Distribution of PBP2a, MecA and Luk-PV Genes among Staphylococcal Isolates in South Eastern Nigeria

Background: Staphylococci are bacteria capable of causing a wide variety of infections in humans. Of the Staphylococci, coagulase-positive species (referred to as Staphylococcus aureus), is the major cause of human infections; panton valentine leukocidin (PVL), encoded by Luk-gene, is considered an important factor in staphylococcal virulence. The introduction of benzylpenicillin and subsequently methicillin, into clinical use, had a dramatic effect on mortality rates due to S. aureus infection. However, since the early 1960s, methicillin-resistant S. aureus (MRSA) and, lately, methicillin resistant coagulase-negative Staphylococci (MR-CoNS) have become recognized as important problems in hospitals and intensive care units worldwide. Methicillin-resistant S. aureus has been defined as S. aureus testing Oxacillin resistant, or positive for MecA gene and PBP2a. The distribution of Staphylococcal PBP2a, as well as MecA and Luk-PV genes, has not been well investigated in our locality, and raised the need for this study. Methods and materials: A total of 109 staphylococcal isolates (98 coagulase-positive and 11 coagulase-negative), recovered from hospital settings, were screened for methicillin susceptibility (by CLSI methods); presence of PBP2a, MecA and Luk-PV genes were investigated by standard molecular methods, using apropriate primers. Results: Of 98 coagulase positive Staphylococci (S. aureus), 20 (20.4%) were methicillin resistant; 18 (90%) of these possessed MecA gene and also tested positive for PBP2a – with Oxacillin MICrange of 4–256 μg/mL, while 2 (10%) neither produced PBP2a nor possessed MecA gene, despite being methicillin resistant. Two other MecA possessing S. aureus tested PBP2a negative and were methicillin susceptible. A total of 15 (15.3%) of the S. aureus isolates were Luk-PV positive. The majority (13 of 15) of Luk-PV positive S. aureus were methicillin susceptible (MSSA). Three of the S. aureus isolates were positive for both MecA and Luk-PV genes – two of these produced PBP2a. Of five isolates of S. aureus recovered from wound, only one possessed the Luk-PV gene. Seven (63.6%) of the coagulase-negative isolates encountered were MR-CoNS. Conclusion: Results tend to suggest that PVL is more associated with MSSA than MRSA and that PBP2a-mediated mechanism is the predominant mode of resistance among MRSA isolates in our locality. Also, it is pertinent to suggest re-appraisal of PVL as important Staphylococcal virulence factor.