Determinants of Group B streptococcal virulence potential amongst vaginal clinical isolates from pregnant women.

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is a Gram-positive bacterium isolated from the vaginal tract of approximately 25% of women. GBS colonization of the female reproductive tract is of particular concern during pregnancy as the bacteria can invade gestational tissues or be transmitted to the newborn during passage through the birth canal. Infection of the neonate can result in life-threatening pneumonia, sepsis and meningitis. Thus, surveillance of GBS strains and corresponding virulence potential during colonization is warranted. Here we describe a panel of GBS isolates from the vaginal tracts of a cohort of pregnant women in Michigan, USA. We determined that capsular serotypes III and V were the most abundant across the strain panel, with only one isolate belonging to serotype IV. Further, 12.8% of strains belonged to the hyper-virulent serotype III, sequence type 17 (ST-17) and 15.4% expressed the serine rich repeat glycoprotein-encoding gene srr2. Functional assessment of the colonizing isolates revealed that almost all strains exhibited some level of ß-hemolytic activity and that ST-17 strains, which express Srr2, exhibited increased bacterial adherence to vaginal epithelium. Finally, analysis of strain antibiotic susceptibility revealed the presence of antibiotic resistance to penicillin (15.4%), clindamycin (30.8%), erythromycin (43.6%), vancomycin (30.8%), and tetracycline (94.9%), which has significant implications for treatment options. Collectively, these data provide important information on vaginal GBS carriage isolate virulence potential and highlight the value of continued surveillance.

Modification of the CpsA protein reveals a role in alteration of the Streptococcus agalactiae cell envelope.

The bacterial cell envelope is a crucial first line of defense for a systemic pathogen, with production of capsular polysaccharides and maintenance of the peptidoglycan cell wall serving essential roles in survival in the host environment. The LytR-CpsA-Psr proteins are important for cell envelope maintenance in many Gram-positive species. In this study, we examined the role of the extracellular domain of the CpsA protein of the zoonotic pathogen group B Streptococcus in capsule production and cell wall integrity. CpsA has multiple functional domains, including a DNA-binding/transcriptional activation domain and a large extracellular domain. We demonstrated that episomal expression of extracellularly truncated CpsA causes a dominant-negative effect on capsule production when expressed in the wild-type strain. Regions of the extracellular domain essential to this phenotype were identified. The dominant-negative effect could be recapitulated by addition of purified CpsA protein or a short CpsA peptide to cultures of wild-type bacteria. Changes in cell wall morphology were also observed when the dominant-negative peptide was added to wild-type cultures. Fluorescently labeled CpsA peptide could be visualized bound at the mid-cell region near the division septae, suggesting a novel role for CpsA in cell division. Finally, expression of truncated CpsA also led to attenuation of virulence in zebrafish models of infection, to levels below that of a cpsA deletion strain, demonstrating the key role of the extracellular domain in virulence of GBS.

Zebrafish as a natural host model for Vibrio cholerae colonization and transmission.

The human diarrheal disease cholera is caused by the aquatic bacterium Vibrio cholerae. V. cholerae in the environment is associated with several varieties of aquatic life, including insect egg masses, shellfish, and vertebrate fish. Here we describe a novel animal model for V. cholerae, the zebrafish. Pandemic V. cholerae strains specifically colonize the zebrafish intestinal tract after exposure in water with no manipulation of the animal required. Colonization occurs in close contact with the intestinal epithelium and mimics colonization observed in mammals. Zebrafish that are colonized by V. cholerae transmit the bacteria to naive fish, which then become colonized. Striking differences in colonization between V. cholerae classical and El Tor biotypes were apparent. The zebrafish natural habitat in Asia heavily overlaps areas where cholera is endemic, suggesting that zebrafish and V. cholerae evolved in close contact with each other. Thus, the zebrafish provides a natural host model for the study of V. cholerae colonization, transmission, and environmental survival.

Transcriptional analysis of the Streptococcus pyogenes salivaricin locus.

The sal lantibiotic locus plays an important role in the virulence of Streptococcus pyogenes. Our transcriptional analysis of the sal locus provides new information on the complex regulation of this operon. Transcription of the operon is regulated by a promoter upstream of the operon and by a second internal promoter upstream of the salKRZ genes. Here we identify the location of the internal promoter and provide information on how this promoter is autoregulated by proteins within the locus. We determined by primer extension that the salKR promoter is located within the salY gene and identified several regulatory regions important for expression. The higher activity of the promoter in a salKR deletion strain indicates a role in repression by the SalR response regulator. Further, this promoter had higher activity in a salA deletion strain, implicating corepression or a signaling role for the SalA peptide. Finally, we demonstrate that this promoter can be controlled by host factors. Analysis of transcriptional regulation of this locus provides a better understanding of the function of the sal locus in S. pyogenes pathogenesis.

Functional analysis of the CpsA protein of Streptococcus agalactiae.

Streptococcal pathogens, such as the group B streptococcus (GBS) Streptococcus agalactiae, are an important cause of systemic disease, which is facilitated in part by the presence of a polysaccharide capsule. The CpsA protein is a putative transcriptional regulator of the capsule locus, but its exact contribution to regulation is unknown. To address the role of CpsA in regulation, full-length GBS CpsA and two truncated forms of the protein were purified and analyzed for DNA-binding ability. Assays demonstrated that CpsA is able to bind specifically to two putative promoters within the capsule operon with similar affinity, and full-length protein is required for specificity. Functional characterization of CpsA confirmed that the ΔcpsA strain produced less capsule than did the wild type and demonstrated that the production of full-length CpsA or the DNA-binding region of CpsA resulted in increased capsule levels. In contrast, the production of a truncated form of CpsA lacking the extracellular LytR domain (CpsA-245) in the wild-type background resulted in a dominant-negative decrease in capsule production. GBS expressing CpsA-245, but not the ΔcpsA strain, was attenuated in human whole blood. However, the ΔcpsA strain showed significant attenuation in a zebrafish infection model. Furthermore, chain length was observed to be variable in a CpsA-dependent manner, but could be restored to wild-type levels when grown with lysozyme. Taken together, these results suggest that CpsA is a modular protein influencing multiple regulatory functions that may include not only capsule synthesis but also cell wall associated factors.

Adult zebrafish model of streptococcal infection.

Streptococcal pathogens cause a wide array of clinical syndromes in humans, including invasive systemic infections resulting in high mortality rates. Many of these pathogens are human specific, and therefore difficult to analyze in vivo using typical animal models, as these models rarely replicate what is observed in human infections. This unit describes the use of the zebrafish (Danio rerio) as an animal model for streptococcal infection to analyze multiple disease states. This model closely mimics the necrotizing fasciitis/myositis pathology observed in humans from a Streptococcus pyogenes infection. The use of a zoonotic pathogen, Streptococcus iniae, which replicates systemic infections caused by many streptococcal pathogens, including dissemination to the brain, is also described. Protocols describing both intraperitoneal and intramuscular infections, as well as methods for histological and quantitative measurements of infection, are also described.

Role of RopB in growth phase expression of the SpeB cysteine protease of Streptococcus pyogenes.

The Rgg family of transcription regulators is widely distributed among gram-positive bacteria; however, how the members of this family control transcription is poorly understood. In the pathogen Streptococcus pyogenes, the Rgg family member RopB is required for transcription of the gene that encodes the secreted SpeB cysteine protease. Expression of the protease follows distinct kinetics that involves control of transcription in response to the growth phase. In this study, the contribution of RopB to growth phase control was examined. The gene encoding the protease (speB) and ropB are transcribed divergently from a 940-bp intergenic region. Primer extension analyses, in conjunction with reporter fusion studies, revealed that the major region controlling the transcription of both speB and ropB is adjacent to ropB and that the promoters for the two genes likely overlap. Furthermore, it was found that RopB is a DNA-binding protein that specifically binds to sequences in this control region. The interrelationship between ropB and speB expression was further reflected in the observation that transcription of ropB itself is subject to growth phase control. However, while expression of ropB from a promoter expressed during the early logarithmic phase of growth could complement a ropB deletion mutant, ectopic expression of ropB did not uncouple the expression of speB from its growth phase signal. These data implicate other factors in growth phase control and suggest that regulation of ropB expression itself is not the central mechanism of control.