MGY 277 Unit 5

Biofilms and Microbial Communities

• Biofilms are organized communities of bacteria and fungi that live on surfaces, encased in polysaccharide/protein.
• Cells in biofilms have different physiological properties than planktonic cells and are more resistant to antibiotics and disinfectants.
• Biofilms have medical implications, including causing dental plaque, tissue infections, and being problematic on medical devices such as contact lenses and catheters.
• The formation of a biofilm involves bacteria adhering to a surface, multiplying, and producing extracellular polymeric substances (EPS).
• Quorum sensing, a mode of regulation in bacteria, involves the production and sensing of chemicals called autoinducers that control social behaviors.
• Prokaryotes interact with other species in mixed microbial communities, which can be cooperative or competitive, influencing their growth and survival.
• Prokaryotes inhabit a wide range of environments, including harsh conditions, and their growth is influenced by factors such as temperature, atmosphere, pH, and water availability.
• Different temperature requirements exist for prokaryotes, with psychrophiles found in Arctic regions, thermophiles in hot springs, and hyperthermophiles in hydrothermal vents.
• Proteins of thermophiles resist denaturing due to their amino acid sequence, and temperature influences food preservation and the growth of disease-causing microbes.
• Microbes have varying oxygen requirements, with aerobes requiring oxygen for respiration, facultative anaerobes being versatile, and obligate anaerobes unable to use or tolerate oxygen.
• Biofilms have industrial implications, such as accumulations in pipes and drains, and are associated with dental plaque, tissue infections, and medical device-related infections.
• The interactions of mixed microbial communities can be cooperative or competitive, influencing the growth and survival of different species.

Methods of Microbial Control

• Biological indicators like G. stearothermophilus are used to ensure the proper functioning of autoclaves, where a color change in the media after autoclaving indicates survival of bacterial spores.
• Commercial canning processes aim to reduce endospores to only 1 (12 D process), critical for preventing the germination of endospores in canned foods.
• Dry heat is less effective than moist heat and requires longer times and higher temperatures, with incineration being a method of dry heat sterilization.
• Filtration methods, including membrane and depth filters, are used for heat-sensitive solutions like beer and involve the application of vacuum or pressure to aid liquid flow.
• Radiation methods include ionizing (X rays, gamma rays) and non-ionizing (UV light) radiation, with ionizing radiation being used to sterilize heat-sensitive materials and approved for use on various foods by the FDA.
• Ultraviolet radiation is used to destroy microbes in air, water, and on surfaces, with limitations in penetrating solids or turbid liquids.
• High pressure, or pascalization, is used in commercial foods to avoid problems with high temperature pasteurization, maintaining color and flavor associated with fresh food.
• Germicidal chemicals are used to disinfect and sterilize surfaces, acting by irreversibly binding proteins, DNA, cytoplasmic membranes, or viral envelopes.
• Germicidal chemical formulations are less effective than heat but are useful for treating countertops, surfaces, bathroom fixtures, doorknobs, and heat-sensitive items.
• Sterilants destroy all microbes, including endospores, while disinfectants cannot destroy all microbes, including endospores.
• Germicidal chemicals typically contain several antimicrobial chemicals and other chemicals, such as buffers, with their exact mechanisms of action often poorly understood.
• These methods are aimed at destroying microorganisms and viruses and play a critical role in ensuring the safety and quality of various products and environments.