Enrofloxacin and Macrolides Alone or in Combination with Rifampicin as Antimicrobial Treatment in a Bovine Model of Acute Chlamydia psittaci Infection

Abstract

Chlamydia psittaci is a zoonotic bacterium with a wide host range that can cause respiratory disease in humans and cattle. In the present study, effects of treatment with macrolides and quinolones applied alone or in combination with rifampicin were tested in a previously established bovine model of respiratory C. psittaci infection. Fifty animals were inoculated intrabronchially at the age of 6–8 weeks. Seven served as untreated controls, the others were assigned to seven treatment groups: (i) rifampicin, (ii) enrofloxacin, (iii) enrofloxacin + rifampicin, (iv) azithromycin, (v) azithromycin + rifampicin, (vi) erythromycin, and (vii) erythromycin + rifampicin. Treatment started 30 hours after inoculation and continued until 14 days after inoculation (dpi), when all animals were necropsied. The infection was successful in all animals and sufficient antibiotic levels were detected in blood plasma and tissue of the treated animals. Reisolation of the pathogen was achieved more often from untreated animals than from other groups. Nevertheless, pathogen detection by PCR was possible to the same extent in all animals and there were no significant differences between treated and untreated animals in terms of local (i.e. cell count and differentiation of BALF-cells) and systemic inflammation (i.e. white blood cells and concentration of acute phase protein LBP), clinical signs, and pathological findings at necropsy. Regardless of the reduced reisolation rate in treated animals, the treatment of experimentally induced respiratory C. psittaci infection with enrofloxacin, azithromycin or erythromycin alone or in combination with rifampicin was without obvious benefit for the host, since no significant differences in clinical and pathological findings or inflammatory parameters were detected and all animals recovered clinically within two weeks.

Acute phase proteins as local biomarkers of respiratory infection in calves

“…Exclusion of co-infections and standard antibiotic treatment after purchase, i.e. about 3 weeks before challenge, was performed as described previously [ 31 , 34 ]. Briefly, the presence of Mycoplasma , Pasteurella , or Mannheimia spp.…”

“…The 13 infected animals in the present study had served as untreated controls in previous studies [ 31 , 34 ].…”

“…-7 d: 7 days before inoculation; −4 d: 4 days before inoculation; dpi: days past inoculation; grey: animals prior to inoculation with C. psittaci; white: animals after inoculation with C. psittaci ( n = 13). The 13 calves served as untreated controls in two previous treatment studies where the general clinical scores and concentrations of LBP in blood sera have been published separately [ 31 , 34 ] …”

“…To address this, it is necessary to determine APP concentrations not only in blood, but also in BALF. From former studies in a bovine model of respiratory infection with Chlamydia (C.) psittaci and Parachlamydia (P.) acanthamoebae we knew that serum levels of some APPs increase after inoculation with these pathogens [ 27 – 34 ]. Prior to this study, data of LBP, Hp, lactoferrin (Lf), and CRP levels in blood of animals enrolled in former studies with the above mentioned model were summarized and are presented in Table 1 .…”

Regeneration of Pulmonary Tissue in a Calf Model of Fibrinonecrotic Bronchopneumonia Induced by Experimental Infection with Chlamydia psittaci

“…The infection model was very efficient, since all calves inoculated with the pathogen developed pneumonia, but none of the controls. The model was highly reproducible, and therefore repeatedly used to examine outcomes of different treatment regimens [23,24]. The localization of lesions corresponded to the inoculation sites and was distinct from field infections that have a cranioventral distribution [25].…”