[01] Abdulhadi Sale Kumurya, Department of Medical Laboratory Science, Faculty of Allied Health Sciences, Bayero University, Kano, Nigeria.

Where laboratories are performing antimicrobial susceptibility testing using cefoxitin, Staphylococcus aureus will likely be correctly identified as methicillin-resistant Staphylococcus aureus (MRSA). Importantly, cefoxitin has been found to be more reliable than oxacillin in disc diffusion, broth microdilution, and agar dilution assays. A balanced opening out of this attempt is the inclusion of cefoxitin into media which is selective for MRSA. This work illustrates the testing of mannitol salt agar containing 4 mg/liter cefoxitin with a unique set of well-characterized MRSA strains and an equal number of known methicillin susceptible Staphylococcus aureus (MSSA) strains. The agar supported the growth of 96.6% of the MRSA strains in the set and inhibited the growth of 100% of the MSSA strains. The study indicates that selective media based on cefoxitin are better to those based on oxacillin for the detection of MRSA. The findings of this study demonstrate that cefoxitin is far superior to oxacillin when it is used in mannitol salt medium. By the use of a 48-h incubation and a 10²-CFU/ml inoculum, the sensitivity and specificity of the cefoxitin MSA plate method were 100% (compared to 90.7% with oxacillin) and 100% (compared to 96.0% for oxacillin), respectively, when the comparison was made for the strains used in both studies.

MRSA, MSA, Cefoxitin, Selective Media, Growth, Staphylococcus aureus

[01] Blanc, D. S., A. Wenger, and J. Bille. 2003. Evaluation of a novel medium for screening specimens from hospitalized patients to detect methicillin-resistant Staphylococcus aureus. J. Clin. Microbiol. 41: 3499-3502. [02] Cuny, C., and W. Witte. 1998. Methicillin-resistant Staphylococcus aureus—diagnostic aspects. Biotest Bull. 6: 51-57. [03] Davies, S., and P. M. Zadik. 1997. Comparison of methods for the isolation of methicillin resistant Staphylococcus aureus. J. Clin. Pathol. 50: 257-258. [04] Felton, A., B. Grandry, P. H. Lagrange, and I. Casin. 2002. Evaluation of three techniques for detection of low-level methicillin-resistant Staphylococcus aureus (MRSA): a disk diffusion method with cefoxitin and moxalactam, the Vitek 2 System, and the MRSA-screen latex agglutination test. J. Clin. Microbiol. 40: 2766-2771. [05] Jayaratne, P., and C. Rutherford. 1999. Detection of methicillin-resistant Staphylococcus aureus (MRSA) from growth on mannitol salt oxacillin agar using PCR for nosocomial surveillance. Diagn. Microbiol. Infect. Dis. 35: 13-18. [06] Perry, J. D., A. Davies, L. A. Butterworth, A. L. J. Hopley, A. Nicholson, and F. K. Gould. 2004. Development and evaluation of a chromogenic agar medium for methicillin-resistant Staphylococcus aureus. J. Clin. Microbiol. 42: 4519-4523. [07] Perry, P. L., G. W. Coombs, J. D. Boehm, and J. W. Pearman. 1998. A rapid (20h) solid screening medium for detecting methicillin-resistant Staphylococcus aureus. J. Hosp. Infect. 40: 67-72. [08] Skov, R., R. Smyth, M. Clausen, A. R. Larsen, N. Frimodt-Möller, B. Olsson-Liljequist, and G. Kahlmeter. 2003. Evaluation of a cefoxitin 30 μg disc on IsoSensitest agar for detection of methicillin-resistant Staphylococcus aureus. J. Antimicrob. Chemother. 52: 204-207. [09] Skov, R., R. Smyth, A. R. Larsen, N. Frimodt-Möller, and G. Kahlmeter. 2005. Evaluation of cefoxitin 5 and 10 μg discs for the detection of methicillin resistance in staphylococci. J. Antimicrob. Chemother. 55: 157-161. [10] Smyth, R. W., G. Kahlmeter, B. Olsson Liljequist, and B. Hoffman. 2001. Methods for identifying methicillin resistance in Staphylococcus aureus. J. Hosp. Infect. 48: 103-107. [11] Wertheim, H., H. A. Verbrugh, C. van Pelt, P. de Man, A. van Belkum, and M. C. Vos. 2001. Improved detection of methicillin-resistant Staphylococcus aureus using phenyl mannitol broth containing aztreonam and ceftizoxime. J. Clin. Microbiol. 39: 2660-2662. [12] Kim, C. (2012). Properties of a novel PBP2A protein homolog from Staphylococcus aureus strain LGA251 and its contribution to the beta-lactam-resistant phenotype. J. Biol. Chem. 287: 36854–36863. [13] Skov, R. (2013). Phenotypic detection of mecC-MRSA: cefoxitin is more reliable than oxacillin. J. Antimicrob. Chemother. 68: 2949–2950. [14] Cartwright, E. J. P. (2013). Use of Vitek 2 antimicrobial susceptibility profile to identify mecC in methicillin-resistant Staphylococcus aureus. J. Clin. Microbiol. 51: 2732–2734. [15] Cuny, C. (2011). Rare occurrence of methicillin-resistant Staphylococcus aureus CC130 with a novel mecA homologue in humans in Germany. PLoS ONE. 6: e24360. [16] Anna-Kaarina, J., Sanna Laakso, P., Anne sAittakorpi, M., Lindfors, L., Huopaniemi, H. and Minna, M. (2009). Rapid identification of bacterial pathogens using a PCR- and microarray-based assay. BMC Microbiology 9: 161. [17] Bignardi, G. E., Woodford, N., Chapman, A., Johnson, A. P. and Speller, D. C. E. (1996). Detection of the mec-A gene and pbenotypic detection of resistance In Staphylococcus aureus isolates with border ine or low-level methicillin Resistance. Journal of Antimicrobial Chemotherapy 37: 53—63. [18] Cavassini, M. A., Wenger, K., Jaton, D. S., Blane, and J. Bille. (1999). Evaluation of MRSA Screen, a simple anti-PBP-2a slide latex agglutination kit, for rapid detection of methicillin resistance in Staphylococcus aureus. Journal of Clinical Microbiology. 37: 1591-1594. [19] Perez, R. E., Claverie, M. F., Villar, J. and Méndez, Á. (2001). Multiplex PCR for Simultaneous Identification of Staphylococcus aureus and Detection of Methicillin and Mupirocin Resistance. Journal of Clinical Microbiology. 39 (11): 4037-4041. [20] Tiemersma, E. W., Brozwaer, S. L., Lyytikainen, O., Degener, J. E., Schrijnemakers. P., Bruinsma, N., Monen, J., Witte, W. and Grundman, H. (2004). Methicillin-resistant Staphylococcus aureus in Europe. 1999-2002. Emerging Infectious Diseases. 10: 1627-1634.