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MICR 4010 (1)

Notes week 1

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MICR 4010
Rob Foster

PATHOGENIC BACTERIOLOGY – WEEK 1 Bacterial mass in each body site Intestines Each gram of feces contains ~10^8 facultative anaerobes and 10 obligate anaerobes. There are more bugs in your gut than people on the planet. Babies don’t have many associated microbes but they quickly develop a microbiota, and everyone has a very specific microbiota. Skin Associated microbiota ~200g (wet weight). Arms and legs are like deserts for microbiota, because they’re very dry. - Head: many sebaceous and sudoriferous glands -> high population density. - Axillae: high moisture, high temperature, high pH -> high microbial density. - Perineum: high moisture, high temperature -> high microbial density. - Toe webs: high moisture, high temperature -> high microbial density. - Arms and legs: few sebaceous glands, no sudoriferous glands, relatively dry – low microbial density. - Hands: no sebaceous glands, exposed area, low water content -> low microbial density.7 Respiratory Tract Lungs are not sterile, and the respiratory tract has many opportunist pathogens. Many residents of the RT include: Viridans spreptococci, Strep. Pyogenes, Strep. Pneumonia, Neisseria spp. Haemophilus spp., Moraxella spp. And Staph. Aureus Mostly in the nose and throat. How would you ensure that a lung microbiota sample from bronchoscopy was not contaminated with oral flora? You don’t know. Droplets are a very effective way of spread diseases Vagina The environment of the vagina changes during the menstrual cycle (hormone levels, pH, host- derived antimicrobial compounds) and during various stages of sexual maturity (oestrogen level, pH, glycogen content, redox potential) Lactobacillus spp. Are the main residents  form a polysaccharide-encased biofilm on epithelial cells. Mouth More than 200 species have been culturing the human mouth. These are marked differences between species resident on the tongue, palate, tooth surface, and gingival crevices. 10 On average, we sallow 8x10 bacteria every day! Eyes Grouping together: eyes, eyelids, eyelashes and lacrimal apparatus. Generally the same as the organisms present on the skin. Different relative numbers. Affected by contact lens wear, sleep. The tears have a lot of antimicrobial components. DEFINITIONS Virulence (pathogenicity) – the ability of a microorganism to cause disease. Symbiosis – close association between 2 different species Parasite – an organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host. Pathogen – an organism that causes disease. Virulence determinants – characteristics of a pathogen that are involved with disease promotion. BASIC STEPS Step 1 – adherence Step 2 – immune system evasion (invasion, secretion of bacterial products) Step 3 – damage to host cell Factors Host factors: age, sex, nutritional status, genetic make-up, immune system status. Pathogen factors: ability to invade, to secrete products detrimental to host health, ability to survive and multiply, antibiotic resistance. Age issues FACTOR CONSEQUENCES Immunosenescence Influences microbiota at all sites Decreased mucociliary clearance Increased microbial colonization of RT Malnutrition Affects composition of host secretions which affects microflora colonization Decreased stomach acid production Increased colonization of the stomach Urinary tract changes Increased colonization of the urinary tract Lack of oestrogen (females) Decreased vaginal pH leading to increased colonization Decreased intestinal mobility Increased colonization of small intestine Gender issues - Males have a significantly higher risk of colonization by Helicobacter pylori - Males have a higher density of bacteria and females a higher diversity of species on their skin. - Females have a higher risk of urinary tract infections than males. - The carriage of Staph. aureus in the nose is higher in males than in females. Host genetic issues - Everyone’s microflora is different and unique to them - However, the e.g. fecal and nasal microflora of monozygotic twins can share a high degree of similarity  points to host genetis playing a role in selecting microbial inhabitants KOCH’S POSTULATES 1. The microorganism must be found in abundance in all organisms suffering from the disease, but not in healthy organisms. 2. The microorganism must be isolated from a diseased organism and grow in pure culture. 3. The culture microorganism should cause disease when introduced into a healthy organism. 4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent. H. pylori It is a human specific organism, there are no know reservoirs. It’s hard to culture and does not survive long out of its host. Its mode of transmission is not understood. Likely to be maternal transfer as well as transfer between siblings. Types of symbiotic relationships Mutualism Both species benefit and depe
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