| Vancomycin resistant enterococci (VRE) have played a major part in causing nosocomial, or hospital borne illnesses. VRE have been found with resistance levels in excess of 256 microg/ml for vancomycin, which makes it very difficult to treat patients infected with VRE. Therefore, it is very important to identify the sources of this organism to control its transmission into the environment. Composting is a process that has been often utilized to inactivate pathogens present in animal waste. The objectives of this study were to (1) enumerate enterococci and VRE from three different composting trials with various compost mixtures, (2) characterize the antibiotic resistance profiles of the VRE isolates obtained from composting trials phenotypically and genotypically, and (3) determine the VRE isolates' changes in heat resistance and persistence during the 4-month composting trial.;In this study, two dairy compost heaps and one vegetable scrap compost heap were constructed on two research farms in Clemson, SC. Samples were taken from each heap from different locations at 8 elected intervals and analyzed for enterococci and VRE counts by spread plating on Bile Esculin agar (BEA) and BEA containing 6 microg/ml of vancomycin, respectively. After 30 days of active composting the average VRE populations declined ca. 4.6, 4.07, 3.97 and 1.6 logs at the top, center, bottom and surface locations of the heaps, respectively, whereas the enterococci populations declined for 4.36, 3.54, 3.10, and 2.28 logs, respectively. Our results revealed that the genus of all 88 VRE isolates was enterococci and that no VRE were Enterococcus faecalis or Enterococcus faecium. However, 9 and 6% of enterococci isolates from Trial 1 were tested as E. faecalis and E. faecium, respectively. For those VRE isolates taken from composting, minimum inhibitory concentration (MIC) testing revealed that 85 out of 88 suspected VRE isolates were resistant to > 256 microg/ml of vancomycin and all 88 isolates were resistant to > 64 microg/ml of teicoplanin. Eighty-three (94%) of VRE isolates were confirmed to contain the vanA gene for vancomycin resistance. The D-values of selected VRE isolates (n=8) from Trial 1 compost heaps were in the range of 9.7-17.73 min at 60°C, 4.73-12.57 min at 65°C, and 1.59-4.44 min at 70°C. The z-values for those VRE isolates ranged from 11.92°C-17.87°C. Box-PCR analysis of VRE isolates (n=12) from Trial 1 revealed that 42% were identical and appeared on compost days 7, 14, and 60, suggesting that this specific strain was able to adapt to the elevated temperatures in compost by developing heat resistance.;Our studies demonstrated that VRE may become inactivated in compost if conditions are optimal and that some enterococci may develop heat resistance during the thermophilic phase of composting. This is important because it suggests that improperly composted manures may serve as a means for the spread of VRE on food products, especially fresh produce, intended for human consumption. |
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