Innovative natural agents for inhibition of pathogenic bacteria and their resistant variants in vitro and in foods

Abstract

Antibiotics are produced by either bacteria or fungi. Actinomycetes produce two-thirds of the known antibiotics. Many of them are the third generations of certain classes of antibiotics, such as the β-lactam group. Unfortunately, many multidrug-resistant (MDR) microbes have recently been isolated from medicinal specimens or polluted foods. This showed that there is a need to find other innovative ways to inhibit MDR bacteria based on natural agents such as lactic acid bacteria (LAB), natural native and modified proteins, and nanoparticles singly or in combination with antibiotics. The resistance mechanisms to antibiotics are due to genetic determinants, the thickening of the bacterial cell wall, or modifications in specific site receptors on which antibiotics act. Also, certain reasons lead to resistance due to the ability of the bacterial pathogen to secrete enzymes that can degrade the antibiotic such as β-lactamases. Of the innovative natural agents which can inhibit bacterial pathogens are LAB; their metabolites such as organic acids, acetaldehydes, ethanol, diacetyl, and bacteriocins inhibit the bacterial pathogens and their resistant variants. Many genera of LAB, such as Lactobacillus, Lactococcus, Carnobacterium, Pediococcus, Leuconostoc, and Enterococcus, produce bacteriocins or antimicrobial proteins of broad spectrum activity against both Gram-positive and Gram-negative bacterial pathogen. Therefore, bacteriocins have been used recently for food preservation and have been shown to extend the shelf life of foods. Natural legume proteins, either native or modified by methylation, showed a broad spectrum antimicrobial activity, as the positive charges of methylated proteins attach negatively charged phospholipids of the bacterial cell membrane, making hydrophobic-hydrophobic interactions. This leads to the formation of pores in cell membranes, from which leakage of electrolytes occurs and causes cell death. In addition, nanoparticles have been recently used in combination with antibiotics in either medical therapy or in food preservation. In Egypt, the shortage of freshwater resources and their pollution constitutes a growing concern. Due to the uncensored use of pesticides in the agricultural regions of Egypt, the contamination risks of ground water increase periodically in planting seasons. Therefore, the present work aims to monitor the occurrence of organochlorine pesticides (OCPs) residues and heavy metals in five ground water samples collected from agricultural area with long-term pesticide application history in Belbis region, El-Sharqia, Egypt. Water samples were processed using a solid-phase extraction technique and gas chromatograph equipped with mass spectrometry (GC-MS). Results revealed that, the concentrations of OCPs in groundwater are in the limits except only 0.65 μg/L of p,p'-DDT recorded in ground water at Hassan Bieh village location, Belbis region, El-Sharqia, Egypt. Levels of iron and manganese in (Elnoba and Awlad Mahnaa) ground water samples were found to be much higher than the lim...