Characterisation and genotyping of methicillin-resistant staphylococcus aureus isolates from a tertiary healthcare centre in Ogun state Nigeria

Abstract

Methicillin-resistant and pathogenic methicillin-susceptible Staphylococcus aureus (MRSA and MSSA) isolates are associated with human infections, sometimes with fatal consequences. Colonisation precedes infection and aids transmission between healthcare workers (HCWs) and the patients they attend to. Previous MRSA and MSSA studies from western Nigeria reported on the genotypes of isolates from Lagos and other cities but not from the hospital site selected in this study. This study characterised and genotyped the nasal MRSA and MSSA isolates and determined the risk factors for MRSA nasal colonisation among HCWs and patients in the gynaecology, intensive care unit (ICU), outpatients and surgical wards of the Federal Medical Centre (FMC) Abeokuta, Ogun state Nigeria. A total of 169 presumptive S. aureus isolates were detected from 32% (81/250) participants using selective culture media. Matrix-assisted laser desorption ionisation time of flight mass spectrometry (MALDI ToF MS) technique and multiplex-PCR (M-PCR) assays confirmed 56% (95/169) of isolates as S. aureus. Multiplex PCR assays detected the mecA and Panton Valentine leukocidin (PVL) toxin genes in 38% (36/95) and 22% (21/95) of these isolates respectively. Only 10% (25/250) and 7.6% (19/250) of the participants carried mecA- and PVL-positive S. aureus isolates respectively. The Vitek® 2 system showed that 38% (36/95) of the confirmed S. aureus isolates were MRSA using cefoxitin screening and showed xv antibiotic resistance to benzylpenicillin (97%), trimethoprim/sulfamethoxazole (81%) and tetracycline (50%). All isolates were sensitive to vancomycin and mupirocin using the Vitek® 2 system and these results were confirmed with E test and disc diffusion methods. According to SCCmec typing, the circulating MRSA strains at this setting were all CA-MRSA IV and V. All four agr types I to IV were detected among these MRSA and MSSA isolates. The 16 representative isolates yielded clonal complexes CC1-ST5, CC1-ST8, CC8-ST88, CC23-ST152, CC1-ST772 and CC14-ST789. The most abundant clones were CC14-ST789 [31% (5/16)] and CC1-ST8 [25% (4/16)]. These results were in agreement with previous reports from western Nigeria, except that this is the first report of ST789 in Nigeria. Questionnaire analysis showed that the awareness for MRSA was higher among doctors than nurses and patients, as expected. Patients that were students or were self/government employed had a higher MRSA knowledge score than other patients that were not in these groups. Significant association existed between MRSA colonisation and hospitalisation (p = 0.015), previous travel (p = 0.05) and ward type (p = 0.001) for patients in this study but not between MRSA colonisation and age (≥ 40 y), antibiotic use, household animals and human contacts, living in crowded housing and immune status of patients. Overall, the presence of PVL-carrying-agr I to IV MRSA and MSSA isolates with high resistance to over-the-counter antibiotics, such as trimethoprim/sulfamethoxazole and tetracycline is a cause of concern. The most prevalent clone CC14-ST789 in this study had not been reported in Nigeria before but was reported in Ghana in a previous study. Patients’ information showed a travel history to this country. It may be possible that this clone might have been transmitted from there. Regular surveillance for pathogenic S. aureus isolates combined with adequate infection control and antibiotic stewardship are recommended at this setting.