Extended-Spectrum β-Lactamase-Producing Escherichia coli and Pediatric UTIs: A Review of the Literature and Selected Experimental Observations

Urinary tract infections (UTIs) are common in children and are predominantly caused by uropathogenic <i>Escherichia coli</i> (UPEC). An increasing proportion of these strains produce extended-spectrum β-lactamases (ESBLs), which render β-lactam antibiotics ineffective. Interestingly, some patients with ESBL-producing UTIs improve clinically following treatment with antibiotics like cephalexin, despite demonstrated in vitro resistance. Working alongside and at times synergistically with antibiotics, host immune factors, such as the antimicrobial peptide cathelicidin (LL-37), contribute to bacterial clearance through direct killing and inhibition of biofilm formation. In this review, we summarize the current understanding of pediatric ESBL-producing UPEC infections and present selected in vitro and in vivo experimental data evaluating the combined effects of LL-37 and cephalexin on clinical isolates. Although no synergy was observed, ESBL-producing isolates demonstrated reduced bacterial burden in vivo compared to a non-ESBL UPEC strain. These findings suggest that host immune factors and environmental conditions may influence the fitness and virulence of drug-resistant UTI pathogens, warranting further investigation.