Genetic Relatedness and Superantigen Expression in Group A Streptococcus Serotype M1 Isolates from Patients with Severe and Nonsevere Invasive Diseases

Abstract

The relatedness of group A streptococcal (GAS) strains isolated from 35 Canadian patients with invasive disease of different severity was investigated by a variety of molecular methods. All patients were infected with M1T1 strains and, based on clinical criteria, were classified as severe (n ‫؍‬ 21) and nonsevere (n ‫؍‬ 14) invasive GAS infection cases. All the M1 strains studied had the emm1.0 allele and the same streptococcal pyrogenic exotoxin (Spe) genotype, speA ؉ speB ؉ speC speF ؉ speG ؉ speH smeZ ؉ ssa. All isolates had the same speA allotype, speA2. The randomly amplified polymorphic DNA banding pattern with two different primers was identical for all strains, and pulsed field gel electrophoresis analysis showed that 33 and 30 isolates had identical banding patterns after DNA digestion with SfiI or SmaI, respectively; the nonidentical isolates differed from the main pattern by only one band. A relatively high degree of polymorphism in specific regions of the sic gene was observed among isolates; however, this polymorphism was not associated with disease severity. Likewise, although the phenotypic expression of SpeA, SpeB, and SpeF proteins varied among the M1T1 isolates, there was no correlation between the amount of Spe expressed and disease severity. Importantly, mitogenic and cytokine responses induced by partially purified bacterial culture supernatants containing a mixture of expressed superantigens were very similar for isolates from severe and nonsevere cases (P > 0.1). Together, the data indicate that highly related invasive M1T1 isolates, some indistinguishable, can cause disease of varying severity in different individuals. These findings underscore the contribution of host factors to the outcome of invasive GAS infections.Group A streptococci (GAS) are responsible for a variety of human diseases ranging from simple pharyngitis to highly severe infections, such as necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS) (16). Since the late 1980s, a marked increase in the incidence and severity of invasive infections has been reported in the United States, Canada, Japan, and many regions of Europe (11,13,16,17,20,22,37). Whether this dramatic rise in the incidence of invasive GAS infections resulted from changes in virulence properties of the bacteria and/or alterations of host protective immunity against specific strains or specific virulence factors remains an area of intense investigation.Among the many virulence factors produced by GAS, the M protein and the streptococcal pyrogenic exotoxins (Spes) are considered important virulence factors in the pathogenesis of invasive GAS infections. The Spes belong to the superantigen (SAg) family and thus can induce massive secretion of inflammatory cytokines, such as gamma interferon (IFN-␥), interleukin-1 (IL-1), and tumor necrosis factor ␣. Overproduction of these cytokines can lead to tissue damage, organ failure, and shock (reviewed by Kotb [15]).GAS are classified by their surface M protein type (4, 10). To date, more than 100 d...

Susceptibility to severe streptococcal sepsis: use of a large set of isogenic mouse lines to study genetic and environmental factors

“…7,61 The bacteria were incubated in THY, that is, Todd Hewitt Broth (DIFCO, Detroit, MI, USA) supplied with 1.5% of yeast extract (DIFCO), for 17 h, washed twice with sterile phosphatebuffered saline solution, PBS (Gibco, Carlsband, CA, USA), then diluted to the final inoculum size with sterile PBS. The original isolate had been aliquoted in THY stocks containing 15% glycerol (Sigma, St Louis, MO, USA) at À801C.…”

“…This human pathogen causes a wide variety of conditions ranging from sore throat to invasive life-threatening diseases (reviewed in Cunningham 6 ), and the same strain of pathogen leads to different outcomes in different individuals. 7 Our laboratory provided direct evidence that the highly polymorphic human leukocyte antigen (HLA) genes confer high risk or protection in rheumatic heart disease; 8 as well as in streptococcal toxic shock (STSS) and necrotizing fasciitis (NF). 9,10 In GAS sepsis, allelic variation in HLA class II molecules plays a major role in modulating infection severity, primarily because they serve as binding and signaling receptors for superantigens, 11,12 which are the primary trigger of the severe inflammatory responses that can lead to organ failure and shock.…”

Streptococcal Mitogenic Exotoxin, SmeZ, Is the Most Susceptible M1T1 Streptococcal Superantigen to Degradation by the Streptococcal Cysteine Protease, SpeB

“…Whereas all GAS isolates examined thus far secrete one or more SAg, different strains can produce very different spectra of the Ͼ24 streptococcal SAgs. One of the most clinically relevant strains, the M1T1 strain, whose appearance coincided with the resurgence of severe streptococcal infections around the world in the 1980s, has the following SAg-encoding genes: speA, speF, speG, speJ, and SmeZ (9). SpeA, a horizontally acquired SAg, that has been recently introduced into this strain, has been shown to be a major player in the pathogenesis of STSS.…”

Vaccination equally enables both genetically susceptible and resistant mice to control infection with group A streptococci

“…Several studies have shown that host genetic factors are critical in determining host susceptibility against GAS infection [7][8][9][10]. Thus, while some individuals might respond to GAS infection with a mild disease, the same streptococcal strain can cause very severe invasive infection in more susceptible persons.…”

“…In the particular case of GAS, several studies have shown that individuals within a single human population vary genetically in their susceptibility to infection with this pathogen [7][8][9][10]. Thus, depending of the genetic makeup, different individuals will develop infections of different severities after encounter with the same streptococcal strain.…”