M. Andrew Stamper, DVM, DACZM
Disney’s Animals, Science and Environment, The Seas, Epcot®, Walt Disney World® Resort, Lake Buena Vista, FL, USA
Microbes are everywhere. In every milliliter of surface seawater, there are 0.5 to 1 million bacteria and 10 million viruses. They are also found on every surface and comprise very complex ecosystems, called biofilms.1 For those who think in terms of bacteria associated with biofiltration bacteria as “good” and pathogens as “bad,” the relationships are much more complex. Unfortunately, our thinking about the aquatic environment has been biased by our previously limited tool of culturing bacteria (which captures <1% of the bacteria in water) which has greatly limited our understanding of microbes in the environment.
Microbes should be considered in two realms: planktonic and sessile. The planktonic state is straightforward, whereas the biofilm ecology is extremely complex. Biofilms include organisms beyond bacteria and comprise fungi, algae, protozoans, and metazoans. An intricate ecologic process occurs as various environmental parameters change. These organisms secrete an assortment of chemicals known as extracellular polymeric substances (EPSs), which add to the total organic carbon (TOC) within the water column and are critical to the health of the organisms and water environment.2
Many factors influence the number and types of microbes in the environment. There have been several papers published on the effects of chemicals on the biofilter, and this is the most important consideration when adding therapeutic agents to water.3-8 It is important to know that most, if not all, of these drug interactions are dose-dependent and affect the biofilter’s efficiency to varying degrees; they should not be considered as having an all-or-nothing relationship.
On the flip side, drugs can also be digested/converted by microbes as a food source. When controlling an environment like the aquarium industry’s current standards, millions of bacterial species are starved into inactivity. These bacteria, although they may not be obvious, could still exploit any limiting nutrient sources, whether it is ammonia, nitrite, or phosphorus. This also applies to other nutrients that might enter the water. Nutrients can be any molecule which includes the needed elements which includes complex molecules such as therapeutics.
When a therapeutic agent is ingested by a human or animal, it is placed in a sterile environment once it is absorbed into the body. This is not the case when the same chemical is placed into a body of water. It is important to recognize the impact of microbes on chemicals, especially those with carbon chains and associated elements that may be nutrient sources. With the diversity of microbes in a water column, it is possible that one species will have an enzyme to break the chemical chains of the therapeutic and use it as a food resource. Therefore, it is important to invest in procedures for monitoring chemical concentration when treating animals. It is also important to recognize that there are different microbial communities in various institutions and even between tanks which will result in a variety of experiences by husbandry staff and clinicians.
The author would like to thank the following people for their additions to this evolving conversation: Kent Semmens and Nick Andrews for all their thoughts around the role of biofilms and planktonic bacteria in marine aquaria; and Stacy Knight, Larry Boles, Matt Dawson, and Amber Thomas for their hard work designing and executing experiments that are helping illuminate the role of bacteria and environmental therapeutics.
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2. Weiner R, Langille S, Quintero E. Structure, function and immunochemistry of bacterial exopolysaccarides. J Indust Microbiol. 1995;15:339–346.
3. Collins MT, Gratzek JB, Daw DL, Nemetz TG. Effects of parasiticides on nitrification. J Fish Res Board Can. 1975;32:2033–2037.
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8. Schwartz MF, Bullock GL, Hankins JA, Summerfelt ST, Mathias JA. Effects of selected chemotherapeutants on nitrification in fluidized sand biofilters for cold water fish production. Int J Recirc Aquacult. 2000;1:61–81.