Please help me answer thes questions? 1. List at least 3 characteristics of Grou

Question

Please help me answer thes questions?

1. List at least 3 characteristics of Group B Streptococci that are mentioned in the “Introduction” that allow the organism to be a human pathogen. Relate these to some of the factors listed in Chapter 15 in your textbook.

2. What is the function of the b-hemolysin/cytolysin? Does the pigmentation serve any purpose for the bacteria, or only for identification by researchers?

3. Regulation of Gene Expression:

(a) In general, what is an operon? Which operon is the focus of this research study?

(b) What is a two component regulatory system? (You may need to do a little research on this one..) Which two component system is the focus of this study?

4. What is the purpose of this research study? What is their sample population?

Streptococcus agalactiae, or group B Streptococcus (GBS), is a Gram-positive bacterium that is usually an asymptomatic member of the human intestinal and vaginal microbiota. However, GBS is also the leading cause of neonatal sepsis and meningitis in developed countries (1–3) and an emerging pathogen in adults, mostly in the elderly (4, 5). Neonatal infections occur predominantly during delivery by inhalation or ingestion of contaminated secretions of the mother’s vagina. Rapid invasive infections may follow, with a mortality rate of up to 10% during the first week of life (early-onset disease [EOD], age of 0 to 6 days) or during the first 3 months of life (late-onset disease [LOD], age of 7 to 89 days). Systematic GBS screening prior to delivery and intrapartum antibiotic prophylaxis have efficiently reduced EOD but not LOD (6), highlighting the need to further improve the diagnosis and treatments.

GBS is an extracellular pathogen and one of its characteristics is the secretion of a potent -hemolysin/cytolysin (-h/c) (7–9). This -h/c has a central role in balancing the pro- and anti-inflammatory responses of the infected host and is necessary to breach the epithelial and endothelial barriers and the phagolysosome membrane (10–15). Remarkably, the GBS -h/c is unique among Gram-positive pathogens and its production is linked to that of a characteristic orange-to-red pigment. This dual and specific -h/c and pigment phenotype is routinely used in clinical settings to identify GBS isolates (16, 17).

It was initially proposed that the GBS protein CylE was, in fact, -h/c and that the pigment was a distinct carotenoid-like molecule (18, 19). However, it was recently established that the -h/c and the pigment correspond to a unique molecule called granadaene (9, 11), a 676-Da ornithine rhamno-polyene (11, 20). Granadaene may be entirely synthesized by the 12 genes of the cyl operon (11, 19, 21). It involves the initial synthesis of the b-h/c core lipid by AcpC, CylD, CylI, and CylG (i.e., the Cyl homologues of fatty acid synthesis enzymes) followed by addition of one ornithine and one rhamnose residue by CylE and CylJ, respectively (11). Finally, export of the -h/c toxin requires the ABC-type transporter encoded by cylA and cylB (22).

Transcription of the cyl operon is controlled by CovSR (Control of virulence Sensor and Regulator), a two-component system and the major regulator of GBS virulence (23, 24). The transcriptional regulator CovR binds directly to the cyl promoter, thereby inhibiting operon transcription (23, 25). CovR activity is itself regulated by phosphorylation by its cognate histidine kinase CovS. In addition, two other proteins control CovR: the serine/threonine kinase Stk1, which also phosphorylates CovR, but not at the same site as that modified by CovS (25, 26), and the transmembrane protein Abx1, which interacts with CovS to control the balance between its kinase and phosphatase activities (27). This regulatory network has been proposed to be the central mediator of the switch between the commensal and the virulent GBS lifestyles (26, 27).

Independent studies clearly demonstrated that -h/c pigment production is associated with virulence (9–15). However, it is currently unclear if b-h/c pigment production correlates strictly with GBS virulence. To date, it has been estimated that 85 to 98% of strains isolated from humans produce the -h/c pigment (16, 28, 29), and it is assumed that nonhemolytic and nonpigmented (NH/ NP)strains rarely cause infection (30, 31). Four NH/NP GBS clinical isolates have been characterized in which the cyl operon was inactivated by the insertion element IS1381 (21, 30). In this study, we report the screening of a large collection of human GBS isolates for the presence or absence of the -h/c pigment. Among 1,776 isolates, 63 (3.5%) were NH/NP. The causative mutations of these NH/NP GBS were identified by whole-genome sequencing or by PCR sequencing of genes known to be involved in -h/c pigment production. Several as yet uncharacterized genes of the cyl operon were also inactivated to accurately characterize and compare the phenotypes of the mutants generated.

Explanation / Answer

1. The group B streptococci are Gram positive bacteria and these bacteria cause asymptomatic infections . These are extracellular pathogens. These bacteria release hemolysin toxin.

2. Beta hemolysin or cytolisin is a toxin that is surface associated and is important in playing a role in the pathogenicity or virulence of an enzyme. Also, it is responsible in making the clear zone, that is present around the colonies of the gbs bacteria.

3. A) cyl operon which would be controlled by the CovSR. Operon is a DNA unit that has a number of genes or gene clusters that would be controlled by a single promoter.

B) CovSR which would be a system having two components, regulating this expression.

4. The purpose of the study is to identify virulence factors in gbs. Sample population is neonates.

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