Comparison of the in vitro efficacies of moxifloxacin and amoxicillin against Listeria monocytogenes

Clinical and Genomic Characteristics of a Clinical Listeria Monocytogenes ST120 Isolate Recovered from a Pregnant Woman

Background

Maternal-fetal listeriosis, caused by Listeria monocytogenes, is a rare but serious infection. Herein, we report the clinical and genomic characteristics of a clinical L. monocytogenes ST120 isolate recovered from a pregnant woman.

Methods

The clinical symptoms and treatment in pregnant woman were described in detail. Whole genome sequencing (WGS) was performed on the L. monocytogenes isolate SJZ_LM001, and the genomic characterization of the isolate was deeply analyzed.

Results

The clinical symptoms in pregnant women were mainly fever, and the placenta experienced severe inflammation. The pregnant woman was treated with ampicillin for effective anti-infective therapy. Genomic analysis showed that isolate SJZ_LM001 is sequence type (ST) 120, belong to clonal complex (CC)8 and lineage II of L. monocytogenes. Additionally, the isolates SJZ_LM001 harbored a novel plasmid pSJZ_LM001, which carried arsenical resistance genes (arsACD and acr3), and cadmium resistance genes (cadAC). Drug susceptibility testing showed that the isolate SJZ-LM001 was susceptible to ampicillin, meropenem, penicillin, and cotrimoxazole.

Conclusion

This is the first to identify a clinical case of infection in a pregnant woman caused by ST120 L. monocytogenes in China. These findings could benefit our understanding of the genomic characteristics of L. monocytogenes, and the pregnancy-related listeriosis and providing early diagnosis and effective targeted treatment.

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

Treatment of Listeria monocytogenes bacteremia with oral levofloxacin in an immunocompromised patient

A 72-year-old woman presented with fever, malaise, and diarrhea. The patient was conscious, and was negative for meningeal signs on physical exam. Blood tests revealed elevated C-reactive protein (CRP) and white blood cell count with neutrophil dominance. Suspecting a bacterial infection, empirical antimicrobial treatment with oral levofloxacin was initiated after collecting two sets of blood culture. On the 3rd day, the patient's fever resolved. On the 7th day, Listeria monocytogenes bacteremia was diagnosed with both blood cultures turning positive. On the 15th day, the patient's symptoms had improved. We ceased treatment when the CRP level decreased. Listeria monocytogenes is a gram-positive bacterium that causes serious infections in elderly and immunocompromised hosts. Penicillin, ampicillin, amoxicillin, and gentamicin are recommended for the treatment of Listeria infections. It has been reported that new fluoroquinolones may be effective in vitro and in animal models. Although further evidence is required, new fluoroquinolones, especially levofloxacin, may provide an option for the treatment of Listeria infection.

Characterisation of Listeria monocytogenes food-associated isolates to assess environmental fitness and virulence potential

The ability of Listeria monocytogenes isolates to survive within the food production environment (FPE), as well as virulence, varies greatly between strains. There are specific genetic determinants that have been identified which can strongly influence a strains ability to survive in the FPE and/or within human hosts. In this study, we assessed the FPE fitness and virulence potential, including efficacy of selected hygiene or treatment intervention, against 52 L. monocytogenes strains isolated from various food and food environment sources. Phenotypic tests were performed to determine the minimum inhibitory concentration of cadmium chloride and benzalkonium chloride and the sensitivities to five clinically relevant antibiotics. A genomic analysis was also performed to identify resistance genes correlating to the observed phenotypic resistance profiles, along with genetic determinants of interest which may elude to the FPE fitness and virulence potential. A transposon element containing a novel cadmium resistance gene, cadA7, a Tn916 variant insert in the hypervariable Listeria genomic island 1 region and an LGI2 variant were identified. Resistance to cadmium and disinfectants was prevalent among isolates in this study, although no resistance to clinically important antimicrobials was observed. Potential hypervirulent strains containing full length inlA, LIPI-1 and LIPI-3 were also identified in this study. Cumulatively, the results of this study show a vast array of FPE survival and pathogenicity potential among food production-associated isolates, which may be of concern for food processing operators and clinicians regarding L. monocytogenes strains colonising and persisting within the FPE, and subsequently contaminating food products then causing disease in at risk population groups.

Comparison of the in vitro activity of ampicillin and moxifloxacin against Listeria monocytogenes at achievable concentrations in the central nervous system

PURPOSE

The aim of this study was to compare the in vitro activity of ampicillin and moxifloxacin against six isolates selected from 154 invasive clinical isolates of Listeria monocytogenes and evaluate their intra- and extracellular activities with achievable central nervous system concentrations obtained using Monte Carlo simulations with conventional and unconventional dosages.

METHODOLOGY

The MICs and minimal bactericidal concentrations (MBCs) of ampicillin and moxifloxacin were determined by using the broth microdilution method. The intra- and extracellular activities were compared using time-kill curves and inhibition of intracellular growth assays.

RESULTS

The MICs50/90 of ampicillin were 0.125/0.5 mg l-1 and the MBC50/90 was ≥16 mg l-1, while the moxifloxacin MICs50/90 were 0.25/0.5 mg l-1 and the MBC50/90 was 0.5 mg l-1. Ampicillin did not show any extracellular bactericidal activity at 24 h, although bactericidal activity was detected at 48 h. For moxifloxacin, the bactericidal effect was evident after 6 h of incubation. Both antibiotics achieved significant reductions in intracellular inoculum after 1-24 h of incubation; however, moxifloxacin becomes bactericidal more rapidly, producing a much greater reduction in the inoculum in the first hour than ampicillin. There were no differences among the MIC and MBC values of moxifloxacin and ampicillin among the strains belonging to different serotypes and/or epidemic clones. This fact was also found in the intra- and extracellular studies.

CONCLUSION

The results of this study demonstrated the faster bactericidal activity of moxifloxacin at achievable central nervous system concentrations against intra- and extracellular forms of L. monocytogenes in comparison with ampicillin.

Management of adult infectious encephalitis in metropolitan France

Infectious encephalitis is a severe disease leading to a high mortality and morbidity. The most frequent causes include Herpes simplex virus, Varicella Zoster virus, Listeria monocytogenes, and Mycobacterium tuberculosis. Urgent treatment is required (anti-infective therapy and nonspecific supportive care). The aim of this study was to define treatment strategy, empirical and after microbiological documentation at 48hours, through a systematic literature review.

Diversity of Listeria monocytogenes Strains of Clinical and Food Chain Origins in Belgium between 1985 and 2014

Listeriosis is a rare but severe disease, mainly caused by Listeria monocytogenes. This study shows the results of the laboratory-based surveillance of Listeriosis in Belgium over the period 1985-2014. Besides the incidence and some demographic data we present also more detailed microbiological and molecular characteristics of human strains isolated since 2000. The strains from the latter period were compared to food and animal strains from the same period. Our study shows that different food matrices were commonly contaminated with L. monocytogenes presenting the same PFGE profile as in patient's isolates. Since 1985, we observed a significant decrease in incidence of the Materno-Neonatal cases (from 0.15 to 0.04 cases /100,000 inhabitants-year), which is probably to be attributed to active prevention campaigns targeting pregnant women. Despite the strengthening of different control measures by the food industry, the incidence of non-Materno-Neonatal listeriosis increased in Belgium (from 0.3 to 0.7 cases /100,000 inhabitants-year), probably due to the rise of highly susceptible patients in an aging population. This significant increase found in non-Materno-Neonatal cases (slope coefficient 7.42%/year, P<0.0001) can be attributed to significant increase in incidence of isolates belonging to serovars 1/2a (n = 393, slope coefficient 6.62%/year, P<0.0001). Although resistance to antimicrobials is rare among L. monocytogenes isolates, a trend to increasing MIC values is evident with chloramphenicol, amoxicillin, tetracycline and ciprofloxacin. We show that fluoroquinolone resistance is not linked to chromosomal mutations, but caused by a variety of efflux pumps. Our study also shows that huge majority of known underlying pathologies (426 out of 785 cases) were cancers (185/426, 43.1%) and haematological malignancies (75/185, 40.5%). Moreover the risk population is susceptible to low levels of contamination in food stressing the need of prevention campaigns specifically targeting these persons.

Redox-Triggered Release of Moxifloxacin from Mesoporous Silica Nanoparticles Functionalized with Disulfide Snap-Tops Enhances Efficacy Against Pneumonic Tularemia in Mice

Effective and rapid treatment of tularemia is needed to reduce morbidity and mortality of this potentially fatal infectious disease. The etiologic agent, Francisella tularensis, is a facultative intracellular bacterial pathogen which infects and multiplies to high numbers in macrophages. Nanotherapeutics are particularly promising for treatment of infectious diseases caused by intracellular pathogens, whose primary host cells are macrophages, because nanoparticles preferentially target and are avidly internalized by macrophages. A mesoporous silica nanoparticle (MSN) has been developed functionalized with disulfide snap-tops that has high drug loading and selectively releases drug intracellularly in response to the redox potential. These nanoparticles, when loaded with Hoechst fluorescent dye, release their cargo exclusively intracellularly and stain the nuclei of macrophages. The MSNs loaded with moxifloxacin kill F. tularensis in macrophages in a dose-dependent fashion. In a mouse model of lethal pneumonic tularemia, MSNs loaded with moxifloxacin prevent weight loss, illness, and death, markedly reduce the burden of F. tularensis in the lung, liver, and spleen, and are significantly more efficacious than an equivalent amount of free drug. An important proof-of-principle for the potential therapeutic use of a novel nanoparticle drug delivery platform for the treatment of infectious diseases is provided.

Structure of the bacterial cell division determinant GpsB and its interaction with penicillin-binding proteins

Each bacterium has to co-ordinate its growth with division to ensure genetic stability of the population. Consequently, cell division and growth are tightly regulated phenomena, albeit different bacteria utilise one of several alternative regulatory mechanisms to maintain control. Here we consider GpsB, which is linked to cell growth and division in Gram-positive bacteria. ΔgpsB mutants of the human pathogen Listeria monocytogenes show severe lysis, division and growth defects due to distortions of cell wall biosynthesis. Consistent with this premise, GpsB interacts both in vitro and in vivo with the major bi-functional penicillin-binding protein. We solved the crystal structure of GpsB and the interaction interfaces in both proteins are identified and validated. The inactivation of gpsB results in strongly attenuated virulence in animal experiments, comparable in degree to classical listerial virulence factor mutants. Therefore, GpsB is essential for in vitro and in vivo growth of a highly virulent food-borne pathogen, suggesting that GpsB could be a target for the future design of novel antibacterials.

Discrete and overlapping functions of peptidoglycan synthases in growth, cell division and virulence of Listeria monocytogenes

Upon ingestion of contaminated food, Listeria monocytogenes can cause serious infections in humans that are normally treated with β-lactam antibiotics. These target Listeria's five high molecular weight penicillin-binding proteins (HMW PBPs), which are required for peptidoglycan biosynthesis. The two bi-functional class A HMW PBPs PBP A1 and PBP A2 have transglycosylase and transpeptidase domains catalyzing glycan chain polymerization and peptide cross-linking, respectively, whereas the three class B HMW PBPs B1, B2 and B3 are monofunctional transpeptidases. The precise roles of these PBPs in the cell cycle are unknown. Here we show that green fluorescent protein (GFP)-PBP fusions localized either at the septum, the lateral wall or both, suggesting distinct and overlapping functions. Genetic data confirmed this view: PBP A1 and PBP A2 could not be inactivated simultaneously, and a conditional double mutant strain is largely inducer dependent. PBP B1 is required for rod-shape and PBP B2 for cross-wall biosynthesis and viability, whereas PBP B3 is dispensable for growth and cell division. PBP B1 depletion dramatically increased β-lactam susceptibilities and stimulated spontaneous autolysis but had no effect on peptidoglycan cross-linkage. Our in vitro virulence assays indicated that the complete set of all HMW PBPs is required for maximal virulence.

High-performance liquid chromatography assay for moxifloxacin in brain tissue and plasma: validation in a pharmacokinetic study in a murine model of cerebral listeriosis

Moxifloxacin is a broad-spectrum antibacterial 8-methoxy-fluoroquinolone. In order to evaluate the pharmacokinetic properties of moxifloxacin in mouse plasma and brain tissue, we developed a high-performance liquid chromatography (HPLC) method. This study was based on single-drug delivery, intravenously dosed in a central listeriosis murine model. The method employed a reversed-phase Lichrospher RP-18 with a precolumn (250 × 4.6 mm) and a mobile phase composed of a mixture of acetonitrile, methanol, and citric buffer (pH = 3.5) with sodium dodecyl sulfate and tetrabutylammonium bromide. Fluorescence detection was performed at an excitation wavelength of 290 nm and an emission wavelength of 550 nm. The relative standard deviation of intra- and inter-day assays was <10%. This validated method led to a short retention time (8.0 min) for moxifloxacin. The standard curves were linear from 5-250 μg/L in plasma and from 0.1-2.5 μg/g of brain tissue. The limits of quantification were 5 μg/L in plasma and 0.1 μg/g in brain tissue. The method enabled the detection of systemic antimicrobial in plasma and in CNS in Listeria-infected mice. Injected moxifloxacin passed through the encephalic barrier within a 30 to 60 min after injection time frame. Moxifloxacin pharmacokinetics are modeled in an infected model compared to control mice.

Impact of a low-oxygen environment on the efficacy of antimicrobials against intracellular Chlamydia trachomatis

Emergence of chronic inflammation in the urogenital tract induced by Chlamydia trachomatis infection in females is a long-standing concern. To avoid the severe sequelae of C. trachomatis infection, such as pelvic inflammatory diseases (PID), ectopic pregnancies, and tubal infertility, antibiotic strategies aim to eradicate the pathogen even in asymptomatic and uncomplicated infections. Although first-line antimicrobials have proven successful for the treatment of C. trachomatis infection, treatment failures have been observed in a notable number of cases. Due to the obligate intracellular growth of C. trachomatis, reliable antimicrobial susceptibility assays have to consider environmental conditions and host cell-specific factors. Oxygen concentrations in the female urogenital tract are physiologically low and decrease further during an inflammatory process. We compared MIC testing and time-kill curves (TKC) for doxycycline, azithromycin, rifampin, and moxifloxacin under hypoxia (2% O2) and normoxia (20% O2). While low oxygen availability only moderately decreased the antichlamydial activity of azithromycin in conventional MIC testing (0.08 μg/ml versus 0.04 μg/ml; P<0.05), TKC analyses revealed profound divergences for antibiotic efficacies between the two conditions. Thus, C. trachomatis was significantly less rapidly killed by doxycycline and azithromycin under hypoxia, whereas the efficacies of moxifloxacin and rifampin remained unaffected using concentrations at therapeutic serum levels. Chemical inhibition of multidrug resistance protein 1 (MDR-1), but not multidrug resistance-associated protein 1 (MRP-1), restored doxycycline activity against intracellular C. trachomatis under hypoxia. We suggest careful consideration of tissue-specific characteristics, including oxygen availability, when testing antimicrobial activities of antibiotics against intracellular bacteria.

Prevalence and characterization of antimicrobial resistance of foodborne Listeria monocytogenes isolates in Hebei province of Northern China, 2005-2007

A total of 2177 food samples collected from nine cities in northern China during 2005 to 2007 were screened for the presence of Listeria monocytogenes. All L. monocytogenes isolates were subjected to serotyping, antimicrobial susceptibility, pulsed-field gel electrophoresis (PFGE), as well as PCR screening to identify genes responsible for tetracycline resistance [tet(L), tet(M), tet(K), tet(S) and tet(B)], transposon Tn916, and class 1 integron. Contamination with L. monocytogenes was detected in 4.13% (90/2177) of the total samples representing various food products. The pathogen was mainly isolated from frozen food made of wheat flour or rice products (26/252, 10.32%) and raw meat products (46/733, 6.28%). Besides, 3.31% (10/302) of cooked meat, 1.17% (4/343) of seafood, 0.98% (2/204) of non-fermented bean products and 0.62% (2/323) of vegetables samples were contaminated by this bacterium. The L. monocytogenes isolates belonged to five serotypes (1/2a, 1/2b, 1/2c, 4b, and 3a), with serotype 1/2a being dominant (48.88%). Antimicrobial resistance was most frequently observed for ciprofloxacin (17.8%), tetracycline (15.6%) and streptomycin (12.2%). Overall, resistance was observed against 14 out of 18 antimicrobials tested while multiple resistances occurred among 18.9% (17/90) isolates. Interestingly, two isolates were resistant to more than five antimicrobials. Among 14 tetracycline-resistant isolates, 13 carried tet(M) gene including nine possessing Tn916, and one harbored tet(S) gene. PFGE analysis revealed genetic heterogeneity among individual serotypes as well as scattered occurrence of some genotypes without any clear-cut correlation to source or food type. The widespread distribution of epidemiologically important serotypes (1/2a, 1/2b and 4b) of L. monocytogenes, and their resistance to commonly used antibiotics indicate a potential public health risk. Our data also indicate that L. monocytogenes could act as a reservoir of mobile tet genes along the food chain.

[Listeriosis in adults - case reports and review of the literature]

Listeriosis is a rare disease with increasing incidence occurring mainly in elderly people and patients suffering from underlying diseases and immunosuppressive therapy. On the basis of three case reports and a review of the literature the most important aspects of epidemiology, pathogenesis, clinical manifestations, diagnostics and therapy of listeriosis are discussed.

Listeriosis: a resurgent foodborne infection

Listeria monocytogenes is the causative agent of human listeriosis, a potentially fatal foodborne infection. Clinical manifestations range from febrile gastroenteritis to more severe invasive forms, including sepsis, meningitis, rhombencephalitis, perinatal infections, and abortions. In recent years, an increasing rate of listeriosis has been reported in several European countries. These increases primarily reflect a higher rate of bacteraemic listeriosis in those > or =65 years of age, and are not otherwise correlated with geography, gender, ethnicity, socioeconomic factors or infectious serotypes. In the late 1980s, an upsurge in listeriosis rates was due to the contamination of a small number of food products. However, a restricted range of strains was responsible for most of the additional cases at that time, and no evidence exists for such a pattern since 2001. From a clinical perspective, the importance of isolating the pathogen as a prerequisite for an accurate epidemiological investigation and ultimately stopping transmission cannot be overemphasized.

The use of Listeria monocytogenes as a DNA delivery vector for cancer gene therapy

Listeria monocytogenes is an intracellular pathogen that lyses the phagosomal vacuole of infected cells, proliferates in the host cell cytoplasm and can actively enter adjacent cells. The pathogen is therefore well suited to exploitation as a vector for the delivery of DNA to target cells as the lifecycle favors cellular targeting with vector amplification and the potential for cell-to-cell spread. We have recently demonstrated DNA transfer by L. monocytogenes in growing tumors in murine models. Our approach exploited an ampicillin sensitive stain of L. monocytogenes which can be lysed through systemic administration of ampicillin to facilitate release of plasmid DNA for expression by infected mammalian cells. Here, we discuss the implications of this technology and the potential for future improvements of the system.

Rapid eradication of Listeria monocytogenes by moxifloxacin in a murine model of central nervous system listeriosis

Listeriosis is a rare but life-threatening infection. A favorable outcome is greatly aided by early administration of antibiotics with rapid bactericidal activity against Listeria monocytogenes. Moxifloxacin, a new-generation fluoroquinolone with extended activity against gram-positive bacteria, has proved its effectiveness in vitro against intracellular reservoirs of bacteria. The efficacies of moxifloxacin and amoxicillin were compared in vivo by survival curve assays and by studying the kinetics of bacterial growth in blood and organs in a murine model of central nervous system (CNS) listeriosis. We combined pharmacokinetic and pharmacodynamic approaches to correlate the observed efficacy in vivo with plasma and tissue moxifloxacin concentrations. Death was significantly delayed for animals treated with a single dose of moxifloxacin compared to a single dose of amoxicillin. We observed rapid bacterial clearance from blood and organs of animals treated with moxifloxacin. The decrease in the bacterial counts in blood and brain correlated with plasma and cerebral concentrations of antibiotic. Moxifloxacin peaked in the brain at 1.92 +/- 0.32 microg/g 1 hour after intraperitoneal injection. This suggests that moxifloxacin rapidly crosses the blood-brain barrier and diffuses into the cerebral parenchyma. Moreover, no resistant strains were selected during in vivo experiments. Our results indicate that moxifloxacin combines useful pharmacokinetic properties and rapid bactericidal activity and that it may be a valuable alternative for the treatment of CNS listeriosis.

Cooperation between prokaryotic (Lde) and eukaryotic (MRP) efflux transporters in J774 macrophages infected with Listeria monocytogenes: studies with ciprofloxacin and moxifloxacin

Antibiotic efflux is observed in both eukaryotic and prokaryotic cells, modulating accumulation and resistance. The present study examines whether eukaryotic and prokaryotic fluoroquinolone transporters can cooperate in the context of an intracellular infection. We have used (i) J774 macrophages (comparing a ciprofloxacin-resistant cell line overexpressing an MRP-like transporter with wild-type cells with basal expression), (ii) Listeria monocytogenes (comparing a clinical isolate [CLIP21369] displaying ciprofloxacin resistance associated with overexpression of the Lde efflux system with a wild-type strain [EGD]), (iii) ciprofloxacin (substrate of both Lde and MRP) and moxifloxacin (nonsubstrate), and (iv) probenecid and reserpine (preferential inhibitors of MRP and Lde, respectively). The ciprofloxacin MICs for EGD were unaffected by reserpine, while those for CLIP21369 were decreased approximately fourfold (and made similar to those of EGD). Neither probenecid nor reserpine affected the moxifloxacin MICs against EGD or CLIP21369. In dose-response studies (0.01x to 100x MIC) in broth, reserpine fully restored the susceptibility of CLIP21369 to ciprofloxacin (no effect on EGD) but did not influence the activity of moxifloxacin. In studies with intracellular bacteria, reserpine, probenecid, and their combination increased the activity of ciprofloxacin in wild-type and ciprofloxacin-resistant macrophages in parallel with an increase in ciprofloxacin accumulation in macrophages for EGD and an increase in accumulation and decrease in MIC (in broth) for CLIP21369. Moxifloxacin accumulation and intracellular activity were consistently not affected by the inhibitors. A bacterial efflux pump may thus actively cooperate with a eukaryotic efflux transporter to reduce the activity of a common substrate (ciprofloxacin) toward an intracellular bacterial target.