Gram-negative

Gram-negative US Medical PG Question 1: A 42-year-old man with a history of gout and hypertension presents to his family physician with a complaint of increased left knee pain over the past 2 days. He also reports swelling and redness of the left knee and is unable to bear weight on that side. He denies any prior surgery or inciting trauma to the knee. His temperature is 97.0°F (36.1°C), blood pressure is 137/98 mm Hg, pulse is 80/min, respirations are 13/min, and oxygen saturation is 98% on room air. Physical examination reveals a left knee that is erythematous, swollen, warm-to-touch, and extremely tender to palpation and with attempted flexion/extension movement. His left knee range of motion is markedly reduced compared to the contralateral side. Joint aspiration of the left knee is performed with synovial fluid analysis showing turbid fluid with a leukocyte count of 95,000/mm^3, 88% neutrophils, and a low glucose. Gram stain of the synovial fluid is negative. Results from synovial fluid culture are pending. Which of the following is the best treatment regimen for this patient?

• A. Ceftriaxone
• B. Piperacillin-tazobactam
• C. Vancomycin and ceftazidime (Correct Answer)
• D. Indomethacin and colchicine
• E. Acetaminophen and ibuprofen

Gram-negative Explanation: ***Vancomycin and ceftazidime*** - The patient presents with **acute monoarticular arthritis** with signs of **septic arthritis**, including a highly inflammatory synovial fluid (95,000 WBCs/mm^3, 88% neutrophils, low glucose) and inability to bear weight. - **Empiric broad-spectrum antibiotic coverage** is crucial before culture results, typically involving an agent effective against **Gram-positive bacteria** (e.g., vancomycin for MRSA) and an agent against **Gram-negative bacteria** (e.g., ceftazidime for *Pseudomonas* or other resistant gram-negatives), especially in patients with comorbidities like gout. *Ceftriaxone* - Ceftriaxone is a **third-generation cephalosporin** that provides good coverage for many Gram-negative bacteria and some Gram-positive bacteria. - However, it **does not cover *Pseudomonas aeruginosa* or methicillin-resistant *Staphylococcus aureus* (MRSA)**, which are important pathogens to consider in septic arthritis, especially without a definitive causative organism. *Piperacillin-tazobactam* - Piperacillin-tazobactam is a **broad-spectrum antibiotic** with good coverage for Gram-positive, Gram-negative (including *Pseudomonas*), and anaerobic bacteria. - While it offers good broad coverage, it also **does not reliably cover MRSA**, which is a significant concern in empirical treatment of septic arthritis given its prevalence. *Indomethacin and colchicine* - This regimen is specific for the treatment of **acute gout flares** by reducing inflammation. - While the patient has a history of gout, the **highly elevated leukocyte count** with a predominance of neutrophils and low glucose in the synovial fluid strongly indicate **septic arthritis**, which is a medical emergency requiring antibiotic treatment. *Acetaminophen and ibuprofen* - These medications provide **analgesia and anti-inflammatory effects** for pain relief. - They are **insufficient as primary treatment** for septic arthritis, which necessitates urgent antimicrobial therapy to prevent joint destruction and systemic complications.

Gram-negative US Medical PG Question 2: 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

Gram-negative 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.

Gram-negative US Medical PG Question 3: An 18-year old college freshman presents to his university clinic because he has not been feeling well for the past two weeks. He has had a persistent headache, occasional cough, and chills without rigors. The patient’s vital signs are normal and physical exam is unremarkable. His radiograph shows patchy interstitial lung infiltrates and he is diagnosed with atypical pneumonia. The patient is prescribed azithromycin and takes his medication as instructed. Despite adherence to his drug regimen, he returns to the clinic one week later because his symptoms have not improved. The organism responsible for this infection is likely resistant to azithromycin through which mechanism?

• A. Mutation in topoisomerase II
• B. Methylation of ribosomal binding site
• C. Presence of a beta-lactamase
• D. Decreased binding to RNA polymerase
• E. Insertion of drug efflux pumps (Correct Answer)

Gram-negative Explanation: ***Insertion of drug efflux pumps*** - **Azithromycin** is a macrolide antibiotic that inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**. - In **Mycoplasma pneumoniae** (the most common cause of atypical pneumonia in young adults), the **most common** mechanism of macrolide resistance is through **efflux pumps**, particularly the **mef genes**. - These efflux pumps actively transport macrolides out of the bacterial cell, reducing intracellular drug concentration and conferring resistance. - This mechanism is responsible for the majority of macrolide-resistant *M. pneumoniae* isolates worldwide. *Methylation of ribosomal binding site* - **Methylation** of the ribosomal binding site (specifically the **23S rRNA** via erm genes) does prevent azithromycin from binding effectively. - While this is a valid macrolide resistance mechanism seen in organisms like *Streptococcus pneumoniae* and *Streptococcus pyogenes*, it is **less common** in *Mycoplasma pneumoniae*. - Efflux pumps (mef) are the predominant mechanism in *M. pneumoniae* resistant strains. *Mutation in topoisomerase II* - **Topoisomerase II** (DNA gyrase) is the target of **fluoroquinolone antibiotics**, not macrolides. - Mutations in this enzyme lead to resistance against fluoroquinolones, such as **ciprofloxacin**. *Presence of a beta-lactamase* - **Beta-lactamase enzymes** inactivate **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) by hydrolyzing their beta-lactam ring. - Additionally, *Mycoplasma pneumoniae* **lacks a cell wall**, making it inherently resistant to all beta-lactam antibiotics regardless of beta-lactamase production. *Decreased binding to RNA polymerase* - **RNA polymerase** is the target for antibiotics like **rifampin**, which inhibits bacterial transcription. - Decreased binding to RNA polymerase would lead to rifampin resistance, not azithromycin resistance.

Gram-negative US Medical PG Question 4: A 77-year-old woman is brought to the emergency department from her nursing home because she was found down overnight. On presentation she was found to be delirious and was unable to answer questions. Chart review shows that she is allergic to cephalosporins. Her temperature is 102.2°F (39°C), blood pressure is 105/52 mmHg, pulse is 94/min, and respirations are 23/min. Physical exam reveals a productive cough. A metabolic panel is obtained with the following results: Serum: Na+: 135 mEq/L Cl-: 95 mEq/L K+: 4 mEq/L HCO3-: 19 mEq/L BUN: 40 mg/dL Creatinine: 2.5 mg/dL Glucose: 150 mg/dL Based on these findings two different drugs are started empirically. Gram stain on a blood sample is performed showing the presence of gram-positive organisms on all samples. One of the drugs is subsequently stopped. The drug that was most likely stopped has which of the following characteristics?

• A. Resistance conveyed through acetylation
• B. Associated with red man syndrome
• C. Single-ringed ß-lactam structure (Correct Answer)
• D. Causes discolored teeth in children
• E. Accumulates inside bacteria via O2-dependent uptake

Gram-negative Explanation: ***Single-ringed ß-lactam structure*** - The patient presents with **sepsis** due to **pneumonia** likely caused by **gram-positive organisms**. Given a cephalosporin allergy, **aztreonam** (a monobactam) would be an initial empirical antibiotic choice to cover gram-negative bacteria, alongside a drug for gram-positive coverage (like vancomycin). - Since the **blood cultures** confirmed **gram-positive organisms**, the drug covering gram-negative bacteria (aztreonam) would be stopped. Aztreonam is characterized by its **single-ringed β-lactam structure**. *Resistance conveyed through acetylation* - This mechanism of resistance is typical of **aminoglycosides** (e.g., gentamicin) and **chloramphenicol**. - Aminoglycosides were unlikely to be one of the empirically started drugs, as they are often used in combination with β-lactams, and this patient has a cephalosporin allergy. *Associated with red man syndrome* - **Red man syndrome** is a common adverse effect associated with **vancomycin** administration, especially with rapid infusion. - Vancomycin would likely be continued, as it effectively targets gram-positive organisms, including **MRSA**, and is a suitable alternative given the cephalosporin allergy. *Causes discolored teeth in children* - This is a characteristic side effect of **tetracyclines** (e.g., doxycycline), which are contraindicated in young children and pregnant women due to their effects on bone and teeth development. - Tetracyclines are not typically first-line empiric therapy for severe pneumonia or sepsis, especially in an elderly patient. *Accumulates inside bacteria via O2-dependent uptake* - This describes the mechanism of uptake for **aminoglycosides**. Their entry into bacteria is an **energy-dependent process** requiring oxygen. - As mentioned, aminoglycosides are less likely to be the initial drug stopped in this scenario, as they target gram-negative bacteria.

Gram-negative US Medical PG Question 5: A 26-year-old woman presents to the emergency department with fever, chills, lower quadrant abdominal pain, and urinary frequency for the past week. Her vital signs include temperature 38.9°C (102.0°F), pulse 110/min, respirations 16/min, and blood pressure 122/78 mm Hg. Physical examination is unremarkable. Urinalysis reveals polymorphonuclear leukocytes (PMNs) > 10 cells/HPF and the presence of bacteria (> 105 CFU/mL). Which of the following is correct concerning the most likely microorganism responsible for this patient’s condition?

• A. Gram-positive cocci that grow in clusters
• B. Pear-shaped motile protozoa
• C. Gram-positive cocci that grow in chains
• D. Gram-negative rod-shaped bacilli (Correct Answer)
• E. Nonmotile, pleomorphic rod-shaped, gram-negative bacilli

Gram-negative Explanation: ***Gram-negative rod-shaped bacilli*** - The symptoms of **fever, chills, abdominal pain, and urinary frequency**, along with urinalysis showing **pyuria (>10 PMNs/HPF) and bacteriuria (>10^5 CFU/mL)**, are highly suggestive of a **urinary tract infection (UTI)**. - **_Escherichia coli_**, a **gram-negative rod-shaped bacillus**, is the most common cause of community-acquired UTIs, accounting for over 80% of cases. *Gram-positive cocci that grow in clusters* - This morphology describes **Staphylococcus species**, which can cause UTIs but are **less common** than *E. coli* in uncomplicated cases. - **_Staphylococcus saprophyticus_** is a notable cause of UTIs in young, sexually active women, but it is not the most likely overall. *Pear-shaped motile protozoa* - This description typically refers to **_Giardia lamblia_**, which causes **gastrointestinal infections** (giardiasis) and is not associated with UTIs. - UTIs are bacterial infections, not protozoal. *Gram-positive cocci that grow in chains* - This morphology describes **Streptococcus species**, such as **_Streptococcus agalactiae_** (Group B Streptococcus), which can cause UTIs, especially during pregnancy. - However, they are **less frequent causes** of uncomplicated UTIs compared to *E. coli*. *Nonmotile, pleomorphic rod-shaped, gram-negative bacilli* - This description might fit certain bacteria like **_Haemophilus influenzae_**, which typically causes **respiratory tract infections or meningitis**, not UTIs. - While *E. coli* is a gram-negative rod, it is **motile**, distinguishing it from this option.

Gram-negative US Medical PG Question 6: 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

Gram-negative 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

Gram-negative US Medical PG Question 7: A 62-year-old man is brought to the emergency department from a senior-care facility after he was found with a decreased level of consciousness and fever. His personal history is relevant for colorectal cancer that was managed with surgical excision of the tumor. Upon admission, he is found to have a blood pressure of 130/80 mm Hg, a pulse of 102/min, a respiratory rate of 20/min, and a body temperature 38.8°C (101.8°F). There is no rash on physical examination; he is found to have neck rigidity, confusion, and photophobia. There are no focal neurological deficits. A head CT is normal without mass or hydrocephalus. A lumbar puncture was performed and cerebrospinal fluid (CSF) is sent to analysis while ceftriaxone and vancomycin are started. Which of the following additional antimicrobials should be added in the management of this patient?

• A. Trimethoprim-sulfamethoxazole (TMP-SMX)
• B. Ampicillin (Correct Answer)
• C. Amphotericin
• D. Meropenem
• E. Clindamycin

Gram-negative Explanation: ***Ampicillin*** - This patient is a 62-year-old, indicating an increased risk for **Listeria monocytogenes** meningitis, which is typically susceptible to ampicillin. - Given his age and presentation with **meningeal signs** and fever, empirical coverage for Listeria with ampicillin is crucial, especially before CSF culture results are known. *Trimethoprim-sulfamethoxazole (TMP-SMX)* - While TMP-SMX can cover Listeria, it is generally considered a **second-line agent** for severe infections like meningitis due to slower bactericidal activity and potential for higher rates of treatment failure compared to ampicillin. - Ampicillin is the **preferred first-line treatment** for Listeria meningitis unless there is a specific contraindication. *Amphotericin* - Amphotericin is an **antifungal agent** used for fungal meningitis. - Although fungemia can occur in immunocompromised individuals or those with indwelling catheters, the initial presentation with bacterial meningitis symptoms and absence of specific risk factors for fungal infection do not support its empirical use. *Meropenem* - Meropenem is a **carbapenem** with a broad spectrum of activity, including many gram-negative and gram-positive bacteria, and some anaerobes. - While it has good CNS penetration and could cover some organisms like penicillin-resistant S. pneumoniae or gram-negative rods, it is not the primary empirical choice specifically for **Listeria monocytogenes**, and there's no indication for its broad-spectrum coverage over standard empirical therapy currently. *Clindamycin* - Clindamycin is primarily active against **gram-positive bacteria**, especially anaerobes and some staphylococci and streptococci. - It has **poor penetration into the CNS** and is therefore not effective for meningitis treatment, especially for common bacterial pathogens or Listeria.

Gram-negative US Medical PG Question 8: A previously healthy 26-year-old woman comes to the physician because of a 2-day history of pain with urination. She has been sexually active with two partners over the past year. She uses condoms for contraception. Vital signs are within normal limits. Physical examination shows suprapubic tenderness. Urinalysis shows neutrophils and a positive nitrite test. Urine culture grows gram-negative, oxidase-negative rods that form greenish colonies on eosin-methylene blue agar. Which of the following virulence factors of the causal organism increases the risk of infection in this patient?

• A. Fimbriae (Correct Answer)
• B. Lecithinase
• C. IgA protease
• D. Biofilm production
• E. Lipoteichoic acid

Gram-negative Explanation: ***Fimbriae*** - The patient's symptoms (dysuria, suprapubic tenderness), urinalysis findings (neutrophils, positive nitrite), and culture results (gram-negative, oxidase-negative rods, greenish colonies on EMB agar) are highly suggestive of a **urinary tract infection (UTI)** caused by **Escherichia coli**. - **P-fimbriae (pili)** are crucial virulence factors for *E. coli* in UTIs, enabling the bacteria to **adhere to uroepithelial cells** and colonize the urinary tract. *Lecithinase* - **Lecithinase (alpha-toxin)** is a virulence factor primarily associated with bacteria like *Clostridium perfringens*, causing gas gangrene, and some *Bacillus cereus* strains. - It is not a significant virulence factor for *E. coli* in the context of UTIs. *IgA protease* - **IgA protease** is an enzyme produced by bacteria such as *Neisseria gonorrhoeae*, *Neisseria meningitidis*, and *Haemophilus influenzae*. - It cleaves IgA antibodies, preventing their protective effects at mucosal surfaces, but it is not a primary virulence factor for *E. coli* in UTIs. *Biofilm production* - While *E. coli* can form biofilms, particularly in chronic infections or on catheters, **biofilm production** is not the primary mechanism that increases the **initial risk** of acquiring an acute uncomplicated UTI in a healthy individual. - The *initial* adherence to uroepithelium, facilitated by fimbriae, is key for colonization and infection establishment. *Lipoteichoic acid* - **Lipoteichoic acid** is a major component of the cell wall in **Gram-positive bacteria** and contributes to their immune stimulation and adherence properties. - The causative organism in this case is a **Gram-negative rod**, making lipoteichoic acid an irrelevant virulence factor.

Gram-negative US Medical PG Question 9: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

• A. "Does the diarrhea typically precede the constipation, or vice-versa?"
• B. "Is the diarrhea foul-smelling?"
• C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
• D. "Are the symptoms worse in the morning or at night?"
• E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)

Gram-negative Explanation: ***Can you tell me more about the symptoms you have been experiencing?*** - This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis. - In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions. *Does the diarrhea typically precede the constipation, or vice-versa?* - While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience. - It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture. *Is the diarrhea foul-smelling?* - Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions. - However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed. *Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life* - Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time. - However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially. *Are the symptoms worse in the morning or at night?* - Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related. - This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.

Gram-negative 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

Gram-negative 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.

Gram-negative Flashcard 1 of 10

Question: Which of the common gram-negative nosocomial infections(Klebsiella, Serratia, Enterobacter)is urease-positive?_____

Answer: Klebsiella

Gram-negative Flashcard 2 of 10

Question: Which gram-negative bacteria is associated with Diabetic Osteomyelitis?_____

Answer: Pseudomonas aeruginosa

Gram-negative Flashcard 3 of 10

Question: Red bacteria of a gram stain are gram _____

Answer: negative

Gram-negative Flashcard 4 of 10

Question: Klebsiella, enterobacter, and serratia commonly exhibit multi-drug _____

Answer: resistance

Gram-negative Flashcard 5 of 10

Question: Beta-lactamase enzymes are found in the periplasm of gram _____ bacteria

Answer: negative

Gram-negative Flashcard 6 of 10

Question: _____ is a gram-negative nocosomial bacterial infection that has respiratory therapy equipment as a risk factor.

Answer: Pseudomonas aeruginosa

Gram-negative Flashcard 7 of 10

Question: Yersinia pestis

Answer:

Extra Information: rats and prarie dogsfleas

Gram-negative Flashcard 8 of 10

Question: Rickettsia typhi

Answer:

Extra Information: endemic typhusfleas

Gram-negative Flashcard 9 of 10

Question: Francisella tularensis

Answer:

Extra Information: tularemiarabbitticks, deer fly

Gram-negative Flashcard 10 of 10

Question: Coxiella burnetti

Answer:

Extra Information: Q fevercattle/sheep amniotic fluid