Surveillance of severe invasive group G streptococcal infections in Japan during 2002-2008

Group G Streptococcus strains isolated from patients with severe invasive infections in the period 2002-2008 were surveyed and their prevalence compared with that observed in the period 1995-2001 in Japan. Strains with genotypes stg485, stg6792, stc36, stg6, and stg652 were isolated in both periods, whereas various new genotypes appeared in 2002-2008 and some genotypes found in 1995-2001 were not found subsequently, thus indicating a change in the prevalent genotyped strains causing severe invasive streptococcal infections.

Highly frequent mutations in negative regulators of multiple virulence genes in group A streptococcal toxic shock syndrome isolates

Streptococcal toxic shock syndrome (STSS) is a severe invasive infection characterized by the sudden onset of shock and multiorgan failure; it has a high mortality rate. Although a number of studies have attempted to determine the crucial factors behind the onset of STSS, the responsible genes in group A Streptococcus have not been clarified. We previously reported that mutations of csrS/csrR genes, a two-component negative regulator system for multiple virulence genes of Streptococcus pyogenes, are found among the isolates from STSS patients. In the present study, mutations of another negative regulator, rgg, were also found in clinical isolates of STSS patients. The rgg mutants from STSS clinical isolates enhanced lethality and impaired various organs in the mouse models, similar to the csrS mutants, and precluded their being killed by human neutrophils, mainly due to an overproduction of SLO. When we assessed the mutation frequency of csrS, csrR, and rgg genes among S. pyogenes isolates from STSS (164 isolates) and non-invasive infections (59 isolates), 57.3% of the STSS isolates had mutations of one or more genes among three genes, while isolates from patients with non-invasive disease had significantly fewer mutations in these genes (1.7%). The results of the present study suggest that mutations in the negative regulators csrS/csrR and rgg of S. pyogenes are crucial factors in the pathogenesis of STSS, as they lead to the overproduction of multiple virulence factors.

Group A streptococcus (GAS) causes life-threatening severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock-like syndrome. Although many studies have attempted to determine factors that are crucial for the onset of streptococcal toxic shock syndrome (STSS), bacterial factors responsible for it have not been clarified. By comparing genome sequences of clinical GAS isolates from STSS with those of non-invasive infections, we showed that mutations of negative regulator genes (csrS, csrR, rgg) were detected at a high frequency of more than 50% in STSS isolates, but at a low frequency of less than 2% in non-invasive isolates. These mutations of negative regulators were found in various emm-genotyped STSS isolates but not in a particular emm genotype. These mutants enhanced virulence in mouse models. Such results indicated that mutations of bacterial negative regulators are crucial for the pathogenesis of STSS due to the overproduction of multiple virulence factors under the de-repressed conditions.

[Mechanism behind streptococcus toxic shock-like syndrome onset--immune evasion and bacterial properties]

Streptococcal toxic shock-like syndrome (STSS) was firstly reported in 1987 in the United States. Japan's first definitive STSS case was reported in 1992, with over 500 cases since confirmed. Mortality is extremely high at 40%. Pathological findings, bacteria aggregation, and a paucity of polymorphonuclear neutrophils (PMN) in the foci of invasive group A streptococcal (GAS) infection suggest that host defense disturbance plays an important role in invasive infection onset. GAS, clinically isolated from severely invasive, but not from non-invasive, infections, could compromise human PMN functions in at least two independent ways-by inducing necrosis to PMN by enhanced production of pore-forming toxin streptolysin O (SLO) and by PMN migration impairment via digesting interleukin-8, a PMN attracting chemokine, through increased serine protease ScpC production. Expression of these genes was upregulated by a loss of repressive function with the csrS gene mutation of the two-component sensor/regulator system.

Incompetence of neutrophils to invasive group A streptococcus is attributed to induction of plural virulence factors by dysfunction of a regulator

Group A streptococcus (GAS) causes variety of diseases ranging from common pharyngitis to life-threatening severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock-like syndrome. The characteristic of invasive GAS infections has been thought to attribute to genetic changes in bacteria, however, no clear evidence has shown due to lack of an intriguingly study using serotype-matched isolates from clinical severe invasive GAS infections. In addition, rare outbreaks of invasive infections and their distinctive pathology in which infectious foci without neutrophil infiltration hypothesized us invasive GAS could evade host defense, especially neutrophil functions. Herein we report that a panel of serotype-matched GAS, which were clinically isolated from severe invasive but not from non-invaive infections, could abrogate functions of human polymorphnuclear neutrophils (PMN) in at least two independent ways; due to inducing necrosis to PMN by enhanced production of a pore-forming toxin streptolysin O (SLO) and due to impairment of PMN migration via digesting interleukin-8, a PMN attracting chemokine, by increased production of a serine protease ScpC. Expression of genes was upregulated by a loss of repressive function with the mutation of csrS gene in the all emm49 severe invasive GAS isolates. The csrS mutants from clinical severe invasive GAS isolates exhibited high mortality and disseminated infection with paucity of neutrophils, a characteristic pathology seen in human invasive GAS infection, in a mouse model. However, GAS which lack either SLO or ScpC exhibit much less mortality than the csrS-mutated parent invasive GAS isolate to the infected mice. These results suggest that the abilities of GAS to abrogate PMN functions can determine the onset and severity of invasive GAS infection.

Characteristics of Streptococcus suis isolated from patients in Japan

Seven cases of Streptococcus suis infection in Japan during 1994 and 2006 were summarized. All cases had porcine exposure and five of them had hand skin injury during the exposure. Five cases presented symptoms of meningitis, three presented symptoms of sepsis, and one resulted in sudden death. All of the isolated S. suis belonged to Lancefield's group D and to serotype 2. They were susceptible to penicillin G, ampicillin, cefotaxime, and ciprofloxacin. However, six of them were resistant to both erythromycin and clindamycin, and four were also resistant to minocycline. Multilocus sequence typing of six isolates showed that they belonged to sequence type (ST) 1, and their pulsed-field gel electrophoresis (PFGE) patterns were similar. The remaining isolate was ST28 and its PFGE pattern was distinct from those of the others.

Surveillance of group B streptococcal toxic shock-like syndrome in nonpregnant adults and characterization of the strains in Japan

Nine group B streptococci (GBS) strains were isolated from five toxic shock-like syndrome cases of nonpregnant adults in Japan from 2001 to 2005. All of them were identified as Streptococcus agalactiae. The serotypes of these strains were Ib, III, V, and VII. Pulsed-field gel electrophoresis revealed that the patterns of the strains isolated from the different patients were variable. Antimicrobial susceptibility tests showed that all of the strains were susceptible to penicillin G, ampicillin, cefotaxime, clindamycin, and telithromycin. One strain showed intermediate resistance to erythromycin.

Use of DNA arrays to identify a mutation in the negative regulator, csrR, responsible for the high virulence of a naturally occurring type M3 group A streptococcus clinical isolate

We previously reported that type M3 group A streptococcus (GAS) showed a wide range of 50% lethal dose values in mice. Analysis using DNA arrays indicated that the most virulent strain, M3-f, expressed significantly higher levels of the products of several virulence genes than did the other M3 isolates. Sequencing of the csrS, csrR, luxS, and rgg genes in the isolates showed that the M-3f csrR gene contained a specific point mutation. Disruption of wild-type (wt) csrR in an M3 strain increased its virulence and the expression of hyaluronic acid, whereas complementation with wt but not type M3-f csrR attenuated these changes. Expression experiments showed that type M3-f CsrR counteracted the effects of wt CsrR. Although wt CsrR bound to the hasA promoter region, type M3-f CsrR did not. Thus, the high virulence of the type M3-f strain is associated with the decreased binding of type M3-f CsrR to its target sequences.

Increased expression of the ska gene in emm49-genotyped Streptococcus pyogenes strains isolated from patients with severe invasive streptococcal infections

Since 2000, emm49-genotyped Streptococcus pyogenes strains have been isolated from patients with severe invasive group A streptococcal infections in Japan, although they had not been isolated before 1999. We compare the characteristics of these strains with those of strains isolated from patients with non-invasive infections. SmaI-digested pulsed-field gel electrophoresis profiles of the isolates were almost indistinguishable between these groups, however, we found that ska (streptokinase gene) transcriptional levels in the strains isolated from patients with severe invasive infections were significantly higher than those in non-invasive infections.

Severity of oral mucositis correlates with the response of oral cancer to preoperative radiochemotherapy

Oral mucositis is a dose-limiting toxic effect of radiotherapy and chemotherapy on oral cancer. The purpose of the present study is to assess the relationship between tumor response and oral mucositis in preoperative radiochemotherapy for oral cancer retrospectively. Fifty-four cases of oral squamous cell carcinoma were treated with concurrent radiochemotherapy prior to surgery. When oral mucositis was evaluated with the WHO scale, severe oral mucositis (Grades 3 and 4) developed in 22 cases (41%). A more than 50% reduction in tumor size was clinically observed in 38 cases (70%). From histopathological analysis of the surgical specimens all tumor cells observed appeared to be non-viable in 16 cases (29%). The cases with Grade 1, Grade 2, Grade 3 and Grade 4 oral mucositis included 33%, 62%, 85% and 89% of clinical good-response cases and 0%, 24%, 31% and 55% of histopathological good-response cases, respectively. This retrospective study suggests that severe oral mucositis promises a good response of oral squamous cell carcinoma to radiochemotherapy.

Antimicrobial susceptibility survey of Streptococcus pyogenes isolated in Japan from patients with severe invasive group A streptococcal infections

We assessed antimicrobial susceptibility against 211 Streptococcus pyogenes strains isolated from patients with severe invasive group A streptococcal infections. Overall, 3.8, 1.4, 1.4, and 0.5% of the isolates were resistant to erythromycin, clindamycin, telithromycin, and ciprofloxacin, respectively, and 10.4% had intermediate resistance to ciprofloxacin. All isolates were susceptible to ampicillin and cefotaxime.

Consideration of cysteine protease activity for serological M-typing of clinical Streptococcus pyogenes isolates

Clinical isolates of Streptococcus pyogenes were classified by serological typing of their surface M protein. Non-M typeable strains with the emm1 gene were characterized as the degradation of M protein caused by overproduction of the extracellular cysteine protease, SpeB. These events are dependent on the growth phase. M protein produced prior to expression of SpeB is degraded in the stationary phase when the active form of SpeB is detected. The proteolytic degradation of M protein should be considered for precise M typing analysis.

Molecular mechanisms of high level tetracycline-resistance in group A streptococcal isolates, T serotypes 4 and 11

The molecular mechanism of high level tetracycline resistance in T serotypes 4 and 11 group A streptococcal (GAS) isolates was examined in 61 tetracycline-resistant isolates in Japan. PCR and sequencing analyses revealed that the T serotype/emm genotype, T4/4 isolates carried tet(O) genes, which were genetically homogenous. The T11/11 and T11/89 isolates carried different subtypes of tet(M) genes, which were present on transposons Tn916 and Tn1545, respectively. In addition, these T11 isolates may have obtained the tet(M) gene after the 1990s, because resistance to tetracycline in T11 isolates was rarely found before then. These results strongly suggested that the T4 and T11 GAS isolates acquired tetracycline-resistance via different molecular mechanisms.

Surveillance of severe invasive group-G streptococcal infections and molecular typing of the isolates in Japan

The number of patients with severe invasive group-G streptococcal (Streptococcus dysgalactiae subsp. equisimilis) infections has been increasing in Japan. The emm genotypes and SmaI-digested pulsed-field gel electrophoresis DNA profiles were variable among the strains isolated, suggesting there has not been clonal expansion of a specific subpopulation of strains. However, all strains carried scpA, ska, slo and sag genes, some of which may be involved in the pathogenesis of the disease.