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Subject:
From:
Donald English <[log in to unmask]>
Reply To:
The Pharmaceutical Microbiology Forum Email List <[log in to unmask]>
Date:
Thu, 3 Oct 2019 13:38:12 -0400
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 Dear all,

If you look at the composition of Burkholderia cepacia Selective Agar
(BCSA) that is used in USP Chapter 60, the following ingredients are being
used to inhibit the growth of other microorganisms: Crystal Violet,
Vancomycin, Polymyxin B, and Gentamicin.  Crystal violet has been shown to
inhibit the growth of Gram-positive organisms such as staphylococcus.  Because
of the limitations of Crystal violet in preventing the growth of
enterococci, Vancomycin had been added to the agar formulation to prevent
the growth enterococci.  Polymyxin B and Gentamicin are used to inhibit the
growth of Gram-negative bacilli such as Pseudomonas.  For isolating
Burkholderia cepacia complex from sputum samples, it is important to have
these inhibitory agents due to the presence of other organisms.

However, it should be realized that BCSA is not 100% effective in
preventing the isolation of non-Burkholderia cepacia complex organisms from
a test sample.  If you look at the 1999 paper by Henry et al. (Reference:
Henry, D, Campbell, M., McGimpsey, C., Clarke, A., Louden, L. Burns, JL,
Roe, MH, Vandamme, P. and Speert, D. 1999.  Comparison of Isolation Media
for Recovery of Burkholderia cepacia complex for respiratory secretions of
patients with cystic fibrous. J. Clin. Microbiol. 37: 1004-1007), they were
able to isolate the following microbial species on BCSA:  Burkholderia
gladioli, Ralsontia pickettii, Achromobacter xylosoxidans, and
Chryseobacterium (Flavobacterium) indologenes.  If you are not using
16srRNA or MALDI-TOF analysis for conducting identification of
microorganisms, Burkholderia gladioli and Ralsontia pickettii are somewhat
difficult to separate biochemically from Burkholderia cepacia complex and
require additional biochemical testing.  For example, Burkholderia gladioli
can be separated from Burkholderia cepacia complex by having a positive
reaction for the oxidation of Maltose and Lactose.  Chryseobacterium
indologenes has a positive indole reaction that can be used to separate it
from Burkholderia cepacia complex.  I have also heard of reports that
Enterococcus faecalis and Stenotrophomonas maltophilia (colistin resistant
strains) can also be isolated from a test sample by using BCSA, but I do
not have a literature reference.

If you are going to perform microbial testing of aqueous samples by using
USP Chapter 60 in which Burkholderia cepacia Selective Agar is used, it is
important not to rely on the presumptive identification of isolates on this
agar due to the possible recovery of non-Burkholderia cepacia complex
species as indicated above.  Instead, I would recommend that any isolate
recovered on BCSA be identified to the species level by using 16s rRNA or
MALDI-TOF analysis.  If those laboratories that do not have gene sequencer
or a MALDI-TOF for conducting identifications of microbial isolates,
additional biochemical tests will need to be used for conducting
biochemical identification of the recovered isolate to confirm the
identification.

 Don

 Donald J. English Microbiological Quality Consulting LLC

Florham Park, New Jersey 07932

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