title: Investigating the decay rates of Escherichia coli relative to Vibrio parahemolyticus and Salmonella Typhi in tropical coastal waters.
abstract: Using the size fractionation method, we measured the decay rates of Escherichia coli, Salmonella Typhi and Vibrio parahaemolyticus in the coastal waters of Peninsular Malaysia. The size fractions were total or unfiltered, <250 μm, <20 μm, <2 μm, <0.7 μm, <0.2 μm and <0.02 μm. We also carried out abiotic (inorganic nutrients) and biotic (bacterial abundance, production and protistan bacterivory) measurements at Port Dickson, Klang and Kuantan. Klang had highest nutrient concentrations whereas both bacterial production and protistan bacterivory rates were highest at Kuantan. We observed signs of protist-bacteria coupling via the following correlations: Protistan bacterivory-Bacterial Production: r = 0.773, df = 11, p < 0.01; Protist-Bacteria: r = 0.586, df = 12, p < 0.05. However none of the bacterial decay rates were correlated with the biotic variables measured. E. coli and Salmonella decay rates were generally higher in the larger fraction (>0.7 μm) than in the smaller fraction (<0.7 μm) suggesting the more important role played by protists. E. coli and Salmonella also decreased in the <0.02 μm fraction and suggested that these non-halophilic bacteria did not survive well in seawater. In contrast, Vibrio grew well in seawater. There was usually an increase in Vibrio after one day incubation. Our results confirmed that decay or loss rates of E. coli did not match that of Vibrio, and also did not correlate with Salmonella decay rates. However E. coli showed persistence where its decay rates were generally lower than Salmonella.
authors.affiliation: Laboratory of Microbial Ecology, Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia. lee@um.edu.my
authors.forename: Choon Weng
authors.initials: CW
authors.lastname: Lee
authors.forename: Angie Yee Fang
authors.initials: AY
authors.lastname: Ng
authors.forename: Chui Wei
authors.initials: CW
authors.lastname: Bong
authors.forename: Kumaran
authors.initials: K
authors.lastname: Narayanan
authors.forename: Edmund Ui Hang
authors.initials: EU
authors.lastname: Sim
authors.forename: Ching Ching
authors.initials: CC
authors.lastname: Ng
mesh_terms: D005591:Chemical Fractionation; D015169:Colony Count, Microbial; D004784:Environmental Monitoring; D004926:Escherichia coli / Q000254:growth & development / Q000302:isolation & purification*; D008296:Malaysia; D010316:Particle Size; D012485:Salmonella typhi / Q000254:growth & development / Q000302:isolation & purification*; D012623:Seawater / Q000382:microbiology* / Q000821:virology*; D014329:Tropical Climate; D014736:Vibrio parahaemolyticus / Q000302:isolation & purification*