Identification and characterization of lytic bacteriophages specific to foodborne pathogenic Escherichia coli O157:H7.

The objective of this study was to identify and characterize five different lytic bacteriophages specific to Escherichia coli O157:H7. vB_EcoM-P12, vB_EcoM-P13, vB_EcoM-P23, and vB_EcoM-P34 phages belonged to the Myoviridae family and vB_EcoS-P24 phage was in the Siphoviridae family. Their plaque sizes changed between 0.48 ± 0.03 and 0.90 ± 0.03 mm in diameter. stx1 and stx2 virulent gene regions were absent in the genome of five Eco-phages and their genome size was 33 kbp. The protein band profiles of the five phages were found to be different from each other. Their latent period, burst size, and burst time changed between 10-15 min, 72-144 PFU/cell and 20-35 min, respectively. Multiplicity of infection values and mutant frequency of the phages were among 0.1-0.001 and 1.14 × 10-7-3.69 × 10-8, respectively. The phages had strong lytic activity against their host bacteria (E. coli NCTC 12900, ATCC 43888, and ATCC 35150) at 5-37 ℃ and adsorbed to their host cells by 92.7-97.5% in the first five minutes of incubation. These phages are thought to be good candidates as therapeutic and biocontrol agents against E. coli O157:H7 in the veterinary science and food industry due to short latent period, high burst size, rapid development in host cells, high lytic activity, high adsorption rate, stability over a wide pH range and high temperature, and absence of stx1 and stx2 genes.

Characterization of SE-P3, P16, P37, and P47 bacteriophages infecting Salmonella Enteritidis.

The aim of this study was to identify and characterize the SE-P3, P16, P37, and P47 phages infecting Salmonella Enteritidis. Transmission electron microscopy analysis showed that the SE phages belonged to the Myoviridae or Siphoviridae family and had plaque sizes between 0.622 ± 0.027 and 1.630 ± 0.036 mm in diameter. sefC, pefA, spvC, sopE, and gipA virulent gene regions were absent in their genome and their calculated genome sizes were between 35.9 and 37.8 kbp. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the protein profiles of each phage were different. The SE phages had a short latent period (10-20 min), large burst size (76-356 PFU/cell), and a short burst time (25-35 min). The multiplicity of infection values and mutant frequency of the phages were 0.01-0.0001 and 10-7 , respectively. They were very infective against their host bacteria when applied at 20°C, 30°C, or 37°C and adsorbed to their host cells by 96.20-97.65% in the first 5 min of incubation, and also Ca2+ ions did not have a significant effect on their adsorption. The SE phages were resistant to wide pH ranges and high temperatures. These results indicate that the SE phages are good candidates as therapeutic and biocontrol agents against foodborne pathogenic S. Enteritidis.

Inhibitory Effect of Lactococcin BZ Against Listeria innocua and Indigenous Microbiota of Fresh Beef.

In this study, the effect of lactococcin BZ on microbiological quality of fresh beef is investigated. For this purpose, the meat samples were treated with various amounts of lactococcin BZ (200-2500 AU/mL), a bacteriocin produced by Lactococcus lactis spp. lactis BZ, and kept at 4-5 °C for 12 days. During storage, the microbiological properties of the meat samples with or without lactococcin BZ were determined. Inhibitory effect of lactococcin BZ depended on its amount. The higher the amount of lactococcin BZ, the higher the inhibitory activity. Treatment with lactococcin BZ at the level of 2500 AU/mL resulted in 4.87, 3.50 and 3.94 log cycle decrease in the counts of mesophilic, psychrotrophic and lactic acid bacteria, respectively, and 1.90·104 and 1.04·102 CFU/g reduction in coliform and faecal coliform bacteria, respectively, at the end of storage as compared to their initial numbers in the control sample. However, the counts of these bacteria in control samples increased during storage. Also, lactococcin BZ at 1600 AU/mL showed very strong antilisterial effect against Listeria innocua in fresh meat and reduced the cell numbers from 6.04 log CFU/g to undetectable level on the 6th day of storage. In conclusion, lactococcin BZ has a potential use as a biopreservation agent to improve safety and shelf life of raw beef.