There will be instances where you will not achieve complete antimicrobial
neutralization during your disinfectant testing using only lecithin and
tween 80. Tween(s) and Lecithin will not neutralize all antimicrobial
chemicals. Possible options include the use of Dey-Engley Neutralizing
Agar. This media contains several chemical neutralizers to inactivate
preservatives, sanitants and disinfectants including: quats, phenolics,
iodine, chlorine, mercurials, formalin and gluteraldehyde.
The recovery media should facilitate the repair of injured microorganisms.
One of the most important elements in microbial recover concerning
sanitization/disinfection is to match the neutralizing chemical in the
recovery media with the sanitant/disinfectant used to achieve
microbiological cleanliness. The neutralizing agent should also act
rapidly. If it does not, the antimicrobial effects may linger, possibly
beyond the visual examination of potential microbial recovery (post
incubation). If the sanitant/disinfectant is still "active" (i.e., still in
a concentration which would inhibit visual growth on the RODAC dish) in the
recovery media, organisms which are still viable will not be detected and
the count will produce a false negative. There is also evidence that some
antimicrobial neutralizers can have a negative effect on some species of
microorganisms such as S. aureus and S. epidermidis. They have been shown
to be sensitive to sodium thiosulfate. Which brings up my second point,
that the neutralizing chemical should not be toxic to the types of organisms
you're trying to recover.
RODACS are notorious for producing low recovery rates. You'll need to
validate (using <100 cfu/plate) the organism recovery rate of the RODAC +
media + neutralizer(s) system (control). Compare this to the organism
recovery in the presence of the disinfectant material (Note: the <100 cfu
inoculum should be added after the neutralizing agents have contacted the
disinfectant for a predetermined time). Generally, the recovery rate is
about 70% of the control but it will probably be lower give the lower
recovery rate for RODAC plates.
Some references for you:
Dey, B.P. and F.B. Engley Jr. (1995) "Comparison of Dey and Engley (D/E)
Neutralizing Medium to Letheen Medium and Standards Medium for Recovery of
Staphylococcus aureus from Sanitized Surfaces", J. Industrial Microbiol.,
Vol. 14, pp. 21-25.
Brummer, B. (1976) "Influence of Possible Disinfectant Transfer on
Staphylococcus aureus Plate
Counts After Agar Contact Sampling," Appl. Environ. Microbiol., July, p.
Kayser, A and G. VanDerPloeg (1965) "Growth Inhibition of Staphylococci by
Sodium Thiosulfate", J. Appl. Bacteriol., Vol. 28, No. 2, pp. 286-293.
Niskanen, A. and M.S. Pohja (1977) "Comparative Studies on the Sampling and
Investigation of Microbial Contamination of Surfaces by the Contact Plate
and Swab Methods," J. Appl. Bacteriol., Vol. 42, pp. 53-63.
Angelotti et. al. (1964) "Comparative Evaluation of the Cotton Swab and
RODAC Methods for the Recovery of Bacillus subtilis Spore Contamination from
Stainless Steel Surfaces," Health Lab Science, October, Vol 1. No. 4, pp.
Favero, M.S., McDade J.J., Robertsen J.A., Hoffman R.K. and R.W. Edwards
(1968) "Microbiological Sampling of Surfaces," J. Applied Bacteriol., Vol.
31, No. 3, September, pp. 336-343.
Bloomfield, S.F. (1995) "Reproducibility and Predictivity of Disinfection
and Biocide Tests", In: Microbiological Quality Assurance: A Guideline
Towards Relevance and Reproducibility of Inocula, Brown, M.R.W. and P.
Gilbert (eds.), Chapter 3.4, pp. 189-220.
Berube, R.; Oxborrow, G.S. (1991) "Methods of Testing Sanitizers and
Bacteriostatic Substances", In: Disinfection, Sterilization and
Preservation, Block, S.S. (ed.), 4th ed., Chapter 60, pp. 1058-1068.
Whyte, W., Carson, W. and A. Hambraeus (1989) "Methods for Calculating the
Efficiency of Bacterial Surface Sampling Techniques," J. Hosp. Infection,
Vol. 13, No. 1, January, pp. 33-41.
Quality Assurance Manager
Perritt Laboratories, Inc.
rfriedel at perrittlab.com
<debra.m.guerra at abbott.com> wrote in message
news:OF27115139.2F4E09A2-ON85256A5B.0061F311 at cmis.abbott.com...
> I am a microbiologist performing a study on the effectiveness of
> from Steris on different microorganisms on 3 different surface types.
> protocol calls for me to innoculate my material samples with bacteria then
> spray the Spor-Klenz on and let it act for different incubation times. At
> end of the time, I am supposed to use rodac plates to sample the
> microorganisms and let it incubate for 48 hours at 35C. However, the
> contain TSA with Lecithin and Polysorbate 80. My concern is that when
> incubation time is up and the sample is still wet with disinfectant, will
> PS80 and Lecithin in the plate neutralize the Spor-Klenz and stop the
> activity? If it doesn't, then I believe my results will be skewed. If it
> does, then i guess i have to wait until the material sample is completely
> before i sample it?
>> Any feedback is very much appreciated.
>> Thank you.
>> Debra M. Arcuri-Guerra
> Sr. Microbiologist
> Abbott Laboratories