Virulence Testing of Multi-drug Resistant Staphylococcus aureus Isolated from Meat and Clinical Samples

Introduction: Over 200 known diseases are transmitted via food, and the causes include bacteria, viruses, parasites, toxins, metals and prions. It is estimated that foodborne diseases are attributable to 76 million illnesses, resulting in 325,000 hospitalizations and 5,000 deaths annually in the United States. Multi-drug resistant Staphylococcus aureus is one of the leading causes of foodborne disease outbreaks, and the incidence of hospital- and community-acquired staphylococcal infections are also increasing which have shown to exhibit multiple virulence factors, such as,  production of clumping factor A, Panton-Valentine leukocidin and ƴ-hemolysin.

Purpose: Therefore, the aim of the study was to determine the virulence properties of multi-drug resistant Staphylococcus aureus isolated from clinical and meat sources.

Methods: Fifty-five strains of multi-drug resistant Staphylococcus aureus isolated from 34 meat and 21 clinical samples were characterized using polymerase chain reaction (PCR) to detect the presence 16S rRNA gene for Staphylococcus spp. and clumping factor A (Clf-A); Panton-Valentine leukocidin (PVL) and hemolysin (ƴ-hly) virulence genes. To determine strain diversity, pulse field gel electrophoresis (PFGE) cluster analysis for the Clf-A and 16SrRNA positive isolates was compared. 

Results: Results of this study indicated that 18 (32.7%) of the clinical and 6 (11.0%) of meat samples were positive for both Clf-A and 16SrRNA genes. All Isolates (100%) were negative for the detection of the Panton-Valentine Leukocidin and hemolysin gene by polymerase chain reaction. When PFGE patterns were compared, 6 (11%) of the SmaI-digested plugs had distinct PFGE cluster patterns.

Significance: Our study demonstrated that higher percentage of virulent strains of multi-drug resistant Staphylococcus aureus could be detected from clinical samples compared to meat samples, which can be attributed to higher incidence of virulent multi-drug resistant S. aureus detected from human samples.