Effect of Bicarbonate Concentration on Aerobic Growth of Campylobacter in a Fumarate-Pyruvate Medium

Introduction: Campylobacter are a major cause of human foodborne illness. These enteropathogens are microaerophilic capnophiles; therefore, cultures are generally grown in modified atmospheres. Campylobacter are unable to metabolize carbohydrates; however, the bacteria can metabolize organic acids such as fumarate and pyruvate. Recent research has indicated that Campylobacterspp. are capable of aerobic growth in media supplemented with fumarate and pyruvate.

Purpose: The purpose of the present study was to examine the effect of sodium bicarbonate (NaHCO₃) concentration on aerobic growth of Campylobacterin a fumarate-pyruvate medium.

Methods: Fumarate-pyruvate broth medium was supplemented with 0.00 to 0.10% NaHCO₃ and inoculated with Campylobacter coli 33559, Campylobacter fetus 27349, Campylobacter jejuni 33560, or Campylobacter jejuni 49349. Aliquots of inoculated media were transferred to wells of a honeycomb plate and placed in a Bioscreen Microbiology Reader. Cultures were incubated aerobically at 37^oC for 72 h, and culture optical density (OD) was measured during incubation (n = 5). Additional experiments were conducted to compare CFU/ml of Campylobacter recovered from media supplemented with 0.05 % NaHCO₃, inoculated with Campylobacter spp., and incubated aerobically or microaerophilically for 72 h at 37^oC (n = 6).

Results: Results indicated that the OD of cultures of all isolates, except C. coli, were significantly (P < 0.05) higher when grown in fumarate-pyruvate medium containing added NaHCO₃. The addition of NaHCO₃ produced significant increases in the OD of most isolates during early periods of growth. Also, there was a 5 to 6 log increase in CFU/ml of all isolates recovered from media supplemented with 0.05% NaHCO₃, and there was no significant difference in the number of CFU/ml recovered from media incubated aerobically or anaerobically.

Significance: Findings indicate that supplementing fumarate-pyruvate broth medium with NaHCO₃ improves the ability of the medium to support aerobic growth of Campylobacter. This medium might provide an alternative to culturing Campylobacter under microaerophilic conditions.