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Factors promoting survival of bacteria in chlorinated water supplies
M W LeChevallier1, C D Cawthon, R G Lee
1American Water Works Service Co., Inc., Belleville Laboratory, Illinois 62220.
Abstract:
Results of our experiments showed that the attachment of bacteria to surfaces provided the greatest increase in disinfection resistance. Attachment of unencapsulated Klebsiella pneumoniae grown in medium with high levels of nutrients to glass microscope slides afforded the microorganisms as much as a 150-fold increase in disinfection resistance. Other mechanisms which increased disinfection resistance included the age of the biofilm, bacterial encapsulation, and previous growth conditions (e.g., growth medium and growth temperature). These factors increased resistance to chlorine from 2- to 10-fold. The choice of disinfectant residual was shown to influence the type of resistance mechanism observed. Disinfection by free chlorine was affected by surfaces, age of the biofilm, encapsulation, and nutrient effects. Disinfection by monochloramine, however, was only affected by surfaces. Importantly, results showed that these resistance mechanisms were multiplicative (i.e., the resistance provided by one mechanism could be multiplied by the resistance provided by a second mechanism).
Insights
Bacterial attachment to surfaces significantly boosts disinfection resistance, offering up to 150-fold protection. Other factors like biofilm age and growth conditions also enhance microbial resistance to disinfectants.
Area of Science:
- Microbiology
- Environmental Science
- Public Health
Background:
- Microbial disinfection resistance is a growing concern in public health and environmental safety.
- Understanding factors that influence bacterial resistance is crucial for effective sanitation.
- Previous studies have explored various resistance mechanisms, but their interplay remains incompletely understood.
Purpose of the Study:
- To investigate the primary mechanisms conferring disinfection resistance in bacteria.
- To quantify the impact of surface attachment, biofilm age, and growth conditions on resistance.
- To determine how different disinfectant types interact with these resistance factors.
Main Methods:
- Experiments were conducted using Klebsiella pneumoniae.
- Bacterial resistance was assessed after attachment to glass microscope slides.
- The influence of biofilm age, encapsulation, and growth media on resistance to chlorine and monochloramine was evaluated.
Main Results:
- Surface attachment provided the most significant increase in disinfection resistance (up to 150-fold).
- Biofilm age, encapsulation, and growth conditions increased resistance 2- to 10-fold.
- Disinfection by free chlorine was affected by multiple factors, while monochloramine resistance was primarily surface-dependent.
- Resistance mechanisms were found to be multiplicative, compounding protection.
Conclusions:
- Bacterial surface attachment is a critical factor in enhanced disinfection resistance.
- Multiple factors contribute to and can synergistically increase microbial resistance to disinfectants.
- Disinfectant choice influences which resistance mechanisms are most effective.