Leslie Stockman

Quantitative Blood Cultures in Candidemia

The relationship between quantitative data on peripheral blood cultures and source of infection was studied in 172 episodes of candidemia that occurred in 169 patients. Clinically, the source of candidemia was an intravascular device in 67 episodes, an extravascular source in 73 episodes, and endocarditis in 2 patients; no source was identified for the other 30 episodes. Colony counts were determined in peripheral blood specimens on the first day of candidemia by the lysis-centrifugation system. High-grade and low-grade candidemia were defined as 25 colony-forming units or more per 10 ml and 10 colony-forming units or fewer per 10 ml of blood, respectively. Of 48 episodes of high-grade candidemia, 43 (90%) were associated with an infected intravascular device; therefore, the presence of high-grade candidemia should prompt the removal of intravascular devices. In contrast, 92 of the 112 episodes of low-grade candidemia (82%) had an extravascular or an unidentified source of candidemia. In patients with infections associated with an intravascular device, colony counts declined significantly within 72 hours after removal of the device in the absence of antifungal therapy; failure to decline suggests an alternative source of persistent infection. Quantitative data from peripheral blood cultures may help distinguish intravascular from extravascular sources of candidemia and aid in assessing the response to the removal of infected intravascular devices.

Laboratory diagnosis of Pneumocystis carinii infections by PCR directed to genes encoding for mitochondrial 5S and 28S ribosomal RNA

PCR with 5S mitochondrial ribosomal RNA (5S) target is a sensitive and specific assay for the detection of Pneumocystis carinii in clinical specimens from the respiratory tract. We developed an oligonucleotide probe directed to a 200 bp amplicon generated by fungal-specific universal primers that anneals with sequences specific for P. carinii in the 28S ribosomal RNA gene (28S). Of 50 archived bronchoalveolar lavage 1(BAL) specimens, 46 of 50 samples (92% agreement) gave the same result (23 positive, 23 negative) by PCR directed to the 5S and 28S assays. Results of calcofluor white staining of BAL smears on slides indicated agreement with the molecular results in 43 of 46 (93.5%) assays. PCR detection of P. carinii by amplification of 28S ribosomal gene target by fungal-specific primers and an organism-specific probe provides an alternate genomic target for the laboratory diagnosis of this organism.