The research group has been working since 2004 with different projects linked to the study of Streptococcus agalactiae (SGB).
GBS still remains one of the most frequent causes of morbidity and mortality in newborns. Colonization of the genital tract of pregnant women at term of their gestational age is significantly associated with these infections. Newborns acquire GBS in utero via the ascending route through rupture of intact membranes or during the birth process.
GBS is a microorganism that is part of the normal microbiota of the human genitourinary and gastrointestinal tracts. It is also recognized as an important pathogen in immunocompromised and immunocompetent patients, being mainly responsible for skin and soft tissue infections, endocarditis and osteoarticular infections.
In order to prevent morbidity and mortality of the newborn, the Center for Disease Control and Prevention (CDC) has recommended two strategies in order to identify mothers who, at term gestational age, are colonized with GBS and prevent perinatological disease.
These strategies consist of identifying the following risk factors: previous birth with invasive GBS disease, GBS bacteriuria during pregnancy, premature delivery (before 37 weeks of gestation), intrapartum temperature equal to or greater than 38ºC, premature rupture of the membrane equal to or greater than 18 hours and the carriage of GBS in the genitoanal tract of the pregnant woman between 35-37 weeks of gestation.
Once maternal colonization is detected, intrapartum prophylaxis (PIP) administered with penicillin or ampicillin results in a significant decrease in neonatal invasive infections. In those pregnant with penicillin intolerance, the administration of erythromycin (ERI) and clindamycin (CLI) are recommended.
The severity of neonatal disease is largely determined by a series of virulence factors encoded among others by the gene cps encoding the capsule (8) and genes encoding surface proteins, all necessary for host-bacteria cell interaction.
An important virulence factor is the capsule. Its polysaccharide structure makes it possible to distinguish between 10 serotypes (Ia, Ib, II, III, IV, V, VI, VII, VIII, IX). These capsular serotypes present in their distribution temporal, ethnic variations and according to the place of residence of the pregnant woman.
The first surface protein identified in GBS was the C antigen, which is composed of α and β proteins. GBS can thus express the α-C protein or the β-C protein or both at the same time.
The α-C protein and the β-C protein are encoded by the genes bca and bac, respectively. α-C is associated with the invasion of the epithelial cell and β-C with the inhibition of phagocytosis by interacting with the Fc fraction of IgA
The Rib protein, closely associated with invasive strains, is encoded by the gene rib.
Another virulence factor, the surface enzyme, ScpB (C5a peptidase) encoded by the gene scpB, is involved in neutrophil damage and fibronectin binding to promote adherence and bacterial invasion of epithelial cells.
A surface protein, Lmb, which mediates adherence to human laminin with epithelial damage, collaborating in host invasion, is encoded by the gene lmb.
The HylB protein encoded by the gene hylB, assists in spread through tissues, with impaired leukocyte transport.
The gene cylE encodes a β-hemolysin which is a toxin associated with tissue injury and systemic spread contributing to meningitis.
Current studies have demonstrated the ability of GBS to invade human cells. However, the events underlying host cell invasion are still poorly understood.
Several important interactions between the extracellular matrix and GBS have been reported and proposed for bacterial adhesion and invasion.
Recently, a fibrinogen adhesion protein has been identified in GBS, which adheres strongly to lung epithelial cells and protects the bacterium from opsonization in the human bloodstream, the FbsB protein encoded by the gene fbsB. The FbsB protein is also associated with epithelial invasion.
A new protein, FbsA, encoded by the gene fbsA it protects the bacterium from opsono-phagocytosis and promotes its adherence to epithelial cells and, above all, to the cerebral endothelium, helping the pathogen to cross the blood-brain barrier, leading to meningitis.
This hypothesis that the invasion of host cells represents an important mechanism in the invasive pathogenesis of GBS and its progression to pneumonia, sepsis and meningitis, was sustained in the development of this work and supported in this report presented here on neonatal invasive strains and its corresponding maternal isolate.
Since Lancefield's observation in the 1970s, working with animal models, referring to the protection conferred by the C antigen against GBS infections, these surface proteins, together with the capsule, have been implicated as generators of a protective immune response which links the study of the aforementioned virulence factors to the generation of maternal vaccines that prevent neonatal disease.
With respect to GBS macrolide susceptibility profiles, the emergence of strains resistant to Erythromycin (ERI) and Clindamycin (CLI) is currently known with certainty, hence the importance of monitoring susceptibility to these antimicrobials and identifying genes associated with it
Two mechanisms of resistance to macrolides have been detected in GBS.
The most frequent mechanism is the modification of the ribosomal target site by methylation and the mechanism called efflux or active transport of the drug.
Methylation of the 23S rRNA subunit by the gene erm (ribosomal methylase erythromycin) ermB, ermA (subclass ermTR), causes a conformational change in the prokaryotic ribosome and blocks the binding of macrolides, lincosamides, and streptogramin B to the binding site on the 50S subunit, leading to resistance.
This mechanism confers resistance to macrolides-lincosamides and streptogramin B (MLSB). Methylases can be constitutively expressed (cMLS constitutive resistance phenotypeB) or in an inducible form (inducible resistance phenotype iMLSB).
The so-called active efflux mechanism was described as mediated by the mefA and confers resistance to macrolides but not to lincosamides or streptogramin B (phenotype M).
cMLS constitutive resistanceB and the inducible iMLSB, both are related to gene expression erm.
The constitutive variable shows a high level of resistance to any antimicrobial of the MLS groupB, unlike the inducible one, which only presents resistance to 14-atom macrolides (ERI) and 15-atom macrolides (azithromycin) and in vitro sensitivity to 16-atom macrolides, lincosamides (CLI) and streptogramin B.
Based on these antecedents and recent studies that incorporate modifications to the probable routes of infection of the newborn, efforts are directed at developing maternal vaccines that provide humoral protection to the child, regardless of the conditions before, during and after delivery and to surveillance of antibiotic resistance.
For all of the above, our effort is devoted to the molecular study of virulence factors that may be involved in the development of vaccine strategies for the region and to the search for genes associated with resistance to macrolides in GBS.
Representative bibliography
Keil A , Laczeski M , Oviedo P , Pegels E , Quiroga M , Fonseca MI , Vergara M . (2010). gene detection rib in invasive and colonizing strains of Streptococcus agalactiae in misions. Journal of Science and Technology 14: 25 – 28
Oviedo P, Pegels E, Laczeski M, Quiroga M, Vergara M. (2013). Phenotypic and genotypic characterization of Streptococcus agalactiae in pregnant women. First study in a province of Argentina. Braz J Microbiol 44(1): 253-258.
Laczeski ME, Pegels ER, Oviedo PN, Quiroga MI, Vergara MI. Remuzgo-Martínez S, Pilares-Ortega L, Icardo JM, Valdizán EM, Vargas VI, Pazos A, Ramos-Vivas J. Streptococcus agalactiae: means of conservation accessible to diagnostic laboratories of low and medium complexity. Cuban Journal of Hygiene and Epidemiology 51(2):129 – 139.
Laczeski M, Pegels E, Oviedo P, Quiroga M, Vergara M. (2013). First Study in Missions of Macrolide Resistance Genes in Streptococcus agalactiae. Rev. Cienc. Tech 20: 66–72.
Laczeski M, Pegels E, Oviedo P, Quiroga M, Vergara M. (2014). Molecular profiles and antimicrobial susceptibility of first isolates of Streptococcus agalactiae serotype IX in Argentina. Adv in Microbiol. (2014) 4(1): 317 – 323.