One of the best courses I took in university was a wildlife
biology ecology course. OBVIOUSLY, the
course material is not relevant to my current job, but the professor spent a
better course of a month drilling into us that there are always two sides to every
story and not to read and believe everything you see in print. He did not care if it was a blog (admittedly
those weren’t around in my university days), a newsletter article or a peer
reviewed journal article. We were taught
to look at what was presented critically and determine if both sides of the
story were being presented equally or if the story, article or study was being
presented in a manner that was a little less balanced. As a result of this course and a couple of
great mentors, I admit I may be a bit jaded when reading articles and
studies. I generally don’t take things
at face value and generally drive people insane with my sometimes never-ending
stream of questions. Much to the chagrin
of my colleagues, I’m the self proclaimed “Ya, but..." girl.
biology ecology course. OBVIOUSLY, the
course material is not relevant to my current job, but the professor spent a
better course of a month drilling into us that there are always two sides to every
story and not to read and believe everything you see in print. He did not care if it was a blog (admittedly
those weren’t around in my university days), a newsletter article or a peer
reviewed journal article. We were taught
to look at what was presented critically and determine if both sides of the
story were being presented equally or if the story, article or study was being
presented in a manner that was a little less balanced. As a result of this course and a couple of
great mentors, I admit I may be a bit jaded when reading articles and
studies. I generally don’t take things
at face value and generally drive people insane with my sometimes never-ending
stream of questions. Much to the chagrin
of my colleagues, I’m the self proclaimed “Ya, but..." girl.
However, there are times when this irritatingly inquisitive
approach comes in handy. Case in point was
with a recent question as to the efficacy of a product against an arm’s length
list of Salmonella strains where I was asked to answer yes or no to whether Product
A was effective against the following:
approach comes in handy. Case in point was
with a recent question as to the efficacy of a product against an arm’s length
list of Salmonella strains where I was asked to answer yes or no to whether Product
A was effective against the following:
- Salmonella enterica – pullorum
- Salmonella enteritidis
- Salmonella schottmuelleri
- Salmonella typhi
- Salmonella typhimurium
As we have discussed in several previous blogs, the number
of kill claims is not what is relevant.
Microorganisms, particularly bacteria that have numerous strains, should
be considered as a single pathogen – if you kill one, you kill them all!
of kill claims is not what is relevant.
Microorganisms, particularly bacteria that have numerous strains, should
be considered as a single pathogen – if you kill one, you kill them all!
In the case with Salmonella
spp, in order to obtain a disinfectant claim in Canada or the US Salmonella enterica is one of the three
surrogate organisms used to ensure a product is considered a hospital
disinfectant with broad-spectrum efficacy against vegetative bacteria. My response to this question was as expected
- If the product kills S. enterica it
would be effective against all strains of Salmonella.
spp, in order to obtain a disinfectant claim in Canada or the US Salmonella enterica is one of the three
surrogate organisms used to ensure a product is considered a hospital
disinfectant with broad-spectrum efficacy against vegetative bacteria. My response to this question was as expected
- If the product kills S. enterica it
would be effective against all strains of Salmonella.
Upon giving that response however, I received an email
citing a study conducted in 2002 that concluded “variations in susceptibility
to disinfectants has been observed between Salmonella
strains” so I did what anyone respectable person would do. I found the reference, reviewed it and called
someone far smarter than I (a world renowned microbiologist) to comment! The response I received back nearly made me
snort my coffee out my nose and took me back to my third year Wildlife Biology
Ecology course.
citing a study conducted in 2002 that concluded “variations in susceptibility
to disinfectants has been observed between Salmonella
strains” so I did what anyone respectable person would do. I found the reference, reviewed it and called
someone far smarter than I (a world renowned microbiologist) to comment! The response I received back nearly made me
snort my coffee out my nose and took me back to my third year Wildlife Biology
Ecology course.
The response I got back was “The paper is not even worth the
paper it is written on, it was a good example of how one can make a mockery of
the peer-review process and should not be given any further
consideration”. This respected
microbiologist then went on to agree with my stance that if you kill one strain
you kill them all. But why did this
microbiologist draw such strong conclusions?
For this person it was easy.
First, the study stated that the disinfectant test method it used was “close” to how the chosen products were
used in the field. Seems reasonable, BUT
the test method, based on a Master’s thesis by the first author, was a carrier
test using pieces of stainless steel and the test disinfectant was sprayed on
the carriers with dried bacterial inocula, which is not a test method accepted
by Health Canada or the EPA for disinfectant product registration.
Further, among its numerous weaknesses with the test method were: (a) no added
soil load, (b) no mentioned neutralizer, (c) no quantitation of viable bacteria
- the results were based on the presence or absence of turbidity in the
inoculated tubes, (d) the fact that at the end of the contact time, the excess
disinfectant was simply drained off into a filter paper - this has major
implications for the degree of dislodgement of the bacteria from the carrier
surface depending on the detergent activity of the formulation under test, (e)
the inclusion of 3% hydrogen peroxide (unformulated) in the testing as a
‘disinfectant’, (f) the requirement of a complete kill as the product efficacy
criterion, (g) no indication of the number of viable bacteria on the carriers
after the inoculum drying process, and (h) the dipping of the entire carrier
into the recovery medium, which could have resulted in turbidity (therefore,
failure of product) from the growth of one single bacterium surviving the
disinfectant treatment.
paper it is written on, it was a good example of how one can make a mockery of
the peer-review process and should not be given any further
consideration”. This respected
microbiologist then went on to agree with my stance that if you kill one strain
you kill them all. But why did this
microbiologist draw such strong conclusions?
For this person it was easy.
First, the study stated that the disinfectant test method it used was “close” to how the chosen products were
used in the field. Seems reasonable, BUT
the test method, based on a Master’s thesis by the first author, was a carrier
test using pieces of stainless steel and the test disinfectant was sprayed on
the carriers with dried bacterial inocula, which is not a test method accepted
by Health Canada or the EPA for disinfectant product registration.
Further, among its numerous weaknesses with the test method were: (a) no added
soil load, (b) no mentioned neutralizer, (c) no quantitation of viable bacteria
- the results were based on the presence or absence of turbidity in the
inoculated tubes, (d) the fact that at the end of the contact time, the excess
disinfectant was simply drained off into a filter paper - this has major
implications for the degree of dislodgement of the bacteria from the carrier
surface depending on the detergent activity of the formulation under test, (e)
the inclusion of 3% hydrogen peroxide (unformulated) in the testing as a
‘disinfectant’, (f) the requirement of a complete kill as the product efficacy
criterion, (g) no indication of the number of viable bacteria on the carriers
after the inoculum drying process, and (h) the dipping of the entire carrier
into the recovery medium, which could have resulted in turbidity (therefore,
failure of product) from the growth of one single bacterium surviving the
disinfectant treatment.
In
a nutshell, there were numerous holes in the method used and while interesting,
the test method used was not reflective of the requirements for manufacturers
to register products, and therefore the results could be considered suspect. The
conclusion of both the microbiologist and me on using representative strains of
pathogens to draw conclusions on the overall field effectiveness of its
products is valid in general, and also endorsed by regulatory agencies.
a nutshell, there were numerous holes in the method used and while interesting,
the test method used was not reflective of the requirements for manufacturers
to register products, and therefore the results could be considered suspect. The
conclusion of both the microbiologist and me on using representative strains of
pathogens to draw conclusions on the overall field effectiveness of its
products is valid in general, and also endorsed by regulatory agencies.
I
hope the next time you read a study you’ll consider if both sides of the story
are being told, particularly when reading a study on the efficacy of products
you consider, and validate if the test method used is one that will be accepted
by regulatory bodies for registration.
If it’s not, the study is interesting, but not necessarily one that you
can apply to your practice.
hope the next time you read a study you’ll consider if both sides of the story
are being told, particularly when reading a study on the efficacy of products
you consider, and validate if the test method used is one that will be accepted
by regulatory bodies for registration.
If it’s not, the study is interesting, but not necessarily one that you
can apply to your practice.
Bugging
Off!
Off!
Nicole
