Susceptibilities of Legionella spp. to Newer Antimicrobials In Vitro

Abstract

The in vitro activities of 13 antimicrobial agents against 30 strains of Legionella spp. were determined. Rifapentine, rifampin, and clarithromycin were the most potent agents (MICs at which 90% of isolates are inhibited [MIC 90 s], <0.008 g/ml). The ketolide HMR 3647 and the fluoroquinolones levofloxacin and BAY 12-8039 (MIC 90 s, 0.03 to 0.06 g/ml) were more active than erythromycin A or roxithromycin. The MIC 90 s of dalfopristin-quinupristin and linezolid were 0.5 and 8 g/ml, respectively. Based on class characteristics and in vitro activities, several of these agents may have potential roles in the treatment of Legionella infections.

Efficacy of Telithromycin in Community-Acquired Pneumonia Caused by Atypical and Intracellular Pathogens

“…To be effective, the antibacterial agent must be able to penetrate into phagocytic cells. Erythromycin is widely used to treat pneumonia caused by Legionella spp, but telithromycin has 4-fold greater activity in vitro than erythromycin against these organisms, 48 and both agents are equally effective in a guinea pig model of L. pneumophila pneumonia. 25 The efficacy of telithromycin in all 13 of the L. pneumophila infections identified in these studies is encouraging as Legionella spp are frequently associated with more severe CAP and a greater risk of mortality, especially among patients who are immunocompromised and those with bacteremia.…”

BTS Guidelines for the Management of Community Acquired Pneumonia in Adults

“…Patients admitted to hospital with CAP caused by Legionella species are more likely to have severe pneumonia179 [ Ia ], so the initial empirical antibiotic regimen should also capture this pathogen within its spectrum of activity 328. Efficacy data from prospective controlled clinical trials are not available.…”

“…CAP is likely to be included among their licensed indications. Many of these new agents are active against respiratory “atypical” pathogens and Legionella species 328. Their activity against S pneumoniae may also give them a more important role in the future should penicillin and erythromycin resistance continue to increase and be associated with demonstrable clinical failure.…”

Telithromycin in the treatment of pneumococcal community-acquired respiratory tract infections: a review

“…This agent has a spectrum of activity that specifically targets common bacterial respiratory pathogens (S. pneumoniae [including isolates resistant to erythromycin and/or penicillin], Streptococcus pyogenes, H. influenzae and M. catarrhalis, 16,17 and atypical/intracellular organisms 18,19 ). The efficacy and safety of telithromycin 800 mg once daily in patients with communityacquired RTIs have been studied in 16 Phase III clinical trials 20-35 , many of which compared the drug with one of a number of antibacterials regarded as representative of current standards of care.…”