Diagnostics, Warner-Lambert Co., Morris Plains, NJ), and AutoMicrobic System (Vitek Systems, Inc., Hazelwood, MO). All ten of these multitest systems have documented accuracies greater than 90% in clinical settings [Baron and Finegold 1990; Koneman et al. 1988]. Biolog (Biolog, Inc., Hayward, CA) is one of the newest multitest systems on the market, but its application to environmental and clinical samples is not well documented [Amy et al. 1992; Miller and Rhoden 1991]. (ii)
Cellular Fatty Acid Analysis Cellular fatty acids (CFA) of bacteria are structural in nature, occurring in the cell membrane or cell wall of all bacteria. When the bacteria are grown under standardized growth conditions, the CFA profiles are reproducible within a genus, down to the subspecies or strain level in some microorganisms. The Microbial Identification System (MIS), developed by MIDI (Newark, DE), provides a chromatographic technique and software libraries capable of identifying various microorganisms based on their CFA composition [Sasser 1990a; Sasser 1990b]. The chromatographic technique is also known as gas chromatography fatty acid methyl ester analysis (GC-FAME). MIS has a database containing the analysis libraries for culturable Gram-negative and Gram-positive bacteria, and yeasts. In a comparison study [Amy et al. 1992], only 8 of 18 isolates, identified by either API multitest or MIDI MIS, were identified accurately using Biolog multitest. A prototype method for extracting and analyzing fungi is currently being distributed by MIDI.
d.
Interpretation of Data Generally speaking, the literature is divided on whether identification is necessary or recommended. If clinical or research aspects of the investigation would benefit by identification of the source of an etiologic agent, the following general guidelines are suggested: Dose-response data are not available for most microorganism exposures. Indoor bioaerosol levels must be compared to outdoor levels or to an asymptomatic control area. In general, indoor levels are lower than outdoor levels, and the taxa are similar [ACGIH 1989, Step two, Fungi, and Bacteria; Solomon et al. 1980]. The Bioaerosol Committee of the American Conference of Governmental Industrial Hygienists (ACGIH) states that outdoor airborne fungi concentration “routinely exceeds 1000 CFU/m3 and may average near 10,000 CFU/m3 in summer months.” No occupational exposure limit for bioaerosols has been promulgated by the Occupational Safety and Health Administration (OSHA). ACGIH [1989, Bacteria] also states that concentrations of less than 100 CFU/m3 may be unhealthy to immunosuppressed people. However, the population of microorganisms must be evaluated for potential toxigenic microorganisms or microorganisms which emit volatile organic compounds. A low airborne concentration of microorganisms, in and of itself, does not indicate a clean and healthful environment. Where local amplification and dissemination of bacteria have not occurred in an occupied, indoor environment, Gram-positive cocci (e.g., Micrococcus and Staphylococcus) are normally dominant [Morey et al. 1986]. ACGIH states that airborne human skin scales and respiratory secretions may contain Gram-positive cocci. Detection of high levels of these microorganisms are an indication of over-crowding and inadequate ventilation. Indoor air that tests high for Gram-negative bacteria
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NIOSH Manual of Analytical Methods
