Novel Levofloxacin-Resistant Multidrug-Resistant Streptococcus pneumoniae Serotype 11A Isolates, South Korea

Streptococcus pneumoniae favors tolerance via metabolic adaptation over resistance to circumvent fluoroquinolones

Streptococcus pneumoniae is a major human pathogen of global health concern and the rapid emergence of antibiotic resistance poses a serious public health problem worldwide. Fluoroquinolone resistance in S. pneumoniae is an intriguing case because the prevalence of fluoroquinolone resistance does not correlate with increasing usage and has remained rare. Our data indicate that deleterious fitness costs in the mammalian host constrain the emergence of fluoroquinolone resistance both by de novo mutation and recombination. S. pneumoniae was able to circumvent such deleterious fitness costs via the development of antibiotic tolerance through metabolic adaptation that reduced the production of reactive oxygen species, resulting in a fitness benefit during infection of mice treated with fluoroquinolones. These data suggest that the emergence of fluoroquinolone resistance is tightly constrained in S. pneumoniae by fitness tradeoffs and that mutational pathways involving metabolic networks to enable tolerance phenotypes are an important contributor to the evasion of antibiotic-mediated killing.IMPORTANCEThe increasing prevalence of antibiotic resistant bacteria is a major global health concern. While many species have the potential to develop antibiotic resistance, understanding the barriers to resistance emergence in the clinic remains poorly understood. A prime example of this is fluroquinolone resistance in Streptococcus pneumoniae, whereby, despite continued utilization, resistance to this class of antibiotic remains rare. In this study, we found that the predominant pathways for developing resistance to this antibiotic class severely compromised the infectious capacity of the pneumococcus, providing a key impediment for the emergence of resistance. Using in vivo models of experimental evolution, we found that S. pneumoniae responds to repeated fluoroquinolone exposure by modulating key metabolic pathways involved in the generation of redox molecules, which leads to antibiotic treatment failure in the absence of appreciable shifts in resistance levels. These data underscore the complex pathways available to pathogens to evade antibiotic mediating killing via antibiotic tolerance.

Serotype Distribution and Antimicrobial Resistance of Streptococcus pneumoniae Causing Invasive Pneumococcal Disease in Korea Between 2017 and 2019 After Introduction of the 13-Valent Pneumococcal Conjugate Vaccine

Background

Streptococcus pneumoniae is a serious pathogen causing various infections in humans. We evaluated the serotype distribution and antimicrobial resistance of S. pneumoniae causing invasive pneumococcal disease (IPD) after introduction of pneumococcal conjugate vaccine (PCV)13 in Korea and investigated the epidemiological characteristics of multidrug-resistant (MDR) isolates.

Methods

S. pneumoniae isolates causing IPD were collected from 16 hospitals in Korea between 2017 and 2019. Serotyping was performed using modified sequential multiplex PCR and the Quellung reaction. Antimicrobial susceptibility tests were performed using the broth microdilution method. Multilocus sequence typing was performed on MDR isolates for epidemiological investigations.

Results

Among the 411 S. pneumoniae isolates analyzed, the most prevalent serotype was 3 (12.2%), followed by 10A (9.5%), 34 (7.3%), 19A (6.8%), 23A (6.3%), 22F (6.1%), 35B (5.8%), 11A (5.1%), and others (40.9%). The coverage rates of PCV7, PCV10, PCV13, and pneumococcal polysaccharide vaccine (PPSV)23 were 7.8%, 7.8%, 28.7%, and 59.4%, respectively. Resistance rates to penicillin, ceftriaxone, erythromycin, and levofloxacin were 13.1%, 9.2%, 80.3%, and 4.1%, respectively. MDR isolates accounted for 23.4% of all isolates. Serotypes 23A, 11A, 19A, and 15B accounted for the highest proportions of total isolates at 18.8%, 16.7%, 14.6%, and 8.3%, respectively. Sequence type (ST)166 (43.8%) and ST320 (12.5%) were common among MDR isolates.

Conclusions

Non-PCV13 serotypes are increasing among invasive S. pneumoniae strains causing IPD. Differences in antimicrobial resistance were found according to the specific serotype. Continuous monitoring of serotypes and antimicrobial resistance is necessary for the appropriate management of S. pneumoniae infections.

Characteristics of Clonal Complex Changes and Quinolone Resistance-Determining Region Mutations of Levofloxacin-Resistant Streptococcus pneumoniae in South Korea

Streptococcus pneumoniae is the most common causative agent of community-acquired pneumonia and invasive pneumococcal diseases with high mortality rates. The aims of this study were to evaluate clonal complex (CC) changes of levofloxacin-resistant S. pneumoniae (LRSP) strains and to investigate the relationship between levofloxacin resistance and pneumococcal serotypes. We analyzed the antimicrobial susceptibility of 145 LRSP strains to 18 antimicrobial agents and the quinolone resistance-determining region mutation. Multilocus sequence typing was performed to investigate the genetic relatedness among LRSP strains. Most LRSP strains (96.6%) were multidrug resistant and had simultaneous mutations in gyrA, parC, and parE (91.7%). The serotypes 11A (44.1%) and 13 (14.5%) accounted for 58.6% of LRSP strains, and 32.0% were nonvaccine serotypes. Most LRSP strains were grouped as CC8279 (N = 83; 57.2%), CC189 (N = 10; 6.9%), or CC320 (N = 5; 3.4%). CC8279 was commonly combined with serotypes 11A and 13. There were numerous changes of serotype and CC accompanying the emergence and spread of LRSP. Continuous monitoring of changes in the serotype and sequence type of LRSP is required to follow the spread of LRSP for public health monitoring.

Investigation of Antibiotic Resistance, Serotype Distribution, and Genetic Characteristics of 164 Invasive Streptococcus pneumoniae from North China Between April 2016 and October 2017

BACKGROUND

Streptococcus pneumoniae infections are the major cause of global morbidity and mortality among children and patients aged more than 65 years. This study aimed to investigate the antimicrobial resistance, bacterial serotype distribution, and genetic characteristics of invasive S. pneumoniae from different cities in North China.

MATERIALS AND METHODS

A total of 164 invasive S. pneumoniae strains were collected from 8 hospitals in 5 regions of North China between April 2016 and October 2017. Minimum inhibitory concentrations (MICs) were determined using the agar dilution method. Capsular serotypes were identified using the Quellung reaction test. Molecular epidemiology was investigated using multilocus sequence typing.

RESULTS

S. pneumoniae isolates were highly resistant to macrolides, clindamycin, and tetracycline in all age groups. The overall rate of resistance to penicillin was 56.7%. However, fluoroquinolones and vancomycin maintained excellent antimicrobial activities. The rate of resistance to β-lactam in strains isolated from children aged less than 18 years was significantly higher than that in strains from other age groups. The most prevalent serotypes were 14 (22.6%), 19F (16.5%), non-vaccine types (14.0%), 19A (9.8%), and 23F (9.1%). The coverage for PCV10 and PCV13 was 59.8% and 75.6%, respectively. The vaccine coverage rate was the highest among children aged less than 5 years. The proportion of penicillin-resistant isolates was higher among vaccine-covered strains compared with non-covered strains. S. pneumoniae showed considerable clonal dissemination, and ST876 (28, 17.1%), ST271 (22, 13.4%), ST81 (17, 10.4%) and ST320 (14, 8.5%) were the major STs.

CONCLUSION

All the 164 invasive S. pneumoniae isolates demonstrated high resistance to antibiotics. The coverage of S. pneumoniae vaccine was higher in children than in adults.

Spread of ceftriaxone non-susceptible pneumococci in South Korea: Long-term care facilities as a potential reservoir

Despite the availability of a pneumococcal National Immunization Program, which provides free PPSV23 vaccination for older adults aged ≥65 years in South Korea, pneumococcal pneumonia remains one of the most common respiratory infections, with increasing antimicrobial resistance. From January to December in 2015, all pneumococcal isolates were collected from a 1,050-bed teaching hospital in South Korea. All isolates were analyzed for serotype, genotype, and antimicrobial susceptibility. Demographic, clinical and microbiological data were compared between ceftriaxone susceptible and non-susceptible cases. Among 92 microbiologically identified pneumococcal isolates, ceftriaxone non-susceptible pneumococci (CNSP) accounted for 32 cases (34.8%). Some of these cases also showed levofloxacin resistance (25%, 8/32 isolates) and all CNSP cases were multidrug resistant. Compared to patients with ceftriaxone susceptible pneumococci (CSP), long-term care facility residents (odds ratio [OR] 7.0, 95% confidence interval [CI] 0.8-62.1) and patients with chronic lung (OR 4.1, 95% CI 1.1-15.0) and renal diseases (OR 9.1, 95% CI 1.2-70.5) were more common among those with CNSP on multivariate analysis. PPSV23-unique serotypes not included in PCV13 were more common in CNSP than in CSP (34.4% versus 13.3%, p = 0.02). Regarding genotypes, ST320 (10 cases), ST166 (7 cases) and ST8279 (3 cases) were dominant in CNSP, and ST8279 was only detected in previous long-term care facility residents. Clonal expansion and spread of CNSP strains should be monitored among patients with chronic lung/renal diseases and residents of long-term care facilities.

Characterization of macrolide-resistant non-invasive pneumococci in the pre-vaccine era in Serbia

Numerous reports have confirmed that increased macrolide use in the treatment of respiratory tract infection has contributed to the emergence of antibiotic resistance worldwide. Studies have also shown that pneumococcal vaccine can reduce pneumococcal resistance. The aim of this study was to determine the prevalence of co-resistance to penicillin and other antibiotics in macrolide-resistant (MR) non-invasive pneumococcal isolates and to evaluate serotype distribution in resistant strains in the pre-vaccine era in Serbia. About 80% of MR isolates expressed the MLS phenotype with very high resistance to both erythromycin and clindamycin. A total of 132 (84.1%) MR isolates were multiresistant, i.e., they were resistant to erythromycin, penicillin, tetracycline, and trimethoprim-sulfamethoxazole. Among 157 MR pneumococci, 11 different serotypes were found. Four serotypes, 19F, 14, 6B, and 23F, accounted for 77.7% of all MR pneumococcal isolates. Among isolates with the cMLS phenotype, serotypes 19F and 14 were predominant, whereas serotype 6A was the most common among those with the M phenotype, followed by 14. In conclusion, co-resistance to macrolides and penicillin in our non-invasive pneumococcal isolates is high. The majority of tested strains (∼80%) belonged to the four serotypes (19F, 14, 6B, and 23F) that are included in all conjugate vaccine formulations.

Disease Burden and Etiologic Distribution of Community-Acquired Pneumonia in Adults: Evolving Epidemiology in the Era of Pneumococcal Conjugate Vaccines

Pneumonia is the leading cause of morbidity and mortality, particularly in old adults. The incidence and etiologic distribution of community-acquired pneumonia is variable both geographically and temporally, and epidemiology might evolve with the change of population characteristics and vaccine uptake rates. With the increasing prevalence of chronic medical conditions, a wide spectrum of healthcare-associated pneumonia could also affect the epidemiology of community-acquired pneumonia. Here, we provide an overview of the epidemiological changes associated with community-acquired pneumonia over the decades since pneumococcal conjugate vaccine introduction.

Emergence of multidrug-resistant clones in levofloxacin-nonsusceptible Streptococcus pneumoniae isolates in Korea

The use of fluoroquinolones to treat respiratory tract infections and pneumonia due to Streptococcus pneumoniae has affected the emergence of resistance to this class of drugs. Increasing pneumococcal resistance to levofloxacin has become a major public health concern. We investigated the prevalence and genetic characteristics of levofloxacin-nonsusceptible S. pneumoniae (LNSP) clinical isolates in Korea. A total of 43 LNSP isolates collected from a national surveillance study at 13 tertiary hospitals between 2008 and 2014 were analyzed for serotype and antimicrobial susceptibilities to 19 antimicrobial agents as well as the quinolone resistance-determining region mutation. Multilocus sequence typing was performed to investigate the genetic relatedness among LNSP isolates. All LNSP isolates (MIC, ≥4 μg/mL) exhibited multidrug-resistant or even extensively drug-resistant (XDR) phenotypes (8 isolates, 18.6%). Most LNSP isolates belonged to sequence type (ST) 8279 and its variants (16 isolates, 37.2%). ST8279 is a double-locus variant of ST156, which is identical to the pneumococcal Spain^9V-3 international clone. The high prevalence of nonvaccine types in LNSP isolates could pose significant therapeutic challenges. A limited number of clones dominated the population of LNSP XDR isolates, and homogeneous antimicrobial resistance profiles support the possibility of clonal dissemination of LNSP. More information on the emergence and spread of these LNSP isolates is necessary in order to prevent its spread.