Hatchery plate evaluation: How to interpret bacteriology plate results
By Victoria Drouet Pratt, DVM, MAM Candidate 2016
Poultry Diagnostic and Research Center, Department of Population Health,
University of Georgia, Athens, GA
Regular agar plate evaluation of your hatchery is important to monitor sanitation trends over time. There are a variety of ways to evaluate the bacterial and fungal load within your facility. Blood agar, MacConkey (Mac) agar plates, Tryptic Soy Agar (TSA) plates, Sabouraud Dextrose Agar (Sab Dex) plates, and swabs are just a few of the methods that can be used. Each type of agar plate will be specific for the growth of different organisms; therefore, it is important to have an idea of what you are expecting.
The Mac and Sab Dex plates may be a good idea for routine sampling of pathogens. Mac plates can help you assess coliform and Salmonella contamination, and SabDex allows fungal pathogen monitoring. TSA plates can to used to evaluate hatchery cleaning and disinfection techniques. In the event of poor chick quality or high early mortality, additional sampling with selective agar may be warranted. The following images will describe how to interpret growth on the Mac and Sab Dex plates.
This plate is designed to isolate Gram negative, enteric bacteria, such as E.coli. It can be used for aerosol sampling or to streak a swab on the plate. Incubate at 37°C for 24 hours. The appearance of pink colonies surrounded by a cloudy pink halo indicate lactose fermentation and most likely an E.coli bacterial growth. Growth of pale colonies can indicate Salmonella growth; however, other bacteria can also have a similar look. If no growth is noted after 24 hours, incubate an additional 24 hours then evaluate. Record the sample location and quantify the type and amount of growth on the plate.
Sabouraud Dextrose Agar:
Designed for the growth of fungi (mold). This plate can be placed in areas of concern in the hatchery to evaluate fungal aerosol load. Sab Dex will grow many types of fungi, including pathogenic ones such as Aspergillus, and may also grow some environmental bacteria. Incubate plates at 30°C for 3-5 days and then interpret growth. Record the sample location and quantify the type and amount of growth on the plate. The next page includes images of mature Aspergillus growth after 4 days.
- Plate 1: This plate shows Aspergillus fumigatus, characterized by a blue-green to deep green colony growth. It often has a white margin around the green colony. On the reverse side of the plate, the colony may appear cream in color. This plate also has the growth of other non pathogen environmental fungi.
- Plate 2: There are several large colonies of Aspergillus fumigatus on this plate. Aspergillus niger is also represented, characterized by a black, brown, or deep purple growth on the plate. On the reverse side of the plate, the A. niger colony may appear cream to dark brown/black in color.
- Plate 3: This plate also demonstrates a mixed Aspergillus growth. Aspergillus flavus is characterized by a green to bright yellow colony, which is occasionally yellow brown. On the reverse side of the plate, this colony may appear yellow to cream in color. A small colony of Aspergillus niger is also present.
Tryptic Soy Agar:
This plate is designed to evaluate the effectiveness of cleaning and disinfecting procedures within the hatchery. This plate can be placed in areas of concern to monitor aerosol contamination following sanitation. Allow the plates to incubate at 35-37°C for 48 hours. For best results, count each colony of growth on the plate and record the sample location, number of plate colonies, and type of growth noted. >200 colonies on a plate indicates poor sanitation in that area of surveillance. Monitor sanitation techniques in areas of heavy growth. Also, consider placing TSA plates before and after disinfection to assess changes in bacterial colony counts.
Article courtesy of The Poultry Informed Professional
Published by the Department of Population Health, University of Georgia
Editor: Dr Stephen Collett, Associate Professor