Rapid microbiological tests for food products

Dear All,

Could you give me an idea regarding reliable rapid methods which can be used test following microbiological parameters ?

1. Total coliform count.

2. Feacal coliform count.

3. Ecoli.

4. Yeast & Mold count.

Dear Athula,

Define "Rapid"

Define "reliable".

Most routine quantitative microbiological measurements are associated with large confidence intervals.

Most "reliable" methods are in reference sources like BAM on-line. Most take between 1 day and 1 week, depending on degree of certainty required and possibly on financial capabilities.

Faecal coliform became obsolete around 10-15 years ago although still in use in some places.

Rgds / Charles.C

Dear Charles,

I need to get the microbiological test results soon as our bottledwater and beverage products are moving fast. Because of the traditional test methods what we use now are time consuming (more than 2 -5 days), we need to stick to quick methods. 

Rgds.

Athula

Hello Athula,

          There are no short-cuts for APC,Coliforms, and yeasts and Molds as there optimum growth characteristics in nutrient medium varies from 24-48 hrs for APC and 72 hrs for yeasts and molds at optimum temperature.

              However it should not be cause of concern if you are following the  GMP,Water filteration process and FSMS and if you don't have any previous issues regarding Microbial contamination of products.

Many Beverages companies are testing these products by traditional methods only.

Hi Athula,

      There are after market rapid test kits for the mentioned microbio needs of your company but be sure that it is an accepted procedure by organizations such as AOAC or ICUMSA.

      We are using a specific brand of test kits that are approved by AOAC and ICUMSA but we also send our samples for third party analysis on specific timetable for counter-checking. One thing also is that you need to validate these test kits with the "long" method.

      Hope we have help you on this matter.

Regards

Chebar

Thanks lot Chebar,

Could you explain what are the brands are being used which are approved by AOAC and ICUMSA ?

Regards.

Athula

I believe 3M had a rapid coliform that we used for yogurt that was a 24 hour test.  They had to be incubated to a certain temperature.

This is what I believe we were using http://solutions.3m....Tbe29BDXSBJ7Fgl

Contact 3M for their petrifilm tests and see if they have what you need.

You can always try a MicroFoss. we used to get results on yogurt in 20 hours on that.

Caz x

Dear athula,

As noted in many of the previous posts, there is usually a trade-off between speed and accuracy. IMEX, some of the available "rapid" methds simply do not work for some products. AOAC usually mention the scope and known exceptions where valid data exists.

If you are looking for results which will be validatable against standard procedures considerable care is advised.

If you wish to approx. test it out, can try following a mesophilic plate count  over the (typical) 2 days by noting the levels after 24 and 48 hours respectively. For frozen (ie maybe "shocked") raw and cooked seafood, i was amazed at the difference (eg post #4).

I think i have had more arguments over origin/reception micro. quality  due to differences in test  procedure than any other aspect. Especially where non-specific quantities like coliforms are concerned.

However if you are only using the data for internal use/judging against a particular standard, you may be able to accept some compromises. Nonetheless, if you are aiming for << 24hrs for the items you mention, not so likely IMO with a commercial product.

But certainly interested to know if you succeed. :smile:

Rgds / Charles.C

From the FDA BAM

Membrane filter method for coliforms.

Filter 100 mL of test sample and transfer the filter to M-Endo medium (M-196²⁸) or LES Endo Agar (M-197²⁹) and incubate at 35 °C± 0.5°C for 22-24 h. Count colonies that are pink to dark red with a green metallic surface sheen. The sheen may vary from pinpoint to complete coverage of the colony. Use of a low power, dissecting-type microscope to examine filters is recommended.

Confirmation - If there are 5 to 10 sheen colonies on the filter, confirm all by inoculating growth from each sheen colony into tubes of LST and incubate at 35 °C± 0.5°C for 48 h. If the number of sheen colonies exceeds 10, randomly select and confirm 10 colonies that are representative of all sheen colonies. Any gas positive LST tubes should be sub cultured to BGLB and incubated at 35°C± 0.5°C for 48 hr. Gas production in BGLB within 48 h is a confirmed coliform test. Report results as number of coliform colonies per 100 mL. NOTE: Standard Method, 1998, 20th ed, p. 9-60 (3), allows for simultaneous inoculation of LST and BGLB during verification. However, BGLB is somewhat inhibitory so the method described above, where samples are sub cultured from LST into BGLB is regarded as a more sensitive verification assay and therefore, recommended.

NOTE: if a sample is found to contain coliforms (at any level) follow procedure outlined in Sec. I. F. above to determine if it is E. coli. Bottled water is not permitted to contain E. coli.

mEndo will test for total coliform, fecal coliform and E. coli. mEndo test will take 24 hour +/- 2 hours, Presumptive positive requires further testing at 2-3 days (product should be put on hold if mEndo results are positive) 500 gram bottle of dehydrated media is very cheap

Yeast/Mold will take 2-3 days but is not a release critieria in bottled water

Idexx Colilert 18 is a rapid test used here in the States but is very expensive.

M

Dear SPL,

As quoted, it seems quicker to use a traditional method on its own ? Or do most membrane users simply skip the confirmation ?

No idea about water per se but IMEX for food products, tube coliforms Pr>Con  is sometimes 90-100% positive, others only 50%. And similarly for traditional plate count methods. If it's low anyway, i guess it doesn't matter. :smile:

The interesting part is how well the 24 hr membrane technique validates against 2-day routine(?) methods. ? Certainly beneficial on sample size and therefore sampling sensitivity, but how much ?

Rgds / Charles.C

Charles,

Here in the States, membrane filter testing is the standard because of time and cost. During my time in the water business, presumptive E.coli and coliform results are rarely seen in post processed water. Conformation steps to not need to done if the selective media (mEndo) does not show presumptive positive. 

Now raw water is a different issue, especially water treated with chlorine products which will inhibit but not fully kill all bacteria. That is where you will encounter bacteria families that grow on mEndo and show coliform traits but will be differentiated during the conformation steps. This is where I would used the Idexx colilert product if I were pressed for time.

Thanks for all!

Athula

3M petrifilm makes plates for wide range of indicator bacterias.  I use 3M petrifilm for Coliform/Ecoli, Anaerobic Plate Count, Y&M and they are cost efficient.  24-48 hours depending on type of micro test conducted. 

3M petrifilm makes plates for wide range of indicator bacterias.  I use 3M petrifilm for Coliform/Ecoli, Anaerobic Plate Count, Y&M and they are cost efficient.  24-48 hours depending on type of micro test conducted. 

IMEX not suitable for routine E.coli use unless sample allows very low dilution or E.coli level is enormous. For most  foods, estimation of low E.coli levels demands MPN technique.

IMEX too expensive for routine aerobic plate count use. But i agree convenient.