Abstract
Streptococcus pyogenes (GAS) is a human pathogen responsible for a wide array of infections, ranging from pharyngitis and impetigo to severe invasive infections such as necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS). The resurgence and persistence of severe forms of GAS diseases reported since the mid 1980s have motivated intensive research on epidemiological, microbiological and clinical aspects of these diseases.A retrospective hospital-based study was conducted including 126 GAS isolates (27 from invasive infections and 99 from non-invasive infections) collected from January 1999 to June 2003. GAS isolates were characterized by emm type and subtype and superantigen (SAg) gene profile (speA-C, speF-J, speL, speM, ssa and smeZ). The prevalence and mechanisms of macrolide, tetracycline and levofloxacin resistance were also determined.
The most common clinical presentations of invasive cases were skin and soft-tissue infections (40.7%). SSTS occurred in four cases (14.8%) and was associated to NF in half of the cases. Most invasive cases were found in adults, in particular among the elderly and the middle-aged, and a large proportion had underlying conditions, the most frequent being skin lesions, HIV infection, injection drug use, and malignancy.
A total of 29 emm types were identified among the 126 isolates; the most prevalent were emm1 (17.5 %), followed by emm3 (8.7 %), emm4 (8.7 %), emm12 (7.1 %), emm28 (7.1 %), emm11 (6.3 %) and emm77 (6.3 %). These seven emm types accounted for 61.9 % of isolates. There were no differences in the emm type distribution between invasive and non-invasive infections, except for emm25 isolates, which were associated with invasive infections in injecting drug users. The SAg gene profiles were closely associated with the emm type and were independent of the disease type.
The prevalence of erythromycin resistance showed an annual progressive increase from 16.6% (1999) to 38.8% (2003) and was caused by isolates belonging to 11 emm types. mef(A)-positive emm types 4, 12 and 75, and erm(B)-positive emm types 11 and 25 were responsible for up to 80% of the erythromycin-resistant isolates. The prevalence of tetracycline resistance fluctuated over the period studied (maximum 34.6% in 2002 and minimum 15.8% in 2001) and was higher in erythromycin-resistant isolates than in susceptible isolates (42.8% vs 18.7%). Among the tetracycline-resistant isolates, the tet(M) determinant was the most prevalent and was distributed in isolates belonging to 14 emm types, whereas tet(O) was only found in emm77 isolates. No significant differences in resistance rates to erythromycin or tetracycline were found between invasive and non-invasive isolates. The rate of resistance to levofloxacin was 3.2%, encompassing four isolates with reduced susceptibility or intermediate resistance (MIC 2-4 µg/ml) and two isolates with a high level of resistance (MIC >32 µg/ml). Low-level resistance was associated with alterations in ParC (Ser80Pro, Ser79Ala, Ser79Phe and Ala121Val), while high-level resistance was associated with alterations involving both ParC (Ser79Phe and Ala121Val) and GyrA (Ser81Tyr).
| Date of Award | 6 Jun 2008 |
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| Original language | Catalan |
| Supervisor | Beatriz Mirelis Otero (Director) & Ferran Navarro Risueño (Director) |