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.

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

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