Survival of Faecal Microorganisms in Marine and Freshwater Sediments.

Survival of Faecal Microorganisms in Marine and Freshwater Sediments.

 

Marine and freshwaters can contain an assortment of pathogenic and non-pathogenic faecal microbes. Faecal contamination can come from a number of sources such as sewage effluents from farming livestock (Sheep, cattle, pigs, etc.), human populations and wildlife. These microbes can pose a significant health risk to bathers who use these waters for recreation. Illness and disease can occur when an infective dose of the pathogen is able to enter the body and colonize. Monitoring and maintaining a safe level of water quality is therefore important.

 

The study by Davies et al (1995) looked at the survival of faecal microorganisms in marine and freshwater sediments in the vicinity of Sydney’s three deep-water ocean outfalls (see paper for exact location of sampling sites). The study looked at the survival of culturable faecal coliforms, faecal streptococci and Clostridium perfringens spores from sites near sewage outfalls. Three different studies were carried out to analyse survival rates: a predation study in the presence and absence of predators, an in situ microcosm survival study and a VNC (Viable but non-culturable) survival study. For the full details of the experiment please read the materials and method section of the paper.

 

The study’s key findings showed that in the predation studies, inhibition of protozoan predators with cycloheximide allowed the faecal coliforms to grow in the sediment whereas in the presence of predators a net die-off occurred. The study also showed that C. perfringens spores did not appear either to be affected by predators or to die off throughout the duration of the experiments (28 days). The situ survival experiments showed that all the test organism except C. perfringens, die-off to 10% of their initial numbers. This die-off occurred in both the marine and freshwater sediments within the 85 days of testing. The usual exponential decay model could not be applied to the survival data except for the faecal streptococci data. This was thought to be due to the complex interrelationship between predation and growth. In the NVC survival study the proportion of culturable E.coli remained the same for the entire duration of the experiment (68 days). This suggests that the sediment does provide a favourable, nonstarvation environment for the faecal bacteria.

 

Overall the study shows that in the absence of predators faecal coliforms may be capable of growth in marine and freshwater sediments however in natural conditions where predators are present a net die-off does occur. The study also suggests that C. perfringens where not preyed upon as much resulting in no net die-off. The NVC experiment suggests a survival strategy to overcome unfavourable conditions while still maintain the ability to form colonies. These results suggest that the bacteria can survive for extended periods of time in the marine sediment however as marine sediment is more often favourable for growth this strategy is unlikely and growth and predation more probable. To conclude, marine and freshwater sediment does provide favourable conditions for faecal bacterial to grow and it can be possible for extended survival of bacteria in the sediment. However the most likely outcome is for predation to result in a net die-off for the bacteria.

 

Cheryl M. Davies, Julian A. H. Long, Margaret Donald and Nicholas J. AShbolt (1995) Survival of Faecal Microorganisms in Marine and Freshwater Sediments, Applied and Environmental Microbiology. Vol 61, No 5 Pg 1888-1896

 

 

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC167451/pdf/611888.pdf