Class 1 integrons as predominant carriers in Escherichia coli isolates from waterfowls in Hainan, China
Graphical abstract
Introduction
Antibiotics are widely utilized as feed additives and therapeutic drugs in humans and animals (Angebault and Andremont, 2013; Fletcher, 2015). The widespread and irrational use of antibiotics in humans and animals has given rise to numerous multidrug resistant (MDR) microbes via the dissemination of antimicrobial resistance genes (AMRg) (Rehman et al., 2017a). The occurrence of AMRg in food producing animals is a rising public health concern (Rehman et al., 2017b). This concern is represented by the immediate increase in resistance against last resort antibiotics (colistin, tigecycline) and other carbapenem and extended-spectrum β-lactamases (ESBL) producing enzymes (He et al., 2019; Wang et al., 2017). These resistance determinants are generally disseminated via mobile elements (integrons, transposons and plasmids) in bacterial populations from animals and humans (Rehman et al., 2017a).
The AMRg are generally carried by integrons, transposons and plasmids (Partridge et al., 2009). Integrons can capture, convert and adapt one or more resistance gene cassettes into functionally expressed genes via self-efficient gene expression system (Gillings, 2014). Integrons can simply transfer these genes between diverse bacterial species due to their linkage with plasmids. Hence, integrons can primarily disseminate and transfer antimicrobial resistance because of their ability and mobility to rapidly obtain various genes encoding resistance to antibiotics (Carattoli, 2003; Gillings, 2014). The most communal forms of these integrons are classified as class 1, class 2 and class 3 integrons based on the integrase gene (intI). Class 1 integrons are the most prevalent type among all other types of integrons, and contain two conserved segment (CS) regions. On the other hand, intl2 genes are considered to be part of the non-replicative Tn7 transposon but the organization of class 2 integrons is almost identical to class 1 integrons and share 46% amino acid identity (Álvarez et al., 2016; Chamosa et al., 2017). In addition, class 3 integrons also seems to be captured by a Tn402 transposon but are very rarely reported in animal isolates.
Hainan Island, located in the south of China, is a tropical island with about 9.25 million inhabitants and one of the famous tourist attractions in China. According to a survey report in 2018, the meat type waterfowl (duck and goose) is one of the largest industry of the Hainan Island with an approximate share of 0.39 billion dollars (Yang et al., 2019). The population of goose and ducks used for meat purpose is around 10.5 million and 52 million, respectively. The ‘bailian Goose’ and ‘Jiaji Duck’ are the famous food of the local inhabitants, which is famous for good taste and high nutritional value in China. Several studies have reported the prevalence of integrons and AMRg in E. coli isolates in humans and food producing animals in China (Gu et al., 2008; Lei et al., 2018; Rehman et al., 2017b). However, so far waterfowls have gained very limited attention and characterization. To the best of our knowledge, this is the first report showing the baseline characteristics of integrons in E. coli isolates from waterfowl in China.
Though integrons and its associated AMRg in Gram-negative bacteria have a wide-reaching distribution, most studies of molecular antibiotic resistance associated with mobile genetic elements have been reported from different species, countries, and geographical areas (Fluit and Schmitz, 2004; Koczura et al., 2016; Ndi and Barton, 2011). Studies from diverse, especially rarely studied species such as the food producing waterfowl birds are urgently required to determine the most common antimicrobial resistance gene determinants by using E. coli as an indicator organism. Therefore, this study was conducted to examine the prevalence of integrons and its associated cassettes array in E. coli isolates from different farms of ducks and geese in Hainan, China, so as to better understand the distribution of integrons and resistance genes in food producing animals in China. Additionally, the possible association between the occurrence of integrons and antibiotic resistance phenotypes was also determined by statistical analysis.
Section snippets
Bacterial strains
All E. coli isolates (n = 311) were obtained from 20 different farms of healthy ducks and geese raised for meat purpose in Wenchang and Haikou districts of Hainan, China during our previous study (Yang et al., 2019). A single E. coli strain was isolated and studied per cloacal swab sample by using standard isolation and identification methods such as, CHROMagar orientation medium (Paris, France), MacConkey agar, Eosin methylene blue agar, and API 20E system (BioMerieux, France) (Yang et al.,
Prevalence of class 1 and 2 integrons
Of the 311 E. coli strains examined, 280 (90%) were positive for class 1 and 2 integrons. Of these, 252 (81%) and 7 (2.3%) were intl and intl2 integrons, respectively. While the remaining 21 (6.7%) were positive for both intl1 and intl2 integrons. Notably, all integrons positive strains were multi-drug resistant and conferred resistance to more than 3 different antibiotics (Table 1 and Fig. 1, Fig. 2).
Characterization of cassette arrays within integrons
The occurrence of VRs within class 1, class 2 and class 1 + 2 integrons positive isolates were
Discussion
Rapid distribution and occurrence of novel antimicrobial resistance genes among bacteria are intensifying problems throughout the world. Class 1 integrons have been reported in a wide range of bacterial genera since their first report in the late 1980s (Fluit and Schmitz, 2004; Yuan et al., 2018). Integrons have been broadly studied as determinants to spread antimicrobial resistance in clinical isolates. The current study aimed to examine the occurrence of integrons and associated gene
Conclusion
To the best of our knowledge, this study is the first report showing the baseline characteristics of integrons in E. coli isolates from waterfowls in Hainan, China. Our results showed that these waterfowl birds are possible reservoirs and a source for the dissemination of antimicrobial resistance genes in the environment. Therefore, strict preventive measures should be taken to stop the spread and emergence of mobile genetic resistance determinants in food producing waterfowl birds in China.
Author contributions
AC, SZ and MR conceived and designed the experiments and wrote the manuscript; SZ, HY, MR, KY, MD, JY, XZ, LZ, YL, YY, BT, LP, YW, XC and QY performed the experiments; ML,SC, RJ, MW, DZ analysis tools and discussion.
Conflicts of interest
The authors declare no competing interests.
Acknowledgments
This work was supported by the National Key Research and Development Program of China (2017YFD0500800), the China Agricultural Research System (CARS-42-17), Sichuan Veterinary Medicine and Drug Innovation Group of China Agricultural Research System (CARS-SVDIP), and the Applied Basic Research Programs of Science and Technology Department of Sichuan Province (2019YJ0410).
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Equal contributions thus sharing first authorship.