Some factors affecting the survival of coliform bacteria in seawater

Abstract

Some experiments were carried out to explain thein situ phenomena that the number of coliform organisms decreased rapidly from estuaries to offshore, and also at deeper layer, and that the appearance of coliform types varied. In natural seawater, experimental results did not show thatEscherichia coli was extinct by ‘self-purification’ or ‘anti-biosis’ action of seawater, but it showed that this organism decreased mainly because of their starvation caused by lack of nourishment. Although the decreasing rate of bacterial density was delayed in enriched seawater, addition of nutrient even at the time of bacterial extinction promoted the appearance of variated form of this bacteria with floc formation. Flocculation of bacterial cells was influenced by quality and quantity of added nutrients. Temperature was shown to have an effect on the floc formation, but appearance of variated form in flocculated cells ofE. coli was not affected by temperature. Flocculated particles of coliform bacteria were adsorbed on suspended particles in seawater and precipitated rapidly. This phenomenon seems to be a cause of the rapid disappearance of coliform bacteria in coastal waters. In bottom deposits the coliform bacteria probably survive longer as physiologically variated forms when suitable nutrients were supplied.