What are biofilms?
Biofilms are complex microbial ecosystems formed from one or several microbes bound in a complex extracellular matrix of their own secretions and formations. Each microbe in the ecosystem make contributions that strengthens the community, creating a strong common bond that translates genomically, chemically and structurally into collective effectiveness, efficacy and their ultimate communal survival.
The microbes include mainly bacteria or fungi or a mixture of different combinations and proportions, which depends on the type of food and environment particularly the micro-environmental factors such as humidity and temperature and the macro-environment like the type of surfaces. Generally, biofilms need water or moisture to continue to grow.
The microbial extracellular matrix is composed, in the main, of polysaccharides, such as cellulose, proteins or exogenous DNA. Biofilms attach to hard surfaces through specialised structures facilitated by the extracellular matrix.
Such hard surfaces in the food, food preparation and food serving areas include various kitchen equipment, tables, taps, hand wash basins, storage surfaces including plastic and glass bottles, jars, or containers, cans, dispensing materials, conveyor belts in food processing plants, transportation, soil and also on biological structures such as vegetables, meat, bones, fruits, etc. Even on supermarket food shelves are not spared.
It has been noted that the extracellular matrix has an important structural role in the determination of the impact of biofilms. Among others, such important roles include:
- provision of a strong persistence and protective biofilms around the microbes
- producing a complex gradient of nutrients and oxygen diffusion
- contains extracellular enzymes used for nutritional purposes
- allowing for the transfer of cell communication molecules, and
- protects the embedded cells against toxic compounds including antimicrobial disinfectants.
Biofilms and Food Public Health Concerns
Microbial biofilms can develop in most environment with the right conditions. They can develop in private and public bathrooms, toilets or restrooms and kitchens, restaurants, butchers’ shops and groceries sections where they help to increase the rate of food spoilage.
Their growth is possible and enhanced when surfaces are not regularly cleaned and wiped dry after use. Biofilms form and grow in small puddles of water and areas that remain wet over a length of time particularly starting and spreading from hard to reach crevices.
Corrosion by biofilm is visible
Three photographs A, B, C and D were taken from washrooms of three different supermarkets selling almost every household item including cooked and uncooked food. Often the washrooms are located very close to the restaurant part of the establishments for the convenience of the dinning customers that use the washrooms.
There are currently no studies to determine the relationship between the spread or incidence of food related health issues, the proximities of the toilets and washrooms, most common location for biofilms, and any existence of biofilms in such establishments.
Washrooms are often equipped with soap dispensers, which may be manual or automatic soap dispensers. The case housing the soap may be clean on the outside. However, the inside is often not easily accessible to the cleaning staff. The wet environment provides ideal opportunities for biofilms to thrive in the crevices of the dispensers:
Thorough cleaning regime is necessary to keep biofilms out. It is necessary to also including the cleaning of inside of dispenser at a determined regular interval. The biofilms can survive some challenging conditions. Pseudomonas spp and Acinetobacter spp have been found predominantly on food conveyor belts at simulated temperatures ranging from 3oC – 76oC.
Overall, biofilm formation offers advantages to the microbial cells in a food preparation and serving environment, such as physical resistance against drying or desiccation, mechanical resistance against liquid streams in pipelines and protection against antagonistic chemicals intended for their eradication.
Detection of Biofilms
Will Classical agar plating still do the job?
The complex composition and interaction in biofilms make detection and proper identification very challenging, hence their high potential to persist when contamination occurs. Classical detection methods consisted mainly of agar plating, isolation and identification by classical microbiology and / or biochemical analysis of isolates. Agar plating is obviously not suitable for modern big food industrial setting and related organisations.
The classical agar method is regarded as not a very effective and efficient method as some food borne microbes are capable of entering into what is referred to as “viable but non-cultural” VBNC states with low metabolic activity. VBNC cells are not detectable by culturing and may survive stress conditions such as low temperature regimes.
Modern microbiological technology
Great advances continue to take place in modern microbiology incorporating biotechnological methods of rapid screening and identification, including automation. Modern methods have been developed for rapid and mass detection of microbial biofilms. On-line tools monitoring and recording, including Polymerase Chain Reaction (PCR) amplification methods to show the number the different genotypes. Other methods include:
- metagenomics and metatranscriptomic for genotyping
- PCR amplification and gel electrophoresis to distinguish the different lengths
Application of new technology
For large food manufacturing settings, new strategies are being developed to detect bioﬁlm formation, where biofilm development is monitored by the introduction of an external perturbation in the system. The external perturbation is then measured or calibrated using a suitable device. In some cases, the perturbation is amplified to make it measurable in values or changed into other forms such as heat and pressure transfers in the system.
For example, specially designed commercial on-line monitoring sensors are available and in use in the food and beverage industry. The sensors are based on thermal pulse analysis. They detect and measure the local thermal conductivity and heat variations resulting from the formation of bioﬁlms. They are, however, able to detect deposits only a few micro-meters thick.
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