Comparative activity of quinolones, macrolides and ketolides against Legionella species using in vitro broth dilution and intracellular susceptibility testing

Isolation and identification of Legionella spp. from hot spring water in Algeria by culture and molecular methods

AIMS

Due to infectious risk associated with the presence of Legionella in warm water, we determined the prevalence of living Legionella spp. in hot spring water in Algeria.

METHODS AND RESULTS

Detection of Legionella by culture was done by using two methods, direct culture on agar plates and co-culture with amoeba. Fifty samples were taken from different hot springs in northern Algeria, including swimming pools, showers and thermal sources. Legionella pneumophila serotypes were predominant, accounting for 60% of positive samples. Direct method allowed the isolation of 13 L. pneumophila only of 50 samples (26%), whereas co-culture using a panel of three free living amoeba allowed the isolation of 119 Legionella species from the same samples (80%) CONCLUSIONS: Amoeba co-culture allowed the isolation of several Legionella sp., while direct culture allowed the isolation of L. pneumophila only. Remarkably, Legionella longbeachae, usually isolated from soil and compost, was isolated for the first time in thermal water in three samples using Vermamoeba vermiformis co-culture.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of Legionella in the water of hot springs in Algeria, which are mainly frequented by individuals at risk of Legionellosis, requires urgent control measures.

Antibiotic Resistance of Legionella pneumophila in Clinical and Water Isolates-A Systematic Review

The current systematic review investigates the antibiotic susceptibility pattern of Legionella pneumophila isolates from the 1980s to the present day, deriving data from clinical and/or water samples from studies carried out all over the world. Eighty-nine papers meeting the inclusion criteria, i.e., “Legionella pneumophila” and “resistance to antibiotics”, were evaluated according to pre-defined validity criteria. Sixty articles referred to clinical isolates, and 18 articles reported water-related L. pneumophila isolates, while 11 articles included both clinical and water isolates. Several methods have been proposed as suitable for the determination of MICs, such as the E-test, broth and agar dilution, and disk diffusion methods, in vivo and in vitro, using various media. The E-test method proposed by the European Society of Clinical Microbiology and Infectious Diseases (EUCAST) seems to be the second most frequently used method overall, but it is the preferred method in the most recent publications (2000–2019) for the interpretation criteria. Erythromycin has been proved to be the preference for resistance testing over the years. However, in the last 19 years, the antibiotics ciprofloxacin (CIP), erythromycin (ERM), levofloxacin (LEV) and azithromycin (AZM) were the ones that saw an increase in their use. A decrease in the sensitivity to antibiotics was identified in approximately half of the reviewed articles.

Antimicrobial Susceptibility Patterns of Legionella spp. Strains Isolated from Water Systems in Morocco

Objective: Legionella is a waterborne pathogen that causes a severe form of pneumonia called Legionnaires' diseases, which is normally acquired by inhalation of aerosols containing Legionella originating from natural and man-made water systems. The aim of this study was to describe the level of antimicrobial susceptibility of environmental Legionella spp. strains to preferred and recommended therapeutic agents to treat Legionella disease. Methods: The minimum inhibitory concentrations (MICs) of 60 environmental Legionella spp. strains were tested using the broth dilution method. Susceptibility testing was performed for 12 antimicrobial agents: macrolides (erythromycin, azithromycin [AZI], and clarithromycin [CLA]), fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin, and gemifloxacin), a ketolide (telithromycin), cefotaxime (CEF), tigecycline (TIG), doxycycline (DOX), and rifampicin (RIF). Results: All tested strains of Legionella spp. were inhibited by low concentrations of fluoroquinolones and macrolides. Regarding the macrolides, CLA was the most active antibiotic, and AZI was the least active. RIF was the most effective antibiotic against the isolates in vitro. All isolates were inhibited by the following antibiotics (in decreasing order of their MICs): DOX>CEF>TIG. Conclusions: No resistance against these drugs was detected, and all isolates were inhibited by low concentrations of the tested antibiotics. Susceptibility testing of environmental Legionella spp. isolates must be monitored often to detect and evaluate the possible development of antibiotic resistance.

In vitro activity of the ketolide cethromycin in multidrug-resistant clinical Neisseria gonorrhoeae isolates and international reference strains

Antimicrobial resistance in Neisseria gonorrhoeae is a major public health problem, which compromises the treatment of gonorrhoea globally. We evaluated the in vitro activity of the ketolide cethromycin against a large panel of clinical gonococcal isolates and international reference strains (n = 254), including numerous multidrug-resistant and extensively drug-resistant isolates. Cethromycin showed potent in vitro activity against most of the gonococcal isolates with the following modal MIC, MIC₅₀ and MIC₉₀: 0.064 mg/L, 0.125 mg/L and 0.5 mg/L, respectively. However, cross-resistance between azithromycin and cethromycin was identified (Spearman's rank correlation coefficient 0.917) and isolates displaying high-level resistance to azithromycin (MIC >256 mg/L; n = 9) also showed high MICs of cethromycin (32-256 mg/L). In conclusion, the cross-resistance with azithromycin indicates that cethromycin may not be considered for empirical first-line monotherapy of gonorrhoea. However, cethromycin might be valuable in combination antimicrobial therapy and for second-line therapy e.g. for cases with ceftriaxone resistance or allergy.

Environmental surveillance and in vitro activity of antimicrobial agents against Legionella pneumophila isolated from hospital water systems in Campania, South Italy: a 5-year study

BACKGROUND

Legionellosis' treatment failures have been recently reported showing the possibility of resistance development to traditional therapy, especially in healthcare related disease cases. Environmental impact of antibiotic residues, especially in hospital waters, may act on the resistome of Legionella resulting in developing resistance mechanisms.

OBJECTIVES

In this study we investigate the antibiotic susceptibility of environmental Legionella pneumophila (Lpn) strains isolated from hospital water systems in Campania, a region located in Southwest Italy.

METHODS

5321 hospital water samples were investigated for the presence of Lpn. Among positive samples, antibiotic susceptibility was tested for a random subset of 125 Lpn strains (25 Lpn isolates from each of the following serogroups: 1, 3, 5, 6, 8). Susceptibility testing was performed, using the E-test on buffered charcoal yeast extract agar supplemented with α-ketoglutarate, for 10 antimicrobial drugs: azithromycin, cefotaxime, clarithromycin, doxycycline, erythromycin, rifampicin, tigecycline, ciprofloxacin, levofloxacin and moxifloxacin. Non parametric tests were used to determine and assess the significant differences in susceptibility to the different antimicrobics between the serogroups.

RESULTS

Among the isolated strains, none showed resistance to the antibiotics tested. Rifampicin was the most active antibiotic against overall Legionella strains, followed by levofloxacin. Between the macrolides the clarithromycin was overall the most active drug, instead the azithromycin was the less active. Analyzing the different serogroups a significant difference was found between serogroup 1 and non-1 serogroup isolates for doxycycline and tigecycline.

CONCLUSIONS

Antibiotic susceptibility of environmental isolates of Legionella spp. might be useful for the early detection of resistance to antibiotics that directly impacts on mortality and length of hospital stay.

Cethromycin: A New Ketolide Antibiotic

OBJECTIVE

To review the pharmacology, chemistry, microbiology, in vitro susceptibility, mechanism of resistance, pharmacokinetics, pharmacodynamics, clinical efficacy, safety, drug interactions, dosage, and administration of cethromycin, a new ketolide antibiotic.

DATA SOURCES

Literature was obtained through searching PubMed (1950-October 2012), International Pharmaceutical Abstracts (1970-October 2012), and a bibliographic review of published articles. Search terms included cethromycin, ABT-773, ketolide antibiotic, and community-acquired pneumonia.

STUDY SELECTION AND DATA EXTRACTION

All available in vitro and preclinical studies, as well as Phase 1, 2, and 3 clinical studies published in English were evaluated to summarize the pharmacology, chemistry, microbiology, efficacy, and safety of cethromycin in the treatment of respiratory tract infections.

DATA SYNTHESIS

Cethromycin, a new ketolide, has a similar mechanism of action to telithromycin with an apparently better safety profile. Cethromycin displays in vitro activity against selected gram-positive, gram-negative, and atypical bacteria. The proposed indication of cethromycin is treatment of mild to moderate community-acquired bacterial pneumonia in patients aged 18 years or older. Based on clinical studies, the recommended dose is 300 mg orally once a day without regard to meals. Cethromycin has an orphan drug designation for tularemia, plague, and anthrax prophylaxis. The Food and Drug Administration denied approval for the treatment of community-acquired pneumonia in 2009; a recent noninferiority trial showed comparable efficacy between cethromycin and clarithromycin. Preliminary data on adverse effects suggest that cethromycin is safe and gastrointestinal adverse effects appear to be dose-related.

CONCLUSIONS

Cethromycin appears to be a promising ketolide for the treatment of mild to moderate community-acquired pneumonia. It was denied approval by the FDA in 2009 pending more evidence to show its efficacy, with more recent studies showing its noninferiority to antibiotics for the same indication.

Legionellosis in Transplantation

Legionella species are emerging opportunistic pathogens in hematopoietic stem cell and solid organ transplant recipients, associated with significant morbidity and mortality. The clinical and radiological features of Legionella infections can mimic other opportunistic pathogens in these profoundly immunocompromised patients. Diagnosis in transplant patients is challenging as non-pneumophila Legionella infections, for which these patients are at risk, cannot be identified using the urinary antigen test. Changes in management of transplant recipients and changes in Legionella epidemiology suggest that the number of transplant patients potentially exposed to Legionella spp. may be on the rise. Yet, evidence-based, transplant-specific guidelines for managing and preventing Legionella infections are not currently available. In this article, we review the epidemiology, clinical features, diagnostic challenges, treatment options, and preventive strategies of Legionella infections in these high-risk patient populations.

Antibiotic susceptibility of Legionella pneumophila strains isolated from hospital water systems in Southern Italy

OBJECTIVES

The purpose of this study was to describe the susceptibility of environmental strains of Legionella spp. to 10 antimicrobials commonly used for legionellosis therapy. A study of environmental strains could be useful to timely predict the onset of antibiotic resistance in the environment before it is evidenced in clinical specimens.

METHODS

The minimum inhibitory concentrations (MICs) of 100 environmental Legionella pneumophila (Lpn) strains belonging to serogroups (sgs) 1, 6, 8, and 10 were tested using the E-test methodology on buffered charcoal yeast extract agar supplemented with α-ketoglutarate. The most frequent sgs were selected from those obtained during microbiological surveillance conducted in 2014 in a hospital in Southern Italy. The MICs were read after 2 days of incubation at 35 °C in a humidified atmosphere without CO2.

RESULTS

All isolates were inhibited by low concentrations of fluoroquinolones and macrolides. Rifampicin was the most active drug against the isolates in vitro. All Lpn isolates were inhibited by the following drugs (in decreasing order of their MICs): doxycycline>tigecycline>cefotaxime. The MICs of azithromycin, ciprofloxacin, levofloxacin, moxifloxacin, and tigecycline were significantly lower for Lpn non-sg 1 than Lpn sg 1 isolates.

CONCLUSIONS

Susceptibility testing of Legionella strains to appropriate antibiotics should be performed often to evaluate the possible emergence of resistance, to improve the outcomes of patients, and to reduce the direct costs associated with hospitalization.

High-Throughput Intracellular Antimicrobial Susceptibility Testing of Legionella pneumophila

Legionella pneumophila is a Gram-negative opportunistic human pathogen that causes a severe pneumonia known as Legionnaires' disease. Notably, in the human host, the organism is believed to replicate solely within an intracellular compartment, predominantly within pulmonary macrophages. Consequently, successful therapy is predicated on antimicrobials penetrating into this intracellular growth niche. However, standard antimicrobial susceptibility testing methods test solely for extracellular growth inhibition. Here, we make use of a high-throughput assay to characterize intracellular growth inhibition activity of known antimicrobials. For select antimicrobials, high-resolution dose-response analysis was then performed to characterize and compare activity levels in both macrophage infection and axenic growth assays. Results support the superiority of several classes of nonpolar antimicrobials in abrogating intracellular growth. Importantly, our assay results show excellent correlations with prior clinical observations of antimicrobial efficacy. Furthermore, we also show the applicability of high-throughput automation to two- and three-dimensional synergy testing. High-resolution isocontour isobolograms provide in vitro support for specific combination antimicrobial therapy. Taken together, findings suggest that high-throughput screening technology may be successfully applied to identify and characterize antimicrobials that target bacterial pathogens that make use of an intracellular growth niche.

Legionella: a Fascinating Bacterium Uncovered in the Twentieth Century

In July 1976, the American Legion held a conference at the Bellevue Stratford Hotel in Philadelphia, PA, to celebrate the nation's bicentennial. This convention resulted in transmission of a gram-negative bacterium to over 200 attendees, who developed a respiratory illness; 34 deaths were attributed to the infections. An investigation of the illness revealed a bacterium that had not been documented before. The disease became known as Legionnaires' disease, and the etiological agent was subsequently named Legionella pneumophila. This is the story of Legionella, with special emphasis on its ecological niche, the diagnosis of human infection, and its isolation from the environment. There are only a handful of diseases that debuted in the 20th or 21st century. They include Legionnaires' disease (the subject of this review), Lyme disease, AIDS, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and West Nile virus.

Description and validation of a spectrum score method to measure antimicrobial de-escalation in healthcare associated pneumonia from electronic medical records data

BACKGROUND

Comparison of antimicrobial de-escalation rates between healthcare settings is problematic. To objectively and electronically measure de-escalation a method based upon the spectrum of antimicrobial regimens administered (i.e., spectrum score) was developed.

METHODS

A Delphi process was used to develop applicable concepts. Spectrum scores were created for 27 antimicrobials based upon susceptibility for 19 organisms. National VA susceptibility data was used to estimate microbial spectrum. Susceptibility estimates were converted to ordinal scores, and values for organisms with multi-drug resistance potential were weighted more heavily. Organism scores were summed to create antibiotic-specific spectrum scores and extended mathematically to score multi-antimicrobial regimens. Vignettes were created from antimicrobial regimens administered to 300 patients hospitalized with pneumonia. Daily spectrum scores were calculated for each case. Hospitalization day 4 scores were subtracted from day 2 scores (i.e., spectrum score ∆). A positive spectrum score ∆ defined de-escalation. Experts ranked each pneumonia case on a 7-point Likert scale (Likert >4 indicated de-escalation). Spectrum score ∆s were compared to expert review. Findings were used to identify score deficiencies. Next, 40 pairs of cases were modified to include antimicrobial administration routes. Each pair contained almost similar regimens; however, one contained oral (PO) the other only intravenous (IV) antimicrobials on day 4 of therapy. Experts reviewed cases as described. Spectrum score ∆ credits to account for PO conversion were derived from the mean paired differences in Likert Score. De-escalation status was evaluated in 100 vignettes containing antimicrobial route by different experts and compared to the modified method.

RESULTS

Initial sensitivity and specificity of the spectrum score ∆ to detect expert classified de-escalation events was 86.3 and 96.0%, respectively. In paired cases, the mean (± SD) Likert score was 5.0 (1.5) and 4.6 (1.5) for PO and IV (P = 0.002), respectively. To improve de-escalation event detection, two credits were added to spectrum score ∆s based upon the percentage of antimicrobials administered PO on day 4. The final method, exhibited sensitivity and specificity to detect expert classified de-escalation events of 96.2 and 93.6%, respectively.

CONCLUSIONS

The final spectrum score method exhibited excellent agreement with expert judgments of de-escalation events in pneumonia.

Evaluation of impermeant, DNA-binding dye fluorescence as a real-time readout of eukaryotic cell toxicity in a high throughput screening format

Interpretation of high throughput screening (HTS) data in cell-based assays may be confounded by cytotoxic properties of screening compounds. Therefore, assessing cell toxicity in real time during the HTS process itself would be highly advantageous. Here, we investigate the potential of putatively impermeant, fluorescent, DNA-binding dyes to give cell toxicity readout during HTS. Amongst 19 DNA-binding dyes examined, three classes were identified that were (1) permeant, (2) cytotoxic, or (3) neither permeant nor cytotoxic during 3-day incubation with a macrophage cell line. In the last class, four dyes (SYTOX Green, CellTox Green, GelGreen, and EvaGreen) gave highly robust cytotoxicity data in 384-well screening plates. As proof of principle, successful combination with a luminescence-based assay in HTS format was demonstrated. Here, both intracellular growth of Legionella pneumophila (luminescence) and host cell viability (SYTOX Green exclusion) were assayed in the same screening well. Incorporation of membrane-impermeant, DNA-binding, fluorescent dyes in HTS assays should prove useful by allowing evaluation of cytotoxicity in real time, eliminating reagent addition steps and effort associated with endpoint cell viability analysis, and reducing the need for follow-up cytotoxicity screening.

Current clinical management of Legionnaires’ disease

Legionella pneumophila is increasingly recognized as a cause of both sporadic and epidemic community-acquired pneumonia. Clinical manifestations of Legionnaires' disease are not specific and current diagnostic scores are of limited use. Urinary antigen detection is an effective test for rapid diagnosis of infection caused by L. pneumophila serogroup 1. Improved outcomes regarding the time to defervescence, development of complications and length of stay, have been recently observed for patients treated with levofloxacin monotherapy. Current case-fatality rates for hospitalized patients with community-acquired Legionella pneumonia are lower than those traditionally reported for this infection. Effective preventive strategies are needed.

Antimicrobial activity of solithromycin against clinical isolates of Legionella pneumophila serogroup 1

The activity of solithromycin was evaluated against clinical Legionella pneumophila serogroup 1 (Lp1) isolates (n = 196) collected in Ontario, Canada, from 1980 to 2011. Its in vitro activity was compared to that of azithromycin (AZM) using the broth microdilution method. Solithromycin had a MIC50 of ≤0.015 μg/ml and a MIC90 of 0.031 μg/ml, making its activity at least 8-fold to 32-fold higher than that of AZM (MIC50 and MIC90, 0.125 μg/ml and 1 μg/ml, respectively). Ninety-nine percent of the isolates had MICs for solithromycin ranging from ≤0.015 μg/ml to 0.031 μg/ml, whereas 83.6% of the isolates showed MICs for AZM ranging from 0.062 μg/ml to 0.25 μg/ml. Interestingly, 96.7% (30 out of 31 clinical isolates) identified with higher AZM MICs (0.5 μg/ml to 2 μg/ml) belonged to the clinically prevalent sequence type 1. To investigate the intracellular activity of solithromycin, in vitro invasion assays were also performed against a subset of representative Lp1 isolates internalized within human lung epithelial cells. Solithromycin and AZM both inhibited growth of all intracellular Lp1 isolates at 1× or 8× MICs, displaying bacteriostatic effects, as would be expected with protein synthesis inhibitor rather than bactericidal activity. Solithromycin demonstrated the highest in vitro and intracellular potency against all Lp1 isolates compared to AZM. Given the rapid spread of resistance mechanisms among respiratory pathogens and the reported treatment failures in legionellosis, the development of this new fluoroketolide, already in phase 3 oral clinical studies, constitutes a promising alternative option for the treatment of legionellosis.

In vivo comparative pharmacokinetics and pharmacodynamics of moxifloxacin and levofloxacin in human neutrophils

OBJECTIVE

Most of the newer fluoroquinolones are active against bacteria such as Streptococcus pneumoniae and Staphylococcus aureus, which are able to multiply inside polymorphonuclear leukocytes (PMNs). The aim of this study was to determine moxifloxacin and levofloxacin intracellular behaviour with their usual dosage regimen.

METHODS

We determined the pharmacokinetics of moxifloxacin and levofloxacin at steady state in the PMNs of ten healthy volunteers receiving moxifloxacin 400mg and levofloxacin 500mg as a once-daily dosing regimen for 3 days.

RESULTS

Both antibacterials showed a high level of intracellular penetration exhibiting PMNs/plasma ratios of 17.34 +/- 8.29 for moxifloxacin versus 8.15 +/- 5.23 for levofloxacin for maximum concentrations (C(max)) and 14.72 +/- 8.29 for moxifloxacin versus 8.15 +/- 5.23 for levofloxacin for the area under the plasma concentration-time curve. Estimation of the most predictive pharmacodynamic surrogate markers for concentration-dependent bactericidal antibacterials in the intracellular milieu by taking into account the susceptibility of S. pneumoniae and methicillin-susceptible S. aureus demonstrated consistently higher values with moxifloxacin than with levofloxacin, even though with both drugs the levels obtained are well above the recommended targets values. Indeed, C(max)/MIC ratios calculated in PMNs for moxifloxacin were 287.3 and 718.2 for S. pneumoniae and S. aureus, respectively, and for levofloxacin were 25.6 and 205.1, respectively.

CONCLUSION

Moxifloxacin and levofloxacin seem to be well adapted for the treatment of infections due to susceptible intracellular bacteria, and moxifloxacin provides a greater margin of safety than levofloxacin.

Detection of Legionella pneumophila on clinical samples and susceptibility assessment by flow cytometry

Culture in selective media represents the standard diagnostic method to confirm Legionella pneumophila infection, despite requiring a prolonged incubation period; antigen detection by immunofluorescence (IFS) and molecular techniques are also available, but they do not allow antimicrobial susceptibility evaluation. Our objective was to optimise flow cytometry (FC) protocols for the detection of L. pneumophila in respiratory samples and for susceptibility evaluation to first-line drugs. In order to optimise the FC protocol, a specific monoclonal antibody, conjugated with fluorescein isothiocyanate (FITC), was incubated with type strain L. pneumophila ATCC 33152. The limit of detection was established by analysing serial dilutions of bacterial suspension; specificity was assayed using mixtures of prokaryotic and eukaryotic microorganisms. The optimised FC protocol was used to assess 50 respiratory samples and compared with IFS evaluation. The susceptibility profile to erythromycin, ciprofloxacin and levofloxacin was evaluated by FC using propidium iodide and SYBR Green fluorescent dyes; the results were compared with the Etest afterwards. The optimal specific antibody concentration was 20 μg/ml; 10(2)/ml Legionella organisms were detected by this protocol and no cross-reactions with other microorganisms were detected. The five positive respiratory samples (10 %) determined by IFS were also detected by FC, showing 100 % correlation. After 1 h of incubation at 37 °C with different antimicrobials, SYBR Green staining could discriminate between treated and non-treated cells. A novel flow cytometric approach for the detection of L. pneumophila from clinical samples and susceptibility evaluation is now available, representing an important step forward for the diagnosis of this very relevant agent.

Cumulative clinical experience from over a decade of use of levofloxacin in community-acquired pneumonia: critical appraisal and role in therapy

Levofloxacin is the synthetic L-isomer of the racemic fluoroquinolone, ofloxacin. It interferes with critical processes in the bacterial cell such as DNA replication, transcription, repair, and recombination by inhibiting bacterial topoisomerases. Levofloxacin has broad spectrum activity against several causative bacterial pathogens of community-acquired pneumonia (CAP). Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation such that patients can be conveniently transitioned between these formulations when moving from the inpatient to the outpatient setting. Furthermore, levofloxacin demonstrates excellent safety, and has good tissue penetration maintaining adequate concentrations at the site of infection. The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP are well established. Furthermore, a high-dose (750 mg) and short-course (5 days) of once-daily levofloxacin has been approved for use in the US in the treatment of CAP, acute bacterial sinusitis, acute pyelonephritis, and complicated urinary tract infections. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent antibacterial activity, decreases the potential for drug resistance, and has better patient compliance.

In vivo efficacy of sivelestat in combination with pazufloxacin against Legionella pneumonia

It is important to regulate excessive inflammation when patients with severe infectious disease are treated. Sivelestat sodium hydrate (sivelestat), a neutrophil elastase inhibitor, is used in the treatment of lung injury but its effect on bacterial pneumonia is unknown. The authors examined the efficacy of sivelestat in combination with a fluoroquinolone in a Legionella pneumophila pneumonia mouse model. The combination therapy did not show a significant survival improvement compared to the treatment with fluoroquinolone alone, but reduced bacteria number and inflammatory cells in the early phase. The combination therapy can contribute to treatment of L. pneumophila pneumonia with protecting lungs.

In vitro antibacterial activity of modithromycin, a novel 6,11-bridged bicyclolide, against respiratory pathogens, including macrolide-resistant Gram-positive cocci

The in vitro activities of modithromycin against Gram-positive and -negative respiratory pathogens, including macrolide-resistant cocci with different resistance mechanisms, were compared with those of other macrolide and ketolide agents. MICs were determined by the broth microdilution method. All 595 test strains used in this study were isolated from Japanese medical facilities. The erm (ribosome methylase) and/or mef (efflux pump) gene, which correlated with resistance to erythromycin as well as clarithromycin and azithromycin, was found in 81.8%, 21.3%, and 23.2% of Streptococcus pneumoniae, Streptococcus pyogenes, and methicillin-susceptible Staphylococcus aureus (MSSA) strains, respectively. Modithromycin showed MIC(90)s of 0.125 μg/ml against these three cocci, including macrolide-resistant strains. In particular, the MIC of modithromycin against ermB-carrying S. pyogenes was ≥ 32-fold lower than that of telithromycin. The activities of modithromycin as well as telithromycin were little affected by the presence of mefA or mefE in both streptococci. Against Gram-negative pathogens, modithromycin showed MIC(90)s of 0.5, 8, and 0.031 μg/ml against Moraxella catarrhalis, Haemophilus influenzae, and Legionella spp., respectively. The MICs of modithromycin against M. catarrhalis and H. influenzae were higher than those of telithromycin and azithromycin. However, modithromycin showed the most potent anti-Legionella activity among the macrolide and ketolide agents tested. These results suggested that the bicyclolide agent modithromycin is a novel class of macrolides with improved antibacterial activity against Gram-positive cocci, including telithromycin-resistant streptococci and intracellular Gram-negative bacteria of the Legionella species.

In vitro activity of antimicrobial agents against Legionella isolated from environmental water systems: first results from Turkey

We evaluated the in vitro activity of antimicrobial agents against Legionella obtained from hotel and hospital water systems in three different regions of Turkey. Sixty-five Legionella strains (Legionella pneumophila serogroup 6 [n=32], L. pneumophila serogroup 1 [n=27], L. pneumophila serogroup 3 [n=2], and Legionella spp. [n=4]) were tested against levofloxacin, ciprofloxacin, clarithromycin, azithromycin, and rifampicin. The minimum inhibitory concentration (MIC) values of each antimicrobial agent for these strains was determined by the microdilution method using buffered yeast extract medium supplemented with 0.1% ketoglutarate broth. L. pneumophila ATCC 33152, Staphylococcus aureus ATCC 29213, and Escherichia coli ATCC 25922 were used as controls. Minimum inhibitory concentration values were in the following ranges: clarithromycin 0.001-0.5 mg/L, azithromycin 0.001-0.5 mg/L, levofloxacin 0.001-0.5 mg/L, ciprofloxacin 0.001-0.125 mg/L, and rifampicin 0.001- 0.5 mg/L. The MIC(90) for rifampicin, levofloxacin, ciprofloxacin, azithromycin, and clarithromycin were 0.015, 0.125, 0.06, 0.125, and 0.06 mg/L, respectively. To the best of our knowledge, this is the first study to determine in vitro activities of antimicrobial agents against Legionella species in Turkey. Rifampicin had the lowest MIC(90) value. It would seem that azithromycin and clarithromycin exhibit good activity as well as levofloxacin and ciprofloxacin against Legionella isolated from environmental water systems in Turkey.

Levofloxacin in the treatment of community-acquired pneumonia

Levofloxacin is a fluoroquinolone that has a broad spectrum of activity against several causative bacterial pathogens of community-acquired pneumonia (CAP). The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP are well established. Furthermore, a high-dose (750 mg), short-course (5 days) of once-daily levofloxacin has been approved for use in the USA in the treatment of CAP, acute bacterial sinusitis, acute pyelonephritis and complicated urinary tract infections. Levofloxacin can be used as a monotherapy in patients with CAP, however, levofloxacin combination therapy with anti-pseudomonal beta-lactam (or aminoglycoside) should be considered if Pseudomonas aeruginosa is the causative pathogen of the respiratory infection. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent antibacterial activity, decreases the potential for drug resistance and has better patient compliance. Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation and the patients can switch between these formulations, which results in more options with respect to the therapeutic regimens. Furthermore, levofloxacin is generally well tolerated, has good tissue penetration and adequate concentrations can be maintained at the site of infections.

Treatment strategies for Legionella infection

Given the nonspecific clinical manifestations of Legionnaires' disease and the high mortality of untreated Legionnaires' disease, we recommend routine use of Legionella testing, especially the Legionella urinary antigen test, for all patients with community-acquired pneumonia. This includes patients with ambulatory pneumonia and hospitalized children. Legionella cultures should be more widely available, especially in hospitals where the drinking water is colonized with Legionella. Azithromycin or levofloxacin can be considered as first-line therapy. Other antibiotics including tetracyclines, tigecycline, other fluoroquinolones and other macrolides (especially clarithromycin) are also effective. The clinical response of quinolones may be somewhat more favorable compared to macrolides, but the outcome is similar. If the Legionnaires' disease is hospital-acquired, culturing of the hospital drinking water for Legionella is indicated.

Levofloxacin : a review of its use as a high-dose, short-course treatment for bacterial infection

Levofloxacin (Levaquin) is a fluoroquinolone antibacterial that is the L-isomer of ofloxacin. A high-dose (750 mg) short-course (5 days) of once-daily levofloxacin is approved for use in the US in the treatment of community-acquired pneumonia (CAP), acute bacterial sinusitis (ABS), complicated urinary tract infections (UTI) and acute pyelonephritis (AP). The broad spectrum antibacterial profile of levofloxacin means that monotherapy is often a possibility in patients with CAP at times when other agents may require combination therapy, although levofloxacin can be used in combination therapy when necessary. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent bactericidal activity and may reduce the potential for resistance to emerge. In addition, this regimen lends itself to better compliance because of the shorter duration of treatment and the convenient once-daily administration schedule. Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation; importantly, patients can transition between the formulations, which results in more options in regards to the treatment regimen and the potential for patients with varying degrees of illness to be treated. Levofloxacin has good tissue penetration and an adequate concentration can be maintained in the urinary tract to treat uropathogens. Levofloxacin is generally well tolerated and has good efficacy in the treatment of patients with CAP, ABS, complicated UTI and AP. The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP, ABS and UTIs is well established, and the high-dose, short-course levofloxacin regimen has been shown to be noninferior to the 10-day regimen in CAP and ABS, and to have a similar tolerability profile. Similarly, the high-dose, short-course levofloxacin regimen is noninferior to ciprofloxacin in patients with complicated UTI or AP. Thus, levofloxacin is a valuable antimicrobial agent that has activity against a wide range of bacterial pathogens; however, its use should be considered carefully so that the potential for resistance selection can be minimized and its usefulness in severe infections and against a range of penicillin- and macrolide-resistant pathogens can be maintained.

Legionella pneumonia in cancer patients

Legionella is an important cause of nosocomial and community-acquired pneumonia in both immunocompetent and immunosuppressed patients worldwide; however, the clinical course and optimal antibiotic therapy of Legionella pneumonia (LP) in patients with cancer is uncertain. We studied retrospectively the risk factors, clinical manifestations, and outcome of 49 cancer patients with a positive Legionella culture or direct fluorescent antibody (DFA) over a 13-year period (1991-2003). The majority of patients (82%) had an underlying hematologic malignancy, and 37% were bone marrow transplant recipients; 80% of the patients had active malignancy. Lymphopenia (47%), use of systemic corticosteroids (41%), and chemotherapy (63%) were the most common underlying conditions. The laboratory diagnosis was established by positive Legionella culture (n = 8, 16%), DFA (n = 29, 59%), or both (n = 12, 25%). In 4 patients (8%), a positive DFA was deemed to represent false-positive results. There was no temporal or geographic clustering of cases. The majority of the cases had multilobar (61%) or bilateral (55%) pulmonary involvement. The mean time to response to therapy was 8 days; 18 patients (37%) developed complications requiring prolonged duration of treatment (mean, 25 d). The case-fatality rate was 31%. Two patients had relapse of LP despite appropriate therapy. Improved outcome, especially in those with severe pneumonia, seemed to correlate with the use of a combination of antibiotics. LP is an uncommon infection in our patient population but is associated with significant morbidity and mortality. Treatment of LP in cancer patients may require a prolonged course with a regimen that includes a newer macrolide or quinolone.

Activity of telithromycin and comparators against isolates of Legionella pneumophila collected from patients with community-acquired respiratory tract infections: PROTEKT Years 1-5

The in-vitro activity of telithromycin and comparator antibacterial agents was determined against clinical isolates of Legionella pneumophila collected in the PROTEKT surveillance study. In total, 133 isolates were collected between 1999 and 2004 from 13 countries (Australia, Belgium, Czech Republic, France, Germany, Hungary, Ireland, Italy, Japan, Portugal, Spain, Sweden and the USA). MICs were determined by broth microdilution. Telithromycin maintained activity between Year 1 (MIC(90) 0.015 mg/L) and Year 5 (MIC(90) 0.03 mg/L), as did the comparator antibacterial agents. Telithromycin appears to be a candidate for coverage of legionellosis in the empirical treatment of community-acquired respiratory tract infection.

[Treatment for Legionnaires' disease. Macrolides or quinolones?]

BACKGROUND

Macrolides and fluoroquinolones are the recommended treatment for Legionnaires' disease. The aim of our study was to analyze the clinical efficacy of clarithromycin, azithromycin and levofloxacin in patients with Legionnaires' disease.

METHODS

Prospective, observational study involving all adult patients with Legionella pneumophila pneumonia attended at Hospital Universitario Vall d'Hebron (Barcelona, Spain) from January 2001 to December 2004. Duration of fever, length of hospital stay and mortality were compared among 52 patients treated with clarithromycin, 43 with azithromycin and 18 with levofloxacin.

RESULTS

The proportion of patients with risk factors for Legionnaires' disease, the initial severity of the pneumonia and the number of patients who required intensive care unit admission were similar in patients treated with clarithromycin, azithromycin and levofloxacin. In-hospital mortality was 5.3%. There were no significant differences in fever duration, length of hospital stay or mortality among the 3 groups of patients.

CONCLUSION

In our experience, clarithromycin, azithromycin and levofloxacin were all efficacious for the treatment of Legionnaires' disease.

[Antibiotherapy for acute CAP in adults]

Community acquired pneumonia is one of the most frequent infections. With time, bacterial epidemiology and bacterial resistance evolve and new antibiotics become available. So an up-date on adequate antibiotic use is necessary. We reviewed the epidemiology of pneumonia and the evolution of bacterial resistance. We also collected data on new antibiotics which can be used for this infection such as levofloxacin, moxifloxacin, telithromycin, and pristinamycin. All these drugs are effective on bacteria involved in pneumonia. At this time, only few Streptococcus pneumoniae strains have developed resistance to these drugs. However, resistance to fluoroquinolones is not easily detected with common laboratory techniques. There is no effectiveness difference between the 2 new fluoroquinolones (levofloxacin, moxifloxacin) in clinical studies. However, in bacteriological and pharmacological studies, moxifloxacin seems to be more effective than levofloxacin (500 mg/day). For the treatment of pneumonia due to Legionella pneumophila, fluoroquinolones are now widely recommended. For Streptococcus pneumonia, amoxicillin remain the drug of choice, even for bacteria with a decreased susceptibility to penicillin. The importance of treating atypical pathogens remains to be documented.

13 – Antibiotic therapy of community-acquired pneumonia (CAP) caused by atypical agents

Macrolides, fluoroquinolones, doxycycline, and ketolides show a good intrinsic activity against intracellular pathogens which are responsible for a variable percentage of community-acquired pneumonia (CAP). These therapeutic agents all seem effective in treating most cases of CAP caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella spp. Among quinolones, the more recent fluoroquinolones, such as gemifloxacin or moxifloxacin, generally show a better intrinsic activity than the older ones. Among macrolides, azithromycin, and clarithromycin show a better pharmacokinetic profile. Both of them are available in intravenous form. It is quite common for M. pneumoniae and C. pneumoniae to continue to be shed in respiratory secretions, weeks after an effective therapy. The clinical relevance of this finding is not clear since most of these patients have a good outcome. Azithromycin, due to its advantageous pharmacokinetic profile, seems the best option when antibiotic prophylaxis is considered in some epidemiological settings. It has been proved effective in closed M. pneumoniae outbreaks.

[Resistance of infectious agents involved in low respiratory tract infections in France]

This review concerning the major lower respiratory tract pathogens in France has for aim to describe the epidemiology of resistance to beta-lactams, macrolides, ketolides, and fluoroquinolones especially in Streptococcus pneumoniae and Haemophilus influenzae. It should also provide new insights on the mechanisms of acquired resistance and the level of resistance conferred, highlighting the related ecological impact. In the context of this XVth consensus conference, this review should contribute to the elaboration of guidelines for the treatment of lower respiratory tract infections in adults.

Legionella: macrolides or quinolones?

Following the first outbreaks of legionnaire's disease, erythromycin emerged as the treatment of choice without the foundation of rigorous clinical trials. The number of therapeutic failures with erythromycin, as well as the side-effects and drug interactions, led to the consideration of other drugs such as the new macrolides and quinolones for the treatment of legionnaire's disease in the 1990s. In this article, 19 studies in in-vitro intracellular models and seven animal studies that compared macrolides to quinolones were reviewed. Quinolones were found to have greater activity in intracellular models and improved efficacy in animal models compared with macrolides. No randomised trials comparing the clinical efficacy of the new macrolides and new quinolones have ever been performed. Three observational studies totalling 458 patients with legionnaire's disease have compared the clinical efficacy of macrolides (not including azithromycin) and quinolones (mainly levofloxacin). The results suggested that quinolones may produce a superior clinical response compared with the macrolides (erythromycin and clarithromycin) with regard to defervescence, complications, and length of hospital stay. Little data exist for direct comparison of quinolones and azithromycin.

[Study of 12 epidemical cases of legionnaire's disease occurred in Meurthe-et-Moselle (France) between July and August 2004]

PATIENTS AND METHOD

To describe epidemiological, clinical, biological, radiological data and therapeutic features of legionnaire's disease during an outbreak occurring in Meurthe-et-Moselle between July-August 2004.

RESULTS

12 cases were recorded including 11 men, 6 smokers, 4 alcoholo-nicotinic, 3 diabetics, 3 with hemopathy, 1 with corticotherapy; in one case no risks factors were found; mean age was 68.5 years [minimum=48; maximum=96]. Nine cases had sudden symptoms. Nine cases had a fever up to 40 degrees C, 9 with dyspnoea, 7 with cough, 7 with a relative bradycardia, 3 with diarrhoea, 3 felt faint, 3 with confusion. Radiology: unilateral unilobe localisation in 10 cases. Biological data: cytolysis in 8 cases, CRP >300 mg/l in 8. The diagnosis confirmed with urinary antigen of Legionella pneumophila serogroup 1 (UrAgLp1) in 12 cases. In 2 cases, UrAgLp1 appeared negative between 3rd and 10th day after the beginning of a treatment although UrAgLp1 was positive before the treatment. In all cases, the first serology realised during first days following occurrence the first symptoms remained negative. Two serology of control in four were positive. One search of L. pneumophila serogroup 1 in sputum was positive in 7. Bitherapy was used in 7 cases with preferential association: fluoroquinolone+rifampicin. Two patients died. Origin of the contamination remains unknown.

CONCLUSION

Culture of Legionella is essential, in epidemic context, to compare clinical and environmental Legionella and to locate the origin of contamination.