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Lecture 26

MBIO 1010 Lecture 26: Lecture 26

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MBIO 1010
Christopher Rathgeber

Microbiology 1010 – Lecture Notes Microflora of the Skin Different areas of the skin vary in chemical composition and moisture content  Provides 3 different microenvironments: o Dry skin, moist skin and sebaceous skin o Each with different microbial populations. Skin is slightly acidic and high salt concentration which in turn dehydrates the microbes. Examples of bacteria that live on skin Dry skin (ex. forearms, hands)  High numbers of Betaproteoacteria Known from 16 rRNA genes   Rarely cultured - no one really knows what they’re doing  Second highest is corynebacteria Most are harmless commensals, but some may cause skin infections  Ex. Corynebacterium diphtheriae o Can cause non-healing ulcers of the skin – cutaneous diphtheria Diphtheriae = we are protected from the toxin in the Dtap vaccine. Examples of bacteria that live on skin (Continued…) Moist skin (ex. armpits, nostrils) o High numbers of corynebacteria and staphylococci Most are harmless commensals:  Ex. Staphylococcus epidermidis  Most frequentl isolated from skin o Some are important pathogens  Ex. Staphylococcus aureus  Cause of boils, abscesses, wound infections. Abscess = anaerobic bubble were the interior has no oxygen and the organisms are living off the puss and dead cells. Vascular/ blood is found within the dermis of the skin 139 Microbiology 1010 – Lecture Notes Examples of bacteria that live on skin (Continued…) Sebaceous skin (ex. oily skin around the nose, on the upper chest and back) High numbers of propionibacteria Anaerobic Atinobacteria that produce propionic acid as an end-product of fermentation Ex. Propionibacterium acnes    Lives in hair follicles, and eats sebum – oil secreted by skin   Overgrowth can trigger inflammation Inflammatory acne  Microflora of the Oral Cavity  Saliva has antimicrobial enzymes: Lysozyme Lactoperoxidase – Catalyzes production of superoxide radi2als O  Oxidative damage to invading microbes Despite this, the mouth is home to a complex microbial community, including aerobes and  anaerobes: Ex. Neisseria mucosa  Aerobic o Lives on mucous membranes like the tongue. Acid waste products when metabolize the products left in the mouth from food – causes the cavities 23.3 Microflora of the Oral Cavity (Continued…) Ex. Streptococcus mutans  Aerotolerant anaerobe Produces a sticky dextran slime layer that lets it stick to  surfaces o Forms biofilms in crevices around the teeth Produces lactic acid as an end-product of fermentation  Degrades tooth enamel Dental carries (cavities) Can lead to inflammation along the gum line:  Gingivitis 140 Microbiology 1010 – Lecture Notes 23.4 Microflora of the Gastrointestinal Tract The Stomach  Low pH and proteolytic enzymes make the stomach inhospitable to most microbes Some bacteria do colonize the stomach Ex. Helicobacter pylori  Colonizes surface of membrane, protected from stomach acids by mucous Has a number of virulence factors: o Exotoxin – kills cells in the membrane Endotoxin – triggers inflammation Cause of stomach ulcers  Treated with antibiotics – tetracycline Gram neg. has the endotoxin on the cell membrane. Stomach ulcers = holes within the stomach. The small intestine  Area of rapidly changing pH As pH becomes more neutral, bacterial numbers increase Ex. Enterococcus – genus of Gram positiv
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