The Effects of Alternating and Direct Electric Currents on Moderately Halophilic Bacteria in Leather Industry

Abstract

Proteolytic and lipolytic moderately halophilic bacteria, originate from salt, may be found on salted sheep skins. Microbial spoilage of sheepskin usually results from the failure to inactivate proteolytic and lipolytic micro-organisms during skin preservation. To solve this problem, an effective inactivation method to be used in the leather industry was examined in this study. Protease and lipase activities of moderately halophilic Staphylococcus saprophyticus subsp. saprophyticus (TR5), Bacillus pumilus (DB5), Bacillus licheniformis (DBA2), Gracilibacillus dipsosauri (EK2) and Idiomarina loihiensis (GA3), isolated from salted sheepskins, were examined. Protease activity of each test isolate was determined by both gelatin agar medium and casein digestion assay at 280nm. Lipolytic activity of each test isolate was determined by both Tween 80 agar medium and measuring hydrolysis of p-nitrophenylbutyrate to p-nitrophenol at 405nm. Antibiotic sensitivities of test isolates to novobiocin, penicillin G, tetracycline, streptomycin, erythromycin, tobramycin, kanamycin and gentamicin were tested using disc diffusion susceptibility method. These isolates were found to be proteolytic, lipolytic and resistant to aforementioned antibiotics. Inactivation effects of direct electric currents and alternating electric currents (0.5A, 1.0A, 1.5A and 2.0A) on the mixed culture of these isolates were separately examined in liquid medium containing 25% NaCl. The mixed culture was killed in 1 minute by 0.5A direct current and 1.5A alternating current treatments. However, 0.5A alternating current and 1.0A alternating current treatments eliminated these micro-organisms respectively in 15 minutes and 10 minutes. In conclusion, electric current applications hold great potential for the eradication of proteolytic and lipolytic, antibiotic resistant, moderately halophilic bacteria in leather industry.