Comparison of the in situ survival and activity ofKlebsiella pneumoniae andEscherichia coli in tropical marine environments

Abstract

A near-shore coastal mangrove island receiving untreated sewage and a coastal cove receiving rum distillery effluent in Puerto Rico were examined for their ability to support survival and activity ofKlebsiella pneumoniae andEscherichia coli. Pure cultures of both bacteria were monitored for 96 hours in situ at both locations using membrane diffusion chambers.K. pneumoniae survived at all sites as measured by AODC and Coulter Counter direct counts. However, at the mangrove island less than 20% of theK. pneumoniae population was active (AODC) after the first 3 hours and less than 10% of this population was respiring (INT). In contrast, the coastal area which was receiving rum distillery effluent was able to maintain 40% of theK. pneumoniae population in an active state with 90% respiring. TheE. coli population declined by two orders of magnitude at the mangrove island, but remained unchanged at the rum distillery outfall. TheE. coli population had a higher proportion of active cells and respiring cells thanK. pneumoniae at all sites. At the rum distillery site, theE. coli population was remarkable in that 95% remained active and 99% were respiring. This study suggests that, when sufficient organic loading exists,E. coli, a "nonsurvivor," can overcome the bactericidal effects of tropical marine waters.K. pneumoniae, a "survivor," could survive under all conditions but could not maintain the activity or respiration that theE. coli population could, even when high organic loads were present. Morphological changes related to nutrient stress in the tropical marine environment were apparent inE. coli, but not inK. pneumoniae. Based on physiological activityE. coli is just as much a "survivor" asK. pneumoniae in tropical marine waters.