Page 1298 - Cote clinical veterinary advisor dogs and cats 4th

654 Methicillin-Resistant Staphylococcal Infections

also infect animal patients, with subsequent incision, immune compromise, abnormal ○ There has been recent (past few months)
risk of exposure of other humans. lower urinary tract conformation) to cause antibiotic exposure.
VetBooks.ir infections are rare, and MRSP is no more • Transmission of MRS can occur in veterinary Advanced or Confirmatory Testing
disease.
• MRSP is a potential zoonosis, but human
likely to cause a zoonotic infection than
Erythromycin-resistant MRSA isolates should
hospitals, and outbreaks can occur, but most
methicillin-susceptible strains.
in the community.
• Zoonotic risks of other MRS are MRS infections are sporadic and originate be tested by D-test (or equivalent) to confirm
that inducible clindamycin resistance is not
inconsequential. present. Confirmation of methicillin resistance
• In a household with at-risk (e.g., immuno- DIAGNOSIS can be performed by mecA PCR or PBP2a latex
compromised) humans, it is important to agglutination test. This should be performed
culture wounds or other potentially infected Diagnostic Overview for any isolate with equivocal results or
sites because of the increased likelihood of • MRS are diagnosed by bacterial culture and multidrug-resistant staphylococci that appear to
a multidrug-resistant infection and the susceptibility testing. be methicillin susceptible because false-negative
potential human health implications. • The potential for contamination or isolation susceptibility results can occur.
○ The benefit is likely greater for the pet of an MRS that is merely colonizing the
(i.e., pet is more likely to have an MRSA sampled site must be considered. This is TREATMENT
infection from the owner) than the owner particularly true for MR-CoNS organisms,
(i.e., to indicate zoonotic disease risk). which tend to be less virulent and are Treatment Overview
• Routine screening of healthy animals for common contaminants. • In general, MRS infections are treated no dif-
MRS carriage is not recommended. • Cytology, imaging, and hematology may be ferently than infections caused by susceptible
necessary for some infection types and to help staphylococci apart from the antimicrobial
Clinical Presentation differentiate colonization or contamination choice, which must exclude beta-lactam drugs.
DISEASE FORMS/SUBTYPES from infection. • Alternatives to beta-lactams are almost always
MRS cause a wide range of opportunistic • Although polymerase chain reaction available, and selection depends on the type
infections, and clinical presentation of patients (PCR) screening tests are available for of infection, site of infection, patient factors,
with MRS infections is not inherently different MRSA in humans, there are currently no and other general principles of antimicrobial
from that of other opportunistic infections. validated rapid diagnostic assays for MRS in therapy.
Pyoderma, otitis, soft-tissue infections, wound animals. • The goal of treatment is elimination of
infections, and surgical site infections are most disease, not microbiologic cure, for infection
common, but infection of virtually any body Differential Diagnosis of nonsterile (e.g., skin) sites.
system or site may occur. • MRS infections do not look any different • Re-culture after clinical cure is rarely
than infections caused by susceptible staphy- indicated.
HISTORY, CHIEF COMPLAINT lococci or other opportunistic pathogens. ○ Persistence of MRS as colonizers in the
Historical factors are indistinguishable from • Some findings support MRS infection rather nose, mouth, intestinal tract, or skin
those of routine, non-MRS infections (e.g., than nonpathogenic colonization by MRS: is common after resolution of clinical
pyoderma [p. 851], urinary tract infection ○ Gross clinical findings consistent with infection, particularly with MRSP, and
[p. 232], otitis externa [p. 728]). Although a infection versus sterile inflammation or some dogs may be prolonged (or even
history of previous antimicrobial therapy or other disease types persistent) carriers.
hospitalization increases the risk, MRS infec- ○ Evidence of staphylococcal infection on
tions can exist in any patient. diagnostic tests (e.g., intracellular cocci Acute General Treatment
on cytology, gram-positive cocci) • Antimicrobial therapy is typically required
PHYSICAL EXAM FINDINGS ○ Sample unlikely to have been contami- and combined with supportive care as
As expected with the primary disease process; nated during collection needed; measures to address inciting causes
see physical exam findings for pyoderma, bacte- may be critical.
rial cystitis, otitis externa, and other bacterial Initial Database ○ Beta-lactams (penicillins, cephalosporins,
infections. • As indicated by initial presentation (as clini- carbapenems) are not appropriate due to
cally appropriate for pyoderma, suspected/ resistance.
Etiology and Pathophysiology confirmed cystitis, otitis externa) • Surgery (e.g., removal of an infected surgical
• Any Staphylococcus species can be methicillin • Routine bacterial culture and susceptibility implant) if applicable
resistant. The most important are MRSP, testing can identify methicillin resistance, • With superficial bacterial folliculitis, topical
MRSA, and Staphylococcus schleiferi (MRSS). confirming the presence of MRS. This application of biocides (e.g., 2%-4%
○ Coagulase-negative staphylococci are often is usually performed by testing oxacillin chlorhexidine) may be effective (p. 851).
resistant (MR-CoNS), but these tend to or cefoxitin susceptibility as a marker of • Topical antimicrobials (e.g., mupirocin,
be of limited clinical consequence. methicillin resistance (i.e., oxacillin- or fusidic acid) suitable for superficial infections
• Like their susceptible counterparts, MRS can cefoxitin-resistant staphylococci are MRS). • Topical honey may be useful for wound
be found as colonizers in healthy animals, • Bacterial culture and susceptibility testing infections.
particularly in the nose, mouth, intestinal should be performed as clinically appropriate, • Nitrofurantoin is often an option for cystitis
tract, and skin. and is considered particularly important in (p. 232).
• The biological behavior of MRS infections some cases: • Regional therapy (e.g., antimicrobial-
is indistinguishable from that of methicillin- ○ There is initial treatment failure. impregnated PMMA beads, collagen sponges)
susceptible staphylococcal infections, except ○ Clinical disease is severe. might be critical for deeper infections,
for the limitation in treatment options (and ○ The animal has had a previous MRS particularly implant-associated infections.
accompanying risk of persistent/intractable infection or has been in contact with an
infection). animal or person with a previous MRS Chronic Treatment
• MRS infections develop no differently from infection. Uncommonly necessary, unless for an unad-
those of any other opportunistic infection ○ Surgery is planned for some other issue dressed nidus (e.g., foreign body, infected
and typically require an inciting cause (e.g., pyoderma patient is scheduled for implant) or inability to control underlying
(e.g., atopic dermatitis, wound, surgical orthopedic surgery). disorder (e.g., atopic dermatitis) exists. In

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