Toll-like receptors (TLRs) play a crucial role in host defense against microbial infection. The microbial ligands recognized by TLRs are not unique to pathogens, however, and are produced by both pathogenic and commensal microorganisms. It is thought that an inflammatory response to commensal bacteria is avoided due to sequestration of microflora by surface epithelia. Here, we show that commensal bacteria are recognized by TLRs under normal steady-state conditions, and this interaction plays a crucial role in the maintenance of intestinal epithelial homeostasis. Furthermore, we find that activation of TLRs by commensal microflora is critical for the protection against gut injury and associated mortality. These findings reveal a novel function of TLRs-control of intestinal epithelial homeostasis and protection from injury-and provide a new perspective on the evolution of host-microbial interactions.

SUMMARY Public health protection requires an indicator of fecal pollution. It is not necessary to analyse drinking water for all pathogens. Escherichia coli is found in all mammal faeces at concentrations of 10 log 9−1, but it does not multiply appreciably in the environment. In the 1890s, it was chosen as the biological indicator of water treatment safety. Because of method deficiencies, E. coli surrogates such as the ‘fecal coliform’ and total coliforms tests were developed and became part of drinking water regulations. With the advent of the Defined Substrate Technology in the late 1980s, it became possible to analyse drinking water directly for E. coli (and, simultaneously, total coliforms) inexpensively and simply. Accordingly, E. coli was re‐inserted in the drinking water regulations. E. coli survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (temperature, microflora, etc.). Bacteria and viruses are approximately equally oxidant‐sensitive, but parasites are less so. Under the conditions in distribution systems, E. coli will be much more long‐lived. Therefore, under most circumstances it is possible to design a monitoring program that permits public health protection at a modest cost. Drinking water regulations currently require infrequent monitoring which may not adequately detect intermittent contamination events; however, it is cost‐effective to markedly increase testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.

Advances in the elaboration of novel genomic types of beta-galactosidase-positive Enterobacteriaceae and comprehensive studies of their habitats have resulted in an innovative approach to the assessment of the merits and shortcomings of the thermotrophic and fecal species Escherichia coli and all other coliforms as markers of the microbiological safety of water. As one of the consequences, it is recommended to abolish the "technical" designation fecal coliforms because their current method of detection will result in the isolation of thermotrophic organisms that have been demonstrated, beyond a doubt, to be of environmental, rather than uniquely enteric origin. Additional population studies have demonstrated that none of the coliforms can function as reliable markers for all enteric pathogens (index organisms sensu Ingram), nor be of use in validating adequate processing for safety of raw water, which represents the indicator function of markers, as defined by Ingram. Future studies along these lines will have to provide the data required to assess the suitability of additional markers for the reliable monitoring of drinking water for microbiological safety.

Two patients with colonic adenocarcinoma and Streptococcus bovis endocarditis suggested a possible association between the two. Non-enterococcal Group D streptococci were isolated from fecal cultures of 11 of 105 controls, 35 of 63 patients with carcinoma of the colon, seven of 25 with inflammatory bowel disease, four of 21 with non-colonic neoplasms and five of 37 with other gastrointestinal disorders. All such streptococci examined for lactose fermentation were S. bovis. The prevalence of S. bovis in fecal cultures from patients with carcinoma of the colon was significantly increased (P less than 0.001) as compared to that in controls, and also to all other groups (P less than 0.001). No other group had results significantly different from those of controls (P less than 0.05) although patients with inflammatory bowel disease were more frequently carriers. The carrier state was unrelated to age, hospitalization status, colonic stasis, gastrointestinal bleeding or recent barium-enema examination. The implications of this association are unknown.

While the literature documents the universal occurrence of heterotrophic plate count (HPC) bacteria in soils, foods, air, and all sources of water, there is a lingering question as to whether this group of organisms may signal an increased health risk when elevated populations are present in drinking water. This paper reviews the relevant literature on HPC bacteria in drinking water, the lack of clinical evidence that elevated populations or specific genera within the HPC flora pose an increased health risk to any segment of the population, and the appropriate uses of HPC data as a tool to monitor drinking water quality changes following treatment. It finds no evidence to support health-based regulations of HPC concentrations.

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Pseudomonas aeruginosa is an ubiquitous environmental bacterium. It can be recovered, often in high numbers, in common food, especially vegetables. Moreover, it can be recovered in low numbers in drinking water. A small percentage of clones of P. aeruginosa possesses the required number of virulence factors to cause infection. However, P. aeruginosa will not proliferate on normal tissue but requires previously organs. Further narrowing the risk to human health is that only certain specific hosts are at risk, including patients with profound neutropenia, cystic fibrosis, severe burns, and those subject to foreign device installation. Other than these very well-defined groups, the general population is refractory to infection with P. aeruginosa. Because of its ubiquitous nature, it is not only not practical to eliminate P. aeruginosa from our food and drinking water, but attempts to do so would produce disinfection byproducts more hazardous than the species itself. Moreover, because there is no readily available sensitive and specific means to detect and identify P. aeruginosa available in the field, any potential regulation governing its control would not have a defined laboratory test measure of outcome. Accordingly, attempts to regulate P. aeruginosa in drinking water would not yield public health protection benefits and could, in fact, be counterproductive in this regard.

Our data suggest that EAEC infection should be considered among persons with diarrhea that does not yield another known etiologic agent.