USP〈60〉 Microbiological Examination of Nonsterile Products—Tests for Burkholderia Cepacia Complex

USP General Chapter <60> establishes the official compendial method for detecting members of the Burkholderia cepacia complex (BCC). BCC is a group of closely related Gram-negative bacteria associated with contamination of aqueous, non-sterile pharmaceutical products.

BCC organisms are intrinsically resistant to many antibiotics and preservatives. They can survive and proliferate in preservative systems (metabolizing them as carbon sources) and form biofilms in water systems, posing severe risks to vulnerable patients (e.g., those with Cystic Fibrosis).

Enforceability: This test is required when specified in a monograph or when risk assessment indicates a potential for BCC contamination in aqueous non-sterile products.

1. Scope of Application USP <60> applies primarily to Non-sterile Aqueous Products and their raw materials, particularly:

• Inhalation & Nasal Products (High risk).
• Oral Liquids & Topicals (aqueous based).
• Water-containing Raw Materials (e.g., polyols like Glycerin, Sorbitol, Propylene Glycol) which are frequent sources of BCC.

2. The Testing Workflow Unlike Salmonella testing (which uses selective broth), USP <60> uses non-selective enrichment followed by highly selective plating.

• Sample Preparation: Dilute the product (typically 1:10) in Soybean-Casein Digest Broth (TSB) adapted with neutralizers if the product contains preservatives.
• Enrichment: Incubate the TSB preparation at 30–35°C for 48–72 h.

Note: This step uses a non-selective broth to revive stressed organisms and increase their numbers before selection.

Selective Plating: Mix the enrichment broth and subculture onto Burkholderia Cepacia Selective Agar (BCSA).

Note: The selectivity of the method resides entirely in the BCSA agar (which contains antibiotics like gentamicin and vancomycin), not in the enrichment broth.

Observation: Incubate plates at 30–35°C for 48–72 h.

Morphology: BCC colonies on BCSA typically appear greenish-brown with a yellow halo, or white/grey. However, colony morphology can vary significantly by species; any growth on BCSA must be investigated.

3. Confirmation Any growth on BCSA is considered presumptive BCC. Confirmation requires identification to the species level (or confirming it is not BCC).

Identification: Automated biochemical methods or Molecular methods (16S rRNA sequencing, MALDI-TOF).

Note: USP explicitly permits automated or molecular identification methods, which are often necessary due to the phenotypic similarity between BCC species.

4. Method Suitability (Validation) Before routine testing, the lab must demonstrate that the product matrix does not inhibit BCC growth.

Spiking: Inoculate product preparation with < 100 CFU of compendial strains (typically B. cenocepacia, B. multivorans, and B. cepacia).

Acceptance: Must show comparable recovery to a positive control (TSB without product).