1. Christopher Smalls
Microbiology
Dr. Brossard Stoos
Current Event
Serratia marcescens
11-3-14
Nosocomial infections have been a growing risk in the clinical setting. There are
many causes of the growth in risk, such as insufficient cleaning agents, and microbial
resistance. The bacteria I’m going to focus the attention of my paper on is Serratia
Marcescens. Serratia Marcescens belongs to the Enterobacteriaceae family, and the Serratia
genus of that family. The Serratia genus is usually associated with nosocomial infection in
many clinical environments. Most recently in a German neonatal department, the outbreak of
Serratia marcescens infected 21 neonates raising global concerns on nosocomial infection.
The article “Serratia marcescens: an outbreak experience” written by Peter Gastmeier
discusses the outbreak from a first hand view.
Peter Gastmeier states “I had one of the worst experiences a hospital epidemiologist
can have: a Serratia marcescens outbreak in a neonatal department with a total of 21
colonized or infected newborns.” Knowing the history of this bacterium he quickly told
health authorities, the other doctors, and educated his team about the caution in dealing with
the isolated infected newborns. The numerous infections brought global attention to the
department’s outbreak. With careful clinical environmental materials tested and none coming
back positive for Serratia marcescens, the source was unknown, raising serious concerns.
After the death of two newborns, the hospital closed the department that caused the media to
demand answers.
After a year of investigation on this outbreak, the state attorneys office determined the
two deaths were from previous heart defects and not the outbreak. The article also discusses
the source of the S. marcescens. After the year of investigation it was clear that the bacterium
was transferred from mother to newborn, and from newborn to neighboring newborn. The
other infected newborns ended up surviving but scientists have found that this specific

2. outbreak of Serratia marcescens contained special virulence factors which led to its rapid
growth of infection within the neonatal department. The bacterium Serratia marcescens is
the topic I am choosing to discuss in detail throughout my paper.
Serratia marcescens belongs to the Enterobacteriareae family and more specifically
to the Serratia genus. There are 8 types of Serratia, and I’m only going to focus on Serratia
marcescens. More importantly I will discuss the structure, transmission, virulence,
epidemiology, diagnosis, treatment, and prevention pertaining to S. marcescens.
The structure of Serratia marcescens is very unique and provides it with many
benefits and resistance factors. For one, Serratia marcescens is a motile gram negative rod,
or bacillus, shaped bacterium that is anaerobic. Meaning this bacterium can live in an
oxygenated environment, or in an oxygen free environment. Serratia marcescens typically
grows from temperatures 5-40 degrees Celsius, and 5-9 Ph. levels. S. marcescens is
opportunistic, pathogenic microorganism. Having these traits poses it to create and form
biofilms on almost any surface. Being a gram-negative motile bacterium also creates benefits
for its survival. Gram-negative cell walls contain a single layer of peptidoglycan, enclosed by
a special lipopolysaccharide outer membrane. This special type of outer membrane allows it
for selective permeability and excluding of toxins. Another survival benefit would be the
motile factor it carries. Having multiple flagellums allow the bacterium to swim solo or swim
in a swarm. Each bacterium can have 100-1000 flagella. (Serratia marcescens, Microbe)
This creates an extremely motile bacterium able to travel throughout a host. These traits all
make Serratia marcescens a bacterium that’s versatile and beneficial for survival.
Virulence factor are aspects that the bacterium either has or produces that prolongs its
life within a host or surface. The virulence factor Serratia posses is the hydrolysis of casein.
“Casein is a protein precipitated from milk that forms the basis of cheese and certain
plastics.” (Serratia marcescens, Microbe) At the molecular level, Serratia marcescens
produces an extra cellular enzyme called protease which breakdown the peptide bonds in
casein. This is helpful for the resistance and growth of S. Marcescens creates. Another
believed factor of virulence is ability to form biofilms. Biofilms are mucus like surface that
allows the bacterium to grow on a surface. It’s extremely helpful to have the ability to form
biofilms for attachment and for survival. These virulence factors give the bacterium its ability
to withstand and grow within a host.

3. Transmission of Serratia marcescens usually originates with contact from water, soil,
plants, or animals. This is known as a ubiquitous organism. This characteristic of
S.Marcescens gives it the ability to be found on multiple surfaces. Although the bacterium is
a pathogenic microorganism, it usually only infects immunocompromised patients. Most of
these infections occur from the transmission of the bacterium on catheters, PICC lines, IV’s,
or during other invasive procedures such as surgery. The bacterium only begins to become
harmful if it truly has the opportunity to do so in the host. This causes it to target
immunocompromised patients that have been exposed. In addition this bacterium usually
target the respiratory system, digestive system, and the urinary tract. In very few cases
Serratia Marcescens can infect soft tissue, including the middle ear. Such was the case for
my younger sister Kayla. Serratia Marcescens doesn’t infect most healthy people due to a
strong immune system, but the disease does target hospital patients of all ages exposed to the
bacterium with an insufficient immune system.
Diagnosing the S. Marcescens bacterium is similar to diagnosing many other bacteria.
Taking a blood culture, urine sample, and isolating the bacteria will all diagnose the
presence. Once Serratia is found in a patient it becomes hard to treat. The resistance to many
antibiotics and the susceptibility of growing more resistance creates a problem for treatment.
The history of treatment allowed for scientists to determine early resistance in many of the
antibiotics. What they did find effective against the bacteria were aminoglycosides and
fluoroquinolone. Although the bacterium is showing growth in resistance to both of these
treatments, it’s still the best option we have. Its toxic cell wall creates another problem. The
release of these toxins within a host could cause harm, which is why doctors don’t want to
prescribe an antibiotic that will rupture the cell wall. With continued research being done on
this bacterium, new methods are beginning to emerge for treatment. The emergence of newer
drugs in combination with aminoglycosides has shown a higher chance of eliminating the
infection. Hopefully with the progressing research there will be a treatment with a higher
percentage of success. Prevention of such nosocomial infection is a growing trend within
hospitals. More treatment options and prevention techniques are decreasing the mortality rate
for patients.
Many prevention steps should be taken by hospitals to decrease infection rates of not
only Serratia marcescens, but also many other nosocomial infections on the rise. The

4. cleaning and sterilization of equipment is a must for hospitals. Use of stronger detergent
could be the start to reducing infection. The increase in use of sterilants such as acid-anionic
sanitizers, quaternary ammonium compounds, aldehydes, and peroxides fully suffices in
cleaning medical equipment. The importance of hand washing and glove use should be
stressed amongst staff, as it is beneficial to the reduced spread of Serratia. To ensure the
cleanliness of doctor’s hands, hospitals should find a more powerful antimicrobial soap. In
addition the increase of daily cleaning from the janitorial staff could prevent the more
frequent infections of nosocomial infection. There is no way to prevent Serratia marcescens
in the environmental world due to its versatile living traits, but we can try to prevent this
bacterium from being in hospitals affecting immunodeficient patients.
I encountered this bacterium through my sister’s experience with Serratia
marcescens. My younger sister Kayla has had multiple surgeries within her middle ear and
mastoid due to a cholesteatoma. This tumor like growth originating in her middle ear has
caused more than ten surgeries. Due to these surgeries she has no cilia in her ear and no
longer produces earwax. This has caused her ear to be immunodeficient opening her up to
possible nosocomial infections. Through her experience I was made aware of little known
infections. Some of her infections she has had to deal with were methicillin resistant
Staphylococcus aureus (MRSA), Achromobacter xylosidans, and Serratia marcescens.
Achromobacter and Serratia marcescens are definite nosocomial infections that are both
highly resistant to many antibiotics. This posed a challenge for her doctors due to the
bacterium learning resistance to the new drugs. Her treatment was long and annoying due to
the switching of antibiotics but the control of bacteria is underway. Due to my sister’s
experience, I’m much more passionate about fighting the risk of nosocomial infection. No
one should be going to a hospital for help and end up leaving with an infection caused by the
hospital’s insufficient cleaning methods. My sister’s experiences also help lead me to my
career choice in the medical field. After my intensive research with Serratia marcescens, and
my sister’s experience, I’ve realized that infection caused by S. marcescens is serious and
requires intensive treatment. I have also learned that antibiotic resistance is a very real and
troubling epidemic. It does not make me aversive to surgery or hospitalization, but instead
has led me to increase the awareness of nosocomial infection to patients.

5. Bibliography
Herra, Falkiner. (n.d.). Serratia marcescens.
http://www.antimicrobe.org/b26.asp
Gastemeir, P. (2014, March 6). Serratia marcescens: An outbreak experience.
http://journal.frontiersin.org/Journal/10.3389/fmicb.2014.00081/full
Hejazi, Falkiner. (1997). Serratia marcescens. The Pathological Society of
Great Britain and Ireland.
Antimicrobial sensitivity and clinical significance. (1981). In Serratia
marcescens : Biochemical characteristics (pp. 35-41).
Serratia marcescens. (n.d.). Retrieved from
https://microbewiki.kenyon.edu/index.php/Serratia_marcescens
Tortora, Funke, Case. (2013). Microbiology (11th ed.). Glenveiw, IL: Pearsons
education.