Why aseptic technique is used
When antimicrobial substances are tested against microorganisms, aseptic techniques reduce contamination by unwanted microorganisms and reduce the risk that the cultured microorganisms escape.
These precautions help maintain safe working conditions and prevent unwanted microbes from interfering with the culture being investigated.
Aseptic precautions
| Precaution | Purpose |
|---|---|
| Sterilise Petri dishes before use. | Heating equipment to a sufficiently high temperature kills contaminating microorganisms. |
| Sterilise the nutrient agar before pouring it into sterile Petri dishes. | Prevents microorganisms already present in the medium from contaminating the culture. |
| Disinfect the work surface with disinfectant or alcohol before inoculation. | Reduces microorganisms that might otherwise enter the culture. |
| Work next to a lit Bunsen burner. | Convection currents reduce contaminants falling onto the growth medium. |
| Use sterile swabs or flame an inoculating loop until red-hot. | Kills unwanted microorganisms that might be transferred with the culture. |
| Flame an inoculating loop before and after inoculation. | Reduces contamination before transfer and kills microorganisms remaining on the loop afterwards. |
| Keep the Petri-dish lid in place when it is not being used and lift it only at an angle during inoculation. | Limits contamination by airborne microorganisms. |
| Secure the lid with tape after plating. | Reduces the risk of cultured microorganisms escaping if the lid is displaced. |
| Incubate at a safe temperature of 25 °C. | Reduces the chance of encouraging pathogenic microorganisms that grow well near human body temperature. |
| Sterilise or safely dispose of equipment after use. | Prevents cultured microorganisms remaining on used equipment. |
Exam Tip: When asked for an aseptic technique, state both the precaution and why it is used. For example, link limited opening of a Petri dish to a reduced chance of airborne contamination.