Molecular epidemiology of Escherichia coli in bloodstream infections from a general hospital in Ningxia, China, 2022-2023.

OBJECTIVE: To analyse the antibiotic resistance, resistance genes and clonal relationship of Escherichia coli in bloodstream infections in Ningxia from 2022 to 2023.

METHODS: We retrospectively analyzed the antibiotic susceptibilities of 257 isolates. PCR was used to detect blaTEM, blaSHV, blaCTX-M, qnrS, qnrA, qnrB, oqxA, qepA, gyrA, gyrB, parC, and parE, and the clonal relationship through multilocus sequence typing (MLST).

RESULTS: One hundred and twenty-nine of 257 patients were male (50.2%). The 257 E. coli isolates were mainly obtained from the Emergency, Hepatobiliary Surgery, and Haematology Departments, accounting for 56.6%, 7.3%, and 6.2%, respectively. There is no significant difference in sex and genes between the two groups over and under 60 years old (P > 0.05), but there is a significant difference in ST between them(P<0.05). The antimicrobial susceptibility testing showed that the 257 isolates had the highest rates of resistance to ampicillin (82.8%), followed by cefazolin (71.6%), and all isolates were susceptible to tigecycline. Based on the antibiotic susceptibility results for ceftriaxone, we tested 126 isolates of E. coli for extended-spectrum beta-lactamase (ESBL) resistance genes. As a result, blaCTX-M was detected in 76 isolates (60.32%), blaSHV in 26 isolates (20.63%), and blaTEM in 38 isolates (30.16%). Based on the ciprofloxacin and levofloxacin antibiotic susceptibility results, we tested for quinolone resistance genes in 148 isolates, revealing 66 isolates of aac(6')-Ib-cr (44.60%), 3 isolates of oqxA (2.02%), 32 isolates of qnrS (21.62%), and 2 isolates of qepA (1.35%). We did not detect qnrA or qnrB. The detection rates of gyrA, gyrB, parC, and parE were 98%, 42.6%, 91.2%, and 87.8%, respectively and the main amino acid mutations were Ser83 to Leu, Asp87 to Asn(75.2%), Leu417 to Ser, Ser418 to Leu (6.3%), Ser80 to Ile (65.2%), and Ser458 to Ala (21.5%), respectively. MLST revealed that the most common sequence types (STs) were ST69 (12.5%), ST131 (8.2%), and ST1193 (7.8%).

CONCLUSION: In our hospital, E. coli was resistant to most commonly used antibiotics, and cefoperazone/sulbactam, cefotetan, amikacin, and tigecycline were empirically selected for the treatment of bloodstream infections. The predominant ESBL genotype in our hospital was blaCTX-M and the major quinolone resistance gene was aac(6')-Ib-cr. Clonal relationship analysis revealed genetic diversity among the isolates.