Gram-Positive Bacteria in the Marine Environment

The classic Gram-positive bacteria used as fecal contamination indicators are enterococci (fecal streptococci) and clostridia. However, many other Gram-positive bacteria of human origin or potentially human pathogens, such as staphylococci, listeriae, mycobacteria, bifidobacteria, may be present in seawater. The route for human infection by these microorganisms may be either by contact with water (Mycobacterium marinum, Mycobacterium balnei, Staphylococcus aureus) or byingestion of contaminatedwater or seafood (classicwater-borne diseases). Thus, a correct evaluation of the microbiological quality of marine water is fundamental for preventing human infection. The methods currently used to assess the microbiological quality of seawater are based only on culture, thus implying that nongrowing bacteria (unable to form colonies) are non-viable, i.e. dead. As is the case with many Gram-negative bacteria, certain survival strategies (e.g. the viable but nonculturable (VBNC) state) activated also by Gram-positive bacteria are at present under investigation. Such strategies allow the bacteria to survive and persist in a viable state even in oligotrophic stress-inducing conditions such as those present in the marine environment. In these conditions, many bacteria are shown to maintain their pathogenic potential (i.e. infectivity and transmissibility), and resuscitation (i.e. recovery of cell division) has been described upon restoration of suitable environmental conditions that coincides, for example, with ingestion by humans. As these bacterial forms may no longer be recoverable by culture, one could argue that culture methods alone would not be considered enough to protect human health. Thus, it could be postulated that culture-independent methods would be preferable.