Hello Revathi.. PDA and VRBA aren't the only techniques which are used for screening. They might be the most primary levels. Either ways any food or other products are extensively tested for their level of microbial counts and type of microbial spp, their anti-microbial and antibiotic type production. There are many multiplate broad spectrum methods which evaluates the detection of more than 31 anti-microbial agents at a single go. My suggestion is that you read through many Food safety protocols which will tell you the levels of extensive analysis at each stage and the type of contamination it eliminates. Also go through papers related to why such techniques were introduced.

One such paper which will tell you various type of media and assays used for milk screening is http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2758187/

Any culture based method is going to miss greater than 99% of the microorgansims present in milk, or any other environment. To identify "all" microbes, a molecular approach is required. Typically this involves the sequencing of 16S RNA coding DNA (in bacteria, referred to as SSU when also looking for eukaryotes and archaea) and comparison of those sequences to a vast database of such sequences collected over the past few decades.

This paper is a good starting point for the power of molecular approaches to microbial identification.

http://jb.asm.org/content/180/18/4765.short

I look at microbial communities in drinking water in my research with Norm Pace. In our studies of US drinking water, we find 10,000 to 100,000 microbes per mL of water at the tap, yet very few of these will grow on the plates they typically use for water testing. This is because their regulations are focused on fecal contamination of water, and the culture methods looks specifically for those organisms, E. coli and the like.

If you decide to take a molecular approach, I can definitely point you in the direction of more papers on the topic.

Yes absolutely. Ribotyping is rather a simple technique with just 33 rounds of PCR we can identify the all the strains of microbes. Although isolating and purifying each amplified product for sequencing requires significant amount of DNA in the sample. By doing multiple rounds of PCR also there will be a loss of the native amplified product.

Tell me what is your observation on ribotyping isolates from water.

The "disinfection" process seems to select for certain types microbes, and the specific process used also appears to impact the community. At the phylum level, there is great similarity from one drinking water system to another. Our group should have an interesting paper on the topic coming out in a few months as one of our graduate students wraps up her thesis work.

@Abhinaya and @Kevin thanks a lot for the solutions you have proposed. but my thesis is based on the study made at a large scale milk production plant. and as you say ribotyping is a very good technique to identify the strains! but you forget...in a developing country like india, feasibility of the process is of primary importance because the consumption rate almost exceeds the supply rate. so my question is that...do we have any other method where the results can be obtained quick enough to prevent any catastrophic effect (before the dispatch of the product) because the tests take about a forthnight or about 5 days(yeast detection). only if we can identify them can we think about disinfecting them.

Go to my page. Check out my publications. I did some work on the molecular diagnosis of infectious disease in the mid/late '90s. These methods will likely have some use for you. I'd be happy to help you adapt these old methods to your current work. I expect there are significant parallels, and modern methods can make the ID of microbes faster and more accurate than what I had to work with back then.

It is based in the 16S RNA work, but is more easily applied than trying to sequence a cohort of microbes. You may just need to get a feel for what you are looking for. It may take a run or two to figure out what you need to look for, but it would be easy to build from there.

The whole point of those studies was rapid identification of the cause of fever in children presenting in the emergency room. It had to be fast and sensitive. If you need to rapidly identify microbial contaminants, this might be a good way to go.

Kevin: thank you. I may suggest the microbiologists at the plant if the molecular approach is possible.

Thanks again :)

Revathi: Your doubt is credible in times of new strain out breaks that we have nowadays. I wish they work on viral contamination too for with bio-terrorism they got to cover this too.

Yeah @karunanithi...bio-terrorism is something worth to keep a look out for. And what better way than to infect the source which has the largest share in terms of consumption good here.

If the bacterial contamination can be curbed..i guess viral contamination can be too.

Hi Revathi...i understand what you looking for. Look this thesis by Franco, B. D. G.de Melo, about - Rapid methods in food microbiology analysis: critical review and evaluation of new methods. Maybe you find some answer.

Abstract:.

This report comprises three parts. In the first part, the author presents ans analyses the most important rapid methods for microbiological analysis of food. Rapid methods were classified in 7 main categories: 1 – methods involved with sample preparation; 2- microscopy methods; 3 – new methods for plating and counting; 4 – indirect methods for viable counting: 5 – genetic techniques; 6 – imunnological methods; 7 – miniaturized procedures for identification of microrganisms. In the second part, results of the evaluation of Petrifilm system for enumeration of total bacteria, total coliforms and yeasts and molds in food consummed in São Paulo, SP., are present and discussed. Food samples included raw and processed meat products (24 samples), pasteurized milk (11 samples), cheese (18 samples) and raw vegetables (10 samples). After proper homogenization and decimal dilution, samples were plated on Petrifilm aerobic count plates, Petrifilm total coliforms plates and Petrifilm yeasts and molds plates, according to 3M Co, Inc., and also plated on conventional plates, according to BAM/AOAC. Statistical analysis (alfa=0.5%) of data indicated that results obtained in Petrifilm plates were equivalent to the ones obtained by conventional procedures, except for raw vegetables. In these products, Petrifilm counts were lower than the ones in conventional plating. In the third part, results of the evalution of he kit Salmonella 1-2 Test (BioControl Systems, Inc., WA, USA) for rapid detection of motile Salmonella in raw pork products are presented and discussed. 100 raw pork meat and 63 raw pork sausages, purchased in Santo Andre, SP., were submitted to detection of Salmonella using the conventional procedures proposed by BAM/AOAC, 1992, and by ISO, 1991, and using the Salmonella 1-2 Test kit, following the sample enrichment protocol recommended by the producer and a modified enrichment protocol. Results indicated that, among 25 samples positive for Salmonella, only 2 were positive when the producer’s protocol was followed. When the modified enrichment protocol was used, the number of Salmonella positive samples increased to 7. Using conventional procedures, 8 samples were positive by BAM/AOAC, 1992 method, and 21 by ISO, 1991 method. Only one Salmonella positive sample was positive by the four methods simultaneously. The low efficiency of Salmonella 1-2 Test kit was probably due to loss of activity of anteserun during transport and storage of kits before use.

http://www.teses.usp.br/teses/disponiveis/livredocencia/9/tde-26052008-141940/pt-br.php

In Brazil, are doing analysis for brucelose using Ring-test methods and for Staphylococcus aureus using positive coagulase. See this paper too: http://www.scielo.br/scielo.php?pid=S0102-09352007000200004&script=sci_arttext

Thanks a lot @giovana, the paper did clear most of my doubts.

I have worked on isolation of lactobacillus species from yogurt and then checked their probiotic properties to be used in broiler chicken. The results were very impressive. Now I want to isolate bacteriocins from these species. These bacteriocins will be used in broiler chicken instead of organisms. All are invited to give comments about it. Thanks

Dr.M. Ashraf, University of Agriculture, Faisalabad Pakistan

@muhammad Ashaf: what are bacteriocins?

Bacteriocins are proteins produced by one bacteria and act against other bacteria like antibiotics but are not antibiotics

I think they are peptide antibiotics. Isnt it @Muhammad Ashraf

So can they be used like antibiotics? And how do they differ?

These are not antibiotics but act against like bacteria from which these are produced

I think must your attention for listeria monocytogenes in milk and it prouducts