[Study of serotype distribution, antimicrobial resistance patterns and molecular epidemiology in 148 isolates of invasive Streptococcus pneumoniae].

OBJECTIVE

To investigate the serotype distribution, antimicrobial resistance patterns and molecular epidemiology of Streptococcus pneumoniae (S. pneumoniae) isolated from invasive pneumococcal diseases in order to provide rationales for antibiotics application and immunity control of S. pneumoniae.

METHODS

A total of 148 isolates of invasive S. pneumoniae were collected from blood, cerebrospinal fluid and other sterile body fluids from 15 regions between January 2005 and August 2008 nationwide. Agar dilution method was used to determine the minimal inhibitory concentrations (MICs) of penicillin and other antibiotics against these isolates. Simplified chessboard system and capsule swelling reaction were used for serotyping of S. pneumoniae. Multilocus sequence typing (MLST) was used to determine the genetic relationship of 53 strains of serogroup-19.

RESULTS

Twenty serotypes/serogroups were identified in 148 strains. The prevalent serotypes (70.9%) were 19A, 19F, 3, 23F, 5, 6, 14 and 9 respectively. Serotypes 19A (22.3%, 33/148) and 19F (16.9%, 25/148) were the most frequent type observed. And serotypes 3 (7.4%, 11/148) and 23F (6.8%, 10/148) were less prevalent. Of all 36 strains isolated from infants under 2 years old, 33.3% (12/36) were covered by 7-valent pneumococcal conjugate vaccine (PCV7). The resistant rates to amoxicillin/clavulanic acid, erythromycin and other antibiotics in PCV7-related pneumococcal strains were significantly higher than those in PCV7-unrelated group (P < 0.05). Fifty-three strains of serogroup-19 were genotyped by MLST and 9 sequence types (STs) identified. ST320 (52.8%, 28/53) and ST271 (22.6%, 12/53) were the most frequent STs.

CONCLUSIONS

The major serotypes of invasive S. pneumoniae are 19A, 19F, 3 and 23F. Antimicrobial-resistant S. pneumoniae has become a serious issue of public health.