Name: measuring the effects of bacteria on c. elegans behavior using an egg retention assay
Uploaded: 2013-10-22T15:00:00
Description: Watch this Scientific Journal Video about Measuring the Effects of Bacteria on C. Elegans Behavior Using an Egg Retention Assay at JoVE.com

The authors would like to thank June Middleton for supplying E. faecalis strains and for guidance with bacteria culture. C. elegans were provided by the CGC, which is funded by NIH Office of Research Infrastructure Programs (P40 OD010440).

1) Preparation of Nematode Growth Media (NGM)
<ol>
	<li>To make 50 plates, add 1.5 g NaCl, 8.5 g Ultrapure Agar, and 1.25 g peptone to a 1 L flask.</li>
	<li>Add 487.5 ml of dH2O to flask. Swirl gently to mix and cover opening of flask with a piece of aluminum foil.</li>
	<li>Sterilize the solution by autoclaving at standard conditions (121 psi, 120 &#176;C, 20 min).</li>
	<li>Allow the solution to cool to 45 &#176;C in a water bath.</li>
	<li>To the solution, add the following in order: 500 &#181;l choleste...

<ol>
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The most critical steps in successfully performing this assay are: 1) using well-fed stocks of C. elegans, 2) culturing single types of bacteria on the assay plate, 3) accurately identifying staged L4 worms for exposure to E. faecalis, 4) keeping exposure time to E. faecalis consistent across all trials and 5) bleaching time should not exceed ten minutes to prevent egg disintegration.
For this assay it is important to pick healthy, well-fed worms. Maternal starvation...

Caenorhabditis elegans, a microscopic, free-living roundworm, is a model organism traditionally used to study developmental and cell signaling processes because of its transparent anatomy, well-characterized development, fully-sequenced genome, short generation-time, and genetic homology to humans. More recently, C. elegans has become a model organism in the field of environmental toxicology and innate immunity10, 11.
	
	These self-fertilizing hermaphroditic worms become sexually mature within two to three days of hatching from the egg. During its life cycle, C. elegans passes through four larval stages (L1-L4), before reaching adulthood. One isolated hermaphrodite can produce, on average, 300 offspring within three days of peak fecundity. In reproductively mature C. elegans hermaphrodites, fertilized eggs are retained within the uterus for several hours before being laid. The normal number of eggs stored in the uterus at any one time (during peak fecundity) is between ten and fifteen12. The number of eggs in the uterus is a function of both the rate of egg production and the rate of egg laying. Fertilized eggs are expelled from the uterus by the contraction of sixteen vulval muscles arranged around the opening of the vulva13. Hermaphrodite-specific motorneurons (HSN's) and VC motorneurons synapse onto vulval muscles affecting muscle contraction and thus egg-laying behavior5,7,13,14. Expulsion of eggs from the uterus occurs due to coordinated activity of neurons and muscles.
	
	Lab cultures of C. elegans are typically raised on a diet of nonpathogenic Escherichia coli OP50. In the natural environment, C. elegans come into contact with a variety of food sources, such as pathogenic bacteria, that can be potentially harmful. When exposed to harmful substances in the environment, C. elegans retain eggs until the environment becomes more favorable. Presumably this egg retention is an effort to protect their progeny.
	
	In this egg in worm (EIW) assay, C. elegans are exposed to the potentially pathogenic bacteria, Enterococcus faecalis, which is found in the environment. Exposure to pathogenic forms of E. faecalis can cause persistent intestinal infection and even death in C. elegans15. Exposure to other forms of pathogenic bacteria have been shown to affect egg retention16,17, however the effect was not quantified. In addition, the effect of mildly pathogenic strains of E. faecalis, strains that are not immediately lethal, on egg-laying behavior has not been studied.
	
	EIW assays involve counting the number of eggs retained in the uterus of C. elegans4. Even though C. elegans are transparent, eggs accumulating in the uterus can be difficult to quantify in an intact animal. The EIW assay involves bleaching gravid adult C. elegans that were exposed to bacteria for a fixed period of time. The bleach solution dissolves the outer cuticle leaving the eggs behind. The eggs are refractive to the effects of bleach due to the presence of a protective eggshell. After bleaching, one is very easily able to count the number of eggs released from the uterus of the worms upon bleaching.
	
	The assay described is a simple, inexpensive, and quick method to quantify the number of eggs in the uterus at one time, and thus quantify the effects of E. faecalis on egg retention. This assay may be used to quantify the effect of other types of bacteria, environmental toxins or drugs on egg retention. This assay also has the potential to be used as a screen for bacterial pathogenicity.

<table border="0" cellpadding="0" cellspacing="0" width="2472">
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	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Agar, ultrapure</td>
			<td style="width:191px;">Affymetrix</td>
			<td style="width:119px;">10906</td>
			<td style="width:1791px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Bacto Peptone</td>
			<td style="width:191px;">Becton Dickinson</td>
			<td style="width:119px;">211677</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Bacto Tryptone</td>
			<td style="width:191px;">Becton Dickinson</td>
			<td style="width:119px;">211705</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Brain Heart Infusion dehydrated medium</td>
			<td style="width:191px;">Carolina Biological Supply</td>
			<td style="width:119px;">781781</td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:19px;width:371px;">C. elegans, N2 strain</td>
			<td style="width:191px;">Caenorhabditis Genetics Center</td>
			<td style="width:119px;"></td>
			<td>http://www.cbs.umn.edu/cgc</td>
		</tr>
		<tr height="18">
			<td height="18" style="height:19px;width:371px;">Cholesterol</td>
			<td style="width:191px;">Alfa Aesar</td>
			<td style="width:119px;">A11470</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Culture plates for C. elegans</td>
			<td style="width:191px;">Tritech Research Inc.</td>
			<td style="width:119px;">T3308</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:371px;">Culture plates for E. faecalis</td>
			<td style="width:191px;">Fisher Scientific-Fisherbrand</td>
			<td style="width:119px;">875713</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:371px;">E. coli (OP50)</td>
			<td style="width:191px;">Caenorhabditis Genetics Center</td>
			<td style="width:119px;"></td>
			<td>http://www.cbs.umn.edu/cgc</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">E. faecalis strains</td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td>provided by J. Middleton. All isolates were confirmed as enterococci</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td>by observing growth on enterococcosel agar (BBL) and in 6% NaCl broth;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td>
			all strains grew at 44.5 &#186;C and were catalase negative and hydrolyzed esculin. A simplified&#160;dichotomous key based on pigmentation and fermentation reactions for six sugars&#160;(arabinose, mannitol, methyl-&#945;-D-glucopyranoside (MGP), ribose, sorbose and sorbitol) allowed&#160;presumptive identification of all E. faecalis strains (Efs lacks pigmentation and is arabinose, MGP&#160;and sorbose negative and sorbitol, mannitol and ribose positive). All presumptive Efs strains&#160;were confirmed using the API 20 STREP system (Biomerieux).
			</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;"></td>
			<td style="width:191px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Microscope</td>
			<td style="width:191px;">Motic</td>
			<td style="width:119px;">SMZ 168B</td>
			<td>any microscope with transmitted illumination and 50X magnification should be sufficient</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Streptomycin sulfate</td>
			<td style="width:191px;">Fisher BioReagents</td>
			<td style="width:119px;">BP910-50</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:371px;">Tryptic Soy Agar (Soybean-Casein Digest Agar Medium), Difco</td>
			<td style="width:191px;">Becton Dickinson</td>
			<td style="width:119px;">236950</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:371px;">Trypticase Soy Broth (Soybean-Casein Digest Medium), BBL</td>
			<td style="width:191px;">Becton Dickinson</td>
			<td style="width:119px;">211768</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:371px;">Yeast extract</td>
			<td style="width:191px;">Acros</td>
			<td style="width:119px;">61180-1000</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring the effects of bacteria on c. elegans behavior using an egg retention assay

C. elegans egg-laying behavior is affected by environmental cues such as osmolarity1 and vibration2. In the total absence of food C. elegans also cease egg-laying and retain fertilized eggs in their uterus3. However, the effect of different sources of food, especially pathogenic bacteria and particularly Enterococcus faecalis, on egg-laying
	behavior is not well characterized. The egg-in-worm (EIW) assay is a useful tool to quantify the effects of different types of bacteria, in this case E. faecalis, on egg- laying behavior.
	
	EIW assays involve counting the number of eggs retained in the uterus of C. elegans4. The EIW assay involves bleaching staged, gravid adult C. elegans to remove the cuticle and separate the retained eggs from the animal. Prior to bleaching, worms are exposed to bacteria (or any type of environmental cue) for a fixed period of time. After bleaching, one is very easily able to count the number of eggs retained inside the uterus of the worms. In this assay, a quantifiable increase in egg retention after E. faecalis exposure can be easily measured. The EIW assay is a behavioral assay that may be used to screen for potentially pathogenic bacteria or the presence of environmental toxins. In addition, the EIW assay may be a tool to screen for drugs that affect neurotransmitter signaling since egg-laying behavior is modulated by neurotransmitters such as serotonin and acetylcholine5-9.

This assay allows one to quantify the number of retained eggs within C. elegans after exposure to E. faecalis. L4 staged worms (characterized by transparent open space above their vulva, Figure 1) were exposed to E. faecalis through adulthood. After forty hours of exposure to E. faecalis, bleaching was performed. As the cuticle disintegrated in the bleach droplet, the eggs became more apparent (Figure 2). The number of retained eggs was easily quantifi...

Watch this Scientific Journal Video about Measuring the Effects of Bacteria on C. Elegans Behavior Using an Egg Retention Assay at JoVE.com

Measuring the Effects of Bacteria on C. Elegans Behavior Using an Egg Retention Assay

An egg-in-worm (EIW) assay is a useful method to quantify egg-laying behavior. Alterations in egg laying can be a behavioral response of the model organism Caenorhabditis elegans to potentially harmful environmental substances such as those produced by pathogenic bacteria.

Measuring the Effects of Bacteria on C. Elegans Behavior Using an Egg Retention Assay

C. elegans egg-laying behavior is  affected by environmental cues such as osmolarity1 and  vibration2. In the total absence of food C. elegans also cease ...

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