Characterization of Staphylococcus aureus isolates obtained from health care institutions in Ekiti and Ondo States, South-Western Nigeria

Abstract

Staphylococcus aureus is one of the major causative agents of infection in all age groups following surgical wounds, skin abscesses, osteomyelitis and septicaemia. In Nigeria, it is one of the most important pathogen and a frequent micro-organism obtained from clinical samples in the microbiology laboratory. Data on clonal identities and diversity, surveillance and new approaches in the molecular epidemiology of this pathogen in Nigeria are limited. This study was conducted for a better understanding on the epidemiology of S. aureus and to enhance therapy and management of patients in Nigeria. A total of 54 S. aureus isolates identified by phenotypic methods and obtained from clinical samples and nasal samples of healthy medical personnel in Ondo and Ekiti States, South-Western Nigeria were analysed. Typing was based on antibiotic susceptibility pattern (antibiotyping), polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) of the coagulase gene and pulsed field gel electrophoresis (PFGE). Of the 54 isolates, 50 were confirmed as S. aureus by PCR detection of the nuc gene. The antibiotic susceptibility testing showed that all the isolates were susceptible to fusidic acid and clindamycin, but 100% resistant to penicillin, 70% to tetracycline, 22% to erythromycin, 6% to gentamicin and 4% to ciprofloxacin. Only one isolate was confirmed to be a methicillin-resistant S. aureus (MRSA). The study established the importance of confirming phenotypic identification of S. aureus and MRSA by molecular techniques. There was a high level of agreement between the three methods in the typing of methicillin-susceptible S. aureus (MSSA). Furthermore, the recognition of a predominant MSSA clone from clinical and nasal samples indicates the possible cross-infection from medical personnel to patients. A total of nine of the 50 isolates were Panton-Valentine leukocidin (PVL) positive suggesting that they are community-associated S. aureus isolates. The study provided baseline information on the need for effective infection control measures in health-care institutions in South-Western Nigeria. Key words: Staphylococcus aureus, phenotypic and molecular typing, methicillin-susceptible S. aureus clone