Abstract:
Antibiotics play a key role in controlling bacterial infections of shrimps. This study
investigated the Antibiotic Sensitivity Testing (AST) of Escherichia coli and
Salmonella from shrimp samples taken from seven shrimp farms in Puttalam District,
Sri Lanka. Twenty-one cultured shrimp samples were analysed and thirteen E. coli and
nrne Salmonella cultures were isolated. Antibiotic sensitivity for isolated bacterial
cultures was tested using the Kirby-Bauer disc diffusion method. The antibiotic
susceptibility pattems of these bacterial species were assayed against five antibiotics
including amoxicillin (30 mcg), oxltetracycline (30 mcg), chloramphenicol (1Omcg),
erythromycin (10 mcg), and tetracycline (10 mcg). The diameter of inhibition zones
was compared with Clinical and Laboratory Standards Institute standards. Among the
2I shrimp samples, 53.84% (7113) of E. coli rsolates were highest resistant to
erythromycin, and 38.46% exhibited resistance towards ambxicillin and tetracycline
with susceptibility towards chloramphenicol. Additionally, E. coli cultures isolated
from pond water samples showed resistance towards erythromycin and tetracycline at
a rate of 33 .33%. All Salmonella isolates in shrimp samples showed 44.44% (419),wtth
the highest resistance to erythromycin and llJl% (Il9), lower resistance to
tetracycline and amoxicillin, while they showed the highest susceptibility to
chloramphenicol and oxytetracycline. Moreover, E. coli and Salmonella isolates from
pond water displayed resistance to erythromycin. E. coli isolates from shrimp samples
were found to have a Multiple Antibiotic Resistance (MAR) index of as high as 0.8
with the antibiotic combination of amoxicillin, erythromycin, oxytetracycline and
tetracycline. These results showed that antibiotic-resistant bacteria are present in
shrimp farms.
