This commentary was aimed at shedding light on the multifunction of bacteriocins mainly those produced by lactic acid bacteria. These antibacterial agents were first used to improve food safety and quality. With the increasing antibiotic resistance concern worldwide, they have been considered as viable agents to replace or potentiate the fading abilities of conventional antibiotics to control human pathogens. Bacteriocins were also shown to have potential as antiviral agents, plant protection agents, and anticancer agents. Bacteriocins were reported to be involved in shaping bacterial communities through inter- and intra-specific interactions, conferring therefore to producing strains a probiotic added value. Furthermore, bacteriocins recently were shown as molecules with a fundamental impact on the resilience and virulence of some pathogens.

e Pathogens resistant to most conventional antibiotics are a harbinger of the need to discover novel antimicrobials and anti-infective agents and develop innovative strategies to combat them. The aim of this study was to assess the in vitro activity of colistin alone or in combination with two bacteriocins, nisin A and pediocin PA-1/AcH, against Salmonella choleraesuis ATCC 14028, Pseudomonas aeruginosa ATCC 27853, Yersinia enterocolitica ATCC 9610, and Escherichia coli ATCC 35150 (O157:H7). The strain most sensitive to colistin was enterohemorrhagic E. coli O157:H7, which was inhibited at a concentration of about 0.12 g/ml. When nisin A (1.70 g/ml) or pediocin PA-1/AcH (1.56 g/ml) was combined with colistin, the concentrations required to inhibit E. coli O157:H7 were 0.01 and 0.03 g/ml, respectively. The in vitro antigenotoxic effect of colistin was determined by using the comet assay method to measure the level of DNA damage in freshly isolated human peripheral blood leukocytes (PBLs) incubated with colistin for 1 h at 37°C. Changes in the tail extents of PBLs of about 69.29 ؎ 0.08 m were observed at a final colistin concentration of about 550 ng/ml. Besides the synergistic effect, the combination of colistin (1 mg/ml) and nisin (2 mg/ ml) permitted us to re-evaluate the toxic effect of colistin on Vero (monkey kidney epithelial) cells.T he emergence of multidrug-resistant pathogenic bacteria highlights a matching need for new therapeutic options. Better management and reasonable use of antibiotics are imperatively required in order to reduce the rate of emergence of antibioticresistant strains. Currently, clinicians and microbiologists are being forced to re-evaluate the clinical use of colistin, a relatively old polypeptide antibiotic, because there appear to be no promising therapeutic agents in the drug development pipeline (1). Colistin became available for clinical use in the 1960s but was replaced in the 1970s with antibiotics considered less toxic. Nephrotoxicity and neurotoxicity were the major side effects that led to the discontinuation of the routine use of colistin (1, 2). Two forms of colistin are commercially available, colistin sulfate, which is for oral and topical use, and colistimethate sodium (sodium colistin methanesulfonate, colistin sulfomethate sodium), which is for parenteral use or inhalation. The structure of polymyxins consists of a cyclic decapeptide bound to a fatty acid (3). Colistin binds to the anionic part of the lipopolysaccharide (LPS), leading to deep disruption in the bacterial membrane, enhancing its permeability and causing cell lysis (4). A role for LPS as a major receptor of colistin was proposed (5), and the mode of action involved a hydrophobic interaction between the nine-carbon fatty acid side chain of colistin and the fatty acid portion of lipid A (6). Strains of Escherichia coli and Klebsiella pneumoniae have become increasingly resistant to expanded-spectrum cephalosporins (7) but remain globally sensitive to tigecycline and colistin (8). The use of polymyxins t...

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Aims:  Divergicin M35 is a new class IIa bacteriocin produced by Carnobacterium divergicin M35. The bactericidal activity of this antimicrobial peptide was tested against a set of 11 strains of Listeria monocytogenes isolated from food. Methods and Results:  The minimal inhibitory concentration (MIC) was determined by the microdilution method. The strains tested displayed a different level of sensitivity to divergicin M35. L. monocytogenes LSD530, referred to as DivS strain, was the most sensitive and appeared to be inhibited by concentration of divergicin M35 below 0·13 μg ml−1. The mutant resistant to divergicin M35, called DivM, was obtained from L. monocytogenes LSD530 (DivS) by gradually increasing the amounts of divergicin M35 until 1·3 μg ml−1. Notably, DivM was stable after 50 generations. DivS parental strain was inhibited by a concentration of 4 μg ml−1. L. monocytogenes LSD530 was shown to be resistant to divergicin M35 at 1·3 μg ml−1. Remarkably, in the presence of divalent cations such as Ca2+, Mg2+ and Mn2+, the lethality caused by divergicin M35 was reduced by 0·48, 0·54 and 0·63 log CFU per ml (after 18 h at 30°C), respectively. The total DNA profiles of DivS and DivM were similar. DivS and DivM showed variable sensitivity to antibiotics. The two‐dimensional (2‐D) electrophoresis of cell wall proteins did not show any significant difference between DivS and DivM strains but their fatty acid composition showed a significant difference in C16:0 content. Conclusions:  Resistance to divergicin M35 is likely ascribed to modification in cell wall fatty acid composition rather than protein modification. Significance and Impact of the Study:  This study provides original results contributing to understanding of the resistance of L. monocytogenes to divergicin M35, a new class IIa bacteriocin.

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