Enhancement of Lactic Acid Bacteria by Radiation to Inhibit Antibiotic Resistance of Some Salmonella sp

Lactic acid bacteria (LAB) play an effective role in fermentation and preservation of food either as the natural micro-organisms or as starter cultures applied under certain conditions. LAB species which have antagonistic activity used for improvement of the quality and safety of meat and dairy products), are able to inhibit the growth of several types of pathogenic bacteria, including Gram-negative species of the Enterobacteriaceae families such as Citrobacter freundii, Proteus mirabilis and Salmonella sp. The aim of the present study was to prove the effect of applying two different Lactobacillus protective cultures, able to produce of production some bacteriocin-like inhibitory substances (BLIS), individually or in mixture, on definite microbiological and chemical parameters during storage of refrigerated poultry meat. Forty nine isolates from 34 samples of various food sources using Salmonella-Shigella medium, 10 only were identified biochemically as Salmonella sp., two of them were multidrug-resistant and they showed resistance to the seven tested antibiotics (ampicillin, streptomycin, gentamicin, nalidixic acid, ciprofloxacin, tetracycline, and amoxicillin). Molecular identification of these isolates proved that they were Citrobacter ferundii and Proteus mirabilis. In this study we make comparaison between acetic acid, lactic acid, citric acid antimicrobial activity and the activated free cell supernatants of Lactobacillus acidophilus and Streptococcus thermophilus against the three pathogenic bacteria to evaluate the efficiency of the activated supernatants to use them parallel to acetic, citric and lactic acids in food preservation field. Results showed that the antimicrobial activity of the irradiated supernatant of S. thermophilus against Citrobacter freundii, and Salmonella typhi were equivalent to the following concentrations ≥2.5, ≥3.5% and 4.0 % of acetic, citric and lactic acids respectively while the same supernatant had the same antimicrobial activity of ≥2.5% of the 3 acids for each against Proteus mirabilis. The antimicrobial activity of L. acidophlilus irradiated supernatant was equal to the antimicrobial activity of 4% of the 3 acids against the 3 pathogens except Citrobacter freundii with lactic acid and the previous supernatant was more stronger than acid. The antimicrobial activity for both lactic acid bacteria and their cell-free supernatant were activated by low doses of gamma radiation (20 Gray). Results showed that the activated supernatants completely killed the three pathogenic strains after 3 hours while the lactic acid bacteria mixture killed them after 4 hours