Foundation To Food Microbiology PDF

ADVANCED CERTIFICATE IN NUTRITION Foundation to Food Microbiology Dr. Sam Leung [email protected] 1 Learning outcome Student should be able to:  Recall the classification of microorganisms  Identify the morphology of bacteria, viruses, microalgae, protozoa, fungi (yeast and molds) 2 Fo...

ADVANCED CERTIFICATE IN NUTRITION Foundation to Food Microbiology Dr. Sam Leung [email protected] 1 Learning outcome Student should be able to:  Recall the classification of microorganisms  Identify the morphology of bacteria, viruses, microalgae, protozoa, fungi (yeast and molds) 2 Food Microbiology  What is Food Microbiology?  The biology of small living organisms (microorganisms) relating to foods Bacteria (細菌) Virus (病毒) Fungus (真菌) 3 Microalgae (微藻) Protozoa (原生動物) Introduction to Microorganisms  Classification  Prokaryotic microorganisms (e.g. bacteria)  Eukaryotic microorganisms (e.g. fungi, microalgae, protozoa)  Viruses 4 Factors affecting microbial growth  Nutrition  Temperature  pH  Light requirement  Growth curve 5 Application in Daily life  Beneficial  Starts for making foods e.g. beer, cheese, soy sauce *Produce nutritional foods e.g. Spirulina cereal, Fat Choi 6 Production of food and health food supplements by microorganisms  Nutritional supplements  antioxidants (e.g. phycocyanin produced by the Spirulina)  omega-6 & omega-3 polyunsaturated fatty acids (PUFAs) e.g. Arachidonic acid (AA) produced by the fungi Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA) produced by diatoms and dinoflagellates 7 Production of fermented food by microorganisms  Foods (e.g. beer, soy sauce, cheese, yogurt, vinegar) 8 Application in Daily life  Harmful  Food poisoning causing illnesses e.g. avian influenza, cholera, ciguatera food poisoning  Food spoilages Affect the appearance, color, flavour and safety of the food 9 Common foodborne diseases/ food spoilages caused by microorganisms (bacteria) e.g. Cholera (霍亂) caused by Vibrio cholera 10 Common foodborne diseases/ food spoilages caused by microorganisms (Viruses, Fungi, Protozoa) e.g. Avian influenza caused by H5N1 virus Ciguatera food poisoning caused by the protozoan Gambierdiscus toxicus  Method to detect microorganisms and toxins in food 11 An Introduction to Microorganisms 12 Classification of microorganisms  Allows logical study of microorganisms e.g. cell shape, size, motility, structure arrangement, etc.  Classification of living organisms  Kingdom → Phylum → Class → Order → Family → Genus → Species → Strain E.g. Vibrio cholerae Kingdom: Eubacteria Phylum: Proteobacteria Class: Gamma Proteobacteria Order: Vibrionales Family: Vibrionaceae Genus: Vibrio Species: cholerae 13 Classification of microorganisms  Scientific name  As an international convention to describe a living organism in a scientific field  Convenient for the communication among scientists  Common name  Communication for the public 14 Classification of microorganisms  Rules for writing a scientific name using Vibrio cholerae as an example Genus Species Italic or underlined Vibrio cholerae Italic: Vibrio cholerae Underlined: Vibrio cholerae The 1st letter of the Genus: Capital letter The 1st letter of the species: Small letter Vibrio cholerae Vibrio cholerae 15 6 Kingdoms 16 6 Kingdoms 1. Protista  Single-celled (microalgae, protozoa, slime molds)  Multi-celled (macroalgae)  Photoautotrophic growth  Heterotrophic growth  Mixotrophic growth (photoautotrophic + heterotrophic) 17 Mode of Growth  Photoautotrophic  Cells require carbon dioxide (CO2) and light to generate glucose via photosynthesis  Photosynthesis  carbon dioxide + light + water → oxygen + glucose  Only occurs in those cells that contain chlorophyll (for light absorption) 18 Mode of Growth  Heterotrophic  Carbon substrates (e.g. glucose, sucrose, acetate) as the sole source of energy  Mixotrophic  Hybrid between photoautotrophic and heterotrophic growth  i.e. Cells use both light and organic substrate for growth 19 6 Kingdoms 2. Fungi  Single-celled (yeasts)  Multi-celled (molds)  No chlorophylls  (no photoautotrophic or mixotrophic growths)  Grow without light, .i.e. heterotrophic Mold (黴菌) Yeast (酵母菌) 20 6 Kingdoms 3. Archaebacteria  Single-celled  Mostly live in extreme conditions e.g. thermophiles (live at high temperatures) 21 6 Kingdoms 4. Eubacteria  Single-celled  Live in most environments e.g. warm place (30-40oC)  Spirulina (a cyanobacterium 藻青菌)  Most bacteria do not contain chlorophylls, i.e. heterotrophic growth  but chlorophyll are found in most cyanobacteria e.g. Spirulina  Photoautotrophic, heterotrophic and mixotrophic growths 22 Bacteria  Bacteria: a great impact on our daily life  Food spoilages and diseases  A source of useful drugs (e.g. antibiotics)  A source of vitamins and nutrients 23 Bacteria  All bacteria are prokaryotes – cells lack a membrane bound nucleus  Bacteria: the smallest living organism observed under light microscope  Cell size: 1-5 µm (1-5 x 10-6 m)  Single-celled 24 Bacteria  A single bacterium cannot be seen with naked eyes, but visible when grown in colonies An agar plate containing mixed bacteria colonies 25 Bacteria binary fission  Reproduction  Asexually (binary fission)  Extremely fast growth  1 cell can generate 109 cells in 10 hour! 26 Bacteria Ref only  Two kinds of bacteria produce spores e.g. Bacillus and Clostridium (both are rod-shaped) - Spores are resistant to unfavourable conditions e.g. heating, chemicals, drying, etc. 27 Bacteria  Spores germinate again in favourable conditions (e.g. high moisture, suitable pH) https://www.youtube.com/watch?v=NAcowliknPs 28 Bacterial cell shapes  Spheres – micrococci e.g. Staphylococcus aureus  Spirals – e.g. Spirulina platensis  Rods – short rods e.g. Escherichia coli – long rods e.g. Bacillus cereus 29 Bacterial cell structure (DNA) 30 Bacteria – cell structure and function  Capsule – a slimy outer layer (polysaccharide) surrounding the cell wall – prevent dehydration  Cell wall – a rigid structure for protection of the whole cells – maintains the structure of cell – allows chemical staining → identification of bacteria 31 Bacteria – cell structure and function  Cell membrane – regulates the substances (e.g. glucose, enzymes) moving in and out of the cell – controls the enzymes secreting into the medium to break down food then control the moving in of the food 32 Cell membrane structure head Protein channel – allows the movement of substance into and out of the cell tail 33 Bacteria – cell structure and function  Nucleoid containing DNA – carries genetic materials  Cytoplasm – holds organelles and storage materials (e.g. starch, fat) inside the cell – a medium for cellular function (e.g. transport of protein inside the cell)  Ribosome – a structure for protein formation  Flagellum – can be absent in some bacteria – locomotion 34 Identification of bacteria – based on cell structure  The bacteria are mostly colourless → require staining Two type of bacteria: Gram positive (blue/purple) Gram negative (red) 35 Picture of Foodborne Bacteria Gram positive bacteria Clostridium botulinum Staphylococcus aureus Streptococcus pyogenes 36 Picture of Foodborne Bacteria Gram negative bacteria Salmonella typhi Escherichia coli Vibrio cholerae 37 Mechanism of bacteria gram staining  Gram staining – identifies the type of bacteria Procedures: - Fixed cells on a slide 1st step 2nd step 3rd step 38 https://www.youtube.com/watch?v=sxa46xKfIOY Mechanism of bacteria gram staining 1st – 2nd step  Gram positive  Forms a crystal violet-iodine (CVI) complex  The dye cannot be removed (cell stained as purple)  Gram negative  The lipid in the outer membrane is dissolved and removed  The purple dye is washed away (cell colour: colourless) 3rd step – safranin (red) 20 sec – rinse with water Gram positive → remain purple Gram negative → stain red 39 Viruses  obligatory intracellular parasites  parasites: microbes that grow, feed and survive on or in other organisms (hosts) but give no benefits to the host  Viruses which invade bacteria (host) are called bacteriophages ---from the Greek word “phag” means “to eat”  A virus comprises ---a hexagonal “head” (made up of protein) containing DNA or RNA ---a “tail” with hooks which helps to attach on the bacteria 40 Viruses  Viruses are host specific ---a virus attacking plant cells does not attack animal cells  A virus is so small with a cell size of 10nm (1 x 10-8m) compare with a bacteria cell 1µm (1 x 10-6m) ▪ A virus replicates by using the DNA and protein formation sites in a bacterium 41 Replication of viruses  Viruses insert the genetic materials into the host cells → Replicate the genetic materials and the sheath by the host → Viruses lyse the host cell wall (kill the host) → Replication completed 42 Viruses invading bacteria bacteria Transparent dots (plaques) represent viruses invading bacteria 43 Bacteriophage/phage Viruses  Some viruses can cause food poisoning Avian Influenza (Bird Flu) caused by H5N1 virus (or other subtypes) 44 Microalgae  A large group of microbes that can be found in soil, fresh water, marina sea and even in snow!  Kingdom: Protista  Photoautotrophic, heterotrophic, mixotrophic growths  Eukaryotes – cells that contain a nucleus  Most of them contain the photosynthesis pigments e.g., chlorophylls (green) and carotenoids (yellow to red)  The green microalgae are one of the major sources of nutritional products e.g. antioxidants, vitamins 45 A microalgal cell structure 46 Microalgal cell structure  Cell wall -- maintains the shape of the cell  Cell membrane – controls the substances moving in and out of cells  Chloroplast –contains chlorophylls for photosynthesis Carbon dioxide + light + water → Oxygen + glucose  Mitochondrion – a site for respiration → energy (ATP)  Glucose + oxygen → carbon dioxide + water + energy 47 Microalgal cell structure  Endoplasmic reticulum: Rough ER (RER) – with ribosomes (site for protein synthesis) attach on it Smooth ER (SER) – a site where NO ribosomes attach on it site for lipid synthesis  Nucleus – carries genetic information (DNA and RNA)  Starch granules – storage materials 48 Green microalgae  Unicellular (2-20µm)  Round (majority) or ellipsoidal 49 Green microalgae  Motile (zoospore) or non-motile (autospore)  Most of them live in fresh water  Chlamydomonas sp., Chlorella sp., Haematococcus sp., Chlorococcum sp.  Some of them live in marine water flagellum 50 Chlamydomonas (motile) Chlorella (non-motile) Green microalgae  Reproduction —asexually by autospores or zoospore formation e.g. Chlorella sp. (autospores) e.g. Haematococcus sp., Chlamydomonas sp., Chlorococcum sp. (zoospores) — sexually by meiosis e.g. Haematococcus sp., Chlamydomonas sp. 51 Green microalgae  Cell replications by the green microalga Chlamydomonas Sexual Asexual 52 Microalgae in Food Industry  Chlorella zofingiensis – Astaxanthin *A red carotenoid found abundantly in some microalgae ---as a natural food colorants Astaxanthin imparts the orange-red colour to the flesh/shell of aquatic animals 53 Microalgae in Food Industry  Chlorella protothecoides – Lutein A yellow carotenoid – as a food colorant in egg yolk Cells of C. protothecoides As a food colorant in egg yolk 54 Protozoa  Kingdom – Protista  Single-celled, eukaryotic  Photoautotrophic, heterotrophic and mixotrophic  Cell size – 10-50 µm (but some can achieve to 500 µm)  4 types 1. Amoebiod 2. Flagellated (3-D, helical) 3. Ciliated (2-D, planar) 4. Non motile ▪ Mostly reproduced by binary fission or budding Crypthecodinium cohnii 55 Budding  A daughter cell is smaller than the parent cell but finally grows to its parental size 56 Protozoa Gonyaulax spp. Gambierdiscus toxicus 57 Food poisoning caused by Protozoa  Ciguatera caused by Gambierdiscus toxicus 58 http://www.cfs.gov.hk/english/whatsnew/whatsnew_fsf/whatsnew_fsf_poison_fish.html Moulds  Kingdom – Fungi  Multi-celled, eukaryotic  Heterotrophic  Most of them are saprophytic (feed on non-living organic matters) e.g. breads, fruits  Secret enzymes to the surroundings to digest the foods  Contain thread-like filaments called hyphae  When hyphae extend and form a large mass = a mycelium 59 Mould – Hyphae and mycelia Inside hyphae: 60 Moulds  Reproduced by forming spores * Spores disperse from parent and germinate under favourable conditions • The fungal spores: resistant to dry conditions: NOT resistant to heat (destroyed by heat) 61 Moulds causing food spoilage hyphae 62 Yeast  Kingdom –Fungi  Single-celled, eukaryotic (moulds: multi-celled)  Heterotrophic  Cell size – 5–10 µm  Growth requirement  most of them grow best at pH 4.5 – 5 temperature 20 – 30oC  Can grow at the presence and in the absence of oxygen (Facultative anaerobic)  Very important in food industry as a starter for producing fermented foods e.g. Saccharomyces cerevisiae 63 Yeasts in Food Industry Saccharomyces cerevisiae  Very important in food industry as a starter for producing fermented foods 64 Oxygen requirement by microbes  Aerobic – oxygen (O2) is required for growth  Anaerobic – O2 is inhibitory for growth -- O2 is toxic to anaerobes  Facultative anaerobic – microbes that can growth on both aerobic and anaerobic environments --if O2 is available → aerobic growth --if O2 is deficient → change to anaerobic growth 65 Microbial maintenance Agar plate/broth can provide nutrients for bacteria growth. 66