Isolation and identification of <i>Enterococcus faecalis</i> from cultured <i>Oreochromis niloticus</i> and <i>Mugil cephalus</i> with a special emphasis on a possible integrated control strategy
Marwa A. Hassan, Nahla S. Abdel‐Naeim, Mahmoud Mabrok, Amina Dessouki, Ahmed M. Hassan
Abstract
Abstract This study investigated the prevalence of Enterococcus faecalis amongst cultured Oreochromis niloticus and Mugil cephalus and evaluated the potential use of oregano essential oil (OEO) and glutaraldehyde (GA)‐quaternary ammonium compounds (QACs) combination for its possible control in the light of levels used in Egyptian aquaculture. The total prevalence of E. faecalis was 50.5%, whereas O. niloticus was the most affected species 59%. Molecular typing revealed that the retrieved isolates shared a common ancestor and showed 99.86% genetic similarity to E. faecalis type strain (CAU: 182). The in vitro assays revealed that the measurement techniques showed a highly significant ( p ≤ 0.01) reduction in E. faecalis count at 1250 mg L −1 OEO with complete inhibition at 2500 mg L −1 . The techniques have a strong positive correlation ( p ≤ 0.01) with a slope of regression ( R 2 = 0.872), and their compatibility reached high levels with the area under the curve (AUC) at different wavelengths. Of interest, GA and QACs had LC 50 of 2.19 and 5.16 mg L −1 , respectively, in red tilapia. Moreover, these chemicals had a synergistic effect, with the best bactericidal activity at T1 conc. (0.5 mg GA + 1.2 mg QACs) after 10 min of exposure in both fresh and marine water. Organic matter delayed the activity of the disinfectant and increase the exposure time to 30 min in marine water. Overall, OEO, GA and QACs could be considered as potential surrogates for antibiotic usage for possible control of E. faecalis .