Investigating the types of bacterial species with antimicrobial resistance genes in Iran's wastewaters: a systematic...

Antimicrobial resistance (AMR) is a major global health threat, with wastewater systems performing as critical reservoirs and dissemination pathways for antimicrobial-resistant bacteria (ARB) and resistance genes (ARGs). Despite rising AMR rates in Iran, a comprehensive understanding of resistance patterns in wastewater remains limited. This systematic review aimed to investigate the prevalence, bacterial diversity, and resistance gene profiles in hospital, municipal, and industrial wastewater across Iran. A systematic search was conducted in Scopus, PubMed, Web of Science, and Iranian databases for studies published between 1990 and September 2024. Data extraction followed PRISMA guidelines, and study quality was assessed using the JBI checklist. A total of 43 studies from 13 provinces met the inclusion criteria, with nearly half originating from Tehran (21/43, 48.8%), indicating uneven national coverage. Hospital wastewater (18 studies, 41.9%) harbored the highest burden of clinically significant AMR, including MRSA (22%), VRE (17%), and ESBL-producing E. coli (17%). Municipal wastewater (31 studies, 72.1%) frequently contained VRE Enterococcus faecium (32%) and Enterococcus faecalis (23%), ESBL-producing E. coli (19%), and MRSA (10%). Industrial wastewater (10 studies, 23.3%), primarily from slaughterhouses, exhibited high ESBL rates in E. coli (80%), with some studies reporting up to 93% ESBL production among isolates. Across studies, the most recurrent ARGs were bla_CTX (16.3%), vanA (20.9%), mecA (9.3%), tetracycline genes, and intI1. Detection methods were predominantly culture- and PCR-based, with limited use of qPCR, molecular typing, or metagenomics. The most frequently detected resistance genes included bla_CTX-M, mecA, vanA, tetA, and intI1. Most studies used culture and PCR-based detection; molecular typing and metagenomic approaches were rarely applied. The persistent detection of MDR pathogens and high-priority ARGs highlights significant gaps in AMR surveillance. Strengthening national wastewater monitoring through standardized protocols, broader geographic coverage, and integration of advanced molecular tools is essential to support effective One Health based public-health strategies.