APPLIED MIICROBIOLOGY, Jan. 1968, p. 182-183 Copyright @ 1968 American Society for Microbiology
Vol. 16, No.
1
Printed in U.S.A.
Use of Laminar Air-Flow Equipment in Microbiology MARTIN S. FAVERO AND KENNETH R. BERQUIST Phoenix Field Station Section, Ecological Investigations Program, National Communicable Phoenix, Arizona 85014 Received for
Disease
Center,
Publication 4 October 1967
tamination of animals, culture media, antigens, antisera, and other materials which must be maintained or handled in a sterile condition. Whlen critical sterility tests or assays for low numbers of microorganisms are performed, extraneous microbial contamination cannot be tolerated. Laminar or minimal-turbulence air-flow systems have been used by the aerospace industry to control particulate contamination such as dust or lint which could affect the reliability of precision parts. In general, the units consist of a bank of ultrahigh-efficiency (HEPA) filters enclosed in a cabinet or hood. The air stream, which travels at approximately 90 ft/min, moves, essentially in parallel patterns so that the cleanliness of the air is independent of activities occurring down- or cross-stream. Laminar flow cabinets have been used extensively in our laboratory to provide an environment free from microorganisms, with excellent and consistent results. In our Virology Unit, a horizontal laminar flow cabinet, having a working area 6 ft long, 22 inches high, and 22 inches deep (183 x 56 x 56 cm), has been used for the preparation of tissue culture (TC). Prior to the use of laminar flow, TC was prepared in isolated cubicles on open benches. Bacterial and fungal contamination occurred sporadically. Since the installation of laminar flow cabinets approximately 1.5 years ago, contamination of TC has been reduced markedly. After 16 months of operation in which no contamination was detected in TC, several TC cell lines became contaminated. It was determined that the air velocity had gradually decreased, owing to a worn fan belt, and was not sufficient to maintain an environment free from contamination. After replacing the fan belt and returning to optimal (90 to 100 ft/min) air velocity, no further contamination occurred.
Considerable technician time has been saved because manipulations can be made without flaming procedures. Previously, all media flasks, TC tubes, and growth bottles were flamed during each manipulation. Although work habits were ;ot changed, personnel were instructed to perform all manipulations downstream from the material being protected from contamination. In addition, it has been possible to prepare antibiotic-free TC routinely. In our Planetary Quarantine Unit, where critical sterility tests and assays for low numbers of microorganisms are performed, the use of laminar flow equipment has eliminated the occurrence of false-positive tests due to extraneous laboratory contamination. It was found that work of this type can be done more quickly and more efficiently in a laminar flow cabinet than in standard "hoods" or germ-free isolators. In the latter case, much time is spent sterilizing items which enter the isolator. Such work is eliminated in the laminar flow system because material kept upstream from the source of contamination will not become contaminated. There are three general areas in the field of microbiology where laminar flow can be applied: (i) "Product" protection. This area includes activities such as critical sterility tests and assays, aseptic filling, tissue culture preparation, and other procedures which require that the material per se be kept sterile, but where personnel protection is not a problem. Standard horizontal laminar flow clean benches can be used for these procedures. (Fig. la and b). (ii) "Personnel" protection. This includes the processing of infectious material and the inoculation of pure cultures of pathogenic microorganisms where technical personnel must be protected. For this, a vertical laminar flow cabinet can be used (Fig. Ic and d). A supply fan passes air down through an ultrahigh-efficiency filter into the work area. A second fan exhausts the air through a grated work surface. Adjustment of the fans to exhaust more air than is supplied results in maintenance of a slight negative pressure which causes ambient air to move from the operator toward the exterior periphery of the work area, thereby creating a protective curtain of air. The air can be
182
Downloaded from http://aem.asm.org/ on June 3, 2018 by guest
For many years microbiologists have attempted to devise more efficient techniques for controlling microbial contamination. These efforts have ranged from the use of cotton-plugged tubes to large germ-free isolators used by gnotobiologists. Experience has shown that considerable care, time, and money are required to prevent con-
VOL. 16, 1968
183
NOTES B
IiiijQ< . DY)>) 1,
7
-*
-.'..
/
-.
A
£
.
.
-.Il
.t
i1-
t
1,
,1
!.I
1,4
I,A
L-1. i
N,
D
.
i
.L ....i
1.
X
I
-.
/r~ I,
\\
]?
\...
-: _ L. . K1
FIG. 1. (A and B) Horizontal laminar flow cabinets. (C and D) Vertical laminar flow cabinets
exhausted completely or can be partially recircu- cabinet (72 inches wide X 22 inches deep x 22 inches high, working space) is about $1,000. A lated if absolute filtration is employed. (iii) Personnel and product protection. When vertical flow unit is slightly higher. When the cost exclusion of microbial contaminants and protec- of most laboratory furniture and biological safety tion of personnel are required, a vertical laminar hoods and their capability are considered, laminar flow cabinet, described above, can be used. flow systems represent a sound investment. Laminar flow cabinets are made by several are minimal and the manufacturers and are available as standard Maintenance requirements 15 years. to 10 from is filters the of life flow items. The cost of a standard horizontal
Downloaded from http://aem.asm.org/ on June 3, 2018 by guest
'I
