Reducing Sources Of Errors In Total Plate Count Testing

In food process facilities, it is common practice for equipment and surfaces to be tested for cleanliness by swabbing. Usually, the recovered microbial load from a swab is submitted for evaluation of the Aerobic Plate Count (APC), also known as Total Viable Count (TVC). The reference methods for enumerating APC (TVC) include the BAM method and ISO 4833:2003. Both of these methods require preparation, dilution and plating on agar, resulting in a high degree of manual labor and long periods of incubation up to 72 hours.

A new technology has been introduced that can reduce testing time and expense for very low bacterial loads on swabs, hence highlighting areas of concern for QC staff and hygienists. GreenLight® is an assay that can relate oxygen depletion to microbial load. In theory even the presence of one bacterium is detectable. By using a commercially available swab product as part of a standard swabbing protocol, GreenLight can replace the reference enumeration method, potentially giving results in less than 12 hours in comparison to the ISO method that takes 72 hours.

Conventional Methods

• Colony Count – Aerobic plate count (APC) ISO 4833:2003 / BAM (Bacteriological Analytical Manual)
• Petrifilm®
• APC Procedures
  • Prepare maximum recovery diluent and plate count agar
  • Food sampling and preparation
  • Prepare serial dilution
  • Inoculum plating
  • Incubation
  • Count colonies and calculate CFU/g

Novel/Rapid Methods

• PCR (Polymerase Chain Reaction)
• GreenLight® Technology
  • Based on optical sensing of oxygen depletion
  • Sensors emit fluorescence signal 
  • Measures bacterial O2 consumption 
  • As aerobes grow, O2 is consumed
  • Less O2 = stronger signal
• GreenLight® Procedures
• Prepare maximum recovery diluent 
• Food sampling and preparation 
• Load the GreenLight® vials 
• Input the GreenLight® parameters
• Run tests
• Output results