chapter 20 (module 7) Flashcards
20.1 The Gastrointestinal Tract and Its Defenses
long tube extending from mouth to anus, composed of eight main sections and augmented by four accessory organs
eight sections of gastro tract + other accessory components
mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus
salivary glands, liver, gallbladder, and pancreas add digestive fluids
intestinal surfaces and their antimicrobial components
lots of microorganisms, and new ones every day
- all intestinal surfaces are coated with a layer of mucus, which confers mechanical protection
- Secretory IgA can be found on MOST intestinal surfaces
peristalsis keeps things moving through intestinal tract (inc. microbes)
various fluids in the GI tract have antimicrobe properties
saliva contains lysozyme and lactoferrin
stomach fluid is antimicrobial by virtue and is extremely highly acidic
bile is also antimicrobial
GALT (gut associated lymphoid tissue)
-tonsils and adenoids in the oral cavity and pharynx, small areas of lymphoid tissue in the esophagus, Peyer’s patches in small intestine, and the appendix are all packets of lymphoid tissue consisting of T and B cells and cells of innate immunity
some normal biota cloak themselves with host sugars to avoid destruction
20.2 Normal Biota of the Gastrointestinal Tract
- large variety of normal biota
- oral cavity alone has more than 600 species including Actinomyces, Lactobacillus, Neisseria, Prevotella, Streptococcus, Treponema, Veillonella
- –> and fungi such as Candida albicans
- –> protozoa such as Trichomonas tenax, Entamoeba gingivalis
what are the biofilms on the teeth
dental plaque
what are generally the first colonizers of the tooth surface after they have been cleaned?
Alpha-hemolytic streptococci, they attach to the pellicle (a membranous cover that has proteins on it)
the large intestines has _________ if microbes, even some archaea species have been found
billions
the gut microbiome influences the _________ system
nervous
In the gut, E. coli synthesizes ___________
vitamin K
Oral defenses and biota
saliva, sIgA, lysozyme, tonsils, adenoids
Biota: hundreds of gram positive and gram negative bacteria, protozoa, and fungi
other GI tract defenses and biota
GALT, lymphoid tissue, Peyer’s patches, appendix, sIgA, normal biota
biota: thousands of microbes of all kinds, aerobic and anaerobic
stomach was previously thought to be sterile due to low pH, but has lots of biota
Accessory organs of GI tract biota
salivary glands, liver, gallbladder, pancreas
–>free of natural microbiome but can be exposed to microbes when normal barriers in the gut are disrupted by a condition broadly called dysbiosis
Dysbiosis: refers to an unhealthy mix of gut microbes in the intestinal tract
–> can result in leakage of bacteria or their metabolic products into internal organs
20.3 GI Tract Diseases Caused by Microorganisms (Nonhelminthic)
Highlight Disease: Acute Diarrhea
diarrhea is usually defined as:
three or more loose stools in a 24 hour period
more than ____________ infants die a year from diarrhea
700,000
diarrheal illnesses are often accompanied by:
fever, abdominal pain and/or cramping, nausea, vomiting, and dehydration
most common culprits of foodborne illness in US
Salmonella, norovirus, Campylobacter, E. coli, Staphylococcus aureus, and Clostridium perfringens
what are the three types of data used to link illnesses to contaminated foods and solve outbreaks?
Epidemiological data:
- patterns in where and when people got sick, and past outbreaks caused by the same microbe
- interviews with sick people to look for foods or other exposures occurring more often than expected
- discovery of clusters or unrelated sick people who ate at the same restaurant, shopped at the same grocery store, or attended same event
Traceback data
- common point of contamination in distribution chain from farm to fork, found by looking into records collected
- inspections in food production facilities, or farms, and in restaurants that identify food safety risks
Food and Environment Testing Data
- the microbe that caused illness is found in a food item collected from a sick person’s home, from a retail location, or in the food production environment
- the same DNA fingerprint linking microbes found in foods or production environment to microbes is found in sick people
antimicrobials are contraindicated in most diarrheal illnesses, but in some, such as in ____________, it is a quick call for antibiotics
shigellosis
Salmonella species characteristics
motile, ferment glucose with acid and sometimes gas
- most produce hydrogen sulfide but not urease
- grow readily on most lab media and can survive outside the host in inhospitable environments such as freshwater and freezing temperatures
- resistant to bile and dyes (which are basis for isolation on selective media)
outbreaks linked to:
small pet turtles, cut fruit, ground beef, ear dog treats, frozen raw tuna, pre-cut melon, pet hedgehogs, papayas, etc.
Salmonella S/S
typhoid fever until recently was most severe manifestation
more recently a milder disease called salmonellosis has been more common, sometimes it is called enteric fever or gastroenteritis
-typhoid fever is caused by the Typhi serotype, gastroenteritises are generally caused by the serotypes known as Typhimurium, Enteritidis, Heidelberg, Newport, and Javiana
–> salmonella bacteria are normal intestinal biota in cattle, poultry, rodents, and reptiles, AND each has been a documented source of infection an disease in humans
can be relatively severe with an elevated body temperature and septicemia as more PROMINENT features than GI tract disturbance
-can also be mild with gastroenteritis, with vomiting, diarrhea, mucosal irritation as its major feature (blood can appear in the stool)
salmonella V Factors
ability to adhere to gut mucosa, evade the immune system
ENDOTOXIN LPS in gram neg bacteria
ID: 50 cells
prevention and tx
avoid contact with bacterium
uncomplicated cases treated with fluid and electrolyte replacement
if patient has underlying immunocompromise or if disease is severe, CIPROFLAXACIN is recommended
Shigella
do not produce urease or hydrogen sulfide
nonmotile, non endospore forming
resemble some types of pathogenic E. coli very closely
Shigella S/S
frequent watery stools, fever, intense abdominal pain
-nausea/vomiting
-blood in stool, and occult blood
diarrhea containing blood is called dysentery
-mucus from GI tract
shigella differs from other GI tract infections in that it invades the villus cells of the______ intestine rather than _______ intestine. and it is not as invasive as salmonella
large
small
Shiga toxin
produced by Shigella dysentery (and some other species); heat labile exotoxin
-seems to be responsible for the more serious damage to the intestine as well as any systemic effects, including injury to nerve cells
trans and epi of Shigella
oral route, direct person-to-person contact, largely b/c of small ID (10-200 bacteria)
mostly associated with lax sanitation, malnutrition, and overcrowding
-spreads epidemically in day cares, nursing homes, military camps, mental institutions
Shiga-Toxin-Producing E. coli (STEC)
S/S
agent of a spectrum of conditions, ranging from mild gastroenteritis with fever to bloody diarrhea
–> minority of patients will develop hemolytic uremic syndrome (HUS), a severe hemolytic anemia that can cause kidney damage and failure
-neurologic sx such as blindness, seizure, stroke, and long-term debilitation are possible
STEC V Factors
Shiga toxins,, are present on prophage genes donated by bacteriophage in E. coli but are on the chromosome of Shigella dysentery, suggesting that E. coli acquired the virulence factor through phage mediated transfer (transduction)
shiga toxin disrupts protein synthesis in target cells
- another V factor: the ability of STEC to efface (rub out or destroy) enterocytes (creates lesion in the gut, usually in large intestine)
- microvilli are lost from the gut epithelium and the lesions produce blood diarrhea
STEC trans and epi
ingestion of contaminated foodstuffs
STEC culture and dx
stool culture
test for shiga toxin
STEC px and tx
good food hygiene
shiga toxin is heat labile and E.coli is killed by heat aa well
antibiotics may be contraindicated due to that they may release more toxin
supportive therapy, plasma transfusion to dilute toxin in blood
other types of E. coli that can cause diarrheal diseases
Enterotoxigenic E. coli (ETEC) Enteroinvasive E. coli (EIEC) Enteropathogenic E. coli (EPEC) (pathogenic to the alimentary canal) Diffusely Adherent E. coli (DAEC) Enteroaggregate E. coli (EAEC)
Campylobacter
one of most common bacterial causes of diarrhea in US, especially Campylobacter jejuni
S/S: frequent watery stools, fever, vomiting, headaches, and abdominal pain
propelled by polar flagella at one or both poles
tend to be microaerophilic
Trans: ingestion of contaminated food or beverage, especially water, milk, chicken, and meat
V Factors: heatlabile enterotoxin, adherence and multiplication in mucus
Infection can lead to Guillain Barre syndrome, (most common precipitating event for onset of GBS)
C. difficile
G+, endospore forming rod
causes condition called pseudomembranous colitis (antibiotic-associated colitis) –> precipitated by therapy with broadspectrum antibiotics (ampicillin, clindamycin, etc.)
-produces Enterotoxins A and B and they cause areas of necrosis in the intestinal walls
more severe cases show: abdominal cramping, fever, leukocytosis
-colon is inflamed and gradually sloughs off loose, membranelike patches called pseudo membranes consisting of fibrin and cells
- in MILD cases of C. diff: metronidazole should be administered
- if more SEVERE vancomycin is choice
–> fecal implants or stool transplantation from healthy donors has been a success
Vibrio cholerae
single polar flagellum
- slightly resemble a comma
- fermentative and grow on ordinary or selective media containing bile at 37 C
- possess unique O and H antigens and membrane receptor antigens
- two major types: classic and El Tor
Vibrio cholerae S/S
inc period of few hours to a few days
-abrupt symptoms of vomiting, copious amounts of watery feces called secretory diarrhea
-intestinal contents are lost very quickly leaving only secreted fluids
so voided fluid contains flecks of mucus hence “rice-water stool”
causes loss of blood volume, acidosis from bicarbonate loss, potassium depletion which manifests as muscle cramps, severe thirst, flaccid skin, sunken eyes, and in young children coma and convulsions
secondary circulatory consequences include hypotension, tachycardia, cyanosis, collapse from shock within 18-24 hours
**if left untreated death can occur in less than 48 hours, and mortality rate is between 55% and 70%
V. cholerae V factor and trans and epi
enterotoxin : cholera toxin (CT)
cold, acidic, dry environments inhibit the migration and survival of Vibrio,
–>whereas warm, monsoon, alkaline, and saline conditions favor them
in nonendemic areas it is spread by water and food contaminated by asymptomatic carriers, but is relatively uncommon
V. cholerae tx and px
proper sewage tx and water purification
-vaccines are available for travelers and people living in endemic regions
prompt replacement of water and lytes rehydration techniques (ie. ORT is very effective
WHO solution consists of a solution of sodium chloride, sodium bicarbonate, potassium chloride, glucose or sucrose dissolved in water and can bring people back from brink of death (GREAT b/c does not require clean needles)
doxycycline in developed countries
Non Cholera Vibrio Species
vibrioses, and two most prominent species are:
- V. vulnificus
- V. parahaemolyticus
infection can be from exposure to sea water but more often is associated with eating contaminated shellfish
scientists suspect the increase in cases is due to:
- increased demand for raw oysters
- increased awareness, meaning more people are diagnoses
- climate change causing a wider habitat for bacteria in bodies of water
in people who are immunocompromised, the infections can be fatal, especially with V. vulnificus
Cryptosporidium
intestinal protozoan of the apicomplexan type
zoonosis
- humans accidentally ingest oocytes with water or food that has been contaminated by feces from infected animals
- oocytes are highly infectious and extremely resistant to disinfectants
cryptosporidium S/S + culture/dx
headache, sweating, vomiting, severe abdominal cramps, and diarrhea
-AIDS patients may experience chronic persistent cryptosporidal diarrhea which can be a criterion to help dx aids
agent can be detected in fecal samples or in biopsies using ELISA or acid-fast staining
—>stool cultures should be performed to rule our bacterial causes on infection
*many diarrheal outbreaks are assoicated with
Rotavirus
consists of an unusual double-stranded RNA genome with both an inner and outer capsid; resembles a spoked wheel
-globally rotavirus the is the primary viral cause of morbidity and mortality resulting from diarrhea, accounting for nearly 50% of all cases
- ->rotavirus vaccine
- ->transmitted by fecal-oral route, including through contaminated water, food, and fomites (for this reason the disease is most common in areas of world with poor sanitation)
- ->babies from 6-24 months old are at greatest risk
S/S: watery diarrhea vomiting dehydration shock intestinal mucosa can be chronically compromised
Norovirus
second most common cause of hospitalizations from foodborne disease in the US, cruise ships are a common place for norovirus outbreak
noroviruses can cause about five times as much foodborne illness as Salmonella
Trans: fecal-oral route via contamination of food and water
-viruses generally cause a profuse, watery diarrhea lasting 3-5 days, mild fever is often seen
Tx: focuses on rehydration
