A 12-month-old girl is brought to her pediatrician for a checkup and vaccines. The patient’s mother wants to send her to daycare but is worried about exposure to unvaccinated children and other potential sources of infection. The toddler was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines. She does not walk yet but stands in place and can say a few words. The toddler drinks formula and eats a mixture of soft vegetables and pureed meals. She has no current medications. On physical exam, the vital signs include: temperature 37.0°C (98.6°F), blood pressure 95/50 mm Hg, pulse 130/min, and respiratory rate 28/min. The patient is alert and responsive. The remainder of the exam is unremarkable. Which of the following is most appropriate for this patient at this visit?

Gross motor workup and evaluation

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?

Alteration of peptidoglycan synthesis

Increased efflux across bacterial cell membranes

Alteration of penicillin-binding proteins

Alteration of ribosomal targets

A team of intensivists working in a private intensive care unit (ICU) observe that the clinical efficacy of vancomycin is low, and proven nosocomial infections have increased progressively over the past year. A clinical microbiologist is invited to conduct a bacteriological audit of the ICU. He analyzes the microbiological reports of all patients treated with vancomycin over the last 2 years and takes relevant samples from the ICU for culture and antibiotic sensitivity analysis. The audit concludes that there is an increased incidence of vancomycin-resistant Enterococcus fecalis infections. Which of the following mechanisms best explains the changes that took place in the bacteria?

Replacement of the terminal D-Ala in the cell wall peptidoglycan by D-lactate

Decreased number of porins in the bacterial cell wall leading to decreased intracellular entry of the antibiotic

Production of an enzyme that hydrolyzes the antibiotic

Protection of the antibiotic-binding site by Qnr protein

Increased expression of efflux pumps which extrude the antibiotic from the bacterial cell

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?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

Multi-drug resistant organism transmission for USMLE Step 2 CK: High-Yield Microbiology Lessons

The MDRO Lineup - Rogues' Gallery

Key multi-drug resistant organisms (MDROs) frequently implicated in nosocomial infections.

MRSA (Methicillin-Resistant Staphylococcus aureus)
- Gram-positive cocci. Resists beta-lactams via altered Penicillin-Binding Protein (PBP2a).
- Commonly colonizes nares, skin.
VRE (Vancomycin-Resistant Enterococcus)
- Gram-positive cocci. Resists vancomycin by modifying peptidoglycan precursor to D-Ala-D-Lac.
- Colonizes GI tract.
ESBL-producing Enterobacteriaceae
- Gram-negative rods (E. coli, Klebsiella). Extended-Spectrum Beta-Lactamases inactivate most penicillins/cephalosporins.
CRE (Carbapenem-Resistant Enterobacteriaceae)
- Gram-negative rods. Produce carbapenemases (e.g., KPC, NDM-1), resisting last-line carbapenems.
Acinetobacter baumannii
- Gram-negative coccobacillus. High intrinsic resistance; survives on dry surfaces.

⭐ MRSA's resistance is conferred by the mecA gene, which encodes for Penicillin-Binding Protein 2a (PBP2a). This altered PBP has a low affinity for beta-lactam antibiotics.

Transmission Pathways - The Great Escape

MDROs exploit breaches in infection control, primarily moving via contact. Understanding these routes is key to containment.

Contact Transmission (Most Common)
- Direct: Person-to-person physical transfer (e.g., patient to healthcare worker).
- Indirect: Via a contaminated intermediate object (fomite).
  - High-touch surfaces: Bed rails, IV pumps, stethoscopes.
  - Shared medical equipment.
Environmental Reservoirs
- Dry surfaces: Acinetobacter baumannii, VRE can persist for weeks.
- Wet environments: Pseudomonas aeruginosa in sinks, drains, and toilets.

⭐ The hands of healthcare workers are the single most important vehicle for transmitting MDROs between patients.

Infection Control - Fortress Defense

Standard Precautions (Universal): Applied to ALL patients. Assumes all blood, body fluids, secretions, excretions (except sweat), non-intact skin, and mucous membranes may contain transmissible infectious agents.
- Hand hygiene (alcohol-based rub or soap/water).
- Use of PPE (gloves, gown, mask, eye protection) based on anticipated exposure.
Transmission-Based Precautions: Additional measures for known/suspected infections.
- Contact: Gown & gloves. (e.g., MRSA, VRE, C. diff)
- Droplet: Surgical mask. (e.g., Influenza, N. meningitidis, Adenovirus)
- Airborne: N95 respirator, negative pressure room. (e.g., TB, Measles, Varicella) 📌 My Chicken Hez Tuberculosis

⭐ For Clostridioides difficile, alcohol-based hand sanitizers are ineffective against spores. Handwashing with soap and water is mandatory.

High‑Yield Points - ⚡ Biggest Takeaways

Contact precautions are paramount for controlling the spread of MRSA, VRE, and CRE.

Hand hygiene is the cornerstone of prevention; use soap and water for C. difficile spores and alcohol-based rubs for most other MDROs.

MRSA commonly colonizes the anterior nares, a key site for active surveillance screening.

VRE frequently spreads through contaminated environmental surfaces and shared patient-care equipment.

CRE transmission is often linked to contaminated medical devices, particularly endoscopes.

Active surveillance cultures are crucial for identifying asymptomatic carriers and preventing outbreaks.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play