In vitro activity of lomefloxacin (NY-198 or SC 47111), ciprofloxacin, and erythromycin against 100 clinical Legionella strains

Abstract

Agar dilution minimum inhibitory concentrations (MICs) of lomefloxacin (LO), ciprofloxacin (CI), and erythromycin (ER) were determined for 100 clinical isolates of Legionella using buffered charcoal yeast extract medium supplemented with alpha-ketoglutarate (BCYEa). The Legionella strains tested included 84 L. pneumophila, 2 L. micdadei, 6 L. dumoffii, 4 L. longbeachae, and one each of L. bozemanii, L. hackeliae, L. wadsworthii, and L. maceachernii. Geometric mean MICs μg/ml were 0.56 for LO, 0.50 for CI, and 0.25 for ER. Ninety percent MICs were 1.0 for LO and CI, and 0.5 for ER. All Legionella strains except one (L. hackeliae) were inhibited by 1.0 μg/ml of LO or CI; this strain had an Er MIC of 1.0 μg/ml and was inhibited by 2.0 μg/ml of LO or CI. Control strains of Eschershia coli and Staphylococcus aureus were also tested on both BCYEa and Mueller-Hinton agar (MHA) to determine BCYEa-mediated inhibition of the antimicrobials. All three antimicrobials were inactivated in varying degrees by BCYEa. BCYEa:MHA MICs of the S. aureus control strain were 4:1 for LO and ER, and >4:1 for CI. BCYEa: MHA MICs of the E. coli control strain were 4:1 for LO and CI, and unmeasurable for ER. Both LO and CI have good in vitro activity against legionella, probably greater than that measured in this study because of antimicrobial inactivation by BCYEa. Since LO is concentrated by phagocytic cells, like ER and CI, it is likely that it will be effective in the treatment of Legionnaires' disease.