| BackgroundIn recent years,as the appearance of multiple drug-resistant bacteria(MDROS),colistin as a last defense line to treat MDROS especially carbapenem resistant Escherichia coli,gradually returning to the public's view in previous studies.In previous studies,colistin resistance was mainly caused by chromosome mutation,but the chromosome is relatively stable and not easy to spread between bacteria,so it has not attracted widespread attention;In 2015,however,studies have shown that plasmid can mediate the spread of colistin resistance gene,this study caused a great sensation in the society.Compared with chromosomes,plasmids are more unstable and easier to transfer.If plasmids carrying the colistin resistance gene mcr-1 keep increasing in Escherichia coli,super bacteria will be more common in the future.All these findings make it urgent to study the transmission mechanism of plasmid-mediated mcr-1 in Escherichia coli.ObjectivesTo explore the transmission mechanism of mcr-1 Escherichia coli among healthy rural residents in Shandong,China,and to provide theoretical basis for the prevention and control of its spread and the treatment of multi-drug resistant Escherichia coli.MethodsA total of 240 healthy residents(80 people in each village)from 3 villages in guan county,liaocheng city,Shandong province were surveyed by questionnaire and entered into the questionnaire with the software EPIDATA.ECC color culture and PCR were used to isolate the mcr-1 positive Escherichia coli.The drug sensitivity of the isolated mcr-1 positive Escherichia coli was tested by agar dilution and microbroth dilution.S1-PFGE and Southern blot experiments were used to determine whether the mcr-1 gene was on the plasmid and the size of the plasmid,and the transferability of the plasmid where the mcr-1 gene was located was verified by the conjugation experiment.Whole genome sequencing and analysis were conducted.The software Easyfig 2.2.3 was used to compare the environment around the mcr-1 gene of positive Escherichia coli,and the phylogenetic tree was constructed to understand the homology of positive samples.SPSS24.0 was used to analyze the risk factors of mcr-1-positive-Escherichia coli in healthy rural residents.ResultsAmong the 218 residents included in the study,68 people belonged to A village,72 people belonged to B village and 78 people belonged to C village,34.40%were males and 65.60%were female.Their ages ranged from 29 to 93 years old,the average age was 61.82±12.83 years old.The actual fecal samples collected from healthy residents were 218,and a total of 9 strains of mcr-1-positive-Escherichia coli were isolated,that is,the carrying rate of mcr-1-positive-Escherichia coli in rural healthy residents was 4.13%." Drinking raw water daily" is a possible risk factor for mcr-1 positive Escherichia coli in healthy rural residents The drug sensitivity test results showed that the positives strains were all resistant to colistin and tetracycline,and the drug resistance rate to cefotaxime reached 44.44%;Among the 9 positive strains,5 strains were multidrug-resistant,indicating that the bacterial resistance was very serious.The results of S1-PFGE and Southern blot showed that the mcr-1 was on the plasmid and the plasmid could transfer to other Escherichia coli.Most of the plasmids carrying mcr-1 were small plasmids with a size of 70kb.Whole genome analysis results show that there are three types of mcr-1 environments in 9 strains,and the 9 strains' homology is very strong.When these strains were compared with the mcr-1-positive Escherichia coli found on NCBI from different sources,it was found that these mcr-1-positive samples also had a great homology with the Escherichia coli found on NCBI,which means that mcr-1 can spread between different villages and different sources.ConclusionThe carrying rate of mcr-1-positive Escherichia coli is high among healthy people in rural areas,and "drinking raw water daily" is the possible risk factors for healthy residents in rural areas carrying the mcr-1-positive Escherichia coli.mcr-1-positive Escherichia coli are highly transmissible and most of them are MDROS.In the future,we should prevent the spread of mcr-1-positive Escherichia coli through health education and tighter regulation of antibiotics. |
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