Irrigation is crucial in cleaning and disinfection of the root canal system, because endodontic instruments are unable to reach a large part of the root canal system (isthmuses, accessory canals, apical ramifications) and bacteria that can reside. Sodium hypochlorite (NaOCl) is currently used as irrigant in root canal therapies for its non-specific protheolytic and antimicrobial properties, but undesirable effects may be observed especially when used near the terminus of apical foramen. This study aims to evaluate antimicrobial properties of Thyme Essential Oil (TEO) used alone or in combination with NaOCl against different bacterial strains, especially Staphylococcus aureus and Streptococcus mutans. TEO non-cytotoxic concentration (9,28mg/mL) showed antimicrobial properties comparable to NaOCl after 1min of contact, both in presence of organic material (6% sheep blood). Moreover, the combination of TEO and NaOCl did not compromise their individual antimicrobial properties at the same time of contact. These data suggest that TEO could be used as antimicrobial irrigant in root canal therapies in association with NaOCl, to reduce concentration of NaOCl and its undesirable side effects. Due to the absence of cytotoxic effects at tested dilution, TEO could be safely used also near the terminus of apical foramen for its cytocompatibility.

Bacillus cereus is a gram-positive bacterium widespread in the environment, especially in soil and dust. It produces two types of toxins causing vomiting and diarrhea. Nowadays, food borne outbreaks due to Bacillus cereus group bacteria (especially Bacillus cereus sensu stricto) are increased, as reported by European Food Safety Authority, representing a very huge problem in agri-food chain. In this work, we analyzed 118 strains belonging to Bacillus cereus group, isolated from several food sources (fruit and vegetables, dairy products, bakery products) concerning their susceptibility to antibiotics currently most used to treat infections. Many strains showing an intermediate susceptibility to clindamycin, erythromycin, and tetracycline were detected, suggesting an evolving acquisition of resistance against these antibiotics. Moreover, one strain showed intermediate resistance to meropenem, another antibiotic currently used to treat infections caused by Bacillus cereus. Beside the antimicrobial characterization, all strains were studied comparing their antimicrobic phenotype with the presence/absence of antimicrobial genes in their genome. The analysis showed a not complete correlation between genes carried by the strains and their phenotype, demonstrating that the antibiotic resistance is due not only to genetic factors, but also to other factors such as the inappropriate use of antibiotics that can determine an acquired resistance for bacteria.