Epidemiology of <i>β</i>-Lactamase-Producing Staphylococci and Gram Negative Bacteria as Cause of Clinical Bovine Mastitis in Tunisia

Abstract

The aim of this study was to determine the species distribution of <i>Staphylococcus,</i> Gram negative bacteria (GNB) and the occurrence of Methicillin Resistant Staphylococci (MRS) and Extended-Spectrum <i>β</i>-lactamase- (ESBL-) producing GNB. Bacterial culture of 300 clinical mastitis milk samples from 30 different farms across different regions of Tunisia during four seasons was realized. The obtained results showed the presence of high frequency of the tested samples with a positive growth for bacteria (64%). In addition a high recovery rate of <i>Staphylococci</i> and/or GNB in these clinical mastitis milk samples (87%) was detected. In addition, a high percentage of GNB (68.2%) compared to <i>Staphylococcus</i> species (32%) was noted. Moreover, a significant variation of the number of these bacteria according to the farm location, the seasons, and cows age was detected. The highest percentage was observed in the North of Tunisia during the winter and the spring seasons in adult cows with a dominance of GNB growth. Coagulase negative <i>Staphylococci</i> (CNS) (n=11) and GNB (n=16) species were identified. <i>Escherichia coli</i> (<i>E. coli</i>) was the most frequently found bacterium followed by <i>Klebsiella pneumoniae.</i> The dominant <i>Staphylococcus</i> isolates was <i>S. xylosus</i> followed by <i>S. aureus</i> the major pathogen isolated. Methicillin resistance was confirmed by the presence of the <i>mec</i>A gene in 3 <i>S. aureus</i> and 14 CNS isolates; all of these isolates were lacking the <i>mec</i>C gene. Various species of GNB, resistant to cefotaxime, were detected (n=15). ESBLs were detected on selective medium in 10 <i>E. coli</i> and 4 <i>K. pneumoniae.</i> All ESBL producers strains carry the <i>bla</i>CTX-M. The presence of different resistant mastitis pathogens in dairy farms may complicate therapeutic options and contaminated animals could become zoonotic agent reservoir for human.