Intracellular multiplication of Legionnaires' disease bacteria (Legionella pneumophila) in human monocytes is reversibly inhibited by erythromycin and rifampin.

Abstract

A B S T R A C T We have previously reported that virulent egg yolk-grown Legionella pneumophila, Philadelphia 1 strain, multiplies intracellularly in human blood monocytes and only intracellularly under tissue culture conditions. In this paper, we have investigated the effect of erythromycin and rifampin on L. pneumophila-monocyte interaction in vitro; erythromycin and rifampin are currently the drugs of choice for the treatment of Legionnaires' disease.The intracellular multiplication of L. pneumophila is inhibited by erythromycin and rifampin, as measured by colony-forming units, whether the antibiotics are added just before or just after infection of monocytes with L. pneumophila, or 2 d after infection when L. pneumophila is in the logarithmic phase of growth in monocytes. Intracellular multiplication of L. pneumophila is inhibited by 1.25 ,tg/ml but not <0.125 ,ig/ml erythromycin and 0.01 ,ug/ml but not <0.001 ,tg/ml rifampin. These concentrations of antibiotics are comparable to those that inhibit extracellular multiplication of L. pneumophila under cell-free conditions in artificial medium; the minimal inhibitory concentration is 0.37 Ag/ml for erythromycin and 0.002 ,gg/ml for rifampin. Multiplication of L. pneumophila in the logarithmic phase of growth in monocytes is inhibited within 1 h of the addition of antibiotics. Intracellular bacteria inhibited from multiplying by antibiotics are not killed. By electron microscopy, the bacteria appear intact within membrane-bound vacuoles, studded with ribosomelike structures.L. pneumophila multiplying extracellularly on artificial medium is killed readily by relatively low con- centrations of erythromycin and rifampin; the minimal bactericidal concentration is 1 ,tg/ml for erythromycin and 0.009 ,ug/ml for rifampin. In contrast, L. pneumophila multiplying intracellularly is resistant to killing by these concentrations of erythromycin and rifampin or by concentrations equal to or greater than peak serum levels in humans. Extracellular L. pneumophila in stationary phase is also resistant to killing by erythromycin and rifampin. These findings, taken together with our previous work, indicate that, in vivo, L. pneumophila is resistant to killing by erythromycin and rifampin.

The amoebae plate test implicates a paralogue of lpxB in the interaction of Legionella pneumophila with Acanthamoeba castellanii

“…Escherichia coli was cultured on LB agar plates or in LB broth, supplemented with chloramphenicol (Cm, 30 mg ml 21 ), sodium ampicillin (Ap, 100 mg ml 21 ) or kanamycin sulfate (Km, 50 mg ml 21 ) if required. Legionella pneumophila was grown on charcoalyeast extract (CYE) agar plates (Feeley et al, 1979) or in ACESbuffered-yeast extract broth (AYE) containing 0?5 % bovine serum albumin (BSA) (Horwitz & Silverstein, 1983). Supplements for L. pneumophila were used at the following concentrations: Cm, 5 mg ml 21 ; Km, 50 mg ml 21 ; IPTG, 0?5 mM.…”

Intracellular pharmacodynamics of antibiotics

“…Unfortunately, much less can be said about the other antibiotics, with the exception of oritavancin, which has been recently studied but for which more experience is needed. No or very little true pharmacodynamic data are available for ansamycins (including rifampin) or tetracyclines, even though these antibiotics were among the first to be claimed to be active in a variety of intracellular infections [94][95][96][97][98].…”

Pathogen effector protein screening in yeast identifies Legionella factors that interfere with membrane trafficking

“…L. pneumophila alters host cell trafficking pathways in both types of host cells. The bacteria reside in a vacuole that does not fuse with lysosomes or acidify but recruits endoplasmic reticulum (ER)-derived vesicles (1)(2)(3)(4). These properties require a type IVB secretion system (TFBSS) known as the Icm͞Dot system (5,6).…”