In this study, we isolated an unknown strain of E. coli that is resistant to meropenem from medical sewage, and then studied its resistant phenotype and genotype. It was found that it contained both blaNDM and blaOXA−10 genes.
The emergence and rapid spread of antibiotic resistance is a growing threat to human health. CRE (Carbapenem-resistant Enterobacteriaceae) has the ability to promote the widely spread of drug resistance genes, mainly through mobile genetic elements including natural transformation, and the process of plasmid conjugation. We found that E. coli AH001 is carrying NDM−1 and OXA−10, both of which are belong to carbapenem resistant enzymes. The aquatic environment, such as the sewage in hospital which are enriched both antibiotics and bacteria, is an important reservoir for drug resistance genes and can be used as a medium to spread ARGs (Antibiotic Resistance Genes) from one ecosystem to another, thereby increasing the risk of MDR (Multi-Drug Resistance) bacteria infection outside the hospital. The widespread detection of CPO (Carbapenemase-producing Organism) in the environment is an emerging environmental problem that may seriously affect public health. Our results are consistent with previous studies, indicating that blaNDM has appeared in many different species and spread rapidly in different environments[15, 16].
In China, a recent study of 10,273 clinical stool samples collected from 52 hospitals found that the total infection rate of intestinal bacteria carrying blaNDM−1 among clinical patients was 14.8%. And these feces can be discharged into hospital sewage, prompting blaNDM−1 to spread in many species and environments. In environments such as sewage, the discovery of two different carbapenemase isolates in the same strain of bacteria has become increasingly frequent[15, 19, 20].
We found the blaOXA−10 gene in AH001, OXA-10 type β-lactamase was previously considered a narrow-band enzyme in E. coli and Pseudomonas aeruginosa. However, Antunes NT proved that when expressed in Acinetobacter baumannii, this enzyme showed high resistance to carbapenems, and the production of OXA-10 increased the MIC of the bacteria to ceftazidime by 32 times. These data clearly demonstrate the importance of OXA-10 as CHDLs, and how to verify that OXA-10 expresses carbapenem resistance on E. coli is worth exploring.
In addition to meropenem, AH001 exhibited resistance to 7 kinds of antibiotic include chloramphenicol, fosfomycin, tetracycline, ampicillin, gentamicin, ofloxacin, and cefotaxime, expect, rifampicin and polymyxin B. The results of drug susceptibility tests indicate that AH001 is severely resistant. Modified Hoge test showed it produces carbapenemase. The results of the conjugation transfer test showed that the drug-resistant plasmid of carbapenem antibiotics mediating AH001 could not be transferred to the recipient strain EC600, and another strain of E. coli isolated from the sewage both carrying blaNDM−4 and blaKPC−2 was able to transfer the resistant plasmid to the recipient strain EC600. It is speculated that the reason may be that the difference between the donor bacteria and the recipient bacteria, and there are cases where the plasmids are incompatible. The AH001 isolated in this study predicted the blaCTX−M−14 and blaCTX−M−15 genes by whole genome sequencing analysis. According to reports, blaCTX−M−14 and blaCTX−M−15 are the major ESBL types in human clinical isolates, regardless of geographic origin. It has been reported that cefotaxime resistance has been observed in patients with cephalosporin treatment of Aeromonas bacteremia.
The serotype of AH001 predicted on the CGE website showed three serotypes, namely O9, O89 and O162, and the coincidence rates were 99.31%, 94.1%, and 93.63%, respectively. It is reported that E. coli of the O8 serotype are commonly associated with septicemia or diarrhea in calves and pose a significant threat to the cattle industry worldwide. It has also been reported that the O89: H9 serotype is related to E. coli that produces ESBLs and carries blaNDM−5 and mcr-1 genes[25–27].
Nowadays, the detection of bacteria in the sewage is often studied by metagenomics, including 16s rDNA sequencing and the whole gene assembly of all bacteria. This study is based on direct phenotypic screening, which still has a certain significance. To the best of our knowledge, this is the first report of a carbapenem-resistant E. coli carrying both blaNDM−1 and blaOXA−10 genes. The sewage of hospital treatment system will continuously discharge a large number of drug resistance genes into the water environment and release it into surface water. This gene can be transferred horizontally in the sewage through the MGE (Mobile Genetic Elements) carrying the gene. Therefore, more attention should be paid to the discharge of hospital sewage.