Classification and characteristics of coagulase-negative, methicillin-resistant staphylococci

Abstract

Sixty-five clinical isolates of coagulase-negative, methicillin-resistant staphylococci were classified as Staphylococcus epidermidis (63.0%), phosphatase-negative S. epidermidis (12.3%), coagulase-negative S. aureus (6.2%), S. haemolyticus (6.2%), S. hominis (3.1%) and S. warneri (1.5%). Five of the organisms (7.7%) could not be classified with certainty as currently recognized species. Novobiocin resistance was encountered in 8 of the strains, but these were not classified as the accepted novobiocin-resistant staphylococcal species. Some differences in antibiotic resistance patterns to those typical of methicillin-resistant S. aureus were noted in that, although 29 strains were resistant to methicillin, penicillin, sulfamethizole, streptomycin and tetracycline, the remainder of the strains were sensitive to streptomycin or tetracycline or both. In a majority of the strains (42 of 65), methicillin susceptibility testing by the disk method at 30 or 37.degree. C in the presence of NaCl did not appear to enhance resistance expression. Most of the strains produced .beta.-lactamase (EC 3.5.2.6), but none of the 21 strains tested produced enterotoxin B.