Identificação de patógenos isolados de mastite bovina por testes bioquímicos e maldi-tof ms

Abstract

Mastitis is an inflammatory process that occurs in the mammary gland of the animal, has a complex and multifactorial etiological character and causes great damage to the milk production chain. The routine identification of mastitis pathogens is based on the morphological evaluation of the microorganism, its growth on different culture media and its biochemical characteristics, which is laborious, timeconsuming, and in some cases do not differentiate microorganisms in species. In recent years there has been a great increase in the use of the MALDI-TOF MS technique (Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry) in microbiology laboratories. The speed of the results, the precision and the low operating costs of a MALDI-TOF MS system allow analysis on a scale that was not possible until recently. The aim of this study was to evaluate the use of MALDI-TOF MS in the identification of bacteria isolated from bovine mastitis and to compare it to biochemical tests and 16S rRNA gene sequencing. For this, 380 bacterial strains isolated from milk of cows with or without signs of mastitis, kept into Embrapa’s Collection of Microorganisms of Interest to Agroindustry and Livestock, were identified by MALDI-TOF MS and the results compared with them obtained by morphological and biochemical identification and by 16S rRNA sequencing. The identification rate by MALDI-TOF MS was 99.2%, 95.5% at the species level and 3.7% at the gender level. Altogether 12 genera and 37 species of bovine mastitis pathogens were identified by MALDI-TOF MS: 13 species of the genus Staphylococcus, eight species of the genus Streptococcus, four species of Enterococcus, two species of Lactococcus, one species of Aerococcus and nine species of Gram-negative bacteria. The morphological and biochemical tests used in this study were appropriate for the identification at the species level of Streptococcus agalactiae and identification at the genus level of Gram-negative bacteria. The same tests were not, however, sufficient or accurate for the identification of Gram-positive catalase negative cocci other than Streptococcus agalactiae, nor for the differentiation between Streptococcus, Enterococcus, Aerococcus and Lactococcus genera. The results of the identification obtained by MALDI-TOF MS from 193 Staphylococcus strains were compared with the identification by 16S rRNA gene sequencing, carried out in a previous study, and the agreement between the two techniques was from 93.2%. MALDI-TOF MS proved to be suitable for the rapid identification of a large number of microorganisms isolated from milk of cows with mastitis, and ideal for use in the identification of strains deposited in biological collections.