Oligotrophic Media Compared with a Tryptic Soy Agar or Broth for the Recovery of Complex from Different Storage Temperatures and Culture Conditions.

The complex (BCC) is capable of remaining viable in low-nutrient environments and harsh conditions, posing a contamination risk in non-sterile pharmaceutical products as well as a challenge for detection. To develop optimal recovery methods to detect BCC, three oligotrophic media were evaluated and compared with nutrient media for the recovery of BCC from autoclaved distilled water or antiseptic solutions. Serial dilutions (10 to 10 CFU/ml) of 20 BCC strains were inoculated into autoclaved distilled water and stored at 6°C, 23°C and 42°C for 42 days. Six suspensions of were used to inoculate aqueous solutions containing 5 µg/ml and 50 µg/ml chlorhexidine gluconate (CHX) and 10 µg/ml benzalkonium chloride (BZK), and stored at 23°C for a further 199 days. Nutrient media such as Tryptic Soy Agar (TSA) or Tryptic Soy Broth (TSB), oligotrophic media (1/10 strength TSA or TSB, Reasoner's 2 Agar [R2A] or Reasoner's 2nd Broth [R2AB], and 1/3 strength R2A or R2AB) were compared by inoculating these media with BCC from autoclaved distilled water and from antiseptic samples. The recovery of BCC in water or antiseptics was higher in culture broth than on solid media. Oligotrophic medium showed a higher recovery efficiency than TSA or TSB for the detection of 20 BCC samples. Results from multiple comparisons allowed us to directly identify significant differences between TSA or TSB and oligotrophic media. An oligotrophic medium pre-enrichment resuscitation step is offered for the United States Pharmacopeia (USP) proposed compendial test method for BCC detection.