Infectious Diseases of the GI System

G- vs G+

G+ = more susceptible, endospores

G- = more resistant - outer membr. blocks antibiotics

Dental Caries

tooth decay

Streptococcus & Lactobacillus families

Virulence: fermentation of sugars → acid → demineralization of enamel → biofilm (plaque) → cavities

Key Features: plaque, cavities

Diagnosis: clinical

Treatment: dental hygiene, restoration

Endodontic Infections (Pulpitis → Necrosis)

bacterial invasion of pulp (innermost layer - deep tissue)

Multiple types of anaerobic bac.

Virulence: fermentation acids & proteolytic enzymes (break down proteins)

Key Features:

• reversible pulpitis = cold sensivity

• irreversible pulpitis = spontaneous, intense pain

• necrosis → abscess

• Possible cellulitis (deep tissue spread) 

Diagnosis: clinical + x-ray

Treatment: root canal

Periodontium

tissues that support/surround teeth

Periodontal Diseases

G- anaerobes

Virulence: catabolic enzymes, inflammation, biofilm

Key Features:

• Gingivitis - reversible

• Periodontitis - tissue destruction

Diagnosis: clinical (look at depth + bone loss)

Treatment: deep teeth cleaning, hygiene

Enteric

Relating to the intestines

Enteritis

Small Intestine Infections

Colitis

Large Intestine Infections

Gastroenteritis

Acute Infectious Inflammation of the Stomach and Small Intestine

Main Symptoms: diarrhea, vomiting, abdominal pain, fever

Virulence:

• Invasion of mucosa

• Adhesion + toxin production

• Enterocyte destruction

• Preformed toxins (no invasion)

Campylobacter jejuni

G-, microaerophilic (grows at avian body temp)

Virulence: cytotoxins, mucosal invasion (has flagella → motile)

Reservoir & Transmission: zoonotic = undercooked poultry

Key Features: watery + bloody diarrhea, fever, ab cramps

Diagnosis: stool PCR/culture

Treatment: supportive, antibiotics if severe

Notes: associated w/ Guillain-Barrè syndrome (autoimmune nerve damage)

Salmonella enteria (non-typhoidal)

G-, motile

Virulence: mucosal invasion, survives in macrophages

Reservoir & Transmission: zoonotic = poultry, eggs, reptiles, livestock

Key Features: watery diarrhea (sometimes mucus or bloody), fever

Diagnosis: stool PCR/culture

Treatment: supportive, avoid antibiotics

Notes: high bac load to infect, survives well in environment

Shigella spp.

G-

Virulence: Shiga toxin (cytotoxin), invasion plasmid for epithelial invasion, motile inside cells

• bac inject proteins that damage host cell cytoskeleton, host cell engulf bac, bac reproduce, bac use host cell actin to move & invade other cells

Reservoir & Transmission: human only, fecal-oral

Key Features: dysentery (bloody, mucous diarrhea), tenesmus (constant urge to poop)

Diagnosis: stool PCR/culture + Shiga toxin detection

Treatment: supportive, antibiotics shorten duration of symptoms

Notes: low infectious dose → outbreaks, acid-resistant (survives GI tract)

Pathogenic E. coli

G-

ETEC, EPEC, EIEC, EAEC, STEC

Virulence:

• ETEC: heat-labile & heat-stable toxins

• EPEC: attaching & effacing lesions

• EIEC: Shigella-like invasion

• EAEC: biofilm

• STEC: Shiga toxin

Reservoir & Transmission: depends on pathotype (ex: cont. food/water, fecal-oral)

Key Features:

• ETEC/EPEC: watery diarrhea

• EIEC/STEC: bloody diarrhea

• EAEC/EPEC: chronic diarrhea

• ETEC: traveler’s diarrhea

• STEC: HUS (hemolytic uremic syndrome - blood vessel damage → kidney failure) risk

Diagnosis: stool PCR + Shiga toxin test

Treatment: rehydration. avoid antibiotics (unless severe)

Notes: avoid antibiotics in STEC due to HUS risk

ETEC

Enterotoxigenic

traveler’s diarrhea

Symptoms: watery diarrhea, ab cramps, no fever

Virulence: heat-labile & heat-stable toxins (cause diarrhea)

EPEC

Enteropathogenic

infants - diarrhea, vomiting

attaching & effacing (A/E) lesions on microvilli

EIEC

Enteroinvasive

dysentery-like

Symptoms: bloody/mucous stools, tenesmus, cramps, fever

Virulence: invasion like Shigella

EAEC

Enteroaggregative

Biofilm

Persistent diarrhea

STEC

Shiga-toxin producing

Hemorrhagic colitis + HUS risk

^^^bloody diarrhea + cramping

Clostridium perfringens (foodborne)

G+, anaerobic, spore-forming

Virulence: enterotoxin produced while spore-forming in intestine

Reservoir & Transmission: foodborne - soil, animal intestines, raw meat, poultry

Key Features: watery diarrhea, no fever

Diagnosis: clinical + stool culture for toxin

Treatment: hydration only

Notes: reheated meat dishes, short disease duration

vibrio cholerae

G-

Virulence: bacteriophage encodes Cholera Toxin, toxin-coregulated pili allow colonization of S.I. (non-invasive, but toxin-releasing)

• Cholera toxin causes massive water loss

Reservoir & Transmission: water & food cont. w/ poop

Key Features: “rice-water stools”, dehydration

Diagnosis: stool PCR/culture

Treatment: immediate oral or IV rehydration, antibiotics shorten symptom duration

Notes: life-threatening, endemic, water sanitation essential

Yersinia enterocolitica

G-

Virulence: Yops proteins prevent phagocytosis (immune evasion)

Reservoir & Transmission: Pigs (undercooked pork)

Key Features: pseudoappendicitis (mimics appendicitis) + diarrhea

Diagnosis: stool PCR/culture

Treatment: supportive (hydration), antibiotics only if severe

Notes: grows at refrigeration temps

Bacillus cereus

G+, spore-forming

Virulence:

• Emetic Type: emetic (vomit-causing) toxin called cereulide

• Diarrheal Type: diarrheal enterotoxins produced in intestine

Reservoir & Transmission: cooked food - rice

Key Features:

• Emetic: nausea & vomiting (less diarrhea)

• Diarrheal: watery diarrhea, ab cramps

Diagnosis: clinical

Treatment: supportive

Staphylococcus aureus (food poisoning)

G+, heat-stable

Virulence: preformed enterotoxins (disease will happen even if bac killed in cooking)

Reservoir & Transmission: zoonotic, creamy foods

Key Features: rapid vomiting, mild diarrhea, no fever

Diagnosis: clinical

Treatment: supportive (hydration), antibiotics don’t work

Notes: short duration, toxin not infection (bc disease caused by the toxins bac produce, not the bac themselves)

Clostridioides difficile

G+, anaerobic, spore-forming

caused by disruption of microbiota (antibiotic use)

Virulence: toxins A & B cause colitis

Reservoir & Transmission: normal gut microbiota

Key Features: antibiotic-associated diarrhea, pseudomembranous colitis (severe colon infl.)

Diagnosis: stool PCR + toxin EIA

Treatment: oral vancomycin. fecal transplant if reccurent

Notes: spores resist disinfectants

Listeria monocytogenes

G+, motile

Virulence:

• Listeriolysin → escapes phagosomes

• actin-based motility

• epithelial invasion

Reservoir & Transmission: soft cheeses, ready-to-eat food, meats

Key Features: severe disease in pregnancy/neonates/elderly (possible meningitis)

Diagnosis: blood/CSF culture

Treatment: antibiotics (ampicillin)

Notes: survives in cold temps (refrigerated foods), avoid soft cheeses during pregnancy

Enteric Viruses

Rotavirus, Norovirus, Astrovirus, Adenovirus 40/41

RNA viruses (except Adenovirus - dsDNA)

Virulence: epithelial destruction → malabsorption

Key Features: vomiting, watery diarrhea

Diagnosis: stool PCR

Notes:

• Rotavirus - vaccine helpful

• Norovirus: low infectious dose + resistant to disinfectants = outbreaks

Protozoa

Giardia, Cryptosporidium, Entamoeba

Virulence:

• Attachment - Giardia

• Chlorine resistance - Cryptosporidium

• Tissue invasion - Entamoeba

Key Features:

• Giardia - greasy diarrhea (steatorrhea)

• Cryptosporidium - watery diarrhea

• Entamoeba - bloody diarrhea (dysentery)

Diagnosis: stool antigen/PCR

Notes: waterborne + travel related

PCR

amplifies & detects DNA sequences

faster, comprehensive, used for viruses

Stool culture

grow microorgs. from sample in lab

can test for antibiotic susceptibility

takes longer