Gastrointestinal Tract Infections

Question 1

Diarrheal disease

Answer 1

-8th leading cause of death worldwide
-severe disease in the elderly
-4-6 million children die each year, most in developing countries
-acute disease in the US is usually self-limiting
-some cases require specific diagnosis and treatment
-can be caused by bacteria, viruses, or parasites

Question 2

Gastroenteritis

Answer 2

-inflammation of the stomach and intestines

Question 3

Gastritis

Answer 3

-inflammation of the stomach

Question 4

enterocolitis

Answer 4

-inflammation of the small and large intestines

Question 5

proctitis

Answer 5

-inflammation of the rectal mucosa

Question 6

Symptoms of GI disease

Answer 6

-nausea/vomiting especially in food poising
-diarrhea
-dysentery

Question 7

diarrhea

Answer 7

-increase in stool volume with a loose liquid consistency

Question 8

dysentery

Answer 8

-invasion of intestinal mucosa causes cramping and abdominal pain

Question 9

Epidemiology: GI disease

Answer 9

-outbreaks occur in shared living spaces (daycare, hospital, nursing home
-hygiene is difficult to control
-some organisms have low infection dose (shigella)
-nosocomial outbreaks
-travelers diarrhea
-food and waterborne outbreaks (food prep/storage conditions)
-transmission is usually fecal-oral with ingestion of contaminated food/water
-immunocompromised hosts susceptible (chemotherapy, organ transplantation, HIV)

Question 10

Nosocomial outbreaks

Answer 10

-hospital-acquired/antibiotic-associated due to C.difficile

Question 11

travelers diarrhea

Answer 11

-poor sanitation
-enteric pathogens contaminate the food and water supply

Question 12

Anatomy: GI

Answer 12

1. stomach
2. small intestines
3. large intestines
4. anus
   -secretory products added fluids removed through the epithelial cells (mucosa)

Question 13

small intestine villa/microvilli

Answer 13

-primary reabsorption site, 90% net fluid absorption

Question 14

small intestine goblet cells

Answer 14

-maintain a protective mucosa layer

Question 15

large intestine

Answer 15

-no villi, absorbs excess fluid

Question 16

Natural defenses and prevention of the GI

Answer 16

-stomach acid, normal peristalsis, mucus layer, normal flora
-secreting and absorbing cells produce a protective barrier
- age and personal hygiene
-normal intestinal flora (ecosystem: stable, balanced, decreases colonization of pathogens)
-peyers patches

Question 17

peyer’s patches

Answer 17

-mucus membrane specialized cells, small and large intestine
-immunologic response to antigenic pathogens

Question 18

Normal flora in upper small intestines

Answer 18

(duodenum, jejunum)
-low numbers of streptococci, lactobacillus, yeast

Question 19

Normal flora in lower small intestines (ileum)

Answer 19

-larger numbers- predominate Enterobacteriaceae, Bacteroides spp

Question 20

Normal flora in large intestines (colon)

Answer 20

-predominate anaerobic bacteria- Bacteroides, clostridium, peptostreptococcus, others
-aerobes- enterobacteriacaea, entercocci, streptococci
-increased bacterial concentration as descends down the large intestine

Question 21

Enterotoxins

Answer 21

-the flow of electrolytes into the intestinal lumen changes the osmotic balance
-leads to watery profuse diarrhea
-generally not bloody, no PMNs, no fever
-ex: vibrio cholera (CT toxin), enterotoxigenic E. Coli (ETEC)- heat stable entertoxin similar to CT toxin

Question 22

Cytotoxins

Answer 22

-destroy epithelial cells leaving the intestinal lining unprotected
-An inflammatory response occurs
-painful cramping common
-blood and PMNs in stool
-ex: clostridium difficle (toxin is marker for diagnosis)
-enterohemorrhagic E. Coli (produces a shiga-like toxin shigella sp.)

Question 23

Neurotoxins

Answer 23

-produced by bacteria in food prior to ingestion (food intoxication)-poisoning
-various symptoms commonly nausea/vomiting
-bacteria usually not found in patients’ stool- test suspect food source
ex:
staphylococcus aureus: vomiting onset 2-6 hours after ingestion, meat and dairy
Bacillus cereus: 2 types of toxins-emetic, diarrheal, rice tables
clostridium perfringens: mild, self-limiting 24-hours, gravies
clostridium botulinum: flaccid and systemic paralysis is life-threatening honey, home canning

Question 24

Pathogenic mechanisms: attachment

Answer 24

-adherence to bowel via colonization factor antigen
-disrupts normal cell function by covering the epithelium
ex: Enteropathogenic E.Coli EPEC
Giardia lamblia: freshwater flagellated parasite, beaver host, “beaver fever”
cyclospora, Isospora: parasites, AIDS patients, daycare, animal exposure

Question 25

Pathogenic mechanisms: Invasions

Answer 25

-occurs after adherence, reaches deep tissues, evades host immune system, mucosal ulceration, and inflammatory response
ex: shigella, salmonella, yersinia entercolitica, plesiomonas shigelloids, rotavirus, norwalk-like virus

Question 26

Shigella: Pathogenic mechanism of invasion

Answer 26

-entry into epithelial cells, multiples in submucosa, spreads to adjacent cells, causing cell death, and tissue destruction, but does not invade further. No bloodstream involvement in healthy individuals

Question 27

Salmonella: Pathogenic mechanism of invasion

Answer 27

-similar to shigella, but multiples in vacuoles, gain access to submucosal layers, lymph nodes, bloodstream, systemic infection by surviving in phagocytotic cells. Can produce a carrier state “Typhoid Mary”

Question 28

Clinical Manifestations: GI disease

Answer 28

fluid/electrolyte imbalance
-no fecal leukocytes, increased watery diarrhea, mild or no fever, intestinal fluid loss
cell destruction/inflammation
-positive for fecal leukocytes, blood and mucus, cramping, pain
invasion/penetration of intestinal mucosa
-symptoms of systemic infection: headache, sore throat, fever, diarrhea, no prominent feature

Question 29

Acceptable specimens for routine bacterial stool culture

Answer 29

-unpreserved stool within 2 hours of collection
-preserved stool in transport media (ex: Carey Blair. 72 hours)
-rectal swab when stool is difficult to obtain (ex: infant)
-previously positive culture requiring three negative specimens prior to return to work
-inpatients <4 days hospitalized

Question 30

Routine organisms that require workup

Answer 30

-salmonella species
-shigella species
-campylobacter species
-Shiga toxin-producing organisms (E.coli 0157:H7) via EIA testing
-Aeromonas species and plesimonas species

Question 31

Routine organisms that require a request to work up

Answer 31

-yersinia enterocoliticia
-vibrio parahaemolyticus
- vibrio cholera
- bacillus cereus
-E.coli 0157

Question 32

Routine bacterial culture media

Answer 32

-TSA with 5% blood sheep (BAP), -MacConkey Agar (MAC)
-Hektoen Agar (HEK)
-Gram Negative Broth (GN)
- Subcultured GN Broth to MacConkey (SMAC)
-Campylobacter Agar (C2)
-BAP, MAC, HEK, GN incubated at 5% CO2, 35 degrees
-C2 incubated at 42 degrees for 2 days, reduced O2 environment 5% O2, 10% CO2
-GN subcultured to SMAC after 6-8 hour incubation, re-incubated for 12 hours, and refrigerated for Shiga toxin EIA testing

Question 33

Special request Bacterial culture media

Answer 33

-Yersinia: CIN agar, incubate at RT
-Vibrio species: TCBS agar, incubate 5% CO2, 35 degrees
-Aeromonas/Plesiomonas: BAP and MAC, 5% CO2, 35 degrees
-Bacillus cereus: BAP
-E.Coli 0157: Macconkey with sorbitol

Question 34

Bacterial stool culture work-up

Answer 34

-All plates are read for 2 days (C2 only on day 2)
BAP: altered Normal flora, screen beta-hemolytic colonies, r/o Aeromonas and plesiomonas
MAC: screen NLF as potential pathogens
HEK: screen any non-yellow (clear/black/green) as a potential pathogen
C2: screen any grey shiny cultures for campylobacter species
CIN: screen any red or pink colonies for Yersinia
TCBS: screen any growth for potential vibrio species
SORB: screen any Non-sorbitol fermenter as poetenial E.coli 0157

Question 35

Identify potential pathogens by API/Vitek II

Answer 35

-Serotype any salmonella, shigella, potential E.coli O157 by latex agglutination
- routinely perform susceptibility testing on Shigella (salmonella by request)
-freeze all isolates and send them to NYS Labs for the EIP program
-report presence/absence of salmonella, shigella, campy, Shiga-toxin producing organisms

Question 36

Ova and Parasites

Answer 36

-formalin preserved stool specimens submitted to Lab
-if unpreserved stool is sent it is placed in formalin ASAP
- in Rochester, NY standard O and P screen only requires test for giardia and cryptosporidium
-Icon EIA-based test screens for these quickly and accurately
-routine screen for intestinal pathogens now done by BD Max

Question 37

Traditional O and P exam

Answer 37

-iodine wet mount to visualize eggs, associated worms, or protozoa
-used for complete O and P exam if the patient has documented foreign travel
-trichrome stain done as well for better visualization and ID of amoebae

Question 38

BD Max

Answer 38

-routine bacterial and parasite PCR panel by BD Max
-real-time PCR
-BD Max assay contains extraction reagent, sample buffer tubes, master mix with probes and primers, reagent strips containing pipette tips, solutions, reaction tubes, waste reservoir, microfluidic cartridge for amplification and detection
-results in 2.5-3.5 hours
nucleic acid detected: salmonella species, campylobacter species, shigella spp, Shiga toxin 1/shiga toxin 2 (E.Coli-STEC, shigella dysenteriae), giardia lamblia, cryptosporidium (C. hominis and C. parvum), entamoeba histolytica
-acceptable specimens:
Bacterial panel (fresh/unpreserved, Cary/Blair preserved stool)
Parasite panel (fresh/unpreserved, stool fixed in SAF or 10% formalin)

Question 39

Salmonella

Answer 39

-family Enterobacteriaceae, GNR, motile, TSI=K/A, GAS +/-, H2S +/-
-mode of transmission: ingestion of contaminated food and water, isolated from most animal species
-occurrence: greatest frequency during warm weather, <5yrs highest incidence
-taxonomy: salmonella strains serotyped and named by group (ex: salmonella group D)
-antigens/virulence factors:
somatic (O) antigens: lipopolysaccharide in cell wall
Flagellar (H) antigens: proteins
Capsular (VI) antigens: in salmonella typhi, may block agglutination by anti-O serum
Pathogenesis: large infective dose (1 million- 1 billion); most org die in pH2 of stomach
-if the organism passes to small intestines can cause gastroenteritis (diarrhea, mucosal invasion), bacteremia, typhoid fever (via lymph and bloodstream, reach gallbladder, seed intestine via bile)
treatment: usually just rehydration therapy, susceptibilities on request