Scenarios For Gram Negative Bacteria

Exam 3

• Scenario: A 22-year-old male presents with painful urination and purulent urethral discharge after unprotected sex.

• Diagnosis: Urethral swab, Gram stain (Gram-negative diplococci), culture on Thayer-Martin agar, PCR.

Neisseria gonorrhoeae

• Scenario: A college student in a dormitory develops fever, headache, stiff neck, and petechial rash.

• Diagnosis: Lumbar puncture (CSF shows Gram-negative diplococci, increased WBCs, decreased glucose), blood culture.

Neisseria meningitidis

• Scenario: A woman has burning urination and increased frequency.

• Diagnosis: Urinalysis (positive nitrites, leukocyte esterase), urine culture (lactose-positive, motile).

Escherichia coli

• Scenario: A hospitalized diabetic patient develops pneumonia and sepsis.

• Diagnosis: Sputum culture (lactose-positive, non-motile, thick capsule), "currant jelly" sputum.

Klebsiella pneumoniae

• A patient develops severe bloody diarrhea after traveling to a developing country.

• Diagnosis: Stool culture (lactose-negative, non-motile, H₂S-negative).

Shigella dysenteriae

• Scenario: A man has diarrhea and fever after eating undercooked chicken.

• Diagnosis: Stool culture (H₂S-positive, lactose-negative, motile).

Salmonella

• Scenario: A hiker in Arizona develops fever and swollen lymph nodes after a flea bite.

• Diagnosis: Blood culture (Gram-negative rod, bipolar staining “safety pin” appearance).

Yersinia pestis

• Scenario: A burn patient develops a green wound infection with a fruity odor.

• Diagnosis: Wound culture (oxidase-positive, pigment-producing, glucose-nonfermenter).

Pseudomonas aeruginosa

• Scenario: A fisherman gets a severe wound infection after handling fish.

• Diagnosis: Wound culture (oxidase-positive, glucose-fermenting, waterborne).

Aeromonas hydrophila

• Scenario: A child develops meningitis and epiglottitis.

• Diagnosis: CSF or blood culture (requires factors X [heme] and V [NAD], capsule testing).

Haemophilus influenzae

• Scenario: A man gets pneumonia after inhaling contaminated air-conditioning water.

• Diagnosis: Sputum culture (requires cysteine, grows on BCYE agar), urine antigen test.

Legionella pneumophila

• Scenario: A child has severe coughing fits followed by a “whoop” sound.

• Diagnosis: PCR, nasopharyngeal swab, Bordet-Gengou agar culture.

Bordetella pertussis

• Scenario: A hunter gets a painful ulcer after handling wild rabbits.

• Diagnosis: Blood culture (requires cysteine), serology.

Francisella tularensis

• Scenario: A traveler has profuse, watery "rice water" diarrhea.

• Diagnosis: Stool culture (alkaline growth conditions, oxidase-positive, curved shape).

Vibrio cholerae

• Scenario: A patient gets fever and diarrhea after eating undercooked poultry.

• Diagnosis: Stool culture (microaerophilic, thermophilic, curved rods)

Campylobacter jejuni

• Scenario: A middle-aged man has chronic stomach pain and gastric ulcers.

• Diagnosis: Urea breath test, biopsy (urease test).

Helicobacter pylori

• Scenario: A patient has a painless genital ulcer followed by a rash on palms and soles.

• Diagnosis: Dark-field microscopy, RPR/VDRL serology.

Treponema pallidum

• Scenario: A hiker develops a bull’s-eye rash and joint pain after a tick bite.

• Diagnosis: ELISA and Western blot for Lyme disease.

Borrelia burgdorferi

• Scenario: A college student gets a dry cough and pneumonia, but Gram stain is negative.

• Diagnosis: Cold agglutinin test, PCR, Eaton agar culture.

Mycoplasma pneumoniae

• Scenario: A hiker develops fever and muscle aches after a tick bite.

• Diagnosis: Blood smear (intracellular bacteria in monocytes), PCR.

Ehrlichia chaffeensis

• Scenario: A refugee develops a fever and body rash from body lice.

• Diagnosis: Serology, PCR.

Rickettsia prowazekii

• Scenario: A camper gets fever, rash, and severe headache after a tick bite.

• Diagnosis: Serology, Weil-Felix test.

Rickettsia rickettsii

• Scenario: A young man has urethritis and dysuria, but Gram stain is negative.

• Diagnosis: PCR, NAAT.

Chlamydia trachomatis

• Scenario: A 45-year-old patient develops a persistent dry cough, sore throat, and mild pneumonia. Symptoms have lasted for weeks but are not severe. No response to β-lactam antibiotics.

• Diagnosis: PCR, serology (IgM/IgG antibodies), culture in HeLa cells.

Chlamydia pneumoniae