Abstract
Foodborne illness caused by consumption of food contaminated with Salmonella is one of the most common causes of diarrheal disease and affects millions of people worldwide. The rising emergence and spread of antimicrobial resistance, especially in some serotypes of Salmonella, has raised a great awareness of public health issues worldwide. To ensure safety of the food processing chain, the development of new food preservatives must be expedited. Recently, thermal- and pH-stable antimicrobial peptides have received much attention for use in food production, and represent safe alternatives to chemical preservatives. A 12-mer cathelicidin-derived, α-helical cationic peptide, P7, displayed rapid killing activity, against strains of drug-resistant foodborne Salmonella enterica serovar Typhimurium and its monophasic variant (S. enterica serovar 4,5,12:i:-) and had minimal toxicity against mouse fibroblast cells. P7 tended to form helical structure in the membrane-mimic environments as evaluated by circular dichroism (CD) spectroscopy. The action mode of P7 at the membrane-level was affirmed by the results of flow cytometry, and confocal, scanning and transmission electron microscopy. P7 killed bacteria through binding to bacterial membranes, penetration and the subsequent accumulation in S. enterica serovar Typhimurium cytoplasm. This induced membrane depolarization, permeabilization, and sequential leakage of intracellular substances and cell death. Except for sensitivity to proteolytic digestive enzymes, P7 maintained its inhibitory activity against S. enterica serovar Typhimurium in the presence of different conditions [various salts, extreme pHs and heat (even at 100°C)]. Moreover, the peptide is unlikely to induce bacterial resistance in vitro. Taken together, this study demonstrated that the membrane-permeabilizing P7 peptide has much potential as a new antimicrobial agent for use in food processing and preservation.
Highlights
Salmonella are gram-negative bacteria and common causes of diarrheal diseases affecting millions of people all over the world, and notably some resistant serotypes have emerged
The antibacterial activity of P7 compared to nisin was determined against S. enterica serovar Typhimurium ATCC 13311 and 35 drug-resistant S. enterica serovar Typhimurium and 4,5,12:i:isolates in Thailand, including 24 foodborne and 11 clinical isolates (Table 1)
At minimum inhibitory concentrations (MICs) concentration, P7 reduced the viable cells of S. enterica serovar Typhimurium more than 103 and 104 CFU/ml within 2 and 4 h, respectively
Summary
Salmonella are gram-negative bacteria and common causes of diarrheal diseases affecting millions of people all over the world, and notably some resistant serotypes have emerged. A monophasic variant of S. enterica serovar Typhimurium (named S. enterica serovar 4,5,12:i:-) that is deficient in the expression of the phase-2 flagellar antigen has emerged. This variant is a growing public health problem because of its drug resistance, pathogenicity, existence among food and veterinary chains, and capability to spread extensively (Arai et al, 2018; Mastrorilli et al, 2018). Besides food hygiene practices, such as "cook thoroughly," recommended by the WHO as a basic preventive strategy (World Health Organization [WHO], 2018), preservative agents are important in keeping food safe and unspoiled by microorganisms
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