Genetic Survey of Invasive S. Pneumoniae Serotypes in Bulgaria for a 5-Year Period

Abstract

Streptococcus pneumoniae colonises the mucosal lining of the upper respiratory tract and is an important cause of invasive infections affecting young children, adults over 65 years of age, the immunocompromised and individuals with chronic diseases. Recent studies have shown variations in virulence based on the high rate of pneumococcal recombination. PCR-based molecular methods are highly sensitive, specific and are becoming the preferred tool for quick and accurate diagnosis of bacterial meningitis which is required to be defined within 2-3 hours.
 During the 5-year survey period (2013-2017), 202 materials received as cerebrospinal fluid samples and pneumococcal strains isolated from patients diagnosed with meningitis, were examined by Real-time PCR in the reference laboratory at NCIPD. Serotyping of S. pneumoniae-positive materials was performed with conventional multiplex PCR and Real-time PCR with primers for 41serotypes/serogroups.
 There is a high incidence of S. pneumoniae serotypes not covered by the pneumococcal conjugate vaccine (PCV10) currently used in Bulgaria. It was found that all cases of meningitis caused by S. pneumoniae vaccine serotypes occurred in patients that were not vaccinated.

Streptococcus Pneumoniae Serotype Distribution After the Introduction of Pneumococcal Conjugate Vaccines

“…Serotypes causing IPD changed throughout the years after PCV implementation and NVT are now responsible for invasive disease. However, the revue data showed severe reduction of VT carriage and VT pneumococcal diseases worldwide and definitely confirmed the positive outcomes of the IPD implementation (11,14,15).…”

“…In Bulgaria a study during a period after the introduction of PCV10 demonstrates distribution of NVT 3 and 19A causing meningitis in vaccinated people. Other serotypes/serogroups in the study causing IPD are 8, 9N/L, 10A/D, 10B, 11A/D, 15B/C, 15A/F, 24 A/B/F that are not included in the PCV10 nor PCV13 (14). According to another study from Bulgaria, in Plovdiv region, serotypes 3 and 19A causing meningitis in the period 2013-2017 were confirmed as most abundant (15).…”

Antimicrobial Susceptibility of S. Pneumoniae Strains Isolated From Children With Nasopharyngeal Carriage

“…However, the nonvaccine serotypes are becoming a severe threat in terms of invasive potential. Serotype 3 and 19A are associated with most of the meningitis cases in our country and these serotypes are also associated with resistance profiles (6,10,11). Monitoring serotype distribution of S. pneumoniae and antimicrobial susceptibility patterns in pneumococcal carriers from several European countries shows decrease in antimicrobial tolerance in vaccinated cases compared to non-vaccinated (12).…”

“…The interpretation of the MIC allowed the definition of microorganisms as sensitive, with reduced sensitivity (intermediate, low susceptibility) or resistant, using the criteria for non-meningitis isolates according to EUCAST v9.0. DNA extraction and typing DNA from all strains was isolated using 5% Chelex 100 with Proteinase K 20 mg/ml method as previously described (11). The detection of pneumococcal DNA was performed with conventional PCR and every reaction was checked for amplification with an internal control for the gene cpsA.…”

“…The expression of a specific capsule enables the survival of pneumococci outside the host and is related to the invasive potential of different serotypes (9). Since the introduction of PCV10 in Bulgaria vaccine serotypes are not found among meningitis cases of vaccinated children that shows the effectiveness of the prevention strategy (10,11). However, the nonvaccine serotypes are becoming a severe threat in terms of invasive potential.…”