The most common bacteria that
contaminate physicians white laboratory coat are usually environmental organism
and skin commensals (Nester et al.,
2004). They include S. aurerus, Diphtherodis, Enterococci,
Pseudomonas aeruginosa etc
Staphylococcus
aureus is a facultative anaerobic Gram-positive non-motile, non-spore
forming coccal bacterium. They can grow on manitol salt agar and over as wide
range of temperature (10-46oc) but their optimum is 37oc.
They belong to a family called Staphylococcae and genus Staphylococcus in the
kingdom Eubactria (Wikipedia, 2011). It is frequently part of the skin flora
found in the nose, skin, and on formities especially hospitals and in this
manner about 20% of the human population are long-term carriers of S. aureus which is the most common
species of staphylococci to cause staph
infections. One of the reasons for this
is a caroteniod pigment staphyloxanthin that is responsible for the
characteristic golden colour of S. aureus colonies. This pigment acts as a
virulence factor, with an antioxidant action that helps the microbe evade death
by reactive oxygen species used by the high immune system.
S.
aureus can cause a range of illnesses from minor skin infections, such as
pimples, impetigo, boils (furuncles), cellulitis, folliculitis, carbuncles,
scalded skin syndrome and abscesses, to life-threatening diseases such as
pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock syndrome (TSS),
bacteraemia and sepsis. Its incidence is from skin, soft tissue, respiratory,
bone, joint, endovascular to wound infection. It is skill one of the five most
common causes of nosocomial infections. Personal hygiene and strict adherence
to hand hygiene by health care workers will help to reduce its effect in our
hospitals.
DIPHTERIODS (Corynebacterium diphtheriae)
Diphtheriods are a group of bacteria
named for their resemblance to diphtheria bacillus, Cornabacterium diphtheria. Their distinctive characteristics are
gram positive catalase positive, non-spore-forming, non-motile, staining rods
and low virulence. Unlike C. diphtheriae,
they do not produce exotoxin. Diphtheriods are responsible for skin odor,
caused by their breakdown of substances in sweat, which is odourless when it is
first secreted (Nester et al., 2004).
A diptheriod found on the skin in
large number is Propionibacterium acnes
which is present on virtually all humans. Surprisingly, most of P. acnes are anaerobic, although some
strains are however aerotolerant and hence grows aerobically (Brooks et al., 2004). P. acens grows primarily
within the hair follicles, where conditions are anaerobic. Its growth is
however, enhanced by oil secretion of the sebaceous glands, and the organism
are usually present in large numbers in areas of the skin here these glands are
especially well developed on the face, upper chest and back.
On blood agar medium, they produce
small (0.1-0.8mm), gray, non-haemolytic colonies. They are catalase positive,
coagulase negative and oxidase negative. They are susceptible to most commonly
used antibiotics.
ENTEROCOCCI
SPP (Enterococci spp)
They are Gram-positive spherical
bacteria that characteristically form pairs or chains during growth. They are
non-capsulated and the majority are non motile (Cheesbrough et al., 2006). There are at least 12
species of Enterococci (Brooks et al.,
2004). Enterococcus faecium causes
(5-10%) of Enterocci infection while E.
faecalis is the most common and cause 90-95% of Enterococci infection
(Brooks et al., 2004).
Enterococci are aerobic organism
capable of growing over a wide temperature range, 10-45oC. Their
colonies are mainly non-haemolytic but some stains show alpha or
beta-haemolysis on blood agar. E. faecalis
ferments lactose and produces small dark red magenta colonies on MacConkey
agar and small yellow colonies on CLED agar (Cheesbrough, 2006).
The Enterococci are among the most frequent cause of nosocomial
infections, particularly in the intensive care units, and are selected by
therapy with cephalosporins and other
antibiotics to which they are resistant. Enterococci are transmitted from one
patient to another primary on the hands of hospital personnel (Murrary et al., 2000). Medical devices occasionally
transmit them. In patients, the most common site of infections is the urinary
tract, wounds, biliary tract and blood (Brooks et al., 2004). Enterococci may cause meningitis and bacteremia in
neonates but in adults, they can cause endocarditis.
Enterococcus species ferments lactose, hydrolyze aeculin, reduce
litmus milk and are catalyse negative (Cheesbrough, 2006). Most Enterococci are
susceptible to ampicillin and resistant to cephalosporins. Resistance is shown
against penicillin and vancomycin resistance appears to be emerging particularly
with hospital infections (Cheesbrough, 2006). Control is by proper hand washing.
PSEUDOMONAS
AERUGINOSA (P. aeruginosa)
Pseudomonades
are the commonest gram-negative rods that belongs to the family
Pseudomonadaceae and they are motile and non-spore forming. They are aerobic
and more than half of all clinical isolates produce water soluble (blue green) pigment
pyocyanin on culture. P. aeruginosa
often has a characteristics sweet odour. These pathogens are widespread in
nature, inhibiting soil, sewage, water, plants and animals (including human
being, skin flora, and most man-made environment throughout the world (Brooks et al., 2004) and (Wikipedia 2011). It
thrives not only in normal atmospheres but also in hypoxic atmospheres, and has
thus, colonised many natural and artificial environments.
Pseudomonades aeruinosona has become an
important cause of infection in hospital environment, especially in patients,
with compromised host defence mechanisms (damaged tissues) or those with
reduced immunity. It is the most common pathogen isolated from patients who
have been hospitalized long than one week. The symptoms of such infections are
generalized inflammation and sepsis. It is a frequent cause of nosocomial
infections such as pneumonia, urinary tract infection (UTIs), bacteremia,
kidney and lungs infection, the result can be fatal and life threatening (Wikipedia
2011).
It measures 0.6 by 2.0u in size (Brooks et al., 2004). Some may be shorter than this. They are obligate
aerobes. P. aeruginosa strains are
haemolytic on blood agar and form smooth colonies with greenish pigmentation.
There is the presence of polysaccharide is responsible for mucoid colonies seen
in culture of patient with cystic fibrosis. It has lipopolysaccharide which
exist in multiple immunotypes and responsible for the endotoxic properties of
the organism (Brooks et al., 2004).
They also produce extracellular enzyme including elasatase, protease and
heomlysin. All these help in the pathogenesis of P. aeruginosa. P. aeruginosa
are mainly pathogenic on immunocopromised individuals where normal deference
has been breached (Nester et al.,
2004). The bacterium is attached to mucoid membrane and produce systemic
disease that is promoted by the presence of pilli, enzyme and toxin and other
virulent factors. Lipopolysacharide play direct role in fever, shock,
oilgouria, leucocytosis, disseminated intravascular coagulation (DIC) and adult
respiratory disease syndrome. It is also involved in skin, wound, urinary
tract, and respiratory infection.
P. aeruginosa are oxidase positive, catalase positive, indole negative and
citrate positive, they are higher resistant to most antibiotics hence contained
therapy should be used (Brooks et al.,
2004).