Forest and Water- Birds as Reservoirs of Some Pathogenic and Antimicrobial-Resistant Bacteria
Date
2018-12
Authors
Journal Title
Journal ISSN
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Publisher
University of Ghana
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 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 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.
Description
PhD.
Keywords
Forest, Water- Birds, Pathogenic, Bacteria