The pathogenic characteristics of Escherichia coli (E.coli) in bacterial infections were analyzed using a combination of multiple molecular typing techniques in order to provide evidence for the management of clinical medication safety.

Samples from some bacterial infection-related cases in a district of Chongqing in 2021 were collected. A total of 30 E.coli strains were selected by a completely random method, and phoA gene PCR assay was performed for identification. Molecular typing of the strains was analyzed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Antimicrobial susceptibility testing was conducted to determine the drug resistance of the strains, and four β-lactamase-encoding genes (blaCTX-M, blaTEM, blaSHV, blaZ) were selected to detect the carriage of resistance genes.

All 30 E.coli strains displayed the phoA gene target band. Their PFGE banding patterns, with a similarity of 50%~98%, could be classified into 8 clusters. Cluster C was the dominant group, accounting for 53.3% (16/30). C1 and C2 exhibited high genetic correlation, indicating a close phylogenetic relationship. One E.coli strain could not be assigned a sequence type (ST) by MLST, while the remaining 29 E.coli isolates were classified into 16 different STs, demonstrating a polymorphic distribution. Among them, 10 isolates belonged to ST131 (10/30, 33.33%). Evolutionary analysis of the 10 ST131 E.coli strains revealed their distribution across different branches, indicating varying degrees of genetic relatedness. Antimicrobial susceptibility testing revealed that all 30 E.coli strains exhibited varying degrees of resistance, with the highest resistance rate observed against the β-lactam antibiotic ampicillin (25/30,83.33%). Among them, 60.0% were multidrug-resistant bacteria (MDRB). These MDRB strains exhibited 16 distinct resistance profiles, displaying a scattered distribution without a dominant resistance pattern. 50.0% (9/18) of the MDRB strains exhibited six-drug resistance, while the most drug-resistant strain showed eight-drug resistance. Furthermore, the blaCTX-M gene carriage rate among the 30 E.coli strains was 86.67% (26/30), while no blaZ gene was detected.

E.coli related to bacterial infections from a Chongqing district exhibited diverse PFGE/MLST patterns and significant drug resistance. The application of multiple molecular typing techniques can reveal the genetic diversity, evolutionary relationships, and antimicrobial resistance characteristics of pathogenic bacteria. Countermeasures　It is recommended to enhance the molecular typing and drug resistance surveillance network for pathogenic bacteria, establish an early warning mechanism, and implement hierarchical management of antibiotics, thereby improving targeted prevention and epidemic traceability capabilities for key drug-resistant bacteria such as ST131.