Methicillin resistant coagulase negative Staphylococcus: From colonizer to a pathogen

The objective of our study was to determine the frequency of methicillin resistance in coagulase negative staphylococcus (cons) and to determine its in-vitro antimicrobial susceptibility to various other routinely used antibiotics. it was a cross sectional study conducted at the department of microbiology,army medical college,rawalpindi,pakistan from june 2011 to may 2012. the organisms were identified on the basis of colony morphology,gram staining,catalase,dnaase and slide/tube coagulase tests. the organisms were considered to be methicillin resistant when the diameter of zone of inhibition was less than 25mm around 30μ g cefoxitin disc. antibiotic sensitivity was determined using the modified kirby-bauer disc diffusion method. from a total of 337 cons,201 were methicillin resistant and were included in the study. all were resistant to penicillin,followed by erythromycin (93•1%),ciprofloxacin (77%),co-trimoxazole (74•8%),gentamicin (68•3%),clindamycin (51•06%),tetracycline (44•6%),fusidic acid (40%),rifampicin (39•5%),chloramphenicol (19•3%),linezolid (2%),minocycline (1•1%),and vancomycin (0%). more than half of cons were methicillin resistant. vancomycin is the only drug to which all of the mrcons were sensitive,with more than 98% of the isolates being sensitive to linezolid and minocycline.