Serological and molecular capsular typing, antibiotic susceptibility and multilocus sequence typing of Streptococcus pneumoniae isolates from invasive and non-invasive infections.

Background: Streptococcus pneumoniae (S. pneumoniae) is a major causative agent of severe infections, including sepsis, pneumonia, meningitis, and otitis media, and has become a major public health concern. We report the pneumococcal serotype and sequence type (ST) distribution, and antimicrobial resistance of 39 S. pneumoniae strains from seven hospitals in China.

Methods: Blood/cerebrospinal fluid (CSF) and sputum isolates from patients were analyzed to determine S. pneumoniae serotypes by polymerase chain reaction (PCR) and the Neufeld Quellung reaction, the multilocus sequence types (MLST) by PCR and sequencing, and susceptibility to antimicrobial agents by the VITEK Gram Positive Susceptibility Card.

Results: A total of 39 isolates were collected including 21 blood/CSF and 18 sputum isolates. Conventional serotyping by the Quellung reaction required 749 reactions. In contrast, PCR based typing needed only 106 PCR reactions. The most frequent serotypes from the blood/CSF isolates were 14 (38.1%), 19A (14.3%), 23F (9.5%), and 18C (9.5%). In the sputum isolates the most frequent serotypes were 19F (33.3%), 23F (16.7%), 19A (11.1%), and 3 (11.1%). The incidence of penicillin resistance in the blood/CSF and sputum isolates was 66.7% and 55.6%, respectively. Statistical analysis showed that patients = 5 years old had a higher resistance to penicillin when they compared with the patients = 65 years old (P = 0.011). Serotypes 14, 19A and 19F were significantly associated with penicillin resistance (P < 0.001). ST320, ST271, and ST876 isolates showed high resistant rates to several antibiotics including penicillin (P = 0.006). All of the isolates of serotype 19A were resistant to both penicillin and erythromycin, and they were all multi-drug resistant (MDR) isolates.

Conclusions: The specificity and sensitivity of multiplex-PCR are good, and this method represents a substantial savings of time and money, and can be widely used in the laboratory and clinical practice. Data from this research showed an extremely high prevalence of penicillin resistance and an increasing prevalence of multi-drug resistant (MDR) rate in S. pneumoniae. A distinctive emergence of serotype 19A was observed which was also associated with the increasing prevalence of antimicrobial resistance. Therefore, nationwide surveillance of pneumococcal resistance and serotypes is strongly warranted.