Microbes in Biology

Microorganisms and Their Impact on Daily Life

• Microorganisms like bacteria, viruses, fungi, and protozoa can cause foodborne illnesses and food spoilage.
• Examples of foodborne diseases caused by microorganisms include cholera, avian influenza, and ciguatera food poisoning.
• Microorganisms can be detected in food using specific methods.
• Microorganisms are classified based on characteristics such as cell shape, size, and structure arrangement.
• The classification of microorganisms involves scientific and common names.
• The scientific name follows specific rules, such as italicizing or underlining the genus and species.
• Microorganisms are classified into six kingdoms, including Protista, Fungi, Archaebacteria, and Eubacteria.
• Protista can be single-celled or multi-celled and exhibit different modes of growth like photoautotrophic, heterotrophic, and mixotrophic.
• Fungi include both single-celled (yeasts) and multi-celled (molds) organisms that grow without light.
• Archaebacteria are single-celled organisms that often live in extreme conditions, such as thermophiles.
• Eubacteria, also single-celled, can live in various environments and can exhibit photoautotrophic, heterotrophic, or mixotrophic growth.
• Bacteria, which are prokaryotes and lack a membrane-bound nucleus, can impact daily life by causing food spoilage and diseases, serving as a source of drugs, and being a source of vitamins and nutrients.

Microbes in Biology

• Bacteria are identified based on cell structure and can be Gram positive (blue/purple) or Gram negative (red).
• Mechanism of bacteria gram staining involves fixed cells on a slide and staining with crystal violet-iodine complex.
• Viruses are obligate intracellular parasites and can be host-specific, with a size of 10nm compared to bacteria cell size of 1µm.
• Viruses replicate by inserting genetic materials into host cells, leading to lysis of the host cell wall.
• Some viruses, like Avian Influenza (Bird Flu) caused by H5N1 virus, can cause food poisoning.
• Microalgae are a large group of microbes found in various environments, including soil, fresh water, and marine environments.
• Microalgal cell structure includes a cell wall, chloroplast for photosynthesis, and mitochondrion for respiration.
• Green microalgae, such as Chlamydomonas and Chlorella, can be unicellular, motile or non-motile, and reproduce asexually or sexually.
• Chlorella zofingiensis is known for producing Astaxanthin, a red carotenoid used as a natural food colorant.
• Chlorella protothecoides produces Lutein, a yellow carotenoid used as a food colorant in egg yolk.
• Protozoa are single-celled, eukaryotic organisms that can be photoautotrophic, heterotrophic, or mixotrophic.
• Food poisoning caused by Protozoa includes Ciguatera, caused by Gambierdiscus toxicus.

Pasteurization and Sterilization in Food Processing

• Pasteurization is a thermal process used to inactivate enzymes and eliminate viable pathogenic microorganisms from heat-sensitive foods such as milk, fruit juice, wine, and egg.
• It involves heating the food to below 100˚C for a specific duration and then rapidly cooling it to slow down microbial growth, requiring refrigeration storage and providing a shelf life of 2-3 weeks.
• Pasteurization involves two main methods: low-temperature pasteurization at 63˚C for 30 minutes and high-temperature short time (HTST) pasteurization at 72˚C for 15 seconds, with the latter being more effective in retaining nutritional and sensory quality.
• HTST pasteurization of raw milk involves heating the milk briefly to 72 °C for about 15 seconds to kill disease-causing microbes, followed by rapid cooling and refrigeration storage.
• Ultra-high temperature (UHT) pasteurization of raw milk involves heating the milk to around 138 °C for 2-3 seconds, then rapidly cooling and packaging it in sterile, hermetically-sealed containers, providing a shelf-stable product for 6 months without requiring refrigeration until opened.
• Sterilization is a process that completely kills or removes all life forms, including bacteria and other organisms, and is commonly achieved through heating methods such as wet heating at 121°C for 15-20 minutes.
• Commercial sterilization combines heat and vacuum seal to destroy all spoilage and pathogenic microorganisms, including endospores of Clostridium botulinum, used in producing canned food through retort processing.
• Canning involves commercial sterilization of low acid foods at 121°C for a duration sufficient to inactivate Clostridium botulinum spores by 12 log and high acid foods at around 100°C to destroy both vegetative cells and spores of spoilage microorganisms.
• One log reduction indicates a 90% reduction in the microbial population, and 12 log reduction signifies a complete eradication of the microorganisms.
• Bacterial populations killed by heat or chemicals tend to die at constant rates, with the microbial death rate curve showing this constant death as a straight line.
• Three important values used to measure thermal-killing efficiency are D value (decimal reduction time), Z value (increase in temperature required to reduce D value by ten-fold), and F value.
• D value represents the time needed to reduce the number of a given microorganism by 90% at a specific temperature, and it decreases as the temperature increases, differing for different microbial species.

Test your knowledge of microbes in biology with this quiz. Explore topics such as bacteria cell structure, gram staining, virus replication, microalgae characteristics, and the classification of microorganisms. Learn about the impact of microorganisms on daily life, including foodborne illnesses and food spoilage.