pspK gene prevalence and characterization of non-typable Streptococcus pneumonia isolates from Asian countries

Serotype replacement and an increase in non-encapsulated isolates among community-acquired infections of Streptococcus pneumoniae during post-vaccine era in Japan

OBJECTIVES

It is feared that the serotype replacement of Streptococcus pneumoniae occurred by the introduction of pneumococcal vaccines as periodical inoculation leads to reduced efficacy of the approved vaccines and altered antimicrobial susceptibility.

METHODS

We determined serotypes of 351 S. pneumoniae isolates collected at a commercial clinical laboratory in Hokkaido prefecture, Japan, from December 2018 to February 2019 by using the polymerase chain reaction procedure of the US Centers for Disease Control and Prevention. Antimicrobial susceptibility and resistance gene profiles were also examined.

RESULTS

Vaccine coverage rates were 7.9% for 13-valent conjugate vaccine, and 32.5% for 23-valent polysaccharide vaccine, respectively. Non-typable strains were 19.7%. cpsA-positive isolates (group I), and null capsule clade (NCC)1, NCC2 and NCC3 (group II) comprised 31.3%, 28.4%, 32.8%, and 7.5% of the 69 non-typable strains, respectively. No penicillin-resistant/intermediate isolates were found; however, serotypes 35B and 15A/F showed low susceptibility to β-lactams. Only five strains (1.4%) were levofloxacin-resistant, and all were from the older persons, and three strains were serotype 35B.

CONCLUSION

The progression of serotype replacement in non-invasive pneumococcal infections has occurred during the post-vaccine era in Japan, and non-encapsulated isolates, such as NCC, have increased. Antimicrobial susceptibility is not worsened.

Identification and molecular epidemiology of routinely determined Streptococcus pneumoniae with negative Quellung reaction results

Background

Some streptococci strains identified as Streptococcus pneumoniae (S. pneumoniae) by routine clinical methods exhibiting negative Quellung reaction results may belong to other species of viridans group streptococci or non‐typeable S. pneumoniae. The purpose of this study was to investigate the identification and molecular characteristics of S. pneumoniae with negative Quellung reaction results.

Methods

One hundred and five isolates identified as S. pneumoniae using routine microbiological methods with negative Quellung reaction results were included. Multilocus sequence analysis (MLSA) was used as a gold standard in species identification, and the capacity of matrix‐assisted laser desorption ionization‐time of flight mass spectrometry (MALDI‐TOF MS) in identification was evaluated. Capsular genes and sequence types of S. pneumoniae isolates were determined by sequential multiplex PCR and multilocus sequence typing. Antimicrobial susceptibility patterns were determined via broth microdilution with a commercialized 96‐well plate.

Results

Among the isolates, 81 were identified as S. pneumoniae and 24 were S. pseudopneumoniae by MLSA. MALDI‐TOF MS misidentified six S. pneumoniae isolates as S. pseudopneumoniae and nine S. pseudopneumoniae isolates as S. pneumoniae or S. mitis/S. oralis. Thirty‐one sequence types (STs) were detected for these 81 S. pneumoniae isolates, and the dominant ST was ST‐bj12 (16, 19.8%). The non‐susceptibility rates of S. pseudopneumoniae were comparable to those of NESp strains.

Conclusions

Some S. pneumoniae isolates identified by routine methods were S. pseudopneumoniae. Most NESp strains have a different genetic background compared with capsulated S. pneumoniae strains. The resistance patterns of S. pseudopneumoniae against common antibiotics were comparable to those of NESp.

Clonal lineages and antimicrobial resistance of nonencapsulated Streptococcus pneumoniae in the post-pneumococcal conjugate vaccine era in Japan

OBJECTIVES

The emergence and spread of nonencapsulated Streptococcus pneumoniae (NESp) is a public health concern in the post-pneumococcal conjugate vaccine era. We analyzed the prevalence, molecular characteristics, and antimicrobial resistance of NESp responsible for noninvasive infections in northern Japan.

METHODS

NESp isolates were identified using molecular and phenotypical methods among 4463 S. pneumoniae isolates from noninvasive infection cases during 4 study periods between January 2011 and January 2019. NESp isolates were analyzed for antimicrobial susceptibility, genotype, and virulence-associated genes.

RESULTS

Seventy-one NESp isolates were identified (1.6% of total clinical isolates) and assigned to the null capsule clade (NCC)1 (pspK+) (94.4%) or NCC2 (aliC+/aliD+) (5.6%). The dominant sequence types (STs) were ST7502 (23.9%), ST4845 (19.7%), ST16214 (11.3%), ST11379 (9.9%), and ST7786 (7.0%). These 5 dominant STs and all 7 novel STs were related to the sporadic NESp lineage ST1106 or PMEN clone Denmark¹⁴-ST230. High non-susceptibility rates of NESp were observed for trimethoprim-sulfamethoxazole, erythromycin, and tetracycline (>92.9%), and multidrug resistance was observed in 88.7% of the NESp isolates, including all ST7502, ST4845, and ST11379 isolates.

CONCLUSIONS

The study revealed that the dominant clonal groups of NESp were associated with a high prevalence of non-susceptibility to antimicrobials in northern Japan.

First report on multidrug-resistant non-encapsulated Streptococcus pneumoniae isolated from a patient with pneumonia

The non-encapsulated Streptococcus pneumoniae (NESp) has emerged and increased in the clinical setting. The majority of NESp strains have been isolated from the nasopharynxes of healthy carriers and from respiratory specimens of patients with otitis media. NESp strains were shown to be more effective than encapsulated counterparts at forming biofilms. Therefore, NESp should become one of the leading causes of emerging refractory respiratory disease after the introduction of pneumococcal conjugate vaccines. We report the first case of multidrug-resistant - including fluoroquinolone-resistant - NESp isolated from the intrabronchial aspirate of a patient with pneumonia. Drug-resistant NESp infections can possibly emerge as a clinical problem and thus the continuous monitoring of NESp infections is of utmost importance.

pspK acquisition contributes to the loss of capsule in pneumococci: molecular characterisation of non-encapsulated pneumococci

With the introduction of the pneumococcal conjugate vaccine (PCV), the number of cases of non-vaccine type pneumococci and non-encapsulated Streptococcus pneumoniae (NESp) infection have increased. In order to clarify how pspK-harbouring NESp might have emerged, we characterised NESp and analysed the correlation between transformation and non-encapsulation. A total of 26 NESp strains were used in this study. The genetic backgrounds were compared using multilocus sequence typing (MLST). The ΔpspK::ermB strain, in which pspK was replaced by ermB in NESp, was constructed by homologous recombination. The genomic DNA of the ΔpspK::ermB strain was transformed into two types of encapsulated S. pneumoniae via transformation. The fitness of the parent and non-encapsulated transformants was compared using the growth curve. All NESp had pspK instead of capsular coding regions and were classified into 14 types by MLST, which indicated that NESp had several genetic backgrounds. Transformation of ΔpspK::ermB genomic DNA resulted in 10^-4‒10^-5 non-encapsulated transformants. Non-encapsulated transformants could grow faster than the encapsulated parent strain. The acquisition of pspK region via transformation contributed to the loss of encapsulation with high frequency. The present results suggest that non-encapsulation through pspK acquisition could be a potential mechanism to evade PCV.

Molecular typing, antibiotic susceptibility, and biofilm production in nonencapsulated Streptococcus pneumoniae isolated from children in Japan

The prevalence of nonencapsulated Streptococcus pneumoniae (NESp) has increased with the introduction of pneumococcal conjugate vaccines in children; however, the bacteriological characteristics of NESp have not been sufficiently clarified. In this study, NESp strains isolated from the nasopharyngeal carriage of children from four nursery schools in Japan were analyzed for molecular type, antibiotic susceptibility, and biofilm productivity. A total of 152 putative S. pneumoniae strains were identified by optochin-susceptibility analysis, of which 21 were not serotypeable by slide agglutination, quellung reaction, or multiplex PCR. Among these 21 strains, three were lytA-negative and, therefore, not S. pneumoniae. The remaining 18 strains were positive for lytA, ply, pspK, and bile solubility and were confirmed as NESp. Therefore, the isolation rate of NESp in the S. pneumoniae strains in this study was 12.0% (18/149). Molecular-typing analyses classified five strains as two existing sequence types (STs; ST7502 and ST7786), and 13 strains formed four novel STs. Horizontal spread was suspected, because strains with the same ST were often isolated from the same nursery school. The NESp isolates were generally susceptible to most antimicrobials, with the exception of macrolides; however, all isolates possessed more than one abnormal penicillin-binding protein gene. Furthermore, NESp strains were more effective than encapsulated counterparts at forming biofilms, which showed obvious differences in morphology. These data indicated that NESp strains should be continuously monitored as emerging respiratory pathogens.

Nonencapsulated Streptococcus pneumoniae: Emergence and Pathogenesis

While significant protection from pneumococcal disease has been achieved by the use of polysaccharide and polysaccharide-protein conjugate vaccines, capsule-independent protection has been limited by serotype replacement along with disease caused by nonencapsulated Streptococcus pneumoniae (NESp). NESp strains compose approximately 3% to 19% of asymptomatic carriage isolates and harbor multiple antibiotic resistance genes. Surface proteins unique to NESp enhance colonization and virulence despite the lack of a capsule even though the capsule has been thought to be required for pneumococcal pathogenesis. Genes for pneumococcal surface proteins replace the capsular polysaccharide (cps) locus in some NESp isolates, and these proteins aid in pneumococcal colonization and otitis media (OM). NESp strains have been isolated from patients with invasive and noninvasive pneumococcal disease, but noninvasive diseases, specifically, conjunctivitis (85%) and OM (8%), are of higher prevalence. Conjunctival strains are commonly of the so-called classical NESp lineages defined by multilocus sequence types (STs) ST344 and ST448, while sporadic NESp lineages such as ST1106 are more commonly isolated from patients with other diseases. Interestingly, sporadic lineages have significantly higher rates of recombination than classical lineages. Higher rates of recombination can lead to increased acquisition of antibiotic resistance and virulence factors, increasing the risk of disease and hindering treatment. NESp strains are a significant proportion of the pneumococcal population, can cause disease, and may be increasing in prevalence in the population due to effects on the pneumococcal niche caused by pneumococcal vaccines. Current vaccines are ineffective against NESp, and further research is necessary to develop vaccines effective against both encapsulated and nonencapsulated pneumococci.