IDENTIFICATION AND CHARACTERIZATION OF MOTILE AEROMONADS ISOLATED FROM FISH AND FISH POND WATER WITH SPECIAL EMPHASIS ON VIRULENT Aeromonas hydrophila
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Date
2022-03
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
Motile aeromonads are one of the troublesome bacteria affecting the aquaculture
industry by causing an assortment of diseases and also implicated in causing illness to
humans by consumption of raw or improperly cooked fish, drinking contaminated water
and contamination of wounds by water having aeromonads etc. The present study was
intended to characterize Aeromonas spp. of fish, fish pond water and also human
diarrhoeal origin with special emphasis to isolate and identify Virulent Aeromonas
hydrophila (VAh) based on cultural and molecular techniques. A total of 330 samples
comprising healthy and diseased fish, fish pond water and human diarrhoeal samples
were analyzed for presence of Aeromonas spp. viz. A. veronii and A. hydrophila.
Overall prevalence of genus Aeromonas was found to be 37.27% (123/330). Out
of 123 Aeromonas isolates, m-PCR revealed 67 (54.47%) were to be A. veronii and seven
(5.69%) were to be A. hydrophila. Out of 74 positive Aeromonas spp. isolated from
different sources, highest prevalence of 56.75% (42/74) was found in healthy fish
followed by diseased fish 25.67 (19/74), fish pond water 16.21% (12/74) and human
diarrhoea 1.35% (1/74). Out of seven A. hydrophila isolates, three isolates were phenotypically positive
for VAh based on inositol fermentation on M9I agar.
Among 74 Aeromonas spp. isolates, the phenotypic virulence factors i.e. biofilm
formation, gelatinase activity, DNase activity, caseinase activity, lipase activity and
hemolysis were detected in 61(82.43%), 70 (94.59%), 69 (93.24%), 52 (70.27%), 48
(64.86) and 70 (94.59%) of the isolates, respectively.
Out of 74 Aeromonas spp. isolates, 49 were positive for atleast one of the
virulence genes. 49 Aeromonas spp. revealed the presence of virulence genes i.e act, ast,
alt, ahyB, fla, lip, aer, ser, gcat and exu which were detected in 35 (47.29%), 9 (12.16%),
14 (18.91%), 15 (20.27%), 3 (4.05%), 26 (35.13), 16 (21.62%), 7 (9.45%), 16 (21.62%)
and 12 (16.21%) of the isolates, respectively.
Antibiogram profiling of 74 Aeromonas isolates unveiled a significant fraction
of the Aeromonas isolates to be resistant towards ampicillin and novobiocin (100%)
followed by vancomycin (71.62%) and erythromycin (54.05%). ESBL production was
confirmed in 24 Aeromonas spp. isolates by both phenotypic and molecular methods and
blaTEM was the predominant gene in 23 isolates and blaOXA gene was detected in only
one isolate. A greater degree of heterogeneity was observed among 24 ESBL positive
Aeromonas spp. isolated from different sources as revealed by presence of 24 genotypes
each by ERIC and REP-PCR analysis. 19 different A. veronii and five A. hydrophila
subtypes were differentiated by ERIC-PCR and REP-PCR. Genotyping of Aeromonas
spp. by ERIC-PCR and REP-PCR was found to be highly significant since the
discriminatory power >0.9 is considered as highly significant (1 for both ERIC –PCR and
REP-PCR). Cluster analysis also revealed a great degree of homogeneity and
heterogeneity among different isolates recovered from different sources thereby
indicating that there is a chance of cross-contamination particularly in the fish markets.
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