Stability of hybridization activity of Coccidioides immitis in live and heat-killed frozen cultures tested by AccuProbe Coccidioides immitis culture identification test

Frozen hyphal suspensions of Coccidioides immitis were evaluated for suitability as positive control cultures in the AccuProbe C. immitis culture identification test. The genetic probe hybridization activity of heat-killed and viable frozen cultures, stored at -20 and -70 degrees C and tested over a 10-month period, was compared to that of a freshly grown culture, and the results were evaluated based upon the manufacturer's established positive and negative photometric light unit (PLU) cutoff values. All C. immitis suspensions produced positive hybridization values well above the positive and negative cutoff values, and no significant decrease in hybridization activity was observed with the frozen cultures after 10 months of storage. The frozen, heat-killed suspensions produced PLU values with less variability (coefficient of variation, 8% over 10 months than the fresh or frozen viable cultures and were deemed the most stable and sale form of positive control material to use.

Identification of Mycobacterium gordonae from culture by the Gen-Probe Rapid Diagnostic System: evaluation of 218 isolates and potential sources of false-negative results

The Mycobacterium gordonae Rapid Diagnostic System (Gen-Probe, Inc., San Diego, Calif.) was evaluated for sensitivity and specificity as well as for its application in the mycobacteriology laboratory. An 125I-labeled cDNA probe complementary to rRNA was employed. Hybridization of greater than or equal to 10% was considered positive. A total of 218 mycobacterial isolates, including 159 isolates of M. gordonae, were tested. Under optimum conditions, the specificity and sensitivity of the probe were 100 and 98.7%, respectively. A number of discrepancies were observed between the probe and conventional biochemical results in one laboratory. Further studies, designed to resolve these discrepancies, revealed a number of potential technical pitfalls. Hybridization incubation temperatures that varied from the manufacturer's recommended optimum, culture suspensions below the density of a no. 1 McFarland nephelometer standard, and extended storage times of culture suspension all adversely affected the final hybridization values. Additionally, it was determined that in one laboratory incorrect functioning of the sonicator caused false-negative hybridization values. The manufacturer's recommendations should be strictly followed, and the performance of the sonicator should be checked on a scheduled basis. Results show that the probe will allow fast and accurate identification of M. gordonae, thus eliminating time-consuming biochemical testing of this organism.

Malassezia furfur: a cause of occlusion of percutaneous central venous catheters in infants in the intensive care nursery

Growth of Malassezia furfur in the intravascular catheter used for administration of lipid emulsion resulted in occlusion of deep intravascular Silastic catheters in 12 infants in 2 intensive care nurseries. At the time of occlusion visible growth was noted in the clear catheter which was connected to the Silastic intravascular line. Five infants showed clinical signs suggestive of sepsis. The yield of M. furfur from blood cultures and catheter tips was low even when oil enrichment was used. The highest yield of M. furfur was found in the connecting catheter (11 of 11). The source from and the route by which M. furfur entered the catheter remain unclear. The potential portals of entry include the proximal and distal ends of the connecting catheter as well as the colonized skin of the infants and caretakers.