Virulence factors play a key step for pathogenic invasion leading to staphylococcal infection in the hospital, community and in environmental settings. Rich diversity of virulence associated genes within S. aureus is reported worldwide [16, 17]. It was observed in the present study that the virulence determinants such as sea, tsst and eta gene were found to be more predominant in the study isolates. However, in an earlier study conducted by Mojtabi et al., 2018, reported high prevalence of eta, etb and etd genes in S.aureus among clinical isolates . In another study by Wu et al., 2011 and van Trijp et al., 2010, low prevalence of eta gene was found as compared to our study [19, 20]. Studies from different countries revealed that sea is the most common enterotoxin recovered followed by seb and sed and also distribution of different Staphylococcal enterotoxins (SE’s) were found from the food poisoning outbreaks . Studies from Korea by Lim et al., 2010, stated that Staphylococcal enterotoxin (seg, sei, sec) genes and toxic shock syndrome toxin (tst) genes were most common in clinical MRSA isolates . Thus from the above study it can be explained that the high frequency of exfoliative toxin (eta) which facilitated colonization and invasion may be due to wound infection and presence of enterotoxin pose a high risk of food borne intoxication.
Our study involved MRSA targeting virulence genes and showed 31% of the occurrence rate which was comparatively lower to the studies of Liang et al., 2019 (55%) and Koosha et al., 2013 (87.6%) [23, 24]. Current study observed sixty three MRSA isolates of which 85.71% of the isolates were found to harbour enterotoxin A (sea) gene. This rate is found to be higher than the previous studies [25, 26].
Mobile genetic element (SCCmec) carries both resistance as well as virulence genes. Different SCCmec types carry different virulence genes. It has been found from the study of Lim et al., 2010 that 97.6% of SCCmec type II carried sec, seg, sei and tst gene; 73% of SCCmec type III strains carried sea gene and 89.7% of SCCmec type IV strain carried sec,seg,sei genes . While our study reveals that 28.2% of SCCmec type II isolates carried sea, seb, cna, tst and eta genes, 10% of SCCmec type III carried sea, seb, cna and tst gene, 34.1% of SCCmec type V was found to carry sea, seb, ica, cna, tst eta and etb genes and 20% of SCCmec type VII carried sea, seb, cna, tst, eta and etb genes. However the rest isolates with SCCmec types I, IV, VI, VIII and XII showed less prevalence rate as compared to the above.
The study conducted by Liang et al., 2016 showed that ST239-SCCmecAIII-t37 clone was more prevalent one as reported from china whereas our current study showed that ST2884-SCCmec type V was more predominant than the other sequence type .
This study involved a comparative analysis of virulence genes found to be prevailing in hospital, community as well as in environmental settings. It was recorded that majority of the isolates containing virulence gene were found in the environmental sources which is in contrast to the other studies where virulence genes were observed in clinical settings [16, 24] and underscores the risk of acting environmental sources as reservoir.