RPLP1 and legionellosis: Of note, 50% (6/12) of Lp1 strains demonstrating reduced susceptibility to doxycycline were found to be susceptible to all the other tested antibiotics, suggesting a cluster of L. pneumophila strains with specific resistance to an antibiotic representing a second-line therapeutic option for the treatment of mild severity LD in immunocompetent subjects, according to the Italian guidelines for the prevention and treatment of legionellosis [25].