22 terms

Chapter 23 - Part 2

Duodenum and jejunum of human intestine - acidic or basic?
Basic pH 8 - due to pancreatic secretions (pH 10) that enter intestine
Basicity of duodenum and jejunum
relieves acid stress for microbes
high pH and bile contents (allows growth of gram +ve cocci, enterococci, lactobacilli & diphtheroids)
How do microbes adapt to basicity?
they have bile salt hydrolase
Ileum and colon of human intestine - acidic or basic?
Acidic ph 5-7 due to lower concentrations of bile salts
more organisms can grow, mostly gram negative anaerobes, 10^9 - 10^11 per gram of feces
Example of bacteria in ileum/colon
Bacteroides thetaiotaomicron - gram negative, breaks down carbohydrates in feces - responsible for 15 - 20% of caloric intake
Can we culture organisms that grow in the intestine?
we identify them through culture independent technique known as ribotyping
Are all organisms in the intestine considered normal flora?
BUTTTT if they escape into nearby tissue they can cause diseases
Examples of microorganisms in the intestine
E. Coli, Bacteroides} Bacteroidetes
Clostridium} firmicutes
Candida albicans} fungi
Trichomonas hominis, Entamoeba hartmanni} protozoa
Explain E. coli's mutualism with the intestine
E. coli makes vitamin B12
other organisms digest complex foods
restore good microbe balance
Genitourinary tract : urethra
has many organisms because it is in such close proximity with the outside world - S. Epidermidis, Enterococcus

if these go up into the bladder they can cause UTI
Composition of vaginal microflora changes
with menstrual cycle (change of nutrients and pH)
pH of vagina
4.5 (acidic)
acid tolerant Lactobacillus acidophilus grows there
Antibiotic kills normal flora
leaves room for Candida albicans (yeast) to grow - not killed by antibiotics
Opportunistic pathogens
cause diseases in compromised host
How do commensal organisms enhance the function of our immune system?
Genetically engineered to produce proteins (from pathogenic species) on their cell surface. modified species elicit immune response. eg. S. Salivarius, Lactococcus/bacillus

Bacterial proteins eg. catalase act as immunoglobulins,
Function of immunoglobulins
modify the secretion of host proteins eg. cytokines and tumor necrosis factor TNF
Function of cytokines
binds to cells in the immune system and regulate extent and duration of responses by those cells
How do non-commensal organisms **** up our intestine?
gram negative non-commensal pathogens produce a protein called Enterotoxin
how does enterotoxin harm us?
they damage the intestine and causes diarrhea
twist to enterotoxin
may protect against colorectal cancer by activating calcium channels in intestinal epethelial cells

increase in membrane conductance for calcium turns on a pathway that provides resistance for colon cancer
Gnotobiotic animal
shows that the presence of normal flora challenges immune system and keeps it active
Gnotobiotic animal - germ free/all microbial species are known. These animals have poorly developed immune systems, low cardiac output, thin intestinal walls.