Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
8 Cards in this Set
- Front
- Back
|
How can microorganisms cause disease without entry? What are the most important examples?
|
-can produce toxins that contaminate animal feeds or water, survive the passage through the gastrointestinal tract, and are then absorbed by the animal
-the most important examples are: botulism and the mycotoxicoses and algal (actually cyanobacterial) blooms |
|
|
What causes bacterial food borne toxicoses? How do they get into the body?Where do they exert their effect?
|
-bacterial food-borne toxicoses are caused by exotoxins
-only a few bacterial exotoxins are toxic on ingestion, as they must be capable of surviving passage through the upper alimentary tract prior to exerting their effect -direct effect on intestine or systemic effect |
|
|
What are mycotoxins? When are they formed in the lifecycle? What animals are they a particular problem for?
|
-mycotoxins are low molecular weight, non-antigenic substances produced by specific species of fungi under favorable temperature & moisture conditions
-exposure, usually by ingestion is referred to as mycotoxicosis -the toxin are a secondary metabolite, formed during the stationary phase of culture rather than during the exponential growth phase -problem for poultry, pigs, dairy, and feedlot beef cattle (it decreases their production) |
|
|
What are the routes of entry for microorganisms?
|
❤SKIN
-may be direct (ie. Brucella & Francisella) -mediated by injury, excessive moisture, arthopod or other animal bites, various husbandry & surgical procedures ❤RESPIRATORY TRACT -aerosols, the size of the particles will determine the site the droplets will be deposited (only those 5 μm in diameter will reach the alveoli) -many orgs have specific receptors that allow them to attach to the cells of the surface they subsequently colonise and invade -concurrent infection will aid colonisation by interference with clearance mechanisms including alveolar macrophages & ciliary motility -high dust & ammonia may aid in infection by interfering with clearance mechanisms ❤INTESTINAL TRACT -food, water, nasal & resp secretions that are swallowed -bacterial motility plays a role -mucinases aid to access epithelium -disturbances to normal flora (ie. antibiotics) -usually require a specific receptor on epithelial cells -those that gain entry via the GIT are resistant to low pH, proteases, & bile salts ❤OROPHARYNX -injury to the oral mucosa ie. rough forage or bones can introduce commensals into deeper tissue -gingival margin a point of entry along teeth -systemic pathogens often enter via this route (esp. tonsilar epithelium) ❤CONJUNTIVA -mechanical damage by dust or scratches, foreign bodies -adhesins important in colonising the eye -droplets of splashes urine, flies ❤UROGENITAL TRACT -specific attachment again is usually necessary -trauma especially at mating -female predisposition to urinary tract contamination (ie shorter urethra, greater diameter, and proximity of the anus) -flagella may aid in colonisation in some cases -can be aspirated into the vulva post-partum, or during therapeutic interventions, particularly at birth ❤MAMMARY GLAND -teat canal opened after milking -milking machine/technique -specific trauma -intramammary antibiotics can transport pathogens -poor hygiene standards ❤UMBILIC CORD -neonatal infections |
|
|
What innate defenses do we have against microorganisms?
|
❤SKIN
-most organisms cannot penetrate the physical barrier (except Brucella abortus and Francisella tularensis) -sebaceous glands secrete substances that maintain a low pH and that are antibacterial, lysozyme, pH, salt -resident flora ❤MUCOUS MEMBRANES -mucus film to trap microorganisms and aids in phagocytosis -lysozyme in mucus and tears ❤RESPIRATORY TRACT -cilia -lowering of the head -humidification of the upper respiratory tract helps maintain the integrity of the lower tract -nasal hairs, sneezing and cough reflexes ❤EYES -nictating membrane wipes eyes -tears wash eyes ❤GASTROINTESTINAL TRACT -saliva, gastric acid, bile salts and proteolytic enzymes -continuous flushing & peristalsis -normal flora ❤UROGENITAL TRACT -lactobacilli in vaginal flora help maintain an acid pH which stabilises normal flora -washing by urine ❤MAMMARY GLAND -teat sphincter -lysozyme, lacterferrin, lactoperoxidase -resident flora around teat orifice may prevent colonisation |
|
|
What are the different mechanisms in which bacteria can adhere?
|
❤PILI OR FIMBRIAE
-pilli or fimbriae are straight filaments arising from the bacterial cell wall, making the bacteria look like a porcupine -composed of a helical array of a single protein pilin -the multiple pillin subunits are non-covaelently attached to each other -the pilus grows by adding subunits to its base -most adhesins are organized into 2 domains separated by a short flexible linker -the proximal domain joins the adhesin to the top pilin subunit, whereas the distal domain binds to a host structure -fimbriae are described as F antigen ❤LIPOTECHOIC ACIDS -in gram positive bacteria -teichoic acid is made up of repeating units of a molecule similar to glycerol attached to peptidoglycan -lipoteichoic acid attached to lipids, has a hydrophic and hydrophilic part, can also mediate attachment to a variety of host cells ❤M protein -hypervariable tip promotes adhesion, can attach it to host or other streptococci ❤Lipoproteins ❤Campylobacter proteins are arranged in a crystalline layer, also promotes adhesion |
|
|
What kinds of motility do bacteria have?
|
❤FLAGELLA
-protein filaments that extend like long tails from the cell membranes of certain gram positive and gram negative bacteria -the flagellum is affixed to the bacteria by a basal body -the basal body spans through the entire cell wall, binding to the inner & outer cell membrane in gram negative bacteria and to the inner membrane in gram-positive bugs -the basal body spins around and spins the flagellum -found on rod shaped organisms -may be polar (at one or both pole) or peritrichous -composed of globular protein, flagellin, assembled into helical filaments -can only see them with special stains (ie. silver) -found in pathogens adapted to a liquid environment ie. gut or urine -distinct serologic types in different strains of the same species (H antigen) ❤Gliding -Mycoplasmas, no flagella ❤Spirochaetes -have a flagellum that is wound around the cell body and they are motile by rotating around their long axis (like a corkscrew) ❤Twitching motility -performed by attachment and retraction of specific pili, and is through to be related to virulence in some species |
|
|
Do bacteria exhibit chemotaxis?
|
-yes
-they are capable of movement toward a chemical stimulus -motility may be used to move to a particular habitat or nutritional source |
