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At least 19 recordsLinked to original sources
PubMed1988

Evaluation of laboratory methods for the classification of oxacillin-resistant and oxacillin-susceptible Staphylococcus aureus.

The purpose of this study was to examine the efficacy of the oxacillin disk diffusion test and the methicillin and oxacillin agar screen tests as predictors of oxacillin resistance as defined by the reference broth microdilution method. A total of 444 clinical isolates of Staphylococcus aureus collected from individual patients over a four-year period were tested by (1) the oxacillin disk diffusion test, with particular attention to the presence of fine growth of a resistant subpopulation within the zone of inhibition (Ox Grow interpretive criteria); (2) the agar screen method using agar plates with 4% NaCl and either 6 mg/L oxacillin or 10 mg/L methicillin; and (3) the oxacillin and methicillin broth microdilution test methods with 2% NaCl supplementation. Overall, 62 (14%) isolates were resistant and 382 (86%) isolates were susceptible to oxacillin with the use of the reference broth microdilution system. The results indicate that the disk diffusion test with the use of the Ox Grow criteria had a high sensitivity (94%) and negative predictive value (98%) but a low specificity (67%) and positive predictive value (32%) when compared with the reference broth dilution test. Similarly, the agar screen tests had a high sensitivity (95-97%) and negative predictive values (99%) but low specificity (64-74%) and positive predictive values (30-37%). These data indicate that the agar screen tests and the oxacillin disk test with the use of the Ox Grow interpretive criteria may be useful as screening tests for detecting resistance to the penicillinase-resistant penicillins but that all resistant isolates should be confirmed by the reference broth dilution method because of the large number of false-resistant screening test results.

Bacteriological Techniques↗
PubMed1994

Genetics of oxacillin resistance in clinical isolates of Streptococcus pneumoniae that are oxacillin resistant and penicillin susceptible.

It has recently been reported that penicillin-sensitive pneumococci may exhibit reduced susceptibility to oxacillin, resulting in their misclassification as being penicillin resistant by oxacillin disk testing. Intermediate oxacillin resistance (MIC, 1.0 microgram/ml) in three of these apparently unrelated penicillin-susceptible clinical isolates of Streptococcus pneumoniae isolated in the United Kingdom and in four Spanish isolates was shown to be solely due to the acquisition of a gene encoding an altered penicillin-binding protein (PBP), PBP2X. PBP2X genes cloned from typical penicillin-resistant isolates of S. pneumoniae that possessed high-level oxacillin resistance were shown to be able to transform susceptible isolates of S. pneumoniae to intermediate oxacillin resistance. In all instances, the intermediately oxacillin-resistant PBP2X transformants retained susceptibility to penicillin (MIC, 0.06 microgram/ml). Under appropriate selective pressure, the acquisition of a low-affinity PBP2X by penicillin-susceptible pneumococci could result in an increasing number of false positives for penicillin resistance among isolates of S. pneumoniae screened with oxacillin. Additionally, these intermediately oxacillin-resistant isolates showed reduced susceptibility to cefotaxime, an agent likely to be prescribed in place of penicillin for the treatment of serious infections due to these apparently penicillin-resistant organisms.

Bacterial Proteins↗
PubMed1987

Relationship between cefamandole and cefuroxime activity against oxacillin-resistant Staphylococcus epidermidis and oxacillin resistance phenotype.

The activity of cefamandole and cefuroxime against oxacillin-resistant staphylococcus epidermidis was studied in vitro to determine whether there was any relationship between oxacillin resistance phenotypes and cephalosporin activity. Oxacillin resistance phenotypes were determined by efficiency-of-plating studies on Mueller-Hinton agar containing oxacillin, with and without NaCl, and incubated at 30 and 35 degrees C. On the basis of MIC and MBC determinations, cefamandole was more active than cefuroxime against oxacillin-resistant S. epidermidis. Although temperature had minimal effect on the activity of either cefamandole or cefuroxime, NaCl significantly decreased the activity of cefuroxime but not of cefamandole. Neither cephalosporin consistently produced greater than or equal to 99.9% bactericidal activity within 24 h in timed killing-curve studies. No consistent relationship was observed between cefamandole or cefuroxime activity and oxacillin resistance phenotype.

Cefamandole↗
PubMedDate not supplied

Antistaphylococcal activity of amoxicillin and ticarcillin when combined with clavulanic acid. Evaluation of oxacillin-resistant and oxacillin-susceptible isolates.

The beta-lactamase inhibitor, clavulanic acid, was combined with amoxicillin and with ticarcillin for in vitro studies with 586 staphylococci: 97 stock cultures of oxacillin-resistant strains recovered before 1982, and 489 blood or wound isolates collected from 40 separate medical centers during 1987-1988 (300 were oxacillin resistant). Over 92% of the staphylococci produced beta-lactamase enzymes and were thus resistant to both penicillins. However, with the addition of clavulanic acid, oxacillin-susceptible strains were rendered susceptible to low concentrations of amoxicillin and ticarcillin. Staphylococcus aureus strains with borderline or partial borderline resistance to penicillinase-resistant penicillins occurred infrequently (72 of 325 S. aureus isolates). Those strains were susceptible to both clavulanic acid combinations, because their methicillin resistance is thought to be due to an excess beta-lactamase production. Strains with chromosomally mediated intrinsic heteroresistance were relatively resistant to both drug combinations. Minimal inhibitory concentration (MIC) breakpoints that best separated those heteroresistant strains from oxacillin-susceptible isolates were as follows: amoxicillin/clavulanic acid, less than or equal to 2.0/1.0 micrograms/ml for susceptible; and ticarcillin/clavulanic acid, less than or equal to 4.0/2.0 micrograms/ml for susceptible. When the broth was supplemented by 2% NaCl, MICs for both drug combinations were increased by less than one doubling dilution. Although oxacillin and methicillin broth microdilution tests were more reliable when 2% NaCl was added, tests with the two drug combinations were only minimally improved by adding 2% NaCl to the broth medium.

Amoxicillin↗
PubMed1994

Mupirocin resistance among consecutive isolates of oxacillin-resistant and borderline oxacillin-resistant Staphylococcus aureus at a university hospital.

Mupirocin resistance was determined in consecutive oxacillin-resistant and borderline oxacillin-resistant Staphylococcus aureus clinical isolates collected over 14 months at a university hospital during 1991 and 1992. Twenty of 86 (23%) oxacillin-resistant and borderline oxacillin-resistant S. aureus isolates were mupirocin resistant; 80% were high-level resistant. Prior mupirocin use was a significant risk factor (relative risk, 6.08; 95% confidence interval, 3.7 to 9.99). Seven of 20 resistant isolates were distinct strains, as determined by pulsed-field gel electrophoresis typing. Two instances of clonal dissemination of a single strain occurred, but several other distinct mupirocin-resistant strains were documented. Mupirocin resistance was unexpectedly common among these isolates.

DNA, Bacterial↗
PubMed1978

[Spectrophotometric method of determining the oxacillin in oxacillin preparations].

The early described procedure for quantitative determination of oxacillin with the spectrophotometric method was used for the assay oxacillin tablets, capsules and injection preparations. It was shown that the excipients used in tablets and capsules did not interfere with oxacillin determination. The reproducibility of the method is +/- 1.5--2 per cent. The results of oxacillin determination with the new method and the currently used methods were compared.

Capsules↗
PubMed1990

In vitro activities of ampicillin-sulbactam and cefoperazone-sulbactam against oxacillin-susceptible and oxacillin-resistant staphylococci.

Ampicillin-sulbactam and cefoperazone-sulbactam were tested against staphylococci that were collected from 40 different medical centers throughout the United States. Oxacillin-resistant strains were resistant to both drug combinations, but oxacillin-susceptible strains were uniformly susceptible. The latter included strains with borderline susceptibility to oxacillin and methicillin.

Ampicillin↗
PubMed1983

Vancomycin treatment of bacteremia caused by oxacillin-resistant Staphylococcus aureus: comparison with beta-lactam antibiotic treatment of bacteremia caused by oxacillin-sensitive Staphylococcus aureus.

The epidemiology and therapy of 29 episodes of bacteremia caused by oxacillin- and aminoglycoside-resistant Staphylococcus aureus (OARSA) were compared with 29 episodes of bacteremia due to oxacillin-sensitive S. aureus (OSSA) that occurred during a 36-month period. Patients with bacteremia due to OSSA were younger (P less than 0.05) and were admitted more frequently with acute traumatic injury (P less than 0.01). The overall survival rate one month after persistent bacteremia was 74% for patients with OARSA bacteremia treated with vancomycin compared with 70% for patients with OSSA bacteremia treated with a beta-lactam antibiotic. The results indicate that vancomycin is an effective antibiotic for the treatment of bacteremia caused by OARSA and suggest that its effectiveness is comparable to that of beta-lactam antibiotic treatment of bacteremia due to OSSA.

Anti-Bacterial Agents↗
PubMed1992

Phage pattern-specific oxacillin-resistant and borderline oxacillin-resistant Staphylococcus aureus in U.S. hospitals: epidemiological significance.

For a 13-year period (1978 through 1990), oxacillin-resistant (MIC, greater than 4 micrograms/ml) Staphylococcus aureus (ORSA) strains were collected from Clinical Center (National Institutes of Health) patients and patients from five other U.S. hospitals. From Clinical Center patients, 251 of 253 isolates (99%) were bacteriophage typed as phage group III. Five other hospitals contributed 203 ORSA strains, of which 188 (93%) were group III. The group III ORSA strains predominantly included a characteristic core pattern of phages, 7/47/53/54/75/77. For the low-level (borderline) oxacillin-resistant strains (MIC, 2 to 4 micrograms/ml), amoxicillin-clavulanic acid combination (Augmentin) testing disclosed 62 hyper-beta-lactamase producers, of which 59 (95%) were of a separate, distinct S. aureus strain, with the phage pattern 92/94/96/292/D-11 (group V). Thus, ORSA and hyper-beta-lactamase producing S. aureus are distinct epidemic strains.

Bacteriophage Typing↗
PubMed1993

New latex reagent using monoclonal antibodies to capsular polysaccharide for reliable identification of both oxacillin-susceptible and oxacillin-resistant Staphylococcus aureus.

A new latex agglutination test (Pastorex Staph-Plus, Sanofi Diagnostics Pasteur), consisting of a mixture of latex particles coated with fibrinogen and immunoglobulin G for the detection of clumping factor and protein A and latex particles sensitized with monoclonal antibodies directed to Staphylococcus aureus serotype 5 and 8 capsular polysaccharides, was compared with three commercially available rapid agglutination methods for the identification of 220 isolates of S. aureus (61 oxacillin resistant) and 128 isolates of coagulase-negative staphylococci. The sensitivity for identification of S. aureus was high with the Pastorex Staph-Plus test (98.6%) compared with those of the other tests, which ranged from 91.8 to 84.5%. Test sensitivities for the identification of oxacillin-resistant S. aureus were as follows: Pastorex Staph-Plus, 95.1%; Pastorex Staph, 73.8%; Staphyslide, 72.1%; and StaphAurex, 49.2%.

Antibodies, Monoclonal↗
PubMed1995

Evaluation of new agglutination test for identification of oxacillin-susceptible and oxacillin-resistant Staphylococcus aureus.

A new agglutination test (Monostaph +; Bionor, Skien, Norway) has been developed. This new agglutination test has been compared with two other agglutination tests for the identification of 128 isolates of Staphylococcus aureus and 82 coagulase-negative staphylococci. The sensitivities of both Monostaph + and Pastorex Staph-Plus were excellent (98.7 and 97.4%, respectively) in detection of oxacillin-resistant Staphylococcus aureus. The specificity was 96.4% (two Staphylococcus epidermidis isolates and one Staphylococcus hominis isolate were false positive).

Agglutination Tests↗
PubMed1988

Evaluation of MicroScan MIC panels for detection of oxacillin-resistant staphylococci.

Clinical isolates of staphylococci (420 Staphylococcus aureus isolates and 248 coagulase-negative staphylococci) were tested by both MicroScan MIC panels (MicroScan, West Sacramento, Calif.) and an oxacillin agar screen (Mueller-Hinton agar [Difco Laboratories, Detroit, Mich.] containing 6 micrograms of oxacillin per ml and 4% NaCl) to evaluate the ability of MicroScan to detect oxacillin-resistant strains. MicroScan panels and oxacillin agar screen plates were incubated at 35 degrees C for 24 h and at 30 degrees C for an additional 24 h. Endpoints were recorded at 24 and 48 h. By MicroScan, 23 (5.5%) and 30 (7%) S. aureus isolates and 161 (65%) and 162 (65%) coagulase-negative staphylococci were oxacillin resistant at 24 and 48 h, respectively. At both 24 and 48 h, 23 (5.5%) S. aureus isolates and 162 (65%) coagulase-negative staphylococci were resistant by the oxacillin agar screen. Five strains for which the oxacillin MIC was 2 or 4 micrograms/ml and eight strains resistant to oxacillin only at 48 h were further evaluated by broth macrodilution testing for oxacillin with and without clavulanic acid, by oxacillin and amoxicillin-clavulanic acid disk diffusion, and by oxacillin agar screen comparing Mueller-Hinton agars purchased from Difco and BBL Microbiology Systems, Cockeysville, Md. By this additional testing, all 10 S. aureus isolates and 1 of 3 coagulase-negative staphylococci examined produced increased amounts of beta-lactamase. One coagulase-negative staphylococcus appeared to be truly intermediately oxacillin susceptible. There was no significant difference in the rate of detection of oxacillin resistance between MicroScan and the agar screen. MicroScan panels should be incubated for 24 h only, because prolonged incubation caused strains producing excessive amounts of beta-lactamase to appear to be falsely oxacillin resistant.

Coagulase↗
PubMed1993

Activity of ampicillin-sulbactam and oxacillin in experimental endocarditis caused by beta-lactamase-hyperproducing Staphylococcus aureus.

Using a rat model of aortic valve infective endocarditis, we previously found that oxacillin was equally effective against an oxacillin-susceptible strain of Staphylococcus aureus and a beta-lactamase-hyperproducing borderline oxacillin-susceptible strain of S. aureus; also, ampicillin-sulbactam was less effective than oxacillin against both isolates and at low doses was less effective against the borderline-susceptible strain than against the fully oxacillin-susceptible strain (C. Thauvin-Eliopoulos, L. B. Rice, G. M. Eliopoulos, and R. C. Moellering, Jr., Antimicrob. Agents Chemother. 34:728-732, 1990). In the present study, we extended this work, using alternative treatment schedules and additional bacterial strains. Extending treatment with low doses of ampicillin-sulbactam (500 and 250 mg/kg of body weight per day, respectively) to 6.5 days resulted in equalization of effectiveness against the previously studied strains BOSSA-1 and OSSA-1 (3.75 +/- 1.61 log10 and 4.71 +/- 1.79 log10 CFU of residual viable bacteria per g, respectively). Against the borderline oxacillin-susceptible strain BOSSA-1, increasing the sulbactam dosage from 500 to 2,000 mg/kg/day while maintaining a fixed dose of ampicillin (1,000 mg/kg/day) by continuous infusion resulted in lower bacterial counts (4.93 +/- 1.84 log10 versus 3.65 +/- 1.26 log10 CFU of residual viable bacteria per g, respectively), but this difference was of only borderline significance; differences in efficacy between the low-dose and high-dose sulbactam regimens were exaggerated when intermittent intravenous administration was used (6.19 +/- 1.90 log10 versus 3.37 +/- 1.41 log10 CFU/g, respectively; P < 0.001). However, for any individual sulbactam dosage, the model of administration (continuous versus intermittent infusion) did not affect the activity of the regimen. When additional strains were used in the model, oxacillin and ampicillin-sulbactam (1,000 plus 2,000 mg/kg/day) were equally effective against both oxacillin-susceptible and borderline oxacillin-resistant strains of S. aureus. These results support the predictions that oxacillin would be clinically effective in the treatment of infections caused by borderline oxacillin-susceptible strains of S. aureus and that, except at very low doses, ampicillin-sulbactam would also be as effective against borderline-susceptible strains as against fully oxacillin-susceptible strains of S. aureus.

Ampicillin↗
PubMed1985

Evaluation of mannitol salt agar with oxacillin as a screening medium for methicillin-resistant Staphylococcus aureus.

We evaluated the use of mannitol salt agar with oxacillin for use as a primary screening medium for the simultaneous detection and identification of methicillin-resistant Staphylococcus aureus in clinical surveillance specimens. Oxacillin agar dilution susceptibility tests with mannitol salt agar and Mueller-Hinton agar were performed in parallel with disk-agar diffusion testing on 95 oxacillin-susceptible and 105 oxacillin-resistant S. aureus stock isolates. MICs were found to be comparable, showing distinct separation of susceptible and resistant isolates into two groups with MICs of less than or equal to 2 and greater than or equal to 32 micrograms/ml, respectively. In accord with these findings, 4 micrograms of oxacillin per ml was selected for use in the screening medium. For performance evaluation, mannitol salt agar with 4 micrograms of oxacillin per ml was compared with mannitol salt agar without oxacillin by performing parallel screening tests on 153 clinical surveillance specimens. For detection of methicillin-resistant S. aureus, mannitol salt agar with 4 micrograms of oxacillin per ml was as sensitive as mannitol salt agar without oxacillin and required significantly fewer confirmatory tests. For primary identification of methicillin-resistant S. aureus, mannitol salt agar with 4 micrograms of oxacillin per ml was 6.4% false-positive and 1.1% false-negative, with a 93.6% positive predictive value. These findings indicate that mannitol salt agar with 4 micrograms of oxacillin per ml can be used as a reliable and cost-effective screening medium for the simultaneous detection and identification of methicillin-resistant S. aureus in clinical surveillance specimens.

Culture Media↗
PubMed1983

In vitro activity of rifampin in combination with oxacillin against Staphylococcus aureus.

The in vitro activity of rifampin alone and in combination with oxacillin was determined for 75 Staphylococcus aureus strains (64 susceptible and 11 resistant to oxacillin). Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were determined by broth microdilution; antibiotic combinations were evaluated by microdilution checkerboard and time-kill studies. The 90% MIC of rifampin was less than or equal to 0.015 micrograms/ml after both 24 and 48 h of incubation. The 90% MBC of rifampin was less than or equal to 2.0 micrograms/ml on subculture at 24 h of incubation and less than or equal to 0.5 micrograms/ml on subculture at 48 h. MIC checkerboards with oxacillin-susceptible strains revealed an additive or indifferent effect in 35 strains (55%) and antagonism in 29 strains (45%). MBC checkerboards performed by subculture at 24 h demonstrated antagonism for all but one of the oxacillin-susceptible strains, with sub-MBCs of rifampin impairing the bactericidal activity of oxacillin. MBC checkerboards performed by 48-h subculture revealed antagonism with 37 strains (58%); in 26 additional strains (40%), a synergistic, additive, or indifferent effect was observed at low antibiotic concentrations, but antagonism was seen at higher concentrations. Time-kill studies tended to show indifference rather than antagonism with oxacillin plus rifampin. In checkerboards performed with oxacillin-resistant strains, the addition of rifampin did not improve oxacillin inhibitory or bactericidal activity to a clinically significant extent; however, the addition of oxacillin improved the bactericidal activity of rifampin at easily achievable serum concentrations.

Drug Interactions↗