Littérature scientifique sur le sujet « Streptococcus agalactiae – Analyse cladistique »

Background: In 2002, the World Health Organization (WHO) launched a regional microbiology external quality assessment (EQA) programme for national public health laboratories in the African region, initially targeting priority epidemic-prone bacterial diseases, and later including other common bacterial pathogens. Objectives: The aim of this study was to analyse the efficacy of an EQA programme as a laboratory quality system evaluation tool. Methods: We analysed the proficiency of laboratories’ performance of bacterial identification and antimicrobial susceptibility testing (AST) for the period 2011–2016. The National Institute for Communicable Diseases of South Africa provided technical coordination following an agreement with WHO, and supplied EQA samples of selected bacterial organisms for microscopy (Gram stain), identification, and antimicrobial susceptibility testing (AST). National public health laboratories, as well as laboratories involved in the Invasive Bacterial Diseases Surveillance Network, were enrolled by the WHO Regional Office for Africa to participate in the EQA programme. We analysed participants’ results of 41 surveys, which included the following organisms sent as challenges: Streptococcus pneumonia, Haemophilus influenzae, Neisseria meningitidis, Salmonella Typhi, Salmonella Enteritidis, Shigella flexneri, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus anginosus, Enterococcus faecium, Serratia marcescens, Acinetobacter baumannii, and Enterobacter cloacae. Results: Eighty-one laboratories from 45 countries participated. Overall, 76% of participants obtained acceptable scores for identification, but a substantial proportion of AST scores were not in the acceptable range. Of 663 assessed AST responses, only 42% had acceptable scores. Conclusion: In the African Region, implementation of diagnostic stewardship in clinical bacteriology is generally suboptimal. This report illustrates that AST is poorly done compared to microscopy and identification. It is critically important to make the case for implementation of quality assurance in AST, as it is the cornerstone of antimicrobial resistance surveillance reporting and implementation of the Global Antimicrobial Resistance Surveillance System.

Streptococcus agalactiae (Group B Streptococcus, GBS) is a major cause of neonatal infections with high morbidity and mortality, and clindamycin is the main antibiotic used to treat GBS infections in patients allergic to penicillin. We aimed to analyse the antibiotic sensitivity, sequence types, serotypes, virulence factors, and antibiotic resistance mechanisms of clinically isolated clindamycin-resistant S. agalactiae and provide basic data for the treatment, prevention, and control of clinical infection of S. agalactiae. A total of 110 strains of clindamycin-resistant S. agalactiae were collected from two tertiary hospitals in Hebei, China. We performed antibiotic sensitivity tests for 11 antibiotics on these strains and whole-genome sequencing analysis. All the strains were susceptible to penicillin, ampicillin, linezolid, vancomycin, tigecycline, and quinupristin–dalfopristin. Resistance to erythromycin, levofloxacin, tetracycline, and chloramphenicol were also observed. Genome sequence analysis revealed that all strains belonged to 12 sequence types (STs) related to six cloning complexes (CCs), namely CC10, CC19, CC23, CC651, CC1, and CC17. Five serotypes were identified, including IA, IB, II, III, and V. The most prominent resistance genes were mreA (100%) and ermB (81.8%). Furthermore, cfb, cylE, pavA and the gene cluster related to the pili were 100% present in all strains, followed by lmb (95.5%) and srr1 (67.2%). This study found that clindamycin-resistant S. agalactiae showed polymorphisms in molecular types and serotypes. Furthermore, multiple virulence factor genes have been identified in their genomes.

The aim of this study was to retrospectively analyse the results of milk samples obtained from South African dairy herds during the period 1996 to April 2007 in order to identify possible trends in isolates of microorganisms and their pathogenicity under field conditions. Milk samples were obtained from 7 of the 9 provinces in South Africa where there are low numbers of dairy cows. Although there is scientific limitation to a country wide survey, such as the variation in herd size, management skills, parity, milk yield, milking frequency and other parameters, the size of this database helps to give a fair indication of general udder health in South Africa. Cytology and routine bacteriology were performed on 379 000 milk samples of lactating cows and bacteriology on 11 946 samples from non-lactating cows. According to the results obtained, mastitis did not decrease in South Africa over the test period. The prevalence of mastitis and teat canal infection was lowest in 2002. Mastitis and teat canal infection increased from 2002 to 2006 from 8.1 % and 24.1 % to 15.4 and 30.0 % respectively. The percentage of mastitogenic pathogens isolated from cows over these years also varied. Previously unknown or almost eradicated mastitogenic pathogens such as αβ haemolytic Staphylococcus aureus which is thought to be of human origin, Streptococcus agalactiae and Enterococcus canis were responsible for numerous mastitis outbreaks seen in the test samples. Coagulase-negative staphylococci were the most frequently isolated bacteria in milk samples from both lactating and dry cows, followed by Staphylococcus aureus and Streptococcus agalactiae. Although Staphylococcus aureus remained the principal mastitogenic pathogen in South Africa, owing to its chronic nature and resultant economic losses, most cases of mastitis were caused by coagulase-negative staphylococci. This finding increases the importance of coagulase-negative staphylococci (formerly described as a minor pathogen) significantly. Isolations of Streptococcus agalactiae peaked between 2000 and 2005 and decreased again by 2007. Coagulase-negative staphylococcal isolates increased from 2002 and were still on the increase in 2007. Streptococcus agalactiae, Streptococcus uberis and Enterococcus canis were isolated more frequently from milk samples of lactating cows compared with dry cows, while Enterococcus faecalis was isolated more frequently from dry cow samples.

AbstractThe aim of this study was to analyse the microbicidal and microbiostatic activity of S. montana hydrolate L., the water-soluble fraction of the hydro-distillation process used to obtain the essential oil, on 14 Gram-positive and Gram-negative bacteria and a fungus of clinical interest. To consider whether this hydrolate is a more environmentally friendly alternative to traditional antibiotics, its effect on non-target microorganisms in the aquatic and terrestrial environment was analysed using natural soil and river microorganism communities, characterized through 16S rRNA gene sequencing. Results showed that S. montana hydrolate was especially effective (25% v/v concentration) against Pasteurella aerogenes, Streptococcus agalactiae and Acinetobacter baumannii (priority 1, WHO). It was also a microbicide for a further 7 bacterial strains and the fungus Candida albicans (50% v/v concentration). The river and soil communities exposed to the hydrolate showed a decrease in their growth, as well as a decrease in their ability to metabolize polymers and carbohydrates (soil microorganisms) and polymers, carboxylic and ketone acids (river microorganisms). Hydrolates could be an alternative to conventional antibiotics, but their impact on the environment must be taken into account.

Nous avons étudié l’intérêt du locus CRISPR1 (associé au système CRISPR-Cas de type II-A), comme marqueur épidémiologique pour le typage et l’analyse phylogénétique des souches de Streptococcus agalactiae, le streptocoque du groupe B (SGB). Par ce travail de thèse, nous avons pu mettre en évidence i) l’activité du système CRISPR-Cas in vivo ainsi que sa faible vitesse d’évolution ii) une conservation des marqueurs ancestraux, permettant d’obtenir des informations sur les lignées phylogénétiques (congruence entre le typage CRISPR et le MLST), iii) un polymorphisme du locus CRISPR1 (notamment des spacers d’acquisition récente), offrant une méthode de typage très discriminante (séparation des isolats au sein d’un même ST définit par MLST). L’analyse de ces spacers nous donne également des informations sur l’évolution récente des isolats, notamment de leurs contacts avec les EGMs. Nous avons montré l’intérêt de cet outil pour le suivi de souches de portage ou l’étude d’une population. Ainsi, à l’issu de ce travail de thèse nous proposons le typage CRISPR comme méthode de référence pour le typage et l’analyse phylogénétique des souches de SGB
We studied the relevance of the CRISPR1 array (associated to a CRISPR-Cas II-A type) as an epidemiological marker for genotyping and phylogenetic analyses of Streptococcus agalactiae (or Group B Streptococcus (GBS)) isolates. We demonstrate that i) spacer acquisition events occurred in vivo which strongly suggest that the CRISPR1-Cas system is functionally active for adaptation ii) ancestral markers (TDR and ancestral spacers) are highly conserved and reflect the phylogenetic structure of the GBS population (in congruence with MLST) iii) CRISPR1 array shared a high degree of polymorphism (especially for leader end spacers) offering a highly discriminatory typing method (allow to separate isolates within a same ST defined by MLST). Leader end analysis also provides specific evidence on isolates recent evolution, especially encounters with MGEs. CRISPR1 array appears as a useful genetic feature to follow vaginal carriage of GBS in women and for evaluate the diversity of GBS vaginal carriage population. On the basis of these data, we assume that this method could pretend to be a reference method for phylogenetic GBS typing

L’hème est une molécule essentielle à de nombreuses fonctions bactériennes. Cependant, cette molécule génère des radicaux libres qui lui confèrent des propriétés toxiques. Nous avons caractérisé les mécanismes de l’homéostasie de l’hème impliquant le transporteur d’efflux HrtBA. Chez L. lactis nous avons démontré que HrtBA empêche l’accumulation membranaire et intracellulaire d’hème exogène par un mécanisme ménaquinone dépendant. HrtBA est aussi présent chez de nombreux pathogènes. Chez S. agalactiae, la transcription de HrtBA est régulée par un système à deux composants HssRS. Le senseur HssS reconnait l’hème exogène internalisé. Pour élucider le rôle de l’hème de l’hôte dans la virulence de S. agalactiae, un modèle d’infection systémique chez la souris utilisant la luminescence (lux) et l’imagerie in vivo (IVIS) a été mis en place. Le suivi de la luminescence de bactéries hypersensibles à l’hème (ΔhrtBA) montre que l’hème de l’hôte est toxique et que la capacité de S. agalactiae à assurer son homéostasie est déterminante pour ’linfection. De manière similaire, en montrant que le métabolisme respiratoire est indispensable pour l’infection (ΔcydA), S. agalactiae dépend donc de sa capacité à acquérir l’hème de l’hôte pour être infectieuse. En utilisant le promoteur de HrtBA couplé à l’opéron lux, nous avons étudié la capacité de S. agalactiae à détecter et acquérir l’hème in vivo au cours de l’infection. Nos résultats montrent que l’hème de l’hôte est particulièrement biodisponible dans le foie. Au contraire dans le cerveau, l’hème n’est pas détecté par la bactérie. Nos résultats démontrent que l’hème de l’hôte est un paramètre important des capacités d’adaptation de S. agalactiae à son hôte lors de l’infection. Bloquer HrtBA ou le senseur d’hème HssS pourrait constituer une cible pour la recherche antibiotique chez S. agalactiae ou d’autres pathogènes. Enfin, nous avons démontré chez E. faecalis que l’expression de HrtBA est aussi dépendante d’un système à deux composants. Nous avons utilisé la même stratégie que pour S. agalactiae pour créer un senseur d’hème spécifique qui a permis de démontrer pour la première fois que E. faecalis rencontre et utilise l’hème du tractus digestif
Heme is a redox-reactive molecule with essential function in bacterial metabolism. However, this molecule generates reactive oxygen species responsible for its toxicity. We characterized the mechanism of heme homeostasis involving the efflux transporter HrtBA. In L. lactis, we demonstrated that HrtBA prevents from membrane and intracellular accumulation of internalized exogenous heme thanks to a menaquinone dependent mechanism. HrtBA is also present in several pathogens. In S. agalactiae, the transcription of HrtBA is regulated by a two-component system HssRS. The HssS sensor recognizes internalized exogenous heme. To clarify the role of heme of the host in the virulence of S. agalactiae, a systemic infection model in mice using luminescence (lux) and in vivo imaging (IVIS) has been set up. The monitoring of luminescence generated by heme hypersensitive (ΔhrtBA) bacteria shows that heme of host is toxic and that the capability of S. agalactiae to control heme homeostasis is crucial for infection. In the same way, by demonstrating that respiratory metabolism is crucial for infection (ΔcydA), we demonstrated that S. agalactiae depends on its capacity to acquire the heme of the host to become infectious. By using the HrtBA promoter coupled with lux operon, we studied the capacity of S. agalactiae to detect and to acquire heme in vivo during the infection. Our results show that host heme is especially biodisponible in the liver. On the contrary, heme is not detected by bacteria in the brain. Our results prove that heme of the host is an important parameter for the adaptation of S. agalactiae to its host during infection. Blocking HrtBA or heme sensor HssS could so be a target for antibiotic research against S. agalactiae and other pathogens. Finally, we show in E. faecalis that HrtBA expression also depends on a two-component system. We used the same strategy as in S. agalactiae to create a specific heme sensor that allowed us to demonstrate for the first time that E. faecalis meets and uses heme in the digestive tract