Flow cytometry a rapid bacteria count alternative to the plate count method

Bacteria in milk
8. 12月, 2018
发件人 Richard Mills
The recent official approval for the BactoScan™ bacteria count method by EU-RL (EU Reference Labs) is just the latest step on the long road to reduced bacteria count in raw milk.

Even though a sample of raw milk today looks exactly as it did 50 years ago, the bacteria count is likely to be far lower. 


This is good news for consumers and dairy producers alike because bacteriological milk quality is an important parameter for heat treatment procedures, shelf- life prediction and determining the the suitability of raw milk for processing different products.


For decades, average levels of bacteria in raw milk have been gradually falling around the world, from hundreds of thousands of Colony Forming Units (CFU) per millimetre in the seventies to less than 10,000 CFU per millilitre today. In many countries, producers consistently attain 5,000 cfu/ml in their milk deliveries. 


Nonetheless, the battle to reduce bacteria levels still goes on with rapid bacteria count analysis of raw milk samples using the FOSS BactoScan analyser ever important in the front line. 


The importance of flow cytometry tests
Recently retired Market Manager for FOSS central milk testing, Steen Kold-Christensen has tracked the development of flow cytometry methods since the early eighties. “It was important to find a way of automating and speeding up the traditional analysis process,” he says. 


The traditional CFU method gives an indication of quality based on colony forming units. The BactoScan method gives the same indication, but is based on the number of individual bacteria cells using flow cytometry technology. An individual result is delivered in just nine minutes compared to the two to three days it takes with plate counting and the BactoScan can test up to 200 samples in an hour. 


The rapid results are important because catching hygiene breaches in raw milk early is essential for minimizing the impact on milk quality. Although pasteurisation will kill the majority of bacteria, their metabolites may cause off flavours and enzymes continue their activities resulting in product defects and reduction of shelf life. 


With the traditional plate count method, hygienic problems on the farm may go undetected for days, making corrective actions more difficult and production losses larger than necessary. With the BactoScan test, farmers can be advised about possible problems the same day as the sample is drawn allowing timely correction for leaks, insufficient cleaning or cooling in the milking system, or health problems in the herd.


Growing acceptance
Kold-Christensen explains how at the time FOSS developed the BactoScan, a number of solutions were available as alternatives to the traditional time-consuming and labour-intensive plate counting method. “BactoScan™ is one that has withstood the test of time,” he says.


The FOSS BactoScan FC+


The lower limit of detection of the flow cytometry technology used with BactoScan proved important as more and more countries tightened up on milk quality and increasingly stringent national regulations came into force. “Many of the other solutions fell by the wayside because they were not accurate enough to meet the new regulations,” he adds. 


The ongoing approval process
One would think that something that could speed up analysis of bacteria would be quickly adopted. But acceptance and approval is a complicated process and has been going on for about 35 years. 


Referring to the various industry and government bodies involved, Kold-Christensen says: “Many people need to be convinced of the complex nature of the parameter total bacterial count, and it takes a long time. In particular, the need to correlate the BactoScan method, based on counting individual bacteria cells, with the traditional method, based on counting colony forming units, has caused much discussion which is still going on to this day.” 


De-facto industry standard
Despite the ongoing discussion, the flow cytometry technology usedin the BactoScan is now widely accepted and BactoScan has become the industrial standard for counting raw milk bacteria in many countries worldwide.  Following approval by The FOSS BactoScan FC+ instrument is now the only rapid method for testing bacteria count in raw milk to be approved by both the EU Reference Labs (EU-RL)) and NCIMS/ FDA in the USA. 


The EU-RL certification of the BactoScan FC+has been performed in accordance with EN ISO/DIS 16140-2:2013, the EURL MMP criteria and the Microval Rules and Certification Scheme. In short, this validates the BactoScan FC+ as a method which is least equivalent to reference method based on plate counting of bacteria colony forming units (EN-ISO 4833-1:2013, parts 1 and 2).
Today, BactoScan is in use in over 50 countries and more than 90 per cent of all milk within the EU is paid for according to BactoScan results.


The FOSS BactoScan FC+

The FOSS BactoScan FC+ instrument is now the only rapid method for testing bacteria count in raw milk to be approved by both the EU-RL in Europe and NCIMS/ FDA in the USA. 



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