BIOFILM CONTROL STRATEGIES
This article has also been published in the SHIPSAN Newsletter under the section “Environmental health and hygiene on ships”. Section Editor: Martin Walker, Port Health Officer, Suffolk Coastal Port Health Authority, Felixstowe, England
We welcome an article from Dr. Maria Elsa Gambuzza. Dr. Gambuzza is a biologist from the Italian Ministry of Health and I would like to thank her for submitting this article about Biofilm Control Strategies. This is an area of particular interest to both shipping companies and port health authorities given the importance of potable water systems and other systems for potential public health risks within vessels. I commend this article to you. As always, comments and points about articles are welcome by the SHIPSAN ACT project and should be submitted to info@shipsan.eu
Key message:
• This section outlines the importance of cleaning and disinfection procedures for biofilm prevention.
• It also provides examples for using alternative prevention strategies.
Microbial adhesion to surfaces and biofilm formation occur in many environments, on board ships (potable water systems, water-treatment facilities, air-conditioning equipment). Biofilms represent a protected mode of growth, allowing microorganisms to survive in hostile environments.
Microbial adhesion to surfaces and biofilm formation occur in many environments, on board ships (potable water systems, water-treatment facilities, air-conditioning equipment). Biofilms represent a protected mode of growth, allowing microorganisms to survive in hostile environments.
These bacterial communities are stick together to a self-produced adhesive matrix of sugars and proteins, that pulls the colonists together and protect them from the outside world.
As the biofilm grows, it attracts other microorganisms, including dangerous pathogens, providing them with numerous appealing anchoring points.
Biofilm development occurs through several key steps: (1) attachment, (2) microcolony formation, (3) extracellular matrix secretion, (4) biofilm maturation, and (5) dispersion which are shown in the figure below:
There is heterogeneity in bacterial activity, chemical microenvironments, and microcolony formation. The aerobic bacteria grow in outer surface exposed to air, whereas the interior portion supports anaerobic microorganisms.
Biofilms can cause many problems including:
- Biofouling and biocorrosion
- Harbourage for dangerous microorganisms
- Difficulties in their removal
- Potential contamination of the water supply
- A tendency to develop on dead-legs of pipework and in low flow areas around the bends in pipework
BIOFILM PREVENTION: CAN BIOFILM BE CONTROLLED?
At present there is no valid method for complete biofilm prevention. A continuous chlorine level can help control biofilm, but it can also persist in chlorinated pools. In addition, once formed, it is very difficult to remove the biofilm and keep it away. The main prevention strategy is the regular cleaning and disinfection, to prevent bacteria from strongly sticking to surfaces. Most disinfectants are more effective in absence of organic compounds. In addition, temperature, pH, water hardness, chemical inhibitors, concentration and contact time generally affect their effectiveness.
Disinfection strategies should achieve the following outcomes:
- Destroy polysaccharide matrix and microorganisms left after cleaning
- Maintain biofilm-free all equipment, inhibiting intermittent biofilm formation
- Maintain or improve the overall quality of the water
Among the oxidizing agents, chlorine dioxide is known to be more effective and safe, when compared with chlorine:
However, to be effective, chlorine dioxide concentration should be at least 0.1 mg/L and should not exceed 0.8 mg/L (according to Environment Protection Agency), and 0.8 mg/L might not be enough to kill completely Legionella. Therefore, it may be necessary to use it at a higher concentration (maybe at 1–2 mg/L) and to provide alternative sources of potable water until Legionellae spp. are shown to be under control.
Bio-enzymatic cleaners, also known as “green chemicals”, or enzyme-based detergents, containing enzymes able to destroy protein-polysaccharide complexes, could contribute to biofilm degradation.
Effective cleaning and sanification protocols are described in Chapters 4-5 EU Manual Hygiene Standards and Communicable Diseases Surveillance on Passenger Ships – EU-Comm-2011
http://www.shipsan.eu/page.php?=27&item=33
REFERENCES
Goeres DM, Palys T, Sandel BB et al. Evaluation of disinfectant efficacy against biofilm and suspended bacteria in a laboratory swimming pool model. Water Res. 2004; 38(13): 3103-9.
Simoes M, Simoes LC, Vieira MJ. A review of current and emergent biofilm control strategies. Food Sci. Technol. 2010; 43(4): 573-83.
Pictures modified by original pictures: http://www.montana.edu.