Investigate controlling microbial contamination from ice.

There have been few studies evaluating the microbial safety of ice. The microbial contamination of ice leading to outbreaks of gastroenteritis has been documented on several occasions over the years. Many of the outbreaks have been associated with the improper handling of ice or by the use of contaminated implements used to scoop ice. However, sources of contamination can also originate from water supply mains, faulty plumbing that allows backflow from drains, and from irregular cleaning of ice machines.

The formation of biofilms in ice machines containing high levels of heterotrophic plate count (HPC) bacteria have become an increasing concern both from an aesthetic as well as a public health perspective. Heterotrophic bacteria are those that require organic carbon rather than carbon dioxide as a carbon source. Virtually all human bacterial pathogens are part of the heterotrophic bacterial population.

The U.S. EPA has suggested that the heterotrophic bacterial counts in drinking water should not exceed 500 colony-forming units (CFUs) per mL. This concentration was initially set in the 1980s to prevent high levels of HPC bacteria from interfering with the detection of coliform bacteria in water samples. However, high numbers of HPC bacteria, which are often indicative of bacterial regrowth, have been suggested as a cause for concern regarding public health.

Most of the heterotrophic bacteria found in drinking water are not human pathogens. However, some of the genera, including Legionella, Mycobacterium, Pseudomonas, Acinetobacter, Xanthomonas, Moraxella and Aeromonas, involve species that are opportunistic pathogens--those that usually cause disease only when the host immune system is weakened.

With the increasing number of immuno-compromised individuals, including AIDS patients, organ transplant and chemotherapy patients, there has been greater interest in controlling opportunistic pathogens. It is not yet clear whether whether any opportunistic pathogens survive freezing and could present a public health risk from the consumption of contaminated ice.

Further information. D. E. Huffman, College of Marine Science, University of South Florida, 140 7th Ave. S., Saint Petersburg, FL 33701; phone: [phone]; URL: www.marine.usf.edu.