Vancomycin tolerance in clinical and laboratory Streptococcus pneumoniae isolates depends on reduced enzyme activity of the major LytA autolysin or cooperation between CiaH histidine kinase and capsular polysaccharide

Abstract

SummaryVancomycin is frequently added to standard therapy for pneumococcal meningitis. Although vancomycinresistant Streptococcus pneumoniae strains have not been isolated, reports on the emergence of vancomycin-tolerant pneumococci are a cause of concern. To date, the molecular basis of vancomycin tolerance in S. pneumoniae is essentially unknown. We examined two vancomycin-tolerant clinical isolates, i.e. a purported autolysin negative (LytA -), serotype 23F isolate (strain S3) and the serotype 14 strain 'Tupelo', which is considered a paradigm of vancomycin tolerance. S3 was characterized here as carrying a frameshift mutation in the lytA gene encoding the main pneumococcal autolysin. The vancomycin tolerance of strain S3 was abolished by transformation to the autolysin-proficient phenotype. The original Tupelo strain was discovered to be a mixture: a strain showing a vancomycin-tolerant phenotype (Tupelo_VT) and a vancomycinnontolerant strain (Tupelo_VNT). The two strains differed only in terms of a single mutation in the ciaH gene present in the VT strain. Most interestingly, although the vancomycin tolerance of Tupelo_VT could be overcome by increasing the LytA dosage upon transformation by a multicopy plasmid or by externally adding the autolysin, we show that vancomycin tolerance in S. pneumoniae requires the simultaneous presence of a mutated CiaH histidine kinase and capsular polysaccharide.

Effect of new alleles of the histidine kinase gene ciaH on the activity of the response regulator CiaR in Streptococcus pneumoniae R6

“…However, in 2010 the first mutation in a ciaH gene of a clinical S. pneumoniae isolate, the vancomycin-tolerant strain Tupelo, was described (Moscoso et al, 2010). The mutated ciaH gene in this strain has been implicated in the vancomycin-tolerance phenotype (Moscoso et al, 2010), which would be consistent with the established role of CiaRH in lysis protection (Dagkessamanskaia et al, 2004;Mascher et al, 2006). Thus, altered ciaH genes do also occur in clinical isolates of S. pneumoniae.…”

“…Increasing CiaR regulon expression further resulted in the accentuation of the block of competence and elevated b-lactam resistance phenotypes. Since these phenotypes appear to be linked, we wondered if prevention of competence and the concomitant effect on autolysis (Mascher, 2006;Moscoso et al, 2010) would also cause b-lactam resistance. Inactivating either comAB or comDE, the genes involved in early steps of competence induction, had virtually no effect on the growth of these mutants on b-lactam-containing agar plates (data not shown).…”

Toxin-Antitoxin Genes of the Gram-Positive Pathogen Streptococcus pneumoniae: So Few and Yet So Many

“…However, studies on the fitness of antibiotic-resistant bacteria indicated that when the numbers of resistant cells increase above a threshold level, they are likely to remain there for a long time (5). In addition, the pneumococcus is naturally transformable with exogenous DNA, and horizontal DNA transfer among closely related streptococci is evident from the mosaic structure of certain virulence factors, such as the choline-and penicillin-binding proteins (106). Thus, the therapy of pneumococcal diseases is hampered by the increasing prevalence of antibiotic-resistant strains and the suboptimal clinical efficacy of the available vaccines.…”

The Sensor Histidine Kinase RgfC Affects Group B Streptococcal Virulence Factor Expression Independent of Its Response Regulator RgfA

“…Reports of spontaneous mutations in TCS have been described in many bacteria that affect various phenotypic characteristics. For example, mutations in TCS have been shown to confer antibiotic resistance in certain strains of Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecium (53)(54)(55)(56). Clinical isolates containing mutations in the TCS CovR/S (also known as CsrR/S) have been reported in GBS and group A streptococci (GAS) (57,58).…”