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

Antibiotic Susceptibility of Environmental Legionella pneumophila Strains Isolated in Northern Italy

Legionella pneumophila is ubiquitous in aquatic environments and responsible for severe pneumonia in humans through inhalation of aerosol containing Legionella spp. Macrolides and fluoroquinolones are frequently used antimicrobials, but treatment failures are increasingly being reported. As susceptibility testing is not routinely performed, this study aimed to determine the minimum inhibitory concentrations (MICs) on 58 environmental Legionella pneumophila strains (24 of serogroup 1 and 34 of non-serogroup 1) isolated in Northern Italy. MICs of azithromycin, erythromycin, ciprofloxacin, levofloxacin, and rifampicin were determined by the microdilution method using buffered yeast extract broth supplemented with α-ketoglutarate (BYEα). Seventy-five percent of Legionella pneumophila isolates showed MIC values below the tentative highest MICs indicated by the European Committee on Antimicrobial Susceptibility Testing (EUCAST); rifampicin was the most active agent with MIC₉₀ values below 0.008 mg/L. Interestingly, one isolate was tested and found to be PCR-positive for the azithromycin LpeAB active efflux system, further confirmed by the reserpine/resazurin microtiter assay. In conclusion, this study has provided additional susceptibility data for environmental Legionella pneumophila isolates from Northern Italy demonstrating, in general, low MICs values for the tested antimicrobials, although one strain tested was shown to possess the LpeAB resistance determinant, indicating that future surveillance studies are warranted.

Meta-analysis of fluoroquinolones versus macrolides for treatment of legionella pneumonia

BACKGROUND

Only a single meta-analysis has reported the clinical benefit of fluoroquinolones (FQs) for Legionella pneumonia; however, there is no robust data available to confirm this result, based on current guidelines.

METHODS

We performed a systematic review and meta-analysis comparing FQs with macrolides (MCs) on their efficacy and safety in Legionella pneumonia, using studies published until January 2020. The outcomes included mortality (overall; 30-day), clinical cure, time to apyrexia, length of hospital stay, and adverse events.

RESULTS

Five RCTs and twelve retrospective studies were identified. Clinical cure was comparable between the treatment groups (risk rate (RR) 1.07, 95% confidential interval (CI) 0.86-1.31). Mortality was significantly higher for MCs than for FQs (overall, odd rate (OR) 0.59, 95% CI 0.35-0.98; 30-day, OR 0.41, 95% CI 0.20-0.85). FQs significantly reduced the length of hospital stay, compared to MCs (mean difference -3.58, 95% CI -5.48-1.69). Other outcomes were not significantly different between the treatment groups (time to apyrexia; mean difference -1.83, 95% CI -5.15-1.5, adverse events; OR 0.61, 95% CI 0.33-1.15). In subgroup analyses, levofloxacin significantly reduced the length of hospital stay over two specific MCs (azithromycin and clarithromycin) (mean difference -3.03, 95% CI -5.33-0.72), whereas mortality was not significantly different between the treatment groups (overall, OR 0.49, 95% CI 0.19-1.24; 30-day, OR 0.38, 95% CI 0.13-1.13).

CONCLUSIONS

FQs exhibited superior effects in terms of mortality and length of hospital stay in Legionella pneumonia. These results support current guidelines recommending FQs for the treatment of Legionella pneumonia.

Comparison of solithromycin with erythromycin in Enterococcus faecalis and Enterococcus faecium from China: antibacterial activity, clonality, resistance mechanism, and inhibition of biofilm formation

Solithromycin (SOL), a fourth-generation macrolide and ketolide, has been reported to have robust antibacterial activity against a wide spectrum of Gram-positive bacteria. However, the impact of SOL on planktonic growth and biofilm formation of clinical enterococcus isolates remains unclear. In this study, 276 Enterococcus faecalis isolates and 122 Enterococcus faecium were retrospectively collected from a tertiary hospital from China. SOL against clinical isolates of enterococci from China were evaluated the antimicrobial activity in comparison with erythromycin, and explore its relationship with the clonality, virulence genes and resistance mechanism of these isolates. Our data showed that the MICs of SOL against clinical E. faecalis and E. faecium isolates from China were ≤4 and ≤8 mg l^-1, respectively. ST16 and ST179 were regarded as the risk factor to SOL resistance in E. faecalis. SOL could inhibit but not eradicate the biofilm formation of E. faecalis. The bactericidal effects of SOL against E. faecalis and E. faecium were demonstrated to be similar to linezolid and vancomycin using time-kill assays. In conclusion, SOL showed significantly enhanced antibacterial activity against clinical isolates of E. faecalis and E. faecium from China in comparison to erythromycin. Furthermore, SOL could inhibit the biofilm formation of E. faecalis and have the similar bactericidal ability as linezolid and vancomycin against both E. faecalis and E. faecium.

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.

Antibiotic-Resistant Community-Acquired Bacterial Pneumonia

Antimicrobial resistance is a global concern, and prudent use of antibiotics is essential to preserve the current armamentarium of effective drugs. Acute respiratory tract infection is the most common reason for antibiotic prescription in adults. In particular, community-acquired pneumonia poses a significant health challenge and economic burden globally, especially in the current landscape of a dense and aging population. By updating the knowledge on the common antimicrobial-resistant pathogens in community-acquired respiratory tract infections, their prevalence, and resistance may pave the way to enhancing appropriate antibiotic use in the ambulatory and health care setting.

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.

Antibiotic Resistance and Azithromycin Resistance Mechanism of Legionella pneumophila Serogroup 1 in China

Legionnaires' disease, caused by Legionella pneumophila, has been treated primarily with antibiotics. However, few reports have been published on antibiotic-resistant Legionella in China. Our aim was to determine the azithromycin resistance mechanism of L. pneumophila serogroup 1 in China. The sensitivities of 149 L. pneumophila serogroup 1 strains, isolated from clinical cases or environmental water in China from 2002 to 2016, to five antibiotics, including erythromycin, azithromycin, levofloxacin, moxifloxacin, and rifampin, were evaluated. The mechanisms of the resistance of L. pneumophila serogroup 1 to azithromycin were studied. The expression levels of efflux pump gene lpeAB and the MIC of azithromycin-resistant strains in the presence and absence of the efflux pump inhibitor carbonyl cyanide-chlorophenylhydrazone (CCCP) were determined. All 149 strains were sensitive to erythromycin, levofloxacin, moxifloxacin, and rifampin, among which 25 of the strains exhibited azithromycin resistance. These 25 strains, including strains of sequence type 1 (ST1), ST144, ST150, ST154, and ST629, were screened. Expression of lpeAB was responsible for the reduced azithromycin susceptibility in all 25 of these strains. The phenotypes of 25 strains with virulence were linked by evaluating the intracellular growth ability in mouse macrophage J774 cells. Among the 25 strains, 60% were more virulent than the ATCC 33152 reference strain. The results determined in our study represent data supporting the further study of the antibiotic sensitivity of L. pneumophila strains in China.

Pharmacokinetic/Pharmacodynamic Evaluation of Solithromycin against Streptococcus pneumoniae Using Data from a Neutropenic Murine Lung Infection Model

Solithromycin (CEM-101) is a novel fluoroketolide antimicrobial agent with activity against typical and atypical pathogens associated with community-acquired bacterial pneumonia. Using a neutropenic murine lung infection model, the objectives of this study were to identify the pharmacokinetic/pharmacodynamic (PK/PD) index most closely associated with efficacy and the magnitude of such indices associated with solithromycin efficacy against Streptococcus pneumoniae Plasma and epithelial lining fluid (ELF) samples for pharmacokinetics (PK) were collected serially over 24 hours from healthy mice administered single doses of solithromycin (0.625 to 40 mg/kg). Neutropenic CD-1 mice infected with 10⁸ CFUs of one of five S. pneumoniae isolates were administered solithromycin (0.156 to 160 mg/kg/day) via oral gavage. Doses were administered in a fractionated manner for mice infected with one isolate, while mice infected with the remaining four isolates received solithromycin as either a regimen every 6 hours or every 12 hours. A three-compartment model best described solithromycin PK in the plasma and ELF (r² = 0.935 and 0.831, respectively). The ratio of total-drug ELF to free-drug plasma area under the concentration-time curve (AUC) from time 0 to 24 hours was 2.7. Free-drug plasma and total-drug ELF AUC to minimum inhibitory concentration ratios (AUC/MIC ratios) were most predictive of efficacy (r² = 0.851 and 0.850, respectively). The magnitude of free-drug plasma/total-drug ELF AUC/MIC ratios associated with net bacterial stasis and a 1- and 2-log₁₀ CFU reduction from baseline was 1.65/1.26, 6.31/15.1, and 12.8/59.8, respectively. These data provided dose selection support for solithromycin for clinical trials in patients with community-acquired bacterial pneumonia.

Erythromycin, Cethromycin and Solithromycin display similar binding affinities to the E. coli's ribosome: A molecular simulation study

Macrolide antibiotics bind to the exit tunnel of the ribosome and inhibit protein synthesis blocking its translocation. Thus, antibiotics including the known macrolide Erythromycin (ERY) are active against bacteria. However, at present, some bacteria show resistance to drugs, which requires the development of new powerful antibacterial agents. One possible way is to use the ERY structure, but change its side chains, while the size of the lactone ring can remain unchanged or change. In this work we consider Cethromycin (CET) and Solithromycin (SOL), which are ketolides with quinolylallyl group at C6 and aminophenyl at C11, respectively (both of them have the same lactone ring as ERY). Experiments have shown that these ketolides have improved efficacy against pathogens, but their binding affinity to the E. coli's ribosome is almost identical. To clarify this issue, we have studied in detail the binding mechanisms of ERY, CET and SOL using the docking and molecular dynamic simulations. In agreement with the experiments, we showed that these compounds have similar binding affinities. Desosamine and lactone ring groups play a critical role in the binding of ERY to the ribosome. In CET and SOL, the contribution of keto and alkylaryl groups is balanced by cyclic carbamate. We have demonstrated that increased fluctuations in the ribosomal residues at the binding site led to an increase in the entropic term in the free binding energy of ERY compared to SOL and CET. The alkyl-aryl arm of both ketolides strongly interacts with A752 and U2609. In addition, the presence of macrolides in the exit tunnel can alter the conformation of U2585, which is located in the peptidyl transferase center, through non-bonded interaction. Therefore, the side chain of ketolides affects not only the binding site but also other residues possibly leading to a strong effect on the protein synthesis process. We predict that to combat bacterial mutations, it is necessary either to design a bulk and charged group as a cladinose, or to use several groups with different signs of charges. This prediction can be used for the development of new efficient antibiotics.

Solithromycin monotherapy for treatment of community-acquired bacterial pneumonia: A meta-analysis of randomised controlled trials

OBJECTIVES

Solithromycin is a new monotherapy option for community-acquired bacterial pneumonia (CABP) patients. However, the efficacy and safety of solithromycin monotherapy for the treatment of CABP remains controversial. The aim of this meta-analysis was to evaluate the role that solithromycin played in the treatment of CABP.

METHODS

We systematically retrieved randomised controlled trials (RCTs) compared solithromycin with other antibiotics in the treatment of CABP, which were published on PubMed, ScienceDirect, Cochrane libary and the Clinical Trials.gov before July 2018. Ultimately, a meta-analysis of all RCTs eligible for inclusion criteria was performed.

RESULTS

Three RCTs, comprising 1855 patients, were included in the meta-analysis. There were no statistically significant differences between patients given solithromycin and those given other antibiotics with regard to early clinical response (ECR) [1855 patients, odds ratio (OR) = 1.00, 95% confidence interval (CI) 0.80 to 1.24, P = 0.99] and clinical success rates at short-term follow-up (SFU) (1855 patients, OR = 0.78, 95% CI 0.60 to 1.01, P = 0.06) in the intention-to-treat (ITT) population, as were the ECR (787 patients, OR = 0.90, 95% CI 0.64 to 1.27, P = 0.55) and clinical success rates at SFU (358 patients, OR = 0.73, 95% CI 0.41 to 1.31, P = 0.30) in microbiological intention-to-treat population (mITT). Similarly, with regard to the occurrence of treatment-emergent adverse events (TEAEs), drug-related adverse events (AEs), serious AEs, serious drug-related AEs and mortality, no statistically significant difference between patients given solithromycin and those given other antibiotics was observed.

CONCLUSION

In the treatment of CABP, solithromycin monotherapy is an effective and safe antibiotic regimen. Other advantages (ie anti-inflammatory effect, potent activity against expected pathogens of CABP and convenient clinical use) of solithromycin may make it a more fascinating option compared with the currently used regimens.

Population Pharmacokinetics and Safety of Solithromycin following Intravenous and Oral Administration in Infants, Children, and Adolescents

Solithromycin is a novel fluoroketolide antibiotic which was under investigation for the treatment of community-acquired bacterial pneumonia (CABP). A phase 1 study was performed to characterize the pharmacokinetics (PK) and safety of solithromycin in children. Eighty-four subjects (median age, 6 years [age range, 4 days to 17 years]) were administered intravenous (i.v.) or oral (capsules or suspension) solithromycin (i.v., 6 to 8 mg/kg of body weight; capsules/suspension, 14 to 16 mg/kg on days 1 and 7 to 15 mg/kg on days 2 to 5). PK samples were collected after the first and multidose administration. Data from 83 subjects (662 samples) were combined with previously collected adolescent PK data (n = 13; median age, 16 years [age range, 12 to 17 years]) following capsule administration to perform a population PK analysis. A 2-compartment PK model characterized the data well, and postmenstrual age was the only significant covariate after accounting for body size differences. Dosing simulations suggested that 8 mg/kg i.v. daily and oral dosing of 20 mg/kg on day 1 (800-mg adult maximum) followed by 10 mg/kg on days 2 to 5 (400-mg adult maximum) would achieve a pediatric solithromycin exposure consistent with the exposures observed in adults. Seventy-six treatment-emergent adverse events (TEAEs) were reported in 40 subjects. Diarrhea (6 subjects) and infusion site pain or phlebitis (3 subjects) were the most frequently reported adverse events related to treatment. Two subjects experienced TEAEs of increased hepatic enzymes that were deemed not to be related to the study treatment. (The phase 1 pediatric studies discussed in this paper have been registered at ClinicalTrials.gov under identifiers NCT01966055 and NCT02268279.).

Macrolide resistance in Legionella pneumophila: the role of LpeAB efflux pump

Objectives

A previous study on 12 in vitro -selected azithromycin-resistant Legionella pneumophila lineages showed that ribosomal mutations were major macrolide resistance determinants. In addition to these mechanisms that have been well described in many species, mutations upstream of lpeAB operon, homologous to acrAB in Escherichia coli , were identified in two lineages. In this study, we investigated the role of LpeAB and of these mutations in macrolide resistance of L. pneumophila .

Methods

The role of LpeAB was studied by testing the antibiotic susceptibility of WT, deleted and complemented L. pneumophila Paris strains. Translational fusion experiments using GFP as a reporter were conducted to investigate the consequences of the mutations observed in the upstream sequence of lpeAB operon.

Results

We demonstrated the involvement of LpeAB in an efflux pump responsible for a macrolide-specific reduced susceptibility of L. pneumophila Paris strain. Mutations in the upstream sequence of lpeAB operon were associated with an increased protein expression. Increased expression was also observed under sub-inhibitory macrolide concentrations in strains with both mutated and WT promoting regions.

Conclusions

LpeAB are components of an efflux pump, which is a macrolide resistance determinant in L. pneumophila Paris strain. Mutations observed in the upstream sequence of lpeAB operon in resistant lineages led to an overexpression of this efflux pump. Sub-inhibitory concentrations of macrolides themselves participated in upregulating this efflux and could constitute a first step in the acquisition of a high macrolide resistance level.

Spotlight on solithromycin in the treatment of community-acquired bacterial pneumonia: design, development, and potential place in therapy

Community-acquired bacterial pneumonia (CABP) is a leading cause of death worldwide. However, antibacterial agents used to treat common pathogens in CABP are marked by adverse drug events and increasing antimicrobial resistance. Solithromycin is a new ketolide antibiotic, based on the macrolide antibiotic structure, being studied for use in CABP. It has efficacy in vitro against the common causative pathogens in CABP including Streptococcus pneumoniae, Haemophilus influenzae, and atypical pathogens. In Phase II and Phase III clinical trials, it has been demonstrated efficacious as a single agent for treatment of CABP with an apparently milder adverse event profile than alternative agents.

Solithromycin: A Novel Fluoroketolide for the Treatment of Community-Acquired Bacterial Pneumonia

Solithromycin is a novel fluoroketolide developed in both oral and intravenous formulations to address increasing macrolide resistance in pathogens causing community-acquired bacterial pneumonia (CABP). When compared with its macrolide and ketolide predecessors, solithromycin has several structural modifications which increase its ribosomal binding and reduce its propensity to known macrolide resistance mechanisms. Solithromycin, like telithromycin, affects 50S ribosomal subunit formation and function, as well as causing frame-shift errors during translation. However, unlike telithromycin, which binds to two sites on the ribosome, solithromycin has three distinct ribosomal binding sites. Its desosamine sugar interacts at the A2058/A2059 cleft in domain V (as all macrolides do), an extended alkyl-aryl side chain interacts with base pair A752-U2609 in domain II (similar to telithromycin), and a fluorine at C-2 of solithromycin provides additional binding to the ribosome. Studies describing solithromycin activity against Streptococcus pneumoniae have reported that it does not induce erm-mediated resistance because it lacks a cladinose moiety, and that it is less susceptible than other macrolides to mef-mediated efflux due to its increased ribosomal binding and greater intrinsic activity. Solithromycin has demonstrated potent in vitro activity against the most common CABP pathogens, including macrolide-, penicillin-, and fluoroquinolone-resistant isolates of S. pneumoniae, as well as Haemophilus influenzae and atypical bacterial pathogens. Solithromycin displays multi-compartment pharmacokinetics, a large volume of distribution (>500 L), approximately 67% bioavailability when given orally, and serum protein binding of 81%. Its major metabolic pathway appears to follow cytochrome P450 (CYP) 3A4, with metabolites of solithromycin undergoing biliary excretion. Its serum half-life is approximately 6-9 h, which is sufficient for once-daily administration. Pharmacodynamic activity is best described as fAUC_0-24/MIC (the ratio of the area under the free drug concentration-time curve from 0 to 24 h to the minimum inhibitory concentration of the isolate). Solithromycin has completed one phase II and two phase III clinical trials in patients with CABP. In the phase II trial, oral solithromycin was compared with oral levofloxacin and demonstrated similar clinical success rates in the intention-to-treat (ITT) population (84.6 vs 86.6%). Clinical success in the clinically evaluable patients group was 83.6% of patients receiving solithromycin compared with 93.1% for patients receiving levofloxacin. In SOLITAIRE-ORAL, a phase III trial which assessed patients receiving oral solithromycin or oral moxifloxacin for CABP, an equivalent (non-inferior) early clinical response in the ITT population was demonstrated for patients receiving either solithromycin (78.2%) or moxifloxacin (77.9%). In a separate phase III trial, SOLITAIRE-IV, patients receiving intravenous-to-oral solithromycin (79.3%) demonstrated non-inferiority as the primary outcome of early clinical response in the ITT population compared with patients receiving intravenous-to-oral moxifloxacin (79.7%). Overall, solithromycin has been well tolerated in clinical trials, with gastrointestinal adverse events being most common, occurring in approximately 10% of patients. Transaminase elevation occurred in 5-10% of patients and generally resolved following cessation of therapy. None of the rare serious adverse events that occurred with telithromycin (i.e., hepatotoxicity) have been noted with solithromycin, possibly due to the fact that solithromycin (unlike telithromycin) does not possess a pyridine moiety in its chemical structure, which has been implicated in inhibiting nicotinic acetylcholine receptors. Because solithromycin is a possible substrate and inhibitor of both CYP3A4 and P-glycoprotein (P-gp), it may display drug interactions similar to macrolides such as clarithromycin. Overall, the in vitro activity, clinical efficacy, tolerability, and safety profile of solithromycin demonstrated to date suggest that it continues to be a promising treatment for CABP.

Antibiotic susceptibility of Legionella strains isolated from public water sources in Macau and Guangzhou

The purpose of this study was to investigate the susceptibility of waterborne strains of Legionella to eight antimicrobials commonly used in legionellosis therapy. The minimum inhibitory concentrations (MICs) of 66 environmental Legionella strains, isolated from fountains and cooling towers of public facilities (hotels, schools, and shopping malls) in Macau and Guangzhou, were tested using the microdilution method in buffered yeast extract broth. The MIC₅₀/MIC₉₀ values for erythromycin, cefotaxime (CTX), doxycycline (DOC), minocycline (MIN), azithromycin, ciprofloxacin, levofloxacin (LEV), and moxifloxacin were 0.125/0.5 mg/L, 4/8 mg/L, 8/16 mg/L, 4/8 mg/L, 0.125/0.5 mg/L, 0.031/0.031 mg/L, 0.031/0.031 mg/L, and 0.031/0.062 mg/L, respectively. Legionella isolates were inhibited by either low concentrations of macrolides and fluoroquinolones, or high concentrations of CTX and tetracycline drugs. LEV was the most effective drug against different Legionella species and serogroups of L. pneumophila isolates. The latter were inhibited in decreasing order by MIN > CTX >DOC, while non-L. pneumophila isolates were inhibited by CTX> MIN >DOC. In this study, we evaluated drug resistance of pathogenic bacteria from the environment. This may help predict the emergence of drug resistance, improve patient outcomes, and reduce hospitalization costs.

Solithromycin for the treatment of community-acquired bacterial pneumonia

INTRODUCTION

Community-acquired pneumonia is a major public health problem worldwide. In recent years, there has been an increase in the frequency of resistance to the antimicrobials such as β-lactams or macrolides which have habitually been used against the causative pathogens. Solithromycin, a next-generation macrolide, is the first fluoroketolide with activity against most of the frequently isolated bacteria in community-acquired pneumonia, including typical and atypical bacteria as well as macrolide-resistant Streptococcus pneumoniae. Areas covered: A detailed assessment of the literature relating to the antimicrobial activity, pharmacokinetic/pharmacodynamic properties, efficacy, tolerability and safety of solithromycin for the treatment of community-acquired bacterial pneumonia Expert commentary: Recent randomized controlled phase II/III trials have demonstrated the equivalent efficacy of oral and intravenous solithromycin compared with fluoroquinolones in patients with lower mild-to-moderate respiratory infections, and have shown that systemic adverse events are comparable between solithromycin and alternative treatments. However, studies of larger populations which are able to identify infrequent adverse events are now needed to confirm these findings. On balance, current data supports solithromycin as a promising therapy for empirical treatment in adults with community-acquired bacterial pneumonia.

In-vitro activity of solithromycin against anaerobic bacteria from the normal intestinal microbiota

Solithromycin is a novel fluoroketolide with high activity against bacteria associated with community-acquired respiratory tract infections as well as gonorrhea. However, data on the activity of solithromycin against anaerobic bacteria from the normal intestinal microbiota are scarce. In this study, 1024 Gram-positive and Gram-negative anaerobic isolates from the normal intestinal microbiota were analyzed for in-vitro susceptibility against solithromycin and compared to azithromycin, amoxicillin/clavulanic acid, ceftriaxone, metronidazole and levofloxacin by determining the minimum inhibitory concentration (MIC). Solithromycin was active against Bifidobacteria (MIC₅₀, 0.008 mg/L) and Lactobacilli (MIC₅₀, 0.008 mg/L). The MIC₅₀ for Clostridia, Bacteroides, Prevotella and Veillonella were 0.5, 0.5, 0.125 and 0.016 mg/L, respectively. Gram-positive anaerobes were more susceptible to solithromycin as compared to the other antimicrobials tested. The activity of solithromycin against Gram-negative anaerobes was equal or higher as compared to other tested agents.

Ecological Effect of Solithromycin on Normal Human Oropharyngeal and Intestinal Microbiota

Solithromycin is a new fluoroketolide. The purpose of the present study was to investigate the effect of orally administered solithromycin on the human oropharyngeal and intestinal microbiota. Thirteen healthy volunteers (median age, 27.3 years) received oral solithromycin at 800 mg on day 1 followed by 400 mg daily on days 2 to 7. Fecal and saliva samples were collected at baseline and on days 2, 5, 7, 9, 14, and 21 for pharmacokinetic and microbiological analyses. Plasma samples were collected predose on days 2, 5, and 7 as proof of exposure, and solithromycin concentration ranges were 21.9 to 258 ng/ml, 18.0 to 386 ng/ml, and 16.9 to 417 ng/ml, respectively. The solithromycin concentrations in feces were 15.8 to 65.4 mg/kg, 24.5 to 82.7 mg/kg, 21.4 to 82.7 mg/kg, 12.1 to 72.4 mg/kg, 0.2 to 25.6 mg/kg, and 0 to 0.5 mg/kg on days 2, 5, 7, 9, 14, and 21, respectively. The numbers of enterobacteria and enterococci decreased and were normalized on day 14. The numbers of lactobacilli and bifidobacteria decreased from day 2 to day 14 and were normalized on day 21. The clostridia decreased on days 2, 7, and 14 and were normalized on day 21. No Clostridium difficile strains or toxins were detected during the study period. The number of Bacteroides strains was not significantly changed. The solithromycin concentrations in saliva were 0 to 1.2 mg/liter, 0 to 0.5 mg/liter, 0 to 0.5 mg/liter, and 0 to 0.1 mg/liter on days 2, 5, 7, and 9, respectively. The numbers of streptococci decreased on day 2 and were normalized on day 5. The numbers of lactobacilli, prevotellae, fusobacteria, and leptotrichiae decreased from day 2 and were normalized on day 21.

Results from the Solithromycin International Surveillance Program (2014)

Solithromycin, a fourth-generation macrolide (a fluoroketolide with enhanced activity against macrolide-resistant bacteria due to interaction with three ribosomal sites) and the first fluoroketolide, was tested against a 2014 collection of 6,115 isolates, including Streptococcus pneumoniae (1,713 isolates), Haemophilus influenzae (1,308), Moraxella catarrhalis (577), Staphylococcus aureus (1,024), and beta-hemolytic streptococci (1,493), by reference broth microdilution methods. The geographic samples included 2,748 isolates from the United States, 2,536 from Europe, 386 from Latin America, and 445 from the Asia-Pacific region. Solithromycin was observed to be very active against S. pneumoniae (MIC50/90, 0.008/0.12 μg/ml), demonstrating 2-fold greater activity than telithromycin (MIC50/90, 0.015/0.25 μg/ml) and 16- to >256-fold greater activity than azithromycin (MIC50/90, 0.12/>32 μg/ml), with all strains being inhibited at a solithromycin MIC of ≤1 μg/ml. Against H. influenzae, solithromycin showed potency identical to that of telithromycin (MIC50/90, 1/2 μg/ml), and both of these compounds were 2-fold less active than azithromycin (MIC50/90, 0.5/1 μg/ml). All but one of the M. catarrhalis isolates were inhibited by solithromycin at ≤0.25 μg/ml. Solithromycin inhibited 85.3% of S. aureus isolates at ≤1 μg/ml, and its activity was lower against methicillin-resistant (MIC50/90, 0.06/>32 μg/ml) than against methicillin-susceptible (MIC50/90, 0.06/0.06 μg/ml) isolates. Little variation in solithromycin activity was observed by geographic region for the species tested. Solithromycin was very active against beta-hemolytic streptococci (MIC50/90, 0.015/0.03 μg/ml), and all isolates were inhibited at MIC values of ≤0.5 μg/ml. In conclusion, solithromycin demonstrated potent activity against global and contemporary (2014) pathogens that represent the major causes of community-acquired bacterial pneumonia. These data support the continued clinical development of solithromycin for the treatment of this important indication.

Legionella pneumophila: The Paradox of a Highly Sensitive Opportunistic Waterborne Pathogen Able to Persist in the Environment

Legionella pneumophila, the major causative agent of Legionnaires’ disease, is found in freshwater environments in close association with free-living amoebae and multispecies biofilms, leading to persistence, spread, biocide resistance, and elevated virulence of the bacterium. Indeed, legionellosis outbreaks are mainly due to the ability of this bacterium to colonize and persist in water facilities, despite harsh physical and chemical treatments. However, these treatments are not totally efficient and, after a lag period, L. pneumophila may be able to quickly re-colonize these systems. Several natural compounds (biosurfactants, antimicrobial peptides…) with anti-Legionella properties have recently been described in the literature, highlighting their specific activities against this pathogen. In this review, we first consider this hallmark of Legionella to resist killing, in regard to its biofilm or host-associated life style. Then, we focus more accurately on natural anti-Legionella molecules described so far, which could provide new eco-friendly and alternative ways to struggle against this important pathogen in plumbing.

A New, Potent, and Placenta-Permeable Macrolide Antibiotic, Solithromycin, for the Prevention and Treatment of Bacterial Infections in Pregnancy

Intrauterine infection–inflammation is a major cause of early preterm birth and subsequent neonatal mortality and acute or long-term morbidity. Antibiotics can be administered in pregnancy to prevent preterm birth either prophylactically to women at high risk for preterm delivery, or to women with diagnosed intrauterine infection, prelabor rupture of membranes, or in suspected preterm labor. The therapeutic goals of each of these scenarios are different, with different pharmacological considerations, although effective antimicrobial therapy is an essential requirement. An ideal antibiotic for these clinical indications would be (a) one that is easily administered and orally bioactive, (b) has a favorable adverse effect profile (devoid of reproductive toxicity or teratogenicity), (c) is effective against the wide range of microorganisms known to be commonly associated with intra-amniotic infection, (d) provides effective antimicrobial protection within both the fetal and amniotic compartments after maternal delivery, (e) has anti-inflammatory properties, and (f) is effective against antibiotic-resistant microorganisms. Here, we review the evidence from clinical, animal, and ex vivo/in vitro studies that demonstrate that a new macrolide-derived antibiotic – solithromycin – has all of these properties and, hence, may be an ideal antibiotic for the treatment and prevention of intrauterine infection-­related pregnancy complications. While this evidence is extremely encouraging, it is still preliminary. A number of key studies need to be completed before solithromycin’s true potential for use in pregnancy can be ascertained.

Current and emerging Legionella diagnostics for laboratory and outbreak investigations

Legionnaires' disease (LD) is an often severe and potentially fatal form of bacterial pneumonia caused by an extensive list of Legionella species. These ubiquitous freshwater and soil inhabitants cause human respiratory disease when amplified in man-made water or cooling systems and their aerosols expose a susceptible population. Treatment of sporadic cases and rapid control of LD outbreaks benefit from swift diagnosis in concert with discriminatory bacterial typing for immediate epidemiological responses. Traditional culture and serology were instrumental in describing disease incidence early in its history; currently, diagnosis of LD relies almost solely on the urinary antigen test, which captures only the dominant species and serogroup, Legionella pneumophila serogroup 1 (Lp1). This has created a diagnostic "blind spot" for LD caused by non-Lp1 strains. This review focuses on historic, current, and emerging technologies that hold promise for increasing LD diagnostic efficiency and detection rates as part of a coherent testing regimen. The importance of cooperation between epidemiologists and laboratorians for a rapid outbreak response is also illustrated in field investigations conducted by the CDC with state and local authorities. Finally, challenges facing health care professionals, building managers, and the public health community in combating LD are highlighted, and potential solutions are discussed.