USP <61>

Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests

The objective is to determine the quantity of mesophilic bacteria and fungi that may grow under aerobic conditions.  Mesophilic bacteria grow best at moderate temperatures, typically between 20 and 45°C. 

Method Suitability

The ability of the test to detect microorganisms in the presence of product must be established.  Suitability is generally a one-time test but must be confirmed if a change in the product may affect the outcome of the test is introduced.  Method suitability is performed by inoculating the sample with a quantity of a microbial load with individual bacteria and fungi or as a suspension. A control is similarly prepared and analyzed.  The responses of the sample and control are compared for acceptance.  The acceptance criteria for the plate count method is 50-200% recovery. 

Minimum Sample Quantity Required

Unless otherwise directed in the monograph, 10 mL or 10g of material is to be tested.  For fluids in aerosol form, 10 containers are sampled.  For transdermal patches, 10 units are sampled.  An ideal submission would be 50g on the first submission to include method suitability and 25g on subsequent submissions. 

Turn Around Time

The turnaround time for regularly submitted samples 10 business days.  Expedited testing less than 5 days is not available due to the incubation time required to complete the test.  Turn-around time for method suitability generally can be completed in 10 business days but may be extended if the acceptance criteria are not met on the first pass.  Expedited testing must be pre-arranged.