<p>The Streptococcus Milleri/Anginosus group (SMG) includes Streptococcus anginosus, Streptococcus constellatus and Streptococcus intermedius. The SMG is found in healthy individuals but these bacteria are most known clinically for being associated with invasive disease and more recently, airway infections including cystic fibrosis (CF). The SMG like many other streptococci are naturally competent, being able to actively bind, uptake and integrate extracellular DNA. Competence regulation involves a competence-stimulating peptide (CSP) derived from the ComC precursor and a two- component signaling system (a histidine kinase ComD and its response regulator ComE). In this study, I examined the distribution of CSP/ComD sequences and competence in 170 SMG clinical isolates from CF airways and invasive disease. Five predicted CSP sequences were observed; one represented a newly predicted CSP and two arose from frameshift mutations in comC and appeared to be non-functional. The three CSPs fall into two functional groups that do not cross-activate due to receptor specificity. In addition, I observed that the Streptococcus constellatus subspecies pharyngis strains could not be transformed. However, I demonstrated that the pharyngis strains possess a functional ComCDE pathway, suggesting that the CSP regulates genes other than those involved in natural transformation. For many strains, I observed high endogenous competence levels that were only marginally induced by added peptide. These strains appear to be constitutively competent during exponential growth. The high basal level of expression and the heterogeneity in the SMG competence systems could impact how the SMG evolve during colonization and infections and specifically acquire antibiotic resistance and virulence genes.</p> / Master of Science (MSc)

The Streptococcus Anginosus/Milleri Group (SMG) is made up of three closely related but distinct bacterial species: Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus. The SMG are recovered from about one-third of healthy, asymptomatic individuals. Despite this, the SMG cause more incidences of invasive streptococcal disease than Group A and Group B Streptococcus combined. Members of this group are somehow able to live a dual lifestyle. Little work has been conducted on the molecular pathogenicity of the SMG and host factors that contribute to host susceptibility to this group have been under-investigated. My research works towards discovering how the host recognizes the SMG as well as what enables the SMG to evade clearance by the immune system. I hypothesize that: 1) recognition of the SMG by toll-like receptor 2 (TLR2) plays a key role in triggering a cytokine response by the innate immune branch (which coordinates the immune response to the SMG), 2) the expression of cytolysins and extracellular polysaccharides by members of the SMG enables evasion of innate immune recognition and cytokine responses. hTLR2 reporter and monocyte-like cell lines as well as human blood samples from healthy donors were used to investigate the host factors that contribute to SMG infection. Five clinical reference SMG strains and a transposon mutant library were used to probe the contributing bacterial factors. It was found that TLR2 activation plays an important role in the cytokine response to the SMG, but there is heterogeneity between strains in their ability to activate TLR2. It was also found that intermedilysin expression by S. intermedius strains enables evasion of recognition; however, different hosts display varying susceptibility to this cytolysin. This study reveals that investigation of both host and microbial factors is essential to build an understanding of the mechanisms of SMG transition from commensalism to pathogenicity. / Thesis / Master of Science (MSc) / The Streptococcus Miller/Anginosus Group (SMG) is a group of bacteria comprised of three species. Members of this group are recovered from roughly one-third of healthy individuals. However, the SMG are also found in samples collected from patients with invasive disease. It is not well understood why some human-SMG relationships are pathogenic and others are not. However, it is likely that the combination of both human and SMG factors determine the nature of the relationship formed between the two. In this study, the human and SMG factors that contribute to infection were investigated. The ways by which human cells recognize members of the SMG and defend themselves from damage was explored. Additionally, SMG factors that potentially contribute to infection were probed to discover their effect on human cells. By investigating both the bacterial and host factors that lead to infection, disease treatments and preventative strategies can be tailored to individual cases.

Cystic fibrosis (CF) is an autosomal recessive disorder affecting 70,000 individuals worldwide. This disease is characterized by the buildup of mucus in the airways leading to chronic lung infections resulting in pulmonary failure and death in 95% of CF patients. Routine surveillance of CF pathogens using traditional microbiology culture guides management and treatment of CF patients. Molecular profiling studies have revealed emerging pathogens that may play a role in CF lung disease by either directly causing infection or upregulating the virulence factors of classic CF pathogens, such as P. aeruginosa; however, routine CF culture protocols have not been modified to detect these organisms. The goal of this study was to expand the data relevant to the use of microbiology cultures for the management and treatment of CF patients at Virginia Commonwealth University Medical Center (VCUMC) by directly selecting for emerging CF pathogens in culture. This was accomplished by developing,optimizing, and implementing an agar to select for colistin-resistant non-fermenting Gram- negative rods (NF GNRS). In addition, McKay agar and anaerobic media were utilized to recover members of the Streptococcus anginosus group (SAG) and anaerobes in CF respiratory samples. The prevalences of SAG, anaerobes, and colistin-resistant NF GNRs recovered on study media from 75 adult and pediatric CF patients at VCUMC were 17.33%, 41.33%, and 4% respectively. Approximately 62% of patients culture-positive for SAG were also infected with P. aeruginosa and 53.8% of SAG recovered in culture were from CF patients experiencing PE. These findings further support the claim that interspecies interactions among emerging and classic CF pathogens may result in periods of clinical instability or PE. Twenty-eight of the 75 patients were culture-positive for Veillonella species, with the majority of samples collected during a period of surveillance. Four colistin-resistant NF GNRs were isolated on the study media alone. The selective nature of the study media prevented the mixed respiratory flora and classic CF pathogens from overgrowing and obscuring the growth of these colistin-resistant NF GNRs. The presence and role of emerging pathogens in the CF patient population at VCUMC warrants further investigation; therefore, the routine culture protocol needs to be revised to recover and select for those organisms thought to play a role in PE and lung function decline.