Bacteriological and PCR Detection of Pvl, Msra and Meca Genes Among Staphylococcus Aureus Isolated From Burn Wounds

Abstract

Background 
 Methicillin-resistant Staphylococcus aureus is a pathogen that is associated with nosocomial and community- burn wound infection. S aureus produces Panton-Valentine -Leukocidin which results in the destruction of leukocytes. Resistance of S. aureus to macrolides, lincosamides, and streptogramin B is associated with the presence of an efflux pump, encoded by Methionine Sulfoxide Reductase A (msrA or msrB) genes. 
 Objectives
 To isolate, determine the antibiotic susceptibility pattern, and to detect the presence of pvl and msrA genes from Staphylococcus aureus, isolated from burn wounds.
 Materials and Methods
 A total of 423 burn wound samples (218 from hospitalized and 205 from outpatients) were cultivated on different bacteriological media. Isolates were identified and S. aureus were further subjected to antibiotic susceptibility testing using disk diffusion method. Susceptibility to methicillin, oxacillin or cefoxitin, were used to determine methicillin-resistant Staphylococcus aureus strains. Polymerase chain reaction was used to detect mecA, pvl, and msrA genes in S. aureus isolates.
 Results
 Bacterial growth was detected from 170 (77.9%) of hospital samples and from 183 (89.26%) community-burn wounds. The predominant isolates were Gram-negative bacilli (71.76%) among hospitalized patients followed by S. aureus (22.35%). From the community samples, Staphylococcus epidermidis was the predominant isolate (86.9%), while few species of other Gram-positive organisms were also detected but no Gram-negatives were isolated. Among the 41 S. aureus isolates, the prevalence of methicillin-resistant S. aureus strains determined by oxacillin disk diffusion method was 58.53%, 65.85% by cefoxitin, whereas, 87.8% were positive for mecA gene by PCR. Pvl was detected in 3 (7.31%), while mrsA gene was detected among 17 (41.46%) of S. aureus isolates. 
 Conclusions
 Infection with Methicillin-resistant Staphylococcus aureus was common in burn wounds. The prevalence of msrA gene among nosocomial and community-burn wound isolates of S. aureus was high, while few S. aureus isolates were found to carry pvl gene.