Purpose: In this study, media supplemented with various concentrations of beef extract were examined for the ability to support aerobic growth of Campylobacter.
Methods: Basal broth composed of tryptose, yeast extract, bicarbonate, and agar was supplemented with 0.0, 2.5, 5.0, or 7.5% (wt/vol) beef extract and inoculated with approximately 103 CFU/ml Campylobacter coli, Campylobacter fetus, Campylobacter jejuni 2b, Campylobacter jejuni 33560, or Campylobacter lari. Aliquots of inoculated media were transferred to wells of honeycomb plates, placed in a Bioscreen Microbiology Reader, and optical densities (OD) were measured during incubation for 48h at 37°C (n = 5). Inoculated media supplemented with 5.0% beef extract was also incubated aerobically in culture flasks for 72h at 37°C, and CFU/ml were enumerated after 48 and 72h incubation by plating serial dilutions of cultures on selective Campylobacter agar (n = 3).
Results: OD of isolates cultured in media supplemented with 2.5, 5.0, or 7.5% beef extract was significantly (P < 0.05) greater than OD of isolates cultured in media not supplemented with beef extract. Optimal growth of most isolates was generally produced in media supplemented with 5.0 or 7.5% beef extract. There were approximately 5 to 6 log increases in CFU/ml of Campylobacter recovered from inoculated media supplemented with 5% beef extract and incubated aerobically. Additionally, there was no significant difference in the number of CFU/ml recovered from supplemented media incubated for 48 or 72h.
Significance: Findings indicate that beef extract contains metabolites that may support aerobic growth of this foodborne pathogen. Use of these media may provide a less expensive method for culturing Campylobacter.