Evaluation of the Usefulness of MacConkey Agar and Colistin-Nalidixic Acid Blood Agar for Body Fluids, Peritoneal Fluid, and Wound/Abscess Specimens

Abstract

Background: Most clinical microbiology laboratories in Korea have difficulty in following the recommendations of the clinical procedure handbook for culture of body fluid and wound/abscess specimens. We evaluated the usefulness of MacConkey (MAC) and colistin-nalidixic acid blood agar (CNA) for the isolation of pathogens from these specimens. Methods: A total of 1,508 clinical specimens [144 peritoneal fluid, 241 body fluids (19 bile, 70 joint fluid, 6 pericardial fluid, 104 pleural fluid, and other fluids in 42 cases) and 1,123 wound/abscess] were inoculated onto basic media [Blood agar plate (BAP), chocolate agar or BAP with streaking of Staphylococcus aureus] and simultaneously inoculated onto MAC and CNA. The pathogens isolated by basic media and by additional use of MAC and/or CNA were compared. Results: With basic media, 885 isolates from 588 specimens were detected, and by additional use of MAC and CNA, an additional 27 isolates from 24 specimens and an additional 128 isolates from 112 specimens were isolated, respectively. Compared to the basic media, by adding MAC, an additional 233.3%, 38.5% and 4.5% of gram-negative bacteria were isolated from peritoneal fluids, body fluid and wound/abscess, respectively, and by adding CNA, an additional 106.7%, 45.0%, and 20.7% of gram-positive bacteria/yeast were isolated, respectively. The isolates detected by additional use of MAC were mainly Enterobacteriaceae (77.0%), and those detected by CNA were S. aureus (21.1%), Coagulase-negative Staphylococcus spp. (20.3%), Enterococcus spp. (16.4%), Streptococcus spp. (10.2%) and yeasts (16.4%). Conclusion: For peritoneal fluid and body fluid specimens, additional use of MAC plus CNA seems necessary for detection of pathogens. For wound/abscess, additional use of CNA will be cost effective. (Ann Clin Microbiol 2015;18:1-6)