Detection of virulence genes in Staphylococcus aureus isolated from paper currency.

Background: Infection with Staphylococcus aureus was initially considered a major problem in hospitals, but over the last few decades the incidence of community-acquired infection has also increased. Paper currency has recently been identified as another mode of spread by which community-acquired S. aureus infection may be transmitted, since paper currency is frequently transferred from one person to another. In the present study, S. aureus strains were isolated from paper currency and screened to detect virulence-associated genes.

Methods: Paper currency was collected randomly from operators in mutton shops, vegetable shops, hospitals, medical stores, snacks corners, and restaurants in the two cities of India, Dehradun and Delhi. Samples were screened for pathogenic S. aureus by various biochemical assays. Three isolates were used to study the survival of S. aureus on paper currency. Virulence genes were amplified by PCR. Antibiotic susceptibility was determined against nine antibiotics by the disk diffusion method.

Results: Sixty-seven isolates of Staphylococcus aureus were isolated from paper currency from the two Indian cities. The maximum number of isolates was recovered from hospitals, followed by mutton shops, and the minimum from restaurants. The test isolates could survive on paper currency for eight days under in vitro conditions (27 degrees C temperature and 30% relative humidity). A set of four virulence genes viz. cna (16 isolates), icaA (19 isolates), hlg (21 isolates), and sdrE (18 isolates) was amplified using gene-specific primers. Only eight isolates possessed all four virulence genes. Antimicrobial susceptibility tests showed that those isolates having all the tested virulence genes were more resistant.

Conclusions: This study clearly suggests that paper currency can serve as a carrier for the spread of resistant bacterial pathogens.