Biological indicator

Typical performance characteristics for some of the most widely used biological indicators are given in Table 2. 

Table 2. Performance Characteristics of Some Biological Indicators ...

Hospital sterilizer loads vary in composition, thus the challenge presented to the test organism can vary considerably, depending on the type and contents of packages in which they are placed. The benefits of a standardized test-pack constmction and test protocol are obvious, and such recommendation is made by AAMI for steam and ethylene oxide sterilizers (11). More recentiy in European (CEN) and International (ISO) standards, biological indicators are considered as additional information supplemental to the measurement of physical parameters. Indeed, for sterilization using moist heat (steam), the biological indicator information is not considered to be relevant. 

Biological indicators for steam sterilization utilize bacillus stearothermophilus. In monitoring industrial cycles, a sufficient number of preparations each having a known degree of resistance are added to the load and retrieved after exposure, and cultured. 

Cruz SE, Mirshahi T, Thomas B, et al Effects of the abused solvent toluene on recombinant N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors expressed in Xenopus oocytes. J Pharmacol Exp Ther 286 334-340, 1998 De Rosa E, Bartolucci GB, Sigon M, et al Hippuric acid and ortho-cresol as biological indicators ofoccupational exposure to toluene. Am J Ind Med 11 529—537,1987 Delteil P, Stoesser F, Stoesser R L theromanie. Ann Med Psychol (Paris) 1 329-340, 1974... 

Saunders, S.R. and Sawchuk, E.R. 1995 Biological indicators of labour and occupational stress Gender comparisons in a Nineteenth Century pioneer community. Paper presented at the American Association of Physical Anthropology Meetings, Oakland, California. 

ATSDR/CDC. 1990. Summary Report Subcommittee report on biological indicators of organ damage and dysfunction. Agency for Toxic Substances and Disease Registry, Centers for Disease Control and Prevention, Atlanta, GA. 

For heat treatment, a D-value only refers to the resistance of a microorganism at a particular temperature. In order to assess the influence of temperature changes on thermal resistance a relationship between temperature and log D-value can be developed leading to the expression of a z-value, which represents the increase in temperature needed to reduce the D-value of an organism by 90% (i.e. 1 log cycle reduction Fig. 20.2B). For bacterial spores used as biological indicators for moist heat (B. stearothermophilus)... 

Table 20.1 Inactivation factors (IF) for selected sterilization protocols and their corresponding biological indicator (Bl) organisms... 

Monitoring of the sterilization process canbe achieved by the rrse of physical, chemical or biological indicators of sterilizer performance. Such indicators are frequently employed in combination. 

I) Chemspor which is a combined chemical and biological indicator the ampoule contains a spore suspension in culture medium together with a second, smaller ampoule which contains a chemical indicator. 

Biological indicators (Bis) for use in thermal, chemical or radiation sterilization processes consist of standardized bacterial spore preparations which are usually in the form either of suspensions in water or culture medium or of spores dried on paper, aluminium or plastic carriers. As with chentical indicators, they are usually placed in dummy packs located at strategic sites in the sterilizer. Alternatively, for gaseous sterihzation these may also be placed within a tubular hehx (Line-Pickerill) device. After the sterilization process, the aqueous suspensions or spores on carriers are aseptically transferred to an appropriate nutrient medium which is then incubated and periodically examined for signs of growth. Spores of Bacillus stearothermophilus in sealed ampoules of cultrrre medium are used for steam sterilization morritoring, and these may be incubated directly at 55°C this eliminates the need for an aseptic transfer. 

Table 23.2 Biological indicators for monitoring sterilization processes ...

Health Technical Memorandum (1994) Sterilisers. HTM 2010. London Department of Health. Hodges, N.A. (1995) Reproducibility and performance of endospores as biological indicators. In ... 

To critically evaluate and rank candidate biological indicators useful for monitoring trends in merctrry... 

To outline approaches for samphng and analysis of recommended biological indicators... 

To identify ancillary data needs and potential confounding factors that should be considered or documented to ensure the defensible interpretation of data on monitored biological indicators... 

AQUATIC BIOLOGICAL INDICATORS 4.3.1 Criteria to Select Indicators... 

The selection of biological indicators shoirld be guided by criteria to ensure that the indicators are relevant, useful, and sufficiently diagnostic to detect a change in the concentration of mercury in whole organisms or specific tissue(s) over multi-year or decadal time scales. We identified 9 criteria for the selection of biological indicators ... 

Relevance. A key criterion in the selection of biological indicators is relevance to human and ecological health and to the development of policy. Fish are directly relevant, for example, given that consumption of fish is the primary pathway for exposure to MeHg. The concentration of MeHg in fish is also a key variable in the issuance of fish-consumption advisories. 

Historical data on the indicator. Existing information on the statistical variation, bias, and other interpretational attributes of potential biological indicators should be examined and considered in the design of a sampling program for assessing trends in mercury bioaccumulation. 

Benthic invertebrates are macroscopic animals that live at or near the sediment/water interface. Some benthic invertebrates, particnlarly mnssels, readily accnmnlate metals, prompting their use as biological indicators of mercnry contamination (Smith... 

The dietary importance of benthic invertebrates to many species of fish, birds, and mammals (Vander Zanden and Vadeboncoenr 2002) signifies their importance in the trophic transfer of MeHg and their potential relevance as biological indicators. Some benthic invertebrates (e g., oysters, clams, shrimp, crabs, and crayfish) are consumed by humans, providing a direct pathway for exposure to MeHg. In the United States, shellfish rank below fish as a source of dietary MeHg in the human population (NRC 2000 Schober et al. 2003). 

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