BACKGROUND AND OBJECTIVES: Streptococcus agalactiae (Group B Streptococcus, GBS) is the leading cause of neonatal infections and deaths in human. It can also cause infections in pregnant women and non-pregnant adults. Penicillin and ampicillin are antibiotics of choice for the treatment of GBS infections. Erythromycin and clindamycin are used as alternative therapy in penicillin allergic patients, however resistance to these agents has been increasingly observed. This present study was undertaken to determine the colonization rate of GBS, susceptibility profile and the mechanism of antibiotic resistance in pregnant women and their babies at Dr. George Mukhari Academic Hospital in Pretoria. METHODS: Rectal and vaginal swabs were collected from pregnant women; ear and umbilical swabs from newborns over an 11 month period. Samples were cultured on selective media (CNA agar and Todd-Hewitt broth) and GBS positively identified using morphological and biochemical tests including Gram staining, hemolytic activity, catalase test, bile esculin, CAMP test and Latex agglutination test. The susceptibility testing was done using the Kirby-Bauer and E-test methods. The D-test method was used to determine the inducible clindamycin resistance. Multiplex PCR with were used to detect different genes coding for resistance. RESULTS: Out of the 413 patients evaluated, 128 (30.9%) were positive with GBS. All isolates were sensitive to penicillin and ampicillin. Erythromycin and clindamycin resistance was 21.1% and 17.2% respectively; of which 69% harbouring constitutive MLBB, 17.4% inducible MLSB. The alteration of ribosomal target encoded by ermB genes was the commonest mechanism of resistance observed in 55% of isolates, 38% of isolates had both ermB and linB genes and efflux pump mediated by mefA genes was detected in one of isolates. Conclusion: This study reaffirms the appropriateness of penicillin as the antibiotic of choice for treating GBS infection. However it raises the challenges of resistance to the macrolides and lincosamides. More GBS treatment options for penicillin allergic patients need to be researched. / Health Studies / M. Sc. (Life Sciences (Microbiology))

Streptococcus suis et Streptococcus du groupe B (GBS) sont deux bactéries encapsulées qui induisent des pathologies similaires chez l’homme et/ou l’animal, incluant septicémies et méningites. La capsule polysaccharidique (CPS) est un facteur de virulence clé de ces deux pathogènes et les anticorps (Ac) anti-CPS présentent un bon potentiel protecteur. Néanmoins, ces molécules sont faiblement immunogéniques et les mécanismes de la génération de la réponse humorale anti-CPS demeurent méconnus. L’objectif principal de cette thèse était d’évaluer les caractéristiques et les mécanismes du développement de la réponse Ac dirigée spécifiquement contre les CPS de S. suis et GBS, ainsi que l’effet de la biochimie de la CPS dans cette réponse. Nous avons étudié S. suis types 2 et 14 et GBS types III et V, dont les CPS présentent plusieurs similarités dans leurs compositions et leurs structures, incluant la présence d’acide sialique, un sucre potentiellement immunosuppresseur, tout en possédant une antigénicité propre. Nous avons tout d’abord analysé la nature de la réponse Ac anti-CPS sérique face à la bactérie entière. Les souris infectées par S. suis développent une réponse très faible (S. suis type 2) voire insignifiante (S. suis type 14) de profil isotypique restreint à l’IgM et sont incapables de monter une réponse mémoire efficace face à une seconde infection. Un profil similaire est obtenu chez le porc infecté par S. suis type 2. On détecte des titres d’IgM anti-CPS significatifs chez les souris infectées par GBS (type III ou V). Toutefois, la magnitude de la réponse reste globalement faible et aucune commutation de classe n’est observée. Nous avons ensuite examiné l’influence de la biochimie de la CPS sur ces profils de réponse en conduisant des expériences avec la CPS hautement purifiée de ces pathogènes. Tandis que la CPS de GBS type III administrée aux souris conserve des propriétés immunogéniques similaires à celles observées durant l’infection par la bactérie intacte, les CPS de S. suis type 2 et GBS type V perdent toute capacité à induire une réponse Ac spécifique. L’analyse de l’interaction in vitro des CPS avec les cellules dendritiques (DC) murines, des acteurs clés dans la détection des pathogènes et l’orchestration des réponses immunitaires subséquentes, révèle que ces molécules stimulent la production de niveaux conséquents de chémokines via différents récepteurs. Néanmoins, les CPS sont inaptes à induire la sécrétion de cytokines et elles interfèrent avec la capacité des DC à exprimer BAFF, une cytokine clé dans la différenciation des lymphocytes B en plasmocytes. L’utilisation de CPS chimiquement désialylées démontre que l’acide sialique ne joue aucun rôle immunosuppresseur majeur dans le développement de la réponse Ac dirigée contre les CPS purifiées de S. suis ou GBS, ni sur l’interaction des CPS avec les DC in vitro, ni sur profil de la réponse in vivo. D’autres propriétés biochimiques intrinsèques à ces CPS seraient responsables de l’inaptitude de l’hôte infecté à monter une réponse Ac adéquate et les identifier constituera un outil précieux pour une meilleure compréhension de l’immunopathogénèse de S. suis et GBS ainsi que pour développer des moyens de lutte efficaces contre ces bactéries. / Streptococcus suis and Group B Streptococcus (GBS) are two encapsulated bacteria that induce similar pathologies in humans and/or animals, including septicemia and meningitis. The capsular polysaccharide (CPS) is a major virulence factor for both pathogens and CPS-specific antibodies (Ab) display a good protective potential. However, CPSs are weak immunogenic molecules and the mechanisms of the generation of the CPS-specific humoral response remain poorly known. Thus, the main objective of this thesis was to evaluate the characteristics and the mechanisms of the development of the Ab response directed against S. suis and GBS CPSs, as well as the influence of the biochemistry of the CPS on this response. We worked with S. suis types 2 and 14 and GBS types III and V, whose CPSs present several similarities in their compositions and structures, including the presence of sialic acid, a potentially immunosuppressive sugar, while being very distinct antigens. Initially, we analyzed the features of the CPS-specific serum Ab response to whole bacteria. S. suis-infected mice developed a very low (S. suis type 2) to undetectable (S. suis type 14) response restricted to the IgM isotype, and were unable to mount an efficient memory response after a secondary infection. A similar profile of response was obtained in S. suis type 2-infected pigs. We detected significant CPS-specific IgM titers in GBS-infected mice (type III or V). Nonetheless, the magnitude of the response remained globally low and no isotype switching was observed. Then, we examined the influence of the biochemistry of the CPS on these response profiles by conducting experiments with highly purified CPSs from these pathogens. Whereas the purified GBS type III CPS administrated to mice retained similar immunogenic properties as those observed during the infection with the intact bacteria, purified S. suis type 2 and GBS type V CPSs were no longer able to induce a specific Ab response. The analysis of the in vitro interaction between the CPSs and murine dendritic cells (DCs), crucial actors in the detection of pathogens and the orchestration of subsequent immune responses, revealed that these molecules stimulate the production of significant levels of chemokines through different receptors. Nevertheless, CPSs were unable to induce cytokine secretion and interfered with the ability of DCs to express BAFF, a key cytokine for B lymphocyte differentiation into plasma cells. The use of chemically desialylated CPSs demonstrated that sialic acid does not play a major immunosuppressive role in the development of the Ab response specific to purified S. suis or GBS CPSs, neither on the in vitro interaction between CPSs and DCs, nor on the profile of the in vivo response. Other biochemical properties intrinsic to these CPSs would be responsible for the inaptitude of the infected host to mount an adequate Ab response, and their identification will be a precious tool for a better understanding of the immunopathogenesis of S. suis and GBS, as well as for the development of efficient strategies to fight against these bacteria.

Le streptocoque du groupe B (GBS) est un agent causant des septicémies et des méningites chez les nouveaux nés et chez les adultes. Une réaction sérologique dirigée contre la capsule polysaccharidique (CPS) permet de différencier les 10 sérotypes de GBS, dont le sérotype III qui est le plus fréquemment isolé en cas de méningite. Actuellement l’efficacité de l’unique traitement disponible, l’antibioprophylaxie intrapartum, est controversée. Dans l’optique d’élargir les options de prévention, cette étude vise à mieux comprendre les interactions entre GBS III et le développement de la réponse adaptative, sujet qui est peu documenté. Cette étude a évalué, par cytométrie en flux (FACS), les sous-populations des lymphocytes B (LB) spléniques impliquées suite à l’infection systémique de GBS III dans un modèle in vivo. De plus, la réponse humorale contre GBS III et contre la CPS III purifiée ainsi que la formation des centres germinatifs (GCs) spléniques dans un contexte de multiples infections par GBS ont été évalués. Les résultats suggèrent que la première infection stimule la production d’anticorps contre GBS III mais peu contre sa CPS. De plus, GBS III activerait la différenciation des LB et induirait la formation des GCs liée au déclenchement d’une réponse mémoire permettant un meilleur contrôle lors des infections subséquentes. Malgré sa faible immunogénicité, la CPS ne semblerait pas interférer avec le développement de l’immunité adaptative humorale contre la bactérie. La production d’anticorps contre GBS III qui implique la commutation de classe serait principalement produite contre des épitopes différents de ceux composant la CPS III. / Group B Streptococcus (GBS) is an agent of septicemia and meningitis in newborns but also in adults. A serological reaction directed against the polysaccharide capsule (CPS) allows to differentiate 10 GBS serotypes, including serotype III which is the most frequently isolated in cases of meningitis. Currently the effectiveness of the only available treatment, intrapartum antibiotic prophylaxis, is controversial. To improve prevention strategies, this study aims to better understand the interactions between GBS and the development of the adaptive response, a subject that is poorly documented. This study evaluated, by flow cytometry (FACS), the splenic subpopulations of B lymphocytes (LB) involved following systemic GBS infection in an in vivo model. This study also evaluated the serum anti-GBS antibody response and against its purified capsule as well as the formation of splenic germinal centers (GCs) in the context of multiple GBS infections. Results suggest that the first infection stimulates the production of antibodies against GBS III but little against its capsule. Furthermore, results suggest that GBS activates B cell differentiation by inducing the production of GCs, which are linked to triggering a memory response allowing better control in subsequent infections. Despite its low immunogenicity, the CPS does not appear to interfere with the development of adaptive humoral immunity against the bacteria. Therefore, the production of antibodies against GBS III, involving class switching, would recognize different epitopes from those found on its capsule.

Streptococcus du Groupe B (GBS) et Streptococcus suis sont deux pathogènes encapsulés qui induisent des pathologies similaires dont la méningite et la septicémie chez les animaux et/ou les humains. Les sérotypes III et V du GBS et les sérotypes 2 et 14 du S. suis (utilisés dans cette étude) sont parmi les plus prévalents et/ou les plus virulents. La capsule polysaccharidique (CPS) définit le sérotype et est considérée comme un facteur de virulence essentiel pour les deux espèces bactériennes. Malgré que plusieurs études aient été réalisées au niveau des interactions entre ces streptocoques et les cellules de l’immunité innée, aucune information n’est disponible sur la régulation de la réponse immunitaire contre ces pathogènes par les cellules dendritiques (DCs) et leur interactions avec d’autres cellules, notamment les cellules ‘natural killer’ (NK). Dans cette étude, différentes approches (in vitro, ex vivo et in vivo) chez la souris ont été développées pour caractériser les interactions entre les DCs, les cellules NK et GBS ou S. suis. L’utilisation de mutants non encapsulés a permis d’évaluer l’importance de la CPS dans ces interactions. Les résultats in vitro avec les DCs infectées par GBS ou S. suis ont démontré que ces deux pathogènes interagissent différemment avec ces cellules. GBS est grandement internalisé par les DCs, et ce, via de multiples mécanismes impliquant notamment les radeaux lipidiques et la clathrine. Le mécanisme d’endocytose utilisé aurait un effet sur la capacité du GBS à survivre intracellulairement. Quant au S. suis, ce dernier est très faiblement internalisé et, si le cas, rapidement éliminé à l’intérieur des DCs. GBS et S. suis activent les DCs via différents récepteurs et favorisent la production de cytokines et chimiokines ainsi que l’augmentation de l’expression de molécules de co-stimulation. Cette activation permet la production d’interferon-gamma (IFN-y) par les cellules NK. Cependant, GBS semble plus efficient à activer les DCs, et par conséquent, les cellules NK que S. suis. La production d’IFN-y, en réponse à la stimulation bactérienne, est principalement assurée par un contact direct entre les DCs et les cellules NK et ne dépend qu’en partie de facteurs solubles. De plus, nos résultats in vivo ont démontré que ces deux streptocoques induisent rapidement la libération d'IFN-y par les cellules NK lors de la phase aiguë de l'infection. Ceci suggère que les interactions entre les DCs et les cellules NK pourraient jouer un rôle dans le développement d’une réponse immune T auxiliaire de type 1 (T ‘helper’ 1 en anglais; Th1). Cependant, la capacité de S. suis à activer la réponse immunitaire in vivo est également plus faible que celle observée pour GBS. En effet, les CPSs de GBS et de S. suis jouent des rôles différents dans cette réponse. La CPS de S. suis empêche une activation optimale des DCs et des cellules NK alors que c’est l’opposé pour la CPS de GBS, indépendamment du sérotype évalué. En résumé, cette étude adresse pour la première fois la contribution des DCs et des cellules NK dans la réponse immunitaire innée lors d’une infection à GBS ou à S. suis et, par extension, dans le développement d’une réponse Th1. Nos résultats renforcent davantage le rôle central des DCs dans le contrôle efficace des infections causées par des bactéries encapsulées. / Group B Streptococcus (GBS) and Streptococcus suis are two encapsulated pathogens that induce similar pathologies, including septicemia and meningitis in animals and/or humans. Serotypes III and V of GBS and serotypes 2 and 14 of S. suis (evaluated in this study) are the most prevalent and/or virulent types. The capsular polysaccharide (CPS) defines the serotype and is considered as a key virulence factor for both bacterial species. Although several studies have addressed the interactions of these streptococci and various cells of the innate immune system, no information is available on the regulation of the immune response against these pathogens by dendritic cells (DCs), and their interactions with other cells, including natural killer (NK) cells. In this study, different approaches (in vitro, ex vivo and in vivo) in mice were developed to characterize the interactions between DCs, NK cells and GBS or S. suis. Non-encapsulated mutants were used to evaluate the importance of the CPS in these interactions. In vitro results with GBS- or S. suis-infected DCs showed that these two pathogens differently interact with these cells. GBS is largely internalized by DCs through multiple endocytosis mechanisms, mainly involving lipid rafts and clathrin. The use of a specific endocytosis pathway might help GBS to survive intracellularly. In contrast, S. suis is poorly internalized and, if the case, rapidly eliminated within the DCs. GBS and S. suis activate DCs through different receptors leading to the release of cytokines and chemokines and increased expression of co-stimulatory molecules. This activation allows the production of IFN- by NK cells. Yet, S. suis capacity to activate DCs and NK cells is lower than that observed for GBS. IFN- release in response to bacterial stimulation was mainly mediated by direct DC-NK cell contact and only partially dependant on soluble factors. In addition, our in vivo results showed that these two streptococcal species rapidly induce the release of IFN- by NK cells during the acute phase of the infection. This suggests that the DC-NK crosstalk might play a role in the development of a T helper 1 (Th1) response. Yet, S. suis capacity to activate the in vivo immune response was also lower than that observed for GBS. In fact, GBS and S. suis CPSs play different roles in this response. S. suis CPS prevents optimal activation of DCs and NK cells whereas it is the opposite for GBS, independently of the serotype tested. In summary, this study addresses for the first time the contribution of DCs and NK cells to the innate immune response against GBS and S. suis infections, and by extension, to the development of a Th1 response. Our results further highlight the central role of DCs in the effective control of infections caused by encapsulated bacteria.

Background: Group B streptococcus (GBS) is regarded as one of the most important causes of maternal and neonatal morbidity and mortality in many parts of the world. GBS recto-vaginal colonization is important in the health of a mother and her neonate, especially in developing countries. Maternal vaginal colonization with GBS at the time of delivery can cause vertical transmission to the neonate. Multilocus sequence typing (MLST) is a technique used to characterize microbial isolates by means of sequencing internal fragments of housekeeping genes and has the advantage of reproducibility and has been shown to correlate with the other typing techniques and thus has emerged as the standard for delineating the clonal population of GBS. The study aimed to investigate the epidemiology of GBS colonization among pregnant women and their neonates, and to characterize the isolates by multilocus sequence typing technique at Dr George Mukhari Academic Hospital, Pretoria. Methodology: A total of 413 pregnant women who visited the antenatal clinic were recruited and screened. Participants were interviewed using a questionnaire to gather demographic and other relevant information such as history of current pregnancy, previous miscarriages and still births. Samples from maternal rectum and vagina as well as neonate ear and umbilical cord were taken for culture using colistin and nalidixic acid (CNA) blood agar and incubated for 24-48 hours. If negative after 48 hours, Todd-Hewitt broth was subcultured after 18-48 hours onto sheep blood agar. Multilocus sequence typing (MLST) was used to characterize seven group B streptococcus isolates collected at Dr George Mukhari academic hospital. Fragments of seven housekeeping genes were amplified by polymerase chain reaction (PCR) for each strain and sequenced. CLC bio software (Inqaba biotech, South Africa; Pretoria) was used to analyse sequenced loci and UPGMA dendrogram was constructed. Results: The colonization rate for GBS in pregnant women and their neonates was 30.9% and 0%, respectively. A higher proportion of GBS were isolated from the rectum (37.9%) as compared to the vagina (20.6%). Most socio-economic, demographic and obstetric factors analysed were not significantly associated with.GBS colonization. On 128 positive samples, the results of Todd-Hewitt enrichment broth and direct plating method using CNA were compared. A total of 45.3% of colonised were positive on direct selective agar (CNA); an additional 54.7% samples were recovered from Todd-Hewitt broth. Three genes (adhP, glnA and tkt) were sequenced successfully for six samples (1, 2. 4,6,12 and 65). The UPGMA tree with 1000 bootstrap showing the relationship between six samples was drawn.Conclusion: This study revealed that pregnant women of all ages are at risk of group B streptococcus colonization. Group B streptococcus was common among pregnant women at Dr George Mukhari Academic Hospital. No socio-economic risk factor was associated with group B streptococcus colonization. Results confirm that the combination of Todd-Hewitt broth and CNA agar plate is a time saving and sensitive method. The allelic profile, characteristics such as G+C (guanine+cytosine) content and dN/dS ratio were not analysed because of the smaller sample size used in this study, which shows that the MLST method was unsuccessful in this study. The UPGMA tree based on differences in consensus of the isolates showed that all group B streptococcus isolates are clustered and descend from a single node. / Life & Consumer Sciences / Life Sciences / M.Sc. (Life Sciences)

Background: Group B streptococcus (GBS) is regarded as one of the most important causes of maternal and neonatal morbidity and mortality in many parts of the world. GBS recto-vaginal colonization is important in the health of a mother and her neonate, especially in developing countries. Maternal vaginal colonization with GBS at the time of delivery can cause vertical transmission to the neonate. Multilocus sequence typing (MLST) is a technique used to characterize microbial isolates by means of sequencing internal fragments of housekeeping genes and has the advantage of reproducibility and has been shown to correlate with the other typing techniques and thus has emerged as the standard for delineating the clonal population of GBS. The study aimed to investigate the epidemiology of GBS colonization among pregnant women and their neonates, and to characterize the isolates by multilocus sequence typing technique at Dr George Mukhari Academic Hospital, Pretoria. Methodology: A total of 413 pregnant women who visited the antenatal clinic were recruited and screened. Participants were interviewed using a questionnaire to gather demographic and other relevant information such as history of current pregnancy, previous miscarriages and still births. Samples from maternal rectum and vagina as well as neonate ear and umbilical cord were taken for culture using colistin and nalidixic acid (CNA) blood agar and incubated for 24-48 hours. If negative after 48 hours, Todd-Hewitt broth was subcultured after 18-48 hours onto sheep blood agar. Multilocus sequence typing (MLST) was used to characterize seven group B streptococcus isolates collected at Dr George Mukhari academic hospital. Fragments of seven housekeeping genes were amplified by polymerase chain reaction (PCR) for each strain and sequenced. CLC bio software (Inqaba biotech, South Africa; Pretoria) was used to analyse sequenced loci and UPGMA dendrogram was constructed. Results: The colonization rate for GBS in pregnant women and their neonates was 30.9% and 0%, respectively. A higher proportion of GBS were isolated from the rectum (37.9%) as compared to the vagina (20.6%). Most socio-economic, demographic and obstetric factors analysed were not significantly associated with.GBS colonization. On 128 positive samples, the results of Todd-Hewitt enrichment broth and direct plating method using CNA were compared. A total of 45.3% of colonised were positive on direct selective agar (CNA); an additional 54.7% samples were recovered from Todd-Hewitt broth. Three genes (adhP, glnA and tkt) were sequenced successfully for six samples (1, 2. 4,6,12 and 65). The UPGMA tree with 1000 bootstrap showing the relationship between six samples was drawn.Conclusion: This study revealed that pregnant women of all ages are at risk of group B streptococcus colonization. Group B streptococcus was common among pregnant women at Dr George Mukhari Academic Hospital. No socio-economic risk factor was associated with group B streptococcus colonization. Results confirm that the combination of Todd-Hewitt broth and CNA agar plate is a time saving and sensitive method. The allelic profile, characteristics such as G+C (guanine+cytosine) content and dN/dS ratio were not analysed because of the smaller sample size used in this study, which shows that the MLST method was unsuccessful in this study. The UPGMA tree based on differences in consensus of the isolates showed that all group B streptococcus isolates are clustered and descend from a single node. / Life Sciences / M.Sc. (Life Sciences)