Upsurge of Conjugate Vaccine Serotype 4 Invasive Pneumococcal Disease Clusters Among Adults Experiencing Homelessness in California, Colorado, and New Mexico.

After 7-valent pneumococcal conjugate vaccine introduction in the United States in 2000, invasive pneumococcal disease (IPD) due to serotype 4 greatly decreased in children and adults. Starting in 2013, serotype 4 IPD incidence increased among adults within 3 of 10 Active Bacterial Core surveillance sites. Of 325 serotype 4 cases among adults in 2010-2018, 36% were persons experiencing homelessness (PEH); incidence of serotype 4 IPD among PEH was 100-300 times higher than in the general population within these 3 areas. Genome sequencing for isolates recovered 2015-2018 (n = 246), revealed that increases in serotype 4 IPD were driven by lineages ST10172, ST244, and ST695. Within each lineage, clusters of near-identical isolates indicated close temporal relatedness. Increases in serotype 4 IPD were limited to Colorado, California, and New Mexico, with highest increases among PEH, who were at increased risk for exposure to and infections caused by these strains.

Invasive Pneumococcal Strain Distributions and Isolate Clusters Associated With Persons Experiencing Homelessness During 2018.

BACKGROUND: We aimed to characterize invasive pneumococcal disease (IPD) isolates collected from multistate surveillance in the United States during 2018 and examine within-serotype propensities of isolates to form related clusters. METHODS: We predicted strain features using whole genome sequencing obtained from 2885 IPD isolates obtained through the Center for Disease Control and Prevention's Active Bacterial Core surveillance (ABCs), which has a surveillance population of approximately 34.5 million individuals distributed among 10 states. Phylogenetic analysis was provided for serotypes accounting for ≥27 isolates. RESULTS: Thirteen-valent pneumococcal conjugate vaccine (PCV13) serotypes together with 6C accounted for 23 of 105 (21.9%) of isolates from children aged <5 years and 820 of 2780 (29.5%) isolates from those aged ≥5 years. The most common serotypes from adult IPD isolates were serotypes 3 (413/2780 [14.9%]), 22F (291/2780 [10.5%]), and 9N (191/2780 [6.9%]). Among child IPD isolates, serotypes 15BC (18/105 [17.1%]), 3 (11/105 [10.5%]), and 33F (10/105 [9.5%]) were most common. Serotypes 4, 12F, 20, and 7F had the highest proportions of isolates that formed related clusters together with the highest proportions of isolates from persons experiencing homelessness (PEH). Among 84 isolates from long-term care facilities, 2 instances of highly related isolate pairs from co-residents were identified. CONCLUSIONS: Non-PCV13 serotypes accounted for >70% of IPD in ABCs; however, PCV13 serotype 3 is the most common IPD serotype overall. Serotypes most common among PEH were more often associated with temporally related clusters identified both among PEH and among persons not reportedly experiencing homelessness.

Expanded sequential quadriplex real-time polymerase chain reaction (PCR) for identifying pneumococcal serotypes, penicillin susceptibility, and resistance markers.

We expanded our current Centers for Disease Control and Prevention triplexed real-time polymerase chain reaction scheme identifying 11 individual serotypes and 10 serogroups to a quadriplex format identifying 34 individual serotypes and 13 small serogroups, 4 antibiotic resistance determinants, pilus targets, and penicillin susceptibility. Newly developed assays are specific for serotypes/serogroups, are sensitive (10 copies/reaction), and further discriminate larger serogroups into individual serotypes or smaller serogroups.

Genome-wide association analyses of invasive pneumococcal isolates identify a missense bacterial mutation associated with meningitis.

Bacterial mutations predisposing pneumococcus to causing meningitis, a more severe form of invasive pneumococcal disease (IPD), are largely unknown. Knowledge of such mutations may improve our understanding of pathogenesis and inform preventive strategies. Here we report a pneumococcal pbp1b gene mutation (pbp1bA641C causing N214T change in PBP1b transglycosylase domain) that is associated with meningitis in an exploratory cohort of IPD patients (n = 2054, p = 6.8 × 10-6), in an independent confirmatory cohort (n = 2518, p = 2.3 × 10-6), and in a combined analysis (n = 4572, p = 3.0 × 10-10). Patients infected by the pbp1b641C genotype pneumococci show 2.8-fold odds (95% CI 1.7 to 4.8) of meningitis compared to those infected by non-pbp1b641C pneumococci, after controlling for pneumococcal serotype, antibiotic resistance, and patient age. The pbp1bA641C change results in longer time needed for bacterial killing by antibiotic treatment and shows evidence of being under positive selection. Thus, a pneumococcal mutation conferring increased antibiotic tolerance is associated with meningitis among IPD patients.

A Population-Based Descriptive Atlas of Invasive Pneumococcal Strains Recovered Within the U.S. During 2015-2016.

Invasive pneumococcal disease (IPD) has greatly decreased since implementation in the U.S. of the 7 valent conjugate vaccine (PCV7) in 2000 and 13 valent conjugate vaccine (PCV13) in 2010. We used whole genome sequencing (WGS) to predict phenotypic traits (serotypes, antimicrobial phenotypes, and pilus determinants) and determine multilocus genotypes from 5334 isolates (~90% of cases) recovered during 2015-2016 through Active Bacterial Core surveillance. We identified 44 serotypes; 26 accounted for 98% of the isolates. PCV13 serotypes (inclusive of serotype 6C) accounted for 1503 (28.2%) isolates, with serotype 3 most common (657/5334, 12.3%), while serotypes 1 and 5 were undetected. Of 305 isolates from children <5 yrs, 60 (19.7%) were of PCV13 serotypes 19A, 19F, 3, 6B, and 23F (58/60 were 19A, 19F, or 3). We quantitated MLST-based lineages first detected during the post-PCV era (since 2002) that potentially arose through serotype-switching. The 7 predominant emergent post-PCV strain complexes included 23B/CC338, 15BC/CC3280, 19A/CC244, 4/CC439, 15A/CC156, 35B/CC156, and 15BC/CC156. These strains accounted for 332 isolates (6.2% of total) and were more frequently observed in children <5 yrs (17.7%; 54/305). Fifty-seven categories of recently emerged (in the post PCV7 period) putative serotype-switch variants were identified, accounting for 402 isolates. Many of these putative switch variants represented newly emerged resistant strains. Penicillin-nonsusceptibility (MICs > 0.12 µg/ml) was found among 22.4% (1193/5334) isolates, with higher penicillin MICs (2-8 µg/ml) found in 8.0% (425/5334) of isolates that were primarily (372/425, 87.5%) serotypes 35B and 19A. Most (792/1193, 66.4%) penicillin-nonsusceptible isolates were macrolide-resistant, 410 (34.4%) of which were erm gene positive and clindamycin-resistant. The proportion of macrolide-resistant isolates increased with increasing penicillin MICs; even isolates with reduced penicillin susceptibility (MIC = 0.06 µg/ml) were much more likely to be macrolide-resistant than basally penicillin-susceptible isolates (MIC < 0.03 µg/ml). The contribution of recombination to strain diversification was assessed through quantitating 35B/CC558-specific bioinformatic pipeline features among non-CC558 CCs and determining the sizes of gene replacements. Although IPD has decreased greatly and stabilized in the post-PCV13 era, the species continually generates recombinants that adapt to selective pressures exerted by vaccines and antimicrobials. These data serve as a baseline for monitoring future changes within each invasive serotype.

Validation of ß-lactam minimum inhibitory concentration predictions for pneumococcal isolates with newly encountered penicillin binding protein (PBP) sequences.

BACKGROUND: Genomic sequence-based deduction of antibiotic minimum inhibitory concentration (MIC) has great potential to enhance the speed and sensitivity of antimicrobial susceptibility testing. We previously developed a penicillin-binding protein (PBP) typing system and two methods (Random Forest (RF) and Mode MIC (MM)) that accurately predicted ß-lactam MICs for pneumococcal isolates carrying a characterized PBP sequence type (phenotypic ß-lactam MICs known for at least one isolate of this PBP type). This study evaluates the prediction performance for previously uncharacterized (new) PBP types and the probability of encountering new PBP types, both of which impact the overall prediction accuracy. RESULTS: The MM and RF methods were used to predict MICs of 4309 previously reported pneumococcal isolates in 2 datasets and the results were compared to the known broth microdilution MICs to 6 ß-lactams. Based on a method that specifically evaluated predictions for new PBP types, the RF results were more accurate than MM results for new PBP types and showed percent essential agreement (MICs agree within ±1 dilution) >97%, percent category agreement (interpretive results agree) >93%, major discrepancy (sensitive isolate predicted as resistant) rate < 1.2%, and very major discrepancy (resistant isolate predicted as sensitive) rate < 1.4% for all 6 ß-lactams. The identification of new PBP types over time was well approximated by a diminishingly increasing curve (Pearson's r = 0.99) and minimally impacted overall MIC prediction performance. CONCLUSIONS: MIC prediction using the RF method could be an accurate alternative of phenotypic susceptibility testing even in the presence of previously uncharacterized PBP types.

Invasive Serotype 35B Pneumococci Including an Expanding Serotype Switch Lineage, United States, 2015-2016.

We used whole-genome sequencing to characterize 199 nonvaccine serotype 35B pneumococcal strains that caused invasive pneumococcal disease (IPD) in the United States during 2015-2016 and related these findings to previous serotype 35B IPD data obtained by Active Bacterial Core surveillance. Penicillin-nonsusceptible 35B IPD increased during post-pneumococcal 7-valent conjugate vaccine years (2001-2009) and increased further after implementation of pneumococcal 13-valent conjugate vaccine in 2010. This increase was caused primarily by the 35B/sequence type (ST) 558 lineage. 35B/ST558 and vaccine serotype 9V/ST156 lineages were implicated as cps35B donor and recipient, respectively, for a single capsular switch event that generated emergent 35B/ST156 progeny in 6 states during 2015-2016. Three additional capsular switch 35B variants were identified, 2 of which also involved 35B/ST558 as cps35B donor. Spread of 35B/ST156 is of concern in view of past global predominance of pathogenic ST156 vaccine serotype strains. Protection against serotype 35B should be considered in next-generation pneumococcal vaccines.

Penicillin-Binding Protein Transpeptidase Signatures for Tracking and Predicting ß-Lactam Resistance Levels in Streptococcus pneumoniae.

UNLABELLED: ß-Lactam antibiotics are the drugs of choice to treat pneumococcal infections. The spread of ß-lactam-resistant pneumococci is a major concern in choosing an effective therapy for patients. Systematically tracking ß-lactam resistance could benefit disease surveillance. Here we developed a classification system in which a pneumococcal isolate is assigned to a "PBP type" based on sequence signatures in the transpeptidase domains (TPDs) of the three critical penicillin-binding proteins (PBPs), PBP1a, PBP2b, and PBP2x. We identified 307 unique PBP types from 2,528 invasive pneumococcal isolates, which had known MICs to six ß-lactams based on broth microdilution. We found that increased ß-lactam MICs strongly correlated with PBP types containing divergent TPD sequences. The PBP type explained 94 to 99% of variation in MICs both before and after accounting for genomic backgrounds defined by multilocus sequence typing, indicating that genomic backgrounds made little independent contribution to ß-lactam MICs at the population level. We further developed and evaluated predictive models of MICs based on PBP type. Compared to microdilution MICs, MICs predicted by PBP type showed essential agreement (MICs agree within 1 dilution) of >98%, category agreement (interpretive results agree) of >94%, a major discrepancy (sensitive isolate predicted as resistant) rate of <3%, and a very major discrepancy (resistant isolate predicted as sensitive) rate of <2% for all six ß-lactams. Thus, the PBP transpeptidase signatures are robust indicators of MICs to different ß-lactam antibiotics in clinical pneumococcal isolates and serve as an accurate alternative to phenotypic susceptibility testing. IMPORTANCE: The human pathogen Streptococcus pneumoniae is a leading cause of morbidity and mortality worldwide. ß-Lactam antibiotics such as penicillin and ceftriaxone are the drugs of choice to treat pneumococcal infections. Some pneumococcal strains have developed ß-lactam resistance through altering their penicillin-binding proteins (PBPs) and have become a major concern in choosing effective patient therapy. To systematically track and predict ß-lactam resistance, we obtained the sequence signatures of PBPs from a large collection of clinical pneumococcal isolates using whole-genome sequencing data and found that these "PBP types" were predictive of resistance levels. Our findings can benefit the current era of strain surveillance when whole-genome sequencing data often lacks detailed resistance information. Using PBP positions that we found are always substituted within highly resistant strains may lead to further refinements. Sequence-based predictions are accurate and may lead to the ability to extract critical resistance information from nonculturable clinical specimens.