Microbiology and Immunology

Disposal of infectious microorganisms WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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other body fluids, and fecal waste material can compromise

disinfectant performance.

Microorganisms can develop resistance to disinfectants,

or can even have built-in, or intrinsic, resistance. For example,

application of some disinfectants to contaminated surfaces for

too short a time can promote the development of resistance in

those bacteria that survive the treatment.

See alsoBacteriocidal and bacteriostatic; Fungicide

DISPOSAL OF INFECTIOUS

MICROORGANISMSDisposal of infectious microorganisms

In research and clinical settings, the safe disposal of microor-

ganismsis of paramount importance. Microbes encountered

in the hospital laboratory have often been isolated from

patients. These organisms can be the cause of the malady that

has hospitalized the patient. Once examination of the microor-

ganisms has ended, they must be disposed of in a way that

does not harm anyone in the hospital or in the world outside of

the hospital. For example, if solutions of the living microor-

ganisms were simply dumped down the sink, the infectious

organisms could find their way to the water table, or could

become aerosolized and infect those who happened to inhale

the infectious droplets.

A similar scenario operates in the research laboratory.

Research can involve the use of hazardous microorganisms.

Facilities can be constructed to minimize the risk to

researchers who work with the organisms, such as fume

hoods, glove boxes and, in special circumstances, whole

rooms designed to contain the microbes. However, steps need

to be taken to ensure that the organisms that are disposed of no

longer present a risk of infection.

In addition to the cultures of microorganisms, anything

that the organisms contacted must be disposed of carefully.

Such items include tissues, syringes, the bedding in animal

cages, microscopeslides, razors, and pipettes. Often glass-

ware and syringe are disposed of in sturdy plastic containers,

which can be sterilized. The so-called “sharps” container pre-

vents the sharp glass or syringe tip from poking out and cut-

ting those handling the waste.

Depending on the material, there are several means by

which items can be treated. The most common methods of

treatment and disposal are disinfectionusing chemicals, steril-

izationusing steam (such as in an autoclave), and burning at

high temperature (which is also called incineration).

Disinfection can be done using chemicals. For example,

a common practice in a microbiology laboratory is to wipe off

the lab bench with alcohol both before and after a work ses-

sion. Other liquid chemicals that are used as disinfectants

include formaldehyde and chlorine-containing compounds

(that are commonly referred to as bleach). Chemical disinfec-

tion can be achieved using a gas. The most common example

is the use of ethylene oxide. Gas disinfection is advantageous

when the sample is such that scrubbing of inner surfaces can-

not be done, such as in tubing.

A second means of waste treatment is sterilization. This

is the complete elimination of living organisms. A very common

means of sterilization is the use of steam. The most common

form of steam sterilization in laboratory settings is the auto-

clave. For example, in disinfection procedures and other labo-

ratory procedures, items such as the adsorbent material used to

wipe the bench and plastic gloves are usually put into a special

biohazard bag. The bag is sealed when it is full and is sterilized,

typically in an autoclave. The seal is typically an indicator tape

that displays marking if the sterilization conditions have been

achieved. The inclusion in the load being autoclaved of a solu-

tion containing spores of Bacillus sterothermophilusis typically

done at regular intervals. Attempts to grow the contents of the

solution after autoclaving should be unsuccessful if the sterili-

zation procedure worked. After successful sterilization, the bag

can be treated as normal waste.

An autoclave is essentially a large pressure cooker.

Samples to be treated are placed in a chamber and a door can

be tightly sealed. The seal is so tight that air cannot escape.

Steam is introduced into the chamber at high pressure. At

higher pressure a higher temperature can be achieved than the

100° C [212° F] possible at atmospheric pressure.

Biohazard technician handles suspected infectious microorganisms.

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