Use of isogenic mutants to study bacterial virulence factors

Solving polymicrobial puzzles: evolutionary dynamics and future directions

Polymicrobial infections include various microorganisms, often necessitating different treatment methods than a monomicrobial infection. Scientists have been puzzled by the complex interactions within these communities for generations. The presence of specific microorganisms warrants a chronic infection and impacts crucial factors such as virulence and antibiotic susceptibility. Game theory is valuable for scenarios involving multiple decision-makers, but its relevance to polymicrobial infections is limited. Eco-evolutionary dynamics introduce causation for multiple proteomic interactions like metabolic syntropy and niche segregation. The review culminates both these giants to form evolutionary dynamics (ED). There is a significant amount of literature on inter-bacterial interactions that remain unsynchronised. Such raw data can only be moulded by analysing the ED involved. The review culminates the inter-bacterial interactions in multiple clinically relevant polymicrobial infections like chronic wounds, CAUTI, otitis media and dental carries. The data is further moulded with ED to analyse the niche colonisation of two notoriously competitive bacteria: S.aureus and P.aeruginosa. The review attempts to develop a future trajectory for polymicrobial research by following recent innovative strategies incorporating ED to curb polymicrobial infections.

pBFK, a new thermosensitive shuttle vector for Streptococcus pyogenes gene deletion by homologous recombination

Streptococcus pyogenes, or Group A Streptococcus (GAS), is a major human pathogen for which genetic manipulation remains an ongoing challenge. We created a new temperature-sensitive plasmid pBFK expressing spectinomycin resistance adapted to homologous recombination procedure to perform a complete gene deletion in GAS. Herein the mutagenesis strategy with pBFK was performed in a highly virulent GAS emm3 genotype.

Construction and phenotypic evaluation of a Vibrio vulnificus vvpE mutant for elastolytic protease

Vibrio vulnificus is an opportunistic gram-negative pathogen that commonly contaminates oysters. Predisposed individuals who consume raw oysters can die within days from sepsis, and even otherwise healthy people are susceptible to serious wound infection after contact with contaminated seafood or seawater. Numerous secreted and cell-associated virulence factors have been proposed to account for the fulminating and destructive nature of V. vulnificus infections. Among the putative virulence factors is an elastolytic metalloprotease. We cloned and sequenced the vvpE gene encoding an elastase of V. vulnificus ATCC 29307. The functions of the elastase were assessed by constructing vvpE insertional knockout mutants and evaluating phenotypic changes in vitro and in mice. Although other types of protease activity were still observed in vvpE mutants, elastase activity was completely absent in the mutants and was restored by reintroducing the recombinant vvpE gene. In contrast to previous characterization of elastase as a potential virulence factor, which was demonstrated by injecting the purified protein into animals, inactivation of the V. vulnificus vvpE gene did not affect the ability of the bacteria to infect mice and cause damage, either locally in subcutaneous tissues or systemically in the liver, in both iron-treated and normal mice. Furthermore, a vvpE mutant was not affected with regard to cytolytic activity toward INT407 epithelial cells or detachment of INT407 cells from culture dishes in vitro. Therefore, it appears that elastase is less important in the pathogenesis of V. vulnificus than would have been predicted by examining the effects of administering purified proteins to animals. However, V. vulnificus utilizes a variety of virulence factors; hence, the effects of inactivation of elastase alone could be masked by other compensatory virulence factors.

The lipopolysaccharide outer core of Yersinia enterocolitica serotype O:3 is required for virulence and plays a role in outer membrane integrity

Lipopolysaccharide (LPS) of Yersinia enterocolitica O:3 has an inner core linked to both the O-antigen and to an outer core hexasaccharide that forms a branch. The biological role of the outer core was studied using polar and non-polar mutants of the outer core biosynthetic operon. Analysis of O-antigen- and outer core-deficient strains suggested a critical role for the outer core in outer membrane properties relevant in resistance to antimicrobial peptides and permeability to hydrophobic agents, and indirectly relevant in resistance to killing by normal serum. Wild-type bacteria but not outer core mutants killed intragastrically infected mice, and the intravenous lethal dose was approximately 10(4)-fold higher for outer core mutants. After intragastric infection, outer core mutants colonized Peyer's patches and invaded mesenteric lymph nodes, spleen and liver, and induced protective immunity against wild-type bacteria. In mice co-infected intragastrically with an outer core mutant-wild type mixture, both strains colonized Peyer's patches similarly during the first 2 days, but the mutant was much less efficient in colonizing deeper organs and was cleared faster from Peyer's patches. The results demonstrate that outer core is required for Y. enterocolitica O:3 full virulence, and strongly suggest that it provides resistance against defence mechanisms (most probably those involving bactericidal peptides).

Mutants of Streptococcus suis types 1 and 2 impaired in expression of muramidase-released protein and extracellular protein induce disease in newborn germfree pigs

The contribution of muramidase-released protein (MRP) and extracellular factor (EF) to the virulence of Streptococcus suis type 1 and 2 infections was studied. For that aim, we constructed mutants of S. suis types 1 and 2 by inactivating the genes encoding MRP and EF. Moreover, we changed a type 2 strain producing the 110-kDa EF protein into a strain producing a modified protein (EF*) of increased molecular mass. The chromosomally located mrp and epf genes were inactivated by replacement recombination by using nonreplicative plasmids. Newborn germfree pigs were inoculated with pathogenic type 1 and 2 strains and with the isogenic mutant strains. Wild-type as well as mutant strains induced fever, specific signs of disease, and lesions. Moreover, all mutant strains could be reisolated from the central nervous system of infected pigs. These results showed that inactivation or alteration of the mrp and epj genes had no measurable effect on the pathogenicity of S. suis types 1 and 2.