Aerobic C&S Stool Culture and Susceptibility Testing - DD (Kirby Bauer Disc diffusion)
Test Code
A93
Also Known As
No data available
Test Parameters Included
No data available
Department
MICROBIOLOGY
Methodology
Conventional Culture and Susceptibility Testing (Disk Diffusion - DD / Kirby-Bauer Method)
This test employs traditional or Conventional Culture methods for bacterial growth and the Kirby-Bauer Disk Diffusion (DD) method for antibiotic susceptibility testing. The process involves:
* Manual Inoculation of Selective Media: The stool sample (or a rectal swab) is manually inoculated onto various selective and differential culture media specifically designed to isolate common enteric (intestinal) bacterial pathogens (e.g., MacConkey, Hektoen Enteric Agar, XLD Agar, Salmonella-Shigella Agar). These media suppress the growth of normal gut flora while promoting the growth of pathogens.
* Manual Incubation: Inoculated plates are then incubated at a specific temperature (typically 35-37°C) for 18-24 hours.
* Colony Selection & Identification (ID): After incubation, laboratory technologists visually inspect the plates for bacterial growth. If colonies suspicious of pathogenic bacteria appear, they are isolated and identified using traditional microbiological methods (e.g., Gram staining, biochemical tests, API strips, or manual rapid identification systems) to determine the specific bacterial species.
* Disk Diffusion (Kirby-Bauer Method): Once the pathogenic bacteria are identified, a standardized bacterial suspension is prepared and uniformly spread onto a Mueller-Hinton agar plate. Paper disks impregnated with a specific concentration of various antibiotics are then placed on the agar surface.
* Diffusion: The antibiotic diffuses from the disk into the agar, creating a concentration gradient.
* Incubation: The plate is incubated for 18-24 hours.
* Zone of Inhibition: If the antibiotic inhibits bacterial growth, a clear circular area (zone of inhibition) appears around the disk.
* Manual Interpretation: The diameter of the zone of inhibition is measured using a ruler or a zone reader. These measurements are then compared against standardized breakpoints (established by organizations like CLSI - Clinical and Laboratory Standards Institute) to determine if the isolate is Susceptible (S), Intermediate (I), or Resistant (R) to each tested antibiotic.
This conventional approach provides reliable results for bacterial identification and antibiotic susceptibility, guiding effective antibiotic therapy for gastrointestinal infections.
Sample Required
STOOL (Fresh Random Stool or Rectal Swab in Transport Media)
* Fresh Random Stool: The preferred sample is a fresh, spontaneously passed stool specimen (not from toilet water). It should be collected in a clean, dry, leak-proof container with a tight-fitting lid.
* Quantity: At least 5-10 grams (a walnut-sized portion) is typically required.
* Avoid Contamination: Instruct the patient to avoid contaminating the sample with urine or toilet paper.
* Rectal Swab: For infants, critically ill patients, or when fresh stool is unavailable, a rectal swab collected in appropriate transport media (e.g., Cary-Blair medium) can be used. The swab should be inserted 2-3 cm past the anal sphincter and rotated to sample crypts.
* Transport Media: If transport to the lab is delayed, the sample should be placed in a suitable transport medium (e.g., Cary-Blair medium) to preserve the viability of pathogens and prevent overgrowth of normal flora. This is particularly important for Shigella and Campylobacter.
* Timely Transport/Refrigeration: The specimen should be transported to the laboratory as soon as possible. If transport media is not used, the sample should be processed within 2 hours or refrigerated at 4°C for up to 24 hours, though immediate processing is always best for stool.
Preparation
Proper collection and timely transport are critical to ensure the viability of pathogens and prevent overgrowth of commensal flora. * Patient Instructions: Provide clear instructions for collecting a ... Read more
Schedule Report
72 Hours
Emergency Report
Yes
Frequently Asked Questions
No data available
Test Description
- High-end laboratory & medical equipment.
- Outstanding doctor team.
- Personalized care & high-quality service.
- Tailormade health screening packages.