First choice therapy

Tiamulin displays exceptional activity against MG in an overview by Hannan and others (1997) where 20 isolates were tested from the UK, Germany, Denmark, USA and Japan.
 

 
 

MICs of antimicrobial agents against field and type strains of MG (20 isolates) MICs (µg/ml)

Antimicrobial Type strain Field strains   NCTC10115 Range MIC 50% MIC 90% Enrofloxacin 0.01 0.025-1.0 0.05 0.1 Danofloxacin 0.005 0.01-0.5 0.05 0.1 Tylosin 0.01 0.0025-10.0 0.01 2.5 Oxytetracycline 0.1 0.05-0.5 0.25 0.5 Denagard® (tiamulin) 0.0025 0.0005-0.25 0.001 0.025

 
 

Tiamulin had extremely low MICs against MG with the MIC 50% being 0.001µg/ml and the MIC 90% at 0.025µg/ml.
 

The fluoroquinolones and oxytetracycline also showed a high level of activity but some strains of tylosin did show high MICs and evidence of resistance.

Hannan and others (1997) compared the MICs of tiamulin against 28 isolates of MS from around the world and again showed tiamulin to be highly active.
 

 

MICs of antimicrobial agents against field and type strains of MS (28 isolates) MICs (µg/ml)

Antimicrobial Type strain Field strains   NCTC10124 Range MIC 50% MIC 90% Enrofloxacin 0.5 0.05-0.5 0.25 0.5 Danofloxacin 0.5 0.1-0.5 0.25 0.5 Tylosin 0.025 0.0025-50 0.025 50 Oxytetracycline 0.11 0.025->100 0.1 100 Denagard® (tiamulin) 0.1 0.05-0.5 0.1 0.25

 
 

All isolates would be considered sensitive to tiamulin with the MIC 50% at 0.1µg/ml and the MIC 90% at 0.25µg/ml as well as the fluoroquinolones. Definite resistance (very high MICs) could be observed with tylosin and oxytetracycline by their MIC 90%, although they would still be considered active at their MIC 50% level.

In a separate study (Valks and Burch, 2001), a search of published literature was carried out and these data were combined with Novartis’ own internal reports. A total of 20 references were compiled. Reports from 1975-1989 and from 1990-2000 were compared. The ranges of MICs of various antimicrobials against the four major mycoplasma species were entered into a database. The maximum and minimum data for each time period were compared for tiamulin, tylosin, oxytetracycline, lincomycin and enrofloxacin.
 

From the 20 references and reports, 13 were from before 1990 and seven from 1990 and after. There was information on 241 isolates of MG, 105 of MS, 28 of M. meleagridis (MM) and 111 of
M. iowae (MI). The comparative data for the four mycoplasma species are summarized in the tables below.
 

 
 

Mycoplasma gallisepticum, MIC ranges (µg/ml) by time period (no. of isolates)

Antimicrobial 1975-1989 (175) 1990-2000 (66) Denagard® (tiamulin) 0.0039-0.78 0.006-0.39 Tylosin 0.5 0.05-0.5 Oxytetracycline 0.5 0.1-0.5 Lincomycin 0.025 0.0025-50 Enrofloxacin 0.11 0.025->100

 
 

Mycoplasma synoviae, MIC ranges (µg/ml) by time period (no. of isolates)

Antimicrobial 1975-1989 (53) 1990-2000 (52) Denagard® (tiamulin) 0.031-1.0 0.006-0.5 Tylosin 0.015-75 0.006-50 Oxytetracycline 0.06-0.08 0.025-100 Lincomycin 0.31-6.0 0.05-1.56 Enrofloxacin 0.1-1.0 0.025-1.56

 
 

Mycoplasma meleagridis, MIC ranges (µg/ml) by time period (no. of isolates)

Antimicrobial 1975-1989 (17) 1990-2000 (11) Denagard® (tiamulin) 0.03-1.0 0.025-3.13 Tylosin 0.015-3.0 0.78-50 Oxytetracycline 0.3-5.0 0.05-25 Lincomycin 0.5-5.0 0.05-25 Enrofloxacin 0.015-1.0 0.1-3.13

 
 

Mycoplasma iowae, MIC ranges (µg/ml) by time period (no. of isolates)

Antimicrobial 1975-1989 (25) 1990-2000 (86) Denagard® (tiamulin) 0.015-10 0.006-0.125 Tylosin 0.05-64 0.05-100 Oxytetracycline 1-3 0.025-100 Lincomycin 3-64 0.05-100 Enrofloxacin 0.1-1.0 0.005-1.0

 
 

MG has shown no resistance development to tiamulin over the last 25 years and all 241 isolates could be considered sensitive. In contrast there is resistance development to tylosin, oxytetracycline, lincomycin and borderline resistance to enrofloxacin and this appears to have increased in the last decade.
 

 
 

MS has shown no increase in resistance to tiamulin and almost all of the 105 isolates would be considered sensitive. In contrast, resistance has developed to tylosin and oxytetracycline. Levels of resistance to lincomycin remained low and all strains could be considered sensitive to enrofloxacin.
 

 
 

MM isolates (28) from turkeys showed some slight increase in resistance to tiamulin and enrofloxacin. However, tylosin, oxytetracycline and lincomycin showed a marked increase in resistance development.
 

 
 

MI has developed almost no resistance to tiamulin and enrofloxacin. In the nineties all isolates would be considered sensitive. High levels of resistance have developed to tylosin, oxytetracycline and lincomycin.
 

 
 

Denagard - your first choice for mycoplasma control in poultry