Homologous Resistant Groups (HRGs) in Multidrug Resistant Staphylococcus aureus Isolated from Retail Foods in Vadapalani, Chennai

摘要

The present study investigated the prevalence of multiple antibiotic resistant Staphylococcus aureus strains in different food sources collected from retail shops and markets in Vadapalani, Chennai. All S. aureus isolates were resistant to methicillin, and 93.75 % of them were multidrug resistant. The S. aureus isolates were typed by UPGMA method based on antibiotic resistance pattern observed. Approximately five homologous resistance groups (HRGs) were observed in typing the isolates. Introduction Food borne diseases are of major concern worldwide. To date, around 250 different food-borne diseases have been described and bacteria are the causative agents for two-thirds of the food-borne disease outbreaks. Among the predominant bacteria involved in these diseases, Staphylococcus aureus is the leading cause of gastroenteritis resulting from consumption of contaminated food (Loir et al., 2003). Occasionally, S. aureus acts as opportunistic pathogen and cause infections of the urinary tract, respiratory tract and intestinal tract (Coltman, 1981). The pathogenicity of S. aureus as indicated by Stokes and Ridgway (1980) include abscesses, boils, conjunctivitis especially in newborn, cross-infections in hospitals septicemia, mastitis and food poisoning (of meats, milk and milk products). Also S. aureus is an etiological infection agent responsible for significant levels of morbidity and mortality (Vieira et al., 2007). S. aureus is an important pathogen due to the combination of toxin-mediated virulence, invasiveness and antibiotic resistance (Fast et al., 1989; Bohach et al., 1990; Hiramatsu, 1995; Murray et al., 1995). The evolution of methicillin resistant Staphylococcus aureus (MRSA) and other drug resistant pathogens has been linked to extensive antibiotic use in medicine and food animal production (Leonard and Markey, 2007; Mathew et al., 2007). Outbreaks of Staphylococcal food poisoning (SFP) are very common across the world; however, there is only one report on SFP from the Indian subcontinent (Nema et al., 2007). The aim of this study was to investigate the prevalence and multiple antibiotic resistance of Staphylococcus aureus strains isolated from different food samples collected from retail shops and markets in Vadapalani, Chennai and also to type the isolates based on antibiotic resistance pattern. This study brings insight into the predominance of multiple drug resistant S. aureus in marketed food samples in Chennai. Materials and methods Bacterial isolationA total of 40 different food samples collected from retail shops and markets in Vadapalani, Chennai were subjected to S. aureus isolation. All the samples were aseptically handled and processed. The samples were plated onto Mannitol Salt Agar (HiMedia). The characteristic yellow colored, round colonies were isolated and stored on Nutrient Agar (HiMedia) slants. The isolates were examined by Gram staining for Gram positive cocci in clusters and biochemical characteristics such as catalase positive, oxidase negative, indole negative, urease positive, citrate negative, Methyl red and Voges-Proskauer positive. All isolates were confirmed as S. aureus by their positive nature for tube coagulase test using rabbit plasma. The standard type strain S. aureus MTCC 1144 was used in each of the steps for the comparative identification of S. aureus. Antibiotic assayAntibiotic resistance test was carried out for all the strains by the disc diffusion method (Bauer et al., 1966). The cultures were enriched in Brain Heart Infusion Broth (BHIB, HiMedia) for 6 - 8 hr. The enriched cultures were then swabbed on the surface of Mueller Hinton Agar (HiMedia) using sterile cotton swabs. Using the antibiotic disc dispenser, the discs were placed on the agar surface sufficiently distanced to avoid overlapping of the inhibition zones. The concentration of each antibiotics used is listed in Table 1. The plates were incubated at 37 o C for 18 - 24 hr. After the incubation period, the diameter of