Comparison of Cefocitin gene with Nuc gene in Staphylococcus aureus from three Tertiary Institution in South Western Nigeria

Abstract

Staphylococcus aureus is a human pathogen of global public health significance. It is implicated in a wide variety of infections. Each S. aureus strain is equipped with a diverse repertoire of genes ranging from the determinant genes, virulence genes, and antibiotic-resistant genes e. g. nuc genes, mecA genes, and PVL genes. Nuc genes (nuclease genes) is a heat-resistant gene that serves as a marker for S. aureus. mecA genes codes for penicillin binding protein 2a (PBP2a) that codes for methicillin resistance in S. aureus, while Panton-Valentine leukocidin genes (PVL) is a virulent gene that codes for toxins which form pores in the membrane of host defense cells. The fatal potentials of these genes mutating in S. aureus stirred up the interest to study their genetic variation in these locations. One hundred and thirty isolates of S. aureus were collected, cultured and phenotypically identified as S. aureus using coagulase test method and their colour change on MSA. Antibiotic susceptibility testing using disk diffusion method were performed on each of the isolates. The DNA was extracted by boiling method and the Polymerase Chain Reaction was performed on the isolates using the conventional PCR technique. The PCR products were tested for Nuc, mecA and PVL genes by running agarose gel electrophoresis. The study showed that there is a statistically significant relationship for the susceptibility testing of most of the antibiotics used, with the exception of Gentamicin, which had a p-value = 0.11. 63.8% of all the S. auerus isolates were MRSA, and 36.2% were MSSA by cefoxitin screening. Many of the isolates have diverse genetic variations. Of the 130 genetically assayed isolates of S. aureus, 81(62.3%) of them were Nuc positive, 60(46.1%) were mecA-positive, while 57(44%) were PVL positive. This study reveals a high prevalence of mecA genes and PVL genes which codes for antibiotic resistance and virulence factors in S. aureus. Some isolates, 9(6.9%) were coagulase positive nuc negative mecA positive S. aureus while 53(63.9%) were mecA negative methicillin resistant Staphylococcus aureus by cefoxitin screening. Some nuc gene negative with mecA and PVL positive S. aureus were also identified. While nuc positive compared with mecA and PVL positive and negative genes results were also ascertained.

All these reveals a remarkable genetic diversity in the whole isolates of this study and suggests the need for further research and monitoring of the genetic variation and evolution of this organism.