ASSESSMENT OF SINGLE AND COMBINED CO-INFECTION OF Aeromonas hydrophila AND Vibrio parahaemolyticus ON DISEASE PATHOGENICITY IN Oreochromis niloticus
Marwa F. Abd El-Kader1; Eman M. M. Moustafa2
1Department of Fish Health, Sakha, Aquaculture Research Unit, Central Lab. For Aquaculture Research- ARC, Egypt.
2Department of Fish Diseases and Management, Faculty of Veterinary Medicine, Kafr El-Sheikh University, Kafr El-Sheikh city, Postal code: 33516, Egypt.
Environmentally transmitted bacterial pathogens might cause both single and combined co-infections in their hosts. Co-infections may lead to increase or decrease virulence of the pathogens, depending on the nature of the interactions between the co-infecting bacterial strains. Four isolated strains of an opportunistic fish pathogens; Aeromonas
hydrophila and Vibrio
parahaemolyticus, containing one or two tested virulence genes/each obtained from different fish farms were used to shed light on the effect of single and combined co-infection of these opportunistic bacteria on their virulence and pathogenicity in Oreochromis
niloticus, recording how different strains with different number of virulence genes affects the disease virulence (measured as mortality and disease signs in O. niloticus). The results revealed that the pathogenicity of the disease were significantly influenced by the combination between strains of different species, the number of the co-infecting strains and the number of virulence genes. Infection with two strains of different species containing the four tested virulence genes recorded the highest fish mortality than other infections. Moreover, the co-infection with two strains of different species regardless the number of the contained virulence genes in both strains; even with two virulence genes were more virulent than two strains of same species with three virulence genes, which might clarify the synergistic action between the two pathogens . However, the pathogenicity of the disease in the single and co-infected groups with the same bacterial species was positively correlated with the number of the virulence genes.
Key words: Co-infection virulence genes Aeromonas hydrophila Vibrio parahaemolyticus