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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.

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