Genomic and Phenotypic Analysis of Salmonella enterica Bacteriophages Identifies Two Novel Phage Species.

Bacteriophages (phages) are potential alternatives to chemical antimicrobials against pathogens of public health significance. Understanding the diversity and host specificity of phages is important for developing effective phage biocontrol approaches. Here, we assessed the host range, morphology, and genetic diversity of eight Salmonella enterica phages isolated from a wastewater treatment plant. The host range analysis revealed that six out of eight phages lysed more than 81% of the 43 Salmonella enterica isolates tested. The genomic sequences of all phages were determined. Whole-genome sequencing (WGS) data revealed that phage genome sizes ranged from 41 to 114 kb, with GC contents between 39.9 and 50.0%. Two of the phages SB13 and SB28 represent new species, Epseptimavirus SB13 and genera Macdonaldcampvirus, respectively, as designated by the International Committee for the Taxonomy of Viruses (ICTV) using genome-based taxonomic classification. One phage (SB18) belonged to the Myoviridae morphotype while the remaining phages belonged to the Siphoviridae morphotype. The gene content analyses showed that none of the phages possessed virulence, toxin, antibiotic resistance, type I-VI toxin-antitoxin modules, or lysogeny genes. Three (SB3, SB15, and SB18) out of the eight phages possessed tailspike proteins. Whole-genome-based phylogeny of the eight phages with their 113 homologs revealed three clusters A, B, and C and seven subclusters (A1, A2, A3, B1, B2, C1, and C2). While cluster C1 phages were predominantly isolated from animal sources, cluster B contained phages from both wastewater and animal sources. The broad host range of these phages highlights their potential use for controlling the presence of S. enterica in foods.

Bacteriophage-Induced Lipopolysaccharide Mutations in Escherichia coli Lead to Hypersensitivity to Food Grade Surfactant Sodium Dodecyl Sulfate.

Bacteriophages (phages) are considered as one of the most promising antibiotic alternatives in combatting bacterial infectious diseases. However, one concern of employing phage application is the emergence of bacteriophage-insensitive mutants (BIMs). Here, we isolated six BIMs from E. coli B in the presence of phage T4 and characterized them using genomic and phenotypic methods. Of all six BIMs, a six-amino acid deletion in glucosyltransferase WaaG likely conferred phage resistance by deactivating the addition of T4 receptor glucose to the lipopolysaccharide (LPS). This finding was further supported by the impaired phage adsorption to BIMs and glycosyl composition analysis which quantitatively confirmed the absence of glucose in the LPS of BIMs. Since LPSs actively maintain outer membrane (OM) permeability, phage-induced truncations of LPSs destabilized the OM and sensitized BIMs to various substrates, especially to the food-grade surfactant sodium dodecyl sulfate (SDS). This hypersensitivity to SDS was exploited to design a T4-SDS combination which successfully prevented the generation of BIMs and eliminated the inoculated bacteria. Collectively, phage-driven modifications of LPSs immunized BIMs from T4 predation but increased their susceptibilities as a fitness cost. The findings of this study suggest a novel strategy to enhance the effectiveness of phage-based food safety interventions.

Reviving Phage Therapy for the Treatment of Cholera.

Cholera remains a major risk in developing countries, particularly after natural or man-made disasters. Vibrio cholerae El Tor is the most important cause of these outbreaks, and is becoming increasingly resistant to antibiotics, so alternative therapies are urgently needed. In this study, a single bacteriophage, Phi_1, was used to control cholera prophylactically and therapeutically in an infant rabbit model. In both cases, phage-treated animals showed no clinical signs of disease, compared with 69% of untreated control animals. Bacterial counts in the intestines of phage-treated animals were reduced by up to 4 log10 colony-forming units/g. There was evidence of phage multiplication only in animals that received a V. cholerae challenge. No phage-resistant bacterial mutants were isolated from the animals, despite extensive searching. This is the first evidence that a single phage could be effective in the treatment of cholera, without detectable levels of resistance. Clinical trials in human patients should be considered.

Complete Genome Sequences of Vibrio cholerae-Specific Bacteriophages 24 and X29.

The complete genomes of two Vibrio cholerae bacteriophages of potential interest for cholera bacteriophage (phage) therapy were sequenced and annotated. The genome size of phage 24 is 44,395 bp encoding 71 putative proteins, and that of phage X29 is 41,569 bp encoding 68 putative proteins.

Complete Genome Sequences of Seven Vibrio cholerae Phages Isolated in China.

The complete genome sequences of seven closely related Vibrio cholerae phages isolated from environmental sites in southeastern China are reported here. Phages QH, CJY, H1, H2, H3, J2, and J3 are members of the Podoviridae family and are highly similar to the previously sequenced Vibrio phages VP2, VP5, and phiVC8.

Prevalence of microorganisms of hygienic interest in an organized abattoir in Mumbai, India.

BACKGROUND: The magnitude of food-borne illnesses in India is unknown because of lack of surveillance networks. Monitoring the prevalence of food-borne pathogens and indicators of contamination in primary production at abattoirs is imperative for creating a data bank and for effective control of such pathogens before they enter the food chain. METHODOLOGY: Microorganisms of hygienic interest were screened for their prevalence at Deonar Abattoir, Mumbai. Swab samples from 96 sheep/goat carcass sites were collected and analyzed for Staphylococcus spp., Bacillaceae, Clostridiaceae and Enterobacteriaceae. RESULTS: Average Staphylococcus aureus and Staphylococcus epidermidis counts were 3.15 +/- 0.18 and 3.46 +/- 0.17 log10 CFU/cm(2), respectively. Bacillus cereus, Bacillus subtilis and Clostridium spp. counts were 3.10 +/- 0.08, 3.41 +/- 0.19 and 0.76 +/- 0.06 log10 CFU/cm(2), respectively. The Escherichia coli count was 3.54 +/- 0.06 and the Klebsiella aerogenes count was 3.22 +/- 0.22 log10 CFU/cm(2). Counts for Proteus vulgaris and Proteus mirabilis were 3.44 +/- 0.14 log10 CFU/cm(2) and 3.71 +/- 0.12 log10 CFU/cm(2), respectively. S. epidermidis had the highest percentage prevalence at (41.6%), followed by K. aerogenes (31.9%), B. subtilis (28.2%) and P. vulgaris (23.6%). Salmonella spp. were not isolated. CONCLUSIONS: The data demonstrate high prevalence and diversity of micro flora on carcasses in the primary Indian production facility, which might be attributed to either human handling or improper dressing especially during evisceration process. Appropriate training for personal and production hygiene is essential for workers in Indian meat production facilities.