Epidemiology of antimicrobial resistant Streptococcus Uberis associated with bovine mastitis

Abstract

Streptococcus uberis is a common bovine mastitis pathogen in dairy cattle. The reduced success of antibiotic treatment for S. uberis intramammary infection (IMI) may be associated with the antimicrobial resistance (AMR) of these bacteria. This study aimed to analyze 228 S. uberis strains associated with bovine mastitis in northern Thailand from 2010 to 2017. AMR and AMR genes were determined by minimum inhibitory concentration (MIC) using a microdilution method and polymerase chain reaction, respectively. The majority of S. uberis were resistant to tetracycline (187/228, 82.02%), ceftiofur (44/228, 19.30%), and erythromycin (19/228, 8.33%). The MIC50 and MIC90 of ceftiofur and penicillin G in 2017 were two- to three-fold higher than those in 2010. A trend analysis indicated that resistance to tetracycline and ceftiofur significantly increased during 2010-2017. The most common gene detected in S. uberis was tetM (199/228,87.28%), followed by ermB (151/228, 66.23 %) and blaZ (15/228, 6.58 %). Association between the resistance to tetracycline and the detection of tetM tetL were statistically significant (P<0.01). Trend analysis revealed that the detection rates of tetM and mefA significantly increased, while the detection rates of tetO and ermB significantly decreased during 2010-2017. AMR monitoring for bovine mastitis pathogens, especially S. uberis, is necessary to understand the trend of AMR among mastitis pathogens, which can help create an AMR stewardship program for dairy farms in Thailand. The rapid identification and characterization of the AMR of S. uberis play an important role in diagnosis and prevention. This will greatly shorten the decision-making time of veterinarians and farmers. In this study, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) was used to screen for biomarkers of S. uberis to predict AMR. The principal component analysis (PCA) method was used to analyze the MALDI-TOF mass spectrum of S. uberis to try to distinguish the difference between antimicrobial resistance and susceptible strains. However, the results did not show a significant difference. This may be due to the size of the target protein molecules and the small number of samples. Analysis of MALDI-TOF MS to distinguish different strains of S. uberis needs to be further investigated.