Research Article: Influence of systemic fluoroquinolone administration on the presence of Pasteurella multocida in the upper respiratory tract of clinically healthy calves

Date Published: September 22, 2008

Publisher: BioMed Central

Author(s): Boudewijn Catry, Siska Croubels, Stefan Schwarz, Piet Deprez, Bianca Cox, Corinna Kehrenberg, Geert Opsomer, Annemie Decostere, Freddy Haesebrouck.


The influence of enrofloxacin administration (5 mg/kg) for five consecutive days on the occurrence of Pasteurella multocida in the upper respiratory tract of two healthy calves was monitored over a 10-day period. From nasal swabs of two additional healthy control calves, which received a placebo saline administration, P. multocida was isolated throughout the study period. In the enrofloxacin treated calves, P. multocida was not demonstrated in the nasopharynx from 48 h after the first injection until two days after the last administration, when P. multocida reappeared and proved to be clonal in nature to the original isolates. During the experiment, no change in minimal inhibitory concentration for enrofloxacin of the P. multocida isolates was detected (MIC ≤ 0.015 μg/mL). Enrofloxacin concentrations were determined in the plasma by a high-performance liquid chromatography method with fluorescence detection. The PK/PD indices AUC/MIC and Cmax/MIC ratio were calculated and found to be 1157.7 and 129.8, respectively. Remarkably, the respiratory pathogen Arcanobacterium pyogenes became the predominant recovered organism in the nasopharynx of one animal following enrofloxacin therapy throughout the remaining of the experiment.

Partial Text

In calves, enrofloxacin is frequently used to treat pneumonic pasteurellosis, a disease mostly due to Pasteurella multocida [1]. P. multocida is a common inhabitant of the upper respiratory tract of calves. To better understand the epidemiology of pneumonic pasteurellosis and the occurrence of antimicrobial resistance, knowledge is needed on how systemic fluoroquinolone administration affects the flora of the nasopharynx in healthy calves. This is important as metaphylaxis is a common practice in the prevention of bovine respiratory diseases. Preventive treatment of “at risk animals” may be associated with a selection pressure leading to antimicrobial resistance or a shift in the population of bacteria present in the nasopharynx.

The authors declare that they have no competing interests.

BC conceived the study and drafted the manuscript. PD, GO, AD, and FH participated in the design and coordination of the study. BC, AD and FH performed the microbiological analysis, except for the PFGE and confirmatory identification test, which were done by CK and SS. SC carried out the HPLC, pharmacokinetic/pharmacodynamic analysis, and substantially helped to draft these sections in the manuscript. BC performed and interpreted the statistical analysis. All authors read and approved the manuscript.