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The Basics of Microbiology Types of microorganisms Ortega, 2002 •  Bacteria •  Molds •  Yeasts – Molds and yeasts are fungi •  Protozoans •  Viruses Bacterial anatomy 1
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Types of flagella Gram posiBve and Gram negaBve bacteria Gram positive
Gram negative
Bacteria are translucent, difficult to visualize Crystal Violet Lugol’s Iodine Hans Christian Joachim
Gram, 1852-1938
Ethanol + acetone Carl Weigart
Safranine Gram + Cell Wall Cytosol Cytoplasmic membrane PepBdoglycan Gram — Cytosol Cytoplasmic membrane PepBdoglycan Lipopolysaccharides and protein 2
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Bacteria reproduce by binary fission Time to 1 cell mulBplying to 106 Salmonella 1a. (20 min) Vibrio parahaemoly0cus 1a. (7 min) 2a. (20 min) 2a. (7 min) 3a. (20 min) 3a. (7 min) 7.6 h 2.3 h Sporeforming bacteria Bacterials spores •  Spores are more resistant than vegetaBve cells –  Heat, drying, irradiaBon, freezing etc. •  Cooked foods are expected to contain bacterial spores including those of pathogenic bacteria –  Clostridium perfringens –  Clostridium botulinum –  Bacillus cereus 3
FSTC 606
Microbiology of Foods
Alejandro Castillo
Associate Professor
Microbiology
• Study of microscopic organisms
• Microscopic = Smaller than the
minimum size detected by the
naked eye
Evolution of microbiology
Francesco Redi
Development of
microscope
1590
Spontaneous
generation debates
1673
Spontaneous
generation disapproval
1760
1865
Applied Microbiology
2003
1865
Food Microbiology
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Evolution of Food Microbiology
• Food
• Food
• Food
• Food
preservation
spoilage
poisoning
legislation
History of food preservation
• 1782 - 1840
– Development and use of canning
process for preservation of food
• 1813
– Use of SO2 as a meat preservative
• 1841 - 1878
– Development and use of freezing for
storing foods for long periods of time
– Food sterilization, development of
condensed and dried milk
History of food preservation (cont.)
• 1890 – 1900
– Development and use of milk pasteurization
• 1907 – 1930
– Use of chemicals for food preservation
– Use of modified and controlled
atmospheres for preservation of fruits and
vegetables
• 1929 - Present
– High energy radiation for food processing
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History of food spoilage
• 1659 - 1780
– Studies on milk souring
– Association between lactic acid and milk souring
• 1866
– Development of pasteurization
• 1839 – 1878
– Studies on sugar slimes
• 1887 – 1902
– Studies that demonstrated bacterial growth at low
temperatures
– Use of the term psychrophile
• 1888 – 1917
– Studies on thermophilic bacteriology
• 1933 – 1964
– Studies on Byssochlamis fulva
History of foodborne disease
• 1820 – 1896
– The etiological role of Salmonella, Staphylococcus and
Clostridium botulinum in food poisoning was proved
• 1904 – 1951
– New foodborne pathogens were described
• Bacillus cereus, Clotridium perfringens (welchii), Campylobacter
(Vibrio), Vibrio parahaemolyticus, Yersinia enterocolitica
• 1955 – 1975
– Toxins from foodborne pathogenic bacteria were isolated
and characterized
– Different virulence mechanisms were described
• 1975 – 1993
– Emerging foodborne pathogens gained importance
• Campylobacter jejuni/coli, Aeromonas spp., Listeria
monocytogenes, Escherichia coli O157:H7, Vibrio vulnificus
• 1995 – present
– Studies on pathogen control
History of food legislation
• 1890 – 1895
– Meat inspection act
(approval and
amendments)
• 1906
– U.S. Federal Food and Drug
Act
• 1910
– Milk pasteurization required
• 1939 - 1954
– Food, Drug and Cosmetic
Act (approval and
amendments)
• 1957
• 1963
– Irradiation approved for
bacon treatment
– Approval withdrawn in
1969
• 1967
– U.S. Wholesome Meat Act
• 1973
– Several microbiological
standards adopted
• 1995 – 2001
– HACCP regulations for
meat and poultry, fishery
products and juice products
– U.S. Compulsory Poultry
and Poultry Products law
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Microorganisms of interest in
Food Microbiology
• Spoilers
• Pathogens
• Starters and probiotics
• Indicators
Spoilage organisms
• Microorganisms causing food deterioration
– Psychrothophs among the most important
• Control by applying methods for food
preservation
– Refrigeration, reduced water activity (aw),
acidification etc.
• Examples
– Pseudomonas producing off odors in
refrigerated raw meats
– Leuconostoc producing slime in juices
– Lactococcus producing acid in raw milk
Pathogens
• Salmonella
• Clostridium perfringens
• Escherichia coli O157:H7
• Campylobacter
• Staphylococcus aureus
• Listeria monocytogenes
• Vibrio cholerae, V. vulnificus
• Yersinia enterocolitica
• Cyclospora
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Starter organisms
• Used for production of fermented foods
• Examples
– Lactococcus lactis and Lactobacillus bulgaricus
• Yogurt
– Propionibacterium shermanii
• Swiss cheese
• Their function is to produce distinctive
aroma or texture
Probiotics
• Organisms that colonize the body and have
beneficial effects for the host
• Examples
– Bifidobacteria
– Lactobacillus casei
– Lactobacillus acidophilus
• Associated with
– Prevention of colon cancer
– Detachment of cholesterol plaque from arteries
Indicator organisms
• Microbial groups whose number or presence is
used as an indicative of Microbial food quality or
safety
• Examples
– Aerobic plate count
• Total levels of bacteria present in a specific food product
– Coliform bacteria
• Indicate adherence to good manufacturing practice during
food processing
– Escherichia coli
• Indicates exposure to fecal contamination
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