Importance of the Molecular Epidemiological Monitoring of Carbapenem-Resistant Pseudomonas aeruginosa
2024; 44(5): 381-382
Ann Lab Med 2023; 43(1): 45-54
Published online September 1, 2022 https://doi.org/10.3343/alm.2023.43.1.45
Copyright © Korean Society for Laboratory Medicine.
Gyu Ri Kim , Ph.D.1,*, Eun-Young Kim , Ph.D.1,2,*, Si Hyun Kim , Ph.D.3, Hae Kyung Lee , M.D.4, Jaehyeon Lee , M.D.5, Jong Hee Shin , M.D.6, Young Ree Kim , M.D.7, Sae Am Song , M.D.1, Joseph Jeong , M.D.8, Young Uh , M.D.9, Yu Kyung Kim , M.D.10, Dongeun Yong , M.D.11, Hyun Soo Kim , M.D.12, Sunjoo Kim , M.D.13, Young Ah Kim , M.D.14, Kyeong Seob Shin , M.D.15, Seok Hoon Jeong , M.D.11, Namhee Ryoo , M.D.16, and Jeong Hwan Shin, M.D.1,2
1Department of Laboratory Medicine, Inje University College of Medicine, Busan, Korea; 2Paik Institute for Clinical Research, Inje University College of Medicine, Busan, Korea; 3Department of Clinical Laboratory Science, Semyung University, Jecheon, Korea; 4Department of Laboratory Medicine, Uijeongbu St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea; 5Department of Laboratory Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea; 6Department of Laboratory Medicine, Chonnam National University Medical School, Gwangju, Korea; 7Department of Laboratory Medicine, College of Medicine, Jeju National University, Jeju, Korea; 8Department of Laboratory Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea; 9Department of Laboratory Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea; 10Department of Laboratory Medicine, School of Medicine, Kyungpook National University, Daegu, Korea; 11Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea; 12Department of Laboratory Medicine, Hallym University College of Medicine, Chuncheon, Korea; 13Department of Laboratory Medicine, Gyeongsang National University College of Medicine, Jinju, Korea; 14Department of Laboratory Medicine, National Health Insurance Service Ilsan Hospital, Goyang, Korea; 15Department of Laboratory Medicine, Chungbuk National University College of Medicine, Cheongju, Korea; 16Department of Laboratory Medicine, Keimyung University School of Medicine, Daegu, Korea
Correspondence to: Jeong Hwan Shin, M.D., Ph.D.
Department of Laboratory Medicine, Busan Paik Hospital, Inje University College of Medicine, 75 Bokjiro, Busanjin-gu, Busan 47392, Korea
Tel: +82-51-890-6475
Fax: +82-51-893-1562.
E-mail: jhsmile@paik.ac.kr
* These authors contributed equally to this work.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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.
Keywords: Streptococcus pneumoniae, Serotyping, Drug resistance, Multiple drug resistance, Bacterial, Mutlilocus sequence typing
A pneumococcal conjugate vaccine (PCV) including serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F was introduced for routine use in 2000, which dramatically reduced IPD prevalence in many countries [4]. After introduction of this 7-valent PCV (PCV7), serotype 19A was detected at a high rate and serotype 3 was detected mainly in adults [2, 5]. PCV10 (PCV7 plus serotypes 1, 5, and 7F) and PCV13 (PCV10 plus serotypes 3, 6A, and 19A) were introduced in 2010.
National immunization programs (NIPs) to prevent pneumococcal infections have been implemented in many countries. In Korea, PCV10 or PCV13 has been available for children since 2014, and pneumococcal polysaccharide vaccine (PPSV)23 for older adults (≥65 years old) has been available since 2013. The use of PCV13 is also recommended for older patients (≥65 years) in high-risk groups, such as immunocompromised patients [6]. The serotype distribution was reported immediately after implementation of NIPs in Korea between 2014 and 2016 [2]. In 2017, the vaccination rates of PCV13 and PPSV23 reached 95.0% for children and 60.0% for the elderly [7]. The stabilized serotype distribution reflecting the high vaccination rate after NIPs could be determined by investigating the serotype distribution between 2017 and 2019.
The prevalence of antimicrobial-resistant strains of
In total, 411
Serotyping was performed using modified sequential multiplex (SM)-PCR, as previously described [8]. We carried out an additional multiplex PCR set for serotypes 2, 10F/10C/33C, 31, 35F/
47F, and 38/25F/25A. Primer sequences provided by the US Centers for Disease Control and Prevention (CDC) (https://www.cdc.gov/streplab/pcr.html) were used to determine pneumococcal serotypes. The modified SM-PCR protocol consisted of seven multiplex PCR sets, and each reaction consisted of five primer pairs. If the serotype could not be determined using modified SM-PCR, the isolate was defined as non-typeable.
We applied the capsular Quellung reaction with factor antisera (Statens Serum Institute, Copenhagen, Denmark) to define specific serotypes 6A/6B/6C/6D, 11A/11D, 12F/12A/12B, 15F/15A/15B/15C, and 22F/22A [9].
We defined vaccine serotypes as those included in PCVs and non-vaccine serotypes as those that were not included in PCVs [10].
Antimicrobial susceptibility tests were performed using Microscan with the MICroSTREP plus Panel (Siemens Healthcare Diagnostics, Sacramento, CA, USA) for amoxicillin/clavulanate, cefotaxime, ceftriaxone, penicillin, clindamycin, erythromycin, levofloxacin, tetracycline, trimethoprim/sulfamethoxazole (SXT), and vancomycin.
MDR was defined as resistance to three or more of the following four classes of antibiotics: β-lactams, macrolides, lincosamides, and fluoroquinolones [12]. Extensive drug resistance (XDR) was defined as resistance to five or more of the following six classes of antibiotics: β-lactams, macrolides, lincosamides, fluoroquinolones, tetracyclines, and folate-pathway inhibitors [12].
MLST was performed for MDR isolates according to a previously described MLST protocol for
Clonal complexes (CCs) were determined using sequence type analysis and recombination tests (START) [14]. For phylogenetic analysis, the sequences of the
Chi-square tests were used to determine significant differences in resistance and serotype distribution, as appropriate. Differences between groups were considered significant at
Of the 411 isolates, 265 (64.5%) were from male patients and 146 (35.5%) were from female patients. By period, 155 (37.7%), 156 (38.0%), and 100 (24.3%) isolates were obtained in 2017, 2018, and 2019, respectively. The most common source was blood (N=337; 82.0%), followed by abscess (N=25; 6.1%), CSF (N=25; 6.1%), other body fluids (N=21, 5.1%; ascitic fluid, N=12; pleural fluid, N=5; peritoneal fluid, N=4), and tissue (N=3, 0.7%). The median age of the patients was 57 (range, 0–104) years, and 46.7% (N=192) of the isolates were collected from patients ≥65 years old; 30 (7.3%) and 13 (3.2%) isolates were collected from patients aged ≤1 year and 1–5 years, respectively. Blood-obtained isolates were most common in all age groups, except for isolates derived from patients aged 6–20 years.
Thirty-four serotypes were detected and four isolates were non-typeable (Table 1). 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. The eight most common serotypes accounted for 59.1% (N=243) of the isolates. In patients ≤5 years of age, serotypes 10A (N=14, 32.6%), 15B (N=4, 9.3%), 19A (N=4, 9.3%), and 23B (N=4, 9.3%) were the most prevalent. Among them, 12 of 14 serotypes 10A, three of four serotypes 19A, and all four serotypes 15B were isolated from children aged ≤1 year. In ≥65-year-old patients, serotypes 3 (N=31, 16.1%), 34 (N=19, 9.9%), 11A (N=15, 7.8%), 10A (N=14, 7.3%), and 35B (N=13, 6.8%) were prevalent.
Table 1 . Serotype distribution of
Serotype | Isolates, N (%) | |||||
---|---|---|---|---|---|---|
Total (N=411) | Age (N) | |||||
≤5 yr (43) | 6–18 yr (12) | 19–50 yr (63) | 51–64 yr (101) | ≥65 yr (192) | ||
3*,† | 50 (12.2) | 1 (2.3) | 1 (8.3) | 3 (4.8) | 14 (13.9) | 31 (16.1) |
10A† | 39 (9.5) | 14 (32.6) | 1 (8.3) | 4 (6.3) | 6 (5.9) | 14 (7.3) |
34 | 30 (7.3) | 1 (2.3) | 0 (0) | 4 (6.3) | 6 (5.9) | 19 (9.9) |
19A*,† | 28 (6.8) | 4 (9.3) | 0 (0) | 7 (11.1) | 5 (5.0) | 12 (6.3) |
23A | 26 (6.3) | 2 (4.7) | 1 (8.3) | 5 (7.9) | 9 (8.9) | 9 (4.7) |
22F† | 25 (6.1) | 1 (2.3) | 1 (8.3) | 4 (6.3) | 9 (8.9) | 10 (5.2) |
35B | 24 (5.8) | 2 (4.7) | 0 (0) | 1 (1.6) | 8 (7.9) | 13 (6.8) |
11A† | 21 (5.1) | 0 (0) | 0 (0) | 4 (6.3) | 2 (2.0) | 15 (7.8) |
15B† | 16 (3.9) | 4 (9.3) | 1 (8.3) | 4 (6.3) | 3 (3.0) | 4 (2.1) |
12F† | 15 (3.6) | 1 (2.3) | 0 (0) | 6 (9.5) | 3 (3.0) | 5 (2.6) |
19F*,†,‡ | 14 (3.4) | 0 (0) | 2 (16.7) | 1 (1.6) | 4 (4.0) | 7 (3.6) |
23B | 13 (3.2) | 4 (9.3) | 0 (0) | 3 (4.8) | 2 (2.0) | 4 (2.1) |
20† | 12 (2.9) | 0 (0) | 0 (0) | 3 (4.8) | 1 (1.0) | 8 (4.2) |
24F/24A/24B | 11 (2.7) | 3 (7) | 1 (8.3) | 1 (1.6) | 4 (4.0) | 2 (1.0) |
15A | 10 (2.4) | 0 (0) | 0 (0) | 2 (3.2) | 1 (1.0) | 7 (3.6) |
13 | 9 (2.2) | 0 (0) | 1 (8.3) | 2 (3.2) | 4 (4.0) | 2 (1.0) |
6A* | 8 (1.9) | 0 (0) | 0 (0) | 0 (0) | 2 (2.0) | 6 (3.1) |
14*,†,‡ | 8 (1.9) | 1 (2.3) | 0 (0) | 0 (0) | 2 (2.0) | 5 (2.6) |
6D | 7 (1.7) | 0 (0) | 0 (0) | 0 (0) | 2 (2.0) | 5 (2.6) |
6C | 6 (1.5) | 0 (0) | 0 (0) | 1 (1.6) | 2 (2.0) | 3 (1.6) |
6B*,†,‡ | 5 (1.2) | 0 (0) | 0 (0) | 1 (1.6) | 1 (1.0) | 3 (1.6) |
38/25F/25A | 5 (1.2) | 3 (7) | 0 (0) | 2 (3.2) | 0 (0) | 0 (0) |
15F | 4 (1.0) | 0 (0) | 1 (8.3) | 0 (0) | 2 (2.0) | 1 (0.5) |
23F*,†,‡ | 4 (1.0) | 0 (0) | 0 (0) | 0 (0) | 3 (3.0) | 1 (0.5) |
16F | 3 (0.7) | 0 (0) | 0 (0) | 1 (1.6) | 0 (0) | 2 (1.0) |
33F† | 3 (0.7) | 1 (2.3) | 0 (0) | 1 (1.6) | 0 (0) | 1 (0.5) |
9N/9L† | 2 (0.5) | 0 (0) | 0 (0) | 0 (0) | 2 (2.0) | 0 (0) |
15C | 2 (0.5) | 1 (2.3) | 0 (0) | 0 (0) | 0 (0) | 1 (0.5) |
31 | 2 (0.5) | 0 (0) | 1 (8.3) | 0 (0) | 1 (1.0) | 0 (0) |
2† | 1 (0.2) | 0 (0) | 0 (0) | 0 (0) | 1 (1.0) | 0 (0) |
7B | 1 (0.2) | 0 (0) | 0 (0) | 1 (1.6) | 0 (0) | 0 (0) |
9V*,†,‡ | 1 (0.2) | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 1 (0.5) |
11D | 1 (0.2) | 0 (0) | 1 (8.3) | 0 (0) | 0 (0) | 0 (0) |
44/46 | 1 (0.2) | 0 (0) | 0 (0) | 0 (0) | 1 (1.0) | 0 (0) |
Non-typeable | 4 (1.0) | 0 (0) | 0 (0) | 2 (3.2) | 1 (1.0) | 1 (0.5) |
*13-valent pneumococcal conjugate vaccine (PCV13) serotype; †Pneumococcal polysaccharide vaccine (PPSV23) serotype; ‡7-valent pneumococcal conjugate vaccine (PCV7) serotype.
Of the 411 isolates, 252 (61.3%) were vaccine serotypes. The coverage rates of PCV7, PCV10, PCV13, and PPSV23 were 7.8%, 7.8%, 28.7%, and 59.4%, respectively. The coverage rate for PCV13 (14.0%) was lower in patients ≤5 years than in those ≥65 years (33.9%,
Antimicrobial resistance of the isolates is presented in Table 2. Overall, 13.1%, 9.5%, and 9.2% of the isolates were resistant to penicillin, cefotaxime, and ceftriaxone, respectively. The proportion of intermediate resistance was high for penicillin (24.1%), cefotaxime (19.7%), and ceftriaxone (20.4%). Resistance rates to erythromycin, clindamycin, and tetracycline were high at 80.3%, 66.7%, and 75.9%, respectively. Resistance rates to SXT and levofloxacin were 27.7% and 4.1%, respectively.
Table 2 . Antimicrobial resistance of 411
Antimicrobial agent | Total (N=411) | ≤5 yr (N=43) | 6–64 yr (N=176) | ≥65 yr (N=192) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
S (%) | I (%) | R (%) | S (%) | I (%) | R (%) | S (%) | I (%) | R (%) | S (%) | I (%) | R (%) | ||
β-Lactams | Penicillin | 62.8 | 24.1 | 13.1 | 58.1 | 23.3 | 18.6 | 61.9 | 22.7 | 15.3 | 64.6 | 25.5 | 9.9 |
Amoxicillin/clavulanate | 69.3 | 8.8 | 21.9 | 74.4 | 0 | 25.6 | 68.2 | 10.2 | 21.6 | 69.3 | 9.4 | 21.4 | |
Cefotaxime | 70.8 | 19.7 | 9.5 | 67.4 | 23.3 | 9.3 | 71.6 | 20.5 | 8.0 | 70.8 | 18.2 | 10.9 | |
Ceftriaxone | 70.3 | 20.4 | 9.2 | 67.4 | 25.6 | 7.0 | 68.2 | 21.6 | 10.2 | 72.9 | 18.2 | 8.9 | |
Macrolides | Erythromycin | 18.7 | 1.0 | 80.3 | 7.0 | 0 | 93.0 | 18.8 | 0 | 81.3 | 21.4 | 2.1 | 76.6 |
Lincosamides | Clindamycin | 33.1 | 0.2 | 66.7 | 30.2 | 0 | 69.8 | 31.3 | 0.6 | 68.2 | 35.4 | 0 | 64.6 |
Quinolones | Levofloxacin | 95.6 | 0.2 | 4.1 | 100 | 0 | 0 | 96.0 | 0 | 4.0 | 93.8 | 0.5 | 5.2 |
Tetracyclines | Tetracycline | 22.6 | 1.5 | 75.9 | 14.0 | 0 | 86.0 | 22.2 | 1.7 | 76.1 | 25.0 | 1.6 | 73.4 |
Folate-pathway inhibitors | Trimethoprim/ sulfamethoxazole | 58.6 | 13.6 | 27.7 | 72.1 | 14.0 | 14.0 | 58.0 | 14.2 | 27.8 | 56.3 | 13.0 | 30.7 |
Glycopeptides | Vancomycin | 100 | 0 | 0 | 100 | 0 | 0 | 100 | 0 | 0 | 100 | 0 | 0 |
Abbreviations: S, susceptible; I, intermediate; R, resistant.
There were some differences in antimicrobial resistance by age, although the difference was not significant. Resistance rates to penicillin (18.6% vs. 9.9%), erythromycin (93.0% vs. 76.6%), and tetracycline (86.0% vs. 73.4%) were higher in children ≤5 years of age than in adults ≥65 years of age. The rates of resistance to levofloxacin (0% vs. 5.2%) and SXT (14.0% vs. 30.7%) were lower in patients ≤5 years of age than in those ≥65 years of age.
The antimicrobial susceptibility results differed according to the serotype (Table 3). Resistance rates were higher in several specific serotypes. The resistance rates to penicillin of serotypes 15B, 19A, 23A, 19F, and 11A were 37.5%, 35.7%, 30.8%, 28.6%, and 23.8%, respectively (
Table 3 . Relation between serotype and antimicrobial resistance
Serotype (N) | Resistance rate (%) and MDR, XDR in each serotype | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
PEN (NS) | AMC | CTX (NS) | CRO (NS) | ERY | CLI | LEV | TET | SXT | VAN | MDR | XDR | |
3*,† (50) | 4.0 (6.0) | 4.0 | 4.0 (4.0) | 4.0 (6.0) | 50.0 | 44.0 | 4.0 | 48.0 | 12.0 | 0 | 4.0 | 4.0 |
10A† (39) | 12.8 (41.0) | 0 | 5.1 (23.1) | 0.0 (28.2) | 89.7 | 87.2 | 0 | 89.7 | 2.6 | 0 | 12.8 | 0 |
34 (30) | 3.3 (10.0) | 0 | 3.3 (6.7) | 3.3 (3.3) | 43.3 | 40.0 | 6.7 | 40.0 | 3.3 | 0 | 6.7 | 3.3 |
19A*,† (28) | 35.7 (85.7) | 67.9 | 14.3 (67.9) | 14.3 (57.1) | 100 | 75.0 | 0 | 100 | 100 | 0 | 50.0 | 50.0 |
23A (26) | 30.8 (65.4) | 65.4 | 7.7 (61.5) | 23.1 (69.2) | 88.5 | 88.5 | 0 | 92.3 | 0 | 0 | 69.2 | 0 |
22F† (25) | 4.0 (12.0) | 0 | 4.0 (4.0) | 4.0 (4.0) | 68.0 | 40.0 | 0 | 40.0 | 4.0 | 0 | 4.0 | 4.0 |
35B (24) | 16.7 (25.0) | 12.5 | 20.8 (25.0) | 20.8 (25.0) | 100 | 95.8 | 20.8 | 87.5 | 20.8 | 0 | 20.8 | 20.8 |
11A† (21) | 23.8 (85.7) | 71.4 | 57.1 (95.2) | 38.1 (90.5) | 95.2 | 95.2 | 14.3 | 90.5 | 95.2 | 0 | 76.2 | 71.4 |
15B† (16) | 37.5 (62.5) | 43.8 | 6.3 (31.3) | 0 (43.8) | 100 | 56.3 | 0 | 100 | 43.8 | 0 | 50.0 | 25.0 |
12F† (15) | 0 (0) | 0 | 0 (0) | 0 (0) | 86.7 | 80.0 | 0 | 93.3 | 6.7 | 0 | 0 | 0 |
19F*,†,‡ (14) | 28.6 (92.9) | 64.3 | 7.1 (57.1) | 0 (57.1) | 100 | 78.6 | 14.3 | 78.6 | 100 | 0 | 50.0 | 50.0 |
23B (13) | 7.7 (61.5) | 53.8 | 0.0 (53.8) | 15.4 (61.5) | 69.2 | 61.5 | 0 | 61.5 | 0 | 0 | 53.8 | 0 |
20 | 8.3 (16.7) | 8.3 | 16.7 (16.7) | 16.7 (16.7) | 83.3 | 83.3 | 16.7 | 83.3 | 16.7 | 0 | 16.7 | 16.7 |
24F/24A/24B (11) | 9.1 (9.1) | 0 | 0 (0) | 0 (0) | 100 | 100 | 0 | 100 | 0 | 0 | 9.1 | 0 |
15A (10) | 0 (50.0) | 0 | 0 (20.0) | 0 (20.0) | 100 | 70.0 | 0 | 100 | 70.0 | 0 | 0 | 0 |
Others§ (77) | 6.5 (31.2) | 13.0 | 7.8 (27.3) | 9.1 (26.0) | 80.5 | 53.2 | 1.3 | 76.6 | 27.3 | 0 | 10.4 | 3.9 |
*13-valent pneumococcal conjugate vaccine (PCV13) serotype; †Pneumococcal polysaccharide vaccine (PPSV23) serotype; ‡7-valent pneumococcal conjugate vaccine (PCV7) serotype; §Other serotypes, including serotypes 2, 6A, 6B, 6C, 6D, 7B, 9N/9L, 9V, 11D, 13, 14, 15C, 15F, 16F, 23F, 31, 33F, 38/25F/25A, and 44/46, and non-typeable isolates.
Abbreviations: NS, non-susceptible; MDR, multidrug-resistant; XDR, extensively drug-resistant; AMC, amoxicillin/clavulanate; CTX, cefotaxime; CRO, ceftriaxone; CLI, clindamycin; ERY, erythromycin; LEV, levofloxacin; PEN, penicillin; TET, tetracycline; SXT, sulfamethoxazole/trimethoprim; VAN, vancomycin.
MDR and XDR isolates accounted for 23.4% (N=96) and 13.1% (N=54) of all isolates, respectively (Fig. 1). Of the total MDR isolates, serotypes 23A, 11A, 19A, and 15B accounted for the highest proportions at 18.8%, 16.7%, 14.6%, and 8.3%, respectively. The percentage of MDR isolates was the highest in serotype 11A (76.2%, N=16;
The results of the MLST, CC, and eBURST tests are shown in Table 4 and Fig. 2. The major CCs were CC166 (N=59, 61.5%) and CC320 (N=20, 20.8%). Eleven singletons (N=17, 17.7%) were detected. The five novel STs belonged to CC166 (ST16441, ST16442, ST16443, and ST16444) and a singleton (ST16440). By ST, ST166 (N=42, 43.8%), ST320 (N=12, 12.5%), ST10120 (N=5, 5.2%), ST1464 (N=5, 5.2%), and ST11189 (N=5, 5.2%) were common. CC166 consisted of 12 STs, including ST166 (N=42, 43.8%), ST10120 (N=5, 5.2%), and ST13214 (N=2, 2.1%). CC320 consisted of four STs: ST320 (N=12, 12.5%), ST1464 (N=5, 5.2%), ST6400 (N=2, 2.1%), and ST2697 (N=1, 1.0%).
Table 4 . MLST of 96 MDR
CC (N) | Sequence type | Serotype (N) | N (%) |
---|---|---|---|
CC166 (59) | 166 | 23A (13), 11A (9), 23B (7), 15B (6), 35B (3), 13 (2), 15C (1), 23F (1) | 42 (43.8) |
10120 | 11A (3), 15B (1), 19A (1) | 5 (5.2) | |
13214 | 20 (2) | 2 (2.1) | |
16444* | 3 (2) | 2 (2.1) | |
8279 | 11A (1) | 1 (1.0) | |
9690 | 22F (1) | 1 (1.0) | |
9875 | 11A (1) | 1 (1.0) | |
16209 | 11A (1) | 1 (1.0) | |
16324 | 23A (1) | 1 (1.0) | |
16441* | 11A (1) | 1 (1.0) | |
16442* | 13 (1) | 1 (1.0) | |
16443* | 23A (1) | 1 (1.0) | |
CC320 (20) | 320 | 19A (10), 19F (2) | 12 (12.5) |
1464 | 19F (5) | 5 (5.2) | |
6400 | 19A (2) | 2 (2.1) | |
2697 | 15B (1) | 1 (1.0) | |
Singleton (17) | 11189 | 10A (5) | 5 (5.2) |
10272 | 23A (2) | 2 (2.1) | |
16202 | 35B (2) | 2 (2.1) | |
189 | 34 (1) | 1 (1.0) | |
338 | 23A (1) | 1 (1.0) | |
558 | 19A (1) | 1 (1.0) | |
1624 | 6B (1) | 1 (1.0) | |
3386 | 24F/24A/24B (1) | 1 (1.0) | |
9395 | 34 (1) | 1 (1.0) | |
16205 | 15F (1) | 1 (1.0) | |
16440* | 23F (1) | 1 (1.0) | |
Total | 96 (100) |
*Novel sequence types identified in our study.
Abbreviations: CC, clonal complex; MLST, multilocus sequence typing; MDR, multidrug-resistant.
Serotypes 23A (N=14 of 18), 11A (N=15 of 16), 15B (N=7 of 8), and 23B (N=7 of 7) were common in CC166. Serotypes 19A (N=12 of 14) and 19F (N=7 of 7) were more common in CC320. All serotype 10A isolates contained a singleton, ST11189. The six common CC-serotype combinations were CC166-23A, CC166-11A, CC166-23B, CC166-15B, CC320-19A, and CC320-19F.
There are several reports showing the decrease of IPDs after the introduction of PCVs and a relative increase of the prevalence of non-vaccine serotypes [15, 16]. Recent reports have shown different serotype distributions in various countries, including the USA (35B, 3, 23A, 11A/11D, 15A/15F), Canada (19A, 3, 7F), Spain (12F, 8, 3, 14), and Japan (12F, 3, 23A, 19A) [17-20].
The serotype distribution of
In our study, serotype 10A was the most common serotype in children (≤5 years old), and most of these isolates were collected from children ≤1 year old. This is completely different from the data of other countries, including the USA (19F, 14B, 6B), France (12F, 24F), and Japan (12F, 24F) [23-25]. There are few reports of an increase in serotype 10A. This serotype has been observed in Spain and Belgium [19, 26], and an increase was reported in pediatric patients with IPDs in Korea and Japan [27, 28]. Serotype 10A is not included among the serotypes targeted by PCV13; continuous surveillance is recommended because of its high prevalence.
Serotype 3 is most prevalent in adults [29]. An increase in serotype 3 was observed in patients aged >50 years, especially in those ≥65 years old, whereas it was hardly ever found in children in this study. We surmise that this difference is attributable to the effectiveness of PCV13 in children, which supports the consideration of vaccination with PCV13 in the older population. Serotype 35B was common in those ≥65 years old in Korea, whereas this serotype is highly prevalent in children in the USA [30].
The coverage rate of PCV13 in Korea decreased to 28.7% compared to that in a previous report (34.5%) between 2014 and 2016 [2]. The coverage rate of PCV13 in children ≤5 years old was 14.0%, which is slightly higher than that observed in Japan (9.2%), although it is significantly lower than those in the USA (39.3%) and France (34.4%) [23-25]. There has been an increase in non-PCV13 serotypes after PCV13 vaccination, which has also been observed in other countries such as England and Wales (8, 12F, 9N, 22F, 15A, 33F, and 23A), the USA (15B/C, 22F, 33F, and 35B/D), Japan (22F, 15A, and 23A), and China (14, 19F, 19A, and 23F) [31-34]. In this study, the common non-PCV13 serotypes were 10A, 34, 23A, 22F, 35B, and 11A.
The rates of resistance and intermediate resistance to penicillin were 13.1% and 24.1%, respectively. Intermediate resistance rates (19.7% and 20.4%) to cefotaxime and ceftriaxone were higher than their resistance rates (9.5% and 9.2%, respectively). We previously reported that the rates of intermediate resistance to penicillin, cefotaxime, and ceftriaxone were 9.0%, 14.7%, and 11.3%, respectively, in Korea between 2014 and 2016 [2]. This increase in the intermediate resistance rate since 2016 warrants attention. High rates of intermediate resistance to penicillin, cefotaxime, and ceftriaxone have also been reported in Taiwan [35]. These results support the view that the resistance to β-lactam antimicrobial agents will increase in the near future. The resistance rate to levofloxacin was higher at 4.1% than that reported in Canada (1.0%) and Japan (1.0%), although it is lower than that in China (6.6%) [17, 25, 36].
MDR was common in serotypes 11A, 19A, and 19F in previous studies [5, 12, 37, 38]. Serotypes 23A and 23B were closely associated with MDR. Serotype 11A was closely related to levofloxacin resistance, as previously reported, which was highly prevalent in serotypes 35B, 19F, and 20 [5, 12, 37, 38].
CC166 and CC320 were the major clones of the MDR
Although the relationship between 19F and CC320 was previously common, it has increased in recent years [12, 36, 37]. In this study, CC320 was common in both the 19A and 19F serotypes. Most serotype 19A isolates were ST320, whereas most serotype 19F isolates were ST1464. The 19F-CC271 combination represents the major serotype-CC combination in China; however, ST271 was not identified in our study [40]. This demonstrates the epidemiological differences by country. We found an increase in the singleton 10A-ST11189, whereas 10A-ST3385 was common in a previous report [41].
We identified five new STs in MDR isolates (ST16440, ST16441, ST16442, ST16443, and ST16444), which all belong to CC166, except for ST16440. Three new STs, ST16441, ST16442, and ST16443, are single-locus variants of ST166. ST16444 is a single-locus variant of ST8279.
Baek,
In conclusion, we found a change in serotype distribution and a high rate of non-PCV13 serotypes after introduction of PCV13 vaccination in Korea. An increase in non-vaccine serotypes such as 23A, 23B, and 35B was noted. Differences in antimicrobial resistance according to the specific serotype were verified. These results highlight the need for continuous monitoring of serotypes and antimicrobial resistance to ensure the appropriate management of
None.
Kim GR and Kim EY: conceptualization, data curation, formal analysis, methodology, writing—original draft; Kim SH: data curation, validation, writing—review and editing; Lee HK, Lee J, Shin JH, Kim YR, Song SA, Jeong J, Uh Y, Kim YK, Yong D, Kim HS, Kim S, Kim YA, Shin KS, Jeong SH, and Ryoo N: resources, writing—review and editing; Shin JH: conceptualization, funding acquisition, project administration, resources, supervision, writing—review and editing. All authors reviewed and approved the manuscript.
None declared.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A3B03934040).