Escherichia coli causing bloodstream infections in Mexican paediatric patients: molecular typing, antimicrobial resistance, virulence factors, and clinical features.

backgroundEscherichia coli is one of the main pathogens causing bloodstream infections (BSIs) in paediatric patients. It is classified into pathogenic (B2, D and F) and commensal (A, B1 and C) phylogroups, with virulence mainly attributed to adhesins, toxins and iron acquisition systems. In recent years, the global spread of high-risk clones such as ST131 and ST405, often associated with extended-spectrum beta-lactamases (ESBLs), has contributed to increased resistance and limited treatment options. The BSI mortality rate in children varies from 14 to 21.6%. This study aimed to describe resistant mechanisms; virulence factors and clonal distribution of E. coli isolates that cause BSIs in children in Mexico and clinical features.

methodsThirty-eight ceftriaxone (CRO)-resistant E. coli isolates were included. Beta-lactamase and virulence genes were detected by PCR. Molecular typing included phylogroup determination, sequence types (ST), and pulsed-field gel electrophoresis (PFGE). Clinical information was acquired.

resultsCTX-M was the most frequently identified beta-lactamase (82%) and aac(6')-Ib-cr was present in 45%. Phylogroup distribution was A (21.1%), C (7.9%), D (28.9%), B2 (23.7%), and F (18.4%). The most common virulence factor was fimH (71%), while papC, sat and irp2 were significantly more frequently in the pathogenic phylogroups (P = 0.029, 0.011 and 0.006, respectively). PFGE identified 5 clusters, 20 non-related isolates and 4 non-typeable. Predominant clonal complexes (CC) were CC405 (23.7%) and CC131 (21.1%), with 82% of isolates belonging to high-risk clones. Survival rates differed significantly with moderate high-grade fever (P = 0.022). All patients who died had complications, compared to 34.8% of survivors (P < 0.0001). Mortality was higher in adolescents (53.3%), patients with leukaemia or lymphoma (40%), those with hospital-acquired infections (86.8%), those with an abdominal or pulmonary focus (33.3% each). No significant differences were found in of haematological parameters.

conclusionsBoth commensal and pathogenic E. coli strains cause BSIs in paediatric patients with underlying diseases. Resistance to 3GCs and 4GCs is mainly mediated by CTX-M, hence treatment with carbapenems was used. Infection-related deaths were more frequent in patients infected by pathogenic phylogroups, where papC, sat, and irp2 were more prevalent. High-risk clones were widely distributed among isolates.