lecture 9

• intramammary infection (IMI)

  infection of the mammary gland, main cause of mastitis; from bacteria and microbes
• fomite

  objects or material that are likely to carry pathogens (dirty clothes/utensils)
• clinical

  can actually observe signs
• subclinical

  cannot observe signs (exists, but no signs seen by naked eye)
• sign

  manifestation of the disease; perceived by physician or farmer
• symptom

  only a patient can describe; can't happen with animals because they cannot talk
• cytokine

  chemical components related to immune system and initiation of immune response; tells cells what to do
• chemokine

  chemical components related to immune system and initiation of immune response; attract cells to come somewhere to glue to site of infection
• why care about defense?

  milk is an excellent medium for bacteria (has sugar, nitrogen, fatty acids and salts/minerals which are required for bacteria growth)
• a multitude of pathogens can be introduced; before collection- brucellosis and mastitis pathogens; after collection- manure and dirty equipment/lines
• possibilities of pathogens that milk grows: staphylococcus spp., streptococcus spp., corynebacterium spp., coliforms, mycoplasma spp., acholeplasma spp., brucella spp., trueperella spp., nocardia spp.
• bacteria are described as being gram positive or gram negative
• gram positive bacteria lack an outer (lipopolysaccharide) membrane, and the peptidoglycan is much thicker
• gram negative bacteria have an outer membrane, and the peptidoglycan is much thinner
• gram positive bacteria are stained purple
• gram negative bacteria are stained pink
• gram staining involves the ability of the bacteria cell wall to retain dye
• host defense of the cow seeks to: prevent an infection from establishing and resolve an infection if it becomes established
• sources for possible bacteria/microbes: manure, dirty parlor equipment, parasites, normal flora (skin), pasture, living environment
• defense mechanisms of the mammary gland: physical, chemical, cellular, and humoral
• physical barriers are the first line of defense against pathogens; includes teat skin and streak canal (smooth muscle around streak canal)
• the streak canal is always open ish; smooth muscle constricted in between milking to close lumen; plugged during dry period; the streak canal is dilated up to 2 hours after milking (less likely to come into contact w bacteria)
• damaged teat skin and ends increases surface area, shields bacteria from disinfectant (harder to clean), and provides nutrients (blood) to the bacteria
• teat end scoring: rated 1-5; 4 and 5 indicated hyperkeratosis
• chemical defenses include: keratin/keratin plug, lactoferrin, lysozyme, and lactoperoxidase thiocyanate system
• chemical defense: streak canal contains keratin (protein w waxy substance); contains antimicrobial peptides (S100 calcium binding proteins causes disruption of membrane) and antimicrobial fatty acids; keratin plug acts as a sebaceous/waxy barrier
• chemical defense: lactoferrin- binds to iron in milk to reduce its availability to bacteria (bacteria need iron to grow); found in mammary secretions, neutrophil granules, and mammary epithelial cells
• lactoferrin: if iron is sequestered its availability to bacteria is reduced; subsequently limits bacteria growth
• lactoferrin is high in colostrum and non-lactating mammary gland secretions
• chemical defense: lysozyme- lysing enzyme, found in secretions (tears, saliva, milk, mucus, egg whites, immune cells); bacteria have a cell wall that gives shape to the prokaryote; get ride of cell wall, remove support of cell and the cell will lyse
• lysozyme mode of action: cleaves beta 1-4 linkages of N-acetylmuramic acid (NAM) and N-acetyl-D-glucosamine (NAG); more simply, cleaves bonds that form peptidoglycan (cell wall polysaccharide)
• chemical defense: lactoperoxidase thiocyanate-H2O2 system- enzyme system is activated in the presence of H2O2; bacteriostatic (limit growth) for gram-positive pathogens, bactericidal (cause death) for gram-negative pathogens
• H2O2 in the lactoperoxidase thiocyanate-H2O2 system comes from immune cells when cell # is high
• goal of the immune response: quick, effective response to completely eliminate the pathogen; after pathogen is cleared, the inflammatory cascade should cease; should this continue too long, tissue damage occurs
• during an IMI, immune cells are recruited to the gland; migrate from the blood, through the tissues, into gland lumen; number of cells in milk is regarded as the somatic cell count (SCC)
• SCC- how many body cells are present correlates to how many immune cells are present and responding to an IMI
• immune cells can be divided into being part of the innate or adaptive immune system
• innate is fast responding and nonspecific
• adaptive immune system is slow but highly specific to the type of pathogen (differentiates)
• innate immunity: fast to respond to first exposure, responds the same to each bacteria even if encountered before, assists in starting up adaptive immune system