Apramycin, florfenicol, marbofloxacin, neomycin, pradofloxacin and spectinomycin have been calibrated by the CDS method for veterinary use.
Ceftiofur, cefovecin, enrofloxacin, orbifloxacin, framycetin, lincospectin and tylosin can be extrapolated from surrogate antibiotics as described in Table 11.2.a and Table 11.2.b and in section 9.1.
Lincospectin is a combination of lincomycin and spectinomycin. When susceptibility testing is requested for this combination: Gram positive isolates are initially tested against erythromycin 5 μg and, if required, against clindamycin 2 μg; Gram negative isolates are tested against spectinomycin 25 μg. Susceptibilities are reported as follows.
Gram positive organisms
- Isolates susceptible to erythromycin are susceptible to clindamycin and lincomycin and therefore lincospectin.
- Staphylococci resistant to erythromycin are usually (98%) resistant to clindamycin and lincomycin and therefore lincospectin. There is no need to perform adjacent disc testing with erythromycin and clindamycin.
- iMLSB phenotypes (ICR positive) of streptococci and corynebacteria show a flattening of the clindamycin inhibitory zone adjacent to erythromycin (see section 4.7). These isolates are resistant to clindamycin and lincomycin and therefore to lincospectin.
- M phenotypes (ICR negative) of streptococci and corynebacteria show a zone of inhibition ≥ 6 mm in annular radius around clindamycin with no flattening of the zone adjacent to erythromycin (see section 4.7). These isolates are susceptible to clindamycin and lincomycin and therefore to lincospectin.
Gram negative organisms
Isolates susceptible to spectinomycin are reported as susceptible to lincospectin. Isolates resistant to spectinomycin are reported as resistant to lincospectin.
As requested by Veterinary Laboratories, erythromycin has been calibrated on Blood Sensitest Agar at 35oC in 5% CO2 atmosphere for the testing of Pasteurella sp. isolated from respiratory infection specimens of dogs and cats.
MIC of susceptible strains ≤ 2 mg/L
Annular radius of susceptible strains ≥ 4 mm
9.3. Oxacillin and Staphylococcus intermedius group (SIG).
The Staphylococcus intermedius group comprises three separate species – Staphylococcus intermedius, Staphylococcus pseudintermedius and Staphylococcus delphini. Methicillin susceptible (mecA gene negative) SIG have a zone of inhibition to oxacillin 1µg discs ≥ 6mm and should be reported as susceptible to methicillin. Methicillin resistant (mecA A gene positive) SIG have a zone of inhibition to oxacillin 1µg disc <6mm and should be reported as resistant to methicillin.
When the identification of the isolate is not available at the time of susceptibility testing then both cefoxitin 10µg disc and oxacillin 1µg discs should be tested. If both have a zone ≥6mm then the isolate should be reported as susceptible to methicillin. See Power point ASM 2015.
Florfenicol is exclusively licensed for use in animals, specifically cattle and pigs, and is only approved as an injectable drug for individual animal therapy. Florfenicol is a fluorinated derivative of chloramphenicol and acts as a potent inhibitor of bacterial protein biosynthesis. Although chloramphenicol and florfenicol have the same spectrum of activity they differ in their mechanisms of resistance1. Florfenicol has been calibrated for the CDS using 30 µg discs.
MIC of susceptible strains ≤ 8.0 mg/mL
Annular radius of susceptible strains ≥ 6 mm
Pradofloxacin is a third generation fluoroquinolone developed for use in veterinary medicine primarily for use in skin infections of dogs and cats2. Pradofloxacin has been calibrated using pradofloxacin 5 µg discs.
MIC of susceptible strains ≤ 2.0 mg/mL
Annular radius of susceptible strain ≥ 6 mm
1 White, D.G., Hudson, C., Maurer, J.J., Ayers, S., Zhoa, S., et al. 2000. Characterization of Chloramphenicol and Florfenicol Resistance in Escherichia coli Associated with Bovine. J. Clin. Microbiology. 38(12), 4593-4598.
2 Silley, P., Stephan, B., Greife, H.A., & Pridmore, A. 2012. Bactericidal properties of Pradofloxacin against veterinary. Veterinary Microbiology. 157, 106‑111.