Role of sublethal injury in decline of bacterial populations in lake water.

Following their addition to lake water, the populations of Escherichia coli and of antibiotic-resistant strains of Pseudomonas fluorescens, Agrobacterium tumefaciens, Micrococcus flavus, Rhizobium meliloti, and Klebsiella pneumoniae declined rapidly, as determined by counting on media containing antibacterial compounds. The estimates of population sizes were occasionally higher if procedures were used that permitted possible resuscitation of injured cells. No resuscitation procedure yielded consistently higher estimates of populations of surviving cells than the use of selective media alone. The patterns of survival of the test bacteria in lake water amended with eucaryotic inhibitors were essentially the same whether a resuscitation procedure was used or not, and the patterns of survival in sterile lake water or buffer were the same whether counts were made on selective media or on media without antibacterial agents. On the basis of the methods used to show sublethal injury caused by stress, we suggest that such injury to the test bacteria is not a significant factor involved in their decline in lake water.