Survival and growth rate of coastal water Escherichia coli isolates in different salt concentrations

Abstract

The effect of salt concentration on the survival and growth rate of Escherichia coli isolated from Lagos Lagoon surface water was investigated. This was necessitated to ascertain the suitability of using E. coli as feacal pollution indicator in this water body which experiences fluctuation in salinity values. The salinity during the study ranged from 25.13 and 35.69‰. All the five E. coli isolated during the entire study period, grew luxuriantly in 0 to 4% salt concentrations with increase in optical density values of 78 - 93% and high (0.005 – 0.45) growth rates within 300 minutes of incubation. The growth of these isolates at 6% salt concentration was also good with 22 -77% optical density increase and growth rate range of 0.25 – 0.37. However, minimal or no growth was noted at 8 to 12% salt concentrations with corresponding low increase in optical density and negligible or even negative growth rate. Although the effect of salt concentrations on the five isolates tested were comparable, the isolate (Ec2) which was isolated during the least salinity period, showed the least growth rate in all salt concentrations. These findings suggest that salinity at point of isolation can influence salt tolerance, but further affirms the use of E. coli as pollution indicator for Lagos Lagoon since they exhibited considerable halo-tolerance and survived salt concentrations up to 6%.

Keywords: Escherichia coli, salt tolerance, feacal pollution indicator, salinity, growth rate, optical density