Suitability Testing by USP Methodology
Suitability testing is performed in order to verify that the method utilized eliminates the effect of any
antimicrobial properties of the product. Therefore, the media diluent combination does not inhibit the
recovery and growth of microorganisms, if present in the sample. The goal of the suitability testing is to
establish the ability of the test to detect microorganisms in the presence of product.
The suitability described in USP <61> verifies the
validity of the testing method by showing the
recovery of microorganisms in presence of the
product. Total Aerobic Microbial Count and Total
combined Yeast and Mold can be carried out by
membrane filtration, pour plating or spread plate
Suitability using USP <62> can use selective media to
detect various organisms such as: Staphylococcus
aureus, Pseudomonas aeruginosa, Escherichia coli,
bile-tolerant gram-negative bacteria, Clostridia,
Salmonella and Candida albicans. The samples are
first enriched by incubating in Trypticase Soy Broth
(TSB) or another appropriate neutralizing media, and then streaked onto selective agars for the
determination of presence of specified or the objectionable microorganisms.
The new USP <61> and USP <62> tests also provide harmonization to existing European Pharmacopeia
methods for testing non-sterile pharmaceutical products. Additional in order to verify the testing
conditions, a negative control is performed using the chosen diluent that shows no growth of
the microorganisms. While conducting the suitability testing precautions must be taken to avoid
contamination so they do not affect the microorganisms that are being tested. The procedure involves
the inoculation of the neutralized sample with low (not more than 100 cfu) and detecting the organisms
by the prescribed method.
Even though USP uses traditional microbiology methods, from the USP <61> and <62> states
that “Alternative microbiological procedures, including automated methods, may be used, provided that their equivalence to the Pharmacopeial method has been demonstrated” and “any validated method,
including, Rapid Methods can be used”.
The New BioLumix Method
A study was recently conducted to show the utilization of BioLumix system (see figure below) in
suitability tests using a variety of products from both the pharmaceutical and cosmetic industries.
Sampling was conducted by taking ten gram of the product
and placing it into 90ml of M Letheen broth (or another
appropriate neutralizing broth) for a final dilution of 1/10.
An overnight culture of the target organism was diluted to
not exceed 100 cfu and the inoculum not exceeds 1% of the
volume of the diluted product. Then 1.0 mL of the
neutralized sample containing organism was placed into the
appropriate vial and a side by side comparison was done
with the appropriate USP method.
The products tested included Aloe, Hand Sanitizer, Lip Balm, Flavored Lip Balm, Medicated Lip Balm,
Breath Spray, Medicated ointment, and Sun Screen. A variety of different types of each product were
32 product samples were tested for suitability. Four bacteria (Staphylococcus aureus ATCC 6538;
Pseudomonas aeruginosa ATCC 9027; Bacillus subtilis ATCC 6633 and Escherichia coli ATCC 8739; a
yeast (Candida albicans ATCC 10231), and a mold (Aspergillus niger ATCC 16404) were used to show the
effectiveness of the neutralization step. Thirty one
products were properly neutralized by the M Letheen
Broth as evidenced by detection time in the vials and
colonies on the plates. Only one product tested contained
a high level of ethanol, which required a 1:100 dilution in
M Letheen Broth to obtain neutralization. There was 100%
correlation between the two methods.
Typical data obtained by the system is shown in the figure:
The product was inoculated with ~ 100 cfu/g of three organisms: Staphylococcus aureus ATCC 6538 (light blue); Bacillus subtilis ATCC 6633 (Dark blue) and Escherichia coli ATCC 8739 (green). The Detection times obtained (shown as triangles on the curves) are comparable to data obtained without product.
What are the advantages of the BioLumix system?
Time Saving: The results are available much faster, for example, the results of the Yeast and Mold vialsoccurred in less than 48 hours, while the Aspergillus took nearly five days for countable colonies. All
products tested with bacteria using the automated BioLumix assay yielded results typically 10-13 hours,
instead of 48 hours for the plate count methodology. The advantage is that you can see results an
entire day early if the product is exhibiting any sort of inhibition. Data generation is slower using classic
microbiology so it can also slow down production improvements as well.
Labor Saving: The setup of the assay can be done much faster using the BioLumix system as opposed
to traditional plating methods, saving significant hands-on labor due to its automation and simplicity of
use. BioLumix can make the microbiological testing simpler, faster, and automated- saving significant
time and labor. It is paperless, increasing efficiency and saving on disposables, time and space, and best
of all the system is unaffected by product interference. The System is extremely easy to operate, with
its straightforward, streamlined testing design it offers accurate results leading to reduced material-
holding time for faster product release.
High Correlation with USP: The BioLumix System showed a high correlation between the instrument
results and the USP methodology. The system is fully automated with automated data archiving,
data maintenance in databases, and automated report generation. Regulators encourage rapid
microbiology methods for improved process control and product release. The BioLumix system
is validated as being at least equivalent to the compendial method. Under general notices of the
USP states that “Automated procedures employing the same basic chemistry as those assay and
test procedures given in the monograph are recognized as being equivalent in their suitability for
USP <61> MICROBIOLOGICAL EXAMINATION OF NONSTERILE PRODUCTS: MICROBIAL ENUMERATION TESTS
USP <62>: MICROBIOLOGICAL EXAMINATION OF NONSTERILE PRODUCTS: TEST FOR SPECIFICIED