The epidemiology, virulence genes, and drug resistance of group A Streptococcus

• Main Authors: Jiun-Nong Lin, 林俊農
• Other Authors: Yen-Hsu Chen
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/56144325950501332693

博士 === 高雄醫學大學 === 醫學研究所-臨床醫學組 === 102 === Background: Group A Streptococcus (GAS), also known as Streptococcus pyogenes, is a Gram-positive coccus that is arranged in pairs or in chains. This microorganism exists ubiquitously in the environment and can cause a wide variety of human infections that range from mild pharyngitis, erysipelas, and cellulitis to life-threatening diseases, such as bacteremia, pneumonia, puerperal sepsis, necrotizing fasciitis, and streptococcal toxic shock syndrome. Both the host and microorganism’s factors are involved in the pathogenesis of GAS infections. The aims of this study are as follows: (1) to identify the clinical manifestations and risk factors of GAS necrotizing fasciitis; (2) to explore the clinical and molecular characteristics of GAS skin and soft-tissue infection; (3) to investigate the relation between GAS superantigen genes and streptococcal toxic shock syndrome; (4) to evaluate the association between polymorphisms in the csrRS two-component regulatory system and invasive GAS infection; and (5) to study the GAS susceptibility to fluoroquinolones and the mutations in the genes of quinolone resistance-determining regions. Methods: All the isolates used in this study were obtained from the clinical laboratory of E-Da Hospital. We characteristized the epidemiological data of GAS, including emm typing, multilocus sequence typing, and pulsed-field gel electrophoresis. We also collected the clinical information of patient with skin and soft-tissue infection, necrotizing fasciitis, and toxic shock syndrome caused by GAS. We investigated the virulence factors of GAS, including superantigen genes and csrRS two-component regulatory system, as well as the mutations in the gyrA, gyrB, parC, and parE of quinolone resistance-determining regions of GAS. Results: First, we found that old age, diabetes mellitus, liver cirrhosis, and gout were risk factors for necrotizing fasciitis, and early surgery is the most important factor to reduce mortality in patients with necrotizing fasciitis. Second, we identified the emergence of GAS emm106 (38.2%) causing skin and soft-tissue infection. Old age, diabetes mellitus, neutrophil ≥ 80%, serum creatinine ≥ 2 mg/dl, high serum C-reactive protein, and bacteremia were associated with invasive GAS skin and soft-tissue infection. Third, the mean age of patients with streptococcal toxic shock syndrome was 54.7 years, and 81.1% were male. The most prevalent underlying disease was diabetes mellitus (45.3%). The overall mortality rate of streptococcal toxic shock syndrome was 32.1%. The most prevalent emm type that caused streptococcal toxic shock syndrome was emm102 (18.9%). Among the superantigen genes, speB was the most frequently detected one (92.5%). The presence of speG was negatively associated with a fatal outcome (P = 0.045). Fourth, phylogenetic analysis showed that the frequency and distribution of polymorphisms in csrR and csrS were significantly different between the invasive and noninvasive infection isolates (P < 0.001). The dN/dS ratio indicated that both csrR and csrS were under purifying selection. The fixation index suggested a moderate evolutionary differentiation of the csrR and csrS alleles between invasive and noninvasive isolates. For CsrR, only one noninvasive isolate was identified to have a V29I mutation. The amino acid substitutions in CsrS included S32P (0.6 %), E265G (0.6 %), E265K (0.6 %), I332V (1.7 %), and N498K (82.6 %). Isolates with an N498K single mutation were more likely to be associated with invasive infections (P < 0.001). Finally, the prevalence of GAS nonsusceptibility to fluoroquinolones was 11%. The nonsusceptible isolates included emm1/ST28, emm4/ST39, emm12/ST36, and emm87/ST62. emm12 (50%) demonstrated the highest prevalence of fluoroquinolone nonsusceptibility. Amino acid alterations of Ser79Phe and Ala121Val in ParC were the most frequently identified mutations in the fluoroquinolone-nonsusceptible GAS. Two high-level ciprofloxacin- and levofloxacin-resistant GAS emm12/ST36, each containing a Ser81Phe mutation in GyrA in addition to the Ser79Phe and Ala121Val mutations in ParC, were identified. There were no amino acid substitutions in GyrB, and one emm87/ST62 exhibited three nonsynonymous mutations in ParE. Conclusions: We identified the unique epidemiology of GAS infections in Taiwan, including emm106 causing invasive skin and soft-tissue infection, emm102 resulting streptococcal toxic shock syndrome, and the high prevalence of fluoroquinolone-nonsusceptible emm12/ST36. We also revealed the superantigen genes distribution in GAS causing streptococcal toxic shock syndrome and the association of csrRS polymorphisms and the invasiveness of GAS infection. Characterization of clinical manifestations, epidemiological information, molecular traits, and virulence determinants of GAS improves our understanding of this old but important microorganism.