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 bla, bla, bla, 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, bla was detected in 76 isolates (60.32%), bla in 26 isolates (20.63%), and bla 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 bla and the major quinolone resistance gene was aac(6')-Ib-cr. Clonal relationship analysis revealed genetic diversity among the isolates.