Campylobacter species are responsible for the greatest number of bacterial-mediated diarrhea outbreaks in the world (World Health Organization, 2013), with the thermophilic Campylobacter jejuni and Campylobacter coli being the most common pathogens. The European Food Safety Agency (EFSA) reports that C. jejuni has caused the most cases of bacterial foodborne diseases in the European Union for many years (European Food Safety Agency and European centre for Disease Prevention and Control, 2015). According to statistics on the number of foodborne pathogenic microorganisms in the United States by the United States Centers for Disease Control and Prevention (USA-CDC) in 2016, the number of cases caused by C. jejuni ranked highest (Centers for Disease Control and Prevention [CDC], 2017). In addition, Campylobacter infection can lead to extraintestinal complications and campylobacteriosis such as Guillain Barré syndrome, reactive arthritis, and irritable bowel syndrome (Nachamkin et al., 1998; Zia et al., 2003; Connor, 2005). An outbreak of C. jejuni resulted in 32 Guillain Barré syndrome patients in Shuangyang District, Changchun City, Jilin Province, China, during 2007 (Zhang et al., 2010b).

Campylobacter can colonize poultry, swine, and ruminants (Gallay et al., 2007; Elhadidy et al., 2018); therefore, people are easily infected when handling and consuming raw and semi-raw contaminated foods, as well as contaminated water (Klein-Jöbstl et al., 2016; Kovanen et al., 2016). Most Campylobacter infections are mild, self-limiting, and resolve within a few days. However, effective antimicrobial treatment is essential for people with severe or prolonged Campylobacter infections, and the elderly, young, or immunocompromised patients (Reddy and Zishiri, 2017). Clinical treatment of gastroenteritis caused by Campylobacter is usually performed with macrolides and fluoroquinolones; however, occasionally, severe systemic infection requires the use of aminoglycoside antimicrobials, such as gentamicin (Blaser and Engberg, 2008; Pernica et al., 2016). Campylobacter isolates from both developed and developing countries show resistance to several antimicrobials, including aminoglycosides, fluoroquinolones, macrolides, and tetracyclines (Padungton and Kaneene, 2003; Ruiz-Palacios, 2007; Ge et al., 2013; Abdi-Hachesoo et al., 2014; Shobo et al., 2016; Reddy and Zishiri, 2017), which led the World Health Organization in 2017 to list Campylobacter spp. as one of the six high-priority antimicrobial-resistant pathogens (World Health Organization, 2017). Therefore, identifying the molecular characteristics of resistant isolates and estimating their frequency in different populations is important for disease prevention aimed at controlling the emergence of resistant isolates and detecting resistant infections rapidly.

Molecular typing of bacteria plays an important role in the epidemiological investigation of pathogen transmission pathways by identifying outbreaks and diseases (O’Mahony et al., 2011). However, only a few studies have investigated the isolation rate and molecular characterization of clinical Campylobacter spp. in China (Zhang et al., 2010a, 2014; Wei et al., 2015; Pan et al., 2016; Ju et al., 2018). To understand the genotypes and antimicrobial resistance of clinical Campylobacter isolates in Beijing, we combined antimicrobial susceptibility tests and molecular subtyping analysis with epidemiological information.

Campylobacter is one of the major causes of gastroenteritis in the world. The transmission chain of Campylobacter spp. is not completely known but chickens are considered to be the major reservoir for transmission to humans. Additional sources of infection are likely to include red meat, unpasteurized milk, and contaminated water (Mylius et al., 2007; Pernica et al., 2016). The present study provides more complete and updated information about the prevalence, antimicrobial resistance, and genetic diversity of Campylobacter isolates during 2017 and 2018 in Beijing. Campylobacter infections can be fatal among very young children (World Health Organization, 2020). Several studies of Campylobacter prevalence in children have been conducted previously. For instance, Zhu et al. (2016) reported that 2.9% of children with diarrhea were infected by Campylobacter in Wuhan (southwest China). Ju et al. (2018) reported that 4.0% of child patients with diarrhea were infected by Campylobacter in Shenzhen (southern China). Our study revealed a Campylobacter prevalence of 3.45% (1/29) in child patients with diarrhea, which was not statistically significantly different from other age groups. Moreover, Wang et al. (2015) reported no Campylobacter infections in child patients with diarrhea in Beijing. The discrepancy in prevalence may be caused by the different choice of surveillance hospitals. Only one of the 19 hospitals selected in this study is a children’s hospital. Our results indicated that the isolation rate of Campylobacter is higher in autumn than in other seasons. We suggest that attention should be paid to food hygiene in this season to reduce the risk of foodborne diseases.

In this study, we also highlighted the higher genetic diversity of Campylobacter isolates circulating in Beijing. We identified a total of 125 STs including 19 new STs, with the new STs reaching ST-10002 in this study. Data from an earlier study involving patient diarrheal isolates of Campylobacter collected in China revealed that the most commonly isolated ST in Hebei province is ST-22, consistent with our study. However, the most commonly isolated STs in Guizhou province, Henan province, Shanghai city, and Shenzhen city are ST-2274, ST-436, ST-6915, and ST-403, respectively (Zhang et al., 2010a; Wei et al., 2015; Pan et al., 2016; Ju et al., 2018). This difference in STs may be due to the low number of isolates. The most commonly isolated CCs in this study were CC-21 (42/200, 21.00%) and CC-828 (30/36, 83.33%) from C. jejuni and C. coli, respectively. Many studies have shown different major CCs of Campylobacter in different countries and regions, but CC-21, CC-45, CC-48, and CC-353 are the major CCs containing the largest number of isolates in many studies (O’Mahony et al., 2011; Klein-Jöbstl et al., 2016; Kovanen et al., 2016; Pernica et al., 2016; Dunn et al., 2018; Rokney et al., 2018). Studies have also shown that CC-21 is the most commonly isolated CC of C. jejuni in China (Zhang et al., 2010a, 2014, 2015; Wei et al., 2015; Pan et al., 2016; Ju et al., 2018), including human and chicken isolates. MLST analyses of Campylobacter in Asian diarrhea patients show that CC-21 is the most commonly isolated CC of C. jejuni in China, Israel, Iran, Japan, and South Korea. CC-1150 of C. coli has been found in Vietnam, Singapore, and China. These data highlight the diversity of Campylobacter spp. in Beijing and confirm previous MLST studies with C. jejuni and C. coli isolates from humans in China.

ST-2274 of C. jejuni and ST-9227 of C. coli caused outbreaks of foodborne diseases resulting in seven and three patients with diarrhea in Beijing, respectively (Qu et al., 2019; Li et al., 2020). ST-2274 was found in Thailand and Guizhou province and Shanghai city of China. ST-9227 has not been reported in the PubMLST database in Asia except in Beijing. An outbreak of Guillain Barré syndrome caused by C. jejuni was previously reported in Changchun City, Jilin Province, China, and the strains isolated from patients were all ST-2993 (Zhang et al., 2010b). However, no other ST-2993 isolates in the PubMLST database were from other country of Asia.

Antimicrobial resistance of Campylobacter is receiving more attention. Infection with antimicrobial-resistant isolates is often associated with longer disease duration, higher risk of invasive disease, and higher healthcare costs (Lopes et al., 2019). The use of antimicrobials in animal agriculture and human medicine can affect the development of resistance in Campylobacter. It is believed that the unrestricted use of antimicrobials, especially in developing countries, has led to increased resistance to Campylobacter spp. (Gibreel and Taylor, 2006; Deng et al., 2015). In some countries, in contrast to therapeutic agents, antibacterial agents are still used as growth promoters (Osterlund et al., 2003; Gibreel and Taylor, 2006; Qin et al., 2011; Wang et al., 2014). Antimicrobial-resistant strains of Campylobacter are a zoonotic pathogens that can be transmitted to humans through contaminated food, water, or milk, seriously jeopardizing treatment (Smith et al., 1999; Piddock et al., 2000; Engberg et al., 2004; Smith and Fratamico, 2010; Schweitzer et al., 2011). Determination of the antimicrobial resistance level of Campylobacter isolates is crucial for the control and prevention of human infection, particularly for cases in which therapy is recommended. Macrolides and fluoroquinolones are the primary choice for treating campylobacteriosis (Chen et al., 2010). However, an increase in erythromycin-resistant Campylobacter in poultry has been observed in China recently (Zhang A. et al., 2016). In our study, 44.44% of C. coli were resistant to erythromycin. We also found that 75.00% of C. coli were MDR isolates and 11 isolates (30.56%) were resistant to macrolide, quinolone, phenicol, tetracycline, and lincosamide. Therefore, the clinical treatment of campylobacteriosis caused by C. coli should be carefully reconsidered. The overall resistance level of C. jejuni is not as high as that of C. coli, but it cannot be ignored. High resistance rates of C. jejuni to quinolone and tetracycline, with a high prevalence of MDR, has been reported in China previously (Zhang T. et al., 2016; Li et al., 2017). In our study, 55.00% of C. jejuni were MDR isolates, with quinolone, phenicols, and tetracycline the most commonly observed MDR combination (11.50%), followed by quinolone, phenicol, tetracycline and lincosamides (10.50%). A significant association between ST-464 and resistance to ciprofloxacin, nalidixic acid, and tetracycline (cip-nal-tet) has been reported (Cha et al., 2016). Five isolates of ST-464 were recovered in our study, all of which were resistant to cip-nal-tet. One study also claims that ST-403 has strong antimicrobial resistance (Ju et al., 2018), which was shown in our study. Some studies, such as in Michigan and Iran (Cha et al., 2016; Divsalar et al., 2019), reported low resistance rate of C. jejuni to florfenicol and clindamycin. However, Higher resistance rates of C. jejuni to these two antimicrobials have been reported in China. Pan et al. (2016) reported 21.8% of C. jejuni isolated from children with diarrhea were resistant to clindamycin. Ju et al. (2018) reported florfenicol resistance rate of C. jejuni close to 70%. A 17-year study of C. jejuni resistance in diarrhea patients of Beijing showed that the resistance rate of florfenicol and clindamycin is increasing (Zhou et al., 2016). Alarming was resistance of C. jejuni to florfenicol (35.00%) and clindamycin (33.50%) in our study. We found 17 ioslates resistant to florfenicol, clindamycin and chloramphenicol. At the same time, all 17 ioslates were resistant to cip-nal-tet, and belong to 17 different STs. The resistance pattern of these antimicrobials limits the choice of suitable antimicrobials for human Campylobacter disease. Thus, we suggest that clinicians should consider multi-drug treatment.

An isolate of C. coli (ST-825, CC-828) sensitive to all antimicrobials was isolated from an adult man who claimed to have eaten seafood at home (unpublished data). We are very curious about this result, because in addition to this isolate, other C. coli isolates were resistant to two or more classes of antimicrobials. Therefore, the detection of resistance genes in C. coli is the focus of our next research.

In China, a few studies have reported the prevalence of Campylobacter in food and animals (Zhang et al., 2015; Han et al., 2016; Zhu et al., 2017). However, descriptions of clinical Campylobacter are very limited. In this study, we described the characteristics of molecular typing and antimicrobial susceptibility profiles of clinical Campylobacter isolates in Beijing, the capital city of China. The clinical isolates analyzed in this study were recovered from a systematic surveillance program, which provided a unique opportunity to characterize Campylobacter spp. in Beijing.

Based on our results, attention should be drawn to the prevalence of isolates with high antimicrobial resistance rates and genetic similarity in Beijing and other districts of China. Food manufacturers should continually assess levels of contamination in food production and processing to effectively decrease Campylobacter infection and dissemination of resistant isolates in humans. Importantly, this study provides detailed insight into the phylogeny and antimicrobial resistance profiles of Campylobacter spp. in Beijing. Further surveillance is necessary to detect emerging resistance patterns and to assess the impact of strategies designed to mitigate antimicrobial resistance.

All relevant data is contained within the article. All datasets generated for this study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

The protocol was approved by the ethics committee of Beijing Center for Disease Prevention and Control (Beijing CDC). Participants received information on the study’s purpose and of their right to keep information confidential. Written consent was obtained from each participant and children’s parents or their guardians.

JJ and XM were involved in the collection of isolates and collected the clinical data. YL, XZ, and PZ performed the molecular subtyping and antibiotic susceptibility tests. XZ, JJ, and PZ performed the data analysis. PZ, XZ, ZS, XM, and QC designed the study, drafted, and revised this manuscript. All authors contributed to the article and approved the submitted version.

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.