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8 - Food Poisoning and E. Coli
Terms in this set (53)
What is a very general explanation of food poisoning? What type of bacteria is it generally caused by?
a mixed bag of disorders centering around the foods we consume
- most are gram negative bacteria
What are the 2 variations of food poisoning?
1. Intoxication: ingestion of preformed toxin of microbial origin (mycotoxins-fungal, botulism-toxin); not ingesting the actual bacteria, just toxin it produces
2. Infection: ingestion of and the colonization of the GI tract with an organism (virus, bacteria, protozoa)
fungal poison (mycotoxin), produced by the mold Aspergillus flavus, which grows on nuts, grains and peanuts that are store improperly
Characteristics of food poisoning
- colonization of GI tract with microorganism
- infection usually occurs in the small and/or large intestine, but other organs can also be involved
What are the local and systematic signs of food poisoning?
local: vomiting, diarrhea, abdominal pain, lack of appetite
systematic: fever, nausea, lymphadenopathy (swollen lymph nodes-salmonella), kidney dysfunction (HUS), infects other organs
- stays in GI tract, but produces toxins that cause vasculitis
What is HUS?
Hemolytic uremic syndrome (HUS) is a condition that can occur when the small blood vessels in your kidneys become damaged and inflamed
What is the most common cause of bacterial disease in the US?
Physical and chemical characteristics of salmonella
- gram negative rods
- facultative anaerobic: doesn't need oxygen for growth, but if oxygen is present it doesn't hurt
How is salmonella named?
2 main ways:
1. Kauffman-White: subdivide into groups based on O-antigen (surface antigens) and further divide into serotypes based on H-antigens (flagellum antigens)
2. 3 species:
a. salmonella thyphi
b. Salmonella cholerasuis
c. Salmonella enterica (2000+ serotypes)
ex. Salmonella enterical serovar equis ( horses )
What is the primary reservoir of salmonella?
intestinal tract of many animals including birds, farm animals, reptiles, and humans
- found in almost all species
What are the 3 forms of salmonella disease?
1. Enteric Fevers (typhoid)
2. Salmonella septicemia
What is generally present with Enteric Fever (typhoid)?
S. typhi bacteria (only found in human species; not common in US)
- inflammation of small intestine with invasion of regional lymph nodes
- invades mononuclear cells(macrophages) = enters blood and infects other organs (liver, spleen, gall bladder)
What are some clinical signs of Enteric Fever (typhoid)?
- abdominal pain
- prolonged fever
- spleen enlargement
- affects skin=rose spots on abdomen
Incubation period of Enteric Fever (typhoid)?
- 1-3 weeks
- longer b/c life cycle
Why do people that take medication to reduce stomach acid have a higher chance of being infected with Enteric Fever (typhoid)?
S. typhi bacteria is negatively affected by stomach acid
- if a person has a decreased level of stomach acid = more likely to be infected
How is Enteric Fever (typhoid) diagnosed?
by a positive culture of fecal sample
- GI bacteria and S. typhi bacteria are both facultative anaerobes so they have to test using selective media
selective media: suppress growth of GI bacteria = allows only salmonella to grow in culture = allows identification
How is Enteric Fever (typhoid) treated?
Most don't need tx (except young and old)
- chloramphenicol (2+ weeks b/c bacteria enters blood = ensure it is all killed)
What happens if someone with Enteric Fever (typhoid) doesn't take their medication for 2+ weeks?
- bacteria doesn't get fully killed
- allows convalescent patients to become carriers and spread it to others (Typhoid Mary)
How can Enteric Fever (typhoid) be controlled?
since it only has a human-only reservoir, break oral-fecal contamination
What two vaccines for Enteric Fever (typhoid) are being studied? Are there any available?
2. oral subunit vaccine
1. killed vaccine- not very effective
What is salmonella septicemia and what is it caused by?
- it is a blood infection not involving the GI tract
- commonly caused by S. cholerasuis (non-host adapted, found in iguanas/turtles)
What are some clinical signs of salmonella septicemia?
- suppurative lesions throughout the body
- possible pneumonia
- multiple organ infection
What are ways to treat salmonella septicemia?
chloramphenicol (2+ weeks)
What is enterocolitis?
- most common presentation of salmonella
- inflammation of the mucosa of the small and large intestine caused by salmonella
- organism remains in gut
- almost all serotypes can cause it
What is the incubation period of enterocolitis?
- short/no macrophage infection
How is enterocolitis diagnosed? Treatment?
RBCs and WBCs and blood in stool
- just supportive care
What is campylobacter and what is it caused by?
- 2nd most common cause of food poisoning in US (2.4 mill)
- gram negative, curved rod possessing a single polar flagella
How is campylobacter acquired?
- most frequently acquired through undercooked poultry ; found in GI tracts of many wild and domestic animal (can also infect eggs)
What is the most common type of campylobacter most associated with human disease?
(95% of human cases out of the 6 different forms)
"Farm days" for school children
What is the incubation period of campylobacter and what does it produce?
- produces an enterotoxin that results in a hyper-secretory state in enterocytes (gut epithelial cells)
(causes watery diarrhea)
What are the clinical signs of campylobacter infection?
severe diarrhea with blood and WBCs in stool
- abdominal pain
- bacteremia that causes vessel necrosis = vasculitis
- some actually have delayed associations with Guillane Barre syndrome
How is campylobacter treated?
- gentamicin (severe-suppresses protein synthesis)
- erythromycin (blocks protein synthesis)
How is campylobacter diagnosed? How can it be controlled?
- fecal culture sample
- sanitation (from slaughter to consumption)
- proper hygiene after handling pets
What is Shigella? How is it most commonly spread?
3rd most common bacterial cause of diarrhea in the US
- gram negative rid which is similar to E. coli (used to be considered subspecies)
- most commonly spread. human to human, but food-borne epidemics can occur (human-only)
What disease does shigella cause? What is the incubation period?
- stays in GI tract and doesn't infect macrophages
IP: 2-5 days
How does shigella move through our body? What does the stool look like?
1. invades gut epithelial cells
2. multiply within the cells
3. produce the exotoxin Shiga toxin (binds to host cells ribosomes and blocks protein synthesis = cell death)
- gross, mucousy stool
What are the clinical signs of Shigella?
- massive fluid and electrolyte loss via GI tract
- abdominal pain
- ulceration of the colon wall
- death usually due to dehydration
How is shigella diagnosed?
selective culture of fecal matter
- can be difficult to isolate (facultative anaerobe similar to cells in GI tract)
How is Shigella treated?
- fluid replacement therapy (IV fluids)
- antibiotic : sulfa-trimethoprim may be effective in non-endemic areas
(multiple antibiotic resistance is common especially in endemic areas)
Who are the most at risk for shigella infection? Why?
Young children and elderly
- less adipose tissue that aids in fluid storage
How can shigella be controlled?
- improved sanitation (human are only reservoirs so we shouldn't be seeing so many cases b/c it is easy to control)
- vaccines are worthless (esp. killed; live provide little benefit)
What type of "bug" is E. coli?
- large family of gram negative rods that are NORMAL inhabitants of GI tract (lower ileum and large intestine)
- certain serotypes are associated with diarrheal disease and septicemia in humans and animals
How is E. coli named?
based on surface antigens
1. O-antigens: based on the repeated sugar component of LPS
2. H-antigen: based on antigens found in the flagellum
3. presence of capsule
How can E.coli be benficial?
- prevents infection of other bacteria b/c of sheer # we have in our gut
How are strains of virulent E. coli classified? Which classification is most clinically important in US?
classified based on virulence properties (6 pathogenic forms)
- Enterohemorrhagic (EHEC): produce Shiga toxin (causes cell death and can get into circulatory system = vasculitis)
How is Enterohemorrhagic E. coli (EHEC) transmitted?
- undercooked ground beef
- unpasteurized milk and juice
- contaminated water
- person to person contact in daycares
(petting zoos, onions, alfalfa sprouts, lettuce)
What are the clinical signs of Enterohemorrhagic E. coli (EHEC)? Most common serotype?
- bloody diarrhea
- abdominal cramps
- little to no fever
Most common: O157:H7
What does E. Coli (O157:H7) cause?
- human diarrhea
- hemorrhagic colitis
- rarely hemolytic uremic syndrome (HUS) - 5-7% of cases
What are some clinical signs of E.coli O157:H7?
- usual EHEC signs
- acquired non-immune hemolytic anemia
- acute renal failure (could result in dialysis)
Epidemiology of E. coli O157:H7
- zoonotic infection (1/3 domestic ruminants are asymptomatic carriers and are the principal reservoir for human infections
- In US, cases increased from 1993 and peaked in 2000 (due to restaurant chains spreading)
- low numbers need for infection (10-200 organisms)
What are ways to treat E. coli O157:H7?
- antibiotics? (increases risk of HUS)
- transfusions to treat anemia (DIC is possible, replace clotting factors)
- hydration therapy
- dialysis for HUS (hopefully temporary)
How is E. coli O157:H7 diagnosed?
- culture with typing -- slow
- pulsed field gel-electrophoresis (newer)
- real time PCR to detect toxin genes (preferred- fast)
How can E. coli O157:H7 be controlled?
- sanitation (slaughter to consumption)
- properly cooking meat
- avoiding unpasteruized milk and juices
- for neonates= not consuming alfalfa sprouts
- proper water sanitation
- vaccine for ruminants? - so humans are less likely to get it
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