Is the Ossila Laminar Flow Hood Sterile?

When working with sensitive samples, you should be confident that a laminar flow hood can maintain a sterile environment. This is especially true during microbiological experiments and preparation, such as growing cell cultures or preparing media plates. You can test if the air flow is sterile using settle plates and if the surfaces are sterile using contact plates.

To check that our laminar flow hood is suitable for microbiological uses, we tested for air and surface contamination. In addition to testing within the hood, we also collected samples on a regular lab bench for comparison.

How to Test Laminar Flow Hood Sterility

We conducted these tests in our horizontal laminar flow hood. Before starting air flow and surface testing, we cleaned the laminar flow hood following our recommended method.

Plates are positioned inside the laminar flow hood, towards the back — Position your plates within the laminar flow hood

Plates are also placed on a normal lab bench in ambient conditions to compare — Comparison plates on a normal lab bench

Exposed plates inside an incubator — After exposure, plates were incubated at 37°C for up to 72 hours

To test the sterility of the air flow inside the Ossila Laminar Flow Hood, we exposed Tryptic Soy Agar Contact (TS3N) plates and Sabouraud Dextrose Agar Contact (SDCL) plates to the internal environment. TS3N plates and SDCL plates will encourage growth of bacterial and fungal colonies, respectively. These plates were exposed for either 7 or 24 hours, before being sealed and incubated at 37°C for 72 hours.

To test how sterile the surface is (after proper cleaning and UV sterilization), we placed TS3N and SDCL plates in direct contact with the tray. These plates were left for 1 hour, before being incubated at 37°C for 72 hours.

For both contact and air flow tests, we made comparison plates on a standard lab bench. This provides a control for how clean the laminar flow hood is compared to a normal laboratory environment.

Horizontal Laminar Flow Hood

Eco-Friendly
Fully Equipped
High Purity Air

Available Now! £2,500

Air Flow Contamination

The results of our air flow tests are contained in the table below.

Agar Plate	No. of Colonies Outside Laminar Flow Hood (after 7 hours)	No. of Colonies Inside Laminar Flow Hood (after 7 hours)
T3SN	10	0
SDCL	3	0

After 7 hours, the plate exposed to a normal laboratory environment were quite contaminated. There is evidence of both bacterial and fungal contamination. However, both plates exposed to the laminar flow hood environment were clean and uncontaminated. This proves that the laminar air flow, along with UV sterilization, can sustain a sterile environment for up to 7 hours.

Bacterial agar plates contamination outside and inside the laminar flow hood — Bacterial agar plates exposed to airflow outside (left) and inside (right) the laminar flow hood.

Fungal agar plates contamination outside and inside the laminar flow hood — Fungal agar plates exposed to airflow outside (left) and inside (right) the laminar flow hood.

We also tested how long the laminar flow hood can prevent contamination, beyond the inital 7 hours. To do this, we left a plate exposed to the internal air flow in the laminar flow hood for 24 hours.

After 24 hours in the laminar flow hood, no contamination was seen in either plate.

Fungal contamination plate after 24 hours in the laminar flow hood.

Bacterial contamination plate after 24 hours in the laminar flow hood.

Surface Contamination

The results of our surface contamination tests are contained in the table below.

Agar Plate	No. of Colonies Outside Laminar Flow Hood (after 1 hour contact)	No. of Colonies Inside Laminar Flow Hood (after 1 hour contact)
T3SN	16	0
SDCL	2 (majority coverage)	0

After 1 hour in contact with a general lab bench, the plates had significant bacterial and fungal growth. However, the plates put in contact with the disinfected and UV sterilized hood tray remained clear after incubation.

Baterial plates after 1 hour contact with the lab bench (with much contamination) or the laminar flow hood tray (with no contamination) — Bacterial agar plates in contact with a general lab work bench (left) and the laminar flow hood tray (right).

Fungal plates after 1 hour contact with the lab bench (with much contamination) or the laminar flow hood tray (with no contamination) — Fungal agar plates in contact with a general lab work bench (left) and the laminar flow hood tray (right).

Maintaining a Sterile Environment

With filtered laminar air flow and UV sterilization, our laminar flow hood creates an exceptionally sterile workspace. This sterility is maintained for extended periods, up to 24 hours in this instance.

By cleaning with disinfectant and using UV sterilization, the internal surfaces of our laminar flow hood are sterile. Whereas, a general lab bench has significant levels of contamination.

These tests demonstrate the sterility of a laminar flow hood workspace is essential for working with sensitive or biological samples.

Laminar Flow Hoods

Vertical/Horizontal Models
Fully Equipped
High Purity Air

Available Now! £2,500

Contributing Authors

Written by

Dr. Mary O'Kane

Application Scientist