Optimized decision algorithm for the microbiological diagnosis of osteoarticular infections in adults using synovial fluid samples: a prospective study in two French hospitals including 423 samples of synovial fluid

No consensus exists about the techniques to use for microbiological diagnosis of bone and joint infections (BJIs). The objective herein was to define an algorithm to optimize BJI diagnosis in adults using various bacteriological methods on synovial fluid samples. This prospective multi-center study included 423 synovial fluids collected from adult patients with suspected BJIs. Culture (using five solid media, an enrichment broth, and blood culture bottles), universal 16S rRNA PCR followed by Sanger sequencing, and seven specific bacterial PCRs were systematically performed. Combinations of methods were compared to arrive at the optimized algorithm. Among 423 synovial fluids, 242 infections were diagnosed (57.2 %): 213 mono- and 29 poly-microbial for a total of 284 bacteria (staphylococci at 54.6 %, streptococci-enterococci at 16.5 %, Gram-negative bacilli at 15.5 %, anaerobic species at 8.8 %). Comparing culture techniques, blood culture bottles had the highest sensitivity (67.6 % for pediatric and 63.9 % for anaerobic bottles) but are not sufficient alone and require being combined with solid media. The 16S rDNA PCR detected only 52.3 % of the bacteria, whereas specific PCRs had a higher sensitivity (Staphylococcus spp. at 66.2 %, S. aureus at 85.2 %, Streptococcus spp. at 91.2 %). Based on these results, an algorithm was proposed associating three solid media; inoculation into blood culture bottles; and 16S, Staphylococcus spp., and Streptococcus spp. PCRs, which would have detected 90.5 % of bacteria in the present cohort versus 79.2 % using all culture techniques on synovial fluid. This prospective study shows that a combination of culture and molecular methods on synovial fluids allows the optimization of bacterial detection.

Tularemia treatment: experimental and clinical data

Tularemia is a zoonosis caused by the Gram negative, facultative intracellular bacterium Francisella tularensis. This disease has multiple clinical presentations according to the route of infection, the virulence of the infecting bacterial strain, and the underlying medical condition of infected persons. Systemic infections (e.g., pneumonic and typhoidal form) and complications are rare but may be life threatening. Most people suffer from local infection (e.g., skin ulcer, conjunctivitis, or pharyngitis) with regional lymphadenopathy, which evolve to suppuration in about 30% of patients and a chronic course of infection. Current treatment recommendations have been established to manage acute infections in the context of a biological threat and do not consider the great variability of clinical situations. This review summarizes literature data on antibiotic efficacy against F. tularensis in vitro, in animal models, and in humans. Empirical treatment with beta-lactams, most macrolides, or anti-tuberculosis agents is usually ineffective. The aminoglycosides gentamicin and streptomycin remain the gold standard for severe infections, and the fluoroquinolones and doxycycline for infections of mild severity, although current data indicate the former are usually more effective. However, the antibiotic treatments reported in the literature are highly variable in their composition and duration depending on the clinical manifestations, the age and health status of the patient, the presence of complications, and the evolution of the disease. Many patients received several antibiotics in combination or successively. Whatever the antibiotic treatment administered, variable but high rates of treatment failures and relapses are still observed, especially in patients treated more then 2-3 weeks after disease onset. In these patients, surgical treatment is often necessary for cure, including drainage or removal of suppurative lymph nodes or other infectious foci. It is currently difficult to establish therapeutic recommendations, particularly due to lack of comparative randomized studies. However, we have attempted to summarize current knowledge through proposals for improving tularemia treatment which will have to be discussed by a group of experts. A major factor in improving the prognosis of patients with tularemia is the early administration of appropriate treatment, which requires better medical knowledge and diagnostic strategy of this disease.

Pathogenicity and virulence of Francisella tularensis

Tularaemia is a zoonotic disease caused by the Gram-negative bacterium, Francisella tularensis. Depending on its entry route into the organism, F. tularensis causes different diseases, ranging from life-threatening pneumonia to less severe ulceroglandular tularaemia. Various strains with different geographical distributions exhibit different levels of virulence. F. tularensis is an intracellular bacterium that replicates primarily in the cytosol of the phagocytes. The main virulence attribute of F. tularensis is the type 6 secretion system (T6SS) and its effectors that promote escape from the phagosome. In addition, F. tularensis has evolved a peculiar envelope that allows it to escape detection by the immune system. In this review, we cover tularaemia, different Francisella strains, and their pathogenicity. We particularly emphasize the intracellular life cycle, associated virulence factors, and metabolic adaptations. Finally, we present how F. tularensis largely escapes immune detection to be one of the most infectious and lethal bacterial pathogens.

Diagnostic performances and therapeutic impact of the Unyvero Implant and Tissue Infection multiplex PCR in periprosthetic joint infections

Aim: We evaluated the diagnostic performances of Unyvero Implant and Tissue Infection multiplex PCR (mPCR) (Curetis) and the clinical impact of this PCR on therapeutic decisions. Materials & methods: A mPCR was performed on 33 joint fluids in addition to standard culture. A group of experts analyzed a posteriori the impact of the mPCR in the patient management. Results: The rate of concordance with culture was 74% (20/27). The sensitivity of the PCR was 59% and the specificity 90%. Clinicians would have started an appropriate treatment sooner for six patients (from 2 to 22 days earlier). Conclusion: The PCR would improve the management of 22% of the patients. For other patients, mPCR results have to be completed with the culture.

Case Studies and Literature Review of Francisella tularensis-Related Prosthetic Joint Infection

Tularemia is a zoonotic infection caused by Francisella tularensis. Its most typical manifestations in humans are ulceroglandular and glandular; infections in prosthetic joints are rare. We report 3 cases of F. tularensis subspecies holarctica-related prosthetic joint infection that occurred in France during 2016-2019. We also reviewed relevant literature and found only 5 other cases of Francisella-related prosthetic joint infections worldwide, which we summarized. Among those 8 patients, clinical symptoms appeared 7 days to 19 years after the joint placement and were nonspecific to tularemia. Although positive cultures are typically obtained in only 10% of tularemia cases, strains grew in all 8 of the patients. F. tularensis was initially identified in 2 patients by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; molecular methods were used for 6 patients. Surgical treatment in conjunction with long-term antimicrobial treatment resulted in favorable outcomes; no relapses were seen after 6 months of follow-up.

Ulceroglandular Infection and Bacteremia Caused by Francisella salimarina in Immunocompromised Patient, France

Although Francisella tularensis is a well-known, highly virulent bacterium that causes tularemia in humans, other Francisella species have been associated with sporadic human infections. We describe a human cutaneous infection with bacteremia caused by F. salimarina, a Francisella species recently identified from seawater and fishes, in an immunocompromised patient in France.

Reuse of medical face masks in domestic and community settings without sacrificing safety: Ecological and economical lessons from the Covid-19 pandemic

The need for personal protective equipment increased exponentially in response to the Covid-19 pandemic. To cope with the mask shortage during springtime 2020, a French consortium was created to find ways to reuse medical and respiratory masks in healthcare departments. The consortium addressed the complex context of the balance between cleaning medical masks in a way that maintains their safety and functionality for reuse, with the environmental advantage to manage medical disposable waste despite the current mask designation as single-use by the regulatory frameworks. We report a Workflow that provides a quantitative basis to determine the safety and efficacy of a medical mask that is decontaminated for reuse. The type IIR polypropylene medical masks can be washed up to 10 times, washed 5 times and autoclaved 5 times, or washed then sterilized with radiations or ethylene oxide, without any degradation of their filtration or breathability properties. There is loss of the anti-projection properties. The Workflow rendered the medical masks to comply to the AFNOR S76-001 standard as "type 1 non-sanitory usage masks". This qualification gives a legal status to the Workflow-treated masks and allows recommendation for the reuse of washed medical masks by the general population, with the significant public health advantage of providing better protection than cloth-tissue masks. Additionally, such a legal status provides a basis to perform a clinical trial to test the masks in real conditions, with full compliance with EN 14683 norm, for collective reuse. The rational reuse of medical mask and their end-of-life management is critical, particularly in pandemic periods when decisive turns can be taken. The reuse of masks in the general population, in industries, or in hospitals (but not for surgery) has significant advantages for the management of waste without degrading the safety of individuals wearing reused masks.

Amoebae can promote the survival of Francisella species in the aquatic environment

Francisella tularensis, a tier 1 select agent, is the causative bacterium of tularemia, a zoonosis with a large animal reservoir. However, F. tularensis, like many other Francisella species, is assumed to have an aquatic reservoir. The mechanisms of Francisella species persistence in surface water remain poorly characterized. In this study, we deeply investigated the long-term interactions of the tularemia agent F. tularensis subsp. holarctica, F. novicida or F. philomiragia with amoebae of the Acanthamoeba species. In amoeba plate screening tests, all the Francisella species tested resisted the attack by amoebae. In in vitro infection models, intra-amoebic growth of Francisella varied according to the involved bacterial species and strains, but also the amoeba culture medium used. In co-culture models, the amoebae favoured Francisella survival over 16 days, which was likely dependent on direct contact between bacteria and amoebae for F. novicida and on amoeba-excreted compounds for F. novicida and for F. tularensis. In a spring water co-culture model, amoebae again enhanced F. novicida survival and preserved bacterial morphology. Overall, our results demonstrate that amoebae likely promote Francisella survival in aquatic environments, including the tularemia agent F. tularensis. However, bacteria-amoebae interactions are complex and depend on the Francisella species considered.

Slowly or Nonresolving Legionnaires' Disease: Case Series and Literature Review

BACKGROUND

Rarely, Legionnaires' disease (LD) can progress into a slowly or nonresolving form.

METHODS

A nationwide retrospective study was conducted by the French National Reference Center for Legionella (2013-2017) including cases of slowly or nonresolving LD defined as persistent clinical symptoms, computed tomography (CT) scan abnormalities, and Legionella detection in lower respiratory tract specimens by culture and/or real-time (RT) polymerase chain reaction (PCR) >30 days after symptom onset.

RESULTS

Twelve cases of community-acquired slowly or nonresolving LD were identified among 1686 cases of culture-positive LD. Median (interquartile range [IQR]) age was 63 (29-82) years. Ten (83.3%) patients had ≥1 immunosuppressive factor. Clinically, 9 patients transiently recovered before further deterioration (median [IQR] symptom-free interval, 30 [18-55] days), 3 patients had uniformly persistent symptoms (median [IQR] time, 48 [41.5-54] days). Two patients had >2 recurrences. CT scan imagery found lung abscess in 5 (41.6%) cases. Slowly or nonresolving LD was diagnosed on positive Legionella cultures (n = 10, 83.3%) at 49.5 (IQR, 33.7-79) days. Two cases were documented through positive Legionella RT PCR at 52 and 53 days (cycle threshold detection of 21.5 and 33.7, respectively). No genomic microevolution and no Legionella resistance to antibiotics were detected. The median (IQR) duration of treatment was 46.5 (21-92.5) days. Two empyema cases required thoracic surgery. At a median (IQR) follow-up of 26 (14-41.5) months, LD-attributable mortality was 16.6% (n = 2).

CONCLUSIONS

Slowly or nonresolving LD may occur in immunocompromised patients, possibly leading to lung abscess and empyema.

Assessment of Respiratory Bacterial Coinfections Among Severe Acute Respiratory Syndrome Coronavirus 2-Positive Patients Hospitalized in Intensive Care Units Using Conventional Culture and BioFire, FilmArray Pneumonia Panel Plus Assay

Background

Approximately 15% of patients infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) present with severe forms of the disease and require hospitalization in intensive care units, which has been associated with high mortality rates. The prevalence of bacterial infections in these patients is not well established, and more data are needed to guide empiric antibiotic therapy and improve patient outcomes.

Methods

In this prospective multicenter study, we assessed bacterial coinfections identified in culture from 99 French patients infected by SARS-Cov-2 and hospitalized in intensive care units. We concomitantly evaluated an innovative molecular diagnostic technology technique, the BioFire, FilmArray Pneumonia Panel plus (FA-pneumo) assay, to identify these coinfections at an early stage, and its concordance with conventional culture.

Results

We showed that a bacterial coinfection was detected in 15% of patients based on conventional culture. Staphylococcus aureus and Haemophilus influenzae were the most prevalent pathogens. The sensitivity of FA-pneumo compared with culture was 100%. In contrast, the specificity varied between 88.4% and 100% according to the pathogen, and our results highlighted that 60.5% of bacterial targets reported using this assay were not recovered by culture; 76.9% of discordant results corresponded to bacteria belonging to commensal oral flora and/or reported with ≤10⁵ copies/mL bacterial nucleic acids.

Conclusions

Based on its excellent sensitivity, the FA-pneumo assay is useful to rule out bacterial coinfections in the context of severe SARS-CoV-2 infection and avoid the inappropriate prescription of antibiotics. However, positive tests should be interpreted carefully, taking into consideration deoxyribonucleic acid bacterial load and all clinical and biological signs.

Risk factors for Staphylococcus aureus surgical site infections after orthopaedic and trauma surgery in a French university hospital

BACKGROUND

Surgical site infections (SSI) after orthopaedic surgery are responsible for reduced quality of life, increased length of hospital stay and costs. The most commonly identified organism is Staphylococcus aureus but risk factors for S. aureus SSI are not well-known. The aim of this study was to evaluate the incidence rate trend of S. aureus SSI over the years and risk factors of these infections in a French University Hospital.

METHODS

SSI rates were expressed as cumulative incidence rates per year. A case-control study nested within a prospective cohort of patients undergoing orthopaedic or trauma surgery from January 1st^, 2012 to April 30th^, 2015 was performed. Cases were patients with S. aureus SSI; controls were patients without SSI. Risk factors of S. aureus SSI were identified by univariate and multivariable analysis.

RESULTS

Of 7438 interventions, 50 (0.7%) S. aureus SSI were identified, without significant increase by years. A total of 46 S. aureus SSI was matched to 91 controls. Risk factors for S. aureus SSI were smoking (odds-ratio (OR) = 8.4, 95%CI 1.2-59.6) and National Nosocomial Infections Surveillance System score (NNISS) ≥1 (OR = 5.8, 95%CI 1.8-19.1). Having 1 or 2 preoperative antiseptic showers (OR = 0.3, 95%CI 0.1-0.7) was a protective factor.

CONCLUSION

The rate of S. aureus SSI is not negligible after orthopaedic and trauma surgery. It seems imperative to strengthen smoking cessation recommendations, and to recall the importance of preoperative antiseptic showers. Systematic screening and decolonization for S. aureus carriage before orthopaedic and trauma surgery could be a means to prevent these infections.

Optimized MALDI TOF Mass Spectrometry Identification of Francisella tularensis Subsp. holarctica

Francisella tularensis is a tier 1 agent causing the zoonosis tularemia. This highly infectious Gram-negative bacterium is occasionally isolated from human samples (especially blood samples) in routine clinical microbiology laboratories. A rapid and accurate method for identifying this pathogen is needed in order to optimize the infected patient’s healthcare management and prevent contamination of the laboratory personnel. MALDI TOF mass spectrometry has become the gold standard for the rapid identification of most human pathogens. However, F. tularensis identification using such technology and commercially available databases is currently considered unreliable. Real-time PCR-based methods for rapid detection and accurate identification of F. tularensis are not available in many laboratories. As a national reference center for tularemia, we developed a MALDI TOF database allowing accurate identification of the species F. tularensis and its differentiation from the closely related neighbor species F. tularensis subsp. novicida and F. philomiragia. The sensitivity and specificity of this database were validated by testing 71 F. tularensis strains and 165 strains from 63 species not belonging to the Francisella genus. We obtained accurate identification at the species level and differentiation of all the tested bacterial strains. In particular, F. tularensis could be accurately differentiated from other small Gram-negative bacilli occasionally isolated from human samples, including species of the HACEK group and Brucella melitensis.

Specific PCR and Quantitative Real-Time PCR in Ocular Samples from Acute and Delayed-Onset Postoperative Endophthalmitis

PURPOSE

Rapid identification of virulent pathogens is essential to strengthen the therapeutic strategy of acute endophthalmitis.

OBJECTIVES

This study sought to compare the contribution of a combination of polymerase chain reaction (PCR)-based tests to culture methods, in patients with postoperative endophthalmitis.

DESIGN

Prospective multicenter study diagnostic evaluation.

METHODS

Setting: university referral centers.

PARTICIPANTS

153 consecutive patients presenting with acute or delayed-onset postoperative endophthalmitis, between 2008 and 2015. There were a total of 284 aqueous humor (AH) and/or vitreous fluid (VF) samples. Outcomes and measurements: microbiological tests of intraocular samples included bacterial culturing of pediatric blood culture bottles; 16SrDNA amplification and sequencing (panbacterial PCR) for detection and identification of all bacterial species; real-time PCR (qPCR) assays targeting the femA or lytA gene for detection of Staphylococcus aureus (S. aureus) or Streptococcus pneumoniae (S. pneumoniae), respectively; and a qPCR assay targeting the tuf gene for detection and quantification of Staphylococcus epidermidis (S. epidermidis).

RESULTS

At the time of admission, the rate of detection of microorganisms by PCR-based tests was not significantly different than that by culturing (38% versus 30% in AH samples [n = 69]; 66% versus 63% in VF samples [n = 82], respectively). In contrast, after 1 intravitreal injection (IVI) of antibiotics, the identification rate by PCR-based tests was higher than that in VF by culturing (62% vs 48%, respectively; n = 94; P = 0.05). Bacteria were identified in 70% of patients, with a predominance of Gram-positive bacteria (93%). Specific qPCR tests targeting S. aureus and S. pneumoniae did not provide additional diagnoses but provided earlier results. The S. epidermidis load in vitreous at the time of patients' admission was higher in cases of final visual acuity (VA) of <20/40 (127,118 ± 125,848 DNA copies/mL) in patients with a VA of ≥20/40 (40350,000 ± 46,912 DNA copies/mL; P = 0.09). No significant changes in S. epidermidis load was found after one IVI.

CONCLUSIONS

Patients with acute or delayed-onset endophthalmitis should benefit from microbiological identification in vitreous samples by combined analysis using bacterial cultures in pediatric blood culture bottles and panbacterial PCR. The last test was more effective than cultures in vitreous samples collected after an IVI of antibiotics. The qPCR tests targeting S. aureus and S. pneumoniae gave earlier results than culture and panbacterial PCR but did not provide additional diagnoses. As for S. epidermidis infections, determination of bacterial load using the qPCR test targeting the tuf gene could help evaluation of the visual prognosis of patients. Its role in the follow-up of patients after antibiotic treatment needs further investigation.

Francisella tularensis: FupA mutation contributes to fluoroquinolone resistance by increasing vesicle secretion and biofilm formation

Francisella tularensis is the causative agent in tularemia for which the high prevalence of treatment failure and relapse is a major concern. Directed-evolution experiments revealed that acquisition of fluoroquinolone (FQ) resistance was linked to factors in addition to mutations in DNA gyrase. Here, using F. tularensis live vaccine strain (LVS) as a model, we demonstrated that FupA/B (Fer-Utilization Protein) expression is linked to FQ susceptibility, and that the virulent strain F. tularensis subsp. tularensis SCHU S4 deleted for the homologous FupA protein exhibited even higher FQ resistance. In addition to an increased FQ minimal inhibitory concentration, LVSΔfupA/B displayed tolerance toward bactericidal compounds including ciprofloxacin and gentamicin. Interestingly, the FupA/B deletion was found to promote increased secretion of outer membrane vesicles (OMVs). Mass spectrometry-based quantitative proteomic characterization of vesicles from LVS and LVS∆fupA/B identified 801 proteins, including a subset of 23 proteins exhibiting differential abundance between both strains which may therefore contribute to the reduced antibiotic susceptibility of the FupA/B-deleted strain. We also demonstrated that OMVs are key structural elements of LVSΔfupA/B biofilms providing protection against FQ. These results provide a new basis for understanding and tackling antibiotic resistance and/or persistence of Francisella and other pathogenic members of the Thiotrichales class.

Tularemia as a waterborne disease: a review

Francisella tularensis is a Gram-negative, intracellular bacterium causing the zoonosis tularemia. This highly infectious microorganism is considered a potential biological threat agent. Humans are usually infected through direct contact with the animal reservoir and tick bites. However, tularemia cases also occur after contact with a contaminated hydro-telluric environment. Water-borne tularemia outbreaks and sporadic cases have occurred worldwide in the last decades, with specific clinical and epidemiological traits. These infections represent a major public health and military challenge. Human contaminations have occurred through consumption or use of F. tularensis-contaminated water, and various aquatic activities such as swimming, canyoning and fishing. In addition, in Sweden and Finland, mosquitoes are primary vectors of tularemia due to infection of mosquito larvae in contaminated aquatic environments. The mechanisms of F. tularensis survival in water may include the formation of biofilms, interactions with free-living amoebae, and the transition to a 'viable but nonculturable' state, but the relative contribution of these possible mechanisms remains unknown. Many new aquatic species of Francisella have been characterized in recent years. F. tularensis likely shares with these species an ability of long-term survival in the aquatic environment, which has to be considered in terms of tularemia surveillance and control.

Genetic and Phenotypic Traits of Staphylococcus Epidermidis Strains Causing Postcataract Endophthalmitis Compared to Commensal Conjunctival Flora

PURPOSE

The aim of this study was to compare the virulence and antibiotic resistance traits of Staphylococcus epidermidis strains causing acute postcataract endophthalmitis to those isolated from the conjunctiva of uninfected control patients.

DESIGN

Case-control study.

METHODS

We isolated an S epidermidis strain from each of the 22 endophthalmitis patients, and from 43 of the 72 controls. Species identification was confirmed using both Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and tuf gene amplification and sequencing. Antibiotic susceptibilities were evaluated using the AST-P631 card and the Vitek II automated system. The S epidermidis strains were tested for the presence of 7 virulence genes (icaA, icaB, icaC, icaD, atlE, aap, and capA), the insertion sequence IS256, and the mecA gene.

RESULTS

The S epidermidis strains from the endophthalmitis patients displayed higher prevalence rates for aap, atlE, and mecA gene carriage compared to those of the control group (77% vs 42%, P = .007; 100% vs 79%, P = .02; and 54% vs 11%, P < .001, respectively). They also harbored the combination of the mecA and icaA genes more frequently compared to the control group (13% vs 2%, P = .01). They were significantly more resistant than control strains to methicillin, fluoroquinolones, and the aminoglycosides.

CONCLUSIONS

A higher capacity of adhesion to the intraocular lens and formation of biofilms as well as greater resistance to antibiotics were found in S epidermidis strains causing postcataract endophthalmitis. The usefulness of such virulence and antibiotic resistance markers warrants further evaluation for prevention, treatment, and prognostic evaluation of S epidermidis endophthalmitis.

Strain-specific estimation of epidemic success provides insights into the transmission dynamics of tuberculosis

The transmission dynamics of tuberculosis involves complex interactions of socio-economic and, possibly, microbiological factors. We describe an analytical framework to infer factors of epidemic success based on the joint analysis of epidemiological, clinical and pathogen genetic data. We derive isolate-specific, genetic distance-based estimates of epidemic success, and we represent success-related time-dependent concepts, namely epidemicity and endemicity, by restricting analysis to specific time scales. The method is applied to analyze a surveillance-based cohort of 1,641 tuberculosis patients with minisatellite-based isolate genotypes. Known predictors of isolate endemicity (older age, native status) and epidemicity (younger age, sputum smear positivity) were identified with high confidence (P < 0.001). Long-term epidemic success also correlated with the ability of Euro-American and Beijing MTBC lineages to cause active pulmonary infection, independent of patient age and country of origin. Our results demonstrate how important insights into the transmission dynamics of tuberculosis can be gained from active surveillance data.

Novel portable platform for molecular detection of toxigenic Clostridium difficile in faeces: a diagnostic accuracy study

BACKGROUND

A novel portable platform for nucleic acid amplification enables rapid detection of diarrhoea causing toxigenic Clostridium difficile directly from faeces, even in resource-limited settings. We evaluated the accuracy and precision of the new commercial molecular test system.

METHODS

One thousand one hundred and sixty faecal samples from patients suspected of having Clostridium difficile infection (CDI) were analysed using the Orion GenRead C. difficile test system (Orion Diagnostica Oy, Espoo, Finland) and comparative methods in three teaching hospital laboratories in Finland and France. The precision of the Orion GenRead C. difficile test system was evaluated in a reproducibility study with a set of blind-coded samples. The test system is based on a new isothermal amplification technology (Strand Invasion Based Amplification, SIBA®) and detection of the tcdB gene of C. difficile. We calculated the sensitivity, specificity, and the overall agreement according to Clinical and Laboratory Standards Institute recommendations.

FINDINGS

The overall agreement of the Orion GenRead C. difficile test when compared to the comparative methods in routine use in the participating laboratories was between 96.7% and 98.8%. In the reproducibility study; the total percent agreement between three laboratories was 99.8%.

INTERPRETATION

The identification of toxigenic C. difficile from faeces with the light-weight portable Orion GenRead test system was highly sensitive and specific, and the results were reproducible in the participating laboratories. This platform could enable fast and accurate molecular pathogen detection even in resource-limited or point-of-care settings.

MALDI-TOF mass spectrometry for rapid diagnosis of postoperative endophthalmitis

This study describes an innovative strategy for rapid detection and identification of bacteria causing endophthalmitis, combining the use of an automated blood culture system with MALDI-TOF mass spectrometry methodology. Using this protocol, we could identify 96% of 45 bacterial strains isolated from vitreous samples collected in acute post-operative endophthalmitis patients.

Massilia timonae as cause of chronic endophthalmitis following cataract surgery

This is the first report of chronic postoperative endophthalmitis caused by Massilia timonae. The gram-negative bacillus was isolated from a patient who developed chronic endophthalmitis after cataract extraction. The microorganism was cultured on brain-heart infusion broth and identified using the 16S rRNA sequence analysis. Biochemically, the organism was positive for catalase and oxidase and negative for arginine dihydrolase. It was pansensitive to β-lactams, fluoroquinolones, aminoglycosides, and trimethoprim-sulfamethoxazole but resistant to aztreonam. Massilia timonae is a new bacterium implicated in postoperative chronic endophthalmitis. Eubacterial polymerase chain reaction was useful in identifying M timonae because phenotyping testing and conventional algorithms could not identify it.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Recurrence and death after Clostridium difficile infection: gender-dependant influence of proton pump inhibitor therapy

GOALS

To determine whether patients with a pre-existing PPI treatment had a higher risk of poor evolution (recurrence or death) when diagnosed with a toxicogenic Clostridium difficile digestive infection.

BACKGROUND

Previous studies identified pump proton inhibitor (PPI) prescription as a risk factor for C. difficile infection. The influence of PPI on the outcome of C. difficile infection is controversial.

STUDY

This was a retrospective monocentric cohort study. All cases of patients in our center with a symptomatic infection by a toxicogenic C. difficile strain during the years 2012 and 2013 were retrospectively analyzed. The primary endpoint was the occurrence of a recurrence or C. difficile infection -related death within 2 months after diagnosis.

RESULTS

373 patients were included in this study (198 men and 175 women), with a mean age of 70.1 ± 18.6 years (2-100 years). Fourteen (3.7 %) patients died secondarily to C. difficile infection (median survival time 5 days), and 88 (23.6 %) experienced recurrence (after a median delay of 30 days). One hundred and ninety eight (53.1 %) patients were already receiving PPI at the time of the C. difficile infection (including 156 patients with a prescription >1 month). When analyzing separately men and women, male patients were more likely to experience recurrence or death in case of pre-existing PPI prescription [HR = 2.32 (1.26-4.27)]; this was not observed in female patients [HR = 0.62 (0.31-1.22)].

CONCLUSIONS

Pre-existing PPI therapy may increase the risk of recurrence or death in male patients with a toxicogenic C. difficile infection. PPI risk-benefit ratio should be carefully assessed.

Various checkpoints prevent the synthesis of Staphylococcus aureus peptidoglycan hydrolase LytM in the stationary growth phase

In Staphylococcus aureus, peptidoglycan metabolism plays a role in the host inflammatory response and pathogenesis. Transcription of the peptidoglycan hydrolases is activated by the essential 2-component system WalKR at low cell density. During stationary growth phase, WalKR is not active and transcription of the peptidoglycan hydrolase genes is repressed. In this work, we studied regulation of expression of the glycylglycine endopeptidase LytM. We show that, in addition to the transcriptional regulation mediated by WalKR, the synthesis of LytM is negatively controlled by a unique mechanism at the stationary growth phase. We have identified 2 different mRNAs encoding lytM, which vary in the length of their 5' untranslated (5'UTR) regions. LytM is predominantly produced from the WalKR-regulated mRNA transcript carrying a short 5'UTR. The lytM mRNA is also transcribed as part of a polycistronic operon with the upstream SA0264 gene and is constitutively expressed. Although SA0264 protein can be synthesized from the longer operon transcript, lytM cannot be translated because its ribosome-binding site is sequestered into a translationally inactive secondary structure. In addition, the effector of the agr system, RNAIII, can inhibit translation of lytM present on the operon without altering the transcript level but does not have an effect on the translation of the upstream gene. We propose that this dual regulation of lytM expression, at the transcriptional and post-transcriptional levels, contributes to prevent cell wall damage during the stationary phase of growth.

Nontuberculous Mycobacteria: An Underestimated Cause of Bioprosthetic Valve Infective Endocarditis

From 2010 to 2013, 5 cases of nontuberculous mycobacteria infective endocarditis (IE), exclusively from bioprosthesis, were diagnosed in three hospitals out of 370 blood culture-negative-suspected IE. The porcine origin of this underestimated etiology is questioned.

Background. Atypical mycobacteria, or nontuberculous mycobacteria (NTM), have been barely reported as infective endocarditis (IE) agents.

Methods. From January 2010 to December 2013, cardiac valve samples sent to our laboratory as cases of blood culture-negative suspected IE were analyzed by 16S rDNA polymerase chain reaction (PCR). When positive for NTM, hsp PCR allowed species identification. Demographic, clinical, echocardiographic, histopathological, and Ziehl-Neelsen staining data were then collected.

Results. Over the study period, 6 of 370 cardiac valves (belonging to 5 patients in 3 hospitals) were positive for Mycobacterium chelonae (n = 5) and Mycobacterium lentiflavum (n = 1) exclusively on bioprosthetic material. The 5 patients presented to the hospital for heart failure without fever 7.1–18.9 months (median 13.1 months) after biological prosthetic valve implantation. Echocardiography revealed paravalvular regurgitation due to prosthesis dehiscence in all patients. Histopathological examination of the explanted material revealed inflammatory infiltrates in all specimens, 3 of which were associated with giant cells. Gram staining and conventional cultures remained negative, whereas Ziehl-Neelsen staining showed acid-fast bacilli in all patients. Allergic etiology was ruled out by antiporcine immunoglobulin E dosages. These 5 cases occurred exclusively on porcine bioprosthetic material, revealing a statistically significant association between bioprosthetic valves and NTM IE (P < .001).

Conclusions. The body of evidence confirmed the diagnosis of prosthetic IE. The statistically significant association between bioprosthetic valves and NTM IE encourages systematic Ziehl-Neelsen staining of explanted bioprosthetic valves in case of early bioprosthesis dysfunction, even without an obvious sign of IE. In addition, we strongly question the cardiac bioprosthesis conditioning process after animal sacrifice.

New therapeutic approaches for treatment of tularaemia: a review

Antibiotic treatment of tularaemia is based on a few drugs, including the fluoroquinolones (e.g., ciprofloxacin), the tetracyclines (e.g., doxycycline), and the aminoglycosides (streptomycin and gentamicin). Because no effective and safe vaccine is currently available, tularaemia prophylaxis following proven exposure to F. tularensis also relies on administration of antibiotics. A number of reasons make it necessary to search for new therapeutic alternatives: the potential toxicity of first-line drugs, especially in children and pregnant women; a high rate of treatment relapses and failures, especially for severe and/or suppurated forms of the disease; and the possible use of antibiotic-resistant strains in the context of a biological threat. This review presents novel therapeutic approaches that have been explored in recent years to improve tularaemia patients' management and prognosis. These new strategies have been evaluated in vitro, in axenic media and cell culture systems and/or in animal models. First, the activities of newly available antibiotic compounds were evaluated against F. tularensis, including tigecycline (a glycylcycline), ketolides (telithromycin and cethromycin), and fluoroquinolones (moxifloxacin, gatifloxacin, trovafloxacin and grepafloxacin). The liposome delivery of some antibiotics was evaluated. The effect of antimicrobial peptides against F. tularensis was also considered. Other drugs were evaluated for their ability to suppress the intracellular multiplication of F. tularensis. The effects of the modulation of the innate immune response (especially via TLR receptors) on the course of F. tularensis infection was characterized. Another approach was the administration of specific antibodies to induce passive resistance to F. tularensis infection. All of these studies highlight the need to develop new therapeutic strategies to improve the management of patients with tularaemia. Many possibilities exist, some unexplored. Moreover, it is likely that new therapeutic alternatives that are effective against this intracellular pathogen could be, at least partially, extrapolated to other human pathogens.

A non-coding RNA promotes bacterial persistence and decreases virulence by regulating a regulator in Staphylococcus aureus

Staphylococcus aureus produces a high number of RNAs for which the functions are poorly understood. Several non-coding RNAs carry a C-rich sequence suggesting that they regulate mRNAs at the post-transcriptional level. We demonstrate that the Sigma B-dependent RsaA RNA represses the synthesis of the global transcriptional regulator MgrA by forming an imperfect duplex with the Shine and Dalgarno sequence and a loop-loop interaction within the coding region of the target mRNA. These two recognition sites are required for translation repression. Consequently, RsaA causes enhanced production of biofilm and a decreased synthesis of capsule formation in several strain backgrounds. These phenotypes led to a decreased protection of S. aureus against opsonophagocytic killing by polymorphonuclear leukocytes compared to the mutant strains lacking RsaA. Mice animal models showed that RsaA attenuates the severity of acute systemic infections and enhances chronic catheter infection. RsaA takes part in a regulatory network that contributes to the complex interactions of S. aureus with the host immune system to moderate invasiveness and favour chronic infections. It is the first example of a conserved small RNA in S. aureus functioning as a virulence suppressor of acute infections. Because S. aureus is essentially a human commensal, we propose that RsaA has been positively selected through evolution to support commensalism and saprophytic interactions with the host.

Staphylococcus aureus is a commensal and an opportunistic pathogen that causes a large range of community and hospital-acquired infections. The bacteria produce an array of virulence factors, the expression of which is regulated by a set of regulators including proteins and RNAs. In recent years, a large number of small non-coding RNAs encoded by the S. aureus genome have been identified but determination of their function is still lagging behind. This study shows that RsaA, a staphylococcal conserved non-coding RNA, operates at the post-transcriptional level by repressing the translation of the master regulatory protein MgrA. The repression is based on a direct interaction of RsaA with the ribosome binding site of mgrA mRNA. Through MgrA regulation, RsaA activates biofilm formation and inhibits capsule synthesis. Using appropriate animal models, we showed that RsaA acts as a suppressor of virulence because the deletion of its gene increases the invasiveness of S. aureus in the mice sepsis model. RsaA is thus part of complex regulatory network that modify the interactions of S. aureus with the eukaryotic immune system. These findings illustrate how small RNAs can have a major impact in bacterial biology.

A new dye uptake assay to test the activity of antibiotics against intracellular Francisella tularensis

Francisella tularensis, a facultative intracellular bacterium, is the aetiological agent of tularaemia. Antibiotic treatment of this zoonosis is based on the administration of a fluoroquinolone or a tetracycline for cases with mild to moderate severity, whereas an aminoglycoside (streptomycin or gentamicin) is advocated for severe cases. However, treatment failures and relapses remain frequent, especially in patients suffering from chronic lymph node suppuration. Therefore, new treatment alternatives are needed. We have developed a dye uptake assay for determination of minimal inhibitory extracellular concentrations (MIECs) of antibiotics against intracellular F. tularensis, and validated the method by comparing the results obtained using a CFU-enumerating method. We also compared MIECs with MICs of the same compounds determined using a CLSI broth microdilution method. We tested the activity of 11 antibiotics against two clinical strains of F. tularensis subsp. holarctica isolated in France. Both strains displayed low MICs (≤1 μg/mL) to fluoroquinolones (ciprofloxacin, levofloxacin and moxifloxacin), gentamicin, doxycycline and rifampicin. Higher MICs (≥8 μg/mL) were found for carbapenems (imipenem and meropenem), daptomycin and linezolid. Erythromycin MICs were 4.0 and 16.0 μg/mL, respectively, for the two clinical strains. MIECs were almost the same with the two methods used. They were concordant with MICs, except for erythromycin and linezolid (respectively, four and eight times more active against intracellular F. tularensis) and gentamicin (four to eight times less active against intracellular F. tularensis). This study validated the dye uptake assay as a new tool for determination of the activity of a large panel of antibiotics against intracellular F. tularensis. This test confirmed the intracellular activity of first-line antibiotics used for tularaemia treatment, but also revealed significant activity of linezolid against intracellular F. tularensis.

Bis-indolic compounds as potential new therapeutic alternatives for tularaemia

Francisella tularensis is the etiological agent of tularaemia and a CDC class A biological threat agent. Few antibiotic classes are currently useful in treating tularaemia, including the aminoglycosides gentamicin and streptomycin, fluoroquinolones, and tetracyclines. However, treatment failures and relapses remain frequent and F. tularensis strains resistant to antibiotics have been easily selected in vitro. In this study, we evaluated the activity of new synthetic bis-indole derivatives against this pathogen. Minimum inhibitory concentrations (MICs) of four compounds (dcm01 to dcm04) were determined for the reference strains F. tularensis subsp. holarctica LVS NCTC10857, F. tularensis subsp. novicida CIP56.12 and F. philomiragia ATCC25015, and for 41 clinical strains of F. tularensis subsp. holarctica isolated in France. Minimal bactericidal concentrations (MBCs) were determined for the dcm02 and dcm04 compounds for the LVS and two clinical strains. Killing curves were also determined for the same three strains exposed to dcm04. All tested bis-indole compounds were bacteriostatic against F. tularensis subsp. holarctica strains, with a MIC90 of 8 μg/mL for dcm01, dcm02, and dcm03, and 2 μg/mL for dcm04. Only one strain was resistant to both dcm01 and dcm03, with MICs > 32 μg/mL. In contrast, F. tularensis subsp. novicida was resistant to all derivatives and F. philomiragia was only susceptible to dcm02 and dcm04, with MICs of 16 and 4 μg/mL, respectively. MBC and killing curve experiments revealed significant bactericidal activity (i.e., 3-log reduction of the bacterial inoculum) of the dcm02 and dcm04 compounds only for the LVS strain. In conclusion, we have identified novel synthetic bis-indole compounds that are active against F. tularensis subsp. holarctica. They may be drug candidates for the development of new therapeutic alternatives for tularaemia treatment. Their further characterization is needed, especially identification of their bacterial targets.

Principles and applications of molecular biology techniques for the microbiological diagnosis of acute post-operative endophthalmitis

The systematic microbiological evaluation of endophthalmitis allows the confirmation of the infectious nature of the disease and the possible adaptation of treatment at the individual level and, at the collective level, the epidemiological characterization of the bacterial spectrum of endophthalmitis. Long reserved for research, the use of molecular biology techniques to complement conventional culture techniques has become important for the diagnosis of endophthalmitis in recent years. These new diagnostic techniques are particularly useful for the microbiological study of bacteria that are difficult or impossible to grow because of their intrinsic properties, their presence in only a small inoculum, their sequestration on prosthetic materials, or their inactivation by prior antibiotic treatment. These techniques are based on the polymerase chain reaction (PCR), which allows the amplification and detection of extracted bacterial deoxyribonucleic acid (DNA) that is initially present in minute quantities in an ocular sample. In practice, these conventional or real-time PCRs allow either the a priori detection of bacterial DNA (universal PCR) or the identification of a specific DNA fragment of a bacterial genus or species (specific PCR). New techniques of PCR will allow more rapid bacterial identification and also characterization of genotypic properties, such as genes of virulence or antibiotic resistance.

FRIENDS Group: clinical and microbiological characteristics of post-filtering surgery endophthalmitis

PURPOSE

To study the clinical and microbiological characteristics as well as the prognostic factors for post-filtering surgery endophthalmitis.

METHODS

Twenty-three eyes were included in the study in four tertiary centres between 2004 and 2010. The clinical and microbiological data were collected prospectively (minimum follow-up, 6 months). Microbiological diagnosis was based on conventional cultures and panbacterial PCR (16SrDNA amplification and sequencing).

RESULTS

The onset of endophthalmitis was early (<6 weeks) in 22 % of the cases and delayed in 78 %. Elevated intraocular pressure and hypopyon were more frequent in delayed than in early presentations (p = 0.04). By combining the results of culture and panbacterial PCR, a bacterial species could be identified in 73.9 % of the cases, including 56.5 % of commensal species of the digestive tract such as Moraxella spp., oropharyngeal streptococci and Enterococcus faecalis. Good final visual acuity (VA ≥ 20/40) was correlated with initial VA greater than light perception (p = 0.05). Poor final VA (≤20/400) was correlated with a higher virulence of the infecting bacterial species (p = 0.006), and was noted in all patients with early-onset endophthalmitis.

CONCLUSION

Acute early- or delayed-onset post-filtering surgery endophthalmitis is frequently caused by bacteria of the digestive tract (e.g., Streptococcus and Enterococcus spp.). The combination of conventional cultures and panbacterial PCR allowed us to identify the causative microorganism in three-quarters of the cases, i.e., 21 % more cases than through culture alone. Despite adequate antibiotic and surgical treatment, the anatomical and visual prognosis remains poor.

Clonal complex 398 methicillin susceptible Staphylococcus aureus: a frequent unspecialized human pathogen with specific phenotypic and genotypic characteristics

Clonal complex 398 livestok-associated-MRSA (CC398 LA-MRSA) clone is described as a major animal pathogen that can also colonize and infect humans. CC398 methicillin susceptible Staphylococcus aureus (CC398 MSSA) is less described. We identified 126 CC398 MSSA strains of human origin within 6380 S. aureus isolates gathered between 2009 and 2011, from the French National Reference Centre for Staphylococci. They were characterized using antimicrobial susceptibility testing, spa typing, DNA microarrays (Identibac S. aureus Genotyping ®, Alere), CC398-specific sequence PCR, ermT (encoding macrolides résistance) PCR. Fifty-three CC398 LA-MRSA collected from French pigs and veal were used as comparators, and phylogenetic relations between human CC398 MSSA and animal CC398 MRSA populations were explored on the basis of spa-typing and DNA microarrays. CC398 MSSA were able to induce a large spectrum of infections (especially skin, bloodstream, and pneumonias). The prevalence rate of this clone was high in MSSA population, i.e., 24.7% in a local prospective study on nasal colonization, and 7.5% in a national prospective study on infective endocarditis. CC398 MSSA isolates were frequently (89%) erythromycin resistant, due to the presence of the ermT gene, a gene not detected in erythromycin resistant CC398 LA-MRSA strains. Expression of staphylococcal complement inhibitor (scn) and the chemotaxis inhibitory protein (chp), was also specific to this population. The CC398 MRSA signature included also a panel of antibiotic resistance genes, especially a type IV or V cassette mec and tetM. CC398 MSSA and CC398 LA-MRSA populations were closely related based on spa-typing and DNA microarrays, with the MRSA strains forming the most derived lineage in phylogenic trees. Both MSSA and MRSA populations may come from common ancestors, which would have evolved in the settings of different selective pressures, explaining the acquisition of ermT, chp and scn for MSSA, and antibiotic resistance genes for MRSA.

Major West Indies MRSA clones in human beings: do they travel with their hosts?

BACKGROUND

Descriptions of the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) have seldom been produced in the Caribbean, which is a major tourism destination.

MATERIALS AND METHODS

Using DNA microarrays and spa typing, we characterized 85 MRSA isolates from human skin and soft-tissue infections from five different islands.

RESULTS

In the French West Indies (n = 72), the most frequently isolated clones were the same clones that are specifically isolated from mainland France [Lyon (n = 35) and Geraldine (n = 11) clones], whereas the clones that were most frequently isolated from the other islands (n = 13) corresponded with clones that have a worldwide endemic spread [Vienna/Hungarian/Brazilian (n = 5), Panton Valentine leukocidin-positive USA300 (n = 4), New York/Japan (n = 2), and pediatric (n = 1) clones].

CONCLUSION

The distribution of the major MRSA clones in the French (Guadeloupe and Martinique) and non-French West Indies (Jamaica, Trinidad, and Tobago) is different, and the clones most closely resemble those found in the home countries of the travelers who visit the islands most frequently. The distribution might be affected by tourist migration, which is specific to each island.

Treatment of tularemia in pregnant woman, France

A pregnant woman who had oropharyngeal tularemia underwent treatment with azithromycin and lymph node resection and recovered without obstetrical complication or infection in the child. Azithromycin represents a first-line treatment option for tularemia during pregnancy in regions where the infecting strains of Francisella tularensis have no natural resistance to macrolides.

Detection of Staphylococcus aureus delta-toxin production by whole-cell MALDI-TOF mass spectrometry

The aim of the present study was to detect the Staphylococcus aureus delta-toxin using Whole-Cell (WC) Matrix Assisted Laser Desorption Ionization-Time-of-Flight (MALDI-TOF) mass spectrometry (MS), correlate delta-toxin expression with accessory gene regulator (agr) status, and assess the prevalence of agr deficiency in clinical isolates with and without resistance to methicillin and glycopeptides. The position of the delta-toxin peak in the mass spectrum was identified using purified delta-toxin and isogenic wild type and mutant strains for agr-rnaIII, which encodes delta-toxin. Correlation between delta-toxin production and agr RNAIII expression was assessed by northern blotting. A series of 168 consecutive clinical isolates and 23 unrelated glycopeptide-intermediate S. aureus strains (GISA/heterogeneous GISA) were then tested by WC-MALDI-TOF MS. The delta-toxin peak was detected at 3005±5 Thomson, as expected for the naturally formylated delta toxin, or at 3035±5 Thomson for its G10S variant. Multivariate analysis showed that chronicity of S. aureus infection and glycopeptide resistance were significantly associated with delta-toxin deficiency (p = 0.048; CI 95%: 1.01-10.24; p = 0.023; CI 95%: 1.20-12.76, respectively). In conclusion, the S. aureus delta-toxin was identified in the WC-MALDI-TOF MS spectrum generated during routine identification procedures. Consequently, agr status can potentially predict infectious complications and rationalise application of novel virulence factor-based therapies.

[Staphylococcus aureus resistance to antibiotics: key points in 2010]

Staphylococcus aureus has a strong adaptive capacity and thus acquired various types of resistance to antistaphylococcal agents. More than 90% of isolates produce a penicillinase. Oxacillin remains active against these strains, but hospital associated staphylococci and more recently community acquired staphylococci have developed crossed resistance between methicillin (MRSA), oxacillin and other beta-lactams by production of a penicillin binding protein (PBP) with low affinity for beta-lactams, PBP2a. The gene encoding PBP2a, mecA is carried by a chromosomal element which also contains other resistance genes to heavy metals and other antibiotics thus explaining the multiresistant profile of hospital associated MRSA. By contrast, community acquired MRSA (CA-MRSA) are only resistant to kanamycin, fusidic acid and tetracycline, in addition to methicillin. This profile is specific of the European CA-MRSA ST80 clone which also encodes for a very particular virulence factor, the Panton-Valentine leukocidin. Glycopeptides, vancomycin and teicoplanin, are alternatives to oxacillin in case of resistance or intolerance. Strains with decreased susceptibility to glycopeptides have been reported. Their detection is difficult but necessary because vancomycin MIC creep seems linked to poor outcome in patients.

Coagulase-positive Staphylococcus pseudintermedius from animals causing human endocarditis

We report a case of infection with coagulase-positive Staphylococcus pseudintermedius related to the implantation of a cardioverter-defribrillator device. This species is usually isolated from infected animals, and contact with a dog was the probable source of infection in this patient. This isolate produced a leukotoxin effective against human polymorphonuclear leukocytes.

Staphylococcus aureus RNAIII binds to two distant regions of coa mRNA to arrest translation and promote mRNA degradation

Staphylococcus aureus RNAIII is the intracellular effector of the quorum sensing system that temporally controls a large number of virulence factors including exoproteins and cell-wall-associated proteins. Staphylocoagulase is one major virulence factor, which promotes clotting of human plasma. Like the major cell surface protein A, the expression of staphylocoagulase is strongly repressed by the quorum sensing system at the post-exponential growth phase. Here we used a combination of approaches in vivo and in vitro to analyze the mechanism used by RNAIII to regulate the expression of staphylocoagulase. Our data show that RNAIII represses the synthesis of the protein through a direct binding with the mRNA. Structure mapping shows that two distant regions of RNAIII interact with coa mRNA and that the mRNA harbors a conserved signature as found in other RNAIII-target mRNAs. The resulting complex is composed of an imperfect duplex masking the Shine-Dalgarno sequence of coa mRNA and of a loop-loop interaction occurring downstream in the coding region. The imperfect duplex is sufficient to prevent the formation of the ribosomal initiation complex and to repress the expression of a reporter gene in vivo. In addition, the double-strand-specific endoribonuclease III cleaves the two regions of the mRNA bound to RNAIII that may contribute to the degradation of the repressed mRNA. This study validates another direct target of RNAIII that plays a role in virulence. It also illustrates the diversity of RNAIII-mRNA topologies and how these multiple RNAIII-mRNA interactions would mediate virulence regulation.

A search for small noncoding RNAs in Staphylococcus aureus reveals a conserved sequence motif for regulation

Bioinformatic analysis of the intergenic regions of Staphylococcus aureus predicted multiple regulatory regions. From this analysis, we characterized 11 novel noncoding RNAs (RsaA-K) that are expressed in several S. aureus strains under different experimental conditions. Many of them accumulate in the late-exponential phase of growth. All ncRNAs are stable and their expression is Hfq-independent. The transcription of several of them is regulated by the alternative sigma B factor (RsaA, D and F) while the expression of RsaE is agrA-dependent. Six of these ncRNAs are specific to S. aureus, four are conserved in other Staphylococci, and RsaE is also present in Bacillaceae. Transcriptomic and proteomic analysis indicated that RsaE regulates the synthesis of proteins involved in various metabolic pathways. Phylogenetic analysis combined with RNA structure probing, searches for RsaE-mRNA base pairing, and toeprinting assays indicate that a conserved and unpaired UCCC sequence motif of RsaE binds to target mRNAs and prevents the formation of the ribosomal initiation complex. This study unexpectedly shows that most of the novel ncRNAs carry the conserved C-rich motif, suggesting that they are members of a class of ncRNAs that target mRNAs by a shared mechanism.

The signal peptide of Staphylococcus aureus panton valentine leukocidin LukS component mediates increased adhesion to heparan sulfates

Staphylococcus aureus necrotizing pneumonia is a severe disease caused by S. aureus strains carrying the Panton Valentine leukocidin (PVL) genes (lukS-PV & lukF-PV) encoded on various bacteriophages (such as phiSLT). Clinical PVL+ strains isolated from necrotizing pneumonia display an increased attachment to matrix molecules (type I and IV collagens and laminin), a phenotype that could play a role in bacterial adhesion to damaged airway epithelium during the early stages of necrotizing pneumonia (J Infect Dis 2004; 190: 1506–15). To investigate the basis of the observed adhesion of S. aureus PVL+ strains, we compared the ability of PVL+ and their isogenic PVL− strains to attach to various immobilized matrix molecules. The expression of recombinant fragments of the PVL subunits and the addition of synthetic peptides indicated that the processed LukS-PV signal peptide (LukS-PV SP) was sufficient to significantly enhance the ability of S. aureus to attach to extracellular matrix (ECM) components. Furthermore, we showed that adhesion to ECM components was inhibited by heparin and heparan sulfates (HS) suggesting that in vivo, HS could function as a molecular bridge between the matrix and S. aureus expressing the LukS-PV signal peptide. Site directed mutagenesis, biochemical and structural analyses of the LukS-PV signal peptide indicate that this peptide is present at the S. aureus surface, binds to HS in solid phase assay, and mediates the enhanced S. aureus matrix component adhesion. Our data suggests that after its cleavage by signal peptidase, the signal peptide is released from the membrane and associates to the cell wall through its unique C-terminus sequence, while its highly positively charged N-terminus is exposed on the bacterial surface, allowing its interaction with extracellular matrix-associated HS. This mechanism may provide a molecular bridge that enhances the attachment of the S. aureus PVL+ strains to ECM components exposed at damaged epithelial sites.