agar and potassium-nitrate

A new medium selective for Bacteroides gracilis was developed. The medium is tryptic soy agar (Difco Laboratories, Detroit, Mich.) containing nalidixic acid, teicoplanin, sodium formate, sodium fumarate, and potassium nitrate. All 18 strains of B. gracilis tested grew with only minimal inhibition. Most of the other 214 organisms tested, including most Bacteroides species, other anaerobes, and a substantial number of facultative anaerobes, were significantly inhibited by the medium. In a diagnostic study of 49 clinical specimens (28 patients with intra-abdominal infection, mostly gangrenous or perforated appendicitis), four strains of B. gracilis were isolated (from 4 different patients) on B. gracilis selective agar but were not detected on standard media.

Topics: Agar; Anti-Bacterial Agents; Appendicitis; Bacteroides; Bacteroides Infections; Caseins; Culture Media; Formates; Fumarates; Gangrene; Glycopeptides; Humans; Nalidixic Acid; Nitrates; Potassium Compounds; Protein Hydrolysates; Saliva; Teicoplanin

For facilitation of the detection of bacteria able to reduce nitrates the presently used method of 24-hour broth culture with KNO3 and the method of growing on slant agar cultures with KNO3 (standard method) were compared, with certain modifications introduced. It was found that shortening of the incubation period from 24 to 6 hours and reduction of the volume of broth with KNO3 from 10 to 0.5 ml made possible obtaining of a greater number of correct results as compared to the standard method. In the 24-hour broth cultures with KNO3 done as yet in case of negative results it is indispensable to confirm them in the test with zinc dust. The placement of Griess reagents on points onto colonies growing on KNO3 agar may lead to false positive results.

Topics: Acinetobacter; Agar; Bacteriological Techniques; Culture Media; Enterobacteriaceae; In Vitro Techniques; Nitrates; Oxidation-Reduction; Potassium Compounds; Time Factors