Fate of gram-positive bacteria in reconditioned, pork-processing plant water

This study investigated the responses of Enterococcus faecium (ATCC 19433), Staphylococcus aureus (196E), and Listeria monocytogenes Scott A in water from a local meat-processing plant. Each bacterium was added to a starting count of 3 log(10) CFU/ml and held from 5 to 28 degrees C. At intervals (0, 2, 7, 14, and 21 days), aliquots were plated on appropriate selective agar s. In contrast to the gram-negative bacteria studied previously and which g rew, the three gram-positive bacteria survived with some slight increase in number in only nonchlorinated, reconditioned water, either filtered (0.22 mu m pore size) or nonfiltered. The presence of chlorine in either potable or reconditioned water contributed to the rapid decline in viable counts fo r all three bacteria. These results further emphasize the importance of res idual chlorine in preventing the growth of these gram-positive bacteria in potable and reconditioned waters.