A Review on Microorganisms Causing Wound
Infections on Skin
R. Solanki*,
B.P. Nagori
Lachoo Memorial College of
Science and Technology, Jodhpur, Rajasthan
*Corresponding Author E-mail:- solankirenu@yahoo.com
ABSTRACT:
Skin is the major
organ of the human body which plays a vital role in maintaining health of human
being. Certain diseases defined as infectious or communicable or transmissible
diseases are caused by pathogenic microorganisms. Some of the most common
causative microorganisms related with infections include Staphylococcus aureus,
Streptococcus pyogenes, Enterococci, Escherichia coli, Klebsiella pneumoniae
and Pseudomonas aeruginosa. Most of the diseases spread by the bacteria which
invade inside the body through skin. Bacterial infections on skin are the
common ailment for generation of other diseases in the body. Bacterial diseases
are type of infectious diseases caused by pathogenic bacteria. Symptoms and
complications related with bacterial infections such as chills, headache,
wound, vomiting and organ failure generally affects the patient’s life. Wound
on skin can occur in all ages of persons and can causes harm in number of ways.
Wound and skin infections represent the invasion of tissues by one or more
species of microorganisms. These infections disturbs the body immune system and
causes inflammation, tissue damage and
thus resulting in delayed wound healing process. This article throws light
on three aspects first on various types of microorganisms found responsible for
causing wound infection on the skin, second on laboratory tests to diagnose the
responsible microorganisms for wound infections and on choice of treatment for
wound healing.
KEYWORDS: Skin, symptoms, bacteria, types of
wound infection, diagnostic test, antibiotics.
INTRODUCTION:
Skin is the major organ of the human body. It collects sensory
information from the environment and functions as a protective barrier to the
human body organs. It helps in maintaining the proper body temperature.
Bacterial infections on skin are the common ailment for generation of other
diseases in the body. Specially, the wound on skin caused by bacteria produces
very chronic results, if it is not properly treated on time. The wound on skin can occur in all ages of
persons and can causes harm in number of ways. Therefore for correct
antimicrobial therapy for the treatment of wound, proper identification of microorganism
is necessary so that wound healing activity can be accelerated in less period
of time1, 2. Wound is a break in the integrity of the skin and
tissues. It may be a superficial cut, scrap or scratch. It may also include
puncture, burn or may be the result of surgical or dental procedures. The
microorganisms which are likely to infect the skin and tissues depend on the
wound extent, its depth, the environment in which it occurs and the types of
microorganisms present on the person skin.
The skin consists of three layers: the outer epidermis, the
dermis where many hair follicles and sweat glands are found and the fatty
subcutaneous layer. Below these layers are membranes that protect connective
tissues, muscles and bones. Wound can penetrate any of these layers and can
cause skin infections3-5.Wound and skin infections represent the
invasion of tissues by one or more species of microorganisms.
This infection disturbs the body immune system and causes inflammation,
tissue damage thus resulting in delayed wound healing
process. Many infections remain confined to a small area like an infected
scratch or hair follicle which usually heals on their own. Others may
persist and if kept untreated may increase in severity and may become cause of
other chronic diseases. Wound healing itself is a complex process which
involves many related systems, chemicals and cells working together so as to
clean the wound, heal its edges and to produce new tissues and blood vessels6-9.
Signs and symptoms
Common signs
and symptoms
of wound infection include redness, warmth, swelling, tenderness and pus
drainage from the skin. Sometimes the skin may also become harden or tighten in
that particular area and red streaks may radiate from the wound. Wound
infections may also cause fevers, especially when spread to the blood. Skin
infections may also cause pustules, pain, scaling, and itching in that
particular wounded area10.
Types
of wound infections and types of microorganisms responsible for wound infection
Wounds may be
typed according to their cause, their extent, the environment in which they
occur and whether they are clean or contaminated. The microorganisms
that infects skin and wound generally depends on immune system of the person,
depth of the wound and the conditions of the surrounding environment.
Bacteria, virus
and fungi can cause wound infections on skin (table 1, 2). Bacteria can be
classified as per the environment in which they grow: aerobic
(grow in air), microaerophilic
(grow in reduced oxygen environment) and anaerobic
(grow in little to no oxygen). Microaerophilic and
anaerobic bacteria are generally found in deeper wounds and abscesses11-
13.
Wound
infections on superficial skin areas
Superficial
infections occur in the outer layer of the skin but may also extend deeper into the subcutaneous
layer. They are caused by aerobic microorganisms; deeper wounds may also be
infected with anaerobic microbes. Bacterial infections are typically caused by
bacteria like Staphylococcus (Staph) and Streptococcus (Strep).
They may also be caused by antibiotic resistant bacteria like MRSA (Methicillin
Resistant Staphylococcus aureus). Brackish water
wound infection occurs due to waterborne Vibrio
or Aeromonas species. Hot tub-associated
infection occurs by Pseudomonas aeruginosa.
When wounds are deeper, the possible pathogens would be anaerobes like Bacteroides and Clostridium species.
Necrotizing fasciitis a serious but uncommon type of infection often involves
Group A Streptococci, which are sometimes called as
“flesh-eating bacteria. Other common skin infections such as ringworm and
athlete’s foot are not caused by bacteria but by fungi. Yeast infections occur
by Candida species which is generally found in the mouth (thrush) or on
other moist areas of the skin.
Wound
infections through bites
A wound
infection due to animal bites tends to reflect the microorganisms which are
generally present in oral cavity of animal which created the bite wound. They
may involve aerobic, anaerobic and microaerophilic
microorganisms. The most of the animal bites are from dogs and cats. The common
bacteria found in these animals oral cavity is Pasteurella
multocida.
Wound
infections through trauma
Trauma is a
type of injury which occurs by the physical force applied on the skin. It
includes injuries from motor vehicle accidents, cuts from knives or other sharp
instruments and gunshot wounds etc. The type of wound infections that trauma
victims acquires depend basically on the environment in which the injury
occurred, the extent of the injury, the microorganisms present on the affected
person skin and the immune status of the infected person. A deep puncture wound
occurs mostly by anaerobic bacteria such as Clostridium
tetani.
Wound
infections through burns
Burns are
generally caused by flammable liquids, fires, chemicals and electricity.
First-degree burns involve the epidermis. Second-degree burns involve the dermis.
Third-degree burns involve all the layers of the skin and thus damages the
tissues below it. Initial infections tend to bacterial. Fungal infections
due to Candida, Aspergillus, Fusarium, and other species may arise later since
they are not inhibited by antibacterial treatment. Viral infections, such as
those caused by the herpes simplex virus, may also occur14-15.
Wound
infections after surgery
Surgical sites
are most commonly infected by exposure to microorganisms in the hospital
environment. Hospital-acquired bacteria like MRSA. Deep surgical wounds become
infected both superficially with aerobic microorganisms and deep within the
body by anaerobes.
Table 1: Microorganisms related with wound
infections and their frequency of occurrence on skin
Pathogens |
Frequency (%) |
Staphylococcus aureus |
20 |
Coagulase-negative staphylococci |
14 |
Enterococci |
12 |
Escherichia coli |
8 |
Pseudomonas aeruginosa |
8 |
Enterobacter
species |
7 |
Klebsiella pneumoniae |
3 |
Streptococci |
3 |
Candida albicans |
3 |
Other gram-positive aerobes |
2 |
Table 2: Some potential wound pathogens
category responsible for wound infection
Pathogen Category |
Name of pathogen |
Gram-positive cocci |
Beta Haemolytic Streptococci (Streptococcus
pyogenes)* |
Enterococci (Enterococcus faecalis) |
|
Staphylococci
(Staphylococcus aureus/MRSA)* |
|
Gram-negative aerobic
rods |
Pseudomonas aeruginosa* |
Gram-negative facultative
rods |
Enterobacter species |
Escherichia
coli |
|
Klebsiella
species |
|
Anaerobes |
Bacteroides |
Fungi |
Yeasts
(Candida) |
Aspergillus |
*Most common
causative microorganisms related with wound infections
Laboratory tests to diagnose the
microorganisms responsible for wound infections
A clinical
evaluation cannot definitively tell the doctor which microorganism
is causing a wound infection or what treatment it is likely to be susceptible
to. For that, laboratory testing is required. Laboratory testing is primarily
used to diagnose bacterial
wound infections, to identify the microorganism responsible, and to determine
its likely susceptibility to specific antimicrobial agents. Sometimes
testing is also performed to detect and identify fungal infections.
Sample collection may involve swabbing the surface of a wound to collect cells
or pus
with a needle and syringe or biopsy16-18.
For fungal evaluation, scrapings of the skin may be collected. Test includes
bacterial wound culture, gram staining, antimicrobial susceptibility test and
fungal as well as urine cultures.
It is a primary test which is
used to diagnose the bacterial infection. The sample is streaked onto nutrient media
and is then incubated at body temperature so as to grow and identify bacteria
if any present in the sample or not. Growth and identification of bacterial
wound cultures is usually available within 24-48 hrs from the time the sample
is received in the lab while for slow growing microorganisms, such as fungi it
may take several weeks for growth and its identification19-20.
After the growth of
microorganism in the culture media, staining allows bacteria to be evaluated
under the microscope. It involves smearing individual colony types onto glass
slides and treating them with a special stain. Under the microscope, the
bacteria can be classified into gram-positive and gram-negative organisms,
there they are distinguished by their shape such as cocci
(spheres) or rods (bacilli) and are easily separated by color into gram
positive or gram-negative microorganisms. This test provides preliminary
information about the quality and potentiality of microorganisms that may be causing
the infection 21-26.
Antimicrobial
susceptibility
When a pathogen is identified
and isolated using the wound culture, this test is used to determine the
bacteria likely susceptibility to certain drug treatments. This information
helps in selecting appropriate antibiotics for the treatment27- 31. Other tests may includes
It
is performed when a fungal infection is suspected32.
It
is performed when a urinary tract infection is suspected.
Treatments
The
risk of wound infection can be minimized with prompt and proper wound cleansing
and treatment. Most wound infections that do occur can be successfully
resolved. Many superficial bacterial and viral infections will resolve on their own without any kind of treatment. Other bacterial
infections may require some type of topical antimicrobial drugs treatment.
Deeper infections typically require oral antimicrobial therapy. The
choice of which type antimicrobials drug is to be used is based upon the data
results of wound culture and antimicrobial susceptibility tests. Patients
with antibiotic resistant bacteria or with an infection which is located in
difficult area for drug therapy to penetrate (such as bone) may require
treatment with intravenous medications. The antimicrobial drugs may act by destroying the bacteria
(bactericidal) or by inhibiting the growth of bacteria (bacteriostatic).
The mechanism of action of these drugs can be divided into
four groups33-36.
Drugs interfering with cell wall
synthesis
Penicillin,
cephalosporin, bacitracin, vancomycin
and cycloserine. All b-lactum
antibiotics bind to receptors (penicillin binding protein at the cell wall
-cell membrane interface). After attachment of the b-lactum
drug to the receptor there is interference with the synthesis of peptidoglycan of cell wall. This makes the cell membrane
vulnerable to damage by solutes of the environment (plasma). The cell walls of
gram negative bacteria being more complex, these drugs cannot penetrate the
cell in adequate concentration.
Drugs affecting cytoplasmic membrane
Polymxcin B and colistin bind selectively with outer membranes of gram
negative bacteria that are rich in phoshatidylethanolamine
and act as cationic detergents. The inhibition of cell membrane function leads
to escape of macro molecules and ions from the cell resulting in cell damage or
death. Polyenes are effective against fungus which
contains sterol on cell membrane. Bacteria generally do not contain sterol on
cell membrane and hence polyene is ineffective in
bacterial infection.
Drugs inhibiting protein synthesis and impairment of function of the ribosomes
Aminoglycosides, tetracyclines, chloramphenicol and macrolide
antibiotics lincomycin inhibit protein synthesis in
bacterial ribosomes (70 S) without any major effect
on mammalian ribosomes (80 S).
Drugs inhibiting synthesis of nucleic acid
These drugs interfere
with transcription of genetic information on the ribosomes.
Rifampin binds with DNA- dependent RNA polymerase, actinomycin binds with deoxyguanosine
residues and quinolones block the DNA gyrase and thus they inhibit DNA synthesis of bacteria.
Choice of treatment
The
choice of which antimicrobials drugs to be used is generally based upon the
results of wound culture and antimicrobial susceptibility tests. Susceptibility testing is used to determine
which antibiotic or antibiotic combinations will be most effective in treating
the different types of bacteria causing the wound infection 37, 38, 39. The test include following three terms:
Susceptible: Likely,
but not guaranteed to inhibit the pathogenic microorganism;
may be an appropriate choice for treatment.
Intermediate:
May be effective at a higher dosage or more frequent dosage or effective only
in specific body sites where the antibiotic penetrates to provide adequate
concentrations but drugs may produce higher risk for medication side effects.
Resistant:
Not effective at inhibiting the growth of the organism; may not be an
appropriate choice for treatment. A combination of antibiotics that work
together to inhibit the bacteria when neither one alone will be
effective.
CONCLUSION:
Bacterial infections are one
of the most prominent causes of chronic diseases and physical disabilities
around the world. The most common causative microorganisms related with wound
infections include Staphylococcus aureus/MRSA, Streptococcus pyogenes,
Enterococci, Escherichia coli, Klebsiella
pneumoniae and Pseudomonas aeruginosa. These pathogens can be easily detected and
identified by using designed laboratory testing procedures and methods. Thus by
the help of wound culture and antimicrobial susceptibility tests, we can
easily find out appropriate antimicrobial therapy for the particular pathogen
responsible for causing wound infection on human skin.
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Received on 10.06.2013 Accepted on 17.07.2013
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Asian J. Pharm.
Tech. 2013; Vol. 3: Issue 3, Pg 121-124