Effect of delays in processing on the survival of Mycobacterium avium-M. intracellulare in the isolator blood culture system

Abstract

Concentrations of Mycobacterium avium-M. intracellulare ranging from 10-1 to 163 CFU/ml were added to blood, placed in Isolator tubes, and held at room temperature for intervals ranging from 4 h to 56 days before being processed (centrifugation and culture on Middlebrook 7H10 agar). At all concentrations tested, M. avium-M. intracellulare was recovered after hold times ranging from 4 h to 7 days; the number of final CFU actually increased progressively for hold times of 8 h or more. Hold times of up to 7 days did not increase the time from processing to the first appearance of visible colonies. At an inoculum of 102 CFU/ml, M. avium-M. intracellulare was recovered from Isolator tubes processed 56 days after inoculation. Two Isolator blood cultures were drawn from a patient with AIDS; M. avium-M. intracellulare was recovered from the sample processed immediately and from the sample processed after a hold time of 7 days. Since M. avium-M. intracelulare survives for prolonged periods in Isolator tubes, blood cultures may be collected in outpatient settings or in hospitals without mycobacterial culture facilities and shipped to reference laboratories for processing without loss of viability.

The Mycobacterium avium complex.

“…Therefore, lysis of the blood cells by a commercial lysis-centrifugation method (Isolator; Wampole Laboratories, Cranbury, N.J.) or treatment of the blood with a lytic agent such as sodium deoxycholate significantly improves the detection of mycobacteria in blood (171,280,504). Using blood inoculated with known concentrations of mycobacteria, von Reyn et al (464) demonstrated that MAC isolates remain viable in Isolator tubes for at least 7 days.…”