Impact of natural lagooning wastewater treatment on antibiotic-resistant bacteria in Morocco

Aquatic environments under anthropogenic pressure serve as critical hotspots for the rapid development of microbial populations, including the growth of antibiotic-resistant bacteria (ARB). This study evaluates the efficiency of natural lagooning wastewater treatment systems at two sites in Settat and Ouled Said, Morocco, focusing on physicochemical characteristics and ARB prevalence in treated effluents. A substantial reduction in total bacterial counts, including coliforms, Enterococcus spp., and Pseudomonas spp., was observed following treatment, demonstrating overall system performance. However, a considerable proportion of resistant strains persisted, with coliforms demonstrating resistance rates of 27.5% to ampicillin and 45.98% to ciprofloxacin. A total of 535 bacterial isolates were detected, demonstrating the presence of human pathogenic species such as Escherichia coli , Klebsiella pneumoniae , and Pseudomonas aeruginosa . These isolates revealed substantial resistance to numerous antibiotics, including ceftazidime and imipenem. Correlation analyses revealed significant associations between physicochemical parameters and antibiotic resistance patterns, with dissolved oxygen and pH showing strong negative correlations with resistant bacterial populations. Low dissolved oxygen levels and high organic load were associated with increased resistance rates. Factor analysis indicated four major components explaining 90.53% of the overall variance, underlining the pivotal importance of temperature, nitrate, and chemical oxygen demand for water quality and ARB dynamics. Spatial and seasonal variations further affected ARB prevalence, with higher resistance rates seen during colder months and in downstream regions. Effluents from wastewater treatment and urban runoff largely contribute to the emergence and spread of ARB. This study provides valuable insights into ARB dynamics in treated wastewater, underlining the necessity for advanced wastewater treatment strategies.