Front. Cell. Infect. Microbiol. Frontiers in Cellular and Infection Microbiology Front. Cell. Infect. Microbiol. 2235-2988 Frontiers Media S.A. 10.3389/fcimb.2023.1179509 Cellular and Infection Microbiology Original Research Antibiotic susceptibility and clonal distribution of Staphylococcus aureus from pediatric skin and soft tissue infections: 10-year trends in multicenter investigation in China Su Wei 1 3 † Liu Ying 1 4 † Wang Qing 2 † Yuan Lin 2 Gao Wei 2 Yao Kai H. 2 Yang Yong H. 2 Ma Lin 1 * 1 Department of Dermatology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, Beijing, China 2 Laboratory of Dermatology, Beijing Pediatric Research Institute, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, Beijing, China 3 Department of Dermatology, Children’s Hospital Affiliated to Capital Institute of Pediatrics, Beijing, China 4 Department of Dermatology, Children's Hospital Affiliated to Zhengzhou University, Zhengzhou, China

Edited by: Mogens Kilian, Aarhus University, Denmark

Reviewed by: William R. Schwan, University of Wisconsin–La Crosse, United States; Xiang Ma, Jinan Children’s Hospital, China

*Correspondence: Lin Ma, bch_maleen@aliyun.com

†These authors have contributed equally to this work

 13 07 2023 2023 13 1179509 24 03 2023 19 06 2023 Copyright © 2023 Su, Liu, Wang, Yuan, Gao, Yao, Yang and Ma 2023 Su, Liu, Wang, Yuan, Gao, Yao, Yang and Ma

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 Background

Skin and Soft Tissue Infections (SSTIs) Surveillance Network of S. aureus In Pediatrics in China was established in 2009 to routinely report epidemiological changes. We aimed to monitor the present antibiotic sensitivity and molecular characteristics of S. aureus and methicillin-resistant S. aureus (MRSA) from SSTIs in children nationwide and track the changes over the past decade.

 Methods

Patients diagnosed with SSTIs from the dermatology departments of 22 tertiary pediatric hospitals in seven geographical regions of China were recruited continuously from May 2019 to August 2021. S. aureus was isolated, and its sensitivity to 15 antimicrobials was evaluated using the broth microdilution method. The molecular characteristics of the MRSA isolates were determined through multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. The presence of the Panton–Valentine leukocidin gene (pvl) was determined.

 Results

The detection rate of S. aureus was 62.57% (1379/2204), among which MRSA accounted for 14.79% (204/1379), significantly higher than the result in previous study in 2009-2011 (2.58%, 44/1075). Compared with previous study, the sensitivity to cephalosporins and fusidic acid decreased to varying degrees, while that to chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, penicillin, and tetracycline increased significantly. The sensitivity to mupirocin, trimethoprim/sulfamethoxazole (TRISUL), and rifampicin still maintained at a high level (97.90%, 99.35% and 96.66% respectively). The leading multidrug resistance pattern of MRSA and methicillin-sensitive S. aureus (MSSA) were erythromycin-clindamycin-tetracycline (55.84%; 43/77) and erythromycin-clindamycin-chloramphenicol (27.85%, 44/158) respectively. 12 high-level mupirocin-resistant strains were detected, and notable differences in geographical distribution and seasonal variation were observed. The main types of MRSA were ST121 (46.08%, 94/204), followed by ST59 (19.61%, 40/204). SCCmec V (65.69%, 134/204) and SCCmec IV (31.86%, 65/204) were dominant epidemic types. ST121-V, ST59-IV, and ST22-V were the most prevalent clones nationwide. The detection rate of pvl had increased markedly from 9.09% (4/44) in 2009-2011 to 22.55% (46/204) in 2019-2021 (P<0.05).

 Conclusion

The antibiotic sensitivity and molecular characteristics of S. aureus from pediatric SSTIs has changed significantly over the past decade. To standardize medical care, provide timely and reasonable clinical treatment, and effectively manage infection control, Chinese pediatric SSTIs guidelines are urgently needed.

 SSTIs Staphylococcus aureus MRSA antimicrobial sensitivity molecular epidemiology China 31900132 QM20191202 National Natural Science Foundation of China10.13039/501100001809 Beijing Hospital Authority10.13039/100016126 section-in-acceptance Clinical Microbiology Introduction

Staphylococcus aureus is the main pathogen that causes skin and soft tissue infections (SSTIs), such as pustules, folliculitis, boils, and abscesses, in pediatric patients (Lowy, 1998) as well as fatal infections, such as necrotizing fasciitis and toxic shock syndrome (Burnham and Kollef, 2018). Methicillin-resistant S. aureus (MRSA) has attracted considerable attention owing to its drug resistance and virulence (Lee et al., 2018). Community-associated MRSA (CA-MRSA) mainly causes SSTIs in young and healthy people in the community (Turner et al., 2019). Over the past decade, CA-MRSA has been considered to be the main cause of the increased burden of MRSA diseases. Some CA-MRSA strains have been increasingly involved in nosocomial infections and have even become dominant strains in medical settings (Elston and Barlow, 2009). The resistance rate of CA-MRSA is increasing, not only to β-lactam antibiotics but also to non-β-lactam antibiotics (Guo et al., 2020). The spectrum of CA-MRSA invasive diseases is expanding and is increasingly becoming the focus of global infection (Hassoun et al., 2017). Epidemiological information on MRSA is important for clinical decision-making and public health monitoring. Furthermore, classification of MRSA is an important part of describing epidemiological trends and formulating infection control strategies (Mediavilla et al., 2012).

To our knowledge, few studies on the antibiotic sensitivity of S. aureus and molecular characteristics of MRSA from SSTIs in China have been conducted (Xiao et al., 2019; Zhao et al., 2022). Furthermore, results from different regions differ, and national studies related to children are rare. A national SSTIs surveillance network of S. aureus in pediatrics, established in 2009 and led by the Department of Dermatology, Beijing Children’s Hospital, is the only available nationwide epidemiological surveillance network with regular investigation in China (Liu et al., 2016). Currently, 22 children’s hospitals have joined. The present study aimed to track the changes in antibiotic sensitivity of S. aureus as well as the molecular characteristics and epidemiology of MRSA in children diagnosed with SSTIs in China.

 Materials and methods Patient enrollment

This was a multi-center, cross-sectional epidemiological study on children diagnosed with SSTIs in the dermatology departments of 22 tertiary pediatric hospitals. According to their geographical location, the hospitals were divided into seven groups: North, Middle, East, South, Northeast, Northwest, and Southwest China. All patients who met the criteria for SSTIs were recruited continuously from the dermatology departments from May 2019 to August 2021. The inclusion criteria were as follows: 1) no history of major congenital malformations or severe chronic diseases, 2) no history of surgery or hospitalization within the past year, 3) no history of dialysis or deep catheterization, and 4) no history of antibiotic use within the past week. Information, including sex, age, predisposing factors, disease type, specimen collection time, and basic medical history, was collected. Patients who could not provide general information were excluded. The enrolled patients were treated according to routine treatment, and the swab specimens of infection sites from the non-repetitive participants were collected continuously.

 Strain identification

The isolated strains were identified using traditional microbial identification methods, coagulase and catalase tests, and latex slide agglutination test (Oxoid Ltd., Basingstoke, UK). All three tests were positive for S. aureus (Weist et al., 2006).

 Identification of MRSA strains

In addition to resistance to cefoxitin and oxacillin, MRSA was further identified through polymerase chain reaction (PCR) amplification of the nuc and mecA genes according to the method described previously (Sahebnasagh et al., 2014). ATCC 29213 and ATCC35601 were used as a negative and positive control, respectively, for the mecA gene.

 Susceptibility profiles

The antibiotic susceptibility profiles of the S. aureus isolates were determined using the Sensititre® Antimicrobial Susceptibility Testing System (Thermo Scientific, UK), following the manufacturer’s instructions. The minimum inhibitory concentration (MIC) to 15 antibiotics (cefazolin, ceftriaxone, cefuroxime, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, fusidic acid, gentamicin, mupirocin, penicillin, rifampicin, tetracycline, TRISUL, and vancomycin) were detected using the broth microdilution method (Novy et al., 2014). S. aureus ATCC 29213 and ATCC 35601 were used for quality control. The antimicrobial sensitivity breakpoints were interpreted according to the current Clinical and Laboratory Standards Institute (CLSI) breakpoints for S. aureus (CLSI, 2019), while sensitivity to cefazolin, ceftriaxone, and cefuroxime was interpreted according to a previous version of CLSI (Clinical and Laboratory Standards Institute/NCCLS, 2005). An E-test ((bioMérieux, Marcy-L’Étoile, France) was further performed on the isolates classified as mupirocin-resistant through broth microdilution.

 Epidemiological typing of MRSA

DNA was extracted for PCR using a bacterial genomic DNA extraction kit (Tiangen Biochemical Technology, China). Multilocus sequence typing (MLST) was performed on MRSA isolates using the method described previously (Enright et al., 2000). Sequences of seven housekeeping genes (arcC, aroE, glpF, gmk, pta, tpi, and yqiL) were compared with known alleles from the MLST database (https://pubmlst.org/organisms/staphylococcus-aureus). Allelic profiles and sequence types (STs) were determined using the database.

The isolates were also subjected to staphylococcal cassette chromosome mec (SCCmec) typing, which is based on multiplex PCR with 10 primers (Omuse et al., 2016). SCCmec types I-V were assigned according to the combination of the cassette chromosome recombinase (ccr) type and mec class. Isolates that could not be assigned to any expected type were defined as non-typable.

 Panton–Valentine leukocidin gene detection

pvl was amplified using PCR as described previously (Hesje et al., 2011) with minor modifications. MRSA N315 was used as a negative control, while ATCC 25923 was used as a positive control.

 Statistical analysis

A database including the age, sex and disease patterns of the patients, antimicrobial resistance and molecular characteristics of the corresponding isolate was constructed in Microsoft Excel 2003. GraphPad Prism 9.0 (GraphPad Software Inc., San Diego, CA, United States) was used to create graphs. All susceptibility data were analyzed using WHONET software (version 5.6). JMP® 11 Statistical Discovery Software (S.A.S. Institute Inc., Cary, North Carolina) was used for statistical analysis. Categorical variables were analyzed using the chi-squared (χ2) or Fisher’s exact test. Significance was set at P < 0.05.

 Results General information

The initial data of S. aureus and MRSA collection as well as the distribution of them are summarized here. From May 2019 to August 2021, 2204 patients with SSTIs were enrolled in 22 children’s hospitals in 19 provinces of seven geographic regions. The overall positive rate of S. aureus was 62.57% (1379/2204). The detection rate of S. aureus was the highest at 75.77% (519/685) in South China and was the lowest at 46.49% (159/342) in North China. The proportion of MRSA was 14.79% (204/1379) nationally, with significantly different proportions across China ranging from 12.73% (21/165) in Middle China to 17.24% (5/29) in North West China. Single institutional prevalence ranged from 4.35% (1/23) to 30.77% (8/26) (P < 0.05). The distribution of enrolled patients and the number of positive S. aureus and MRSA isolates in each geographic region are shown in Figure 1 .

The distribution of specimens, S. aureus and MRSA as well as prevalent clones, by region. All seven geographical regions were included as follows: Northeast, green, North China, gray; East China, blue; Northwest, yellow; Middle China, khaiki; Southwest, pink; South China, orange. *pvl-positive clones contained.

The clinical features of patients from whom the strains were collected are analyzed as follows. The age of patients ranged from 3 days to 18 years old, with 77.16% (1064/1379) aged 1–6 years. Of the patients, 58.45% (806/1379) were males and 41.55% (573/1379) were females. Detailed clinical features are presented in Table 1 .

Clinical features of patients from children with SSTIs in the present study.

Variable Numbers (%) Region Hospital Patients/SA/MRSA (n)
General information East China
Total patients 2204  Anhui province AHCH 96/74/13
SA 1379 (62.57%)  Zhejiang province HZCH 100/58/8
 MSSA 1175 (85.21%)  Shandong province JNCH 52/23/1
 MRSA 204 (14.79%)  Jiangsu province NJCH 36/21/2
Sex  Jiangsu province XZCH 100/78/6
 Male 806 (58.45%)  Zhejiang province ZJCH 95/26/8
 Female 573 (41.55%) Middle China
Ages  Hubei province HBMCHH 34/18/2
 0-28 days 11 (0.80%)  Hunan province HNCH 98/61/12
 1-12 months 167 (12.11%)  Henan province ZZCH 100/86/7
 1-3 years 401 (29.08%) North China
 3-6 years 496 (35.97%)  Beijing BJCH 140/50/10
 6-12 years 278 (20.16%)  Inner Mongolia province NMGCH 95/47/5
 12-18 years 26 (1.89%)  Beijing CIOPCH 107/62/8
Types of SSTIs SA/MRSA North East
 Primary infection 1059/155  Jilin province CCCH 99/50/15
 Impetigo 543/75  Liaoning province DLCH 97/60/5
 Furuncle 274/42  Heilongjiang province HBCH 37/12/0
 Folliculitis 176/28 North West
 Abscess 36/7  Shaanxi province XACH 62/29/5
 Paronychia 16/2 South China
 SSSS 11/1  Guangdong province SZCH 332/281/48
 Acne 2/0  Guangxi province LZMCHH 94/60/7
 Omphalitis 1/0  Guangdong province GZCC 161/115/18
 Secondary infection 320/49  Hainan province HNMCHH 98/63/11
 Secondary infection of eczema 177/19 South West
 Secondary infection of trauma 75/16  Sichuan province CDCH 90/68/7
 Secondary infection of herpes 36/8  Yunnan province KMCH 81/37/6
 Secondary infection of fungi 7/2
 Others 25/4

MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive S. aureus; SA, Staphylococcus aureus.

Dalian Children’s Hospital of Dalian Medical University, DLCH; Children’s Hospital of Changchun, CCCH; Harbin Children’s Hospital, HBCH; Beijing Children’s Hospital, BJCH; Children's Hospital Affiliated to Capital Institute of Pediatrics, CIOPCH; Inner Mongolia maternal and Child Health Hospital, NMGCH; Xuzhou Children’s Hospital, XZCH; Children's Hospital Affiliated to Zhejiang University, ZJCH; Anhui children's Hospital, AHCH; Nanjing Children's Hospital, NJCH; Qilu Hospital Jinan children's Hospital, JNCH; Hangzhou Children's Hospital, HZCH; Xi'an Children's Hospital, XACH; Hubei Maternal and Child Health Hospital, HBMCHH; Hunan Children’s Hospital, HNCH; Zhengzhou Children’s Hospital, ZZCH; Chengdu Children's Hospital, CDCH; Kunming children's Hospital, KMCH; Guangzhou Women and Children’s Medical Center, GZCC; Hainan maternal and Child Health Hospital, HNMCHH; Guangxi Liuzhou Maternal and Child Health Hospital, LZMCHH; Shenzhen Children's Hospital, SZCH.

Great changes on infection patterns had occurred during the past decade. The top three primary infections in this study were impetigo (39.38%; 543/1379), furuncles (19.87%; 274/1379), and folliculitis (12.76%; 176/1379). Compared with our study conducted in 2009-2011 (Liu et al., 2016), the distribution of deep infections such as folliculitis and furuncle in 2019-2021 increased significantly from 1.20% (21/1749) to 12.76% (176/1379) and from 0.57% (10/1749) to 19.87% (274/1379) with P<0.001, respectively. The distribution of superficial infections such as impetigo and staphylococcal scalded skin syndrome had decreased from 79.87% (1397/1749) to 39.38% (543/1379) and from 4.69% (82/1749) to 0.80% (11/1379) with P<0.001, respectively. The detailed composition of infections caused by S. aureus in 2009-2011 and 2019-2021 is shown in Figure 2 .

The comparation on distribution of major infection pattern caused by S. aureus in 2009-2011 and 2019-2021 respectively.

 Characteristics of resistance pattern of <italic>S. aureus</italic> and change trend

The results of the antimicrobial susceptibility test on strains collected in this present study are shown in Table 2 . The resistance rates of MRSA to ciprofloxacin, clindamycin, erythromycin, and tetracycline were significantly higher than those of MSSA (P<0.05).

Results of the antimicrobial sensitivity of the isolates in the present study.

Antimicrobial agent MRSA (n=204) MSSA (n=1175)
Sensitivity (%) Resistance (%) MIC50 (μg/mL) MIC90 (μg/mL) MICrange (μg/mL) Sensitivity (%) Resistance (%) MIC50 (μg/mL) MIC90 (μg/mL) MICrange (μg/mL)
CEFAZO 88.24 11.76 2 >8 1~>8 99.15 0.85 1 1 ≤0.25~>8
CEFTRI 49.51 50.49 16 64 6~>256 98.21 1.79 4 4 ≤0.25~>16
CEFURO 46.08 10.78 8 32 ≤4~>64 98.38 0.34 ≤4 ≤4 ≤4~64
CHLORA 47.55 11.27 16 >32 ≤4~>32 55.74 7.32 8 16 ≤4~>32
CIPROF 93.14 4.41 ≤0.25 0.5 ≤0.25~>4 92.00 1.53 ≤0.25 0.5 ≤0.25~>4
CLINDA 31.86 66.18 >16 >16 ≤0.5~>16 47.40 49.96 2 >16 ≤0.5~>16
ERYTH 5.39 87.74 >64 >64 0.032>64 14.98 75.91 >64 >64 0.125>64
FUSIDA 97.06 2.94 ≤0.125 0.25 ≤0.125~>2 95.15 4.85 0.25 0.25 ≤0.125~>2
GENTAM 97.55 1.47 ≤0.125 0.25 ≤0.125~>32 96.60 1.79 ≤0.125 0.25 ≤0.125~>32
MUPIRO 96.57 2.45 ≤0.125 0.25 ≤0.125~>512 98.13 1.19 ≤0.125 ≤0.125 0.06~>512
PENICI 0 100 >8 >8 0.12~>8 6.81 93.19 8 >8 ≤0.125~>8
RIFAMP 93.63 0.49 ≤0.015 1.5 ≤0.015~4 97.19 0.43 ≤0.015 0.5 0.002~>32
TETRA 65.20 34.80 ≤0.5 32 ≤0.5~32 90.04 9.36 ≤0.5 2 ≤0.5~>32
TRISUL 99.51 0.49 ≤0.125 1 ≤0.125~8 99.32 0.68 0.5 1 ≤0.125~16
VANCOM 100.00 0.00 ≤0.5 1 ≤0.5~2 100.00 0.00 ≤0.5 1 ≤0.5~2

CEFAZO, Cefazolin; CEFTRI, cefatriaxone; CEFURO, Cefuroxime; CHLORA, Chloramphenicol; CIPROF, Ciprofloxacin; CLINDA, Clindamycin; ERYTH, Erythromycin; FUSIDA, Fusidic acid; GENTAM, Gentamicin; MUPIRO, Mupirocin; PENICI, Penicillin; RIFAMP, Rifampin; TETRA, Tetracycline; TRISUL, Trimethoprim-sulfamethoxazole; VANCOM, Vancomycin.

S. aureus with resistance to three or more classes of antimicrobial agents were defined as multidrug-resistant (MDR). In this study, MDR was observed in 37.75% (77/204) of MRSA strains and 13.45% (158/1175) of MSSA strains. The predominant resistance patterns of MRSA to non-β-lactam antibiotics were erythromycin-clindamycin-tetracycline (55.84%; 43/77), followed by erythromycin-clindamycin-tetracycline-chloramphenicol (18.18%; 14/77). The resistance patterns of MSSA were very different from that of MRSA, the most common profiles of which were erythromycin-clindamycin-chloramphenicol (27.85%, 44/158) and erythromycin- clindamycin-tetracycline (22.15%, 35/158). Among different STs of MRSA strains, the proportion of MDR in ST121 was the highest (49.35%; 38/77), followed by ST59 (22.08%; 17/77) and ST338 (6.49%; 5/77).

A total of 12 high-level mupirocin-resistant (MuH) strains (MIC ≥ 512 μg/mL) were detected, including nine MSSA strains and three MRSA strains. The differences in ST distributions of MuH strains were irregular, while notable in the differences in geographical distribution and the seasonal variation. MuH strains mainly distributed in South China (66.67%, 8/12)、East China (16.67%, 2/12) and Middle China (16.67%, 2/12). Of the hospitals, the isolates were predominantly separated from Shenzhen Children’s Hospital (41.67%, 5/12), which was geographically assigned to South China. The infection patterns were mainly secondary infection, including secondary infection of eczema (5/12), trauma (2/12) and herpes (1/12). The infections caused by MuH isolates mainly occured in autumn (8/12), followed by summer (4/12). The children mainly aged >3y (66.67%, 8/12).

The changes of resistance patterns of S. aureus collected in this study with strains collected in 2009-2011were analyzed. The current resistance rates of S. aureus to cefazolin, ceftriaxone, cefuroxime, and fusidic acid had increased significantly (P<0.05), and that to chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, rifampicin, tetracycline, and TRISUL decreased significantly (P<0.0001), while no significant difference was found in resistance to vancomycin and mupirocin. Besides, the resistance rate to penicillin decreased from 96.8% to 94.13% (P=0.0004). The comparison of the antimicrobial sensitivity of S. aureus isolates between 2009-2011 and 2019-2021 is shown in Figure 3 .

Comparison of antimicrobial susceptible, intermediate and resistant rates of S. aureus isolates in 2009-2011 and 2019-2021. S, susceptible; I, intermediate; R, resistant.

 Molecular characteristics of MRSA isolates

Overall, 25 STs were detected, of which ST121 accounted for 46.08% (94/204), followed by ST 59 (19.61%, 40/204) and ST22 (9.80%, 20/204). In SCCmec classification, 65.69% (134/204) were type V, and 25.98% (53/204) were type IV. ST121-V, ST59-IV, and ST22-V were the most prevalent clones nationwide. The molecular biological characteristics of MRSA isolates and the dominant MRSA clones by region are summarized in Table 3 ; Figure 1 .

Molecular biological characteristics of MRSA isolates in the present study.

CC MLST n pvl SCCmec
+ - IV V NT
CC121 ST121 94 94 94
ST488 1 1 1
CC59 ST59 40 14 26 31 6 3
CC22 ST22 20 19 1 5 15
CC45 ST508 5 5 5
ST45 3 3 3
CC1 ST1 3 3 3
ST834 1 1 1
ST4855 1 1 1
CC8 ST72 1 1 1
ST630 1 1 1
CC5 ST6 1 1 1
CC30 ST30 1 1 1
NT ST509 11 11 6 5
ST338 7 7 7
ST88 2 1 1 1 1
ST398 1 1 1
Others 11 4 7 6 4 1
Total 204 46 158 53 134 17

MLST, multilocus sequence typing; pvl, panton-valentine leukocidin gene; SCCmec, Staphylococcal cassette chromosome mec; NT, non-typable.

+, postive; -, negative.

 Major features of ST121 and ST59 strains

ST121 was the most prevalent type of MRSA strains, which all typed as SCCmec V and pvl negative. ST121 strains were mainly distributed in Northwest and South China with a positive rate of 80.00% (4/5) and 69.05% (58/84), respectively, while they were not detected in Northeast China. Compared with non-ST121 isolates, ST121 isolates had a significantly higher resistance rate to clindamycin and lower resistance rates to cefazolin, cefuroxime, and ciprofloxacin. The detection rate of ST59 was second to that of ST121. ST59, which was opposite to ST121, was mainly distributed in Northeast and North China, with a positive rate of 80.00% (16/20) and 40.91% (9/22), respectively. Inconsistent with ST121, ST59 strains were mainly typed as SCCmec IV (77.50%, 31/40). The positive rate of pvl was 35.00% (14/40), significantly higher than that of ST121 (0.00%, 0/94). The resistance rate of ST59 isolates to ciprofloxacin, cefazolin, and cefuroxime was significantly higher than that of ST121 isolates (P<0.05), and there was no significant difference in the resistance rate to other antibiotics.

 Clinical and molecular characteristics of <italic>pvl</italic>-positive MRSA strains

The detection rate of pvl had increased markedly from 9.09% (4/44) in 2009-2011 to 22.55% (46/204) in 2019-2021 (P<0.05). Infection patterns caused by pvl-positive and pvl-negative MRSA strains in this study are shown in Figure 4A . pvl-positive MRSA strains mainly caused furuncle (41.30%,19/46) and folliculitis (21.74%,10/46), higher than pvl-negative strains with P<0.0001 and P=0.073 respectively, while pvl-negative MRSA strains mainly caused impetigo (44.94%,71/158) and secondary infection (25.95%,41/158), higher than pvl-positive strains with P<0.0001 and P=0.067 respectively. Among the pvl-positive strains, ST22 (41.30%, 19/46), ST59 (30.43%, 14/46) and ST338 (15.22%, 7/46) were the most common types as shown in Figure 4B , which were significantly higher than the ratio of pvl-negative strains with P<0.05 respectively. In contrast, among pvl-negative strains, ST121 (59.49%,94/158) was the most prevalent ST, the ratio of which was significantly higher than that of pvl-positive strains (P<0.0001).

Clinical and molecular characteristics of pvl-positive MRSA strains. (A), infection patterns caused by pvl-positive and pvl-negative MRSA strains. (B), ST distribution of pvl-positive MRSA strains.

 Discussion

This study was the second to conduct national multicenter epidemiological monitoring of S. aureus for SSTIs in pediatrics since the surveillance network was established in China in 2009. The epidemiological trends of SSTIs in 22 tertiary children’s hospitals in seven geographical regions of mainland China were investigated. Compared with the study conducted 10 years ago, we presented four major findings: 1) the resistance profiles of S. aureus isolates had changed considerably; 2) the prevalence of CA-MRSA and its pvl-positive strains, increased significantly; 3) the proportion of deep infections increased significantly; and 4) ST121-V was the dominant clone, with the percentage increased.

In this study, MRSA accounted for 14.79%, significantly higher than in 2009-2011 (2.58%). It was reported that antimicrobial agents should be chosen to target MRSA and MSSA if MRSA accounts for >10% of S. aureus among SSTIs (David and Daum, 2017). Either clindamycin or TRISUL was recommended because of the low cost and activity against community-associated MRSA and MSSA strains of each of these drugs (Williams et al., 2011). According to previous studies, one of these antimicrobials should be used in addition to incision and drainage for a skin infection (Miller et al., 2015; Daum et al., 2017). In this study, we identified a low resistance rate of S. aureus to TRISUL (0.4%–2%). The long-term use of TRISUL remains a suitable option for treating complex hyperimmunoglobulin E syndrome and chronic granulomatous disease (Hashemi et al., 2017). Clindamycin was reported to be effective at treating infections caused by susceptible CA-MRSA isolates (Miller et al., 2015). However, in this study, though significantly decreased compared with that in 2009-2011, the resistance rate of clindamycin was still higher than 50%, indicating that it is not a good choice for treating SSTIs in children in China.

For empiric or targeted therapy for S. aureus, an anti-staphylococcal β-lactam drug was the most appropriate choice (David and Daum, 2010). Furthermore, it was reported that cephalosporins and penicillin are most commonly used in China (Li et al., 2016). Therefore, the MICs of the clinical strains to penicillin as well as cephalosporins was detected to track changes in sensitivity. The resistance rates of S. aureus to penicillin, though decreased significantly, remained at a high level (94.13%). On the contrary, the sensitivity to cephalosporins was maintained at a high level (90.65%–97.53%). According to this result, cephalosporins might be a suitable alternative to penicillin for empiric therapy.MDR to non-β-lactam antibiotics was detected in both MRSA and MSSA. The presence of MDR strains in outpatients with SSTIs can lead to persistent or recurrent MRSA infections (Lee et al., 2017).

Clinically, most SSTIs can be controlled only with topical antibiotics. Mupirocin is a topical antibiotic that has been extensively used for treating MRSA skin and soft-tissue infections, decreasing certain types of surgical site infections and eliminating nasal colonisation of MRSA among patients and medical staff. In the present study, the sensitivity to mupirocin was still high, consistent with previous results (Liu et al., 2016; Chen et al., 2020). However, high-level mupirocin strains were detected in both MRSA and MSSA strains in this study. Dadashi et al. reported that the incidence of high-level mupirocin resistance in MRSA was the highest in Asia (12.1%), followed by Europe (8.0%) and the USA (5.9%) (Dadashi et al., 2020). In China, it was reported that mupA mainly accounted for high level mupirocin resistance (Jin et al., 2018; Guo et al., 2023). The mupA gene is typically located on mobile genetic elements and is plasmid mediated, which maybe the reasons for transmission of clones (Liu et al., 2010). In this study, high-level mupirocin resistant strains were mainly isolated from South China, which were generally with higher economical levels than others. Easy access to antibiotics without prescriptions, a high rate of antibiotic misuse, and the frequency of empiric treatment in these regions may lead to the situation. The results suggested that the rational use of mupirocin should be strengthened, and drug resistance should be further monitored.

Fusidic acid was also an important choice for SSTIs. The worldwide resistance rate of S. aureus, especially MRSA, to fusidic acid was reported to be 0.3%–64% (Gajdács, 2019). In the present study, the resistance rate of S. aureus to fusidic acid increased from 1.8% to 4.57%, which was still low, similar to that identified previously (Gu et al., 2016). The resistance rate in MSSA (4.85%) was higher than that in MRSA (2.94%), consistent with previous study (Zhanel et al., 2021). The increased detection rate of fusidic acid-resistant strains suggests that the drug should be used in moderation.

Based on the above results of antimicrobial sensitivity, we call for the timely introduction of guidelines for the treatment of SSTIs in children in China to develop scientific and effective diagnosis and treatment programs.

MRSA has been the focus of global SSTIs (Mediavilla et al., 2012). Recently, an upward trend in the incidence of pvl-positive MRSA was observed in Europe and Japan (Bouchiat et al., 2017; Nakaminami et al., 2020). Concern was raised as pvl-positive MRSA strains usually cause deep infections such as furuncles and abscesses (Shallcross et al., 2013). Compared with the study conducted 10 years ago, the detection rate of MRSA in the present study had increased by 5.65-fold (14.79% vs. 2.58%; P<0.0001), and the positive rate of pvl had increased by 2.3-fold (22.55% vs. 9.8%; P<0.05). In addition, the infection spectrum had changed, as deep infections including folliculitis, furuncle, and abscesses increased significantly, while superficial infections decreased. Therefore, according to our surveillance, there was an increasing trend in the prevalence of pvl-positive MRSA among SSTI isolates in Chinese children, which was probably connected with the increase in deep infections. Attention should be paid to the surveillance of pvl-positive MRSA in the future.

MLST is a universal method for understanding the molecular epidemiology of MRSA (Enright et al., 2000). Previous studies demonstrated that the most prevalent clones of CA-MRSA from SSTIs had unique geographic distribution, as ST8 was mostly reported in the USA (Otter and French, 2010), while ST80 was mainly in Europe, and ST59 was mainly in the Asia–Pacific region (Deurenberg and Stobberingh, 2008). In mainland of China, Taiwan, and Hong Kong, ST59 was reported as the most prevalent ST of MRSA strains from SSTIs (Yu et al., 2015), while ST121 was rarely dominant for clinical infections (Chuang and Huang, 2013; Wang et al., 2019). The epidemiological data hint that most ST121 strains were MSSA (Goering et al., 2008; Rao et al., 2015). However, in the present survey, ST121 (46.08%; 94/204) was the dominant ST in MRSA strains, followed by ST59, which was consistent with the results of our previous study (Liu et al., 2016). This was probably due to the differences in the population. In the present study, the enrolled children were at preschool age (1–6 years). It was reported that among preschool children, ST121 was the most prevalent clone in China (Fan et al., 2009). Besides, they were all outpatients who had no history of hospitalization. Therefore, the study was more representative of infections from the community.

In conclusion, tremendous changes in the antibiotic sensitivity of S. aureus from SSTIs in Chinese children had been observed compared with the results obtained 10 years ago. The incidence of MRSA as well as the positive rate of pvl had increased significantly, with ST121, ST59, and ST22 being the main epidemic types. With the significant changes, further research tracking sensitivity to antibiotics as well as the molecular epidemiological characteristics of MRSA is needed. Moreover, to standardize medical care, help clinicians make evidence-based treatment decisions, and effectively manage infection control, guidelines for SSTIs in pediatrics in China are urgently needed.

 Data availability statement

The original contributions presented in the study are included in the article/supplementary materials. Further inquiries can be directed to the corresponding author.

 Ethics statement

This project (2019-k-123) was approved by the Research Ethics Committee in Beijing Children’s Hospital, China on May 21, 2019.

 Author contributions

YL, KY, YY and LM designed the study. WS, YL, QW, LY and WG conducted the experiments. WS, YL and QW collected and analyzed the data, interpreted the results, and drafted the manuscript. All authors contributed to the article and approved the submitted version.

 Funding

National Nature Science Foundation of China (31900132, 81903668), The Special Fund of the Pediatric Medical Coordinated Development Center of Beijing Hospitals Authority (XTZD20180502); Beijing Hospital Authority (QM20191202); BINC Nutrition and Care of Maternal & Child Funding Project (2019BINC-MCF116).

 Acknowledgments

Thanks for the support of Chinese Dermatologist Association. We also thank the following hospitals and their staff members for participating in this study: Beijing Children’s Hospital, Children’s Hospital Affiliated to Capital Institute of Pediatrics, Shenzhen Children’s Hospital, Dalian Children’s Hospital of Dalian Medical University, Children’s Hospital of Changchun, Harbin Children’s Hospital, Inner Mongolia maternal and Child Health Hospital, Xuzhou Children’s Hospital, Children’s Hospital Affiliated to Zhejiang University, Anhui Children’s Hospital, Nanjing Children’s Hospital, Children’s Hospital Affiliated to Shandong University, Hangzhou Children’s Hospital, Xi’an Children’s Hospital, Hubei Maternal and Child Health Hospital, Hunan Children’s Hospital, Zhengzhou Children’s Hospital, Chengdu Children’s Hospital, Kunming Children’s Hospital, Guangzhou Women and Children’s Medical Center, Hainan Maternal and Child Health Hospital, Guangxi Liuzhou Maternal and Child Health Hospital.

 Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

 Publisher’s note

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