GI tract Flashcards
Salmonella species biochemical reactions
Indole −
Citrate +
H2S +
LDC + ∗
LDA −
Urease −
Ornithine decarboxylase (ODC) +
Motility +
TSI agar K/A
Gas production Variable
Salmonella species gram stain
GNRs
Salmonella species growth requirements
mainly aerobic but facultative anaerobe as well, 37 °C with growth
in 16–24 hours of inoculation
Salmonella species colony morphology
opaque or translucent, smooth, 2–4 mm in diameter on supportive
media, green or transparent with black center on Hektoen enteric agar, transparent or red
with black centers on xylose-lysine-deoxycholate agar
Shigella species biochemical reactions
Indole Variable
Citrate −
H2S − ∗
LDC −
LDA − ∗
Urease −
ODC Variable
Motility − ∗
TSI agar K/A
Gas production −
Shigella species gram stain
GNRs
Shigella species growth requirements
aerobic and facultative anaerobe, 35 °C with growth 18–24 hours
after inoculation
Shigella species colony morphology
clear or slightly pink on MacConkey agar, green or transparent on
Hektoen agar, transparent or red on xylose-lysine-deoxycholate agar
Toxigenic Escherichia coli biochemical reactions
Indole +
Citrate –
H2S –
LDC +
LDA –
Urease –
ODC +
Motility +
TSI agar A/A
Gas production +
Toxigenic E. coli gram stain
GNRs
Toxigenic E. coli growth requirements
aerobic and facultative anaerobe, grow best at 37 °C
Toxigenic E. coli colony morphology
circular, convex colonies, gray, translucent to opaque on sheep blood
agar, pink, opaque on MacConkey, green with a metallic sheen, opaque on eosin methylene
blue agar
Campylobacter species biochemical reactions
Catalase +
Oxidase +
Hippurate +
Campylobacter species gram stain
Gram-negative bacilli, small curved rods, “seagull appearance”
Campylobacter species growth requirements
Microaerophilic, Campylobacter-selective agar at 42 °C
Campylobacter species colony morphology
mucoid, flat, grayish colonies with irregular edges, potentially
swarming.
Vibrio species biochemical reactions
Catalase +
Oxidase +
Vibrio species gram stain
Gram-negative bacilli, curved rod with polar flagella
Vibrio species growth requirements
aerobic and facultative anaerobe, require media with increased salt
concentration, sodium chloride, and acidic pH, 35–37 °C for 6–8 hours for APW or 35–37 °C
18–24 hours to TCBS and all other media
Vibrio species colony morphology
creamy white, smooth and convex; yellow-green on TCBS, colorless
on MacConkey agar
Yersinia enterocolitica biochemical reactions
Indole V
Citrate –
H2S –
LDC –
LDA –
Urease V
ODC +
Motility V*
TSI agar K/A
Gas production –
Catalase +
Oxidase –
*Motile at 22–25 °C; nonmotile at 37 °C (body temperature)
Yersinia enterocolitica gram stain
GNRs
Yersinia enterocolitica growth requirements
aerobic and facultative anaerobe, grow optimally at room
temperature (22–25 °C)
Yersinia enterocolitica colony morphology
translucent or opaque or gray-white, slightly mucoid (after 24 hours
of growth) on sheep blood agar, flat, colorless or pale pink on MacConkey agar, “bulls-eye”
appearance with deep-red center and translucent outer zone on cefsulodin irgasan
novobiocin (CIN) agar
Aeromonas species biochemical reactions
Indole +
Citrate +
H2S V
LDC +
Urease –
ODC –
Motility V
TSI agar K/A
Gas production V
Catalase +
Oxidase +
Aeromonas species gram stain
Gram-negative bacilli, single, in pairs, or short chains
Aeromonas species growth requirements
aerobic and facultative anaerobe, grow best at 35–37 °C
Aeromonas species colony morphology
circular, gray on sheep blood agar, dark green on sheep blood agar
after 72 hours due to beta-hemolysis, deep-red center surrounded by translucent outer
zone of colony on CIN agar
Plesiomonas shigelloides biochemical reactions
Indole +
Citrate
H2S
LDC +
LDA
Urease
ODC –
Motility
TSI agar K/A
Gas production –
Catalase +
Oxidase +
Plesiomonas shigelloides gram stain
GNRs
Plesiomonas shigelloides growth requirements
aerobic and facultative anaerobe, grow best at 35–37 °C
Plesiomonas shigelloides colony morphology
clear and colorless on MacConkey, CIN, and XLD agars, clear and
green on Hektoen agar
DIRECT AND MOLECULAR TECHNIQUES FOR DETECTING CLOSTRIDIUM DIFFICILE- AND SHIGA TOXIN-
PRODUCING ORGANISMS
PCR and nucleic acid amplification testing molecular methods
Direct immunochromatographic C. diff testing
Due to their ability to cause life-threatening infections, the rapid detection of
C. difficile- and Shiga
toxin-producing E. coli organisms is pertinent for prompt patient care.
Direct immunochromatographic C. difficile testing methods simultaneously target the
glutamate
dehydrogenase (GDH) antigen and toxins A and B produced by toxigenic strains
Rapid tests for Shiga toxins 1 and 2 use
antibody-labeled assays to determine the presence or absence of
toxigenic strains of E. coli
C. difficile evaluation
o GDH antigen and toxin absent: no C. difficile infection
o Both GDH antigen and toxin present:
❖ Symptomatic: consistent with active infection
❖ Asymptomatic: consistent with C. difficile colonization
o Either GDH antigen or toxin present: inconclusive; molecular testing recommended
Shiga toxin (ST1 and ST2): evaluation
o ST1 and ST2 absent: no Shiga toxin-producing E. coli present
o Either ST1 or ST2 or both present: Shiga toxin-producing E. coli present.
PCR and nucleic acid amplification testing molecular methods provide a definitive rule-out or
supportive diagnosis of
toxigenic infections
Nucleic acid amplification testing targets genes specific
to toxigenic C. difficile strains including
A and B and 16S ribosomal RNA. Genes for ST1, ST2, E. coli O157:H7, and Shigella dysenteriae type 1 are targeted for detection of Shiga toxin-producing
organisms.
SEROTYPING E. COLI, SALMONELLA, AND SHIGELLA ORGANISMS
allows for the differentiation of species and subspecies of organisms that otherwise
have indistinguishable physical and biochemical properties
Determining the serotype of enteric
pathogens allows for
further insight on disease manifestations and proper treatment methods
Serotyping can be completed using the following test methodologies:
bacterial, latex, or
coagglutination, and fluorescent or enzyme-labeled immunoassay
E. coli, Salmonella, and Shigella species and subspecies are differentiated from one another by
antigenic properties of their O, K, and H antigen
Present in the outermost layer of the bacterial cell
wall, the
O antigen is a polymer of immunogenic repeating oligosaccharides.
The K antigen is
present in
the capsular polysaccharides
threadlike structure portion of the flagella in motile
organisms contains the
H antigen
More than 2,000 Salmonella serotypes have been detected and
are determined by their
individual expression of the O and H antigens
Shigella organisms are organized into four main species, or serogroups:
A (S. dysenteriae)
B (S. flexneri)
C (S. boydii)
D (S. sonnei)
E. coli subspecies are differentiated based on the
composition and immunogenic
properties of the O, K, and H antigens
E. coli O157:H7 is the extremely dangerous
subspecies that produces a
Shigella-like toxin that causes an enterohemorrhagic response
MAJOR GASTROINTESTINAL PATHOGENS
Salmonella
Shigella
P. shigelloides
Aeromonas species
Y. enterocolitica
Campylobacter species
E. coli
Vibrio species
Gastrointestinal infections occur from
humans ingesting bacteria present in raw, undercooked, or
unpasteurized products or human to human via the fecal–oral route
Salmonella reservoir
Poultry
Salmonella virulence factors
Lipopolysaccharide endotoxin: intracellular survival
O and H antigens: immunogenic, motility
Adhesion, colonization, and antiphagocytic properties
Type III secretion system for survival in macrophages
Shigella reservoir
Human
Shigella virulence factors
Endotoxins: invasion, multiplication, and
antiphagocytic properties
Adhesion factor: colonization
O antigen, Shiga toxin: immunogenic, inhibits cell
protein synthesis causing life-threatening disease
Type III secretion system: invading macrophage
P. shigelloides reservoir
soil
water
seafood
Aeromonas species reservoir
Amphibians, reptiles,
fish; more prevalent
during warm-
weather months
P. shigelloides virulence factors
Lophotrichous flagella: motility
Various toxins, proteases, hemolysins, lipases,
adhesins, and agglutinins
Y. enterocolitica reservoir
Swine
Y. enterocolitica virulence factors
Lipopolysaccharide endotoxin
Protein capsular antigen: protects against
phagocytosis
Proteins to promote adhesion and invasion
Campylobacter species reservoir
poultry
cattle
sheep
Campylobacter species virulence factors
Lipopolysaccharide endotoxin and exotoxins
Superoxide dismutase: harmful to cells’ DNA or
membrane factors
Siderophores: iron sequestering
E. coli reservoir
cattle
E. coli virulence factors
O, K, and H antigens: immunogenic, encapsulation,
motility
K1: inhibits phagocytosis, resists serum antibody
activity
O157:H7: hemorrhagic effects
Vibrio species reservoir
water
oysters
seafood
Vibrio species virulence factors
Adhesion factor, pili: colonization, mucosa adherence
Hemagglutination protease: intestinal inflammation
and degradation
Cholera toxin: quickly causes severe dehydration
Siderophores
DETECTION METHODS FOR HELICOBACTER PYLORI
Serological tests
urea breath test
histological identification
culture
rapid urease test
PCR
Serological tests using monoclonal IgG H. pylori antibodies or polyclonal H. pylori antibodies can
used to screen for a past or present infection
Antigens produced by the presence of H. pylori can
be detected in
serum or stool samples by binding to antibodies embedded in a test cartridge and
migrating to a test window where they produce a colored line
The urea breath test is a
confirmatory method used for the detection of an active H. pylori
infection or to monitor the efficacy of treatment
H. pylori rapidly metabolizes urea, and it is
excreted as
carbon molecules in the breath
For this method, patients
ingest urea capsules that
contain radioactively labeled carbon molecules and then they exhale into a collection container 10–
15 minutes after swallowing the capsule
Breath samples are qualitatively analyzed for
the
presence or absence of the radioactive labeled carbon molecules
Direct detection of H. pylori can be determined from
gastric or duodenal biopsy specimens via
microscopy, culture, or molecular methods
Histological identification of the organism observed in Gram-stained smears or imprints of
biopsy samples yields the
presence of curved Gram-negative bacilli.
Culture of these specimens is
required if
antibiotic susceptibility testing is needed for treatment options.
rapid urease test
placing a biopsy specimen
in agar or on a reaction strip containing urea, a buffer, and a pH indicator.
Urease from H. pylori will
metabolize the urea to ammonia and bicarbonate, increasing the pH in the test system, and change
the color of the pH indicator to reflect the alkaline environment.
Results can be determined in
1-24 hours
Polymerase chain reaction (PCR) testing is
highly specific and is more sensitive for H. pylori
detection than other methods.
