Rapid detection of methicillin resistant staphylococcus aureus bacteraemia in bactec blood culture bottles of ICU patients

ABSTRACT

Methicillin resistance and infections caused by methicillin-resistant Staphylococcus aureus [MRSA] represent a growing problem and a challenge for health-care institutions. Resistance to methicillin is primarily associated with acquisition of mecA gene. The aim of the current study was to find out the incidence of MRSA bacteraemia among ICU bacteraemic patients and evaluate direct mecA gene detection from blood culture bottles and the oxacillin [methicillin] disk diffusion method commonly used in hospitals to identify MRSA using PCR for mecA detection in isolates as the golden. The study was conducted on 300 ICU patients with pyrexia of unknown origin. Blood samples were collected under complete aseptic precautions for blood culture onto BACTEC blood culture bottles. Detection of mecA gene by Polymerase Chain Reaction [PCR] was carried directly on any bottle showing Gram-positive cocci in clusters in film. Isolates of all positive blood culture bottles were identified. For Staph aureus isolates oxacillin disk diffusion and mecA gene detection was carried. Out of 300 samples included in the study, 190 [63.3%] yielded growth. Methicillin resistant Staph aureus was isolated from 88/190 patients [46.3%]. The agreement between the results of mecA gene detection among isolates and those among blood culture bottles was found to be 100% [Kappa = 1] and the sensitivity 100%. Disk diffusion method detected 79 cases out of the 88 MRSA strains The agreement between the results of oxacillin disk diffusion sensitivity method and mecA detection either in isolates or blood culture bottles was found to be 94% [Kappa= 0.87] and the sensitivity was 89. 8%.Methicillin resistant Staph. aureus bacteraemia is a major problem in ICU. Detection of mecA gene by PCR from blood culture bottles is a good tool for rapid detection of methicillin resistance in staph aureus bacteremia. To confirm the specificity of this test, more samples from patients with Enterococcus and Streptococcus species bacteraemias need to be studied