Background: Although enriched broth cultures have been recommended as an adjuvant to the direct plating of tissue and body fluid specimens, the cost-effectiveness of broth cultures has been questioned in regard with the clinical significance of “broth only isolates (BOI)”. The purpose of this study was to investigate the usefulness of thioglycollate broth (THIO) cultures.

Methods: We reviewed retrospectively results in the culture specimens of body fluids, tissue biopsies, and puses received during the month of July 1997. All specimens were inoculated into THIO in addition to agar plates. We reviewed the medical records of culture-positive patients to determine the clinical significance and relevance of their isolates. Clinically significant isolates were defined as those for which an appropriate antimicrobial therapy was done except one judged as contaminants by clinicians and clinically relevant isolates as the clinically significant one isolated first.

Results: Of 2,008 specimens, 512 (25.4%) from 365 patients grew 561 isolates including 464 plate isolates and 97 BOI. Two hundred eighty nine (62.3%) of the 464 isolates from plate cultures were clinically significant, compared to only 12 (12.4%) of 97 BOI (P<0.05). Only four (4.1%) BOI were clinically relevant, including one Pseudomonas aeruginosa from ascites, one Klebsiella pneumoniae and two Staphylococcus aureus from tissue specimens.

Conclusion: A routine use of enriched broth culture rarely recover clinically relevant isolates. Considering the laboratory and medical costs of the recovery of contaminants and clinically irrelevant isolates, the enrichment broth cultures should be used more selectively. (Korean J Clin Microbiol 2000;3(1):69-74)