ADVANCEMENT OF THE PRACTICE
Open Access
THE PRACTITIONER’S TOOL KIT
An Alphabet of Values: D, z, and F
James J. Balsamo, Jr., MS, MPH, MHA, RS, CP-FS, CSP, CHMM, DEAAS Nancy Pees Coleman, MPH, PhD, RPS, RPES, DAAS
Brian Collins, MS, REHS, DLAAS Gary P. Noonan, CAPT (Retired), MPA, RS/REHS, DEAAS Robert W. Powitz, MPH, PhD, RS, CP-FS, DABFET, DLAAS Vincent J. Radke, MPH, RS, CP-FS, CPH, DLAAS Charles D. Treser, MPH, DEAAS
in the 1880s by Sergei Winogradsky (1856– 1953) and consists of a tall glass column filled with pond mud and water. A carbon and sulfur source (e.g., paper and gypsum) are added to this mixture and the column is incubated in sunlight for months (mostly on a windowsill). The result is the readily observable formation of an aerobic/anaerobic gradient, as well as a sulfide gradient, along with color changes and gas formation. The Winogradsky column is a valuable tool to observe the dynamics of whole com- munities of microorganisms and their inter- action with each other and particularly, how they modify their environment. By observing changes over time, it gives us an appreciation of what happens with the biome of the gut and upper respiratory tract, as well as resi- dent and transient flora of hands. It can give us a better understanding of how a septic or sewage system works and serves as a dynamic predictive model of food spoilage. It demon- strates the dynamics of structural decay, and it can even provide us with the understanding and rationale of the microbiology of drinking water, recreational water, and landfills, just to name a few. The bottom line is the Wino- gradsky column demonstrates what happens without intervention and gives us an appre- ciation of how we can eect dynamic change, specifically with the decline phase, without destroying the surrounding environment. This discussion now brings us to the con- cept of D-, z-, and F-values and how these values are indispensable to our practice. D-Values The D-value is another way of saying deci- mal reduction time. The D-value of a spe-
Editor’s Note: The National Environmental Health Association (NEHA) strives to provide relevant and useful information for environmental health practitioners. In a recent membership survey, we heard your request for information in the Journal that is more applicable to your daily work. We listened and are pleased to feature this column from a cadre of environmental health luminaries with over 300 years of combined experience in the environmental health field. This group will share their tricks of the trade to help you create a tool kit of resources for your daily work. The conclusions of this column are those of the authors and do not necessarily represent the ocial position of NEHA, nor does it imply endorsement of any products, services, or resources mentioned.
I ntroduction Everything in our professional realm of practice having to do with infectious dis- ease prevention and environmental control of microorganisms somehow begins and ends with microbial growth. We know that in a laboratory closed system—where no food is added or wastes removed—bacteria will grow in a predictable pattern. The resulting growth curve is comprised of four distinct phases: 1) lag phase, 2) exponential or log phase, 3) sta- tionary phase, and 4) death or decline phase. Our work includes controlling these phases by monitoring time, temperature, water activ- ity, and pH levels of foods; fomite disinfection; ware washing sanitization; milk pasteuriza- tion; and container sterilization. All of these controls are basic to food production including fermentation processes, preservation, and shelf life. They are major factors in potable and rec- reational water safety, as well as microbiologi- cal control of septage, sewage, and water reuse.
Over the past decade, we have been inun- dated with survivability data of SARS viruses on various surfaces. Most rules, regulations, and guidelines that are part of our daily vocational training and activities somehow focus on hindering growth and destroying unwanted microorganisms. The science that relates to microbiological demise relies on the interpretation of D-, z-, and F-values. This column will explore what these essential val- ues are and highlight how we use them. Let us begin by observing a world where we can see and try to understand the dynam- ics of growth and succession of living things not controlled by a laboratory environment. Those professionals who were fortunate to have taken a course in environmental and food microbiology or classic ecology as part of their studies were introduced to the Wino- gradsky column. This simple device is used for culturing and observing a large diversity of microorganisms. The device was invented
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Volume 87 • Number 3
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