PHENOTYPING, VIRULENCE CHARACTERISTICS OF AEROMONAS SPECIES AND THE EFFECTS OF ESSENTIAL PLANT OILS AS ANTIMICROBIAL AGENTS AGAINST PATHOGENIC ISOLATES FROM DIFFERENT SOURCES

Abstract

Aeromonas species are increasingly recognized as enteric pathogens. Faecal samples from 20 cow, 45 sheep; 60 goat and 60 camels were examined for the presence of Aeromonas species, which was also sought in the available drinking water (55 well water and 52 drinking chlorinated tap water were also examined). Aeromonas species was isolated more frequently from goats (21.7%) than from other animal groups sampled and isolated more frequently from well water (38.2%) than chlorinated supplies (23.0%). A. hydrophilia was the most dominant species isolated from different kinds of samples (13.4%). Whereas A. sobria and A. caviae were isolated in much lower rates 4.7 and 2.1% respectively. There was significant association between the isolation of Aeromonas species from all animal faeces and its presence in drinking water. All isolated strains were examined for the characteristics that are reputed to have roles in pathogenicity. The data reported in this study indicates that the distributions of virulence factors, that regulate the pathogenicity of Aeromonads, are different in clinical and enviromental samples. Aeromonas isolates exhibited multi-drug resistanc amoxicillin, carbenicillin and ampicillin. The most potent antibiotics against Aeromonas species isolated in this study were ceftriaxone, ceftazidime, cefotaxime, cefepime. Essential oils have been tested for in vitro and in vivo antimicrobial activity. Clove, Olive and Peppermint oil exhibited a wide spectrum of antimicrobial activity against all strains used in this study, showed a zone of inhibition ranging from 10.00±0.8 to 14.82±0.41 mm in diameter. Minimum Inhibitory Concentration (MIC) for selected oils ranged from 12.8 to 25.6 mg mL^-1. Treatment of mice with essential oil for 15 days led to enhance antibody levels in all treated groups and significant clearance of A. hydrophilia from animals. The treated animals had minimal histopathological changes and lower bacterial loads in the organs examined. In conclusion, these findings indicate that aeromonads have the potential to cause human illness and confirm the role of water as vehicles for Aeromonas diseases. This study also demonstrated that the multi-factorial nature of the diseases and the influence of environmental conditions in the expression of the putative virulence properties. These results suggested the potential value of essential oils as an additional or supporting treatment in gastrointestinal inflammations.