Wound Care
Wounds - whether accidental (caused by cars, other animals, sharp objects,
gunshots, blunt impact or falling) or intentional (ear cropping, tail docking,
surgery) - can result in pain, bleeding, infection and loss of function. Basic wound
management includes:
- control of bleeding
- removal of debris and tissue debridement
- drainage
- promotion of vascularization
- wound closure
Unattended wounds are an ideal breeding ground for infection.
Aerobic Infections
A common aerobic pathogen, Staphylococcus intermedius,
is implicated in many infected wounds. Staphylococcus aureus is sometimes isolated as well.
Gaining entry through broken skin or mucous
membranes, the cocci begin to multiply. Tissue trauma often produces
ischemia, reduced or obstructed blood supply, which shields the bacteria
from the host's immune system and favors continued growth. Certain
staphylococci also produce enzymes and toxins that accelerate the death,
or necrosis, of surrounding cells and tissue. Some strains encapsulate
themselves, creating a physical barrier between the infection and the
body's defenses.
The typical staph infection produces inflammation, necrosis and pus-filled
abscesses. If staphylococci enter the bloodstream, they readily invade
almost any tissue and organ in the body, including bone. Osteomyelitis
(infection of the bone and associated tissues), pyoderma (pus-associated
skin infection), and pyometra (pus in the uterus) can all be caused by
staphylococci.
Effective treatment of staphylococcal infections often starts with surgical
drainage of the pus and cleansing of the wound. Antibiotic therapy requires a
drug active against staphylococci and one that penetrates beyond the body's
circulation to the site of infection.
Anaerobic Infections
The body's normal bacterial population (flora) is predominantly anaerobic.
Obligate anaerobes colonize virtually every mucous membrane surface of
the body. In the mouth, for example, obligate and facultative anaerobes
outnumber other bacteria 10 to 1. Anaerobes survive in the mouth because
oral streptococci lower the oxidation-reduction, or redox potential,
creating a welcoming environment. Such bacterial synergy is important in
the pathogenesis of anaerobic infections.
How Infections Start
Most anaerobic infections begin with a break in the skin or mucous
membranes that permits normally present bacteria to invade underlying
tissues. Strict aerobes and facultative anaerobes deplete the available
oxygen, creating the ideal environment for obligate anaerobes. Most
anaerobic infections are polymicrobial or mixed, containing both obligate
and facultative anaerobes. Mixed infections often progress through several
stages as the bacterial populations shift in accordance with the changing
microenvironment.
The virulence of anaerobic infections increases if the bacteria produce
enzymes or toxins capable of destroying surrounding tissue. Common
veterinary pathogens - including Bacteroides and
Clostridium perfringens - all release enzymes or toxins. Dense bacterial
populations within abscesses often manufacture beta-lactamase, which can
inactivate cephalosporins and penicillins.
Bacterial synergy also increases the virulence of anaerobic infections. In a
mixed infection, Bacteroides melaninogenicus sometimes protects nearby
bacteria by inhibiting the body's immune system response. And
nonpathogenic streptococci produce the vitamin K, required by
Bacteroides melaninogenicus for continued growth.
Clinically Important Anaerobes
In a survey of veterinary pathogens, the most common anaerobes (in
decreasing order of frequency) were:
- Bacteroides
- Clostridium
- Propionibacterium
- Actinomyces
- Peptostreptococcus
- Peptococcus
Anaerobes typically thrive in the nose, mouth, and digestive and
reproductive tracts.
Clues to Anaerobic Infections
Suspect anaerobic infections when:
- foul-smelling discharge is present
- standard culture techniques produce no microbial growth from
abscess samples
- infection sets in after surgery
- abdominal trauma or sepsis involves penetration of mucosal
surfaces
- deep abscesses, infection of malignant tumors, or pyometra occur
- infections do not respond to conventional antibiotic therapy
Anaerobic infections typically smell foul, produce little or no swelling,
spread along tissue planes, and result in necrosis.
Anaerobes in Clinical Syndromes
Because anaerobes are difficult to culture in the laboratory, they may be
overlooked in treatment decisions. However, these
clinical syndromes frequently involve anaerobes.
- Periodontal disease and bacterial endocarditis from dental
manipulations - Bacteroides is consistently present in gingivitis.
Peptostreptococcus is also common.
- Lung infection resulting from aspiration pneumonia - Bacteroides and Peptostreptococcus are frequently found
- Postsurgical infection
- Bacteremia and intra-abdominal sepsis
- Gynecologic infections, usually due to Bacteroides
- Central nervous system infection or cerebral abscesses
Treatment Considerations
Preliminary diagnosis of an anaerobic infection is usually based on clinical
clues, because culturing anaerobes is a difficult and time-consuming
process. Successful treatment of anaerobic infections almost always begins
with drainage and debridement, strategies that restore normal circulation
and tissue oxygenation. Antimicrobial therapy aims to eradicate anaerobic
pathogens and prevent their spread to adjacent tissues. If necrotic tissue
remains or antimicrobial therapy is inappropriate, the infection is sure to
recur.
Several factors influence the choice of an appropriate antimicrobial.
Among them:
- The polymicrobial nature of anaerobic infections. The additive
effect of toxins and enzymes can increase the severity of the
infection, and production of beta-lactamase by one bacterium species
can protect the entire microbial population.
- The consistent presence of Bacteroides, some strains of which are
resistant to penicillins, cephalosporins and tetracycline.
- The frequent failure of beta-lactamase antibiotics. Beta-lactamase
inhibitors sometimes fail because:
- bacteria produce sufficient beta-lactamase to
overwhelm them
- exposure to beta-lactams stimulates some bacteria to
produce large amounts of beta-lactamase
- beta-lactamase inhibitors can't stop all beta-lactamase
production
Antibiotic Options
For more information on antibiotic options, please visit the ANTIROBE® AQUADROPS® (clindamycin hydrochloride) Liquid, CLAVAMOX® (amoxicillin trihydrate, clavulanate potassium) Drops, and ZENIQUIN® (marbofloxacin) Tablets overviews.
When ANTIROBE was tested in clinical trials, vomiting and diarrhea were occasionally observed.
CLAVAMOX is contraindicated for use in animals with a history of allergic reaction to any of the penicillins or cephalosporins. Safety of use in pregnant or breeding animals has not been determined.
ZENIQUIN, as with all fluoroquinolones, is not recommended for use in immature cats during the rapid growth phase, or in cats known to be hypersensitive to fluoroquinolones. The most common adverse reactions observed during clinical studies were decreased activity, loss of appetite, vomiting and diarrhea.
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