Incubation Period Guidance

Aquagenx CBT Kits and GEL Kits enable ambient temperature incubation at 25° Celsius and above and work at variable temperatures. Constant temperature control in an incubator is not required.

Recommended incubation temperatures and periods at ambient conditions for our test kits are:

35-37°C: 20 hours
31-34°C: 24-30 hours
25-30°C: 40-48 hours

These features provide tremendous advantages with water quality testing in the field, especially in low resource, rural, and remote areas. The reason this is possible, is Aquagenx microbial growth media detect E. coli by specific enzymatic reactions during hydrolysis of our chromogenic substrates.

Following is additional detail on incubation periods with Aquagenx water quality test kits.

When Ambient Temperature Varies Between Day and Night

Aquagex CBT and GEL tests can be incubated at ambient temperatures between 25-37°C and provide reliable results in 20 to 48 hours. The longer incubation time of 48 hours is needed when the temperature remains between 25°C and 30°C. This is because bacteria feed and multiply at slower rates in cooler temperatures.

Nevertheless, the bacteria will feed and multiply effectively, but at slower rates, even if the temperature cycles from day to night anywhere in the temperature range of 25-37°C . If temperatures drop below 25°C but then go back to or above 25°C, the bacteria will still remain present, multiply and feed, but at slower rates.

However, when the temperature gets too low, roughly below 20°C, some E. coli might not grow at all at these lower temperatures and they become inactive. If and when temperatures go back above 20°C, particularly when they go above 25°C, they will feed and multiply again.

Therefore, it is possible for Aquagenx microbial growth media to provide reliable results where temperatures cycle at a lower range that includes 25°C and higher, if they are incubated long enough to give the bacteria more time to feed and grow when the ambient temperature is at or above 25°C.

When Ambient Temperature Remains Below 25° Celsius

When ambient temperatures remain below 25° C, especially closer to, at or below 20°C long periods of time, it is necessary to place water samples in locations that provide elevated temperatures for the bacteria to feed and grow. Constant temperature control is not required, but samples need to be maintained anywhere between 25-37°C.

This can be done by using portable field incubators. If a portable incubator is unavailable, other incubation methods can be used to maintain water samples between 25-37°C:.

Some examples include:

• In or near a heat source such as a cook stove or other source of heat for cooking or keeping people warm
• Inside warm rooms at temperatures of 25°C or higher
• Inside thermal picnic coolers or insulated bags
• Under an incandescent light bulb in a box
• Warming or incubation-type units that keep food warm
• Reptile or poultry incubators
• Yogurt makers
• Exposing to sunlight as a source of heat, but covered with black cloth, black plastic or black metal that absorbs heat, warms the sample and prevents direct sunlight exposure of the bag.