The highly conserved serine threonine kinase StkP of Streptococcus pneumoniae contributes to penicillin susceptibility independently from genes encoding penicillin-binding proteins

Abstract

BackgroundThe serine/threonine kinase StkP of Streptococcus pneumoniae is a major virulence factor in the mouse model of infection. StkP is a modular protein with a N-terminal kinase domain a C-terminal PASTA domain carrying the signature of penicillin-binding protein (PBP) and prokaryotic serine threonine kinase. In laboratory cultures, one target of StkP is the phosphoglucosamine mutase GlmM involved in the first steps of peptidoglycan biosynthesis. In order to further elucidate the importance of StkP in S. pneumoniae, its role in resistance to β-lactams has been assessed by mutational analysis in laboratory cultures and its genetic conservation has been investigated in isolates from infected sites (virulent), asymptomatic carriers, susceptible and non-susceptible to β-lactams.ResultsDeletion replacement mutation in stkP conferred hypersensitivity to penicillin G and was epistatic on mutations in PBP2X, PBP2B and PBP1A from the resistant 9V clinical isolate URA1258. Genetic analysis of 55 clinical isolates identified 11 StkP alleles differing from the reference R6 allele. None relevant mutation in the kinase or the PASTA domains were found to account for susceptibility of the isolates. Rather the minimal inhibitory concentration (MIC) values of the strains appeared to be determined by their PBP alleles.ConclusionThe results of genetic dissection analysis in lab strain Cp1015 reveal that StkP is involved in the bacterial response to penicillin and is epistatic on mutations PBP 2B, 2X and 1A. However analysis of the clinical isolates did not allow us to find the StkP alleles putatively involved in determining the virulence or the resistance level of a given strain, suggesting a strong conservation of StkP in clinical isolates.

Eukaryote-Like Serine/Threonine Kinases and Phosphatases in Bacteria

“…The importance of PknB and its cognate phosphatase in the synthesis of peptidoglycan and wall teichoic acid was further supported by the impact of the ⌬pknB mutation on S. aureus metabolism (92). Similar division and growth defects, as well as antibiotic susceptibility phenotypes, were described for Streptococcus pyogenes, Streptococcus agalactiae, S. pneumoniae, and Streptococcus mutans (9,37,72,132,144,149,174), as well as Enterococcus faecalis (82).…”

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

“…StkP (Ser/Thr kinase) is involved in pneumococcal cell division (131) and has been shown to colocalize with PBP2x at the cell division site (132). Inactivation of stkP in a penicillin-resistant clinical isolate with altered PBPs abrogated penicillin resistance; however, a survey of penicillin-resistant isolates revealed no altered stkP alleles (133).…”

Control of cell division in Streptococcus pneumoniae by the conserved Ser/Thr protein kinase StkP

“…PASTA domains of StkP were shown to bind synthetic and native PG subunits and β-lactam antibiotics (28). A strain in which stkP is deleted is still viable in vitro but grows more slowly, is less competent for genetic transformation, and is more susceptible to several environmental stresses (29)(30)(31)(32). StkP also plays an essential role for in vivo survival, because stkP mutants were strongly attenuated in virulence in mouse models (29,30).…”