In Vitro Antimicrobial Inhibition Profiles ofMycoplasma BovisIsolates Recovered from Various Regions of the United States from 2002 to 2003

Abstract

Antimicrobial therapy continues to be important in reducing losses due to pneumonic forms of Mycoplasma bovis disease in beef and dairy calves. Although M. bovis diseases have been documented as frequent and economically important in the United States, there are no published reports on the antimicrobial activity of approved compounds against US strains. In this study, the authors report on the activity of 9 different antimicrobials against 223 recently recovered isolates of M. bovis. These isolates represent accessions from 5 geographic regions of the United States and were grouped by 4 tissues of origin (milk, respiratory, joint, or ear and eye). A broth microdilution test was used to determine minimum inhibitory concentration (MIC) values by reading redox changes detected in broth with alamarBlue (resazurin) indicator. For each antimicrobial, the median, MIC50, MIC90, mode, and range were calculated, and the values used for comparisons. In the absence of accepted breakpoint values, published MIC cutoff values for animal mycoplasmas as well as Clinical Laboratory Standards Institute interpretive criteria were used as a reference to define in vitro activity. The MIC values from active antimicrobials were found to distribute independently of region of origin of the isolates or of tissue of origin. Enrofloxacin, florfenicol, and spectinomycin were found to be active compounds in vitro. Oxytetracycline and chlortetracycline were active against more than half of the isolates. Very few isolates were inhibited by tilmicosin and none by erythromycin, ampicillin, or ceftiofur. The antimicrobial profiles determined for these US strains were remarkably similar to those reported for European isolates. However, unlike in Europe, there appears to be no diversity of profiles when US isolates are grouped by region or tissue of origin.

In vitro antimicrobial inhibition of Mycoplasma bovis isolates submitted to the Pennsylvania Animal Diagnostic Laboratory using flow cytometry and a broth microdilution method

“…17 Antimicrobial susceptibility testing was performed using the redox reagent resazurin b following a previously described broth microdilution procedure. 15 Early log phase suspensions of M. bovis (3 × 10 3 -3 × 10 5 cfu/ml) were exposed to doubling concentrations of enrofloxacin c starting at 0.0125 µg/ml, spectinomycin c at 1 µg/ml, erythromycin c at 0.0125 µg/ml, tetracycline c at 0.025 µg/ml, oxytetracycline c at 0.05 µg/ml, ceftiofur d at 0.49 µg/ml, and florfenicol e at 2 µg/ml in the presence of 5% resazurin. These levels were selected as starting concentrations based upon previous re search.…”

“…These methods have included broth dilutions, solid agar testing, E-strip testing, and most recently, flow cytometry. 2,6,9,10,15,16,18 The MIC values have been determined for Mycoplasma agalactiae, Mycoplasma hyopneumoniae, Mycoplasma putrefaciens, Mycoplasma capricolum, and Mycoplasma mycoides using a selection of antimicrobials with flow cytometry for one isolate of each. …”

“…These levels were selected as starting concentrations based upon previous re search. 2,4,6,9,10,15,16,18 All plates were sealed to prevent gas exchange between wells. Each isolate was run in duplicate on a sterile 96-well round-bottom plate composed of 9 dilutions of the 7 antimicrobials, 1 negative control (no antimicrobial and no culture), and 2 positive controls (no antimicrobial present with culture).…”

Mycoplasma bovis in Australian feeder cattle

“…Infrequent or no resistance has been reported to enrofloxacin or florfenicol (Francoz et al, 2005, Gerchman et al, 2009, Hirose et al, 2003, Rosenbusch et al, 2005, Siugzdaite et al, 2012. Successful treatment of M. bovis pneumonia and arthritis in calves using valnemulin in the milk from four days of age for three weeks has also been reported (Stipkovits et al, 2001).…”

“…In addition, in the past decade, in vitro susceptibility studies have shown an increased resistance to antimicrobials commonly used to treat infections associated with M. bovis; in particular oxytetracyclines, spectinomycin, tilmicosin and chlortetracycline (Francoz et al, 2005, Gerchman et al, 2009, Hirose et al, 2003, Rosenbusch et al, 2005, Siugzdaite et al, 2012. Infrequent or no resistance has been reported to enrofloxacin or florfenicol (Francoz et al, 2005, Gerchman et al, 2009, Hirose et al, 2003, Rosenbusch et al, 2005, Siugzdaite et al, 2012.…”