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PubMed1983

Characterization of Phage-Sensitive Mutants from a Phage-Insensitive Strain of Streptococcus lactis: Evidence for a Plasmid Determinant that Prevents Phage Adsorption.

A phage-insensitive strain of Streptococcus lactis, designated ME2, was used as a prototype strain for the study of mechanisms and genetics of phage resistance in the lactic streptococci. Mutants sensitive to a Streptococcus cremoris phage, varphi18, were isolated at a level of 17% from cultures of ME2 after sequential transfer at 30 degrees C. Phage-sensitive mutants of ME2 were not fully permissive to varphi18. The efficiency of plating of varphi18 on the mutants was 5 x 10 as compared with <10 for varphi18 on ME2. Further characterization of the mutants showed that they efficiently adsorbed varphi18 at levels of >99.8%, whereas ME2 adsorbed only 20 to 40% of varphi18. These results suggest that increased phage susceptibility of the mutants may result from the loss of a mechanism that inhibits phage adsorption. Moreover, the high frequency of spontaneous mutation in ME2 indicates the involvement of an unstable genetic determinant in this phage defense mechanism. ME2 was shown to possess 13 plasmids ranging in size from 1.6 to 34 megadaltons. Of 40 mutants examined that had increased efficiencies of plating, all were missing a 30-megadalton plasmid, pME0030. These data suggest that pME0030 codes for a function that prevents phage adsorption. Further phenotypic characterization of the phage-sensitive mutants showed that some mutants were deficient in the ability to ferment lactose (Lac) and hydrolyze milk proteins (Prt). However, the Lac and Prt phenotype segregated independently of the phage-sensitivity phenotype. One phage-sensitive adsorption mutant, designated N1, was tested for susceptibility to 14 different phages. N1 showed increased capacity to adsorb 4 and to replicate 2 of these 14 phages, thereby indicating a phage resistance mechanism in ME2 that generalizes to phage interactions other than the specific varphi18-ME2 phage-host interaction. These data provide evidence for a unique plasmid-linked phage defense mechanism in phage-insensitive strains of lactic streptococci.

Journal Article↗
PubMed1997

Molecular population genetic analysis of a Streptococcus pyogenes bacteriophage-encoded hyaluronidase gene: recombination contributes to allelic variation.

Many strains of the human pathogenic bacterium Streptococcus pyogenes produce hyaluronidase, an enzyme that degrades hyaluronic acid, a major component of the extracellular matrix. Degradation of hyaluronic acid is thought to aid in host tissue invasion and dissemination of S. pyogenes. The molecular population genetics of the bacteriophage-encoded hyaluronidase gene (hyl) was analysed by sequencing the gene from 13 streptococcal strains representing seven well-differentiated multilocus enzyme electrophoretic types and eight M or T protein serotypes. Substantial levels of allelic polymorphism were identified, and the analysis found strong statistical evidence that recombinational processes have contributed to the generation of molecular variation in this gene. A 111 base pair segment of hyl encoding a collagenous motif, that may bind collagen, was absent in a serotype M14 isolate and 13 serotype M18 multilocus enzyme electrophoretic type 20 strains examined. The analysis provides a molecular population genetics framework for studies examining the role of naturally occurring hyaluronidase variation in host-pathogen interactions.

Alleles↗
PubMed1993

In vivo definition of the functional origin of replication (ori(+)) of the promiscuous plasmid pLS1.

We have defined the minimal origin of replication of the plasmid pLS1 leading strand, as comprised within a 247 bp region, by in vivo deletion analyses. Cloning of pLS1 DNA regions containing its oriV(+) into a compatible replicon resulted in weak incompatibility towards pLS1, but only when the cloned fragment included the entire pLS1 oriV(+). Plasmids lacking a functional repB gene (which encodes the pLS1 initiator of replication RepB protein) could be established in Streptococcus pneumoniae only when RepB was supplied in trans. We conclude that all the pLS1-encoded gene products involved in its replication and control are efficient trans-complementing plasmid elements.

Bacterial Proteins↗
PubMedDate not supplied

Biological roles of two new murein hydrolases of Streptococcus pneumoniae representing examples of module shuffling.

We have found two murein hydrolases (LytB and LytC) tightly bound to the cell envelope that have completely changed the domain building plan previously reported for the murein hydrolases of Streptococcus pneumoniae. The active center of LytB and LytC is located at the C-terminal, whereas the binding domain is at the N-terminal. LytC has been characterized as the first lysozyme of S. pneumoniae and behaves as an autolysin at 30 degrees C. LytB appears as the main hydrolase responsible for cell separation since inactivation of lytB leads to the formation of long chains of more than 100 cells. These findings indicate that genetic adaptation of mobile domains is extremely efficient in pneumococcus.

Bacterial Proteins↗
PubMed1999

Genetic linkage of exotoxin alleles and emm gene markers for tissue tropism in group A streptococci.

In group A streptococci, genetic markers for principal tissue reservoir are located within emm genes, which encode surface proteins that have a role in virulence. A worldwide collection of 160 isolates was evaluated for two traits: chromosomal emm gene markers for tissue tropism (designated patterns A-E), and bacteriophage-associated genes (speA and speC) encoding pyrogenic exotoxins. The speA and speC alleles of organisms harboring the emm marker for a pharyngeal reservoir (pattern A-C) differ from spe alleles that predominate in organisms with the emm marker for impetigo (pattern D). However, organisms that display the emm marker for both tissue sites (pattern E) are not intermediate for the distribution of either speA or speC alleles, but instead resemble pattern A-C isolates for speA and pattern D strains for speC. Statistically significant nonrandom associations between exotoxin alleles and emm patterns were observed but cannot be readily explained by niche separation alone.

Alleles↗
PubMed2004

Progress toward characterization of the group A Streptococcus metagenome: complete genome sequence of a macrolide-resistant serotype M6 strain.

We describe the genome sequence of a macrolide-resistant strain (MGAS10394) of serotype M6 group A Streptococcus (GAS). The genome is 1,900,156 bp in length, and 8 prophage-like elements or remnants compose 12.4% of the chromosome. A 8.3-kb prophage remnant encodes the SpeA4 variant of streptococcal pyrogenic exotoxin A. The genome of strain MGAS10394 contains a chimeric genetic element composed of prophage genes and a transposon encoding the mefA gene conferring macrolide resistance. This chimeric element also has a gene encoding a novel surface-exposed protein (designated "R6 protein"), with an LPKTG cell-anchor motif located at the carboxyterminus. Surface expression of this protein was confirmed by flow cytometry. Humans with GAS pharyngitis caused by serotype M6 strains had antibody against the R6 protein present in convalescent, but not acute, serum samples. Our studies add to the theme that GAS prophage-encoded extracellular proteins contribute to host-pathogen interactions in a strain-specific fashion.

Alleles↗
PubMed2004

The bifunctional peptidoglycan lysin of Streptococcus agalactiae bacteriophage B30.

A group B streptococcal (GBS) bacteriophage lysin gene was cloned and expressed in Escherichia coli. The purified recombinant enzyme, calculated to have a molecular mass of 49 677 Da, lysed GBS cells. The susceptibility of GBS cells to lysis by the enzyme depended upon the growth stage at which they were harvested, with early exponential phase cells most sensitive. Calcium ions enhanced the activity of the enzyme. The enzyme also lysed other beta-haemolytic streptococci, including groups A, C, E and G streptococci, but not common oral streptococci, including Streptococcus mutans. The generation of both reducing activity and N-terminal alanine residues during lysis indicated that the lysin is a bifunctional enzyme, possessing both glycosidase and endopeptidase activities. This is consistent with the presence of two conserved sequence domains, an Acm (acetylmuramidase) domain associated with lysozyme activity, and a CHAP (cysteine, histidine-dependent amidohydrolases/peptidases) domain associated with endopeptidase activity. Site-directed mutagenesis of conserved cysteine and histidine residues in the CHAP domain and conserved aspartate and glutamate residues in the Acm domain confirmed their importance for lysozyme and endopeptidase activity respectively.

Bacteriolysis↗
PubMed1995

High level expression of Streptococcus pyogenes erythrogenic toxin A (SPE A) in Escherichia coli and its rapid purification by HPLC.

The speA gene encoding streptococcal erythrogenic toxin A (SPE A) from Streptococcus pyogenes bacteriophage T12 was overexpressed in Escherichia coli under the control of the T7 promoter. Since most of the expressed protein was found in the periplasmic space, an osmotic shock extraction with 0.5 M sucrose resulted in a highly enriched preparation of SPE A. An additional two-step purification employing high pressure liquid chromatography resulted in a purified SPE A protein.

Bacterial Proteins↗
PubMed2001

Rapid killing of Streptococcus pneumoniae with a bacteriophage cell wall hydrolase.

Nasopharyngeal carriage is the major reservoir for Streptococcus pneumoniae in the community. Although eliminating this reservoir would greatly reduce disease occurrence, no suitable intervention has been available for this purpose. We show here that seconds after contact, a purified pneumococcal bacteriophage lytic enzyme (Pal) is able to kill 15 common serotypes of pneumococci, including highly penicillin-resistant strains. In vivo, previously colonized mice revealed undetectable pneumococcal titers 5 hours after a single enzyme treatment. Pal enzyme had little or no effect on microorganisms normally found in the human oropharynx, and Pal-resistant pneumococci could not be detected after extensive exposure to the enzyme.

Animals↗
PubMed2006

The cell lysis activity of the Streptococcus agalactiae bacteriophage B30 endolysin relies on the cysteine, histidine-dependent amidohydrolase/peptidase domain.

The Streptococcus agalactiae bacteriophage B30 endolysin contains three domains: cysteine, histidine-dependent amidohydrolase/peptidase (CHAP), Acm glycosidase, and the SH3b cell wall binding domain. Truncations and point mutations indicated that the Acm domain requires the SH3b domain for activity, while the CHAP domain is responsible for nearly all the cell lysis activity.

Amidohydrolases↗
PubMed1999

The autolysin-encoding gene (lytA) of Streptococcus pneumoniae displays restricted allelic variation despite localized recombination events with genes of pneumococcal bacteriophage encoding cell wall lytic enzymes.

The lytA-encoded autolysin (N-acetylmuramoyl-L-alanine amidase) of Streptococcus pneumoniae is believed to play an important role in the pathogenesis of pneumococcal infection and has been identified as a putative vaccine target. Allelic diversity of lytA in an extensive collection of clinical isolates was assessed by restriction fragment length polymorphism and confirmatory sequencing studies. Genetic diversity within lytA is limited, especially compared to the high levels of diversity seen in other pneumococcal virulence factor genes, although small blocks generating mosaic structure were identified. Sequence comparisons with genes encoding cell wall lytic enzymes of pneumococcal bacteriophage suggest that localized recombination events have occurred between host lytA and these bacteriophage genes. These results confirm earlier suggestions that recombination between DNA encoding bacteriophage autolytic enzymes and chromosomally encoded lytA might be important in the evolution of lytA. The implications of these findings for understanding the evolution of lytA and the potential utility of LytA as a vaccine target are discussed.

Alleles↗
PubMed2003

Prophage induction and expression of prophage-encoded virulence factors in group A Streptococcus serotype M3 strain MGAS315.

The genome of the highly virulent group A Streptococcus (GAS) serotype M3 strain MGAS315 has six prophages that encode six proven or putative virulence factors. We examined prophage induction and expression of prophage-encoded virulence factors by this strain under in vitro conditions inferred to approximate in vivo conditions. Coculture of strain MGAS315 with Detroit 562 (D562) human epithelial pharyngeal cells induced the prophage encoding streptococcal pyrogenic exotoxin K (SpeK) and extracellular phospholipase A(2) (Sla) and the prophage encoding streptodornase (Sdn). Increased gene copy numbers after induction correlated with increased speK, sla, and sdn transcript levels. Although speK and sla are located contiguously in prophage Phi315.4, these genes were transcribed independently. Whereas production of immunoreactive SpeK was either absent or minimal during coculture of GAS with D562 cells, production of immunoreactive Sla increased substantially. In contrast, despite a lack of induction of the prophage encoding speA during coculture of GAS with D562 cells, the speA transcript level and production of immunoreactive streptococcal pyrogenic exotoxin A (SpeA) increased. Exposure of strain MGAS315 to hydrogen peroxide, an oxidative stressor, induced the prophage encoding mitogenic factor 4 (MF4), and there was a concomitant increase in the mf4 transcript. All prophages of strain MGAS315 that encode virulence factors were induced during culture with mitomycin C, a DNA-damaging agent. However, the virulence factor gene transcript levels and production of the encoded proteins decreased after mitomycin C treatment. Taken together, the results indicate that a complex relationship exists among environmental culture conditions, prophage induction, and production of prophage-encoded virulence factors.

Bacterial Proteins↗
PubMedDate not supplied

[Use of bacteriophages as selective factors in bacteriological diagnosis of mixed infections].

A new method is proposed for detecting aerobic and anaerobic bacteria during diagnostic culturing by exposure of mixed microorganism populations to bacteriophages. By lysing homologous bacteria, the phages facilitate the detection and isolation of associates resistant to them in pure cultures. The proposed method is compared with the selective media techniques and a conclusion is made on the advantages of selective decontamination of biological samples by bacteriophages in experiments and diagnostic culturing of material from patients with pyo-inflammatory processes.

Bacterial Infections↗