11. Application to veterinary Medicine
Apramycin, Marbofloxacin, Neomycin and Spectinomycin have been calibrated by the CDS methods for veterinary use.
Ceftiofur, cefovexin, enrofloxacin, framycetin, lincospectin, ofloxacin, orbifloxacin and tylosin can be extrapolated from surrogate antibiotics as described in tables Table 12.2.a and Table 12.2.b and in section 8.1.
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.
- 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 4.8). 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 4.8). These isolates are susceptible to clindamycin and lincomycin and therefore to lincospectin.
Isolates susceptible to spectinomycin are reported as susceptible to lincospectin. Isolates resistant to spectinomycin are reported as resistant to lincospectin.
11.2. Erythromycin and Pasteurella species
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.
Annular radius of susceptible strains ≥ 4 mm
Susceptible MIC ≤ 2 mg/L
11.3.Oxacillin and Staphyloccus intermedius group SIG).
The Staphylococcus intermedius group comprises three separate species – Staphylococcus intermedius, Staphylococcus pseudintermedius and Staphylococcus delphini. Methicillin susceptible (mec A gene negative) SIG have a zone of inhibition to oxacillin 1µg discs > 6mm and should be reported as susceptible to methicillin. Methicillin resistant (mec 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.