P. 518

An Urban Experience
The pathogenesis of S. equi subsp. zooepidemicus in dogs and cats is still unclear. Co-infection with other contagious respiratory pathogens and bacterial virulence factors may contribute to the severity of disease. Other environmental factors such as overcrowding may also contribute to stress and severe disease manifestations.
Other Streptococcal Species
Other streptococcal species reported to cause disease in dogs and cats are S. dysgalactiae, Streptococcus suis, Streptococcus constellatus, Group B streptococci (S. agalactiae), and S. bovis group organisms
(now reclassi ed as Streptococcus gallolyticus and Streptococcus infantarius).
Enterococcus spp.
Enterococci are commensals of the gastrointestinal tract of humans and other animals, and important nosocomial pathogens. Enterococci survive harsh environmental conditions and are often resistant to a wide variety of different antimicrobial drug classes. Multidrug resistant enterococcal infections, especially those that are resistant to vancomycin (vancomycin-resistant enterococci or VRE) are a signi cant problem in human medicine. Resistance among enterococci occurs as a result of both intrinsic and acquired resistance mechanisms. Intrinsic resistance to low levels of most β-lactam antimicrobials occurs because enterococci possess low af nity penicillin binding proteins. In addition, all enterococci have intrinsic resistance to cephalosporins. Enterococci also have low-level intrinsic resistance to aminoglycosides, which results from decreased drug uptake. However, uptake
of aminoglycosides is enhanced when enterococci are exposed to β-lactams, which explains the synergistic activity of this combination. Enterococci are also resistant to trimethoprim-sulfamethoxazole because they utilize exogenously produced folate. Enterococcal resistance to other antimicrobials, such as macrolides and vancomycin, results from acquired resistance mechanisms.
E. faecium is more likely to show high-level resistance to penicillins and carbapenems than E. faecalis. However, E. faecalis is more likely to produce bio lms than E. faecium. An increase in the prevalence of multidrug resistant E. faecium infections has occurred in human medicine.
In healthy dogs and cats, enterococci can be found
on the skin and within the oral cavity, nasal cavity and gastrointestinal tract. Although less pathogenic than many streptococci, enterococci possess virulence factors that enable them to invade tissues and cause disease. Their ability to form bio lms means they can be dif cult to eradicate.
Because enterococci are intrinsically resistant to a number of antimicrobials, treatment with broad-spectrum
antibiotics may select for gastrointestinal colonization by enterococci. Enterococci can contaminate the hospital environment and survive for long periods on fomites. Inoculation may occur via urinary, intravenous, or other invasive devices. Enterococci can be isolated from dogs and cats with UTIs, cholangiohepatitis, pancreatitis, hepatic abscesses, peritonitis, mastitis, bacteremia and endocarditis, wound infections, and diskospondylitis. There have been rare reports of gastrointestinal illness in association with Enterococcus infection in dogs and cats.
In general, Streptococcus spp. infections should be treated with a β-lactam drug. In animals with severe disease, initial treatment should be with a broad- spectrum antimicrobial drug combination, such as
a β-lactam and an aminoglycoside. Prompt surgical exploration and debridement is of critical importance for NF. Aggressive  uid resuscitation with crystalloids and blood products may also be required. In human patients, NF and STSS are treated with both high-dose penicillin and clindamycin. This is because clindamycin suppresses exotoxin production by GAS, is more active than penicillin in experimental NF, and has a longer half-life than penicillin, but clindamycin resistance exists in some GAS, whereas all GAS remain susceptible to penicillin.
Meningitis/Meningoencephalitis. Penicillins typically have limited CSF penetration. Trimethoprim-sulfamethoxazole was used with apparent success to treat some dogs and cats with streptococcal meningitis. Ceftriaxone has been used as an alternative to benzylpenicillin for treatment of human streptococcal meningitis.
Enterococcal Infections. Aminopenicillins such as ampicillin generally have more potent activity against enterococci than penicillin or carbapenems. Bactericidal regimens should be used for treatment of systemic infections such as endocarditis or bacteremia, which consist of a β-lactam and gentamicin. Enterococci are usually resistant to aminoglycosides at dilutions used in routine broth microdilution methods (low-level resistance). When the synergistic combination of an aminoglycoside and penicillin is indicated, but low-level resistance is present, isolates can be tested for high-level resistance (HLR) to aminoglycosides. Aminoglycoside HLR has been reported in E. faecium and E. faecalis isolated from dogs and cats. When enterococci are penicillin resistant, the glycopeptide vancomycin can be substituted, but
this requires prolonged hospitalization for intravenous administration. Single-agent treatment with linezolid represents an oral alternative. However, resistant strains have appeared. Chloramphenicol may be successful
for treatment of resistant enterococcal bloodstream infections when administered orally, but is bacteriostatic and concerns regarding adverse effects exist.

   516   517   518   519   520