Sequence types and antimicrobial susceptibility of invasive streptococcus pneumoniae isolates from a region with high antibiotic selective pressure and suboptimal vaccine coverage

Immunization with pneumococcal neuraminidases NanA, NanB and NanC to generate neutralizing antibodies and to increase survival in mice

Purpose. Pneumococcal virulence protein-based vaccines can provide serotype-independent protection against pneumococcal infections. Many studies, including clinical observational studies on Thomsen-Friedenrich antigen exposure and haemolytic uremic syndrome, defined the role of neuraminidases NanA, NanB and NanC in host-pneumococcus interaction. Since neuraminidases are major virulence proteins, they are potential targets for both vaccines and small molecule inhibitors. Here we explored the utility of three neuraminidases as protein vaccine antigens to generate neutralizing antibodies and to increase survival following pneumococcal infections.Methodology. Rabbits and mice were immunized subcutaneously with enzymatically active recombinant NanA, NanB and NanC as individual or a combination of the three neuraminidases. Antisera titres were determined by ELISA. Neuraminidase activity inhibition by antiserum was tested by peanut lectin and flow cytometry. Clinical isolates with serotype 3, 6B, 14, 15B, 19A and 23F were used to infect immunized mice by tail vein injection.Results/Key findings. Presence of high levels of IgG antibodies in antisera against NanA, NanB and NanC indicates that all of the three neuraminidases are immunogenic vaccine antigens. To generate potent NanA neutralizing antibodies, both lectin and catalytic domains are essential, whereas for NanB and NanC a single lectin domain is sufficient. Immunization with triple neuraminidases increased the survival of mice when intravenously challenged with clinical isolates of serotype 3 (40 %), 6B (60 %), 15B (60 %), 19A (40 %) and 23F (30 %).Conclusion. We recommend the inclusion of three pneumococcal neuraminidases in future protein vaccine formulations to prevent invasive pneumococcal infection caused by various serotypes.

Invasive pneumococcal disease caused by ceftriaxone-resistant Streptococcus pneumoniae in Taiwan

BACKGROUND

Invasive pneumococcal disease (IPD) was associated with mortality, but the risk factors associated with mortality remains controversial.

METHODS

A retrospective cohort study was designed. All patients with IPD from 2011 to 2013 admitted in a medical center were screened and collected for their clinical presentations and laboratory characteristics.

RESULTS

Approximately half of the 134 IPD isolates derived from these patients belonged to three major serotypes (19A, 6A and 3), which are included in 13-valent pneumococcal conjugate vaccine (PCV13), but not in 7-valent pneumococcal conjugate vaccine (PCV7). Ceftriaxone resistance according to non-meningitis criteria was identified in 38% of the IPD isolates, and was the major independent risk factor associated with inappropriate initial therapy that subsequently contributed to mortality of the patients. Infection by serotype 6A, 15B, 19A, 19F, or 23F was the major independent risk factor associated with ceftriaxone resistance (non-meningitis criteria). 77.6% of these isolates belonged to additional PCV13 serotypes, with more than 40% expressing resistance to ceftriaxone. In terms of serotype coverage, PCV13 covered 94.1% of the IPD isolates with ceftriaxone resistance, in comparison to 21.6% only by PCV7.

CONCLUSIONS

The increase of ceftriaxone resistance in pneumococci in part driven by PCV7 vaccination in Taiwan is worrisome. The use of PCV13 in children as well as in the elderly population is likely to offer protection from the infection caused by ceftriaxone-resistant pneumococci. It is important to give an effective drug such as penicillin, fluoroquinolones or vancomycin in 2 days for improving outcome of IPD patients.

Pneumococcal disease and use of pneumococcal vaccines in Taiwan

The use of pneumococcal vaccine plays an important role for prevention of invasive pneumococcal disease (IPD). However, introducing the pneumococcal vaccine into the national immunization program (NIP) is complex and costly. The strategy of progressively integrating the pneumococcal conjugate vaccine (PCV) into the NIP in Taiwan provides valuable experience for policy makers. The 7-valent PCV (PCV7) was first available in Taiwan in late 2005. PCV7 was first provided free to children with underlying diseases, those in vulnerable socioeconomic status, and those with inadequate health care resources. The catch-up immunization program with the 13-valent PCV was launched in 2013 and the national pneumococcal immunization program was implemented in 2015. Children aged 2-5 years had the highest incidence of IPD among pediatric population in Taiwan. Although the incidence of IPD caused by PCV7 serotypes has declined, the overall incidence of IPD remained high in the context of PCV7 use in the private sector. A surge of IPD caused by serotype 19A occurred, accounting for 53.6% of IPD cases among children aged ≤ 5 years in 2011-2012. After the implementation of the national pneumococcal immunization program, serogroup 15 has become the leading serogroup for IPD in children. Continued surveillance is necessary to monitor the serotype epidemiology in Taiwan.

Expansion and evolution of Streptococcus pneumoniae serotype 19A ST320 clone as compared to its ancestral clone, Taiwan19F-14 (ST236)

BACKGROUND

The Streptococcus pneumoniae serotype 19A sequence type (ST) 320 clone, derived from an international Taiwan(19F)-14 (ST236) clone, has become prevalent in many countries.

METHODS

The dynamics of invasive pneumococcal disease (IPD) were determined using the database of the National Notifiable Disease Surveillance System in Taiwan. The virulence of 19A ST320 and Taiwan(19F)-14 (ST236) were assessed in mice. By constructing an isogenic serotype 19F variant of the 19A ST320 strain (19F ST320), we analyzed the role of capsular type and genetic background on the difference in virulence between 19A ST320 and Taiwan(19F)-14 (ST236).

RESULTS

Between 2008 and 2011, IPD due to serotype 19A increased from 2.1 to 10.2 cases per 100 000 population (P < .001); IPD due to any serotype also significantly increased (P = .01). Most serotype 19A isolates belonged to ST320. Using competition experiments in a murine model of colonization, we demonstrated that 19A ST320 outcompeted Taiwan(19F)-14 (ST236; competitive index, 20.3; P = .001). 19F ST320 was 2-fold less competitive than the 19A ST320 parent (competitive index, 0.47; P = .04) but remained 14-fold more competitive than Taiwan(19F)-14 (ST236; competitive index, 14.7; P < .001).

CONCLUSIONS

Genetic evolution of pneumococcal clones from Taiwan(19F)-14 (ST236) to 19A ST320 has made this pneumococcus better able to colonize of the nasopharynx. This evolution reflects not only a switch in capsular serotype but also changes in other loci.

Necrotizing pneumonia caused by nanC-carrying serotypes is associated with pneumococcal haemolytic uraemic syndrome in children

Streptococcus pneumoniae infection is a leading cause of morbidity and mortality worldwide. One of the most severe complications of invasive pneumococcal disease (IPD) is haemolytic uraemic syndrome (HUS). This study was undertaken to determine the risk factors and role of pneumococcal neuraminidases in HUS in children with IPD. Eighteen cases of HUS and 54 patients with IPD without HUS were identified. The controls were patients with culture-confirmed IPD without HUS. Clinical and laboratory characteristics of the two groups of patients were compared. Bacterial isolates from both groups were serotyped, sequence typed and examined for their carriage of three neuraminidase genes. Necrotizing pneumonia and serotype 3 infection were significantly associated with HUS in children with IPD, suggesting that a severe pulmonary suppurating disease increase the risk of HUS. Serotype 14 was associated with necrotizing pneumonia but not HUS. Children with HUS were more likely to require surgery and had a longer duration of hospitalization. The study identified a significantly higher carriage of a neuraminidase gene, nanC, in the causative pneumococcal isolates from patients with HUS (89% versus 41%, p 0.001). The sensitivity and specificity of nanC to predict HUS were 89% and 59%, respectively. In conclusion, necrotizing pneumonia, serotype 3 infection and neuraminidase gene nanC were associated with HUS in children with IPD. The result suggests that NanC could provide an additive effect to NanA and NanB in the overall activity of pneumococcal neuraminidases to expose Thomsen-Friedenreich antigen on various cells in patients with HUS.

Pneumococcal carriage and antibiotic resistance in young children before 13-valent conjugate vaccine

BACKGROUND

We sought to measure trends in Streptococcus pneumoniae carriage and antibiotic resistance in young children in Massachusetts communities after widespread adoption of heptavalent 7-valent pneumococcal conjugate vaccine (PCV7) and before the introduction of the 13-valent PCV (PCV13).

METHODS

We conducted a cross-sectional study including collection of questionnaire data and nasopharyngeal specimens among children aged <7 years in primary care practices from 8 Massachusetts communities during the winter season of 2008-2009 and compared with similar studies performed in 2001, 2003-2004, and 2006-2007. Antimicrobial susceptibility testing and serotyping were performed on pneumococcal isolates, and risk factors for colonization in recent seasons (2006-2007 and 2008-2009) were evaluated.

RESULTS

We collected nasopharyngeal specimens from 1011 children, 290 (29%) of whom were colonized with pneumococcus. Non-PCV7 serotypes accounted for 98% of pneumococcal isolates, most commonly 19A (14%), 6C (11%), and 15B/C (11%). In 2008-2009, newly targeted PCV13 serotypes accounted for 20% of carriage isolates and 41% of penicillin-nonsusceptible S. pneumoniae. In multivariate models, younger age, child care, young siblings, and upper respiratory illness remained predictors of pneumococcal carriage, despite near-complete serotype replacement. Only young age and child care were significantly associated with penicillin-nonsusceptible S. pneumoniae carriage.

CONCLUSIONS

Serotype replacement post-PCV7 is essentially complete and has been sustained in young children, with the relatively virulent 19A being the most common serotype. Predictors of carriage remained similar despite serotype replacement. PCV13 may reduce 19A and decrease antibiotic-resistant strains, but monitoring for new serotype replacement is warranted.

Nasopharyngeal carriage of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Alloiococcus otitidis in young children in the era of pneumococcal immunization, Taiwan

We applied a multiplex polymerase chain reaction (PCR) and culture to detect Streptococcus pneumoniae and detected 3 other respiratory pathogens--Haemophilus influenzae, Moraxella catarrhalis, and Alloiococcus otitidis--simultaneously by PCR, in the nasopharynx of 386 children aged under 5 y. S. pneumoniae was the most common pathogen carried by children in all age groups, with the rate ranging from 15.8% in children aged 3-4 y to 28.6% in children aged 2-3 y. H. influenzae and M. catarrhalis showed similar carriage rates across all the age groups. Only 2 young children (0.5%) carried A. otitidis. Higher carriage of S. pneumoniae was found in children who had not received the heptavalent pneumococcal conjugate vaccine (PCV7). Cefotaxime non-susceptibility was high (51.4%) in S. pneumoniae nasopharyngeal isolates. Serotype 6B was the most common in fully immunized carriers and also in those who received catch-up immunization. Due to low PCV7 coverage in Taiwan, the carriage of vaccine and non-vaccine serotypes of S. pneumoniae in children remains common.

Predominance of ST320 among Streptococcus pneumoniae serotype 19A isolates from 10 Asian countries

BACKGROUND

After 7-valent pneumococcal conjugate vaccine (PCV7) introduction, non-vaccine serotypes such as 19A are increasing among Streptococcus pneumoniae. However, only limited data on 19A S. pneumoniae are available in Asian countries.

METHODS

Out of 1637 S. pneumoniae clinical pneumonia isolates collected during 2008 and 2009 from 10 Asian countries (Korea, Malaysia, Taiwan, Thailand, Saudi Arabia, Hong Kong, India, Japan, the Philippines and Vietnam), 91 serotype 19A S. pneumoniae isolates were identified. Capsular swelling reaction identified serotype 19A isolates. Antimicrobial susceptibility testing was performed on the serotype 19A isolates using the broth microdilution method, and the genotypes of the isolates were assessed using multilocus sequence typing.

RESULTS

Thirty different sequence types (STs) were identified. The most prevalent clone was ST320 (46 isolates, 51.1%). ST320 was found in Hong Kong, India, Korea, Malaysia, Saudi Arabia and Taiwan. ST320 isolates were mostly multidrug resistant (MDR) and showed significantly higher resistance rates than other STs for cefuroxime, clindamycin, and trimethoprim/sulfamethoxazole.

CONCLUSIONS

Although diverse clones were identified among 19A S. pneumoniae isolates, MDR ST320 was the predominant clone in Asian countries. Its predominance, even in countries with no or low coverage of PCV7, may indicate that its emergence and dissemination was due to more than just vaccine selection pressure in Asian countries. A longitudinal investigation of the change of serotypes and genotypes since the introduction of PCV7 is required to understand the emergence and dissemination mechanisms of a certain clone of 19A S. pneumoniae isolates.