Resistance enterobacteria in urban slums: key sociodemographic and environmental factors

Abstract Environmental exposures and urban vulnerabilities in informal settlements contribute to the spread of antimicrobial resistance (AMR). Most research has focused on clinical settings, but community contexts with structural vulnerabilities also play a key role. Informal settlements, characterized by overcrowding and a lack of basic services, are linked to high levels of resistant enterobacteria, particularly among children. We conducted a cross-sectional study in an informal urban settlement in Chile's Metropolitan Region. Enterobacteria were isolated from 37 fecal samples using two MacConkey agar plates, one supplemented with ciprofloxacin (CIP) and the other with ceftazidime (CAZ). Colonies were selected based on typical lactose-fermenting morphology. Antimicrobial susceptibility was assessed using the Kirby-Bauer method, following CLSI 2024 guidelines. The study was approved by the Ethics Committee of Universidad Andrés Bello. Socio-environmental data were collected through 37 household surveys. Data were analyzed using descriptive statistics and Fisher or Wilcoxon tests (p < 0.05). Resistance to ciprofloxacin and ceftazidime was found in 21.6% and 29.7% of samples, respectively. E. coli was the most frequent resistant organism (77.8% of 54 isolates). Therefore, comparisons between colonized and non-colonized children focused on multidrug-resistant E. coli. Significant differences were found based on contact with a local river (p = 0.0051) and household water source (p = 0.022). Other factors, such as overcrowding and poor sanitation, were more common among colonized children, though not statistically significant. Our findings highlight the critical role of environmental exposures in AMR colonization among healthy children in informal settlements and underscore the urgent need for interventions targeting water quality and sanitation. Key messages • Environmental exposures, particularly unsafe water sources and river contact, differ significantly between MDR E. coli-colonized and non-colonized healthy children. • Improving water, sanitation, and surveillance in informal settlements is critical to reduce AMR colonization risk among vulnerable populations.