Rapid Sterility Testing: A Comparison to the Compendial Method

Dawn McIver of MicroWorks, Inc., discusses studies that she has done comparing traditional compendial methods of microbiological testing.

By Paul Thomas, Senior Editor

At PDA 2010 in Orlando, Dawn McIver of MicroWorks, Inc., discussed studies that she has done comparing traditional compendial methods of microbiological testing—namely, the USP Chapter <71> methodology—and the BacT/ALERT, an automated, non-destructive rapid microbiological method that her firm purchased recently from bioMerieux. (Note: McIver does not have a professional relationship with bioMerieux.)

“We wanted to study the workflow differences, as well as the specificity of information that we gain from each method,” she said. McIver studied various gram-positive and gram-negative organisms, from client-supplied isolates.

Organisms were prepared from stock cultures, and suspensions were prepared and cell density determined with a hemocytometer. Based on cell density dilutions, McIver developed samples of 25 to 50 organisms each. Sample descriptions were entered into bioMerieux’s Observa software and bottles were loaded into the instrument. Canisters were observed on a daily basis for growth, McIver said.

In terms of the time that it took to get results, McIver found that results for the rapid method were usually less than a day, while compendial methods varied from two days to even four to six days, depending on the organism being investigated. However, there were several organisms that required as much as five or six days in the BacT/ALERT, and sometimes required more time than the compendial method. At other times, it was not possible to gain data for some organisms via the rapid method, and some organisms via compendial methods.

McIver noted that it was extremely interesting to her to see how differing organisms were easily and quickly identified via rapid methods, but that this did not apply across the board. While the rapid methods did indeed accelerate testing for most major bacteria and other microbes, it was still microbe-dependent. 

Does it make sense to put a rapid microbiological system in place? On the whole, yes, McIver suggested. It’s also helpful to look at set-up and read time comparisons, she reminded. It was typically one hour to set up the five sterility tests for compendial testing, as compared to 15 minutes for the BacT/ALERT. Daily reads of compendial methods took approximately 30 minutes, as compared to three to five minutes typical of the BacT/ALERT.

As far as subjectivity, McIver noted that compendial methods required technicians to be much more observant, whereas with the rapid method reading was “not subjective at all.”

As a cost per test comparison, McIver found that the rapid test was $12-$15 per test, versus $20-$25 per test with compendial methods.

In conclusion, McIver noted:

  • The BacT/ALERT provides an alternative method that automates the sterility test process.
  • Results demonstrated comparability between the two methods.
  • The rapid system took about ¼ quarter of the time, and the cost per test was lower.
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