In situ survival of Vibrio cholerae and Escherichia coli in tropical coral reefs

Abstract

Vibrio cholerae and Escherichia coli were inoculated into membrane diffusion chambers and placed around two small coral reef islands in Puerto Rico and monitored for 5 days. Several chambers were also buried in the sands of one of the reefs. Both E. coli and V. cholerae densities declined by 2 orders of magnitude, as measured by direct particle counts with a Coulter Counter (Coulter Electronics, Inc., Hialeah, Fla.). However, the density of neither bacteria changed dramatically when the same samples were analyzed by epifluorescent direct counts. Differences in the two direct count methods were accounted for by changes in cell morphology that occurred in both bacteria after exposure to seawater. Morphological changes occurred more rapidly in E. coli compared with those in V. cholerae. Bacteria in chambers exposed to sediment did not show significant changes in morphology and had only a slight decline in density. Physiological activity declined by more than 40% for both bacteria within 24 h. The decline in activity was less severe in the sediments. Tropical coral reef sands and turtle grass beds were shown to be less stressful environments for V. cholerae and E. coli than would have been predicted from temperate and microcosm studies. V. cholerae can survive the in situ conditions of a tropical coral reef and could become a source of bacterial contamination for fish and shellfish in this environment. The simultaneous monitoring of E. coli levels established that this bacteria can not be used as an indicator of V. cholerae or other fecal-borne pathogens in coral reef environments because of the greater stress these environments put on E. coli. Both bacteria could be of greater public health importance in tropical marine areas than previously imagined. It is known that Vibrio cholerae and other vibrios are part of the indigenous microflora of most estuaries (8, 18). Considering the reports of recent outbreaks of cholera traced to shellfish from warm water environments, it has become increasingly important to understand the ecology of these bacteria. Many studies have suggested that V. cholerae is incapable of surviving in seawater at salinities of 35%o and that high temperatures, i.e., >250C, are stressful (17, 22).

Human enteric viruses in groundwater indicate offshore transport of human sewage to coral reefs of the Upper Florida Keys

“…Faecal indicator bacteria, traditionally used by regulators for evaluating water quality, tend to rapidly lose culturability in marine water (e.g. Vasconcelos and Swartz, 1976;Fujioka et al, 1981;Perez-Rosas and Hazen, 1988;Fujioka and Yoneyama, 2002) and may be derived from sources other than human (e.g. Griffin et al, 2003).…”

Long-term survival and plasmid maintenance of Escherichia coli in marine microcosms

“…Until recently, very little was known about survival of E. coli in seawater, since it had been assumed that E. coli died off when discharged into the sea. Studies of survival of E. coli in tropical coral reefs showed that the physiological activity of E. coli declined by more than 40% within the first 24 h [2]. Direct counts of the bacteria remained constant at original levels, however, showing that E. coli cells did not lyse in the highly saline environment nor did significant, if any, cell division take place.…”

“…Studies using filtered seawater have shown that E. coli survives in the culturable state for at least 10 days, although at 0.5 log units below the original inoculum [1]. E. coli ceils exposed to seawater in tropical coral reefs at a temperature of 26°C showed a 40% decline in physiological activity within the first 24 h [2]. Examination of these bacteria by direct counting methods found the cells remaining as intact cells, indicating that the high salinity did not induce lysis.…”

In situ survival of Vibrio cholerae and Escherichia coli in a tropical rain forest watershed

“…Recent in situ studies by our laboratory in Puerto Rico, using direct enumeration and activity measurements, have shown that Vibrio cholerae can survive and remain moderately active on a tropical coral reef (14). In Puerto Rico and other parts of the Caribbean, V. cholerae has even been isolated from near-shore coastal waters when the salinity was 35%o and the temperature was 25°C (3,7,21).…”

“…1 Methods for the Examination of Water and Wastewater (1). All measurements were as described before (4,11,14,22). For V. cholerae enumeration, water samples were filtered through 0.45-,um-pore-size membrane filters (Millipore Corp., Bedford, Mass.).…”