ENTEROCOCCAL ISOLATES FROM RAW MILK AND DAIRY PRODUCTS IN RIYADH REGION AND THEIR SUSCEPTIBILITY TO COMMON ANTIBIOTICS

Abstract

A total of 100 samples of raw milk, various cheeses, labnah, yogurt, and egett were collected from appropriate suppliers and markets in Riyadh region. Bacteriological analysis for typing of enterococci and other lactic Acid Bacteria (LAB) was carried out by plating appropriate dilutions of each sample on sheep blood agar and Edwards blood agar plates. After overnight aerobic incubation at 37°, the presumptive identification was done by colony morphology, cultural characteristics, Gram-stain and catalase production. Final identification to the genera and species level of the total 125 bacterial isolates was completed by API-20 strips as well as Lancefield-serogrouping. Results revealed that Enterococcus faecium (88 isolates) accounts of 70% of total bacterial isolates, while Enterococcus faecalis (26 isolates) accounts of up to 21% and other LAB constituted about 9% of total recovered isolates. The later isolates comprises 3, 3, and 5 isolates of Enterococcus gallinarum, Enterococcus durans, and Aerococcus viridans respectively. The results revealed that nature of sample, its pH, and salinity clearly affect the incidence and number of recovered bacterial isolates. Thus as pH rises towards neutrality, with no salt or low salinity, E. faecalis and other LAB were recovered more frequently, and vice versa. In contrast, E. faecium was routinely isolated from most of the examined samples regardless of their pH range and salinity- content, reflecting its ubiquitous nature and its tolerance to drastic environmental conditions, thereby facilitating person to person transmission. The dominance or persistence of enterococci in examined samples is most probably attributed to their wide range of growth temperatures, their tolerance to heat, salt and acid. In addition, the MIC of each of the tested 120 isolates was determined by serial dilution in Muller Hinton sheep blood agar against 9 antibiotics. All isolates were sensitive to ampicilin with the exception of one E. faecalis strain that showed an MIC of 4 ug/ml. While Erythromycin (EM) exhibited also a good activity with an MIC50/MIC90 of 1/1, 1/4, 2/8 and 4/4 ug/ml. for E. gallinarum, E. faecalis, E. faecium, and E. durans or Aerococcus viridans isolates respectively. Whereas all isolates were resistant to cefoxitin and about 50% were also resistant to Chloramphenicol (CM), Tetracycline (TC), or Trimethoprim / Sulfamethoxazole (SXT). Thus at the breakpoint of MIC (>16 ug/ml.) (TC) resistance rate for E. faecalis was 16% and for E. faecium and E. gallinarum was 35% and 100% respectively. Whereas that for vancomycin (VM) the figures were 44%, 19% and 100% respectively. It is concluded that the examined samples may constitute a potential source for the dissemination of antibiotic resistant determinants to human.