Antibacterial activity of organic acids and an aqueous lime-peel extract against selected foodborne pathogens

Food of animal origin contaminated with food-borne pathogens still concerns the public and food experts due to its harm toward public health. Using organic acids is one of the most important interventions for controlling the microbiological safety and quality of food and has been widely used. An increase of bacterial acid resistant species gave the motivation to find an alternative way to control foodborne pathogens in meat. Limited experimental studies have investigated the antibacterial activity of organic acids and an aqueous lime-peel extract combination on chicken meat against foodborne pathogens. The inhibitory effects of citric, propionic, acetic and lactic acid in combination with an aqueous lime-peel extract (Citrus aurantifolia) against foodborne pathogens and on the organoleptic properties of chicken meat were examined. The minimum inhibitory concentration (MIC) of an aqueous lime-peel extract was investigated using spectrophotometer (TECAN) at 30°C. The MIC of an aqueous lime-peel extract with lactic, citric, acetic and propionic acids in nutrient broth individually against Salmonella Typhimurium DT104 were 2 % w/v, 8 mmol/l, 5.5 mmol/l, 5 mmol/l and 5mmol/l respectively, while against E.coli K12 were 1.5 % w/v, 7 mmol/l, 4 mmol/l, 4 mmol/l and 4mmol/l respectively at 30°C. MIC of lactic acid combined with citric or acetic or propionic acids against Salmonella Typhimurium DT104 were 8 mmol/l - 4.5 mmol/l, 7 mmol/l - 4.5 mmol/l and 7.5 mmol/l - 4 mmol/l respectively. While, against E.coli K12 the MIC of lactic acid combined with citric or acetic or propionic acids were 7 mmol/l - 3 mmol/l, and 6.5 mmol/l - 3.5 mmol/l 6 mmol/l - 3.5 mmol/l respectively. Immersion treatment (10 minutes) of lactic acid combined with acetic acid (208 mmol/l - 96 mmol/l) was used against Salmonella on chicken meat showed a negligible effect at 30°C. A combination of an aqueous lime-peel extract and acetic acid (41.6 % w/v – 1.12 mmol/l) including 1% NaCl on chicken meat was able to significantly inhibit the growth of Salmonella after 9 hours. Applying a sensory evaluation experiment revealed that treating raw chicken meat with lime added a citrusy flavour and made chicken more palatable after cooking. In spite of the induction of virulence and acid tolerance genes of salmonellae which were grow in nutrient broth (pH 2.25) after been treated with an aqueous lime-peel extract and acetic acid combination, salmonellae did not survive more than 2.5 hours at pH 2.5. This study shows that combining both organic acids and an aqueous lime-peel extract on chicken meat can inhibit the bacterial growth of Salmonella and make it more palatable than an untreated sample (control)Ministry of Higher Education and Scientific Research, Ira

Strain and serovar variants of Salmonella enterica exhibit diverse tolerance to food chain-related stress

Non-Typhoidal Salmonella (NTS) continues to be a leading cause of foodborne illness worldwide. Food manufacturers implement hurdle technology by combining more than one approach to control food safety and quality, including preservatives such as organic acids, refrigeration, and heating. We assessed the variation in survival in stresses of genotypically diverse isolates of Salmonella enterica to identify genotypes with potential elevated risk to sub-optimal processing or cooking. Sub-lethal heat treatment, survival in desiccated conditions and growth in the presence of NaCl or organic acids were investigated. S. Gallinarum strain 287/91 was most sensitive to all stress conditions. While none of the strains replicated in a food matrix at 4 °C, S. Infantis strain S1326/28 retained the greatest viability, and six strains exhibited a significantly reduced viability. A S. Kedougou strain exhibited the greatest resistance to incubation at 60 °C in a food matrix that was significantly greater than S. Typhimurium U288, S Heidelberg, S. Kentucky, S. Schwarzengrund and S. Gallinarum strains. Two isolates of monophasic S. Typhimurium, S04698–09 and B54Col9 exhibited the greatest tolerance to desiccation that was significantly more than for the S. Kentucky and S. Typhimurium U288 strains. In general, the presence of 12 mM acetic acid or 14 mM citric acid resulted in a similar pattern of decreased growth in broth, but this was not observed for S. Enteritidis, and S. Typhimurium strains ST4/74 and U288 S01960-05. Acetic acid had a moderately greater effect on growth despite the lower concentration tested. A similar pattern of decreased growth was observed in the presence of 6% NaCl, with the notable exception that S. Typhimurium strain U288 S01960-05 exhibited enhanced growth in elevated NaCl concentrations

A hybrid and poly-polish workflow for the complete and accurate assembly of phage genomes: a case study of ten przondoviruses

Bacteriophages (phages) within the genus Przondovirus are T7-like podoviruses belonging to the subfamily Studiervirinae, within the family Autographiviridae, and have a highly conserved genome organisation. The genomes of these phages range from 37 to 42 kb in size, encode 50–60 genes and are characterised by the presence of direct terminal repeats (DTRs) flanking the linear chromosome. These DTRs are often deleted during short-read-only and hybrid assemblies. Moreover, long-read-only assemblies are often littered with sequencing and/or assembly errors and require additional curation. Here, we present the isolation and characterisation of ten novel przondoviruses targeting Klebsiella spp. We describe HYPPA, a HYbrid and Poly-polish Phage Assembly workflow, which utilises long-read assemblies in combination with short-read sequencing to resolve phage DTRs and correcting errors, negating the need for laborious primer walking and Sanger sequencing validation. Our assembly workflow utilised Oxford Nanopore Technologies for long-read sequencing for its accessibility, making it the more relevant long-read sequencing technology at this time, and Illumina DNA Prep for short-read sequencing, representing the most commonly used technologies globally. Our data demonstrate the importance of careful curation of phage assemblies before publication, and prior to using them for comparative genomics