FOREST AND WATER- BIRDS AS RESERVOIRS OF SOME PATHOGENIC AND ANTIMICROBIAL-RESISTANT BACTERIA

ABSTRACT

Wild birds, particularly, migratory species can move from one place to the other within a short time. Their ability to fly over distances presents them with the potential to pick and spread pathogens. Despite their potential to acquire and spread pathogens, not many researchers have investigated their gastrointestinal flora. Apparently healthy birds have received little attention when it comes to surveillance for the occurrence of enteric pathogens. Many of the studies that have been conducted have focussed on a few species of birds or were conducted in the event of disease outbreaks with high mortality. In this study, apparently healthy wild birds were investigated for gram-negative enteric bacteria. Gram-negative bacteria were considered because they are the commonest in the environment. Similarly, enteric pathogens were considered because they can be found along the gastrointestinal tract and are mainly obtained from the diet of the bird. The birds were sampled from the Ankasa Conservation Area, Esiama beach and the Densu Delta Ramsar Site. Birds that were sampled from the Ankasa Conservation Area were forest birds and birds from the Densu Delta Ramsar Site and Esiama beach were waterbirds. Overall, 15 gram-negative enterobacteria genera were obtained from 377 cloacal swabs from the sampled birds. The overall prevalence of gram-negative bacteria in the birds was 61.8% (233/377). The prevalence in forest and water- birds were 65.2% (90/138) and 59.8% (143/239) respectively. Common genera of bacteria isolated from the birds were Escherichia (22.3%), Yersinia (19.4%), Enterobacter (12.2%) and Klebsiella (11.4%). On the whole, the most frequently isolated genus was Escherichia, which was obtained from 20 species of sampled birds. However, in the waterbird samples, the genus Yersinia was frequently isolated. The genera Ochrobactrum (0.5%), Morganella (0.3%), Achromobacter (0.3%) and Alcaligenes (0.3%) were the least isolated. Though wild birds do not use antimicrobial agents and rarely come into contact with antimicrobials in the

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wild, bacteria isolated from 15.5% of the birds were resistant to Colistin by the agar dilution method. The prevalence of Colistin-resistant bacteria in the forest and water- birds were 10% (9/90) and 18.8% (27/143) respectively. Colistin-resistant isolates were recorded in seven forest bird species and six waterbird species. Similarly, the overall prevalence of Ciprofloxacin-resistant bacteria in the birds was 41.7% (97/233). The prevalence in forest and water- birds were 35.6% (32/90) and 41.3% (59/143). Ciprofloxacin-resistant isolates were recorded in 11 forest bird species and nine waterbird species. When the Colistin-resistant isolates (106) were subjected to multidrug resistance tests by the disc diffusion method, the prevalence of gram-negative bacteria resistant to antimicrobial agents tested were Ampicillin (73.6%), Streptomycin (50.9%), Oxytetracycline (52.8%) and Ciprofloxacin (8.5%). Colistin and Ciprofloxacin- resistant isolates were further investigated for plasmid-mediated resistance genes. Plasmid-mediated polymyxin-resistant genes mcr-1, mcr-2, mcr-3, mcr-4 and, mcr-5 were recorded in bacteria isolated from the birds. The mcr-3 gene was the most prevalent polymyxin-resistant gene in this study and was recorded in bacterial isolates from both forest and water- birds. The mcr-1 gene was recorded in bacterial isolate from a forest bird, while mcr-2, mcr-4 and mcr-5 were recorded in bacterial isolates from waterbirds. Similarly, plasmid-mediated quinolone-resistant genes (qnrB, qnrD, qnrS and qnrVC) were recorded in bacteria isolates from sampled birds. The prevalent gene was qnrVC and occurred in 9.8% (16/164) of the Ciprofloxacin-resistant isolates. Moreover, bacterial isolates belonging to the gram-negative bacteria genera Salmonella, Escherichia, Yersinia and Shigella were examined for the occurrence of the species Yersinia pseudotuberculosis, Yersinia enterocolitica, Shigella flexneri, Shigella dysentariae, Enterotoxigenic E. coli, and Salmonella enterica. These species are known to cause severe diarrhoeal infections in humans. Only enterotoxigenic E. coli (ETEC) was detected among

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the isolates. The prevalence of ETEC was 38.6% and 62.5% in forest and water- birds respectively. Phylogenetic analysis of all E. coli isolates obtained from this study showed that 60.6% of the E. coli isolates belonged to virulent phylogenetic groups, while 39.4% belonged to commensal groups. The results obtained from this study suggest that wild birds are reservoirs of enteric bacteria and may serve as sources of infection to humans, domestic animals, and other wild animals. The findings also suggest that wild birds harbour antimicrobial-resistant bacteria that carry plasmid-mediated genes. These genes are reported to have the potential to confer resistance to other bacteria isolates. Evidence from the study shows that enterotoxigenic E. coli occurs in the wild birds and these birds may serve as sources of infection to humans. In conclusion, apparently healthy wild birds harbour pathogenic gram-negative bacteria, though they may seem asymptomatic. Therefore, is it important to monitor wild birds for the occurrence of pathogenic bacteria as well as antimicrobial-resistant bacteria. Although prevalence may be low, the potential to spread pathogens is considerable. From a conservation standpoint, the occurrence of antimicrobial-resistant bacteria could hamper conservation efforts as birds carrying resistant bacteria could serve to disperse bacteria between widely separated locations and from hotspots to vulnerable populations.