprofloxacin. Fleroxacin is an effective antimicrobial agent against most staphylococci.     

Low-level resistance to glycopeptides amongst staphylococcus species: surveillance in a university hospital and evaluation of a vancomycin screening agar.

The prevalence of low-level resistance to glycopeptides (teicoplanin MIC > or = 8 microg/mL and vancomycin MIC > or = 4 microg/mL) among staphylococci was investigated over a 15 month period. A total of 2,279 isolates (1,519 S. aureus, 760 coagulase-negative staphylococcus (CNS)) were screened using inoculum of 10(6) CFU/mL and Mueller-Hinton agars supplemented with 8 microg/mL of teicoplanin. Of these, 218 isolates (136 S. aureus and 82 CNS) grew on the screening agar. For these isolates, teicoplanin and vancomycin MICs were determined by agar dilution method and a vancomycin agar screening method was evaluated. The prevalence of low-level resistance to teicoplanin and vancomycin was 7.8% and 0.1% for S. aureus and 8.8% and 0.8% for CNS, respectively. The brain heart infusion agar containing 4 microg/mL of vancomycin failed to detect two out of eight staphylococcal isolates with vancomycin MICs of 4 microg/mL. Furthermore, the method appeared to lack reproducibility. Considering the increasing incidence of vancomycin treatment failure in staphylococcal infection, a more reliable screening method is required.     

Oxacillin susceptibility testing of coagulase-negative staphylococci using the disk diffusion method and the Vitek GPS-105 card

One hundred and ninety-three isolates of coagulase-negative staphylococci (CoNS) were tested against oxacillin by agar dilution, disk diffusion, and Vitek (GPS-105 card), and the presence of the mecA gene determined by multiplex PCR. The results obtained by all testing methods were in agreement for 190 isolates. Two mecA-negative isolates (S. lugdunensis and S. haemolyticus) had MICs of < or = 0.25 microg/ml by agar dilution and Vitek but were resistant by disk diffusion. One mecA-positive isolate was resistant by Vitek and disk diffusion but had an agar dilution MIC of < or = 0.25 microg/ml. For the species of CoNS tested, oxacillin susceptibility results obtained with the Vitek GPS-105 card and disk diffusion correlated well with results obtained by National Committee for Clinical Laboratory Standards agar dilution and with the presence of the mecA gene.     

Activities of daptomycin and teicoplanin against Staphylococcus haemolyticus and Staphylococcus epidermidis, including evaluation of susceptibility testing recommendations.

The in vitro activities of daptomycin, teicoplanin, and three other antimicrobial agents were determined against 105 strains of Staphylococcus haemolyticus and 92 strains of Staphylococcus epidermidis. The MICs for 90% of strains tested (MIC90s) of fusidic acid and rifampin were less than or equal to 0.25 microgram/ml. The MIC90s of daptomycin and vancomycin were less than or equal to 4 micrograms/ml. Teicoplanin had a comparable MIC90 of less than or equal to 4 micrograms/ml for isolates of S. epidermidis. However, MIC90s were 8 and 16 micrograms/ml for oxacillin-susceptible and oxacillin-resistant S. haemolyticus, respectively. Disk diffusion tests were evaluated for daptomycin and teicoplanin. Disks with 30 micrograms of teicoplanin performed satisfactorily when S. epidermidis was tested, but when S. haemolyticus was tested, there was a very major error rate of 10% and a minor error rate of 38%.     

In vitro activity of LY264826, a new glycopeptide antibiotic, against gram-positive bacteria isolated from patients with cancer.

The in vitro activity of LY264826, a novel glycopeptide antibiotic produced by Amycolatopsis orientalis, was compared with those of vancomycin, teicoplanin, and oxacillin against 311 gram-positive clinical isolates from patients with cancer, LY264826 had lower MICs for 90% of isolates (MIC90) than vancomycin for all species tested. It was active against oxacillin-resistant isolates including Staphylococcus aureus (MIC90, 0.5 micrograms/ml), Staphylococcus haemolyticus (MIC90, 2.0 micrograms/ml), Enterococcus spp. (MIC90, 0.5 micrograms/ml), Bacillus cereus (MIC90, 0.25 micrograms/ml), and Corynebacterium jeikeium (MIC90, 0.12 micrograms/ml). For S. aureus, including oxacillin-resistant isolates, the MICs of LY264826 were similar to those of teicoplanin. For coagulase-negative staphylococci, however, LY264826 had MICs that were 4- to 32-fold lower than those of teicoplanin. Against most streptococcal species the activities of LY264826 and teicoplanin were similar. Bactericidal activity against Staphylococcus spp. and most Streptococcus pyogenes isolates was less than or equal to 1 dilution of the MIC. One isolate of S. pyogenes and all Enterococcus faecalis strains tested were tolerant of LY264826, with MBCs greater than or equal to 32-fold greater than the MICs. The addition of 50% human serum resulted in a significant increase in activity only against Staphylococcus epidermidis. Variations in pH from 6.4 to 8.4 and in inoculum from 10(3) to 10(7) CFU/ml did not significantly affect the activity of LY264826.     

In vitro activity of quinupristin/dalfopristin,linezolid, telithromycin and comparator antimicrobial agents against 13 species of coagulase-negative staphylococci

OBJECTIVES: To determine in vitro susceptibilities of a large series of speciated coagulase-negative staphylococci (CNS) against three new antibiotics, linezolid, quinupristin/dalfopristin and telithromycin. METHODS: Susceptibilities to three new antibiotics and oxacillin, vancomycin, clindamycin and erythromycin were determined by the agar dilution method, as described by the NCCLS. RESULTS: Resistance to linezolid was not observed in any isolates, although MIC90 values varied between species. Fifteen of 658 (2.3%) isolates were resistant to quinupristin/dalfopristin, but < 1% of the clinically most important isolates of Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis demonstrated resistance to this agent. Susceptibility to clindamycin correlated with susceptibility to quinupristin/dalfopristin; however, resistance to clindamycin did not predict quinupristin/dalfopristin resistance. Telithromycin was the least active of the new agents tested, showing activity similar to that of clindamycin. Susceptibility and resistance to clindamycin were predictive of susceptibility and resistance to telithromycin. CONCLUSION: Clindamycin susceptibility can be used as a surrogate marker for susceptibility to quinupristin/dalfopristin and telithromycin. Quinupristin/dalfopristin and linezolid show good activity against both mecA-positive and -negative CNS.     

Simultaneous detection of the mecA and ileS-2 genes in coagulase-negative staphylococci isolated from Brazilian hospitals by multiplex PCR

Coagulase-negative Staphylococcus spp. (CNS) has been associated with primary bloodstream infections and implanted medical devices. Its importance is increasing due to the acquisition of resistance to oxacillin (Oxa) and, recently, resistance to mupirocin (Mup). Mupirocin, a topical antimicrobial, has been used in the prevention of staphylococci catheter colonization. Susceptibility to Oxa and Mup was analyzed by different testing methods in clinical CNS isolates. Among 112 CNS strains, 69 (61.6%) were Oxa(R) by the disk diffusion (DD) method and 72 (64.2%) grew on the oxacillin agar screen plate. S. epidermidis and S. haemolyticus presented high rates of oxacillin resistance, 75.4% and 96.1%, respectively. Twenty four (21.4%) strains were Mup(R) by the DD test and 21 of them (87.5%) were identified as S. epidermidis. The detection of the mecA and ileS-2 genes, determined by multiplex-PCR, showed that 72 (64.2%) CNS strains possessed the mecA gene, while 16 (14.3%) possessed the ileS-2 gene. Fifteen of these strains presented the two resistance genes simultaneously. The isolates containing the ileS-2 gene presented a minimum inhibitory concentration (MIC) >1024 microg/mL in the E-test, while low-level mupirocin resistance (MICs of 12-16 microg/mL) was observed in those strains without ileS-2. The resistances to high and low levels of mupirocin could not be distinguished when the DD test was used. The analysis of the Mup(R) S. epidermidis strains by Pulsed Field Gel Electrophoresis showed that 17 (80.9%) strains belonged to one of two patterns (A and B), which have been shown to be prevalent in hospitals in Rio de Janeiro. This report showed that the PCR method for detection of oxacillin and mupirocin resistance in CNS is necessary to determine accurate rates of these resistance, and will can help in the staphylococcal infections prevention and control policies in Brazil.     

Antimicrobial resistance in nosocomial isolates of Staphylococcus haemolyticus.

Staphylococcus haemolyticus is frequently cultured from hospitalized patients and is characterized by resistance to multiple antimicrobial agents. We found that S. haemolyticus represented 70 of 524 (13%) coagulase-negative staphylococcal isolates identified by the clinical microbiology laboratories of two hospitals over 2 months. S. haemolyticus isolates were recovered from wounds (44%), urine (26%), blood (10%), and other sources (20%). All S. haemolyticus isolates were tested for susceptibility to six antimicrobial agents; 77% were resistant to three or more agents, and 41% were resistant to five or six agents. In addition, among 47 multiply resistant isolates, high MICs (greater than or equal to 6.25 micrograms/ml) of vancomycin (62% of isolates) and teicoplanin (91% of isolates) were found. DNA probes which were derived from S. epidermidis or S. aureus and which contained sequences associated with resistance to antimicrobial agents were used to detect specific genes in the total cellular and plasmid DNAs of 10 resistant S. haemolyticus isolates. Resistance gene probes and the numbers of resistant isolates hybridizing were as follows: methicillin, 10 of 10; gentamicin, 9 of 10; erythromycin, 7 of 10; and trimethoprim, 0 of 10. Genes for resistance to methicillin were found only in chromosomal locations, genes for resistance to gentamicin were found in both chromosomal and plasmid locations, and genes for resistance to erythromycin were found in plasmid locations only. With the exception of trimethoprim resistance determinants, similar genes were found among concurrently isolated multiply resistant S. epidermidis isolates from our hospitals. S. haemolyticus is a potentially important nosocomial species which readily acquires antimicrobial resistance genes and which shares, to some extent, in a common gene pool with S. epidermidis.     

Detection of mecA-mediated resistance using reference and commercial testing methods in a collection of Staphylococcus aureus expressing borderline oxacillin MICs

Phenotypic methods for detecting mecA-mediated resistance in Staphylococcus aureus include both oxacillin and cefoxitin susceptibility tests; many laboratories perform multiple tests. Conflicting oxacillin and cefoxitin susceptibility results are most likely to occur for isolates that either have reduced susceptibility to oxacillin by a non-mecA-mediated mechanism or are mecA positive but are very heteroresistant. To understand the performance of oxacillin and cefoxitin tests for such isolates, we tested 135 S. aureus isolates using either cefoxitin or oxacillin and compared the results with mecA polymerase chain reaction. These strains either expressed borderline oxacillin MICs (1-4 microg/mL) and had undetermined mecA status or were mecA positive but were not detected by oxacillin broth microdilution (BMD) or disk diffusion (DD) in original testing. For 24-h readings, performance of cefoxitin tests (sensitivity/specificity) were DD (99/100), Etest using < or =6 microg/mL as susceptible (99/98), and Phoenix MIC using < or =4 microg/mL as susceptible (98/100). Using 6 microg/mL of cefoxitin as a screen test in both BMD and agar dilution also worked well (98/98-100). Sensitivity/specificity of oxacillin methods were oxacillin agar screen (BBL: 80/86; Remel, Lenexa, KS: 85/50), DD (91/59), BMD (85/88), MicroScan (89/96), VITEK Legacy (82/93), VITEK 2 (91/73), and Phoenix, (67/96). These results suggest that a cefoxitin test can be used alone to predict mecA-mediated resistance in S. aureus.     

European glycopeptide susceptibility survey of Gram-positive bacteria for 1995

In the European Glycopeptide Susceptibility Survey 7078 Gram-positive isolates collected in 1995 from 70 centers in 9 countries of Western Europe were examined, using a standardized, quantitative susceptibility testing method. Of the 7078 isolates, 6824 (96.4%) were tested by the national coordinating centers. Teicoplanin (mode MIC 0.5 μg/mL) was generally twice as active as vancomycin (mode MIC 1 μg/mL) against Staphylococcus aureus (n = 2852). All isolates were susceptible to vancomycin (MIC ≤4 μg/mL) and all but four to teicoplanin (MIC ≤8 μg/mL); these four isolates were of intermediate susceptibility (MIC 16 μg/mL). With coagulase-negative staphylococci (n = 1444), the distribution of MIC of teicoplanin was wider than for vancomycin. Two and two-tenths percent of coagulase-negative staphylococci excluding Staphylococcus haemolyticus required 16 μg/mL teicoplanin for inhibition (intermediate) and 0.4% ≥32 μg/mL (resistant). Among isolates of S. haemolyticus, 4.4% were of intermediate susceptibility (MIC 16 μg/mL) and 3.3% were resistant (MIC ≥32 μg/mL) to teicoplanin. However, this species represented only 6.3% of the isolates of coagulase-negative Staphylococcus spp. Generally, teicoplanin (mode MIC ≤0.12 μg/mL) was four to eight times more active than vancomycin (mode MIC ≤0.5 μg/mL) against the 770 streptococcal isolates. Glycopeptide-susceptible Enterococcus spp. (n = 1695) were generally four times more susceptible to teicoplanin (mode MIC 0.25 μg/mL) than to vancomycin (mode MIC 1 μg/mL). Combined vancomycin and teicoplanin (VanA phenotype) resistance was observed more frequently (9.3%) in isolates of Enterococcus faecium than in Enterococcus faecalis (0.8%). Four isolates of unspeciated enterococci (1.4%) also expressed this resistance phenotype. Four isolates of E. faecium and four of E. faecalis expressed the VanB-type (low-level, vancomycin only) resistance. Spain was the only country not to submit resistant E. faecium strains while resistant E. faecalis isolates came only from Spain and Italy.     

Glycopeptide susceptibility profiles of Staphylococcus haemolyticus bloodstream isolates

Twelve clinical strains of Staphylococcus haemolyticus (eight methicillin resistant and three methicillin susceptible), isolated from blood cultures between 1982 and 1997, were investigated for teicoplanin and vancomycin susceptibility profiles. On the basis of conventional MIC tests and breakpoints, four isolates were susceptible (MICs, 1 to 8 microgram/ml) and eight were resistant (MICs, 32 to 64 microgram/ml) to teicoplanin while all were susceptible to vancomycin (MICs, 1 to 2 microgram/ml). All four strains for which the conventional teicoplanin MICs were within the range of susceptibility expressed heterogeneous resistance to teicoplanin and homogeneous vancomycin susceptibility. Of the eight strains for which the conventional teicoplanin MICs were within the range of resistance, six expressed heterogeneous and two expressed homogeneous teicoplanin resistance while seven showed heterogeneous vancomycin resistance profiles (with subpopulations growing on 8 microgram of the drug per ml at frequencies of >/=10(-6) for six strains and 10(-7) for one) and one demonstrated homogeneous vancomycin susceptibility. Of six bloodstream isolates of other staphylococcal species (S. aureus, S. epidermidis, and S. simulans), for all of which the conventional teicoplanin MICs were >/=4 microgram/ml and the vancomycin MICs were 相似文献   

In vitro susceptibilities of four species of coagulase-negative staphylococci.

The in vitro susceptibilities of 260 strains of coagulase-negative staphylococci to penicillin G, oxacillin, nafcillin, methicillin, cephalothin, and seven non-beta-lactam antimicrobial agents were determined and compared with the susceptibilities of 54 strains of Staphylococcus aureus with known patterns of susceptibility. Penicillin G susceptibility for S. aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, and Staphylococcus hominis was readily determined by using beta-lactamase tests with induced cells and with a standardized microdilution test. MIC criteria for susceptibility used for S. aureus were applicable to the coagulase-negative species. Percentages of organisms susceptible were as follows: S. epidermidis, 7%; S. haemolyticus, 5%; and S. hominis, 47%. Oxacillin susceptibility for these four species was readily determined by using a modification of the microdilution test. MIC criteria for susceptibility used for S. aureus were applicable to S. haemolyticus and S. hominis, but alternate criteria were necessary for S. epidermidis. Percentages of organisms susceptible were as follows: S. epidermidis, 29%; S. haemolyticus, 36%; and S. hominis, 97%. Staphylococcus saprophyticus differed from the other staphylococcal species; all strains were beta-lactamase negative and were penicillin susceptible but had higher penicillin G MICs than did susceptible strains of the other species. There was total cross resistance among the penicillinase-resistant penicillins and cephalothin for the coagulase-negative staphylococci as well as for S. aureus; oxacillin MICs were more reliable than MICs of the other drugs or a standardized disk diffusion test for distinguishing resistant from susceptible strains. Vancomycin, rifampin, and ciprofloxacin were consistently active against all staphylococci. Erythromycin, clindamycin, gentamicin, and trimethoprim-sulfamethoxazole were more active against oxacillin-susceptible staphylococci than against oxacillin-resistant staphylococci.     

Bactericidal action of nafcillin, vancomycin, and three cephalosporins against nafcillin-susceptible and nafcillin-resistant coagulase-negative staphylococci

Coagulase-negative staphylococci (S. epidermidis, 43 strains; S. warneri, 16 strains; S. haemolyticus, five strains; and others, four strains) were tested by the agar dilution method for nafcillin susceptibility: 53 were susceptible with a minimal inhibitory concentration (MIC) of less than or equal to 2 micrograms/ml; four were of indeterminate susceptibility, MIC = 4-16 micrograms/ml; and 11 were resistant, MIC greater than or equal to 32 micrograms/ml. The bactericidal activities from 0 to 24 hr for nafcillin, vancomycin, cephalothin, cefazolin, and cefamandole, each at 16 micrograms/ml in broth, were determined for all the isolates. The data indicate that a nafcillin agar dilution susceptibility test result of resistance does not consistently predict lack of killing activity by the cephalosporins. It is likely that each cephalosporin would have to be tested against individual coagulase-negative staphylococci in order to determine a suitable therapeutic or prophylactic cephalosporin, if a cephalosporin were to be used. Vancomycin was bactericidal for all the nafcillin-resistant coagulase-negative organisms tested.     

Activities of two new teicoplanin amide derivatives (MDL 62211 and MDL 62873) compared with activities of teicoplanin and vancomycin against 800 recent staphylococcal isolates from France and the United States.

MDL 62211 is the amide derivative of the teicoplanin complex and MDL 62873 is a more focused amide derivative of the teicoplanin A2-2 peak. Each investigational compound had nearly identical activity and was 2- to 16-fold more active than teicoplanin or vancomycin. The MDL 62873 MICs for 90% of the strains tested were as follows: Staphylococcus aureus, oxacillin susceptible, 0.12 micrograms/ml; S. aureus, oxacillin resistant, 0.25 micrograms/ml; coagulase-negative staphylococci (CNS), oxacillin susceptible, 0.25 micrograms/ml; and CNS, oxacillin resistant, 2 micrograms/ml. CNS isolates from France were generally more susceptible than those tested in the United States. Teicoplanin-resistant U.S. isolates were usually Staphylococcus haemolyticus (1.8% of all tested strains), for which MICs ranged from 32 to greater than 128 micrograms/ml. MDL 62873 was not active against the Bacteroides fragilis group but was generally effective against gram-positive anaerobic strains.     

Detection of Methicillin Resistance in Coagulase-Negative Staphylococci Initially Reported as Methicillin Susceptible Using Automated Methods

Reliable detection of methicillin resistance in coagulase-negative staphylococci (CNS) is required for appropriate therapy of serious infections from these pathogens. To determine the most accurate method of measuring methicillin resistance in CNS initially reported as methicillin susceptible by automated methods, we compared mecA detection by polymerase chain reaction (PCR) with phenotypic methods. One hundred eighty-eight blood culture isolates of CNS that were initially reported as susceptible to methicillin using commercial methods (Vitek or MicroScan) were tested by agar dilution, disk diffusion, oxacillin salt agar screen plate, and a multiplex PCR assay using primer sets for mecA and 16S rRNA. Sixteen isolates (8.5%) previously reported as methicillin susceptible by automated methods contained the mecA gene. MICs of these isolates ranged from 0.5 μg/mL to ≥128 μg/mL. Ten of these isolates had MICs equal to or below the NCCLS breakpoint of 2 μg/mL. Six of the 10 isolates (4 with MICs of 0.5 μg/mL and 2 with MICs of 2 μg/mL) did not grow on any of the oxacillin screen plates after 48 h of incubation at 30°C or 35°C. All six isolates were induced to grow in the presence of oxacillin at 128 μg/mL by serial passaging on plates containing increasing concentrations of antibiotic. Retesting with MicroScan and Vitek detected methicillin resistance in 7 and 10 isolates, respectively. Disk diffusion testing with incubation for 48 h proved to be the next best method after PCR for detection of methicillin resistance (15 of 16 isolates). Commercial automated methods and some methods recommended by National Committee for Clinical Laboratory Standards may not detect methicillin resistance in CNS that carry the mecA gene and have MICs just below breakpoint.     

In vitro antistaphylococcal activities of two investigative fluoroquinolones, CI-960 and WIN 57273, compared with those of ciprofloxacin, mupirocin (pseudomonic acid), and peptide-class antimicrobial agents.

By using broth microdilution, 373 clinical isolates of staphylococci were studied to determine their susceptibilities to CI-960, WIN 57273, ciprofloxacin, mupirocin, vancomycin, teicoplanin, and ramoplanin. Test strains comprised 179 strains of Staphylococcus aureus and 194 strains of coagulase-negative species. Strains of S. aureus were susceptible to CI-960, which had a mode MIC of 0.032 micrograms/ml and an MIC for 90% of the strains of 2 micrograms/ml. CI-960 was equally active against methicillin-susceptible and -resistant S. aureus strains as well as ciprofloxacin-resistant strains. Similarly, WIN 57273 was highly active, with a mode MIC of 0.008 micrograms/ml and an MIC for 90% of the strains of 1 micrograms/ml. No cross-resistance to CI-960 and WIN 57273 among ciprofloxacin-resistant strains was detected. Mupirocin was four- to eightfold more active than ramoplanin, vancomycin, and teicoplanin. With regard to coagulase-negative staphylococci, CI-960 and WIN 57273 were the most active of the test compounds, inhibiting all strains at 0.5 and 1 micrograms/ml, respectively. Against the same strains, mupirocin was fourfold more active than ramoplanin and eightfold more active than vancomycin. Five strains of S. haemolyticus were found to be resistant to ciprofloxacin, while resistance to teicoplanin was found among strains of S. epidermidis, S. haemolyticus, S. hominis, S. saprophyticus, S. simulans, S. warneri, and S. xylosus.     

Combinations of Vancomycin and β-Lactams Are Synergistic against Staphylococci with Reduced Susceptibilities to Vancomycin

Evidence of synergism between combinations of vancomycin and beta-lactam antibiotics against 59 isolates of methicillin-resistant staphylococci (Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus haemolyticus) for which vancomycin MICs ranged from 1 to 16 microg/ml were tested by broth microdilution checkerboard, disk diffusion, agar dilution, and time-kill antimicrobial susceptibility tests. The combination of vancomycin and oxacillin demonstrated synergy by all test methods against 30 of 59 isolates; no antagonism was seen. Synergy with vancomycin was also found by modified disk diffusion testing for ceftriaxone, ceftazidime, cefpodoxime, and amoxicillin-clavulanate but not for aztreonam. Evidence of synergy correlated directly with vancomycin MICs. The efficacy of vancomycin given alone and in combination with nafcillin was tested in the rabbit model of experimental endocarditis caused by three clinical isolates of glycopeptide-intermediate-susceptible S. aureus (GISA) (isolates HIP5827, HIP5836, and MU50). Two of the GISA isolates (isolates MU50 and HIP5836) were extremely virulent in this model, with 27 of 42 (64%) animals dying during the 3-day trial. Therapy with either vancomycin or nafcillin given as a single agent was ineffective for animals infected with HIP5827 or MU50. However, the combination of vancomycin and nafcillin resulted in a mean reduction of 4.52 log10 CFU/g of aortic valvular vegetations per g compared to the reduction for controls for animals infected with HIP5827 and a reduction of 4. 15 log10 CFU/g for animals infected with MU50. Renal abscesses caused by HIP5827 were sterilized significantly better with the combination of vancomycin and nafcillin than by either treatment alone. We conclude that the combination of vancomycin and beta-lactams with antistaphylococcal activity is an effective regimen for the treatment of infections with clinical strains of staphylococci which demonstrate reduced susceptibility to glycopeptides.     

凝固酶阴性葡萄球菌菌种鉴定与苯唑西林耐药凝固酶阴性葡萄球菌检测准确性

目的 评价凝固酶阴性葡萄球菌(CNS)菌种鉴定与苯唑西林耐药凝固酶阴件葡萄球菌(MRCNS)检测的准确性.方法 139株临床分离CNS,经ID 32 STAPH鉴定到种,用头孢西丁(FOX)、苯唑西林(OXA)纸片扩散法检测MRCNS,以Slidex MRSA detection乳胶凝集法检测青霉素结合蛋白2a(PBP2a)作为参考方法.结果 139株CNS鉴定为8个种,依次为溶血葡萄球菌、表皮葡萄球菌、人葡萄球菌、木糖葡萄球菌、腐生葡萄球菌、耳葡萄球菌、模仿葡萄球菌、沃氏葡萄球菌.FOX纸片法总的敏感度和特异度为99.0%和86.0%;OXA纸片法总的敏感度和特异度为91.7%和74.4%.影响FOX纸片法敏感度的菌种为1株表皮葡萄球菌;影响其特异度的菌种包括木糖葡萄球菌、沃氏葡萄球菌、腐生葡萄球菌;而影响OXA纸片法敏感度的菌种包括溶血葡萄球菌、人葡萄球菌、模仿葡萄球菌、耳葡萄球菌;影响其特异度的菌种包括人葡萄球菌、模仿葡萄球菌、木糖葡萄球菌、耳葡萄球菌、腐生葡萄球菌、沃氏葡萄球菌.结论 FOX纸片法检测MRCNS准确性因菌种不同有所差异,尤其应关注木糖葡萄球菌、沃氏葡萄球菌、腐生葡萄球菌的影响.建议检测MRCNS时,尽可能将CNS鉴定到种,视菌种必要时用PBP2a或mecA基因予以确认.