Infectious Diseases (IRAT 10)

Which bacteria is a gram negative bacilli with motile polar flagellum?

Campylobacter Jejuni

How is Campylobacter Jejuni transmitted?

1. Fecal—> oral

2. Food Borne ( unpasteurized milk, contaminated water, undercooked poultry)

3. Contact with infected animal ( pigs, dogs, cats)

What’s the incubation period for Campylobacter Jejuni?

INCUBATION PERIOD: 2-4 days

At what temperatures does Campylobacter Jejuni grow best?

high temperatures

What are the initial clinical findings seen with Campylobacter Jejuni?

Initial watery diarrhea —> progress to BLOOD DIARRHEA (enterocolitis) with fever, muscle pain, malaise, HA.

What abdominal presentation can mimic appendicitis in Campylobacter Jejuni infection?

What GI condition can Campylobacter also present as?

Pseudoappendicitis; Colitis.

Is Campylobacter Jejuni usually self-limited? How long does it last?

Yes — lasts about 5–7 days. Will get better on its own 

Which group is more likely to have complications from Campylobacter Jejuni?

HIV patients

What high-yield neurologic complication is associated with Campylobacter Jejuni?

Guillain-Barré syndrome (GBS).

What autoimmune complication can follow Campylobacter Jejuni infection?

Reactive arthritis.

What severe GI complication can occur, especially in immunocompromised patients with Campylobacter Jejuni?

Toxic megacolon.

What are the two main virulence factors of Campylobacter Jejuni?

Flagellar filaments (flagellin)
Cytolethal distending toxin (CDT)

What is the MOA of Campylobacter Jejuni

Antiganglioside abs attack peripheral organ—> Guillain-Barré syndrome (GBS).

What would you use to diagnose Campylobacter Jejuni?

⭐PCR OR Stool culture (Skirrow’s agar) Which

How do you treat a Campylobacter Jejuni?

1. Supportive Care (hydration)

2. SEVERE: Antibiotics:

   • (Azithromycin or Fluoroquinolones)

🦞Which bacteria is a gram negative rod with a motile polar flagellum and causes high volume fluid loss with electrolyte derangements

🦞Vibrio cholerae

(⚠ Severe dehydration → can cause hypovolemic shock) 

How is Vibrio cholera transmitted?

💩➡👄 Fecal–oral route

What are the two main sources of cholera infection?

🚰 Contaminated water
🦪 Uncooked seafood (esp. raw shellfish)

Where do cholera outbreaks commonly occur?

🌍 Areas with poor sanitation
👥 Overcrowded regions (refugee camps, disaster zones)

What is the incubation period (exposure to developing infection) for cholera?

⏱ 0–2 days (very rapid onset)

What are the key symptoms of Cholera?

Key Symptoms

🌡 Low-grade fever
🤮 Vomiting + abdominal pain
💦 Profuse non-bloody watery diarrhea (“rice-water stool”)

Major Risk with Cholera?

⚠ Hypovolemic shock from massive fluid + electrolyte loss

What is the pathophysiology of Vibrio cholera?

🦠 Cholera toxin activates adenylate cyclase → ↑ cAMP → stimulates CFTR channels → massive Cl⁻ secretion + inhibited Na⁺/Cl⁻ absorption → huge water loss into the intestinal lumen (“rice-water diarrhea”).

⭐ What the Diagram Shows (Simplified)1⃣ Cholera toxin enters the intestinal cell

The toxin binds → activates a G-protein inside the cell.

2⃣ G-protein turns ON adenylate cyclase

Adenylate cyclase → increases cAMP levels.

📈 More cAMP = cell becomes a salt-secreting machine

3⃣ High cAMP forces CFTR channels to pump OUT chloride (Cl⁻)

The purple channel → CFTR
It starts secreting HUGE amounts of Cl⁻ into the GI lumen.

⬆ Cl⁻ goes OUT into the gut

4⃣ When Cl⁻ is pushed out… Na⁺ and water follow it

Opposites attract → the body must keep charges balanced.

So:

• 🧂 Na⁺ follows Cl⁻

• 💧 Water follows Na⁺ + Cl⁻

• Result = massive watery diarrhea

5⃣ Why you wrote “H⁺” and “pH↑”?

In MASSIVE diarrhea:

• You lose lots of H⁺ from the GI tract

• Losing acid (H⁺) → makes the blood more alkalotic

• This causes metabolic alkalosis → pH increases

So your arrow 🡅 pH ↑ = blood becomes more alkaline.

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Putting it all together (super clear)

Cholera toxin → ↑ cAMP → ↑ CFTR → Cl⁻ pumped into gut → Na⁺ + water follow → huge water loss → “rice-water diarrhea” → dehydration + ↑ blood pH (alkalosis).

🔍 How is cholera diagnosed?

• 👀 Clinical presentation

• 💧 Dipstick rapid test (initial)

• 🧫 Stool culture (confirmatory)

💧 What is the most critical treatment for cholera?

➡ Aggressive fluid + electrolyte replacement

💊 Which antibiotics are used for cholera?

• Doxycycline (preferred)

• Azithromycin

• Ciprofloxacin
  (Used to shorten course; reserved for severe cases)

🧫 Which species cause non-typhoidal Salmonellosis?

• S. enteriditis

• S. typhimurium

🔬 What type of bacteria are non-typhoidal Salmonella?

• Gram-negative bacilli

• Encapsulated

🚩 Do Salmonella have flagella?

Yes — they contain flagella (motile).

🍗 What is Salmonella (*hint: animals) a common cause of in the U.S.?

Foodborne disease (poultry, raw eggs, milk products) OR Contact with reptiles (i.e. turtles, snakes) 

Whats the incubation period for NON-typhoidal Salmonella?

0-2 days

🤒 What are the common symptoms of non-typhoidal Salmonella?

• Fever

• Nausea

• Vomiting

• Myalgia

💩 What type of diarrhea occurs in Salmonella?

• Brown-green “pea soup” diarrhea

• Can be bloody

⚠ What complications occur (esp. in immunocompromised patients)?

• Reactive arthritis

• Systemic disease: osteomyelitis, myocarditis, aortitis

Where does Salmonella colonize?

📍 Ileum and colon

How does Salmonella invade cells?

🧬 Uses Type III Secretion System (T3SS) to inject proteins and invade intestinal epithelial cells

How does Salmonella cross the mucosa?

➡ Penetrates M cells and is taken up by macrophages

What immune response does Salmonella trigger?

🔥 Releases pro-inflammatory cytokines, recruiting neutrophils

What causes tissue injury in a Salmonellosis (non-typhoidal infection?

🧨 Neutrophil influx → injury + disruption of tight junctions

How do we diagnose Salmonellosis *non-typhoidal infection?

Stool culture

How do you treat a Salmonellosis infection? 

1. Mild-Moderate: supportive care ONLY( hydration)

2. Severe: Immunocompromised or invasive disease: ☆Abx ☆

💊 Should antibiotics be used?

➡ Generally NO — they can prolong carriage
✔ Use ONLY if:

• Invasive disease

• Immunocompromised patient

• Severe infection (systemic, hospitalized, ≥9 diarrheal episodes/day)

Which bacteria is a Gram-negative bacilli, encapsulated. It contains flagella and causes🤒 Typhoid fever.

Salmonella Typhi

How does Salmonella Typhi spread?

👤 Human host ONLY
🍽🚰 Spread through contaminated food or water (fecal-oral route)

What are the clinical findings associated with Salmonella Typhi?

🤒 Enteric Fevers: Persistent fever + headaches + myalgias
🚽 ➡ Constipation → non-bloody “pea-soup” diarrhea”

⭐Rose spots

🌹 Faint pink macules on abdomen/trunk (classic sign)

What are the complications of Salmonella Typhi (Typhoid fever)?

⭐Complications

🫀 Hepatosplenomegaly
🩸 GI bleeding (ulceration)

❤‍🩹 What is “relative bradycardia” associated with Salmonella Typhi?

➡ Fever with a slow pulse, classic for Typhoid. (high temp, low HR)

🚪 How does Salmonella Typhi enter the body?

➡ Penetrates via M-cells in the intestinal epithelium

🧫 What intestinal structure becomes hypertrophied in Typhoid?

➡ Peyer’s patches (in the submucosa)

🩸 How does Salmonella Typhi disseminate?

➡ Through lymphatics + bloodstream

🏥 Where does Salmonella Typhi replicate?

➡ Reticuloendothelial system (RES)
(liver, spleen, bone marrow)

🫀 What major finding results from RES involvement?

➡ Hepatosplenomegaly

Pathophysiology of Salmonella Typhi?

Salmonella Typhi enters through M-cells → infects and hypertrophies Peyer’s patches → spreads via lymphatics + bloodstream → replicates in the reticuloendothelial system (liver, spleen, bone marrow) → causes hepatosplenomegaly.

How do you diagnose Salmonella Typhi?

1. Blood or bone marrow culture

2. Bloodwork Findings: mild normocytic anemia and leukopenia

What is the treatment for Salmonella Typhi?

Fluoroquinolones (☆Cipro) OR Azithromycin

🔬 What type of bacteria is Shigella?

➡ Gram-negative rods

🇺🇸 Which Shigella species is most common in the U.S.?

➡ S. sonnei

☠ Which Shigella species produces the most toxin?

➡ S. dysenteriae

How does Shigellosis spread?

How is Shigella transmitted?

🍽 Foodborne (unpasteurized milk, raw unwashed vegetables)
💩➡👄 Fecal-oral

🍑 Can Shigella spread through sexual contact?

➡ Yes — oral-anal sexual contact

⚠ How infectious is Shigella?

➡ Highly infectious — very low inoculum required

⏱ What is the incubation period?

➡ 0–2 days

What are the Classic Symptoms of Shigellosis?

🤒 High fever
🤕 Abdominal cramps
🚽 Tenesmus (painful urge to poop)

What is the diarrhea pattern of Shigellosis?

💦➡🩸 Explosive watery diarrhea → progresses to bloody, mucoid diarrhea (dysentery)

What are the major complications of Shigella?

⚠ Major complications of Shigella:

• 🔥 Reactive arthritis

• 🩸 HUS (hemolytic uremic syndrome)

• 💥 Toxic megacolon

Shigella — Pathophysiology?

🦠 Shiga toxin (Shiga toxin → vessel damage → microclots → RBC destruction → kidney failure)
🔹 Inactivates 60S ribosome → stops protein synthesis
🔹 Endothelial damage → hemorrhage
🔹 ↑ Cytokines → HUS ( hemolytic uremic syndrome)

How would you diagnose and treat a Shigellosis infection?

☆Diagnose: Stool Culture💩

☆Treatment:

1. Supportive Care: Hydration

2. Antibiotics: Azithromycin or Cipro—> used to shorten duration and reduce spread.

Which gram-negative rod commonly causes traveler’s diarrhea and is transmitted through contaminated food and water?

☆Enterotoxigenic E. coli (ETEC)

What are the Clinical Findings of ETEC?

Abrupt onset abdominal cramps—> vomiting—> watery, NON-bloody diarrhea

How does Enterotoxigenic Escherichia coli attach to the intestine?

🧲 Using fimbriae to stick to intestinal epithelium

What toxins does Enterotoxigenic Escherichia coli produce?

☠ LT (heat-labile) + ST (heat-stable) enterotoxins

What does heat-labile (LT) toxin do?

⚡ It activates adenylate cyclase, which increases cyclic adenosine monophosphate (cAMP)

What does the heat-stable (HT) toxin do?

💥 It activates guanylate cyclase, which increases cyclic guanosine monophosphate (cGMP).

What is the result of increased cAMP and cGMP?

💦 They cause increased chloride secretion and decreased sodium and chloride absorption → leading to major water loss → watery diarrhea.

What condition is Enterotoxigenic Escherichia coli (ETEC) known for causing?

✈🌎 Traveler’s diarrhea.

Which bacteria is the 0157:H7, gram-negative rod due to contaminated beef products?

⊹ ࣪ ˖Enterohemorrhagic E. coli⊹ ࣪ ˖

Enterohemorrhagic E. coli — Transmission?

🍽 Foodborne:

• Ingestion of undercooked meat

• Contaminated water

• Raw leafy vegetables

What are the clinical findings of Enterohemorrhagic E.coli?

Bloody stool, low grade fever, cramping, & vomiting

How does Enterohemorrhagic Escherichia coli enter the intestinal tissue?

🚪 Enterohemorrhagic Escherichia coli crosses the intestinal lining by passing through M cells.

What does Enterohemorrhagic Escherichia coli do once it reaches the lamina propria?

🧫 Once in the lamina propria, the bacteria produce a shiga-like toxin that induces cell death.

What is the main virulence toxin produced by Enterohemorrhagic Escherichia coli?

☠ The main virulence toxin is the shiga-like toxin, also called verotoxin.

How does the shiga-like toxin cause cellular injury?

🛑 The shiga-like toxin inactivates the 60S ribosome, which stops protein synthesis and leads to cell death.

How does the shiga-like toxin damage blood vessels?

💥 It causes endothelial cell injury, which results in hemorrhage.

What life-threatening complication can result from shiga-like toxin?

⚠ The toxin increases cytokine release, which can trigger hemolytic-uremic syndrome (HUS).