In the present study, we isolated three thermophilic Bacillus strains from the soil samples collected from the coast sediments of the Burnaz Stream located in Erzin. The isolates were entitled as Bacillus sp. CT1, CT2, and CT3, respectively. The maximum α-amylase production was revealed at 60°C for CT1 strain, and at 80°C for CT2 and CT3 strains, respectively. The optimum enzyme activity was observed at 90°C for CT1 α-amylase, whereas at 60°C for CT2 and CT3 α-amylases. On the other hand, optimum pH value for CT2 α-amylase was 7.0, whereas 8.0 for CT1 and CT3 α-amylases. The specific activities of CT1, CT2, and CT3 amylases were 317.6, 113.3 and 362.7 U/mg at 55°C, respectively. The estimated molecular weight of CT1 and CT3 α-amylase was 65 kDa, and for CT2 α-amylase was 38 kDa by zymogram analysis.

Yoghurt is the common fermented dairy product consumed worldwide and it is considered a potential source of probiotic bacteria (Lactobacilli and Lactococci). To assess the in-vitro probiotic properties of lactic acid bacteria, Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii and Lactobacillus plantarum species isolated from yoghurt sold in different local markets of Chittagong region in Bangladesh were examined by morphological characteristics and biochemical tests. In the preliminary test, all isolates were grown well at acidic pH (pH 3-5) while the optimum growth temperature was 37°C and better growth was observed in the presence of 1-8% NaCl concentrations. In addition, the selected isolates were able to survive up to 3% bile salt concentrations while the best tolerance was at 1% bile salt. The strains successfully inhibited the growth of common pathogenic bacteria likely Escherichia coli, Pseudomonas aeruginosa, Salmonella Paratyphi, Staphylococcus aureus and Bacillus subtilis examined by in vitro growth inhibition test. Most of the isolated strains exhibited resistance pattern against ten commonly used antibiotics in foodborne illness in the country. However, the strains in yoghurt sold at Chittagong city have ideal probiotic characteristics and this fermented dairy product could be a potential source of human probiotic bacteria.

The aim of this study was to isolate, purify and determine host ranges of bacteriophages infecting Escherichia coli O157:H7 from different environment such as river/stream water, sewage, raw food, animal troughs, wastewaters of food processing plants, slaughterhouse and fish farms. For screening of E. coli O157:H7 bacteriophages, 92 samples were used. It was found that in respect to anti-E. coli O157:H7 bacteriophages, food processing wastewaters, sewage and slaughterhouse wastewaters are the richest sources, and streams, troughs and fisheries wastewater are rich in the middle, and raw foods were the poorest source. A total of 37 phages were isolated and purified. The phages counts of the purified samples were changed among 30×103 - 34×108 PFU/mL. The isolated phages were generally infective against E. coli O157:H7 and E. coli strains and 81.08% of the phages (30 out of 37) formed clear plaques and were capable to lyse at least 1 out of 5 E. coli O157:H7 strains. In addition to E. coli, some phages were capable to infect some Salmonella enterica serovars. This results show that inhibitor spectra of the phages were wide.

Salmonellosis is a critical challenge in commercial poultry farming. This study aimed to calculate seroprevalence, identify Salmonella spp., and its pathological investigation from January to December 2019. One hundred fifty (150) serum samples and fifty (50) cloacal swabs from apparently ill and healthy birds were collected in this study. Seroprevalence was observed by serum plate agglutination (SPA) tests. The tentative diagnosis of salmonellosis was made based on history, clinical signs and bacteriological studies. Salmonella spp. was further confirmed using an automated microbiological method (VITEK®2). Post mortem examination was done in apparently sick birds, and gross and microscopic pathological lesions were investigated and recorded in a datasheet. The overall seroprevalence of salmonellosis was 42.67% in commercial chickens. Age wise prevalence of avian salmonellosis showed significantly highest infection rate in adult layers (≥ 45 days old) 65.31%, then 40.74%up to 45 days. In case of broiler, the prevalence rate in 0-10 days, 11-20 days, and 21-35 days were 13.63%, 44.12%, and 16.67%, respectively. Seasonal influence showed significantly highest proportionate prevalence of salmonellosis during summer 66.15%in comparison to winter 25.00% and rainy 24.44% seasons respectively. In bacteriological study, 12 samples were positive for Salmonellae among 50 cloacal samples. Out of 12 positive samples 5 samples were selected for the automated microbiology system VITEK® 2, and only two samples were confirmed as Salmonella gallinarum. Gross pathology of representative organs revealed bronze-colored enlarged liver, hemorrhages in the spleen and lungs, and hemorrhages in the ovary with stalk development. Microscopically, multifocal nodule formation and infiltration of inflammatory cells in the liver parenchyma and marked congestion with inflammatory cells in the spleen, hemorrhage and congestion in the lungs and intestine.