Rhodococcus equi
📖 About
- Rhodococcus equi → opportunistic pathogen mainly affecting immunocompromised patients (HIV/AIDS, chronic steroids, malignancy).
- Recognised zoonotic pathogen, also infects foals and other animals.
🔬 Characteristics
- Gram-positive, aerobic, partially acid-fast coccobacillus.
- Can be misidentified as diphtheroids (Corynebacterium-like) in labs → needs careful recognition.
- Intracellular survival in macrophages → contributes to chronicity.
🏠 Source
- Reservoirs: Soil & animal faeces (esp. herbivores 🐎 horses, cattle).
- Transmission: Inhalation of contaminated dust or direct contact with soil/animals (esp. in agricultural settings).
⚠️ Pathogenicity
- Pulmonary disease:
- Cavitating pneumonia (resembles TB) with slow progression.
- Can form lung abscesses & pleural involvement.
- Disseminated infection:
- Brain abscesses 🧠, subcutaneous abscesses, lymphadenitis.
- High mortality if untreated in immunocompromised patients.
💊 Sensitivities
- Generally sensitive to vancomycin, carbapenems, rifampicin, and fluoroquinolones.
- Combination therapy reduces relapse risk.
🧬 Resistance
- Resistance can emerge with prolonged/monotherapy.
- Patterns vary → always perform susceptibility testing.
🩺 Management
- Prolonged combination antibiotic therapy:
- Typical: Rifampicin + (carbapenem / fluoroquinolone / vancomycin).
- Duration: often many weeks to months, tailored to response.
- Surgical intervention: Drainage of abscesses (lung, brain, soft tissue) may be required.
- Close monitoring: Relapse risk is high in HIV/immunosuppressed patients.
⚠️ Exam pearl: Rhodococcus equi causes cavitating pneumonia in HIV patients, mimicking TB, and may be misidentified as diphtheroids in labs. Requires prolonged, multi-drug therapy + sometimes surgery.