lecture 10

• gram-staining process: 1. application of crystal violet (abt 1 min, then washed with water), 2. application of iodine (trapping agent), 3. alcohol wash (decolorization), 4. application of safranin (counterstain- stains gram neg pink)
• gram stain dyes the peptidoglycan wall
• reservoir: where the pathogen is found; can be the infected mammary gland, environment, etc.
• dry cow therapy: infusing and treating cows with antibiotics the last day of milking (before the dry period)
• lactating cow therapy: infusing with antibiotics during lactation; not as effective
• why care about mastitis?

  it is the most expensive disease in the dairy industry; both in US and globally; 2 billion dollar disease in the US alone
• mastitis is so expensive mainly due to reduction in milk yield bc cows won't produce as much bc of the infection; also expensive because of vet costs, discarded milk, antibiotic usage, and having to cull the affected animals
• mastitis is inflammation of the mammary gland, typically caused by infection
• inflammation is hard to define; considered a local response to cell injury marked by capillary dilation, leukocytic infiltration, redness, heat, and pain; serves as mechanism for initiating the elimination of noxious agents and damaged tissue
• inflammation can be hard to measure; in the context of bovine, SCC is the most commonly used gauge (above 200,000 indicates mastitis, below indicates nothing)
• somatic cells are any cell with all chromosomes; not sex cells
• measuring inflammation: aside from SCC, you can also look at blood in milk (salts), inflammation related proteins, proteins/enzymes related with immune response
• mammary inflammation can be caused by: trauma, chemicals, heat, random foreign antigen (oyster glycogen), and intramammary infection
• factors affecting IMI development: stress, spread, and exposure
• most important mastitis concept: prevention is key, not therapy or genetics; no antibiotic, vaccine, or genetic selection program will solve mastitis problems
• "mastitis is a disease of the producer with signs in the cow"; meaning it is more of a management issue
• the gland cistern (contains milk) has everything that bacteria needs to reproduce
• neutrophils infiltrate the gland; vibration of the neutrophils cause sloughing of alveoli (myoepithelial cells); disrupts the cell, causing it to produce less milk
• mastitis pathogens can be organized into categories based on reservoir and how the reservoir influences transmission; include contagious and non-contagious (environmental and opportunistic)
• the reservoir for contagious pathogens is the mammary gland; pathogen spread across a herd through milking
• the reservoir for environmental (non-contagious) pathogens may include manure, dirty water, etc.
• the reservoir for opportunistic (non-contagious) pathogens is the teat skin (breaches into gland)
• 4 main contagious pathogens: staphylococcus aureus, streptococcus agalactiae, corynebacterium bovis, and mycoplasma spp.
• all contagious pathogens primary reservoir is the infected mammary gland, with the exception of mycoplasma spp
• staphylococcus aureus: gram-positive coccus; assembled into grape like clusters; most studied; hard to get rid of; has a considerable number of virulence factors; very capable pathogen; gold ish in color
• staphylococcus aureus virulence factors: fibronectin binding proteins, protein A, leukocidin, coagulase, capsule, hemolysins
• fibronectin binding protein (staph aureus virulence factor): helps bacteria adhere well to mammary gland
• virulence factor: strategy to live/survive
• protein A (staph aureus virulence factor): has ability to bind to F.C. region; guarantees antibodies can't bind to bacteria (bottom of Y shape)
• leukocidin (staph aureus virulence factor): helps form pores which causes white blood cell death
• coagulase (staph aureus virulence factor): coagulates plasma and forms a barrier to prevent white blood cells from coming near (not often present in other bacteria)
• capsule (staph aureus virulence factor): surrounds, prevents harm of bacteria
• hemolysins (staph aureus virulence factor): lyses red blood cells
• significance of staph. aureus: not the problem it once was but still dangerous, spreads easily, cause significant tissue damage (mainly secretory tissues), causes gangrenous mastitis and necrosis (via vasoconstriction
• staph. aureus treatment: many infections will spontaneously cure, but these were unnoticed in the first place; those that remain are often refractory and seldom cure, "once a staph. cow, always a staph. cow"
• prevention of staph. aureus is key (milking hygiene and teat health); bringing new animals into herd (including heifers); flies will pass this pathogen around (parasite vector)
• heifer IMI/mastitis is a thing; staph aureus is the 2nd most prevalent pathogen in heifers (even though have never lactated)
• staph aureus does not respond to antibiotics
• lesions and scabs harbor staph. aureus
• study in washington state found mastitis outbreaks in winter; conclusion was that teats were being damaged in -10 degree F weather