Coagulase-negative variants of methicillin-resistant Staphylococcus aureussubsp. aureus strains isolated from hospital specimens

At the Department of Clinical Bacteriology of Medical University of Warsaw, S. aureus strains displaying negative reactions in the coagulase tube-test were isolated with a relatively high frequency from clinical specimens. As many as seventeen of such strains all from different patients were isolate d during 1994 among MRSA strains. Despite coagulase negativity all strains were positive in tests for clumping factor (CF), protein A and thermonuclea se. Biochemical characteristics, phage patterns and antibiotic resistance c haracteristics of these strains were tested. Most of the coagulase-negative strains possessed a heterogenous type of methicillin resistance. Apart fro m methicillin most of them were resistant to many other antimicrobials. All were resistant to gentamicin, tetracyclines and macrolide-lincosamide-stre ptogramine B. An occurrence of coagulase-negative S. aureus strains may lea d to problems in their identification and the necessity of an application o f other methods like CF, protein A or biochemical reactions.