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Genetics of
pathogenic streptococci
In the initial works of the scientists of the
Department the genetic research was targeted to the analysis of
extrachromosomal factors of the streptococcal genetics (phenomenon of
lysogeny and temporate phages, group A and C virulent phages, plasmids
encoding resistance to antibiotics as well as a new class of
minicirculating cryptic plasmids) has been made. In parallel, a work has
been carried out on genetic transformation of streptococci by
electroporation. The results allowed to make vector constructions for
the intra- and inter-species genetic exchange of streptococcal genes and
their cloning, as well as to provide conditions for studying genes and
their localization on the microbial chromosome. So, the streptococci
became classical objects for microbial genetics. During the recent 10
years significant results have been obtained and, in particular:
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First GAS and GBS genetic maps have been constructed
with localization on the chromosome of genes coding DNA recombination
and reparation proteins, ribosome proteins, the origin of chromosome
replication and certain pathogenic factors. The microbial cell wall
protein genes (protective Bac-protein, glutamin-synthetase,
antihemotaxic factor C5a-peptidase, adhesion factors) and genetic region
of the virulence regulone (microbial proteins interacting with blood
proteins) have been also studied. The Department participated and
successfully finished an international project on complete sequencing of
the group A streptococcus genome (serotype M1).
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The information value of a complex approach
(different kinds of PCR-analysis, DNA electrophoresis in PFGE, DNA
hybridization with probes to different genes, determination of ribotype
and the type of distribution of different IS-elements) has been
evaluated for molecular epidemiology and detection of the genome
polymorphism of GAS and GBS strains. The same approach has detected
distinctions in the set of pathogenicity genes in GBS isolated from
humans and "mastitis" cows that points to distinctions in the
pathogenicity mechanisms of strains of contrast ecotypes of the same
kind microbe.
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A comparison of genomes GAS and GBS by the
method of subtracting hybridization has revealed unknown GBS genes that
allowed mapping the genome sites different for both kinds of bacteria.
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Gene bac — one of the main genes of the GBS
pathogenicity responsible for binding IgA was mapped on the GBS genome.
The presence of gene bac was first shown in the "pathogenicity island"
which in addition to bac contains the genes of transposase GAS, IS1381
analogue, sensory histidinkinase and DNA-binding protein of the response
regulator, homologous to those of pneumococcus. The two latter code the
two-component regulatory system unknown earlier to GBS.
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an analysis of clinical GBS strains has
revealed a correlation between the character of the process caused by
them and the presence in the genome of sspB1 and sspB2 genes coding
these proteins of the microbial cell wall
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