Issues relating to culturing of microorganisms
Background
Microorganisms are microscopic organisms, such as bacteria, fungi (moulds and yeast), viruses, microscopic algae and protozoa. Culturing microorganisms can lead to the growth of dangerous pathogenic organisms. Potential health risks arise from the hazards of infection by pathogens, as a result of contact with skin, eyes, puncture wounds, inhalation, or ingestion. Risks are minimised by:
- Careful choice of organisms or sources of organisms from the environment, so as to avoid culturing pathogenic microorganisms. Organisms can also be ordered from reputable suppliers.
- Culturing in closed containers, which are taped before examination and remain unopened, so that there is no generation of harmful microbial aerosols.
- No sub-culturing or transferring of organisms from one medium to another to avoid concentrating the bacteria any further.
- Killing the microorganisms before disposal.
Key safety points
- Do not collect microorganisms from toilets, from human body fluids (including from sneezes or coughs) or skin (other than hands and fingers), to reduce the likelihood of culturing pathogens.
- Do not culture from animal sources (e.g bird cages, dead animals, faecal material) to reduce the likelihood of culturing pathogens.
- Do not use agar culture media that selects for human pathogens e.g. blood agar, MacConkey’s agar, dung or faecal agar.
- Do not incubate plates above 30 ºC, as this will discourage the growth of pathogens.
- Invert agar plates before incubating to avoid condensation dripping on to cultures. Any drips from a partially sealed Petri dish are potential sources of infection.
- Tape the lid and base of each agar plate together with 2-4 short strips of adhesive tape, but not around the full circumference. This guards against the possibility of anaerobic organisms growing due to lack of air.
- Ensure the plates are sealed before inspection by students.
- Students should avoid contact with cultures, and introducing objects into their mouths such as eating, licking labels or sucking pencils.
- All cuts or broken skin must be covered by a water resistant dressing and gloves.
- Count the plates out and in again, if there is any chance of students taking the plates away.
- Students should wash their hands with soap and water before leaving the laboratory.
- Ensure that disinfectant solution is available, should there be a spill.
- Do not sub-culture or transfer organisms from one medium to another.
- Do not keep the cultures for more than 7 days.
- Sterilise the cultures by placing them in autoclavable bags and using an autoclave or pressure cooker (see manufacturer’s directions for appropriate time, pressure and temperature). Chemical disinfectants should not be used, as they may be inactivated by contact with organic material. After sterilization, cultures may be disposed of in the autoclavable bags in an industrial waste bin.