Streptococcus pneumoniae from Palestinian nasopharyngeal carriers: serotype distribution and antimicrobial resistance

Abstract

Infections of Streptococcus pneumoniae in children can be prevented by vaccination; left untreated, they cause high morbidity and fatalities. This study aimed at determining the nasopharyngeal carrier rates, serotype distribution and antimicrobial resistance patterns of S. pneumoniae in healthy Palestinian children under age two prior to the full introduction of the pneumococcal 7-valent conjugate vaccine (PCV7), which was originally introduced into Palestine in a pilot trial in September, 2010. In a cross sectional study, nasopharyngeal specimens were collected from 397 healthy children from different Palestinian districts between the beginning of November 2012 to the end of January 2013. Samples were inoculated into blood agar and suspected colonies were examined by amplifying the pneumococcal-specific autolysin gene using a real-time PCR. Serotypes were identified by a PCR that incorporated different sets of specific primers. Antimicrobial susceptibility was measured by disk diffusion and MIC methods. The resulting carrier rate of Streptococcus pneumoniae was 55.7% (221/397). The main serotypes were PCV7 serotypes 19F (12.2%), 23F (9.0%), 6B (8.6%) and 14 (4%) and PCV13 serotypes 6A (13.6%) and 19A (4.1%). Notably, serotype 6A, not included in the pilot trial (PCV7) vaccine, was the most prevalent. Resistance to more than two drugs was observed for bacteria from 34.1% of the children (72/211) while 22.3% (47/211) carried bacteria were susceptible to all tested antibiotics. All the isolates were sensitive to cefotaxime and vancomycin. Any or all of these might impinge on the type and efficacy of the pneumococcal conjugate vaccines and antibiotics to be used for prevention and treatment of pneumococcal disease in the country.

Figure 1. A representative DNA electrophoresis gel showing the RFLP patterns of the serotypes 6A/C and 6B after BsrI digestion of the amplified cps amplicon (273 bp) for isolates of S. pneumonia of the serogroup 6.

DNA was visualized in 2% agarose gel: lane 1 100 bp ladder; lane 12 50 bp ladder. Lanes 2–4 and 7–8 S. pneumonia serotype 6A/C patterns (yielding fragments of 145, 69 and 59 bp, with both smaller fragments showing as one thick band owing to low separation). Lanes 5–6 and 9–11 S. pneumonia serotype 6B (yielding fragments of 214 and 59 bp).