GI Gram Neg

Question 1

Which bugs commonly infect the billiary tract from the large intestine? (3)

Answer 1

E coli, Bacteroides fragilis, and Clostridium spp

Question 2

Bacterial overgrowth syndrome

Answer 2

Overgrowth of normal microbiota from large intestine invading the small intestine.

Question 3

Which pathogens can adhere to the mucosa of the small intestine? (3)

Answer 3

V. cholerae, E coli, and Clostridium perfringens

Question 4

Which bugs are first colonizers of large intestine in newborns?
What is added w/ breast feeding?
What comes to replace most of these?

Answer 4

1st: E coli and Strep. Create anaerobic environment.
These may be replaced by Bifidobacterium (anaerobic gram pos rod) in babies who are breast-fed.
Next comes Bacteroides (gram neg obligate anaerobe) in very high numbers.

Question 5

Characteristics of diarrhea

Answer 5

Frequent stools. Usually painless w/o fever.

Question 6

Characteristics of dysentery

Mediated by what?

Answer 6

Pus / blood in stool. Usually painful (cramps, tenesmus) w/ fever.
Cytotoxins may cause tissue destruction in large intestine.

Question 7

Where are Peyer’s Patches found?

Answer 7

Ileum

Question 8

Enteric fever

Answer 8

Systemic infection (bacteremia) originating in GI tract. Ex: typhoid fever

Question 9

What 2 things are found in breast milk that aid in immune defense for infants?

Answer 9

IgA and lactoferrin

Question 10

3 examples of obligate human pathogens

Mode of transmission?

Answer 10

S. typhi, Shigella, Helicobacter pylori

Fecal / oral transmission

Question 11

4 examples of zoonotic pathogens (3).

Where are they found?

Answer 11

• E coli – ground beef, EHEC
• Non-typhoid Salmonella – Poultry, eggs, pet reptiles
• Campylobacter – poultry, milk
• Infected humans can also be source via fecal / oral

Question 12

Preformed Toxin
Site
Clinical features
Examples (2)

Answer 12

Small bowel
Severe NVD
Staph aureus and Bacillus cereus

Question 13

Secretory Toxin
Site
Clinical features
Examples (2)

Answer 13

Small bowel
Profuse water diarrhea, painless, usually no fever.
ETEC and V cholerae

Question 14

Cytotoxin
Site
Clinical features
Examples (2)

Answer 14

Large bowel
Bloody diarrhea, painful cramps, fever
EHEC and some Shigella

Question 15

Mucosal colonization / destruction
Site
Clinical features
Examples (3)

Answer 15

Small bowel
NVD, fever
EPEC, Salmonella, and Campylobacter (early)

Question 16

Deep invasion
Site
Clinical features
Examples (3)

Answer 16

Large bowel
Purulent bloody dysentery, painful cramps, fever
EIEC, Shigella, and Campylobacter (late)

Question 17

Systemic dissemination
Site
Clinical features
Examples

Answer 17

GI –> blood –> liver –> back to GI
Enteric fever
Salmonella typhi

Question 18

4 most common causes of bacterial enteric disease

Answer 18

1) Campylobacter (50%)
2) Salmonella (25-30%)
3) Shigella (15%)
4) E coli (5%)

Question 19

E coli transmission

Answer 19

Fecal / oral or contaminated foods (meats, fruits, vegetables).

Question 20

ETEC
Name
Disease
Transmission
Virulence factors
Sxs
Similar to which other bacterium?

Answer 20

Enterotoxigenic.
“Traveler’s diarrhea” for 3-4 days.
Mainly passed from person-to-person.
Virulence factors - plasmid-mediated secretory toxins (heat-stable ST or heat-labile LT) that cause increased cAMP → increased secretion by enterocytes.
Watery diarrhea, cramps, nausea, low fever. Similar to Vibrio cholerae.

Question 21

EPEC
Name
Site of infection
Sxs
Transmission
Similar to which other bacterium?

Answer 21

Enteropathogenic.
Colonization / destruction of mucosa of small intestine.
Causes infantile diarrhea, gastroenteritis, fever, NVD, non-bloody mucus filled stools.
Mainly passed person-to-person.
Similar to non-typhoid Salmonella.

Question 22

EHEC
Name / number
Inoculum
Transmission (specific foods)
Population
Sxs
Mediated by?
Similar to what other bacterium?
What is contraindicated?
Tx

Answer 22

Enterohemorrhagic.
Especially caused by O157:H7.
Small inoculum required (1-100 bugs).
Transmitted via cow intestines or infected humans. May also be caused by alfalfa sprouts, unpasteurized milk, cheese, or cider.
Most often affecting kids in warm months.
Causes severe cramps, hemorrhagic colitis, HUS, and thrombocytopenic purpura (TPP).
Absence of bloody stools does not rule out EHEC.
Mediated by cytotoxins (verotoxin and Shiga-like toxin, which are used for diagnosis) which inhibits protein synthesis → cell death.
Similar to Shigella.
Do NOT use AB’s –> lysis / toxin release
Tx w/ fluids

Question 23

HUS
Name
Cause / mechanism
Sxs
Population

Answer 23

Hemolytic uremia syndrome.
Mainly associated w/ EHEC, but also some Shigella.
E coli cytotoxins (verotoxin and Shiga-like toxin) produced in intestinal lumen enters blood circulation → systemic disease. Toxins cause inflammation, thrombosis, attach to endothelial cells, inhibit protein synthesis, and induce apoptosis.
May cause thrombotic microangiopathy, hemolytic anemia, and thrombocytopenia w/ renal lesions / failure.
Rare, but highest risk in kids and elderly.

Question 24

EIEC
Name
Mechanism
Sxs
Similar to what other bacterium?

Answer 24

Enteroinvasive.
Plasmid-mediated deep invasion of large intesetinal mucosa causes bacillary dysentery (blood and pus in poop).
Causes fever, cramps, watery diarrhea, and dysentery.
Similar to Shigella.

Question 25

Inoculum for Salmonella | Population

Answer 25

Large inoculum due to being sensitive to acid. | Most common in children during warm months.

Question 26

``` Salmonella typhi Reservoir Transmission Virulence factors Enteric Fever mechanism / sxs Other causes of enteric fever Timing for lab cultures 2 types of vaccines ```

Answer 26

•Obligate human pathogen. •Transmission – Human-human transmission via fecal / oral route (food handlers or contaminated water). •Virulence factors – endotoxin and Vi polysaccharide capsule •Enteric fever – systemic dissemination. Bugs enter through Peyer’s Patches → macrophages → lymphatics → bacteremia → replicate in liver → return to gut via common bile duct. Sxs include fever / abdominal pain, followed by diarrhea. 30% of pxs have maculopapular rash on trunk (rose spots). Enlarged liver / spleen may be present. •Other causes of enteric fever include Salmonella paratyphi, Salmonella enteritidis, Yersinia enterocolitica, and late Campylobacter jejuni, or non-cholera Vibrio. •Labs: blood cultures positive w/in 1 week, stool w/in 3 weeks, urine by 4th week (due to hematogenous seeding of kidneys). Ab titer positive b/w week 2-6. •Vaccination is available for high-risk travel or occupations. 2 types: oral live-attenuated vaccine or injected capsular polysaccharide vaccine. Neither prevents non-typhoid enteric fever. Only 50-70% effective.

Question 27

``` Salmonella enterica Transmission Mechanism of invasion Similar to what other bug? Sxs Resistance ```

Answer 27

•Transmission – Animal infection via consumption of food products (eggs, poultry, dairy) or direct contact (reptiles / turtles). •Organisms invade epithelial cells of small intestine and can replicate inside macrophages. •Gastroenteritis – due to mucosal colonization / destruction. Similar to EPEC. Abdominal pain, low grade fever, non-bloddy diarrhea. “Rotten Egg” odor of stool due to sulfhydryl compounds (H2S). Semi-resistant to bile salts.

Question 28

``` Shigella Reservoir Population Inoculum Transmission / setting Mechanism Sxs Virulence factor Similar to which other bugs? Tx ```

Answer 28

* Obligate human pathogen * Most common in kids * Small inoculum required (1-100) * Transmission – fecal / oral (food or person-to-person), common in DAYCARE, anal sex * Deep invasion of large intestine causes bacillary dysentery (similar to EIEC). Less often gastroenteritis. Does NOT invade blood stream. * Some strains make cytotoxin (Shiga toxin, similar to EHEC) → epithelial cell death. * Tx w/ rehydrating fluids. AB’s (TMP-sulfa) usually only given if young, however the main problem is the toxins. AB’s may actually cause lysis of bugs → further toxin release. Don’t give anti-motility drugs due to possibility of increased toxin absorption.

Question 29

``` Campylobacter jejuni Impressive stat Morphology Temp Oxygen requirements Transmission (specific foods) Sxs Similar to which other bugs? Virulence factor Diagnosis ```

Answer 29

* Most common bacterial enteric infection in US. Curved GNR, grows best at 42 degrees (chicken body temp). Microaerophile. * Transmission – fecal / oral, contaminated food (unpasteurized milk or meat, especially POULTRY), or domestic animal contact (cattle, chickens, dogs). * Causes early gastroenteritis due to mucosal colonization / destruction (similar to EPEC). Sometimes late dystentery w/ enterocolitis from deep infection (similar to EIEC). Rare enteric fever. Affects both small and large intestine. Has cholera-like enterotoxin. * Diagnosis – characteristic darting motility seen microscopically in stool samples due to polar flagellum. Slightly curved GNR. WBCs may be found in stool.

Question 30

Yersinia enterocolitica / pseudotuberculosis Transmission Sxs (4 things)

Answer 30

* Transmission – fecal / oral or animals. Usually infects during cold months. Rare in US. Human-human transmission via fleas or respiratory droplets → plague. * Causes gastroenteritis, diarrhea, terminal ileitis, and sometimes pseudoappendicitis

Question 31

``` Vibrio cholerae Transmission Virulence factor / mechanism Similar to what other bug? Sxs Risk factors Tx ```

Answer 31

Very large inoculum required •Transmission – fecal / oral, ingestion of contaminated food / water. •Secretory toxin (cholera toxin) → constant cAMP production → massive water / electrolyte secretion. Similar to ETEC. No invasion, just mucosal colonization. •Produce 10-20L of diarrhea / day. “Rice water stools” due to mucus flakes. May cause shock / death. •Risk factors – lack of water / sewage treatment or host gastric achlorhydria (due to malnutrition / drugs) •Treat w/ hydration and electrolytes. No AB’s.

Question 32

Vibro parahemolyticus Transmission Sxs Geography

Answer 32

Transmission - salt water, shellfish, and sushi Causes gastroenteritis. Occurs in northeast / northwest US coast

Question 33

Vibrio vulnificus Transmission Sxs Population

Answer 33

* Transmission – salt water, shellfish, and skin abrasion * Does NOT cause GI problems. * Would infection → bullous lesions. Septicemia is deadly. * Most common in immunocompromised and alcoholics.

Question 34

``` Helicobacter pylori Reservoir Transmission Population Mechanism / virulence factor Sxs Diagnosis Tx Prevention ```

Answer 34

* Obligate human pathogen. * Transmission – fecal / oral * Common in kids abroad and adults in US. * Long term / lifelong colonization of stomach. May be asymptomatic. Avoids / survives acidic environment by releasing urease → hydrolyzes urea to CO2 + ammonia → increased pH. Also aided by mucosal secretions of stomach lining. * Causes gastritis, gastric / duodenal ulcers, gastric cancer. * Urease used for diagnosis. * Tx: 2+ AB’s (amoxicillin and clarithromycin), PPI (kills bugs and reduces damage) * If not infected, don’t use antacids, H2 antagonists, or PPI’s to prevent infection.

Question 35

Reactive arthritis | Cause

Answer 35

Complication occurring 1-4 weeks after Salmonella, Shigella, Campylobacter, or Yersinia GI infection. Also seen after GU infection. AB’s not helpful.

Question 36

AB's are usually not used for enteric infections. Exceptions Tx for those exceptions

Answer 36

Exceptions: At risk pxs (old, young, immunocompromised) or prolonged / severe infections. Use fluoroquinolones.

Question 37

What does PMN's in stool indicate?

Answer 37

Bacterial infection

Question 38

What 4 bacteria cause dysentery?

Answer 38

Shigella, enterohemorrhagic E coli, Campylobacter, and Salmonella (severe)

Question 39

What special characteristic of Staph allows it to grow on ham?

Answer 39

Salt-tolerant.

Question 40

How do you treat Staph aureus food poisoning?

Answer 40

Fluids and possibly anti-emetics. NOT AB's due to toxin release.

Question 41

What bacterium causes food poisoning in rice?

Answer 41

Bacillus cereus