The cationic peptide enterocin CRL35 is a promising alternative to clinical antibiotics against clinical enterococci

MASÍAS, EMILSE; CORDOBA, JOSEFINA; ARAOZ, EMILSE; FARIZANO, JUAN V.; SAAVEDRA, LUCILA; MINAHK, CARLOS

Salta

Congreso; LV ANNUAL SAIB meeting and XIV PABMB congress; 2019

SAIB and PABMB

Among the opportunistic pathogens that are isolated from nosocomial infections, Enterococcus faecalis and E. faecium are particularly tricky because they are often difficult to treat due to their intrinsic and acquired resistance to a number of conventional antibiotics. As a matter of fact, the emergence and unstopable spreading of antibiotic resistance not only in enterococci but in many other bacteria species is one of the most urgent concerns of the health systems worldwide. That is why new treatment options that allow to fight against these multidrug-resistant microorganisms are critically needed. In these regard, the antimicrobial peptides surge as promising novel antibiotics that might help to control resistant isolates. Even though there are a myriad of cationic peptide displaying antibacterial activity, the bacteriocins from lactic acid bacteria constitute interesting candidates because the specificity and the particularly high specific activity. Among them, enterocin CRL35 has been studied in our group since a long time ago, and many features of this peptide have been characterized. This a pediocin-like bacteriocin produced by Enterococcus mundtii CRL35 that had been almost exclusively considered for the control of the foodborne pathogen Listeria monocytogenes so far. However, since bacteriocins are tipically active against phylogenetically related bacteria, we hypothetized that enterocin CRL35 should be active against clinical isolates of E. faecium and E. faecalis. We focused on the strains isolated from patients with invasive infections in the Angel C. Padilla Hospital from San Miguel de Tucumán city (Tucumán, Argentina). Thirty-four strains were isolated and characterized. The resistance pattern of each isolate was determinated using qualitative (agar diffusion) and quantitative (minimum inhibitory concentration) techniques according to the Clinical and Laboratory Standards Institute recommendations. VITEK 2® Compact automated system was used as a second approach to confirm the previous characterization. Antimicrobial activity of enterocin CRL35 was initially evaluated by the cross streak method. Subsequently, the MIC was determined with the agar diffusion method and then with serial dilutions in liquid medium. The results showed that 90% of all strains under study were sensitive to the cationic peptide. Most importantly, those isolates that were labeled as resistant to ampicillin, gentamicin and even vancomycin turned out to be sensitive to enterocin CRL35. The sensitivity was also checked by kill curve assays. We observed a rapid lose of viability of all the enterococci tested. Moreover, some bacteria proved to be hypersensitive to the peptide, undergoing even cell lysis with the highest concentrations tested. Overall, we can conclude that enterocin CRL35 represents a good candidate for the treatment of enterococcal infections.