Antibiotic Susceptibility Testing (AST’s)

Antibiotic Susceptibility Testing (AST) – MIC’s & Antibiogram

Welcome to Envirocare Laboratory, an ISO/IEC 17025-accredited testing facility, providing Antibiotic Susceptibility Testing (AST) in accordance with internationally recognised and validated methodologies.

Our AST services are performed under a SANAS-accredited quality management system, ensuring that all results are:

  • Technically valid
  • Traceable to recognised standards
  • Generated using validated methods
  • Subject to ongoing quality control and proficiency monitoring

We support clients across clinical, veterinary, food safety, and environmental sectors, enabling informed decision-making through reliable antimicrobial efficacy data.

  1. Minimum Inhibitory Concentrations (MICs)

The Minimum Inhibitory Concentration (MIC) is defined as the lowest concentration of an antimicrobial agent that inhibits visible growth of a microorganism under specified test conditions.

At Envirocare Laboratory, MIC determinations are:

  • Performed using standardised methods aligned with internationally recognised guidelines
  • Conducted under controlled environmental and incubation conditions
  • Verified through the use of appropriate positive, negative, and quality control strains
  • Supported by calibrated equipment and traceable reagents, in line with ISO/IEC 17025 requirements
  • MIC₅₀ (MIC 50)

The MIC₅₀ represents the concentration at which 50% of tested isolates are inhibited.

From a technical perspective:

  • Provides a statistical measure of central tendency within a microbial population
  • Supports comparative analysis between antimicrobial agents or products
  • Useful for method validation, product development, and performance benchmarking
  • MIC₉₀ (MIC 90)

The MIC₉₀ represents the concentration at which 90% of tested isolates are inhibited.

From a technical perspective:

  • Reflects upper-bound susceptibility within a population, including less susceptible isolates
  • Provides a conservative indicator of antimicrobial performance
  • Widely used in regulatory, veterinary, and surveillance applications
  1. Antibiogram

An antibiogram is a consolidated summary of antimicrobial susceptibility results for a defined set of microbial isolates tested against a panel of antimicrobial agents.

At Envirocare Laboratory, antibiograms are:

  • Generated from standardised AST methodologies
  • Based on validated datasets and controlled test conditions
  • Interpreted using recognised breakpoint criteria where applicable

What Our Antibiograms Provide

  • Percentage distribution of isolates classified as:
    • Susceptible (S)
    • Intermediate (I)
    • Resistant (R)
  • Comparative effectiveness of antimicrobial agents
  • Insight into emerging resistance patterns

Quality & Accreditation Assurance

All antibiotic susceptibility testing data is derived from testing performed under our ISO/IEC 17025 quality system

Supported by:

  • Internal quality controls
  • Reference strains (ATCC, NCTC, etc..)
  • Proficiency testing participation
  • Internationally accepted methodologies

Accreditation & Standardisation Context

Antibiotic susceptibility testing is conducted in alignment with internationally accepted frameworks such as:

  • Clinical and Laboratory Standards Institute (CLSI)
  • European Committee on Antimicrobial Susceptibility Testing (EUCAST and VETCAST)

Envirocare Submission Forms

Download the below fillable PDF and send to info@envirocarelab.co.za once completed.
(important: open in Acrobat Reader after downloading)

Veterinary analysis request