Effects of environmental factors on streptococcal erythrogenic toxin A (SPE A) production by Streptococcus pyogenes

Therapeutic failures of antibiotics used to treat macrolide-susceptible Streptococcus pyogenes infections may be due to biofilm formation

Streptococcus pyogenes infections often fail to respond to antibiotic therapy, leading to persistent throat carriage and recurrent infections. Such failures cannot always be explained by the occurrence of antibiotic resistance determinants, and it has been suggested that S. pyogenes may enter epithelial cells to escape antibiotic treatment. We investigated 289 S. pyogenes strains isolated from different clinical sources to evaluate their ability to form biofilm as an alternative method to escape antibiotic treatment and host defenses. Up to 90% of S. pyogenes isolates, from both invasive and noninvasive infections, were able to form biofilm. Specific emm types, such as emm6, appeared to be more likely to produce biofilm, although variations within strains belonging to the same type might suggest biofilm formation to be a trait of individual strains rather than a general attribute of a serotype. Interestingly, erythromycin-susceptible isolates formed a significantly thicker biofilm than resistant isolates (P < 0.05). Among resistant strains, those carrying the erm class determinants formed a less organized biofilm than the mef(A)-positive strains. Also, prtF1 appeared to be negatively associated with the ability to form biofilm (P < 0.01). Preliminary data on a selection of strains indicated that biofilm-forming isolates entered epithelial cells with significantly lower efficiency than biofilm-negative strains. We suggest that prtF1-negative macrolide-susceptible or mef(A)-carrying isolates, which are poorly equipped to enter cells, may use biofilm to escape antimicrobial treatments and survive within the host. In this view, biofilm formation by S. pyogenes could be responsible for unexplained treatment failures and recurrences due to susceptible microorganisms.

Reciprocal, temporal expression of SpeA and SpeB by invasive M1T1 group a streptococcal isolates in vivo

The streptococcal pyrogenic exotoxins (Spes) play a central role in the pathogenesis of invasive group A streptococcal (GAS) infections. The majority of recent invasive GAS infections have been caused by an M1T1 strain that harbors the genes for several streptococcal superantigens, including speA, speB, speF, speG, and smeZ. However, considerable variation in the expression of Spe proteins among clonal M1 isolates has been found, and many of the speA-positive M1 strains do not produce detectable amounts of SpeA in vitro. This study was designed to test the hypothesis that speA gene expression can be induced in vivo. A mouse infection chamber model that allows sequential sampling of GAS isolates at various time points postinfection was developed and used to monitor the kinetics of Spe production in vivo. Micropore Teflon diffusion chambers were implanted subcutaneously in BALB/c mice, and after 3 weeks the pores became sealed with connective tissue and sterile fluid containing a white blood cell infiltrate accumulated inside the infection chambers. Representative clonal M1T1 isolates expressing no detectable SpeA were inoculated into the implanted chambers, and the expression of SpeA in the aspirated aliquots of the chamber fluid was analyzed on successive days postinfection. Expression of SpeA was detected in the chamber fluid as early as days 3 to 5 postinfection in most animals, with a significant increase in expression by day 7 in all infected mice. Isolates recovered from the chamber and grown in vitro continued to produce SpeA even after 21 passages in vitro, suggesting stable switch on of the speA gene. A temporal relation between the upregulation of SpeA expression and the downregulation of SpeB expression was observed in vivo. These data suggest that in vivo host and/or environmental signals induced speA gene expression and suppressed speB gene expression. This underscores the role of the host-pathogen interaction in regulating the expression of streptococcal virulence factors in vivo. The model described here should facilitate such studies.

Isolation of human plasma-inducible, growth phase- and temperature-regulated gene fusions in Streptococcus pyogenes using a Tn917-lacZ transposon

Streptococcus pyogenes is capable of causing a variety of human diseases ranging from superficial or deep tissue infections to non-infectious post-streptococcal infection sequelae. In this paper, we report the use of a Tn917-lacZ transposon to isolate random lacZ transcription fusions in the S. pyogenes chromosome. Libraries of random Tn917-lacZ mutants were generated in a representative opacity factor positive strain CS101 (M49) and an opacity factor negative strain 1881 (M1). Several different mutant phenotypes were isolated. These included: temperature-regulated promoters, growth phase/cell density-regulated promoters and a human plasma-inducible promoter. Expression of the temperature-regulated fusions was 5-10-fold higher when grown at 30 degrees C compared to growth at 37 degrees C. The growth phase-regulated fusions were induced 30-fold at late exponential phase and were repressed by a diffusible S. pyogenes factor(s). Expression of the human plasma-inducible fusion was induced 10-15-fold by human plasma or sera, 4-fold by rabbit sera and was repressed by horse and mouse sera. In addition, hemolysin negative and capsule over expression mutants were isolated. These results demonstrate the utility of Tn917-lacZ mutagenesis for the identification of S. pyogenes promoters.