Emerging bacterial pathogens US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Emerging bacterial pathogens. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Emerging bacterial pathogens US Medical PG Question 1: A 28-year-old man presents to his primary care provider complaining of intermittent stomach pain, non-bloody diarrhea, and weight loss for the last 3 months. He has occasional abdominal pain and fever. This condition makes studying difficult. He has tried omeprazole and dietary changes with no improvement. Past medical history is significant for occasional pain in the wrists and knees for several years. He takes ibuprofen for pain relief. His temperature is 38°C (100.4°F). On mental status examination, short-term memory is impaired. Attention and concentration are reduced. Examination shows no abnormalities or tenderness of the wrists or knees. There are no abnormalities on heart and lung examinations. Abdominal examination is normal. Upper endoscopy shows normal stomach mucosa but in the duodenum, there is pale yellow mucosa with erythema and ulcerations. Biopsies show infiltration of the lamina propria with periodic acid-Schiff (PAS)-positive macrophages. Which of the following best explains these findings?
- A. Wilson’s disease
- B. Celiac disease
- C. Giardia lamblia infection
- D. Whipple’s disease (Correct Answer)
- E. Crohn’s disease
Emerging bacterial pathogens Explanation: ***Whipple’s disease***
- The combination of **gastrointestinal symptoms** (diarrhea, weight loss, abdominal pain) with **arthralgia**, **fever**, **neurological symptoms** (impaired short-term memory, reduced attention/concentration), and **PAS-positive macrophages** in duodenal biopsies is highly characteristic of Whipple's disease.
- This multisystemic bacterial infection, caused by *Tropheryma whipplei*, often presents with diverse, non-specific symptoms before the classic GI findings, and central nervous system involvement is common.
*Wilson’s disease*
- This is a disorder of **copper metabolism** leading to copper accumulation in organs like the liver, brain, and eyes (Kayser-Fleischer rings).
- While it can cause neurological symptoms and liver disease, the GI and biopsy findings (PAS-positive macrophages) are not consistent with Wilson's disease.
*Celiac disease*
- Characterized by **malabsorption** due to an immune reaction to gluten, presenting with diarrhea, weight loss, and abdominal pain.
- However, jejunal biopsies would show **villous atrophy** and crypt hyperplasia, not PAS-positive macrophages, and neurological findings are less common and typically peripheral in nature.
*Giardia lamblia infection*
- This parasitic infection causes **diarrhea**, abdominal cramps, and malabsorption.
- Diagnosis is usually made by identifying **trophozoites or cysts** in stool samples or duodenal aspirates/biopsies, not PAS-positive macrophages.
*Crohn’s disease*
- An **inflammatory bowel disease** characterized by transmural inflammation, skip lesions, and granulomas, which can affect any part of the GI tract.
- While it can present with abdominal pain, diarrhea, weight loss, and arthralgia, the presence of **PAS-positive macrophages** in the duodenum and neurological involvement are not typical features of Crohn's disease.
Emerging bacterial pathogens US Medical PG Question 2: A 30-year-old woman comes to the emergency department because of fever, watery diarrhea, and abdominal cramping for the past 24 hours. She recently went to an international food fair. Her temperature is 39°C (102.2°F). Physical examination shows increased bowel sounds. Stool cultures grow gram-positive, spore-forming, anaerobic rods that produce alpha toxin. The responsible organism also causes which of the following physical examination findings?
- A. Diffuse, flaccid bullae
- B. Subcutaneous crepitus (Correct Answer)
- C. Facial paralysis
- D. Rose spots
- E. Petechial rash
Emerging bacterial pathogens Explanation: ***Subcutaneous crepitus***
- The description of gram-positive, spore-forming, anaerobic rods producing alpha toxin is characteristic of *Clostridium perfringens*.
- This organism causes **two main clinical syndromes**: (1) **food poisoning** with diarrhea (as in this patient), and (2) **gas gangrene** (clostridial myonecrosis).
- **Gas gangrene** is characterized by muscle necrosis, gas production in tissues (leading to **crepitus** on palpation), and rapid tissue destruction.
*Diffuse, flaccid bullae*
- This finding is more commonly associated with **staphylococcal scalded skin syndrome (SSSS)** caused by *Staphylococcus aureus* exfoliative toxins.
- *Clostridium perfringens* infections typically lead to **gas formation** and tissue necrosis rather than superficial bullae.
*Facial paralysis*
- **Facial paralysis** is characteristic of *Clostridium botulinum* (botulism), which produces neurotoxins that block acetylcholine release.
- *Clostridium perfringens* does not produce neurotoxins that cause paralysis; its pathogenicity is due to **alpha toxin** (phospholipase C) causing tissue destruction.
*Rose spots*
- **Rose spots** are characteristic of **typhoid fever**, caused by *Salmonella Typhi*.
- They are faint, salmon-colored maculopapular lesions on the trunk that blanch with pressure.
*Petechial rash*
- A **petechial rash** is often seen in conditions like **meningococcemia** (*Neisseria meningitidis*), **Rocky Mountain spotted fever**, or bacterial **endocarditis** due to vascular damage.
- While *Clostridium perfringens* can cause severe sepsis, a petechial rash is not its classic presentation.
Emerging bacterial pathogens US Medical PG Question 3: A 42-year-old woman with a history of multiple sclerosis and recurrent urinary tract infections comes to the emergency department because of flank pain and fever. Her temperature is 38.8°C (101.8°F). Examination shows left-sided costovertebral angle tenderness. She is admitted to the hospital and started on intravenous vancomycin. Three days later, her symptoms have not improved. Urine culture shows growth of Enterococcus faecalis. Which of the following best describes the most likely mechanism of antibiotic resistance in this patient?
- A. Increased efflux across bacterial cell membranes
- B. Production of beta-lactamase
- C. Alteration of penicillin-binding proteins
- D. Alteration of peptidoglycan synthesis (Correct Answer)
- E. Alteration of ribosomal targets
Emerging bacterial pathogens Explanation: ***Alteration of peptidoglycan synthesis***
- **Vancomycin** targets the **D-Ala-D-Ala terminus** on the peptidoglycan precursor, preventing cross-linking during bacterial cell wall synthesis.
- **Vancomycin resistance in Enterococcus faecalis** occurs through acquisition of resistance genes (vanA, vanB) that encode enzymes modifying the peptidoglycan precursor from **D-Ala-D-Ala to D-Ala-D-Lac**.
- This structural change reduces vancomycin's binding affinity by approximately 1000-fold, rendering the antibiotic ineffective.
- The mechanism directly involves **alteration of the peptidoglycan synthesis pathway**, specifically the terminal amino acid residues of the pentapeptide precursor.
*Increased efflux across bacterial cell membranes*
- This mechanism involves **efflux pumps that actively transport antibiotics out of the bacterial cell**, reducing intracellular concentration.
- While efflux pumps contribute to resistance for antibiotics like **tetracyclines, fluoroquinolones, and macrolides**, this is not the primary mechanism of vancomycin resistance in Enterococcus.
*Production of beta-lactamase*
- **Beta-lactamase enzymes** hydrolyze the **beta-lactam ring** of antibiotics like **penicillins and cephalosporins**, rendering them inactive.
- **Vancomycin is a glycopeptide antibiotic, not a beta-lactam**, so its efficacy is not affected by beta-lactamase production.
*Alteration of ribosomal targets*
- This mechanism confers resistance to antibiotics that target **bacterial ribosomes** to inhibit protein synthesis, such as **macrolides, aminoglycosides, and tetracyclines**.
- **Vancomycin acts on cell wall synthesis**, not protein synthesis, so alteration of ribosomal targets is not relevant to vancomycin resistance.
*Alteration of penicillin-binding proteins*
- **Penicillin-binding proteins (PBPs)** are the targets of **beta-lactam antibiotics** (penicillins, cephalosporins, carbapenems).
- Alterations in PBPs cause resistance to beta-lactams, not to vancomycin.
- **Vancomycin does not interact with PBPs**; it binds directly to the D-Ala-D-Ala terminus of peptidoglycan precursors in the cell wall.
Emerging bacterial pathogens US Medical PG Question 4: A 52-year-old man presents with 2 months of diarrhea, abdominal pain, and fatigue. He reports a weight loss of 4 kg (8 lb). He also says his joints have been hurting recently, as well. Past medical history is unremarkable. Review of systems is significant for problems with concentration and memory. Physical examination is unremarkable. A GI endoscopy is performed with a biopsy of the small bowel. Which of the following histologic finding would most likely be seen in this patient?
- A. PAS positive macrophages (Correct Answer)
- B. Non-caseating granulomas in the small intestine
- C. Absence of nerves in the myenteric plexus
- D. Blunting of the villi
- E. Crypt hyperplasia with increased intraepithelial lymphocytes
Emerging bacterial pathogens Explanation: **PAS positive macrophages**
- The clinical presentation with **diarrhea**, abdominal pain, weight loss, joint pain, and **neurological symptoms** (problems with concentration and memory) is classic for **Whipple's disease**.
- **Whipple's disease** is caused by the bacterium **Tropheryma whipplei**, which is characterized histologically by **foamy macrophages** in the lamina propria that stain **positive with Periodic Acid-Schiff (PAS)** due to undigested bacterial cell wall material.
*Non-caseating granulomas in the small intestine*
- **Non-caseating granulomas** are characteristic of **Crohn's disease**, which typically presents with abdominal pain, diarrhea, and weight loss, but **neurological symptoms** are not a primary feature.
- While Crohn's disease can cause joint pain (arthritis), the combination of GI and neurological symptoms points away from it.
*Absence of nerves in the myenteric plexus*
- An **absence of nerves in the myenteric plexus** is the hallmark of **Hirschsprung's disease**, which is a congenital disorder primarily affecting neonates and infants, causing intestinal obstruction and chronic constipation.
- This finding is inconsistent with the patient's age and presenting symptoms of diarrhea and neurological issues.
*Blunting of the villi*
- **Villi blunting** is characteristic of **celiac disease** (gluten-sensitive enteropathy), which presents with malabsorption symptoms like diarrhea, weight loss, and abdominal pain.
- However, **celiac disease** typically does not involve **neurological symptoms** like concentration and memory problems as a prominent feature, and the PAS-positive macrophages are specific to Whipple's.
*Crypt hyperplasia with increased intraepithelial lymphocytes*
- **Crypt hyperplasia** and **increased intraepithelial lymphocytes (IELs)** are seen in various small bowel pathologies, including **celiac disease** and **microscopic colitis**.
- While these findings suggest intestinal inflammation, they are not specific to **Whipple's disease** and do not account for the characteristic neurological involvement.
Emerging bacterial pathogens US Medical PG Question 5: A 57-year-old HIV-positive male with a history of intravenous drug abuse presents to the emergency room complaining of arm swelling. He reports that he developed progressively worsening swelling and tenderness over the right antecubital fossa three days prior. He recently returned from a trip to Nicaragua. His past medical history is notable for an anaphylactoid reaction to vancomycin. His temperature is 101.4°F (38.6°C), blood pressure is 140/70 mmHg, pulse is 110/min, and respirations are 20/min. Physical examination reveals an erythematous, fluctuant, and tender mass overlying the right antecubital fossa. Multiple injection marks are noted across both upper extremities. He undergoes incision and drainage and is started on an antibiotic that targets the 50S ribosome. He is discharged with plans to follow up in one week. However, five days later he presents to the same emergency room complaining of abdominal cramps and watery diarrhea. Which of the following classes of pathogens is most likely responsible for this patient’s current symptoms?
- A. Gram-negative curved bacillus
- B. Gram-negative bacillus
- C. Anaerobic flagellated protozoan
- D. Gram-positive bacillus (Correct Answer)
- E. Gram-positive coccus
Emerging bacterial pathogens Explanation: ***Gram-positive bacillus***
- The patient was administered an antibiotic targeting the **50S ribosomal subunit** following incision and drainage for a suspected skin infection (likely **MRSA** given IV drug abuse). This strongly suggests **clindamycin** was used.
- **Clindamycin** is a known risk factor for developing **Clostridioides (formerly Clostridium) difficile infection (CDI)**, which is caused by a **Gram-positive, spore-forming bacillus** and manifests with **abdominal cramps and watery diarrhea**.
*Gram-negative curved bacillus*
- This class of pathogens includes organisms like **Vibrio cholerae** or **Campylobacter jejuni**, which can cause diarrhea.
- However, the patient's presentation with **colitis** after antibiotic use is more consistent with **Clostridioides difficile**, not typically a curved Gram-negative bacillus.
*Gram-negative bacillus*
- While some Gram-negative bacilli (e.g., E. coli, Salmonella) can cause diarrhea, their association with **antibiotic-induced colitis** following treatment for a skin abscess is less direct than that of *Clostridioides difficile*.
- The initial skin infection in IV drug users is most commonly staphylococcal (Gram-positive coccus), for which a 50S targeting antibiotic would be prescribed.
*Anaerobic flagellated protozoan*
- This description often refers to pathogens like **Giardia lamblia** or **Trichomonas vaginalis**, which are not bacteria.
- While *Giardia* can cause diarrhea, it typically causes **malabsorption** and **greasy stools**, and wouldn't be triggered by recent antibiotic use for a skin infection.
*Gram-positive coccus*
- **Gram-positive cocci** (e.g., Staphylococcus aureus) are the likely cause of the initial skin infection/abscess.
- However, they do not typically cause **antibiotic-associated colitis** with watery diarrhea; rather, the *antibiotic treatment itself* for these organisms can predispose to *Clostridioides difficile*.
Emerging bacterial pathogens US Medical PG Question 6: A 63-year-old man with aortic valve disease is admitted to the hospital for a 3-week history of progressively worsening fatigue, fever, and night sweats. He does not smoke, drink alcohol, or use illicit drugs. Temperature is 38.2°C (100.8°F). Physical examination shows a systolic murmur and tender, erythematous nodules on the finger pads. Blood cultures show alpha-hemolytic, gram-positive cocci that are catalase-negative and optochin-resistant. Which of the following is the most likely causal organism?
- A. Streptococcus pneumoniae
- B. Staphylococcus epidermidis
- C. Viridans streptococci (Correct Answer)
- D. Streptococcus pyogenes
- E. Streptococcus gallolyticus
Emerging bacterial pathogens Explanation: ***Viridans streptococci***
- The patient's presentation with **subacute onset** of fever, fatigue, cardiac murmur, and **Osler nodes** (tender finger nodules) points to **infective endocarditis**. The micro-organism is described as **alpha-hemolytic**, **catalase-negative**, and **optochin-resistant**, which are characteristic features of **Viridans streptococci**.
- **Viridans streptococci** are a common cause of **subacute bacterial endocarditis**, especially in patients with pre-existing valvular disease like the **aortic valve disease** mentioned.
*Streptococcus pneumoniae*
- While **Streptococcus pneumoniae** is also **alpha-hemolytic** and **catalase-negative**, it is typically **optochin-sensitive** and a common cause of **pneumonia** and **meningitis**, not usually subacute endocarditis from oral flora.
- Endocarditis caused by *S. pneumoniae* is rare and usually associated with a more fulminant course.
*Staphylococcus epidermidis*
- **Staphylococcus epidermidis** is a **coagulase-negative staphylococcus** that is a common cause of **prosthetic valve endocarditis** and is **catalase-positive**, unlike the organism described here.
- It is not typically alpha-hemolytic.
*Streptococcus pyogenes*
- **Streptococcus pyogenes** is **beta-hemolytic** and **catalase-negative**, and typically causes **pharyngitis** and **skin infections**, or sometimes **acute endocarditis**.
- It does not fit the description of an **alpha-hemolytic**, **optochin-resistant** organism.
*Streptococcus gallolyticus*
- **Streptococcus gallolyticus** (formerly *Streptococcus bovis*) is associated with **bacteremia** and **endocarditis**, particularly in patients with **gastrointestinal malignancies**.
- While it is **alpha-hemolytic** and **catalase-negative**, it is typically differentiated by its growth in **bile esculin** and is not primarily defined by optochin resistance characteristic of Viridans group.
Emerging bacterial pathogens US Medical PG Question 7: A 44-year-old woman presents to her primary care physician for worsening dysuria, hematuria, and lower abdominal pain. Her symptoms began approximately 2 days ago and have progressively worsened. She denies headache, nausea, vomiting, or diarrhea. She endorses feeling "feverish" and notes to having foul smelling urine. She has a past medical history of Romano-Ward syndrome and is not on any treatment. She experiences profuse diarrhea and nausea when taking carbapenems and develops a severe rash with cephalosporins. Her temperature is 100.4°F (38C), blood pressure is 138/93 mmHg, pulse is 100/min, and respirations are 18/min. On physical exam, the patient appears uncomfortable and there is tenderness to palpation around the bilateral flanks and costovertebral angle. A urinalysis and urine culture is obtained and appropriate antibiotics are administered. On her next clinical visit urine studies and a basic metabolic panel is obtained, which is shown below:
Serum:
Na+: 140 mEq/L
Cl-: 101 mEq/L
K+: 4.2 mEq/L
HCO3-: 22 mEq/L
BUN: 20 mg/dL
Glucose: 94 mg/dL
Creatinine: 2.4 mg/dL
Urinalysis
Color: Yellow
Appearance: Clear
Blood: Negative
pH: 7 (Normal 5-8)
Protein: Negative
Nitrite: Negative
Leukocyte esterase: Negative
Cast: Epithelial casts
FeNa: 3%
Urine culture
Preliminary report: 10,000 CFU/mL E. coli
Which of the following antibiotics was most likely given to this patient?
- A. Aztreonam (Correct Answer)
- B. Vancomycin
- C. Clindamycin
- D. Levofloxacin
- E. Tobramycin
Emerging bacterial pathogens Explanation: ***Aztreonam***
- This patient presents with **pyelonephritis** (fever, flank pain, dysuria, hematuria, CVA tenderness) with confirmed *E. coli* urinary tract infection
- She has **severe allergies to both carbapenems and cephalosporins**, eliminating most beta-lactam options
- **Aztreonam** is a monobactam antibiotic with excellent activity against **gram-negative bacteria** including *E. coli*
- Critically, aztreonam **does not cross-react** with other beta-lactams due to its unique monocyclic structure, making it safe in patients with penicillin/cephalosporin allergies
- **No QT prolongation** - safe in Romano-Ward syndrome
*Vancomycin*
- Primarily effective against **gram-positive bacteria** (MRSA, enterococci)
- **No activity against gram-negative organisms** like *E. coli*
- Would not be appropriate for this urinary tract infection
*Clindamycin*
- Used primarily for **anaerobic infections** and some gram-positive bacteria
- **Limited to no activity against *E. coli*** and other gram-negative organisms
- Not an effective choice for gram-negative pyelonephritis
*Levofloxacin*
- Fluoroquinolone with excellent gram-negative coverage and urinary penetration
- Generally a good choice for *E. coli* pyelonephritis
- **CONTRAINDICATED in this patient**: Fluoroquinolones cause **QT interval prolongation**, which is dangerous in patients with **Romano-Ward syndrome (congenital long QT syndrome)**
- This critical drug-disease interaction eliminates fluoroquinolones as an option
*Tobramycin*
- Aminoglycoside with good gram-negative coverage including *E. coli*
- **Highly nephrotoxic** - contraindicated in this patient with **acute kidney injury** (elevated creatinine 2.4 mg/dL, epithelial casts, FENa 3%)
- Risk of worsening renal function and ototoxicity makes it a poor choice
Emerging bacterial pathogens US Medical PG Question 8: A group of scientists studied the effects of cytokines on effector cells, including leukocytes. They observed that interleukin-12 (IL-12) is secreted by antigen-presenting cells (APCs) in response to bacterial lipopolysaccharide. When a CD4+ T cell is exposed to this interleukin, which of the following responses will it have?
- A. Responds to extracellular pathogens
- B. Cell-mediated immune responses (Correct Answer)
- C. Releases granzymes
- D. Activate B cells
- E. Secrete IL-4
Emerging bacterial pathogens Explanation: ***Cell-mediated immune responses***
- **IL-12** from antigen-presenting cells promotes the differentiation of **naïve CD4+ T cells** into **Th1 cells**.
- **Th1 cells** are the primary drivers of **cell-mediated immunity**, producing cytokines like **IFN-γ** that activate macrophages and cytotoxic T cells to combat intracellular pathogens.
*Responds to extracellular pathogens*
- Responses to extracellular pathogens are primarily mediated by **Th2 cells** and **humoral immunity**.
- **Th2 cells** are induced by cytokines like **IL-4** and are involved in allergic reactions and antiparasitic responses.
*Releases granzymes*
- **Granzymes** are released by **cytotoxic T lymphocytes (CTLs)** and **natural killer (NK) cells** to induce apoptosis in infected or cancerous cells.
- While Th1 cells help activate CTLs, they do not directly release granzymes themselves.
*Activate B cells*
- **B cell activation** and antibody production are primarily driven by **Th2 cells** and **follicular helper T (Tfh) cells**.
- Th1 cells are more involved in responses against intracellular pathogens, which typically do not involve direct B cell activation.
*Secrete IL-4*
- **IL-4** is the signature cytokine of **Th2 cells**, which are primarily involved in humoral immunity and allergic responses.
- **IL-12** inhibits Th2 differentiation and promotes Th1 differentiation, so a CD4+ T cell exposed to IL-12 would not secrete IL-4.
Emerging bacterial pathogens US Medical PG Question 9: An 8-year-old child is brought to the emergency department because of profuse diarrhea and vomiting that have lasted for 2 days. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. Past medical history is noncontributory. The family recently made a trip to India to visit relatives. Today, his heart rate is 100/min, respiratory rate is 22/min, blood pressure is 105/65 mm Hg, and temperature is 37.2ºC (99.0°F). On physical examination, he appears unwell with poor skin turgor and dry oral mucosa. His heart has a regular rate and rhythm and his lungs are clear to auscultation bilaterally. His abdomen is sensitive to shallow and deep palpation. A gross examination of the stool reveals a 'rice water' appearance. Diagnostic microbiology results are pending. Which of the following is the best diagnostic test to aid in the identification of this patient's condition?
- A. Methylene blue wet mount
- B. Gram stain of stool sample
- C. Dark-field microscopy
- D. Rapid diagnostic test for cholera toxin
- E. Stool culture on TCBS agar (Correct Answer)
Emerging bacterial pathogens Explanation: ***Stool culture on TCBS agar***
- The patient's symptoms (profuse watery diarrhea, vomiting, dehydration, history of travel to India) strongly suggest **cholera**, caused by *Vibrio cholerae*.
- **Thiosulfate-citrate-bile salts-sucrose (TCBS) agar** is a highly selective medium specifically used for isolating *Vibrio* species.
*Methylene blue wet mount*
- This test is primarily used to identify **white blood cells (leukocytes)** in stool, which indicate an inflammatory process, such as in *Shigella* or *Salmonella* infections.
- Cholera is a **non-inflammatory** diarrhea, so a methylene blue wet mount would likely be negative for leukocytes and therefore not helpful for diagnosis.
*Gram stain of stool sample*
- While Gram stain can classify bacteria, it is generally **not useful for diagnosing diarrheal diseases** caused by specific enteric pathogens, as stool contains a vast array of Gram-negative and Gram-positive bacteria.
- It would be difficult to identify *Vibrio cholerae* among the normal flora using this method alone.
*Dark-field microscopy*
- This technique is typically used to visualize **spirochetes**, such as *Treponema pallidum* (syphilis), due to their characteristic motility and morphology.
- While *Vibrio cholerae* are motile rods, dark-field microscopy is **not the standard or most sensitive method** for its identification in a stool sample, especially compared to selective cultures.
*Rapid diagnostic test for cholera toxin*
- While such tests exist and can be useful in epidemic settings for quick screening, they generally have **lower sensitivity and specificity** compared to culture-based methods.
- **Culture remains the gold standard** for definitive diagnosis, especially for guiding treatment and epidemiological surveillance.
Emerging bacterial pathogens US Medical PG Question 10: A 12-year-old boy admitted to the intensive care unit 1 day ago for severe pneumonia suddenly develops hypotension. He was started on empiric antibiotics and his blood culture reports are pending. According to the nurse, the patient was doing fine until his blood pressure suddenly dropped. Vital signs include: blood pressure is 88/58 mm Hg, temperature is 39.4°C (103.0°F), pulse is 120/min, and respiratory rate is 24/min. His limbs feel warm. The resident physician decides to start him on intravenous vasopressors, as the blood pressure is not responding to intravenous fluids. The on-call intensivist suspects shock due to a bacterial toxin. What is the primary mechanism responsible for the pathogenesis of this patient's condition?
- A. Inactivation of elongation factor (EF) 2
- B. Inhibition of GABA and glycine
- C. Inhibition of acetylcholine release
- D. Release of tumor necrosis factor (TNF) (Correct Answer)
- E. Degradation of lecithin in cell membranes
Emerging bacterial pathogens Explanation: ***Release of tumor necrosis factor (TNF)***
- The patient's presentation with **warm limbs** and **hypotension** despite fluid resuscitation in the setting of severe pneumonia is highly suggestive of **septic shock**.
- **Bacterial toxins**, particularly **endotoxins** from gram-negative bacteria or **exotoxins** like superantigens, trigger a massive **inflammatory response** by stimulating immune cells to release pro-inflammatory cytokines such as **TNF-α**, IL-1, and IL-6, leading to systemic vasodilation and capillary leak.
*Inactivation of elongation factor (EF) 2*
- This is the mechanism of action of **diphtheria toxin** and **exotoxin A** from *Pseudomonas aeruginosa*.
- While these toxins can cause severe systemic illness, their primary role is not typically the induction of septic shock characterized by widespread vasodilation and warm extremities.
*Inhibition of GABA and glycine*
- This mechanism is characteristic of **tetanus toxin**, which prevents the release of inhibitory neurotransmitters and leads to spastic paralysis.
- This is not consistent with the patient's presentation of septic shock.
*Inhibition of acetylcholine release*
- This is the mechanism of action of **botulinum toxin**, which causes flaccid paralysis by blocking acetylcholine release at the neuromuscular junction.
- This effect is not associated with the pathogenesis of septic shock.
*Degradation of lecithin in cell membranes*
- This mechanism is associated with **alpha toxin** of *Clostridium perfringens* (lecithinase), which causes gas gangrene and hemolysis.
- While this toxin contributes to tissue damage in certain infections, it is not the primary mechanism behind the systemic inflammatory response and vasodilation seen in septic shock.
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