Biocontrol of pathogenic salmonellain pleed and deveined shrimp using bacteriophages

MFSc Thesis

ABSTRACT
The use of lytic bacteriophages for the biocontrol of food borne pathogens in food
industry is gaining increasing acceptance. In recent years it has become widely recognized
that bacteriophages have several potential applications in the food industry as a biocontrol
agent. But in the seafood industry we are still using chemicals to control the food borne
bacterial pathogens. Hence this study has been under taken to control food borne
Salmonella infections in peeled and deveined (PD) shrimp using bacteriophage.
In this study we could isolate Salmonella phage from raw sewage sample collected
from Fort Kochi using Salmonella Typhimurium (MTCC 1264) as the host bacterium. The
host specificity of the isolated phage was determined by spotting the higher dilution of
phage onto the bacterial overlay. The phage isolated in the present study showed high
specificity towards the Salmonella Typhimurium whereas it didn’t show any specificity to
the other isolates tested. The efficacy of the isolated Salmonella phage as a biocontrol
agent against Salmonella was checked by conducting challenge experiments in PD shrimp.
PD shrimp was experimentally contaminated with Salmonella Typhimurium (103 cfu/ml)
and treated with Salmonella phage at a concentration of 7x108 pfu/ml and kept at 8°C with
negative and positive controls which was mock treated with 2ml distilled water and 2 ml of
freshly prepared Salmonella Typhimurium culture, respectively. The samples were
collected from all the controls and treatments at four time intervals viz.0th, 3rd, 6th, 9th h.
The results showed that the log reduction between the positive and treatment trials
at 0th and 3rd hour interval as 0.24 and 0.95 log unit, respectively. But from 6th hour
onwards the host bacterial count showed high reduction in Salmonella count when
compared to 0th and 3rd hour. At the 6th hour, the Salmonella count obtained for the positive
control was 3.08×103 cfu/ml and for the treatment, the bacterial count was 1.4×101. The
log reduction in host bacterial count between the positive and treatment at 6th hour was
2.34 whereas at 9th hour the log reduction was 2. 51 log unit. The statistical analysis using
ANOVA showed that there was a significant difference in the bacterial count between the
treatment and positive control as well as at various time intervals with 95 percentage
confidence interval. Overall, the result indicates that the isolated phage is useful to control
food borne pathogen Salmonella Typhimurium in PD shrimp. Hence the study shows the
potential effectiveness of this isolated Salmonella phage as a biocontrol agent of
Salmonella Typhimurium in PD shrimp.