BMS-284756 (T-3811ME) a new fluoroquinolone: in vitro activity against Legionella, efficacy in a guinea pig model of L. pneumophila pneumonia and pharmacokinetics in guinea pigs.

The activity of BMS-284756 was studied against extracellular Legionella spp. and intracellular Legionella pneumophila, and for the treatment of guinea pigs with L. pneumophila pneumonia. The BMS-284756 MIC(50) of 22 different Legionella spp. strains was 0.008 mg/L, compared with 0.016 and 0.125 mg/L for levofloxacin and azithromycin, respectively. BMS-284756 (1 mg/L) reduced the intracellular concentrations of two L. pneumophila strains grown in guinea pig alveolar macrophages by c. 1.5 log(10 )cfu/mL, and was more active than erythromycin, but less active than azithromycin or levofloxacin at the same drug concentrations. Efficacy studies of BMS-284756, levofloxacin and azithromycin were performed in guinea pigs with L. pneumophila pneumonia. In infected guinea pigs given BMS-284756 10 mg/kg ip, mean peak plasma levels were 1.8 mg/L at 0.5 h and 0.7 mg/L at 1 h post-dose. The elimination half-life in plasma was 0.5 h, and the AUC(0-24 )was 1.7 mg*h/L, about 2% of the AUC(0-24 )for a single 400 mg oral dose in man. Sixteen of 18 L. pneumophila-infected guinea pigs treated with BMS-284756 10 mg/kg ip once daily for 5 days survived for 7 days post-antimicrobial therapy, as did 11 of 12 guinea pigs treated with azithromycin 15 mg/kg ip once daily for 2 days. All 12 animals that were treated with levofloxacin 10 mg/kg ip once daily for 5 days survived. None of 12 control animals treated with saline survived. Animals treated with BMS-284756 had significantly higher residual lung counts of L. pneumophila at the end of therapy than did animals treated with levofloxacin or azithromycin, which may be attributable to the very low drug concentrations that were obtained. BMS-284756 was more active than erythromycin against L. pneumophila in infected macrophages, and effectively treated animals with experimental L. pneumophila pneumonia. These data support further studies of BMS-284756 for the treatment of Legionnaires' disease.

In vitro activity of ABT-773 against Legionella pneumophila, its pharmacokinetics in guinea pigs, and its use to treat guinea pigs with L. pneumophila pneumonia.

The activity of ABT-773 was studied against extracellular and intracellular Legionella pneumophila and for the treatment of guinea pigs with L. pneumophila pneumonia. The ABT-773 MIC at which 50% of isolates are inhibited (MIC(50)) for 20 different Legionella sp. strains was 0.016 microg/ml, whereas the MIC(50)s of clarithromycin and erythromycin were 0.032 and 0.125 microg/ml, respectively. ABT-773 (1 microg/ml) was bactericidal for two L. pneumophila strains grown in guinea pig alveolar macrophages. In contrast, erythromycin and clarithromycin had easily reversible static activity only. Therapy studies of ABT-773 and erythromycin were performed with guinea pigs with L. pneumophila pneumonia. When ABT-773 was given to infected guinea pigs by the intraperitoneal route (10 mg/kg of body weight), mean peak levels in plasma were 0.49 microg/ml at 0.5 h and 0.30 microg/ml at 1 h postinjection. The terminal half-life phase of elimination from plasma was 0.55 h, and the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) was 0.65 microg. h/ml. For the same drug dose, mean levels in the lung were 15.9 and 13.2 microg/g at 0.5 and 1 h, respectively, with a half-life of 0.68 h and an AUC(0-24) of 37.0 microg. h/ml. Ten of 15 L. pneumophila-infected guinea pigs treated with ABT-773 (15 mg/kg/dose given intraperitoneally once daily) for 5 days survived for 9 days post-antimicrobial therapy, as did 14 of 15 guinea pigs treated with erythromycin (30 mg/kg given intraperitoneally twice daily) for 5 days. All of the ABT-773-treated animals that died appeared to do so because of drug-induced peritonitis rather than overwhelming pneumonia. None of 12 animals treated with saline survived. ABT-773 is as effective as erythromycin against L. pneumophila in infected macrophages and in a guinea pig model of Legionnaires' disease. These data support studies of the clinical effectiveness of ABT-773 for the treatment of Legionnaires' disease.

In vitro activity of gemifloxacin (SB-265805, LB20304a) against Legionella pneumophila and its pharmacokinetics in guinea pigs with L. pneumophila pneumonia.

The activity of gemifloxacin against intracellular Legionella pneumophila and for the treatment of guinea pigs with L. pneumophila pneumonia was studied. Gemifloxacin, azithromycin, and levofloxacin (1 microg/ml) reduced bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 2 to 3 log(10) units. Gemifloxacin and levofloxacin had roughly equivalent intracellular activities. In contrast, erythromycin had static activity only. Therapy studies of gemifloxacin, azithromycin, and levofloxacin were performed in guinea pigs with L. pneumophila pneumonia. When gemifloxacin (10 mg/kg) was given by the intraperitoneal (i.p.) route to infected guinea pigs, mean peak levels in plasma were 1.3 microg/ml at 0.5 h and 1.2 microg/ml at 1 h postinjection. The terminal half-life phase of elimination from plasma was 1.3 h, and the area under the concentration-time curve from 0 to 24 h (AUC(0--24)) was 2.1 microg. h/ml. For the same drug dose, mean levels in lungs were 3.4 microg/g at both 0.5 and 1 h, with a half-life of 1.5 h and an AUC(0--24) of 6.0 microg. h/ml. All 15 L. pneumophila-infected guinea pigs treated with gemifloxacin (10 mg/kg/dose given i.p. once daily) for 2 days survived for 9 days after antimicrobial therapy, as did 13 of 14 guinea pigs treated with the same dose of gemifloxacin given for 5 days. All 12 azithromycin-treated animals (15 mg/kg/dose given i.p. once daily for 2 days) survived, as did 11 of 12 animals treated with levofloxacin (10 mg/kg/dose given i.p. once daily for 5 days). None of 12 animals treated with saline survived. Gemifloxacin is effective against L. pneumophila in infected macrophages and in a guinea pig model of Legionnaires' disease, even with an abbreviated course of therapy. These data support studies of the clinical effectiveness of gemifloxacin for the treatment of Legionnaires' disease.

In vitro activity of quinupristin/dalfopristin (Synercid, RP 59500) against Legionella spp.

The activities of quinupristin/dalfopristin (Synercid), erythromycin and azithromycin against 22 Legionella spp. isolates were measured by a microbroth dilution method. The MICs that inhibited 90% of strains tested were 0.5, 0.35, and 0.5 microg/mL for quinupristin/dalfopristin, erythromycin, and azithromycin, respectively. Quinupristin/dalfopristin was only partially active against intracellular L. pneumophila at high (2 microg/mL), but not low (1 microg/mL) concentration. Activity of the drug in a guinea pig model of Legionnaires' disease could not be accurately determined because of drug toxicity for the guinea pig, although there was evidence that the drug has in vivo activity.

Discovery of virulence genes of Legionella pneumophila by using signature tagged mutagenesis in a guinea pig pneumonia model.

Legionella pneumophila is the cause of Legionnaires' disease, which is a form of potentially fatal pneumonia. To identify genes required for virulence of the bacterium, a library of 1,386 L. pneumophila signature tagged transposon mutants was studied for guinea pig virulence. The mutants were screened in pools of 96 each in a guinea pig model of L. pneumophila pneumonia. Sixteen unique mutant clones were determined to have attenuated virulence after being screened twice in the animal model. All 16 mutants failed to multiply in both lungs and spleens. Four of the sixteen had no apparent defect for intracellular multiplication in macrophages. Partial DNA sequences of the interrupted genes adjacent to the transposon insertions showed that six of them had mutations in five known L. pneumophila virulence genes: dotB, dotF/icmG, dotO/icmB, icmX, and proA. Three of the sequenced clones contained mutations in genes without known homology to other published bacterial genes, and seven clones appeared to be homologous to five different known bacterial genes but are still being characterized. With this methodology, we demonstrate the existence of L. pneumophila genes responsible for non-macrophage-related virulence. The discovery of L. pneumophila virulence genes indicates the utility of the signature tagged mutagenesis technique for pulmonary pathogens.

In vitro activity of SCH 27899 (Ziracin) against Legionella species.

The activities of Sch 27899 (Ziracin), erythromycin, and ofloxacin against 102 Legionella spp. isolates were measured by a microbroth dilution method. The MICs that inhibited 90% of strains tested were 0.25, 0.5, and 0.06 microgram/mL for Sch 27899, erythromycin, and ofloxacin, respectively. The activity of Sch 27899 against intracellular Legionella pneumophila could not be determined because of complete inactivation of the drug by tissue culture medium components.

In vitro activity of the ketolide HMR 3647 (RU 6647) for Legionella spp., its pharmacokinetics in guinea pigs, and use of the drug to treat guinea pigs with Legionella pneumophila pneumonia.

The activities of HMR 3647, HMR 3004, erythromycin, clarithromycin, and levofloxacin for 97 Legionella spp. isolates were determined by microbroth dilution susceptibility testing. Growth inhibition of two Legionella pneumophila strains grown in guinea pig alveolar macrophages was also determined. The concentrations required to inhibit 50% of strains tested were 0.06, 0.02, 0.25, 0.03, and 0.02 microg/ml for HMR 3647, HMR 3004, erythromycin, clarithromycin, and levofloxacin, respectively. BYEalpha broth did not significantly inhibit the activities of the drugs tested, as judged by the susceptibility of the control Staphylococcus aureus strain; however, when Escherichia coli was used as the test strain, levofloxacin activity tested in BYEalpha broth was fourfold lower. HMR 3647, HMR 3004, erythromycin, and clarithromycin (0.25 and 1 microg/ml) reduced bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 0.5 to 1 log10, but regrowth occurred over a 2-day period. HMR 3647, erythromycin, and clarithromycin appeared to have equivalent intracellular activities which were solely static in nature. HMR 3004 was more active than all drugs tested except levofloxacin. In contrast, levofloxacin (1 microg/ml) was bactericidal against intracellular L. pneumophila and significantly more active than the other drugs tested. Therapy studies with HMR 3647 and erythromycin were performed in guinea pigs with L. pneumophila pneumonia. When HMR 3647 was given (10 mg/kg of body weight) by the intraperitoneal route to infected guinea pigs, mean peak plasma levels were 1.4 microg/ml at 0.5 h and 1.0 microg/ml at 1 h postinjection. The terminal half-life phase of elimination from plasma was 1.4 h. All 16 L. pneumophila-infected guinea pigs treated with HMR 3647 (10 mg/kg/dose given intraperitoneally once daily) for 5 days survived for 9 days after antimicrobial therapy, as did all 16 guinea pigs treated with the same dose of HMR 3647 given twice daily. Fourteen of 16 erythromycin-treated (30 mg/kg/dose given intraperitoneally twice daily) animals survived, whereas 0 of 12 animals treated with saline survived. HMR 3647 is effective against L. pneumophila in vitro, in infected macrophages, and in a guinea pig model of Legionnaires' disease. HMR 3647 given once daily should be evaluated as a treatment for Legionnaires' disease in humans.

Activity of trovafloxacin (CP-99,219) against Legionella isolates: in vitro activity, intracellular accumulation and killing in macrophages, and pharmacokinetics and treatment of guinea pigs with L. pneumophila pneumonia.

The activity of trovafloxacin against 22 clinical Legionella isolates was determined by broth microdilution susceptibility testing. The trovafloxacin concentration required to inhibit 90% of strains tested was < or = 0.004 micrograms/ml, in contrast to 0.032 micrograms/ml for ofloxacin. In guinea pig alveolar macrophages, trovafloxacin achieved intracellular levels up to 28-fold over the extracellular concentration, which was similar to the levels obtained with erythromycin. Trovafloxacin (0.25 micrograms/ml) reduced bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by > 2 log10 CFU/ml, without regrowth, under drug-free conditions over a 3-day period; trovafloxacin was significantly more active than ofloxacin or erythromycin (0.25 to 1 microgram/ml) in this assay. Single-dose (10 mg of prodrug CP-116,517-27 per kg of body weight given intraperitoneally [i.p.], equivalent to 7.5 mg of trovafloxacin per kg) pharmacokinetic studies performed in guinea pigs with L. pneumophila pneumonia revealed peak serum and lung trovafloxacin levels to be 3.8 micrograms/ml and 5.0 micrograms/g, respectively, at 0.5 h and 4.2 micrograms/ml and 2.9 micrograms/g, respectively, at 1 h. Administration of a lower prodrug dose (1.4 mg of trovafloxacin equivalent per kg i.p.) gave levels in lung and serum of 0.4 microgram/g and 0.4 microgram/ml, respectively, 1 h after drug administration. The terminal half-lives of elimination from serum and lung were 0.8 and 1.1 h, respectively. All 15 infected guinea pigs treated for 5 days with CP-116,517-27 once daily (10 mg/kg/day i.p., equivalent to 7.5 mg of trovafloxacin per kg/day) survived for 10 days after antimicrobial therapy, as did all 15 guinea pigs treated with ofloxacin once daily (10 mg/kg/day i.p.) for 5 days. None of 13 animals treated with saline survived. In a second experiment with animals, trovafloxacin (1.4 mg/kg/day i.p. for 5 days) protected all 16 guinea pigs from death, whereas all 15 animals treated with saline died. Trovafloxacin is an effective antimicrobial agent against Legionella in vitro and in vivo, with the ability to concentrate in macrophages and kill intracellular organisms.

Natamycin as a selective antifungal agent in media for growth of Legionella spp.

The growth of 18 different Legionella sp. strains and 76 different yeast isolates was tested on buffered charcoal yeast extract medium supplemented with alpha-ketoglutarate (BCYE alpha medium) and with natamycin, an antifungal agent. Bacterial growth was no different on BCYE alpha medium made with or without natamycin, whereas complete inhibition of yeasts occurred in BCYE alpha medium containing 200 to 500 micrograms of natamycin per ml. Selective BCYE alpha media made with natamycin rather than anisomycin had no (formulation with vancomycin, polymyxin B, and agar) or little (formulation with cefamandole, polymyxin B, and agar) inhibitory effect on the growth of 14 different Legionella sp. bacteria. Natamycin is an inexpensive alternative to anisomycin in the formulation of selective BCYE alpha media.

In-vitro activity of levofloxacin against clinical isolates of Legionella spp, its pharmacokinetics in guinea pigs, and use in experimental Legionella pneumophila pneumonia.

The activities of levofloxacin and ofloxacin against 22 clinical legionella isolates was determined by microbroth dilution susceptibility testing. Growth inhibition of two Legionella pneumophila strains grown in guinea pig alveolar macrophages by levofloxacin, ofloxacin, or erythromycin was also determined. The drug concentrations required to inhibit 90% of strains tested was 0.032 mg/L for levofloxacin or ofloxacin, and was 0.016 mg/L for ciprofloxacin. BYE alpha broth significantly inhibited the activities of all three drugs tested, as judged by the susceptibility of control Escherichia coli strains. Levofloxacin (0.25 mg/L) reduced bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 1 log10, but regrowth occurred over a 3 day period; levofloxacin (1 mg/L) reduced bacterial counts by 2-3 log10 cfu/mL. Levofloxacin was significantly more active than erythromycin, and as active as ofloxacin or ciprofloxacin in this assay. Pharmacokinetic and therapy studies of levofloxacin and ofloxacin were performed in guinea pigs with L. pneumophila pneumonia. For the pharmacokinetic study, levofloxacin was given (10 mg/kg) by the intraperitoneal route to infected guinea pigs; mean peak plasma and lung concentrations were 3.4 mg/L and 1.4 micrograms/g, respectively, at 0.5 h and 2.6 mg/L and 0.6 micrograms/g at 1 h. The terminal half-life phase of elimination from plasma and lung was c. 1 h. All 15 infected guinea pigs treated with levofloxacin (10 mg/kg/day given ip once daily) for 5 days survived for 9 days after antimicrobial therapy, as did all 14 guinea pigs treated with the same dose of ofloxacin. None of 13 animals treated with saline survived. Levofloxacin is effective against L. pneumophila in vitro and in a guinea pig model of legionnaire's disease. Levofloxacin should be evaluated as a treatment of human legionnaires' disease.

In vitro extracellular and intracellular activities of clavulanic acid and those of piperacillin and ceftriaxone alone and in combination with tazobactam against clinical isolates of Legionella species.

The activities of ceftriaxone, piperacillin, tazobactam, clavulanic acid, and combinations of ceftriaxone or piperacillin with tazobactam against 22 clinical Legionella isolates were measured by broth microdilution and macrodilution methods and in macrophages. The broth microdilution MICs that inhibited 90% of strains tested were 2 and 1 microgram/ml for ceftriaxone and tazobactam, respectively. Broth macrodilution MICs were 8 and 1 microgram/ml, respectively, for the two Legionella pneumophila strains tested with piperacillin and were 0.25 and 0.5 microgram/ml, respectively, for clavulanate. No significant intracellular anti-L. pneumophila activity was observed for ceftriaxone (32 micrograms/ml), piperacillin (32 micrograms/ml), tazobactam alone (16 micrograms/ml), clavulanate alone (2 micrograms/ml), or tazobactam in combination with ceftriaxone (ceftriaxone/tazobactam at 32/4 and 16/16 micrograms/ml) or piperacillin (32/4 micrograms/ml). Erythromycin (1 microgram/ml) was active against intracellular L. pneumophila in the same macrophage model of infection. It is very unlikely that tazobactam or clavulanate, alone or in combination with beta-lactam antimicrobial agents, will be effective for the treatment of Legionnaires' disease in humans.

Azithromycin pharmacokinetics and intracellular concentrations in Legionella pneumophila-infected and uninfected guinea pigs and their alveolar macrophages.

Azithromycin pharmacokinetics in Legionella pneumophila-infected and uninfected guinea pigs were assessed by measuring the drug concentration in whole lungs or the drug content in bronchoalveolar lavage (BAL) fluid in separate experiments. Azithromycin concentrations were measured by using a bioassay. The mean azithromycin content in the BAL fluid of infected guinea pigs was higher than that in controls at 10 h (0.87 versus 0.39 microgram; P = 0.05), 24 h (1.10 versus 0.37 microgram; P = 0.003), and 48 h (1.21 versus 0.28 microgram; P = 0.05) after a single intraperitoneal injection of drug (15 mg/kg). The mean peak lung azithromycin concentration was higher in control animals than in infected animals (15.8 versus 13.4 micrograms/ml). The mean lung azithromycin concentration in infected animals was significantly higher than that in controls 48 h after dosing (12.7 versus 10.4 micrograms/g; P = 0.04). There were no significant differences between infected and uninfected animals in serum azithromycin levels. Complementary experiments assessed intracellular/extracellular concentration ratios of azithromycin and erythromycin in L. pneumophila-infected and control guinea pig alveolar macrophages. Azithromycin was highly concentrated in alveolar macrophages, and the intracellular/extracellular concentration ratios for infected cells were significantly higher (P < 0.0001) than those observed in controls after 4 h (127 versus 119), 24 h (481 versus 361), and 48 h (582 versus 520) of incubation. Erythromycin was also preferentially concentrated in infected cells (P < 0.0001). AZ intracellular concentrations were at least fivefold higher than those measured for erythromycin, and this differential increased with incubation time. Thus, azithromycin recovery from BAL fluid, and from guinea pig lungs at the 48-h time point, was higher in the presence of experimental Legionnaires' disease. This likely results from recruitment of phagocytes, including macrophages, that have an enhanced capacity to highly concentrate the drug.

Intracellular growth of Legionella pneumophila serogroup 1 monoclonal antibody type 2 positive and negative bacteria.

Epidemiological evidence suggests that monoclonal antibody type 2 positive (MAB 2+) Legionella pneumophila serogroup 1 (LP1) more often causes disease than do MAB 2- isolates, and there is evidence that MAB 2- LP1 grow less well in cells than do MAB 2+ bacteria. We tested the intracellular growth rates of ten randomly selected MAB 2- LP1 isolates, by using guinea-pig alveolar macrophages, and human monocyte-derived macrophages. Save a low virulence control, all ten MAB 2- isolates grew as well in cells as a virulent MAB 2+ isolate. Heterogeneity of MAB 2- LP1 growth in cells exists, making poor intracellular growth an unlikely explanation for why MAB 2+ LP1 appear to cause disease more often.

Comparison of three buffers used in the formulation of buffered charcoal yeast extract medium.

Growth of Legionella spp. on buffered charcoal yeast extract medium supplemented with alpha-ketoglutarate and formulated with 3-(n-morpholino)propanesulfonic acid (MOPS), 3-(n-morpholino)-2-hydroxypropanesulfonic acid (MOPSO), or n-(2-acetamido)-2-aminoethanesulfonic acid (ACES) buffer was similar. With three exceptions, growth was no different in buffered yeast extract broth supplemented with alpha-ketoglutarate and formulated with MOPS or ACES buffer.

In vitro activity of RP 74501-RP 74502, a novel streptogramin antimicrobial mixture, against clinical isolates of Legionella species.

Agar and broth microdilution MICs of RP 74501-RP 74502, a mixture of streptogramin antimicrobial agents that inhibited 90% of 22 Legionella strains tested, were 0.64 and 0.08 microgram/ml, respectively; respective erythromycin values were 1.0 and 0.12 microgram/ml. RP 74501-RP 74502 at 1 microgram/ml was more active than the same erythromycin concentration in a macrophage system for both L. pneumophila strains studied but at a lower concentration (0.25 microgram/ml) was much less active than erythromycin.

In vitro activities of fleroxacin against clinical isolates of Legionella spp., its pharmacokinetics in guinea pigs, and use to treat guinea pigs with L. pneumophila pneumonia.

The activities of fleroxacin against 22 clinical Legionella isolates were determined by agar and broth microdilution susceptibility testing. The fleroxacin MIC required to inhibit 90% of strains tested on buffered charcoal yeast extract agar medium supplemented with 0.1% alpha-ketoglutarate was 0.64 micrograms/ml and was 0.04 microgram/ml when testing was done with buffered yeast extract broth supplemented with 0.1% alpha-ketoglutarate. Fleroxacin (0.25 microgram/ml) reduced the bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 1 log10 CFU/ml, but regrowth occurred over a 3-day period; fleroxacin was significantly more active than erythromycin in this assay. Single-dose (10 mg/kg of body weight given intraperitoneally) pharmacokinetic studies performed in guinea pigs with L. pneumophila pneumonia revealed peak levels in plasma and lungs to be 3.3 micrograms/ml and 3.5 micrograms/g, respectively, at 0.5 h and 0.8 microgram/ml and 0.8 microgram/g, respectively, at 1 h. The half-life of the terminal phase of elimination from plasma and lung was approximately 2 h. All 17 infected guinea pigs treated with fleroxacin (10 mg/kg/day) for 2 days survived for 14 days post-antimicrobial therapy, as did all 16 guinea pigs treated with the same dose of fleroxacin for 5 days. Only 1 of 16 animals treated with saline survived. The animals treated with fleroxacin for 2 days lost more weight and had higher temperatures than those treated with the antibiotic for 5 days. Fleroxacin is effective against L. pneumophila in vitro and in a guinea pig model of Legionnaires' disease. Fleroxacin should be evaluated as a treatment for human Legionnaires' disease.

In vitro activity of Ro 23-9424 against clinical isolates of Legionella species.

Agar and broth microdilution MICs of Ro 23-9424 that inhibited 90% of 22 Legionella clinical isolates tested were 0.64 and 0.08 micrograms/ml, respectively; respective erythromycin values were 1.0 and 0.12 micrograms/ml. Ro 23-9424 (1 microgram/ml) was slightly more active than the same erythromycin concentration in a macrophage system, for both Legionella pneumophila strains studied.

Comparison of different agars used in the formulation of buffered charcoal yeast extract medium.

The effect of agar type used for buffered charcoal yeast extract medium supplemented with 0.1% alpha-ketoglutarate was tested based on the growth and size of Legionella pneumophila. Oxoid Agar no. 1, Difco Bacto and Bitek agars, and BBL Granulated, Grade A, and Select agars were tested. For colony size the agars were ranked in the following order: Oxoid agar no. 1 much greater than Bacto greater than Bitek approximately Granulated approximately Grade A greater than Select. Colony yield per plate was similar for all agars except for Grade A, which gave significantly fewer colonies after 3 days, but not 4 days, of incubation. Agar type significantly influences L. pneumophila growth on buffered charcoal yeast extract medium supplemented with 0.1% alpha-ketoglutarate.

In vitro activity of azithromycin against clinical isolates of Legionella species.

The activities of azithromycin, erythromycin, and ciprofloxacin against 21 Legionella isolates were measured by an agar dilution method and in macrophages. The MICs for 90% of strains tested were 2.0, 1.0, and 0.5 micrograms/ml for azithromycin, erythromycin, and ciprofloxacin, respectively. Azithromycin and ciprofloxacin were both bactericidal in the macrophage system, but erythromycin was bacteriostatic.