The Relation of Methicillin-Resistance to Growth Time in Staphylococci

Abstract

Background: With the biochemical and molecular studies on penicillin-binding proteins associated with methicillin-resistance in staphylococci the determination and interpretation of the resistance have been changed. Particularly careful evaluation of staphylococci isolated from blood cultures before instituting therapy is of utmost significance in regard to morbidity and mortality. One of the important criteria of this evaluation is the growth tune of staphylococci. The purpose of this study was to determine the relation of methicillin-resistance to growth time in Staphylococcus aureus and methicillin-resistant staphylococci. Methods: The study was carried on a total of 66 clinical isolates of staphylococci including 18 methicillin-susceptible Staphylococcus aureus (MSSA), 14 methicillin-resistant Staphylococcus aureus (MRSA), 19 methicillin-susceptible coagulase-negatiye staphylococci (MSCNS) and 15 methicillin-resistant coagulase-negative staphylococci (MRCNS). Following growth on subculture under similar conditions, all isolates were inoculated in equal quantities into hemoculture bottles, the optimum time-of-positivity in minutes for each isolate was calculated, and the growth times of the 4 isolate groups were statistically compared. Results: The longest growth time was detected in MRCNS. The growth time was longer in MRSA and MRCNS than in MSSA and MSCNS, respectively; however, a statistically significant difference was observed between MRCNS and MSCNS isolates. Conclusion: In conclusion, it is known that in methicillin resistant Staphylococcus aerus, PBP2a which is responsible for methicillin resistance takes over the role penicillin-binding protein of PBP1. PBP2 and PBP3 in peptidoglycan synthesis. But, other possible factors affecting the resistance mechanisms or growth time of MRCNS should be investigated.