GI Microbiology Flashcards by Geun Young Park

lymphoid tissue in GI tract; tolerates commensal microbes by default and prevents intestinal disorders like food allergies, celiac disease, and IBS

GALT (GI-Associated Lymphoid Tissue)

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Default setting of GALT immune responses induces

tolerance

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Ways that GALT “samples” ingested antigens

1) Microfold (M) cells absorb antigens and pass on to dendritic cells or other immune cells in Peyer’s Patches
2) Dendritic cells samples directly using its dendrites and directly absorb antigens

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Another term for GALT in ileum

Peyer’s patches

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Describe how GALT tissue can contribute to oral tolerance

If an antigen was injected directly into the blood stream, IMMUNITY (or disease) would develop
If an antigen was given orally, then TOLERANCE would develop b/c of antigen sampling in GALT.

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Which immune cells are believed to contribute to oral tolerance

T reg cells

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IFNy is considered (pro/anti)-inflammatory

pro-inflammatory

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TGF-b is considered (pro/anti)-inflammatory

anti-inflammatory

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The majority of Ig-secreting cells are located in what organ system?

GI tract (70-80%)

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What are the two most synthesized immunoglobulins

IgA (mucous membranes)
IgG

Total IgA > Total IgG

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immunoglobulin secreted as a dimer; involved with mucous membrane immunity; when combined with a secretory component, it is resistant to proteolytic enzymes in GI tract

IgA

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What helps prevent the breakdown of IgA in the GI tract by proteolytic enzymes

Secretory component added by epithelial cells

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The most common primary immunodeficiency is due to a lack of what immunoglobulin?

IgA

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most common primary immunodeficiency; may be asymptomatic, but can also have chronic GI inflammatory issues (diarrhea, ulcerative colitis, Crohn’s disease, recurrent mucosal infections)

IgA deficiency

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Chronic diarrhea
Ulcerative colitis
Crohn's disease
Recurrent oral/mucosal infections 
... are common symptoms of

IgA deficiency

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The levels of IgG will be higher following vaccination with an antigen with or without prior feeding of the antigen?

Without prior feeding (more pro-inflammatory Ig response b/c of lack of oral tolerance)

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The levels of IgA will be higher following vaccination with an antigen with or without prior feeding of the antigen?

About the same (slightly higher without prior feeding of antigen)

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The Fc region of IgE helps bind to _________, while the Fc region on IgG helps bind to ________

mast cells (IgE); macrophages (IgG)

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Which immunoglobulin isotype commonly presents as a dimer?

IgA

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Which immunoglobulin isotype commonly presents as a pentamer?

IgM

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Early HIV causes the near depletion of…

GALT T cells

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What type of T cell provides protection against colitis and maintains GI homeostasis?

T reg

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What cytokine is produced by T reg?

IL-10 (anti-inflammatory)

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Lactobacilli, Streptococci, Candida and Helicobacter pylori are the prominent bacteria in the (Stomach/SI/LI)

Stomach

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Lactobacilli, E. coli and Enterococci are the prominent bacteria in the (Stomach/SI/LI)

Small Intestine

Lactobacilli, Bacteroides, Bifidobacteria, and Clostridia are the prominent bacteria in the (Stomach/SI/LI)

Large Intestine

There seems to be a correlation between gut flora and obesity and psychiatric issues (True or False)

True

Many Gram-negative enteric bacteria express......

flagella (makes sense for motility in fluid --> turbidity)

Flagella vs. Pili: | large, complex filaments for locomotion

Flagella

Flagella vs. Pili: | smaller, simpler fibers for adherence

Pili

Which branch of the immune system is most important for bacterial protection from viral infection: Innate, Humoral or Cell-Mediated

Innate: the normal gut flora helps prevent infection Ex. TLR signaling

What is an essential gene required for immunoglobulins and T-cell receptor gene rearrangements (variability of mRNA splicing)?

Recombination Activating Genes (RAG 1 & RAG 2)

Bacterial disease associated with antibiotic treatments; normal gut flora wiped out after antibiotic, allowing for these normal spore-forming bacteria to vegetate and predominate

Clostridium difficile

C. difficile is part of the normal gut flora and is in phylum

Firmicutes

Obligate aerobes will be where in an inoculated test tube

Top

Obligate anaerobes will be where in an inoculated test tube

Bottom - Clostridium - Bacteroides

Facultative anaerobes will be where in an inoculated test tube

Throughout, but heavy at top - Candida albicans - E. Coli - Staphylococcus - Streptococcus

Microaerophiles will be where in an inoculated test tube

NEAR the top - H. pylori

Aerotolerant bacteria will be where in an inoculated test tube

even throughout (can't use oxygen, but unaffected by it's presence)

Anaerobes metabolize glucose and produce what products during metabolism?

Ethanol and CO2

Anaerobic bacteria are not found in the mouth because of the presence of air (True or False)

False: can survive in even shallow layers of fluid (mucous) due to the low solubility of Oxygen in water

Which are more prominent in the GI tract: aerobes or anaerobes

Anaerobes (1000:1)

Two predominant phyla of anaerobes in the GI tract

Bacteroidetes | Firmicutes

Most anaerobic infections, like abscesses, are mix infections containing both anaerobic and aerobic bacteria (True or False)

True (b/c of synergy between mixed species)

What is bacterial biofilms that form in mouth/teeth?

Plaque

Dental PAB (plaque-associated biofilm) is composed of

host and bacterial proteins, polysaccharides, and over 700 species of bacteria

Multispecies form communities in bacterial biofilms (T or F)

True

What bacterial species are more prominent in supra-gingival PAB?

Aerobic or aerotolerant Gram + * Actinomycetes

What bacterial species are more prominent in sub-gingival PAB?

Anaerobic Gram - * Bacteroides

What are the most common reasons of oral and gut infection?

1. Opportunistic pathogens that are outside the normal environment 2. Intestinal or oral injury compromising epithelial barrier 3. Aspiration of oral bacteria into lung 4. Tissue ischemia and lowered redox potential leading to development of anaerobic infections (typically as mixed infections)

Gram negative, non-spore forming, anaerobic bacilli; found in oropharynx, GI tract and female genital tract; predominant flora in GI tract and helps prevent infection by utilizing nutrients (carbs, nitrogen, etc.) and colonizing surfaces; also most common genus isolated from anaerobic infections

Bacteroides *(B. fragilis most common)

Most common genus of gut flora isolated from anaerobic infections

B. fragilis

Why does B. fragilis require synergy from facultative bacteria to cause disease?

B. fragilis is unable to invade cell or tissues and requires breach of epithelial barrier to cause infection in deeper tissues

Gram positive, non-spore forming, anaerobic bacilli; has hyphae-like structures; part of normal oral flora; can cause dental carries/disease, especially following dental procedures (opportunistic pathogen); can cause "Lumpy Jaw"

Actinomyces spp.

Actinomyces's nickname b/c of its hyphae-like structure

ray fungus

chronic infection of Actinomyces (A. israelii) resulting in a swelling mass on the face; contains sulfur granules in drained fluid; requires prolonged antibiotic therapy (IV penicillin and oral antibiotics up to a year)

Actinomycosis (Lumpy jaw)

Why does Actinomycosis have "mycosis" in it's name?

Because it forms "hyphae-like" structures

"Lumpy jaw" with sulfur granules makes you think of a __________

Actinomycosis

Gram positive, spore forming bacilli; firmicutes phylum; common in external environment, but a MINOR component of the normal flora; infection can produce a very foul odor

Clostridium spp.

Clostridium spp. that is strict anaerobe

C. difficile

Clostridium spp. that are aerotolerant

C. Perfringens | C. Septicum

What do Clostridium spp. produce foul odor?

They can ferment nutrients (carb, protein, FA) and produce reaction metabolites that have foul odor

Clostridium species associated with gas gangrene (produce gas in gangrenous tissue)

C. Perfringens | C. Septicum

What Clostridium species can spread via bloodstream b/c it is aerotolerant?

C. Septicum

Clostridium species associated with food poisoning and wound botulism; secretes a toxin that prevents the release of stimulatory transmitters, causing flaccid paralysis

C. botulinum * Don't feed honey to babies

Clostridium species; secretes a toxin that prevents the release of inhibitory neurotransmitters, causing spasticity and tetanus

C. tetani

Clostridium species associated with antibiotic-associated diarrhea, colitis and horrendous smell

C. difficile

All Clostridium produce

toxins

Endotoxin, Exotoxin or Enterotoxin: | integral part of gram- bacteria; LPS (lipid A + polysaccharide)

Endotoxin

Endotoxin, Exotoxin or Enterotoxin: | secreted toxin

Exotoxin - Botulinum - S. aureus toxins - Streptococcal pyogenic toxins

Endotoxin, Exotoxin or Enterotoxin: | secreted toxin that targets enteric cells

Enterotoxin - E. coli (Shiga toxin) - cholera toxin - S. aureus enterotoxin

What type of toxins are produced by C. tetani and C. botulinum?

Exotoxins * Binary A-B toxins (proteins linked by S-S bond)

What type of toxin is produced by C. perfringens?

a-toxin (lecithinase degrades tissue/cell membranes)

What type of toxin is produced by C. diff?

Toxin B (cytotoxic and inflammatory) * single protein with different domains

What is another term for gas gangrene?

Clostridial myonecrosis

C. Perfringens cause what type of gas gangrene?

Traumatic (Traumatic tissue damage allows anaerobic metabolism and C. perfringens spores contaminate wound and germinate --> tissue destruction/septic shock --> mortality about 25% )

C. Septicum cause what type of gas gangrene?

Spontaneous (Breaks in GI mucosa allows C. septicum to enter the bloodstream since it's aerotolerant --> invades mucle and other sites --> septic shock/tissue destruction --> mortality up to 100%)

Common pathogens involved with peritonitis

Synergy of Enterobacteriaceae (E. coli) + B. fragilis

What's B. fragilis role in causing peritonitis?

Its capsular polysaccharide recruits PMN

How can you diagnose an anaerobic infection?

- Aspirate abscesses, tissue or blood (specimens must not have contacted mucus membrane) - Rapid transport is essential to preserve anaerobes - Gram stain (for cell morphologies)

Treatment for anaerobic infections

Drainage Debridement Antibiotic therapy

Best antibiotics for anaerobes

Best: Azoles, Carbapenems, B-lactams/B-lactamase inhibitors Next Best: Clindamycin, Tygecycline, Cephalosporins (cef-) Never Active: Aminoglycosides, TMP-SMX, Aztreonam

inflammation of the esophagus; caused by Candida or Herpesviruses; treated with fluconazole

Esophagitis

Pathogens involved with esophagitis

Candida | Herpesviruses

Candida esophagitis is treated with

Fluconazole

gram negative spiral bacteria with flagella; plays a role in the pathogenesis of peptic ulcer disease

Helicobacter pylori

Discoverers of H. pylori playing a role in gastritis and peptic ulcer disease

Marshall and Warren

Explain the pathogenesis of H. pylori with peptic ulcer disease

1) Flagella allow to penetrate mucous layer and colonize epithelial cells 2) Urease in bacteria converts urea to ammonia, neutralizing acid (increase pH) 3) Replicate at alkaline pH 4) Bacterial mucinases damage epithelia and induce inflammation

The presence of virulence factors (CAG genes) in a specific cluster in a bacterial genome

CAG pathogenicity island

What gene strain must be present in H. Pylori in development of peptic ulcers and gastric cancer?

CAG+ (Cytotoxin-Associated Genes)

How to diagnose H. pylori with peptic ulcers

Biopsy smears and gram stains Urea breath test (radiolabeled CO2 produced is measured upon urea ingestion) Antigen detection (stool) Serology

Treatment for peptic ulcers

Combination of antibiotics (to prevent resistance) Proton pump inhibitors Bismuth subsalicylate