Micro Chapter 20 (Exam 4)

gastrointestinal tract

GI tract, digestive tract, enteric tract
a long tube, extending from mouth to anus

8 main sections of the GI tract

1) mouth
2) pharynx
3) esophagus
4) stomach
5) small intestine
6) large intestine
7) rectum
8) anus

4 accessory organs of the GI tract

1) salivary glands
2) liver
3) gallbladder
4) pancreas

what is the role of the 4 accessory organs in the GI tract?

add digestive fluids & enzymes to assist in digestion & processing food

The GI tract contains minimal microorganisms.

a. true
b. false

b
encounters a tremendous amount of microorganisms & encounters millions of new ones each day

GI tract microbial defenses

mucus
secretory IgA (antibody- mucous membranes)
peristalsis (keeps food & microorganisms moving through the tract)
saliva (contains lysozyme & lactoferrin)
stomach fluid (highly acidic)
bile (antimicrobial)

how much of the immune system is located in the intestinal tract?

70%

gut-associated lymphoid tissue (GALT)

lymph nodes
Peyer's patches

lymph nodes

centers where waste is taken (higher number of immune cells)

Peyer's patches

actively allow microbes to cross out of intestines & into body for cells to test & address

other gastrointestinal organs

tonsils & adenoids (in the oral cavity & pharynx)
lymphoid tissue in the esophagus
appendix

oral cavity normal microbiota

>600 known species of microorganisms including bacteria, fungi, & protozoa
dental plaque

dental plaque

synergistic community of bacteria on teeth; a type of biofilm (detrimental if allowed to get too large)

stomach normal microbiota

previously thought sterile due to very low pH
evidence for around 128 different species of microbes found

large intestine normal microbiota

haven for billions of microbes (bacteria, fungi, protozoa, even archaea)
10^11 microbes per gram of contents

function of normal microbiota in the gastrointestinal tract

provides protection
helps with digestion
provides nutrients that we cannot provide ourselves (E. coli synthesizes vitamin K)
"teaches" the immune system to react to microbial antigens
composition can influence host's chances for obesity or autoimmune disease

2 types of digestive system diseases (generally)

1) infections
2) intoxications

infections

pathogens enter GI tract & multiply
typically delay in GI disturbance as bacteria grow
fever is common

intoxications

ingestion of preformed toxin
sudden symptoms & GI disturbance
fever not as common
(living microbes that died & became toxins)

dysentery

severe diarrhea containing blood and/or mucous

gastroenteritis

inflammation of the stomach & intestinal mucosa

acute diarrhea

3 or more loose stools in a 24-hr period
often accompanied by fever, abdominal pain, cramping, nausea, vomiting, dehydration

how common is acute diarrhea in the U.S.?

1.2 to 1.9 cases per person per year
rate doubles in children

how common is acute diarrhea in developing countries?

>10 episodes per year for children
too many bouts of diarrhea in young children can cause permanent physical & cognitive defects
more than 700,000 infants a year die from diarrhea (bc of the malnutrition & dehydration it causes)

what is most acute diarrhea caused by in the U.S.?

around 1/3 of cases are due to contaminated food

acute diarrhea from contaminated food

around 48 million people are sickened each year, 3,000 die
most cases are self-limiting & do not require treatment
antibiotic treatment typically avoided, but quick treatment with antibiotics is sometimes necessary (shigellosis)
most cases identification of the cause is not performed

Salmonella

very large genus of bacteria
normal intestinal biota in cattle, poultry, rodents, & reptiles (sometimes humans)
survives outside the host in inhospitable environments (raw meat)

Salmonellosis

caused by Salmonella enterica (bacteria)

symptoms of severe Salmonellosis

elevated body temps & septicemia
death is infrequent, except in debilitated patients

symptoms of mild Salmonellosis

vomiting, diarrhea, & mucosal irritation
blood can appear in the stool
(gastroenteritis type of symptoms)
subsides within 2 to 5 days

ID50

infectious dose
measurement of how many organisms must be ingested to cause disease

high ID50

a lot of organisms must be ingested for disease to result

transmission of Salmonellosis

high ID50
animal products (meat & milk) - contaminated during slaughter, collection, & processing

Salmonellosis treatment

fluid & electrolyte replacement for mild cases

Shigella

(bacteria) primarily human parasites, but can infect apes
invades cells of the large intestine & initiates an inflammatory response that causes extensive tissue destruction

Shigellosis signs & symptoms

frequent watery stools, fever, intense abdominal pain
nausea & vomiting are common
dysentery (occult blood)

occult blood

not visible to the naked eye

notable Shigella toxins

endotoxin
enterotoxin (exotoxin)
shiga toxin

endotoxin

causes fever

enterotoxin (exotoxin)

affects GI tract, damages the mucosa & villi

shiga toxin

responsible for serious damage to intestine & systemic effects

Shigellosis transmission

orally & through direct person-to-person contact
small ID50 (10-200 bacteria)
associated with lax sanitation, malnutrition, & crowding
spread in day care centers, prisons, mental institutions, nursing homes, military camps
some people may become chronic carriers for several months

Shigellosis treatment

fluid & electrolyte replacement for mild cases

virulence of shiga-toxin-producing E. coli (STEC)

due to shiga toxin
identical exotoxin as in Shigella species
toxin genes due to prophage (integrated bacteriophage)
destroys cells in the large intestine, resulting in bloody diarrhea
confirm infection with stool culture & test for shiga toxin (positive specimens sent to state or local health departments for characterization & outbreak monitoring)

transmission of shiga-toxin-producing E. coli (STEC)

ingestion of contaminated or undercooked food (most often beef)

STEC treatment

antibiotics are contraindicated; may increase pathology by releasing more toxin
supportive therapy (ex: plasma transfusions to dilute toxin) is a good option

5 other categories of E. coli that can cause diarrheal diseases

1) enterotoxigenic E. coli (ETEC)
2) enteroinvasive E. coli (EIEC)
3) enteropathogenic E. coli (EPEC)
4) diffusely adherent E. coli (DAEC)
5) enteroaggregative E. coli (EAEC)

Campylobacter jejuni

(bacteria) most common cause of diarrhea in the U.S.
inhabits intestinal tract, genitourinary tract, and oral cavity of humans & animals

Campylobacter transmission

ingestion of contaminated beverages & food (water, milk, chicken, other meat)

where does C. jejuni inhabit the human body?

last segment of the small intestine near its junction with the colon

Campylobacter signs & symptoms

frequent watery stools, fever, vomiting, headaches, abdominal pain (enterotoxin causes diarrhea similar to cholera)
may last longer than 2 weeks (may subside & recur over a 2-week span)

Guillain-Barre syndrome (GBS)

20-40% of cases caused by Campylobacter infection
rare, serious neuromuscular paralysis

Campylobacter treatment

rehydration & electrolyte balance therapy

Clostridioides difficile

gram-positive, endospore-forming anaerobe (what makes it really bad - dormant, spore-protected)
normal biota of the intestine

pseudomembranous colitis

caused by Clostridioides difficile
colon is inflamed & gradually sloughs off membranelike patches called pseudomembranes

what triggers pseudomembranous colitis?

therapy with broad-spectrum antibiotics
able to infect the large intestine when drugs have disrupted the normal biota

severe pseudomembranous colitis

abdominal cramps, fever, & leukocytosis
if disease is not stopped, perforation of the cecum & death can result
difficult to eradicate; stubborn infections decrease patient's quality of life

transmission of C. difficile

66% are healthcare associated
C. diff releases endospores, which contaminate the environment
hospital patients must be put in isolation conditions & constant attention to disinfection & infection control is required
(there can be a delay in infection due to the nature of dormant endospores; highly resistant)

Vibrio cholerae

slightly curved, gram-negative rod with single flagellum
produces cholera toxin

Vibrio cholerae transmission

associated with salty water (high ID50 - have to drink a ton of them)

cholera toxin

causes the host cells to secrete electrolytes & water
causes "rice water stools"
can lose 12-20 liters of fluid per day (causes shock, collapse, organ failure, & death)

Vibrio cholerae treatment

IV fluid replacement

2 prominent non-cholera Vibrio species in the U.S.

1) V. vulnificus
2) V. parahaemolyticus

non-cholera Vibrio infections

can be from exposure to sea-water; more often associated with eating contaminated shellfish
can be fatal if immunocompromised
nationally notifiable diseases (along with V. cholerae)

Cryptosporidium

intestinal protozoan that infects a variety of mammals, birds, & reptiles
invade intestinal epithelium

Cryptosporidium transmission

drinking water or food contaminated by feces from infected animals (causes half of the outbreaks of diarrhea from swimming pools)

Cryptosporidium symptoms

mimic other types of gastroenteritis: headache, sweating, vomiting, severe abdominal cramps, diarrhea

Cryptosporidium treatment

not usually required for otherwise healthy patients

viral gastroenteritis

90% caused by rotavirus or norovirus
one of the most common diseases in humans

rotavirus

common in children; low mortality
2-3 day incubation; low-grade fever, diarrhea, vomiting
prevented with a live oral vaccine

norovirus

fecal-oral transmission
low ID50
18-48 hr incubation
diarrhea & vomiting

food poisoning

severe nausea & frequent vomiting accompanied by diarrhea
others sharing meal have same symptoms
onset within 1-6 hrs

what bacteria cause symptoms in the gut that are caused by a performed toxin of some sort?

Staphylococcus aureus
Bacillus cereus
Clostridium perfringens

intoxication

can be caused by fish, shellfish, or mushrooms
symptoms are violent
incubation time is short

Staphylococcus aureus exotoxin

toxins produced when the organism is allowed to incubate in food at room temperature
ingested toxin acts on the gastrointestinal epithelium
stimulates nerves - causes symptoms of cramping, nausea, vomiting, & diarrhea
recovery is rapid, usually within 24 hr

Clostridium perfringens

forms endospores, produces an exotoxin
acute abdominal pain, diarrhea, & nausea in 8-16 hrs

Bacillus cereus

forms endospores - spores survive heating, germinate, & produce toxins
diarrheal-type disease or emetic (vomiting) disease

chronic diarrhea

lasting longer than 14 days
can have infections causes or can reflect noninfectious conditions

irritable bowel syndrome (IBS) and ulcerative colitis

not caused by a microorganism
increasing evidence that a chronically disrupted intestinal biota can contribute to these conditions

AIDs patients & chronic diarrhea

caused by opportunistic microorganisms
(HIV status should be considered if a patient presents with chronic diarrhea)

Cyclospora cayetanensis

protozoan
has become very common since 1990

Cyclospora transmission

fecal-oral
most cases associated with consumption of fresh produce & water contaminated with feces
not spread from person to person

Giardia duodenalis

flagellated protozoan
typically transmitted in contaminated water
attaches to the intestinal wall

Giardia duodenalis symptoms

prolonged diarrhea, abdominal pain, flatulence
stools have a greasy, foul-smelling quality

dental caries

caused by Streptococcus mutans (& others)
tooth decay
dental plaque is the biofilm involved in the formation of these
involves the dissolution of solid tooth surface due to the metabolic action of bacteria
penetrate from enamel into dentin, can reach pulp (contains blood supply & nerve cells)

how many species of bacteria are in the oral cavity?

700

Streptococcus mutans

an important cariogenic organism
gram-positive coccus
converts sucrose to lactic acid (breaks down the bone)
produces sticky polysaccharides that contribute to biofilm formation

gingivitis

inflammation & infection of the gums

periodontitis

bone & tissue supporting the teeth are destroyed

calculus

hard, porous substance produced above & below gingival margin; induces varying degrees of periodontal damage

mumps virus

targets the parotid salivary glands
most infections are self-limiting with complete, uncomplicated recovery & permanent immunity

mumps symptoms

fever, nasal discharge, muscle pain, malaise
painful swelling may occur 16-18 days after exposure (parotitis)

mumps transmission

salivary & respiratory secretions
(guys - infection can spread to reproductive organs)

mumps treatment

symptomatic - fever, dehydration, & pain relief
prevented with MMR vaccine

Helicobacter peptic ulcer disease

caused by Helicobacter pylori
infects 30-50% of the population in the developed world
grows in the stomach acid by producing urease (converts urea to alkaline ammonia)
disrupts stomach mucosa, causing inflammation

hepatitis

inflammatory disease marked by necrosis of hepatocytes & an inflammatory response that swells & disrupts the liver architecture

jaundice

yellow tinge in the skin & eyes caused by bilirubin accumulation in the blood & tissues

hepatitis can be caused by...

...Cytomegalovirus, Epstein-Barr virus, GBV-C, hepatitis viruses A-E
noninfectious conditions: autoimmune diseases, drugs, alcohol abuse

hepatitis C virus

parenteral (puncture through skin) transmission; often blood transfusions
destroys the liver by using genetic variation to evade to immune response
kills more in the U.S. than AIDS
85% of cases become chronic
25% develop liver cirrhosis or cancer
treatment but no vaccine

gastrointestinal tract diseases caused by helminths

amazingly diverse (very small or very large)
usually accompanied by an additional set of symptoms that arise from the host response to the helminth