Prova da redutase adaptada na avaliação da susceptibilidade antimicrobiana e eficácia do tratamento de vacas com mastite clínica

Abstract

The objectives of the present study were to determine the association between results of in vitro antimicrobial susceptibility testing, by means of disk diffusion test (DDT) and adapted methylene blue reductase test (ART), of pathogens isolated from cows with clinical mastitis (CM) and treatment outcomes. Milk samples (n = 227) were collected from the affected quarters of cows at the onset of CM (PRE) and after the end of treatment (POST), according to performed protocol. Cows were treated using an intramammary product containing: gentamicin (150 mg), cefoperazone (250 mg), spiramycin (200 mg) and neomycin (200 mg), cefalexin (100 mg) and neomycin (100 mg), cloxacillin (200 mg) and ampicillin (75 mg), or cefquinome (89 mg), with frequency of treatment according to the manufacturer's instructions. Two treatment protocols were perfomed: protocol 1 (P1), infusion for 3 days and results assessed 4 days after the end of treatment; protocol 2 (P2), daily infusion up to 9 days and results assessed 14 days after the end of treatment. PRE samples were tested for antimicrobial susceptibility by means of ART and bacterial isolates from PRE samples by means of DDT. Clinical cure was defined as absence of symptoms of CM, from any moment between the last infusion and the day POST samples was collected. Bacteriological cure was defined as absence of pathogens in the POST sample. Using P1, CC rate was greater for cases caused by susceptible isolates (81%) as compared with cases caused by resistant isolates (30%), tested by means of ART. CC rates were not significantly different for cases caused by susceptible or resistant bacteria, neither when tested by means of DDT using P1, nor of ART using P2. BC rate was greater for cases caused by susceptible isolates (67%) as compared with cases caused by resistant isolates (0%), tested by means of ART using P2. BC rates were not significantly different for cases caused by susceptible or resistant bacteria, neither when tested by means of DDT using P1, nor of ART using P1. Although ART showed accuracy and sensitivity similar to DDT as predictors of CC and BC, its specificity was approximately 2 times greater than DDT specificity to predict the treatment outcomes. The simplicity of the method and the quick way the results were obtained were important advantages of PRA over ADD. In spite of the need of further research, the use of PRA to guide intramammary mastitis treatment may be recommended based on results of this study.