Abstract
Estimations of the bacterial content of air can be more easily made now than a decade ago, with colony formation the method of choice for enumeration of airborne bacteria. However, plate counts are subject to error because bacteria exposed to the air may remain viable yet lose the ability to form colonies, i.e., they become viable but nonculturable. If airborne bacteria exhibit this phenomenon, colony formation data will significantly underestimate the bacterial populations in air samples. The objective of the study reported here was to determine the effect of aerosolization on viability and colony-forming ability of Serratia marcescens, Klebsiella planticola, and Cytophaga allerginae. A collision nebulizer was used to spray bacterial suspensions into an aerosol chamber, after which duplicate samples were collected in all-glass impingers over a 4-h period. Humidity was maintained at ca. 20 to 25%, and temperature was maintained at 20 to 22 degrees C for each of two replicate trials per microorganism. Viability was determined by using a modified direct viable count method, employing nalidixic acid or aztreonam and p-iodonitrotetrazolium violet (INT). Cells were stained with acridine orange and observed by epifluorescence microscopy to enumerate total and viable cells. Viable cells were defined as those elongating in the presence of antibiotic and/or reducing INT. CFU were determined by plating on tryptic soy agar and R2A agar. It was found that culture techniques did not provide an adequate description of the bacterial burdens of indoor air (i.e., less than 10% of the aerosolized bacteria were capable of forming visible colonies). It is concluded that total cell count procedures provide a better approximation of the number of bacterial cells in air and that procedures other than plate counting are needed to enumerate bacteria in aerosol samples, especially if the public health quality of indoor air is to be estimated.
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- Alvarez A. J., Buttner M. P., Toranzos G. A., Dvorsky E. A., Toro A., Heikes T. B., Mertikas-Pifer L. E., Stetzenbach L. D. Use of solid-phase PCR for enhanced detection of airborne microorganisms. Appl Environ Microbiol. 1994 Jan;60(1):374–376. doi: 10.1128/aem.60.1.374-376.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hobbie J. E., Daley R. J., Jasper S. Use of nuclepore filters for counting bacteria by fluorescence microscopy. Appl Environ Microbiol. 1977 May;33(5):1225–1228. doi: 10.1128/aem.33.5.1225-1228.1977. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kingston D. Selective media in air sampling: a review. J Appl Bacteriol. 1971 Mar;34(1):221–232. doi: 10.1111/j.1365-2672.1971.tb02280.x. [DOI] [PubMed] [Google Scholar]
- Kogure K., Simidu U., Taga N. A tentative direct microscopic method for counting living marine bacteria. Can J Microbiol. 1979 Mar;25(3):415–420. doi: 10.1139/m79-063. [DOI] [PubMed] [Google Scholar]
- Kreiss K. The sick building syndrome in office buildings--a breath of fresh air. N Engl J Med. 1993 Mar 25;328(12):877–878. doi: 10.1056/NEJM199303253281210. [DOI] [PubMed] [Google Scholar]
- Lundholm I. M. Comparison of methods for quantitative determinations of airborne bacteria and evaluation of total viable counts. Appl Environ Microbiol. 1982 Jul;44(1):179–183. doi: 10.1128/aem.44.1.179-183.1982. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Marthi B., Lighthart B. Effects of betaine on enumeration of airborne bacteria. Appl Environ Microbiol. 1990 May;56(5):1286–1289. doi: 10.1128/aem.56.5.1286-1289.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Menzies R., Tamblyn R., Farant J. P., Hanley J., Nunes F., Tamblyn R. The effect of varying levels of outdoor-air supply on the symptoms of sick building syndrome. N Engl J Med. 1993 Mar 25;328(12):821–827. doi: 10.1056/NEJM199303253281201. [DOI] [PubMed] [Google Scholar]
- Paszko-Kolva C., Shahamat M., Colwell R. R. Effect of temperature on survival of Legionella pneumophila in the aquatic environment. Microb Releases. 1993 Sep;2(2):73–79. [PubMed] [Google Scholar]
- Rodriguez G. G., Phipps D., Ishiguro K., Ridgway H. F. Use of a fluorescent redox probe for direct visualization of actively respiring bacteria. Appl Environ Microbiol. 1992 Jun;58(6):1801–1808. doi: 10.1128/aem.58.6.1801-1808.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Roszak D. B., Colwell R. R. Survival strategies of bacteria in the natural environment. Microbiol Rev. 1987 Sep;51(3):365–379. doi: 10.1128/mr.51.3.365-379.1987. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Thom S. M., Horobin R. W., Seidler E., Barer M. R. Factors affecting the selection and use of tetrazolium salts as cytochemical indicators of microbial viability and activity. J Appl Bacteriol. 1993 Apr;74(4):433–443. doi: 10.1111/j.1365-2672.1993.tb05151.x. [DOI] [PubMed] [Google Scholar]
- Thorne P. S., Kiekhaefer M. S., Whitten P., Donham K. J. Comparison of bioaerosol sampling methods in barns housing swine. Appl Environ Microbiol. 1992 Aug;58(8):2543–2551. doi: 10.1128/aem.58.8.2543-2551.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Woods J. E. Cost avoidance and productivity in owning and operating buildings. Occup Med. 1989 Oct-Dec;4(4):753–770. [PubMed] [Google Scholar]
- Zimmerman N. J., Reist P. C., Turner A. G. Comparison of two biological aerosol sampling methods. Appl Environ Microbiol. 1987 Jan;53(1):99–104. doi: 10.1128/aem.53.1.99-104.1987. [DOI] [PMC free article] [PubMed] [Google Scholar]