An 18-year-old female college student is brought to the emergency department by ambulance for a headache and altered mental status. The patient lives with her boyfriend who is with her currently. He states she had not been feeling well for the past day and has vomited several times in the past 12 hours. Lumbar puncture is performed in the emergency room and demonstrates an increased cell count with a neutrophil predominance and gram-negative diplococci on Gram stain. The patient is started on vancomycin and ceftriaxone. Which of the following is the best next step in management?

Add ampicillin to treatment regimen

Add ampicillin, dexamethasone, and rifampin to treatment regimen

Add dexamethasone to treatment regimen

Treat boyfriend with ceftriaxone and vancomycin

A 22-year-old female with no past medical history presents to her primary care physician with a 3-day history of knee pain. She denies any recent injury or trauma. On physical examination her knee is warm, erythematous, and has diminished range of movement. The patient reports having multiple sexual partners over the last year and does not use protection regularly. Her blood pressure is 124/85 mmHg, heart rate is 76/min, and temperature is 38.3℃ (101.0℉). A joint aspiration is performed and a growth of gram-negative diplococci is noted on bacterial culture. What is the treatment of choice for this patient's condition?

Ceftriaxone monotherapy and joint aspiration

Nafcillin monotherapy and joint aspiration

A 15-year-old boy is brought to the Emergency department by ambulance from school. He started the day with some body aches and joint pain but then had several episodes of vomiting and started complaining of a terrible headache. The school nurse called for emergency services. 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. He is a good student and enjoys sports. At the hospital, his blood pressure is 120/80 mm Hg, heart rate is 105/min, respiratory rate is 21/min, and his temperature is 38.9°C (102.0°F). On physical exam, he appears drowsy with neck stiffness and sensitivity to light. Kernig’s sign is positive. An ophthalmic exam is performed followed by a lumbar puncture. An aliquot of cerebrospinal fluid is sent to microbiology. A gram stain shows gram-negative diplococci. A smear is prepared on blood agar and grows round, smooth, convex colonies with clearly defined edges. Which of the following would identify the described pathogen?

Oxidase-positive and ferments glucose and maltose

Oxidase-positive test and ferments glucose only

Catalase-negative and oxidase-positive

No growth on Thayer-Martin medium

A 25-year-old man with no significant past medical history is brought in by ambulance after a witnessed seizure at home. On physical exam, temperature is 102.3 deg F (39.1 deg C), blood pressure is 90/62 mmHg, pulse is 118/min, and respirations are 25/min. He is unable to touch his chin to his chest and spontaneously flexes his hips with passive neck flexion. Appropriate empiric treatment is begun. CT head is unremarkable, and a lumbar puncture sample is obtained. Gram stain of the cerebrospinal fluid (CSF) reveals gram-positive diplococci. Which of the following would you expect to see on CSF studies?

Elevated opening pressure, elevated protein, low glucose

Elevated opening pressure, elevated protein, normal glucose

Normal opening pressure, normal protein, normal glucose

Elevated opening pressure, elevated protein, elevated glucose

Normal opening pressure, elevated protein, normal glucose

An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?

Intramuscular ceftriaxone plus oral azithromycin

Intravenous cefoxitin plus oral doxycycline

A 71-year-old woman presents with high-grade fever and chills, difficulty breathing, and a productive cough with rust-colored sputum. She complains of a sharp left-sided chest pain. Physical examination reveals increased fremitus, dullness to percussion, and bronchial breath sounds on the lower left side. A chest X-ray shows left lower lobe consolidation. The offending organism that was cultured from the sputum was catalase-negative and had a positive Quellung reaction. The organism will show which gram stain results?

Cannot be seen with gram staining since the organism lacks a cell wall

Gram-positive cocci in clusters

A 19-year-old male is found to have Neisseria gonorrhoeae bacteremia. This bacterium produces an IgA protease capable of cleaving the hinge region of IgA antibodies. What is the most likely physiological consequence of such a protease?

Impaired mucosal immune protection

Membrane attack complex formation is impaired

Impaired antibody binding to mast cells

Opsonization and phagocytosis of pathogen cannot occur

Impaired adaptive immune system memory

Neisseria species (meningitidis, gonorrhoeae) for USMLE Step 1: High-Yield Microbiology Lessons

Neisseria Basics - The Diplomatic Cocci

Gram-negative diplococci, non-motile, kidney-bean shaped.
Aerobic, oxidase-positive, and most are catalase-positive.
Fastidious: Grow on chocolate agar enriched with CO₂.
Selective medium: Thayer-Martin agar (VPN).
Key virulence factors: Pili (antigenic variation, attachment), IgA protease (cleaves IgA at hinge region), LOS (endotoxin activity).

Gram stain of Neisseria gonorrhoeae within neutrophils

⭐ Individuals with C5-C9 complement deficiency (MAC complex) have a significantly increased susceptibility to disseminated Neisseria infections.

N. meningitidis - The Meningitis Menace

Gram-negative diplococcus, oxidase ⊕, kidney-bean shape.
Grows on chocolate agar & Thayer-Martin medium.
📌 Meningitidis ferments Maltose (and Glucose); Gonorrhoeae ferments Glucose only.
Virulence: Polysaccharide capsule (antiphagocytic), IgA protease, Lipooligosaccharide (LOS) endotoxin.
Transmission: Respiratory droplets, often in close quarters (dorms, barracks).

Neisseria diplococci in CSF sample

⭐ Patients with C5-C9 complement deficiency (impaired MAC complex) have significantly increased susceptibility to recurrent Neisseria infections.

Treatment: Ceftriaxone. Rifampin or ciprofloxacin for close contact prophylaxis.
Vaccines: Conjugate vaccine (Serogroups A, C, Y, W-135), Recombinant protein vaccine (Serogroup B).

N. gonorrhoeae - The Groin Goblin

Microbiology: Gram-negative diplococcus, oxidase ⊕, facultative intracellular within neutrophils. Lacks a polysaccharide capsule. Pili demonstrate antigenic variation, aiding immune evasion.
Culture: Requires Thayer-Martin agar (chocolate agar with Vancomycin, Polymyxin, Nystatin). Ferments glucose only.

Gram stain of N. gonorrhoeae in neutrophil

Clinical Syndromes:
- Genital (local): Urethritis in men (purulent discharge); cervicitis & Pelvic Inflammatory Disease (PID) in women, which can be asymptomatic.
- Disseminated Gonococcal Infection (DGI): Presents as an arthritis-dermatitis syndrome (septic arthritis, tenosynovitis, pustular rash).
- Neonatal: Ophthalmia neonatorum (purulent conjunctivitis).

⭐ High-Yield: The leading cause of septic arthritis in sexually active adolescents and young adults.

Diagnosis & Treatment:
- Dx: Nucleic Acid Amplification Test (NAAT) is the standard.
- Tx: Ceftriaxone. Co-treat for frequent Chlamydia co-infection (doxycycline or azithromycin).

Meningo vs. Gono - The Twin Showdown

Feature	N. meningitidis	N. gonorrhoeae
Capsule	Yes (polysaccharide)	No
Maltose Ferm.	Yes	No
Vaccine	Yes (capsular)	No
Transmission	Respiratory droplets	Sexual contact
Key Disease	Meningitis	Gonorrhea, Septic Arthritis

High-Yield Points - ⚡ Biggest Takeaways

Gram-negative diplococci, oxidase-positive, and cultured on Thayer-Martin agar; both produce IgA protease.

N. meningitidis ferments both glucose and maltose; N. gonorrhoeae ferments glucose only.

Meningitidis has a polysaccharide capsule (vaccine target), spreads via droplets, and causes meningitis with a petechial rash.

Gonorrhoeae is uncapsulated, sexually transmitted, and a leading cause of septic arthritis in young adults.

Deficiency in late complement components (C5-C9) increases susceptibility to disseminated Neisseria infections.

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