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Food Microbiology - Escherichia coli O157:H7 in Meat

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Food Microbiology - Escherichia coli O157:H7 in Meat

Postby kady123 » Sun Jan 11, 2009 8:47 pm

Greetings,
I have an important project concerning food microbiology, and I need answers for the following:
I am detecting Escherichia coli O157:H7: in lamb meat.I will grow the sample homogenates on Sorbitol MacConkey Agar!
For preparing the sample homogenate, what is the preferable diluent to be used? Why ?Is it sterile water, MRD, MacConkey broth, thyioglycolate ??
Is it it enough to prepare it from 1 g of meat??
Thank u for ur help
Take care
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Re: Food Microbiology - Escherichia coli O157:H7 in Meat

Postby Sepals » Mon Jan 12, 2009 1:58 pm

Have you searched articles on analysing E.coli in meat?

I've never used meat samples, with clincal samples I would plate it out on nutrient agar, blood agar and MacConkey agar and then add a colony to nurtient broth the next day, from which I could dispense into various liquid media for testing sugar fermentation. For solid media I would add a colony directly.
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Postby canalon » Tue Jan 13, 2009 4:23 am

There are some protocols published for that but I thought that for most of this kind of organisms, samples should be 25g and the diluent peptone water (225ml). But that was a long time ago. I think for your homogenate, 1g might be a little too small a sample.
For O157:H7 no need for blood agar, Nutrient agar is not selective so not good. SMAC is used for isolation of O157:H7 as it will select for coliforms (bile salts) and O157:H7 uses sorbitol, it will become a nice red (if my memory is still OK)
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Re: Food Microbiology - Escherichia coli O157:H7 in Meat

Postby JorgeLobo » Sat Jan 17, 2009 10:29 pm

Finding E. coli in ground meat is expected - so you need a way to enrich/select for 0157. go to the FDA's BAM for rthe best methodology.
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