under the microscope
By Rodney E. Rohde, PhD, MS, SM(ASCP)CM SVCM, MBCM, FACSc
(Bio)filming in the Environment
The Pseudomonads include many “true” Pseudomonas
species as well as several other genera formerly classified
with this group. Over 100 species once made up the genus
Pseudomonas but in the past decade or so, many of these
have been reclassified into other genera. Like last month’s bug,
Acinetobacter, the bacteria found in this group are typically
associated as natural residents of soil and water. They rarely cause
infections in healthy people; however, there are several groups
within the Pseudomonads that can cause medical problems,
including the fluorescent Pseudomonas spp., Burkholderia spp.,
Brevundimonas spp., Stenotrophomonas maltophilia, and other
less frequent ones occasionally found in clinical specimens and
the hospital environment.
Pseudomonas aeruginosa is the most common infection-causing
species and are usually encapsulated, Gram-negative, rodshaped
bacterium that can cause disease in plants and animals,
including humans. P. aeruginosa is an opportunistic species
especially with existing diseases or conditions – most notably
cystic fibrosis (CF) and traumatic burns. It generally affects the
immunocompromised but can also infect the immunocompetent
as in hot tub folliculitis. Treatment of P. aeruginosa infections can
be difficult due to its natural resistance to antibiotics.
This organism is notorious for its survival in all types of manmade
and artificial environments. It can live in diverse atmospheres
at normal or low oxygen levels. It is most famous for thriving
in moist environments and subsequent colonization of surfaces
via extensive biofilm production. In cases of human infection,
its versatility enables the organism to infect damaged tissues or
those with reduced immunity. Inflammation (general) and sepsis
are common symptoms. Colonization in critical body organs,
such as the lungs, the urinary tract, and kidneys, can be fatal.
CF patients will often deal with life-threatening “blue-green”
phlegm from lung infections while burn victims will also exhibit
the common pigmented skin infection.
In 2017, multidrug-resistant Pseudomonas aeruginosa caused
an estimated 32,600 infections among hospitalized patients and
2,700 estimated deaths in the U.S. [Source: 2019 AR Threats
Report]. Like many of the microbes I have discussed in my column,
this one is considered a healthcare-associated infection (HAIs).
Those most at risk include patients in hospitals, especially those:
● CF patients
● on breathing machines (ventilators)
● with devices such as catheters
● with wounds from surgery or burns are in intensive care units
● premature infants and neutropenic cancer patients
● urinary tract infections (UTI)
● have prolonged hospital stays
Infection can be increased by many factors, including prior
antibiotic exposure, ICU admission, use of a central venous
catheter, and mechanical ventilation or hemodialysis use. P.
aeruginosa can be transmitted to patients because of their
persistence on environmental surfaces and because of biofilms
on medical devices and equipment. As I have often mentioned, all
#SurfacesMatter all the time, to everyone in the war on pathogen
transmission. Pseudomonas spp. can live for long periods on
environmental surfaces and shared equipment if they are not
properly cleaned and disinfected.
Pseudomonas aeruginosa lives in the environment and can be
spread to people in healthcare settings when they are exposed
to water or soil that is contaminated with these germs. Resistant
strains of the germ can also spread in healthcare settings from
one person to another through contaminated hands, equipment,
or surfaces. Recently, research has shown that this organism (and
others) can create problematic, long-standing biofilms in sink
drains and other water based environmental areas and surfaces.
Pseudomonas aeruginosa infections are generally treated
with antibiotics. Unfortunately, in people exposed to healthcare
settings like hospitals or nursing homes, Pseudomonas aeruginosa
infections are becoming more difficult to treat because of
increasing antibiotic resistance.
Depending on the nature of infection (UTI, soft skin, etc.),
an appropriate specimen is collected and sent to a medical
laboratory for identification. Typically, a Gram stain is performed,
which should show Gram-negative “thin long” rods and/or white
blood cells. P. aeruginosa produces colonies with a characteristic
“grape-like” or “fresh-tortilla” odor on some growth media. In
mixed cultures, it can be isolated as clear colonies on MacConkey
agar (as it does not ferment lactose) which will test positive for
oxidase. Confirmatory tests include production of the bluegreen
pigment pyocyanin on cetrimide agar and growth at 42
degrees C. A Triple Sugar Iron slant is often used to distinguish
non-fermenting Pseudomonas species from enteric pathogens.
Following identification and to specify the best antibiotic(s)
to treat P. aeruginosa infections, the laboratory will perform an
antibiotic susceptibility test which allows for growth against a set
of antibiotics to determine which are active against the bacteria.
The best antibiotic(s) is then chosen based on the activity of
the antibiotic and other factors, like potential side effects or
interactions with other drugs. For some multidrug-resistant types
of Pseudomonas aeruginosa, treatment options might be limited.
How you can avoid getting an infection:
● Hand hygiene from healthcare professionals and patients
(and others)
● Wash hands with soap and water or use alcohol-based
hand sanitizer, particularly before and after caring for wounds
or touching medical devices
● Allow environmental services (housekeeping staff) and
healthcare staff to clean their room daily when in a healthcare
setting
Rodney E. Rohde, PhD, MS, SM(ASCP)CM SVCM, MBCM, FACSc,
serves as chair and professor of the Clinical Laboratory Science
Program at Texas State; associate director for the Translational Health
Research Initiative; as well as associate dean for research in the College
of Health Professions. Follow him on Twitter @RodneyRohde / @
TXST_CLS, or on his website: http://rodneyerohde.wp.txstate.edu/
8 july 2020 • www.healthcarehygienemagazine.com