Toinvestigate the molecular characteristics including antibiotic resistance, strain type, serotype, virulence, biofilm formation of Streptococcus pneumoniae isolated from Shanghai adult patients.

A total of 37 non-repetitive S. pneumoniae isolates causing community acquired and hospital acquired infections of adults were collected from Shanghai Huashan Hospital from January 2011 to December 2013.The inhibitory zone diameter or minimum inhibitory concentrations (MICs) of 9 antimicrobial agents(penicillin, vancomycin, erythromycin, clindamycin, levofloxacin, cefprozi, ceftriaxone, cefotaxime and linezolid) were determined by Kirby-bauer (K-B) method or Etest method; Serotypes were tested by polymerase chain reaction (PCR) and S. pneumoniae antisera agglutination; Genomic characteristics of different serotype strains were determined by pulsed field gel electrophoresis (PFGE) method; Multilocus sequence types (MLST) was used for strain type; Semi quantitative biofilm formation test was used for the biological membrane formation.Ten main pneumococcal virulence genes (cbpA, pspA, cps2A, lytA, nana, pavA, piaA, ply, psaA and spxB) were detected by PCR and gel electrophoresis.Statistical analysis was performed using Stata software and association statistics were tested using Fisher's exact test.

The most frequent serotypes were 19F (13.5%), 23F (13.5%), 14 (10.8%), 19A (10.8%). The penicillin resistance rate was 64.9%.Serotypes 19F, 19A and 23F were significantly associated with penicillin resistance (χ²=5.89, P=0.015) and the isolates belonged to these serotypes were all multi-drug resistant (MDR). ST81 and ST271 showed high resistance rates to several antibiotics including penicillin (χ²=4.57, P=0.033). Biofilm formation was significantly associated with serotypes 19A (χ²=5.55, P=0.018) and strain type ST320 (χ²=4.33, P=0.037), but not associated with penicillin resistance (χ²=0.16, P=0.686). Virulence gene lytA, pavA, ply, psaA, spxB were found in all isolates.

Penicillin resistance rate of S. pneumoniae in adult is rising.Specific serotype, epidemic clone and antibiotic resistance are closely related, and can provide the basis for the infection control.The virulence factors such as PspA will be the new targets for vaccine development to reduce S. pneumoniae infection in the future.(Chin J Lab Med, 2015, 38: 256-261)

Streptococcus pneumoniae; Microbial sensitivity tests; Serotyping; Multilocus sequence typing; Virulence factors; Electrophoresis, gel, pulsed-field; Molecular epidemiology