Oxoid Thermofisher Scientist Patrick Duggan Address Culture Media For Isolation and Detection of Cronobacter Species
Editor's Note: This is another report on the presentations that were made in Dublin earlier this year at the 1st International Meeting on Cronobacter (Enterobacter Sakazakii). In this segment, we hear from Dr. Patrick Druggan, Oxoid Ltd., Thermo Fisher Scientific, Basingstoke, Hampshire RG24 8PW, United Kingdom.
Biography: Patrick Druggan is Principle Scientist, Oxoid Thermofisher, Basingstoke, UK.
He received an Honours BSc in Food Science from the University of Strathclyde, Glasgow, UK. He has worked in the diagnostics industry for 22 years. He designed his first chromogenic medium in 1989 while working at Gibco.
Patrick studied part-time for his Ph.D. at the Pharmacy Department of University of Brighton, UK. His thesis was on improvements in the resuscitation of heat-injured Salmonella species from processed food samples.
He synthesized a number of autocytotoxic compounds that could be used during pre-enrichment to inhibit competitive microflora while allowing injured Salmonella spp. to resuscitate and grow.
This invention lead to the development of Inhibigens.™ His skills in chemistry and microbiology have allowed him to design a number of successful rapid biochemical tests and chromogenic culture media, including Druggan-Forsythe-Iversen Agar for the isolation of Cronobacter spp.
Summary – - Culture media for isolation and detection of Cronobacter species
In 2001 a pre-term infant died of meningitis caused by Enterobacter sakazakii (Cronobacter spp.). Infant formula milk (IFM) was implicated as a potential source of the infection.
The Food and Drug Administration (FDA) independently develop a method for enumeration of this emerging pathogen in IFM using culture collections from national bodies that have later been shown to be poorly defined.
This method was introduced in 2002 and has regulatory standing for the import of IFM and skimmed milk powder in to the USA and a number of other countries. The FDA method is a modification of the procedure for the detection of Enterobacteriaceae, with the addition of yellow pigmentation of colonies for presumptive identification of Cronobacter spp.
It should be remembered that the FDA method was developed in a short time due to a public health concern, and this would have put a time constraint and significant pressure on those working on Enterobacter sakazakii (Cronobacter) to get a working method in the field as soon as possible. The FDA method has been shown to have a sensitivity of around 50 percent and a specificity of around 70 percent. Only 75 percent of Cronobacter strains phenotypically express yellow pigmentation, and the low specificity of the method coupled with the recommendation that only five presumptive Enterobacteriaceae colonies are tested from Violet Red Bile Glucose Agar (VRBGA) may explain the poor sensitivity of the method.
Assuming the prevalence of Cronobacter spp. in IFM is around 2 percent, the FDA method will fail to detect around 50 percent of batches contaminated with Cronobacter, while around 95 percent of rejected batches will not contain this organism.
This high rate of failure has lead many stakeholders to question the usefulness of the FDA method. This presentation reviews developments in culture media since the release of the FDA method in 2002, with specific emphasis on media that have improved the specificity of methods for Cronobacter spp. The unique phenotypic trait of this emerging pathogen that aid and hinder design of methods is discussed.
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