FAQs: Microbiological Testing and Laboratory Services | Biosan Laboratories, Inc.

FAQ

If the agar on the dip slide has not dried out and still remains intact, it will usually be acceptable to use.

If you have an incubator, incubate the dipslides at approximately 30°C. If you are incubating the dipslides at room temperature, an extended incubation time is recommended (see the following FAQ).

"If you are incubating the dipslides at room temperature, we recommend an incubation period of 48 hours or longer. If you are incubating at 30°C, the dipslides can be read after 24 hours as long as the reading is the same at 48 hours and beyond. False negatives are possible if you read the dipslides too early, however, you cannot get a false positive by extending the incubation time."

Either environment is acceptable because the presence of light has no impact on the dipslide itself.

No, it is acceptable to incubate the dipslides for 48 hours or more. However, keep in mind that the longer the dipslides are left to incubate, the larger the colonies may appear on the agar surface. When large numbers of microorganisms are present, an extended incubation period may result in dipslides that are difficult to interpret.

No, the "dot" or colony size on a dipslide is independent of the number of microorganisms. If lower numbers of microorganisms are present, the colonies may grow in size on the dipslide but this does not always occur.

 

The colonies turn red on the dipslide because of the reduction of an indicator dye. This dye is added to the dipslide in order to aid the viewing of the colonies against the agar surface. Certain bacteria do not always reduce this dye which would result in an occasional colorless colony.

Specific agents are present in the fungal agar to inhibit the growth of bacteria. However, some bacteria are resistant to the inhibitors and may still appear on the fungal agar. The same is true for the bacterial agar. Certain inhibitors are present to deter the growth of fungi but some may still appear on the bacterial agar. If you are unsure of the interpretation of a dipslide, send us the item in question and we can determine what types of microorganisms are actually present. At Biosan Laboratories, we offer free technical service with all of our microbiological test kits.

No, this is most likely a chemical reaction. The dye that is added to the media on the dipslide in order to color the colonies red, reacts when the sugar in the media is broken down. This reaction may be caused by bacteria or even by certain chemicals. If the color change is due to a chemical reaction, it should happen within the first 15-30 minutes. Also, no colonies would be visible on the dipslide surface within that time period.

We suggest to soak dipslides and test strips in a 5% bleach solution for 30 minutes before disposal. This solution can be poured directly into the dipslide vial or the test strip incubation pouch. For other suggestions, contact our Technical Service Department at (800) 253-6800.

The superscript number specifies the power of 10. If a dipslide is interpreted to contain 103 microorganisms/mL, this means that there are 10 x 10 x 10 or 1000 microorganisms present. If 104 microorganisms are present, this corresponds to 10,000 microorganisms and so on.

Although you should determine what is an acceptable level of bacteria for your unique system, a general guide would be 105-106 CFU/ml for cooling water and 106-107 CFU/ml for metalworking fluid.

Our Sani-Check SRB Test Kit will detect sulfate-reducing bacteria which are also anaerobic. However, we do not have a test kit or a dipslide that will detect other types of anaerobic bacteria.

The identification of specific microorganisms is more complex and usually performed only within a microbiology laboratory. Biosan Laboratories can analyze your samples for a variety of microorganisms including Legionella and Mycobacterium.

For additional information, please contact our Technical Service Department at (800) 253-6800