Staphylococcus species and their Methicillin-Resistance in 7424 Blood Cultures for Suspected Bloodstream Infections

Abstract

Objectives: The aim of this study was to evaluate the distribution of Staphylococcus species in bloodstream infections and to assess their susceptibility to methicillin. Material and Methods: Between January 1^st 2008 - December 31^st 2010, 7424 blood culture sets were submitted to the Laboratory Department of the Hospital for Clinical Infectious Diseases in Cluj-Napoca, Romania. The blood cultures were performed using BacT/Alert until January 2010 and BacT/Alert 3D automated system (bioMérieux) after that date. The blood culture bottles were incubated at 37°C in a continuously monitoring system for up to 7 days. The strain identifications were performed by conventional methods, ApiStaph galleries and  Vitek 2 Compact system. Susceptibility to methicillin was determined by disk diffusion method with cefoxitin disk and by using Vitek 2 Compact system. Results: From the total number of performed blood cultures, 568 were positive with Staphylococcus species. From 168 bacteriemic episodes 103 were with Staphylococcus aureus. Among 65 coagulase-negative staphylococci isolates, Staphylococcus epidermidis was the most frequently isolated species (34), followed by Staphylococcus hominis (15), Staphylococcus haemolyticus (8), Staphylococcus saprophyticus (3), Staphylococcus cohnii (1), Staphylococcus auricularis (1), and 3 strains that were not identified at species level. Methicillin resistance was encountered in 53.40% of Staphylococcus aureus strains and in 80% of coagulase-negative staphylococci. Conclusions: An important percentage of blood cultures were contaminated with Staphylococcus species. The main species identified in true bacteriemia cases were Staphylococcus aureus and Staphylococcus epidermidis. The percentage of methicillin-resistance, proved to be high not only for coagulase-negative staphylococci but also for Staphylococcus aureus.