Mycobacterial blood cultures
Mycobacterial BSIs occur in immunocompromised patients
(either as a consequence of iatrogenic immunosuppression, or
associated with an immunosuppressive condition) and patients
with long-term vascular access devices. Investigation tailored
to the recovery of mycobacterial blood isolates should thus
generally be limited to patients with such characteristics.
As mycobacteria are commonly located intracellularly,
approaches to growing them in vitro often include lysis of
leukocytes prior to incubation in a rich medium that contains
fatty acids. Mycobacteria may be optimally recovered, with
extended incubation of 4 weeks, with manual methods such as
lysis centrifugation or the use of commercial ‘lytic’ media in
manual or instrumented systems. These blood culture formulations
typically contain a proprietary mixture of fatty acids
that support mycobacterial growth, along with antimicrobial
agents. Limited comparisons between formulations suggest
some variability in the performance of lytic culture media, but
comprehensive comparative studies of all formulations have
not been performed [52–56].