Numerous articles have documented the existence of filterable bacteria. Where filtration is the chosen method of sterilization for medicinal or media components, these bacteria will by definition render products non-sterile. They may further represent a health hazard to the end user. A wide-range of bacterial genera were found in bottled and tap water filtrates from 0.2 μm filters, including genera housing opportunistic pathogens (e.g. Methylobacterium) and endospore formers (Paenibacillus). Two municipal tap water isolates were only distantly related to named species. One of these grew on agar, and could potentially provide hitherto unharvested useful biological products. The other grew only in water, and failed to produce colonies on media targeting either heterotrophs or autotrophs. The present study is one of very few looking at filterable bacteria in bottled waters intended for human consumption and the first identifying the filterable portion. It extends the range of known habitats of filterable bacteria and provides data on two new or novel species.

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