Investigation of optimum temperature for coagulase test in Stahylococcus aureus strains

Abstract

Objective: Temperature of the incubator is important in microbiology laboratories. The recommended temperature is generally 35±2 OC for the detection of growing and antimicrobial susceptibility of bacteria. Nevertheless it is known that temperature over 35 OC is inappropriate for detecting methicillin resistance in Staphylococcus aureus. In different references, the optimum temperature for tube coagulase test used for differentiating S. aureus from other staphylococci is recommended as 35 OC, 37 OC, and 35 OC - 37 OC. In this study it was aimed to investigate the most appropriate incubator temperature for tube coagulase test in S. aureus strains. Methods: The study was conducted in Infectious Diseases Laboratory of our hospital. VITEK 2 automated system was used for identification of bacteria. Totally 110 S. aureus strains isolated from various clinical samples were included in the study. Rabbit plasma was used for tube coagulase test and the test was performed according to the manufacturer's instructions. Two identical sets of tubes were prepared for each strain and each tube was incubated at 35 OC and 37 OC in different incubators. All the tubes were read at the end of first, second, third, fourth and 24th hour for clot formation. Results were evaluated in three groups. Group 1: No clot formation Group 2: Weak clot formation Group 3: Strong clot formation SPSS 15.0 program was used for data analysis and McNemar Bowker test was used for comparing groups. Results: All of the strains had clot formation at both of the incubator temperatures during test period. The clot formation degree of strains were examined at 35 °C and 37 °C according to time. The statistical analysis showed no significant differences between incubation temperatures and groups. Conclusion: According to the results obtained in this study, both 35 °C and 37 °C was found appropriate for determining coagulase positivity in S. aureus.