Comparison of susceptibility testing methods with mecA gene analysis for determining oxacillin (methicillin) resistance in clinical isolates of Staphylococcus aureus and coagulase-negative Staphylococcus spp.
(9/449)
Ninety-nine clinical staphylococcal isolates (58 coagulase-negative Staphylococcus spp. [CoNS] and 41 Staphylococcus aureus isolates) were evaluated for susceptibility to oxacillin. The following susceptibility testing methods, media, and incubation conditions were studied: agar dilution by using Mueller-Hinton (MH) medium (Difco) supplemented with either 0, 2, or 4% NaCl and incubation at 30 or 35 degrees C in ambient air for 24 or 48 h; disk diffusion by using commercially prepared MH medium (Difco) and MH II agar (BBL) and incubation at 35 degrees C in ambient air for 24 or 48 h; and agar screen (spot or swab inoculation) by using commercially prepared agar (Remel) or MH agar (Difco) prepared in-house, each containing 4% NaCl and 6 microg of oxacillin/ml (0.6-microg/ml oxacillin was also studied with MH agar prepared in-house for the agar swab method and CoNS isolates) and incubation at 35 degrees C in ambient air for 24 or 48 h for swab inoculation and at 30 or 35 degrees C in ambient air for 24 or 48 h for spot inoculation. The results for these methods were compared to the results for mecA gene detection by a PCR method. Given the ability to support growth and the results for susceptibility testing (the breakpoint for susceptible isolates was +info)
Evaluation of the BBL Crystal MRSA ID System for detection of oxacillin resistance in Staphylococcus aureus.
(10/449)
AIMS: To evaluate the BBL Crystal MRSA ID System for detection of oxacillin resistance in Staphylococcus aureus. METHODS: 52 methicillin resistant S aureus (MRSA) from five different countries and 85 methicillin susceptible S aureus (MSSA) were included. The species was confirmed by tube coagulation and detection of the clumping factor using the Staphaurex Plus. Clonal non-identity of the MRSA isolates was shown by pulsed field gel electrophoresis. MIC values (oxacillin) were determined using the Etest. Polymerase chain reaction was carried out to detect the mecA gene. The BBL Crystal MRSA ID System was carried out according to the manufacturer's instructions. RESULTS: The BBL Crystal MRSA ID System showed fluorescence in 45 of 52 MRSA (sensitivity 86.5%; negative predicitive value 92.2%), and the specificity was 97.6% (positive predicitive value 95.7%). Two of seven MRSA that failed to show fluorescence had MIC values (oxacillin) of 4 mg/litre. CONCLUSIONS: The BBL Crystal MRSA ID System is a valuable test for detecting oxacillin resistance in S aureus. Its major advantage is the short time (4-5 hours) required to perform the test when organisms are grown on tryptic soy agar or sheep blood agar. Difficulties may arise in borderline resistant isolates. (+info)
Treatment of hospitalized patients with complicated gram-positive skin and skin structure infections: two randomized, multicentre studies of quinupristin/dalfopristin versus cefazolin, oxacillin or vancomycin. Synercid Skin and Skin Structure Infection Group.
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Quinupristin/dalfopristin (Synercid), the first injectable streptogramin antibiotic available for the treatment of complicated gram-positive skin and skin structure infections, was compared with standard comparators (cefazolin, oxacillin or vancomycin) in one USA and one international trial. These two randomized, open-label trials of virtually identical design enrolled a total of 893 patients (450 quinupristin/dalfopristin, 443 comparator). The majority of patients had erysipelas, traumatic wound infection or clean surgical wound infection. Staphylococcus aureus was the most frequently isolated pathogen in both treatment groups and polymicrobial infection was more common in the quinupristin/dalfopristin group than in the comparator group. The clinical success rate (cure plus improvement) in the clinically evaluable population was equivalent between the two treatment groups (68.2% quinupristin/dalfopristin, 70.7% comparator; 95% CI, -10.1, 5.1) despite a shorter mean duration of treatment for quinupristin/dalfopristin patients. In the bacteriologically evaluable population, by-patient and by-pathogen bacteriological eradication rates were somewhat lower for quinupristin/dalfopristin (65.8% and 66.6%, respectively) than for the comparator regimens (72.7% and 77.7%, respectively). The lower bacteriological response rates in the quinupristin/dalfopristin group were, in part, due to a higher rate of polymicrobial infections and a higher incidence of patients classified as clinical failure, a category which included premature discontinuation of treatment because of local venous adverse events. The bacteriological eradication rate for quinupristin/dalfopristin was higher in monomicrobial infections than in polymicrobial infections (72.6% versus 63.3%, respectively), whereas the corresponding rate for the comparator regimens was lower for monomicrobial infections than polymicrobial infections (70.8% versus 83.1%). This finding was not unexpected, since the spectrum of quinupristin/dalfopristin is focused on gram-positive pathogens and additional antibiotics to treat gram-negative bacteria were not required per protocol. The systemic tolerability of both treatment regimens was qualitatively similar. A higher rate of drug-related venous adverse events was reported for quinupristin/dalfopristin (66.2%) than for the comparator regimen (28.4%). Premature discontinuation of study drug was primarily due to adverse clinical events for quinupristin/dalfopristin (19.1%), whereas the most common reason for discontinuation among those receiving the comparator regimens was treatment failure (11.5%). Quinupristin/dalfopristin is an effective alternative for the treatment of hospitalized patients with complicated skin and skin structure infections due to quinupristin/ dalfopristin-susceptible gram-positive organisms, including methicillin- and erythromycin-resistant S. aureus. (+info)
Inducible oxacillin-hydrolyzing penicillinase in Aeromonas hydrophila isolated from fish.
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An inducible penicillinase was shown to be present in a strain of Aeromonas hydrophila subsp. hydrophila isolated from freshwater fish. Enzyme induction was observed with benzylpenicillin or 6-aminopenicillanic acid, and the enzyme was cell bound. The penicillinase was purified 50-fold from a crude cell extract. The molecular weight was estimated to be 23,000 by gel filtration. The pH and temperature optima for the enzyme activity were 8.0 and 35 degrees C, respectively. The penicillinase showed a unique substrate profile by hydrolyzing oxacillin about twice as rapidly as benzylpenicillin. The enzyme activity was weakly inhibited by sodium chloride but was not affected by p-chloromercuribenzoate. The property of penicillinase production by the A. hydrophila strain could not be transferred to Escherichia coli and also could not be eliminated from the bacteria by ethidium bromide treatment. (+info)
Phenotypic detection of nosocomial mecA-positive coagulase-negative staphylococci from neonates.
(13/449)
Over a 3-year period, we screened antimicrobial resistance genotype (mecA-positive or -negative) in clinically significant coagulase-negative staphylococci isolated from patients residing in our neonatal intensive care unit. For the 152 study strains, the accuracy of standard methods (agar dilution MIC, disc diffusion and agar screen tests) in detecting oxacillin resistance during 48 h of incubation was evaluated. Using mecA gene PCR and Southern blot hybridization as the gold standard, the differential in MICs of additional antibiotics selected for their relevant clinical use in our setting was also compared with mecA status of the isolates. The frequency of mecA was 48.6% among study strains. When applying the previous (1998) and most current (1999) NCCLS interpretive criteria, the specificities of oxacillin agar dilution MICs in detecting the 78 mecA-negative isolates were 100 and 89.7%, respectively, at 24 h, and 100 and 80.7%, respectively, at 48 h. In this respect, the sensitivities of oxacillin agar dilution MICs in detecting the 74 mecA-positive strains were 75.6 and 97.2%, respectively, at 24 h, and 86.4 and 100%, respectively, at 48 h. When applying the previous and most current NCCLS zone size interpretive criteria, oxacillin zone diameters were in false-susceptible error for 13.5 and 8.1%, respectively, of the 74 mecA-positive strains tested at 24 h, and for 6.7 and 2.7%, respectively, at 48 h. Accordingly, when the 78 mecA-negative strains were considered, oxacillin zone diameters were in false-resistant error for 2.5 and 8.9%, respectively, at 24 h, and for 8.9 and 15.3%, respectively, at 48 h. The oxacillin salt agar screen assay accurately identified all mecA-negative strains at both 24 and 48 h. However, 26 (35.1%) and 7 (9.4%) of the mecA-positive strains were misinterpreted as susceptible by the agar screen test at 24 and 48 h, respectively. Using the presence of mecA as the reference standard for interpreting oxacillin susceptibility results, strains lacking mecA were more likely to be susceptible to ampicillin, ceftazidime, gentamicin, netilmicin and rifampicin than were mecA-positive strains. Vancomycin was the only antibiotic tested for which all strains, regardless of mecA status, remained susceptible. (+info)
Methods for improved detection of oxacillin resistance in coagulase-negative staphylococci: results of a multicenter study.
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A multilaboratory study was undertaken to determine the accuracy of the current National Committee for Clinical Laboratory Standards (NCCLS) oxacillin breakpoints for broth microdilution and disk diffusion testing of coagulase-negative staphylococci (CoNS) by using a PCR assay for mecA as the reference method. Fifty well-characterized strains of CoNS were tested for oxacillin susceptibility by the NCCLS broth microdilution and disk diffusion procedures in 11 laboratories. In addition, organisms were inoculated onto a pair of commercially prepared oxacillin agar screen plates containing 6 microg of oxacillin per ml and 4% NaCl. The results of this study and of several other published reports suggest that, in order to reliably detect the presence of resistance mediated by mecA, the oxacillin MIC breakpoint for defining resistance in CoNS should be lowered from >/=4 to >/=0.5 microg/ml and the breakpoint for susceptibility should be lowered from /=18 mm for susceptibility is suggested. Due to the poor sensitivity of the oxacillin agar screen plate for predicting resistance in this study, this test can no longer be recommended for use with CoNS. The proposed interpretive criteria for testing CoNS have been adopted by the NCCLS. (+info)
MICs of mutacin B-Ny266, nisin A, vancomycin, and oxacillin against bacterial pathogens.
(15/449)
Peptide antibiotics, particularly lantibiotics, are good candidates for replacing antibiotics to which bacteria have become resistant. In order to compare two such lantibiotics with two antibiotics, the MICs of nisin A, mutacin B-Ny266, vancomycin, and oxacillin against various bacterial pathogens were determined. The results indicate that nisin A and mutacin B-Ny266 are as active as vancomycin and oxacillin against most of the strains tested. Furthermore, mutacin B-Ny266 remains active against strains that are resistant to nisin A, oxacillin, or vancomycin. The wide spectrum of activity of mutacin B-Ny266, its low MICs against bacterial pathogens, and its activity against bacteria resistant to other inhibitors support the development of this substance for therapeutic use. (+info)
Comparison of PCR detection of mecA with methicillin and oxacillin disc susceptibility testing in coagulase-negative staphylococci.
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The provisional BSAC method for the detection of methicillin sensitivity in coagulase-negative staphylococci (CNS) requires incubation of isolates for 48 h and raises the problem of timely reporting of susceptibility data. The forthcoming withdrawal of methicillin raises another difficulty. We evaluated 42 clinically significant CNS blood culture isolates by PCR, methicillin and oxacillin disc testing and by using methicillin Etests. Our results suggest that, although oxacillin disc susceptibility testing is a reasonable first line step, optimal and timely detection of resistance or susceptibility may require a combination of phenotypic and genotypic methods. (+info)