Seasonal assessment of microbial indicators, antibiotic resistance, and heavy metal tolerance in water, sediment, and edible fish from an urban tropical coastal lagoon (Jansen Lagoon, São Luís, Brazil)

Introduction Urban coastal lagoons frequently receive untreated sewage and stormwater runoff, favoring fecal contamination and the selection of antibiotic-resistant bacteria. This study evaluated seasonal patterns of microbial indicators, antibiotic resistance, and heavy metal tolerance in different environmental compartments of Jansen Lagoon (São Luís, Brazil). Methods Five sampling campaigns were conducted in 2018 during rainy (February–April) and dry (July–November) seasons. Surface water (n = 25), sediment (n = 15), and fish (n = 10) were collected at five sites. Thermotolerant coliforms and Pseudomonas spp. were enumerated by MPN; presumptive Clostridium perfringens was detected on SPS agar; and Enterobacterales were identified by biochemical tests. Antimicrobial susceptibility was assessed by disk diffusion following CLSI guidelines. Heavy metal tolerance (Pb and Cu) and physicochemical parameters were also evaluated. Results Physicochemical parameters varied seasonally, with higher TDS during the rainy season and consistently alkaline pH (8.4–8.7). Thermotolerant coliforms peaked in rainy-season water samples (up to 1,600 MPN/100 mL), while sediments showed higher counts during the dry season. A total of 130 gram-negative strains (19 species) were isolated, predominantly Escherichia coli . High resistance was observed to cephalothin (70%) and tetracycline (41%), while chloramphenicol susceptibility was high (91%); five species met MDR criteria. Pseudomonas spp. were more abundant in fish and largely susceptible to gentamicin (92.5%). Presumptive C. perfringens was detected only in the dry season. Most isolates tolerated high Pb concentrations (3500 ppm), and Cu tolerance was dose-dependent. Discussion Jansen Lagoon shows recurrent fecal contamination and significant levels of antibiotic resistance across environmental compartments, with seasonal variation. These findings highlight potential co-selection mechanisms and reinforce the need for improved sewage management to mitigate human exposure risks within a One Health framework.