Investigation of the distribution of motile Aeromonas within Grampian water supplies.

Gavriel, Andros Antonios

Abstract

Aeromonas is ubiquitous in freshwater aquatic environments covering a wide range of trophic conditions. Its association with gastrointestinal disease has led various workers to investigate the prevalence and significance of Aeromonas in drinking water supplies. This examination of a Scottish public drinking water supply revealed a widespread occurrence of motile Aeromonas with prevalence varying within the distribution system and isolations sometimes made from water samples with high chlorine residuals. Levels of Aeromonas isolations from the water supply displayed a seasonal pattern with counts peaking during mid to late summer and no isolations made during winter months. Comparison of the seasonal data for isolations and rainfall showed a relationship where Aeromonas densities and frequencies of isolation increased with increasing rainfall. Evaluation of a new selective medium for the isolation of Aeromonas, SGAP-1OC, showed it to be less effective than ADA selective medium for maximising recoveries of different strains when using pure cultures. Ampicillin, the selective agent in these media, was shown to exert an inhibitory effect on some Aeromonas strains bringing into question the usefulness of such media in investigations aiming to recover and quantify the different Aeromonas species present in any source. The commonly accepted incubation temperature of 36°C for mesophilic Aeromonas was also shown to critically affect recovery of one of the strains examined. Findings suggested that a maximum temperature of 30°C be used for incubation of mesophilic Aeromonas. An evaluation of the suitability of Aerokey 2 for identifying water isolates to species level found that this scheme, designed originally for clinical isolates and not tested with drinking water isolates to date, was incapable of reliably speciating such environmental isolates. Chlorine resistance of Aeromonas was examined and found to vary between different strains all of which were, however, more susceptible to the biocidal/biostatic effects of chlorine than Escherichia coli and Pseudomonas aeruginosa. An investigation was conducted into the possibility of increasing the resistance to chlorine in Aeromonas by pre-exposing cells to low doses. Results showed that this could induce greater tolerance to this disinfectant although the repeatability of this effect was difficult to achieve and has not previously been demonstrated by other investigators.

Citation

GAVRIEL, A.A. 2000. Investigation of the distribution of motile Aeromonas within Grampian water supplies. Robert Gordon University, MPhil thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2807393

• Thesis Type: Thesis
• Deposit Date: Sep 12, 2025
• Publicly Available Date: Sep 12, 2025
• DOI: https://doi.org/10.48526/rgu-wt-2807393
• Keywords: Aeromonas; Freshwater; Gastrointestinal disease; Ampicillin; Aerokey 2; Incubation temperature; Grampian water
• Public URL: https://rgu-repository.worktribe.com/output/2807393
• Award Date: Aug 31, 2000