Antimicrobial Resistance in Leptospira, Brucella, and Other Rarely Investigated Veterinary and Zoonotic Pathogens.

Leptospira, Brucella, and Borrelia are major agents of zoonotic disease, causing high morbidity and, in some cases, significant mortality in humans. For all three genera, prompt diagnosis and appropriate antimicrobial therapy are required to prevent the development of chronic, debilitating illness. Leptospira spp. are intrinsically resistant to several antimicrobial classes; however, there is little evidence in the literature for development of acquired resistance to antimicrobial agents used for clinical treatment of acute leptospirosis. For Brucella infections, there are numerous reports of relapses following therapy, but it is unclear whether this is due to sequestration within infected sites (e.g., bone) or the development of acquired resistance. Brucella have maintained their susceptibility to doxycycline and rifampicin, which in combination remain the most common treatments of brucellosis in humans. In vitro induced point mutations are described as imparting resistance to rifampicin (rpoB) and fluoroquinolones (gyrA). The clinical significance of these mutations is unclear. For Borrelia burgdorferi, although acquired resistance to some antimicrobial agents has been described, resistance due to bacterial persister cells surviving in the presence of antimicrobial, with no apparent increase in the MIC of the organism, have been recently described. Of the remaining veterinary fastidious pathogens, Lawsonia intracellularis is the most interesting from an antimicrobial resistance perspective because it can only be grown in cell culture, making in vitro susceptibility testing challenging. MIC testing has been undertaken on a small number of isolates, and some differences in susceptibility to macrolides have been demonstrated between isolates obtained from different regions.

A randomised clinical trial on the efficacy of oxytetracycline dose through water medication of nursery pigs on diarrhoea, faecal shedding of Lawsonia intracellularis and average daily weight gain.

Oral treatment with antimicrobials is widely used in pig production for the control of gastrointestinal infections. Lawsonia intracellularis (LI) causes enteritis in pigs older than six weeks of age and is commonly treated with antimicrobials. The objective of this study was to evaluate the efficacy of three oral dosage regimens (5, 10 and 20mg/kg body weight) of oxytetracycline (OTC) in drinking water over a five-day period on diarrhoea, faecal shedding of LI and average daily weight gain (ADG). A randomised clinical trial was carried out in four Danish pig herds. In total, 539 animals from 37 batches of nursery pigs were included in the study. The dosage regimens were randomly allocated to each batch and initiated at presence of assumed LI-related diarrhoea. In general, all OTC doses used for the treatment of LI infection resulted in reduced diarrhoea and LI shedding after treatment. Treatment with a low dose of 5mg/kg OTC per kg body weight, however, tended to cause more watery faeces and resulted in higher odds of pigs shedding LI above detection level when compared to medium and high doses (with odds ratios of 5.5 and 8.4, respectively). No association was found between the dose of OTC and the ADG. In conclusion, a dose of 5mg OTC per kg body weight was adequate for reducing the high-level LI shedding associated with enteropathy, but a dose of 10mg OTC per kg body weight was necessary to obtain a maximum reduction in LI shedding.

Evaluation of lincomycin in drinking water for treatment of induced porcine proliferative enteropathy using a Swine challenge model.

A single-location, challenge-model study was conducted to evaluate the effectiveness of lincomycin against porcine proliferative enteropathy when administered through the drinking water at 125 and 250 mg/gallon. The primary variables of interest were pig removal rate, diarrhea scores, demeanor scores, and abdominal appearance scores. Ancillary performance variables examined included average daily feed intake, average daily gain, and feed per gain. After a 3-day acclimation period, pigs were challenged on 2 consecutive days with a mucosal homogenate containing a total dose of 1.4 x 10(9) cells of Lawsonia intracellularis. Five days later, when porcine proliferative enteropathy was well established, drinking water medicated with 125 mg (L125) or 250 mg (L250) lincomycin/gallon was provided to two groups of pigs for 10 days. Pigs were observed for 13 days following the treatment period. A third group of pigs served as controls and received unmedicated drinking water throughout the study. The L250 group experienced a significantly lower (P < .05) pig removal rate than the control group over the 23-day observation period. Additionally, for every primary variable, the L250 group experienced a significantly decreased (P < .01) number of abnormal days compared with the control group. The L125 group showed a significant reduction (P < .05) in abnormal demeanor and abnormal abdominal appearance scores compared with controls.