Comparative Emergence of Resistance to Clofoctol, Erythromycin, and Amoxicillin against Community-Acquired Bacterial Respiratory Tract Pathogens in Italy

Due to increasing bacterial resistance and poor availability of new antibiotics, physicians need to use old, still active antibiotics more frequently. In this study, we focused on clo-foctol and aimed to verify the emergence of clofoctol resistance over time. Additionally, the ability of clofoctol to induce resistance under static and dynamic conditions was evaluated. The minimum inhibitory concentration (MIC) values measured in pathogens isolated from 1990 to 1995 were compared to those isolated from 2017 to 2018. The behaviour of clofoctol is similar to that of amoxicillin, while erythromycin shows a different behaviour with an increase in MIC. A rapid decline in CFUs with complete eradication at 96 and 120 h in the case of clofoctol and amoxicillin, respectively, was observed in a dynamic in vitro model of a pharmacokinetic simulation. Erythromycin provides a reduction in CFUs of approximately one order of magnitude for up to 72 h, and then re-growth is observed. The MIC trend was observed during 5 days of kinetic simulation. The clofoctol MICs remain almost stable up to 96 h, after which the colonies are no longer detectable. The MICs of amoxicillin show a 2-fold increase starting from 36 h; however, at 120 h the colonies are no longer detectable. The MICs of erythromycin show a progressive increase starting from 72 h and reaching 32-fold. Clofoctol maintains its activity towards the common pathogens of respiratory tract infections and, similarly to amoxicillin, does not induce resistance in a strain of Streptococcus pneumoniae, resulting in complete eradication, while erythromycin was able to select resistant mutants.