Escherichia coli is the main Gram-negative pathogen associated with bloodstream infection (BSI). Pandemic lineages present different antimicrobial resistance profiles, extended-spectrum beta-lactamase (ESBL) production, virulence factors, and association with community-acquired or healthcare-associated infections (HAIs). Among these, ST131, ST1193, ST69, ST73, and ST95 stand out, responsible for approximately 50% of human infections. The objectives of this study were to determine the frequency of pandemic lineages, evaluate antimicrobial susceptibility, ESBL production, and the origin of infections—community or hospital.

A total of 376 E. coli samples isolated from patients with BSI treated at a university hospital in Rio de Janeiro between 2014 and 2023 were obtained. ST detection was performed by multiplex PCR. Susceptibility testing to 18 antimicrobials was performed by disk diffusion and double-disk approximation for ESBL identification. Infections diagnosed after 48 hours of hospitalization were classified as HAIs.

Of the 376 isolates, 180 (48%) belonged to pandemic lineages distributed throughout the study period: ST69 (29%), ST131 (27%), ST73 (19%), ST95 (16%), and ST1193 (9%). ST131 and ST1193 were mostly associated with HAIs (52% and 62.5%, respectively). ST69, ST73, and ST95 predominated in community infections (57%, 56%, and 62%). ST131 showed the highest resistance rates, including ampicillin (88%), trimethoprim-sulfamethoxazole (67%), ciprofloxacin (63%), cefazolin (50%), and cefotaxime (38%). ST1193 was 100% resistant to ciprofloxacin, followed by ampicillin (75%), trimethoprim-sulfamethoxazole (38%), and cefotaxime (13%). Among ST69 isolates, resistance rates were observed to ampicillin (57%), trimethoprim-sulfamethoxazole (51%), cefazolin (26%), and cefotaxime (17%). ST73 and ST95 had the lowest resistance rates compared to the others. ESBL production was more frequent in ST131 isolates (38%), followed by ST69 (17%) and ST1193 (6%).

The five lineages were continuously isolated throughout the analyzed period, indicating their persistence among strains circulating in the population, with high antimicrobial resistance rates, including ESBL production. These findings reinforce the importance of continuous surveillance of these lineages in hospital settings.