Bacteriological culture and tests for antibiotic sensitivity

Описание: Bacteriological culture and antibiotic sensitivity testing are cornerstone methods in microbiology and orthopedics (especially for bone and joint infections like osteomyelitis or prosthetic joint infections). They help identify the causative organism and determine which antibiotics will be effective.

🔎 Bacteriological Culture
Definition: Growth of microorganisms from clinical specimens (blood, pus, synovial fluid, bone biopsy) on nutrient media under controlled conditions.

Steps:

Specimen collection: Sterile technique (e.g., aspirated pus, tissue biopsy).

Inoculation: Onto culture media (blood agar, MacConkey agar, etc.).

Incubation: At appropriate temperature (usually 35–37°C).

Identification: Colony morphology, Gram stain, biochemical tests, automated systems.

Purpose: To isolate and identify the specific pathogen causing infection.

🧪 Antibiotic Sensitivity Tests
Definition: Laboratory tests to determine which antibiotics inhibit or kill the isolated bacteria.

Methods:

Disk diffusion (Kirby–Bauer test):

Paper disks impregnated with antibiotics placed on agar plate with bacteria.

Zone of inhibition measured → sensitive, intermediate, or resistant.

Broth dilution / MIC (Minimum Inhibitory Concentration):

Serial dilutions of antibiotic in broth.

Lowest concentration preventing visible growth = MIC.

E‑test (gradient diffusion):

Strip with antibiotic gradient placed on agar.

MIC read where bacterial growth intersects strip.

Automated systems: VITEK, Phoenix, MicroScan → rapid results.

📊 Clinical Importance in Orthopedics
Osteomyelitis: Culture and sensitivity guide long‑term antibiotic therapy.

Septic arthritis: Synovial fluid culture determines causative organism.

Prosthetic joint infection: Biofilm‑forming bacteria (e.g., Staphylococcus aureus, Staphylococcus epidermidis) require targeted therapy.

Open fractures: Cultures help tailor prophylaxis and treatment.

⚖️ Advantages
Identifies exact pathogen.

Provides targeted antibiotic therapy → avoids empirical overuse.



#Bacteria