Caenorhabditis elegans  
This tiny roundworm is only one millimeter long. It is ubiquitous in soil, especially near rotting vegetation.

C. elegans is so hearty that it was the only living creature to survive the Columbia space shuttle disaster. When the
shuttle broke up, it was carrying more than 60 scientific experiments, with animals including bees, fish and spiders. The
other animals perished, but the C. elegans were found in the rubble, swimming in their Petri dishes inside a metal
locker, totally oblivious to the tragedy.
May 4, 2007

Location: Environmental Microbial Safety  

Authors    Kenney, S. - UNIVERSITY OF GEORGIA    Anderson, G. - UNIVERSITY OF GEORGIA    Williams, P. -
UNIVERSITY OF GEORGIA    Millner, Patricia    Beuchat, L. - UNIVERSITY OF GEORGIA   

Submitted to: International Journal of Food Microbiology  Publication Type: Peer Reviewed Journal  Publication
Acceptance Date: November 1, 2004  Publication Date: May 1, 2005  Citation: Kenney, S.J., Anderson, G.L., Williams,
P.L., Millner P.D., Larry R. Beuchat. 2005.

Persistence of Escherichia coli O157:H7, Salmonella Newport, and Salmonella Poona in the gut of a free-living
nematode, Caenorhabditis elegans, and transmission to progeny and uninfected nematodes. International Journal of
Food Microbiologyl. 101:227-236.  

Interpretive Summary:
Foodborne illness outbreaks have raised interest in identifying pre- and postharvest sources that can contaminate raw
and minimally processed fruits and vegetables. Soil that contacts produce may become contaminated with human
pathogenic bacteria in a variety of ways: raw or improperly composted manure, contaminated irrigation water, runoff
from pastureland, or excreta from wild animals that visit the crop areas. Higher populations of bacteria and nematodes
are known to reside in the rhizosphere of plants compared to bulk soil. Free-living nematodes (microscopic worms)
such as Caenorhabditis elegans are attracted to areas in soil in which large populations of bacteria are present
because they feed on them, including human pathogenic bacteria. In the research reported here, we tested the
hypothesis that free-living nematodes may ingest human enteric pathogens present in soil matrices and harbor them in
their gut, where they could survive even after the worm dies and produce has be treated with sanitizer. Ingested
pathogens may then colonize the gut and be protected against environmental stresses imposed by produce sanitizers,
even after the worm has died. Worms were fed cells of E. coli OP50, E. coli O157:H7, and salmonellae then incubated
at 4, 20, and 37°C for up to 5 days. Initial populations of ingested pathogens significantly increased nearly 100-fold per
worm within 1 day at 20°C and remained constant for an additional 4 days. Results also show that E. coli O157:H7 and
salmonellae grew from about 230 per worm to approx. 200,000 per worm and survived at least 5 days after ingestion
by C. elegans. Infected worms may come into contact with pre-harvest fruits and vegetables and contaminate their
surfaces by excreting pathogens. If worms on the surface of produce become attached to the surface and die, the
pathogens in their gut can remain viable for several days. A strong sanitizer, 1% sodium hypochlorite, pH 13,
successfully disinfected the worms and their eggs of E. coli and salmonellae Evidence also showed that worms infected
with S. enterica serotype Newport could transfer this salmonellae strain to uninfected wild type , and the pathogen
persisted in the gut of adult wild type C. elegans two generations removed from exposure to the pathogen. This
information will help inform produce packers, scientists, and others interested in determining the mechanisms of pre-
harvest produce contamination and issues of concern at post-harvest disinfection.  

Technical Abstract:
A study was done to determine the persistence of Escherichia coli O157:H7 and Salmonella enterica in the gut of a
free-living nematode, Caenorhabditis elegans, as affected by temperature and relative humidity and to determine if
infected worms transmit Salmonella enterica serotype Newport to progeny and uninfected worms. Worms were fed cells
of E. coli OP50, E. coli O157:H7, and salmonellae followed by incubating at 4, 20, and 37°C for up to 5 days. Initial
populations of ingested pathogens significantly increased by up to 2.93 log10 cfu/worm within 1 day at 20°C on K agar
and remained constant for an additional 4 days. When plated on Bacto agar, populations of pathogens remain
constant at 4°C, decreased significantly at 20°C, and increased significantly at 37°C within 3 days. Worms fed E. coli
OP50 or S. enterica serotype Newport were also incubated at 4 or 20°C at relative humidities of 33, 75 or 98% for 24
h. Populations of ingested E. coli OP50 and S. enterica serotype Newport decreased by up to 1.65 and 3.44 log10
cfu/worm, respectively, in worms incubated at 20°C and 33% relative humidity for 24 h. Placement of adult worms
labeled with green fluorescent protein (gfp) that had ingested gfp-labeled S. enterica serotype Newport on K agar with
uninfected wild type worms resulted in transfer of the pathogen to gut of wild type worms. S. enterica serotype Newport
was isolated from adult C. elegans two generations removed from exposure to the pathogen.

II. Nematodes
Worms (helminths) include nematodes, cestodes, and trematodes. Nematodes are non-segmented roundworms, and
the majority are free-living in the soil or water. While there are billions of nematodes that live in the soil, most (about
99%) are non-parasitic.
Caenorhabditis elegans is the best known example of a nematode, free-living in soil. C.
elegans is an ideal animal for genetics research, and its genome has been sequenced – it has 19,080 genes.
Parasites have many more genes than their free-living counterparts because they need a wider biological arsenal to
keep your immune system at bay. They live in strange places – your kidney, your lung, your brain, muscle tissue, and
gut tract. All parasitic nematodes are transmitted by living close to the ground – by putting dirt in your mouth or by just
stepping on the ground with your bare feet. Everybody poops and everybody eats, and parasitic nematodes take
advantage of this, utilizing feces to transmit disease. In many parts of the world, fecally-contaminated water is sprayed
onto vegetables as fertilizer. The vegetables are washed in contaminated water before being sold on the market. Raw
produce has the potential to transmit environment-resistant stages of parasites (cooked, frozen, or peeled produce is
generally safe). This may present a problem to us only when we travel to certain parts of the world, however, these
parasites represent background infection for the 4 billion people today who harbor at least one species of parasitic
nematode. While our immune system has methods to fight parasitic helminths, namely the eosinophil reaction (see
Figure 1, courtesy of Dave Anthony), many of today’s parasites have developed ways to evade the immune response.

Infection of Caenorhabditis elegans by Salmonella typhi Ty2
Several serovars of Salmonella infect and kill the nematode C. elegans. However, here we report that Salmonella typhi
Ty2, a representative strain of this human pathogen, readily infects the intestinal lining of C. elegans without
significantly affecting its viability. Our observation suggests extending the use of the C. elegans model system for the
study of host parasite relationships, to address problems concerning the biology of S. typhi.

Here, we report that the S. typhi Ty2 WHO reference strain does not kill C. elegans but can infect the nematode’s
intestinal lining. Consequently, C. elegans is suitable for exploring cell invasion by S. typhi and possibly its persistence
in this host.

Worming into the cell: Viral reproduction in Caenorhabditis elegans
(6) in this issue of PNAS, now demonstrates that viruses that infect mammalian cells can infect, replicate, and assemble
within C. elegans cells (7–9). These advances suggest that C. elegans could become an important system for
understanding basic aspects of virus–host interplay.

Drugs lengthen worm's life span.
By: Brownlee, Christen. Science News, 2/5/2005, Vol. 167 Issue 6, p94-94
The article reports on antiseizure drugs that have been shown to increase the life span of the roundworm. A class of
antiseizure drugs slows aging and increases life span in the roundworm Caenorhabditis elegans. Previous studies
have identified genetic modifications that can increase the worms' life span. However, few studies have examined
whether drugs might have a life-extending effect as well, says Kerry Kornfeld of the Washington University School of
Medicine in Saint Louis. Kornfeld's team found that ethosuximide, an anticonvulsant drug, increased the worms' life
span by 17 percent. The anticonvulsant drugs increased the worms' motility and stimulated egg laying, suggesting that
the chemicals interact with C. elegans' nervous system. Reading Level (Lexile): 1390;

Share Alike.
By: Barry, Patrick. Science News, 9/1/2007, Vol. 172 Issue 9, p131-131
The article reports on a study conducted by scientists that reveals information about the frequency of DNA transfer
from bacteria to insects and roundworms. Scientists believed that this transfer only happened occasionally, but through
this series of tests, they discovered that bacteria living in the eggs of certain insects and worms can lead to a common
amount of DNA swapping. This also means a higher rate of these insects acquiring new genetic traits. Reading Level
(Lexile): 1270;

Survivors Extraordinaire!
By: Silcox, Felicia Ann. Odyssey, Dec2004, Vol. 13 Issue 9, p28-29
The article focuses on the U.S. National Aeronautics and Space Administration's (NASA's) space craft which prepared
for flight in Columbia. During a last-minute check of Columbia's mid-deck section, NASA scientists found room for one
more project inside a nine-pound locker. The roundworm project belonged to Catharine "Cassie" Conley, a biologist at
the NASA Ames Research Center in California. Conley's goal for the worms' first space mission was simply to discover
if they would be able to survive space flight when eating a new artificial food. The researcher's worms were alive, the
only living things to survive Columbia's breakup. Reading Level (Lexile): 1060;