Antibiotic resistance and virulence genes in nisin‐resistantEnterococcus faecalisisolated from raw buffalo milk modulate the innate functions of rat macrophages

Abstract

Aims: To elucidate the antibiotic resistance and virulence genes of nisinresistant Enterococcus faecalis isolated from raw buffalo milk and to study the effect of nisin-sensitive and -resistant E. faecalis on the innate immunity of rats. Methods and Results: Slanetz-Bartley agar plates containing nisin were used to isolate nisin-resistant E. faecalis. The virulence factors were ascertained using quantitative real-time polymerase chain reaction. Cell viability, phagocytosis, intracellular survival and enzyme assays were performed to investigate the interaction of E. faecalis with rat macrophages. Nisin-resistant E. faecalis was less prone to phagocytosis and survived longer inside the macrophages, due to reduced production of reactive oxygen species and nitric oxide. The viability and activation of macrophages was also reduced in the presence of resistant E. faecalis, as observed by enhanced lactate dehydrogenase production and reduced b-galactosidase. Conclusions: Nisin-resistant E. faecalis and its virulence factors were reported in raw buffalo milk. This study shows that nisin-resistant variants exhibited cross resistance to antibiotics and suppressed the innate immune responses of rats by directly affecting macrophage activity. Significance and Impact of the Study: This study elucidated the contamination of raw buffalo milk by nisin-resistant E. faecalis, which may pose food safety risk.Enterococcus faecalis is prevalent in human and animal faeces and is a major cause of contamination in dairy products (Giraffa et al. 1997). Enterococcus faecalis collected from the milk of healthy animals and humans has also been reported as a reservoir of virulence and antibiotic-resistant genes, which exhibit resistance to clinically used drugs such as tetracycline, quinolones, vancomycin, macrolides, streptogramins and glycopeptides (Jim enez et al. 2008;Klibi et al. 2015). There are complex relationships between multidrug-resistant and virulence genes in bacteria. Schaufler et al. (2016) reported that extended spectrum b-lactamase plasmids for resistance enhance virulence in the carrier strains by affecting gene expression. Enterococcus faecalis harbours many virulence factors including aggregation substances, as-I, as-II and asa-Journal of Applied Microbiology 127, 897--910

Enterococcus faecalis sustained infection induces macrophage pro‐resolution polarization

“…The mechanisms by which the bacteria survived in the phagosomes merit further study, as the surviving macrophage population had an elevated level of internal ROS (Figure 2b). The present findings agree with those of Kumar et al (2019) in terms of intracellular survival of nisin‐resistant E . faecalis within macrophages.…”

“…The present findings agree with those of Kumar et al (2019) in terms of intracellular survival of nisin-resistant E. faecalis within macrophages. However, in their study, diminished ROS activity was suggested as the mechanism of bacterial survival, whereas in the present study, the internal ROS activity was elevated in the macrophage after 48 h (Kumar et al, 2019).…”

“…The mechanisms by which the bacteria survived in the phagosomes merit further study, as the surviving macrophage population had an elevated level of internal ROS (Figure 2B). The present findings agree with those of Kumar et al (2019) in terms of intracellular survival of nisin-resistant E. faecalis within macrophages. However, in their study, diminished ROS activity was suggested as the mechanism of bacterial survival, whereas in the present study, the internal ROS activity was elevated in the macrophage after 48 h (Kumar et al, 2019).…”

Identification of HPr kinase/phosphorylase inhibitors: novel antimicrobials against resistant Enterococcus faecalis

“…Approximately, 80–90% of enterococcal infections are caused by Enterococcus faecalis , a commensal bacterium inhabiting the gastrointestinal tracts of humans [ 1 , 4 ]. E. faecalis has developed resistance to commonly used antibiotics such as vancomycin, aminoglycosides, daptomycin, tetracycline, linezolid, and quinolones [ 5 , 6 ]. In concert with antibiotic resistance, E. faecalis has also been reported to possess a reservoir of virulence genes and it can transfer these genes to other pathogenic bacteria [ 7 ].…”

“…This suggests that HPrK/P plays an important role in the fitness of antibiotic resistant E. faecalis . Therefore, the present study is aimed at identifying active-site targeted HPrK/P inhibitors against nisin-resistant E. faecalis that showed resistance to antibiotics [ 5 ]. Nisin is a class I bacteriocin that is used as a preservative for many food products.…”