A descriptive analysis of urine cultures: pure versus mixed isolates

Out of 5,670 urine cultures performed in 1989, 1,448 positive cultures with unique results were analyzed. Of these 1,448, 67% were pure cultures, and 50% had at least one isolate with a colony count greater than 100,000 colony forming units/ml. Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis, Klebsiella pneumoniae, Staphylococcus aureus, and diphtheroids were more likely (p < 0.01) to occur in mixed than pure culture, while Escherichia coli was more likely to occur in pure than mixed culture. The most common organism combinations were diphtheroids-coagulase negative Staphylococcus (30 cultures), E. faecalis-coagulase negative Staphylococcus (28), E. faecalis-P. aeruginosa (13), K. pneumoniae-P. aeruginosa (9), and E. coli-P. aeruginosa (9).