An investigation of staphylococcus lugdunensis and similar bacteria and their antibiotic susceptibility in coagulase negative staphylococci̇ isolated from blood cultures

Staphylococcus lugdunensis is a coagulase negative staphylococcus (CoNS) and a member of normal skin flora. According to CLSI criteria, although S. lugdunensis strains are CoNS, the growth inhibition zone of methicillin should be evaluated as Staphylococcus aureus. Therefore, identification of S. lugdunensis strains is important. S. lugdunensis is the only CoNS species in which PYR (pyrrolidonyl arylamidase) and ODC (ornithine decarboxylase) tests are both positive. The aim of this study was to investigate S. lugdunensis and similar bacteria in CoNS isolated from blood culture and to determine their antibiotic susceptibility. In our study, 250 CoNS strains isolated from blood culture samples were evaluated. ODC and PYR tests were performed on CoNS strains. When positive results were obtained in either of these two tests, the strain was identified with API Staph and antibiotic susceptibility tests were performed by disc diffusion method. In our study, five strains (2%) were identified as Staphylococcus epidermidis being ODC positive and PYR negative, 14 (5.6%) were identified as Staphylococcus haemolyticus and three (1.2%) were Staphylococcus chromogenes a total of 17 CoNS strains were PYR positive and ODC negative. There were no S. lugdunensis strain that was positive for both of ODC and PYR tests. Two hundred and twent eight (91.2%) of CoNS were PYR and ODC negative. Twenty of the 22 CoNS were found to be methicillin-resistant and two were methicillin-sensitive. The most effective antibiotics were linezolid (100%), telithromycin (77.3%), gentamicin (59.0%), trimethoprim-sulfamethoxazole (54.5%), clindamycin (27.2%), levofloxacin (22.7%) and erythromycin (13.6%) respectively. All strains were resistant to penicillin. As conclusion, it was found that the rates of S. epidermidis, S. haemolyticus and S. chromogenes isolated from blood culture were lower than expected. The use of ODC and PYR tests in the routine diagnostic laboratory was found to be very valuable. In our study, it was thought that beta-lactam antibiotics should not be selected in empirical treatment because of our high methicillin resistance rate. Key Words: Blood culture, Coagulase negative staphylococci, Staphylococcus lugdunensis, antibiotic susceptibility test