The Majority of 9,729 Group A Streptococcus Strains Causing Disease Secrete SpeB Cysteine Protease: Pathogenesis Implications

Abstract

bGroup A streptococcus (GAS), the causative agent of pharyngitis and necrotizing fasciitis, secretes the potent cysteine protease SpeB. Several lines of evidence suggest that SpeB is an important virulence factor. SpeB is expressed in human infections, protects mice from lethal challenge when used as a vaccine, and contributes significantly to tissue destruction and dissemination in animal models. However, recent descriptions of mutations in genes implicated in SpeB production have led to the idea that GAS may be under selective pressure to decrease secreted SpeB protease activity during infection. Thus, two divergent hypotheses have been proposed. One postulates that SpeB is a key contributor to pathogenesis; the other, that GAS is under selection to decrease SpeB during infection. In order to distinguish between these alternative hypotheses, we performed casein hydrolysis assays to measure the SpeB protease activity secreted by 6,775 GAS strains recovered from infected humans. The results demonstrated that 84.3% of the strains have a wild-type SpeB protease phenotype. The availability of whole-genome sequence data allowed us to determine the relative frequencies of mutations in genes implicated in SpeB production. The most abundantly mutated genes were direct transcription regulators. We also sequenced the genomes of 2,954 GAS isolates recovered from nonhuman primates with experimental necrotizing fasciitis. No mutations that would result in a SpeB-deficient phenotype were identified. Taken together, these data unambiguously demonstrate that the great majority of GAS strains recovered from infected humans secrete wild-type levels of SpeB protease activity. Our data confirm the important role of SpeB in GAS pathogenesis and help end a long-standing controversy.

Null Mutations of Group A Streptococcus Orphan Kinase RocA: Selection in Mouse Infection and Comparison with CovS Mutations in Alteration of In Vitro and In Vivo Protease SpeB Expression and Virulence

“…These data are consistent with the findings that no RocA mutations are detected but CovS mutations are frequent in clinical SpeB AϪ isolates (39). As shown in Fig.…”

“…In addition, the majority (84.6%) of invasive M1 GAS isolates are SpeB Aϩ , and no MGAS2221 CovRS mutants were detected among isolates recovered from muscle infections in nonhuman primates (39). However, it should be noted that the percentage of SpeB isolates among clinical invasive emm1 GAS isolates in that study (39) was similar to the percentage of SpeB AϪ variants among GAS isolates from infected mice obtained at day 4 after inoculation in this study. The GAS isolates were recovered at day 1 after inoculation in that nonhuman primate study, and a lack of CovRS mutants in that study could have been due to the short duration of infection (39).…”

“…However, it should be noted that the percentage of SpeB isolates among clinical invasive emm1 GAS isolates in that study (39) was similar to the percentage of SpeB AϪ variants among GAS isolates from infected mice obtained at day 4 after inoculation in this study. The GAS isolates were recovered at day 1 after inoculation in that nonhuman primate study, and a lack of CovRS mutants in that study could have been due to the short duration of infection (39). Furthermore, the downregulation of SpeB expression and speB deletion may have different consequences.…”

“…On the other hand, speB is critical for the virulence of the M3 AM3 strain in intraperitoneal infections in mice (13). In addition, the majority (84.6%) of invasive M1 GAS isolates are SpeB Aϩ , and no MGAS2221 CovRS mutants were detected among isolates recovered from muscle infections in nonhuman primates (39). However, it should be noted that the percentage of SpeB isolates among clinical invasive emm1 GAS isolates in that study (39) was similar to the percentage of SpeB AϪ variants among GAS isolates from infected mice obtained at day 4 after inoculation in this study.…”

Catch Me if You Can: <b><i>Streptococcus pyogenes</i></b> Complement Evasion Strategies

“…Moreover, speB is expressed during infection, humans generate anti-SpeB antibodies, and acute-phase sera from patients suffering from GAS bacteraemia have lower SpeB antibodies than patients with uncomplicated tonsillitis [2, 34]. Furthermore, a recent study analysing > 9,000 GAS strains highlighted that the overwhelming majority of isolates derived from serotypes associated with invasive disease secrete SpeB [35]. …”