Abstract
Few studies evaluating susceptibility testing of methicillin-resistant staphylococci have included isolates of Staphylococcus epidermidis, a known pathogen in many types of serious infections. We tested 175 S. epidermidis and 95 Staphylococcus aureus isolates to determine the most sensitive procedures for detecting methicillin-resistant staphylococci. Reference procedures included agar dilution with methicillin and 4% NaCl in the agar and broth microdilution with methicillin and 2% NaCl in cation-supplemented Mueller-Hinton broth. After 24 h of incubation, the results from both methods correlated well and were within 1 log2 dilution for all isolates tested. Only one-half of all resistant isolates (92 of 183) were detected at 18 h by using the standard disk diffusion technique with 5-micrograms methicillin disks, and even fewer were detected with 10-micrograms methicillin disks and newly recommended zone-size criteria. However, the standard disk diffusion method with 4% NaCl in the agar increased the sensitivity and specificity for identification of the proper phenotype to greater than 92%. The spread plate and new spot techniques, both using agar with 4% NaCl, were also sensitive methods. Of 47 S. epidermidis isolates tested against oxacillin, 6 (13%) were oxacillin susceptible but methicillin resistant. Two automated systems, the Automicrobic system (Vitek Systems) and MicroScan (American MicroScan), as well as two broth screening systems available from Remel and Austin Biological Laboratories, failed to detect several resistant isolates, depending on the species.
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Selected References
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- Archer G. L. Antimicrobial susceptibility and selection of resistance among Staphylococcus epidermidis isolates recovered from patients with infections of indwelling foreign devices. Antimicrob Agents Chemother. 1978 Sep;14(3):353–359. doi: 10.1128/aac.14.3.353. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hansen S. L., Freedy P. K. Variation in the abilities of automated, commercial, and reference methods to detect methicillin-resistant (heteroresistant) Staphylococcus aureus. J Clin Microbiol. 1984 Sep;20(3):494–499. doi: 10.1128/jcm.20.3.494-499.1984. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hansen S. L., Pope W. A. Screening method for rapid detection of methicillin-resistant (heteroresistant) Staphylococcus aureus. J Clin Microbiol. 1985 Nov;22(5):886–887. doi: 10.1128/jcm.22.5.886-887.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hindler J. A., Inderlied C. B. Effect of the source of Mueller-Hinton agar and resistance frequency on the detection of methicillin-resistant Staphylococcus aureus. J Clin Microbiol. 1985 Feb;21(2):205–210. doi: 10.1128/jcm.21.2.205-210.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jorgensen J. H., Redding J., Johnson J. E., Holloway V., Almeida R. J. Rapid recognition of methicillin-resistant Staphylococcus aureus by use of automated test systems. J Clin Microbiol. 1984 Sep;20(3):430–433. doi: 10.1128/jcm.20.3.430-433.1984. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lally R. T., Ederer M. N., Woolfrey B. F. Evaluation of the newly modified AutoMicrobic system gram-positive susceptibility-MIC card for detection of methicillin-resistant Staphylococcus aureus. J Clin Microbiol. 1986 Feb;23(2):387–387. doi: 10.1128/jcm.23.2.387-.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McDougal L. K., Thornsberry C. New recommendations for disk diffusion antimicrobial susceptibility tests for methicillin-resistant (heteroresistant) staphylococci. J Clin Microbiol. 1984 Apr;19(4):482–488. doi: 10.1128/jcm.19.4.482-488.1984. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Thornsberry C., McDougal L. K. Successful use of broth microdilution in susceptibility tests for methicillin-resistant (heteroresistant) staphylococci. J Clin Microbiol. 1983 Nov;18(5):1084–1091. doi: 10.1128/jcm.18.5.1084-1091.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Woolfrey B. F., Lally R. T., Ederer M. N. Evaluation of the AutoMicrobic system Gram-Positive Susceptibility-MIC card for detection of oxacillin-resistant coagulase-negative staphylococci. J Clin Microbiol. 1986 Mar;23(3):629–630. doi: 10.1128/jcm.23.3.629-630.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]