Evaluating method and potential risks of chlorine-resistant bacteria (CRB): A review

Area of Science:

• Environmental microbiology
• Water treatment technologies
• Bacterial resistance mechanisms

Background:

• Chlorine-resistant bacteria (CRB) can survive and regrow despite chlorine disinfection, posing risks including pathogenicity, antibiotic resistance, and microbial growth.
• While pathogenicity and antibiotic resistance of CRB receive attention, their microbial growth risks in water treatment and reclamation systems are often overlooked.
• Existing methods for evaluating chlorine resistance lack standardization, hindering comparative analysis of CRB strains across studies.

Purpose of the Study:

• To systematically review and analyze the risks associated with CRB, emphasizing microbial growth.
• To summarize and evaluate methods used for assessing bacterial chlorine resistance.
• To propose a standardized method for evaluating chlorine resistance and identifying CRB.

Main Methods:

• Literature review of studies on chlorine-resistant bacteria and their resistance evaluation methods.
• Analysis of reported CRB genera, sources, and chlorine resistance levels.
• Synthesis of current evaluation methods to propose a standardized approach.

Main Results:

• Among 44 CRB strains from 17 genera, Mycobacterium, Bacillus, Legionella, Pseudomonas, and Sphingomonas were most frequently reported.
• Most frequently isolated CRB genera are pathogenic or opportunistic pathogens.
• Information on chlorine resistance levels is often limited to species or strain level, with genus-level differences poorly understood.

Conclusions:

• A standardized method using logarithmic removal rate and E. coli as a reference strain is proposed for evaluating CRB.
• The proposed method aims to provide a common range of chlorine resistance for bacterial genera, aiding in environmental distribution analysis.
• Standardization is crucial for consistent identification and comparison of CRB, addressing risks in water treatment and reclamation.