Isolation and Characterization of Coagulase-Negative Methicillin-Resistant <i>Staphylococcus aureus</i> from Patients in an Intensive Care Unit

Objective: To report the isolation and charac- terization of four coagulase-negative methi- cillin-resistant Staphylococcus aureus iso- lated from patients admitted to the ICU of a Kuwait hospital by bacteriological and mo- lecular methods. Methods: The isolates were characterized by cultural characteristics, Gram stain, catalase, coagulase, DNase and biochemical tests and typed by a combina- tion of antibiogram and pulsed-field gel elec- trophoresis to evaluate their relatedness. Re- sults: These isolates were gram-positive coc- ci in clusters, catalase, DNase and slide coa- gulase-positive but tube coagulase-negative. They gave negative results for ornithine de- carboxylase and pyrrolidonyl-arylamidase tests, which indicated that these were not Staphylococcus lugdunensis or Staphylococ- cus schleiferi, and were identified as S. au- reus by API Staph. They had identical antibio- grams and pulsed-field gel electrophoresis patterns which suggested that they had a common origin. Conclusion: The results highlight the need to complement the coagu- lase tests with other tests such as DNase and biochemical tests to correctly identify S. au- reus. Coagulase-negative S. aureus appears to be an increasing problem that clinical lab- oratories should be aware of. They are as virulent as those producing coagulase and can colonize, cause infections and spread among patients.