Name: examination of host phenotypes in gambusia affinis following antibiotic treatment
Uploaded: 2017-02-22T14:00:00
Description: Watch this Scientific Journal Video about Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment at JoVE.com

This project was partially funded by a FAST (Faculty and Student Team) Award to TPP and JMC from EURECA (Center for Enhancing Undergraduate Research Experiences and Creative Activities) at Sam Houston State University.

All animal experiments were conducted under approval of IACUC protocols, numbered 14-05-05-1018-3-01, 13-04-29-1018-3-01, and 14-04-17-1018-3-01.
1. Animal Collection, Handling, and Ethical Care
<ol>
	<li>Collect Gambusia affinis from the field site (identification guide at http://www.sms.si.edu/irlspec/Gambusia_affinis.htm) using a small dip net and place into 19 L buckets. Use visual inspection to identify species.</li>
	<li>Rest fish for 1 - 2 d&#160;in a bucket with pond water. Afterwards, transfer ...

<ol>
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Some challenges require a rest period in clean APW after antibiotic treatment for the drug to be depleted in fish tissues. If the rest period is skipped then antibiotic presence can confound the results, especially when the assay involves exposure to bacteria. In order to examine effects from an altered microbiome composition without large changes in the total number of microbes on the host, preliminary experiments monitoring microbiome composition (16S profiling or whole genome sequencing) and population density (16S qu...

It has been established that antibiotics can disrupt the human microbiome leading to dysbiosis, meaning a microbial community imbalance. The microbiota&#39;s compositional alteration after antibiotic treatments has been shown to lower the community&#39;s diversity, reduce key members, and alter community metabolism, especially in the gut1,2. Antibiotic disturbance of the gut microbiome can reduce colonization resistance to Clostridium difficile3,4 and Salmonella5.
Additionally, the disruption of the microbiota has been linked to the development of many syndromes and diseases in humans (e.g., antibiotic-associated enterocolitis, inflammatory bowel disease, metabolic disorders, etc.). Antibiotics are also widely implemented in agriculture as growth promoters in livestock and poultry production6. The usage of these powerful tools is not without collateral effects, which is evident in the rapid rise of antibiotic resistance, as well as the effects of a disrupted microbiome has with its inhabited host. Many studies have shown that broad-spectrum antibiotic usage has long lasting consequences to the structure and function of the microbiota, yet the side effects from an antibiotic-disrupted microbiome impacting host physiology are only speculations which have yet to be supported.
The interplay between host, microbiota, and antibiotics is far from being understood in a concise manner. Therefore, a simple and more tractable model is advantageous to shedding light on the highly complex mammalian system. Mucosal surfaces in humans, including the gut, harbor the highest density and diversity of microbes, and also the most intimate microbe-host interactions. The mucosal skin microbiome of fish offers several advantages as a model system. The Teleostei (bony fish) is one of the earliest lineages to diverge within the Vertebrata meaning that teleosts have both innate and acquired immune systems that have co-evolved a relationship with commensal bacterial communities7. Fish skin shares many characteristics with type 1 mucosal surfaces of mammals, such as physiological functions, immunity components, and arrangement of mucus-producing cells8. The external location of the fish skin mucosal surface offers a microbiome easy to experimentally manipulate and sample.
The Western mosquitofish, Gambusia affinis (G. affinis), is a model fish that has been used in the past for studying mating and toxicology9,10,11. Given the small size, population abundance in the wild as an invasive species, minimal care cost, and hardy nature, we have developed G. affinis as a mucosal microbiome model. Further, Gambusia share the physiology of giving birth to live young with viviparous mammals, which is uncommon in fish species. We completed the most extensive study at the time of fish skin normal microbiota using 16S profiling with Gambusia12. Further work demonstrated three negative effects on the host following disruption of the skin and gut microbiota using a broad-spectrum antibiotic13.
Five different effects were examined in the fish following antibiotic exposure. The most well established host benefit of the microbiome is competitive exclusion of pathogens. The fish pathogen Edwardsiella ictaluri is known to cause outbreaks of enteric septicemia in commercial catfish farms14. E. ictaluri has also been shown to lethally infect zebrafish15,16 and Gambusia17. A challenge with this pathogen from the water column can serve as a measure of exclusion. As a comparison to susceptibility to an individual pathogen, survival during exposure to a high density of mixed organisms was also carried out. Feces and organic-rich soil were used as commonly-encountered sources of microbial communities.
Another established role the bacterial gut community performs is nutrient processing and energy harvest, thus affecting the overall nutritional uptake for the host. As a gross measurement of nutrition, fish body weight was compared before and after one month of being fed a standard diet. Antibiotic-treated fish as an average lost weight while control fish on average gained weight over the month. The mechanism for this lack of weight gain is unclear. One possible contributing factor is transit time of food in the gut. A GI motility method was adapted from zebrafish (Adam Rich, SUNY Brockport, personal communication) to determine transit time. It has not yet been determined if antibiotic-treated fish have an altered transit time.
A common challenge experienced in the natural environment by all organisms, especially fish, is osmotic stress. Gambusia have been shown to quickly adapt when acutely stressed in high concentrations of salinity18. Surprisingly, fish with an antibiotic-altered microbiome exhibited lowered survival to a high salt stress. The mechanism for this novel phenotype is under investigation. Another common stress on aquatic animals, especially in aquaria, is toxic forms of nitrogen (ammonia, nitrate, and nitrite). Survival against nitrate was not significantly different between antibiotic-treated and control fish. The methods presented in this manuscript can be used with Gambusia or similar fish model organisms, such as zebrafish and medaka, to measure phenotypes in the fish following experimental manipulation.

<table border="0" cellpadding="0" cellspacing="0" width="568">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:184px;">Rifampicin</td>
			<td style="width:104px;">Calbiochem</td>
			<td style="width:127px;">557303-1GM</td>
			<td style="width:153px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sodium Nitrate</td>
			<td>Sigma Aldrich</td>
			<td>S5506</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:184px;">Fluorescein-labeled 70 kDa anionic dextran</td>
			<td style="width:104px;">ThermoFisher Scientific</td>
			<td>D1823</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PBS tablets</td>
			<td>Calbiochem</td>
			<td>6500-OP</td>
			<td>tablets dissolve in water to make phosphate-buffered saline</td>
		</tr>
	</tbody>
</table>

examination of host phenotypes in gambusia affinis following antibiotic treatment

The commonality of antibiotic usage in medicine means that understanding the resulting consequences to the host is vital. Antibiotics often decrease host microbiome community diversity and alter the microbial community composition. Many diseases such as antibiotic-associated enterocolitis, inflammatory bowel disease, and metabolic disorders have been linked to a disrupted microbiota. The complex interplay between host, microbiome, and antibiotics needs a tractable model for studying host-microbiome interactions. Our freshwater vertebrate fish serves as a useful model for investigating the universal aspects of mucosal microbiome structure and function as well as analyzing consequential host effects from altering the microbial community. Methods include host challenges such as infection by a known fish pathogen, exposure to fecal or soil microbes, osmotic stress, nitrate toxicity, growth analysis, and measurement of gut motility. These techniques demonstrate a flexible and useful model system for rapid determination of host phenotypes.

An overall schematic diagram of the experimental system used to study fish host effects from antibiotic exposure13 is represented in Figure 1A and includes the technique for extracting the skin (Figure 1B) and gut (Figure 1C) microbiomes from the fish. Three days was selected as the antibiotic period of exposure because previous data reveals that while the total skin culturable number drops early in treatment, it h...

Watch this Scientific Journal Video about Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment at JoVE.com

Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment

This study involves methods to reveal effects on a model fish host following alteration of the skin and gut microbiome communities&#160;composition by an antibiotic.

Examination of Host Phenotypes in Gambusia affinis Following Antibiotic Treatment

The commonality of antibiotic usage in medicine means that understanding the resulting consequences to the host is vital. Antibiotics often decrease host ...

The overall goal of this experimental system is to examine the negative side effects to a host organism after antibiotic treatment. So this method can help answer key questions in the microbiome field, such as enbac associated side effects on the host's health that is mediated by a disrupted microbiome. So the main advantages of this technique are that this system is straightforward, inexpensive in examining vertebrate hosts'physiological phenotypes, and allows for noninvasive disruption to the mucosal microbiome.This technique's implications characterize how a disruption in the microbiome of an animal can lead to major side effects. To begin, streak a previously obtained and frozen infectious strain of Edwardsiella ictaluri onto E.Ictaluri selective and differential medium agar. Incubate the culture at 27 degrees Celsius for two days.Transfer a pure isolated colony from the culture and innoculate a 150 milliliter flask containing 40 milliliters of nutrient broth. Place the flask in a shaking incubator at 27 degrees Celsius and 150 RPM for two days. Following the incubation, to calibrate the E.Ictaluri culture for desired infectious dose volumes, use PBST to dilute a sample of the culture to an OD 650 of 0.2.After collecting Gambusia affinis, and treating the fish with rifampicin in the water column for three days, transfer both antibiotic treated and untreated control fish groups into individual plastic cups containing 130 milliliters of fresh artificial pond water, or APW, for approximately 10 hours for drug clearance from fish tissues. Then, separate the fish again into individual eight ounce plastic cups containing 130 milliliters of clean APW. Administer a lethal dose of E.Ictaluri culture to each fish and incubate the fish at 27 degrees Celsius for 24 hours.Following the E.Ictaluri bath, transfer each fish into a new cup with 130 milliliters of APW. Without feeding the fish, record fish mortality over the duration of a week. Gather collected fecal matter into a sterile plastic bag before transferring it into a sterile 15 milliliter conical tube, then use PBST to create a stock concentration of the fecal matter at 500 to 800 milligrams per milliliter, using a one milliliter or larger plastic pipette with the tip cut off, prepare 130 milliliters per cup of 15 milligram per milliliter or 10 milligram per milliliter of fecal matter in APW.Transfer antibiotic treated or untreated fish into individual cups of the solution, and then incubate the fish at 25 degrees Celsius for two days, closely observing and recording mortality during this time. To treat fish with soil, collect one to kilograms of rich organic topsoil, approximately seven for 15 centimeters deep, and transfer it into a clean plastic container. Prepare individual plastic cups containing 18.2 grams of soil and 130 milliliters of APW, mixing the soil well by hand, then transfer the antibiotic treated or untreated fish into the cups and leave at 25 degrees Celsius for three days while recording any mortality.After a 10 hour rest period in APW following antibiotic treatment, transfer fish into individual cups containing 17.5 milligram per milliliter of sodium chloride and APW, observe the fish over 36 hours for mortality, to carry out a nitrate toxicity challenge, after a 10 hour rest period as before, separate fish into individual cups containing either 10 or 17.5 milligram per milliliter of sodium nitrate and 130 milliliters of APW. Observe fish over the course of one day for mortality at the high dose of sodium nitrate, and four days for the fish at the low dose. After completing three day antibiotic or control exposure in groups, for individual fish, fill eight ounce styrofoam cups with 150 milliliters of APW, and after weighing the filled cups, transfer the fish into the cups, then record the total body weight for initial assessment.Feed the fish daily with two pellets of food per fish, monitor the consumption by visually recording uneaten pellets. At the end of each week over the course of four weeks, determine the fish weight by first weighing a cup of fresh APW and record the weight, then pour the fish into a dip net, and transfer it into the new cup, before weighing the cup again. For groups of fish, place 150 milliliters of APW into a cup and tare the scale.Keep the fish together in both groups when transferring them into new containers of APW, then record the total group weight. Repeat the weighing at the end of each week over the course of a month. To analyze gut transit time, add 360 microliters of sterile deionized water and 52 milligrams of gelatin into a sterile 1.7 milliliter tube, and place it on a 60 degrees Celsius heat block until the gelatin melts and is fully dissolved.Using a mortal and pestle, grind the goldfish food flakes into a fine powder, and add 40 milligrams of the powder to the tube along with 20 microliters of fish oil. After mixing, add 1.6 milligrams of FitC dextran. Dispense 20 microliter drops of the hot liquid onto parafilm on the lab bench, and let them quickly cool and solidify.Place the parafilm onto half of a Petri dish and float it on sterile water inside a sealed plastic container. Store the solidified drops in the refrigerator for up to four days before they become too hard for the fish to eat. Just before feeding, use a razor blade to cut drops into quarter sections.Acclimate the fish to individual styrofoam cups for two days without feeding, place four quarters of the food into the fish cup, and observe the fish for 30 minutes for how many pieces of the food they each eat. To begin monitoring, transfer individual fish into cups with 80 milliliters of APW, and every two hours, take a 1 milliliter sample. Store it in a labeled 1.7 milliliter tube at four degrees Celsius.After completion of the assay, place an entire one milliliter sample into a cuvette, and use a fluorescence spectrophotometer to record fluorescence at an excitation of 495 nanometers, and an emission of 520 nanometers for all the samples at the same time. as shown here, fish with an antibiotic-altered microbiome were more susceptible to an E.Ictaluri infection than control fish. The difference in mean time to death for the treated versus control fish was not significant.This is likely due to the small group size. This graph illustrates that fish exposed to rifampicin were more susceptible to osmotic stress than control fish, with this assay, salinity levels above 18 milligrams per milliliter resulted in rapid fish death. As demonstrated in this table, when exposed to the toxin nitrate in the water column, pre-exposure to antibiotic treatment did not affect survival.At 10 milligrams per milliliter, 50%lethality was observed for both the antibiotic treated and control groups at 90 hours. In this experiment using control fish in an aquarium, either two sections of FitC dextran labeled food, or one section were fed to fish to examine food transit time by measuring fluorescence in the surrounding water over time. Following this procedure, other methods like measuring total body fat stores and quantifying skin mucous production can be performed in order to understand mechanisms, and narrow down confounding factors that might contribute to negative host effects.

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