The genusStreptococcusincludes Gram-positive organisms shaped in cocci and organized in chains. They are commensals, pathogens, and opportunistic pathogens for humans and animals. MostStreptococcusspecies of veterinary relevance have a specific ecological niche, such asS. uberis, which is almost exclusively an environmental pathogen causing bovine mastitis. In contrast,S. suiscan be considered as a true zoonotic pathogen, causing specific diseases in humans after contact with infected animals or derived food products. Finally,Streptococcusspecies such asS. agalactiaecan be sporadically zoonotic, even though they are pathogens of both humans and animals independently. For clarification, a short taxonomical overview will be given here to highlight the diversity of streptococci that infect animals. Several families of antibiotics are used to treat animals for streptococcal infections. First-line treatments are penicillins (alone or in combination with aminoglycosides), macrolides and lincosamides, fluoroquinolones, and tetracyclines. Because of the selecting role of antibiotics, resistance phenotypes have been reported in streptococci isolated from animals worldwide. Globally, the dynamic of resistance acquisition in streptococci is slower than what is experienced inEnterobacteriaceae, probably due to the much more limited horizontal spread of resistance genes. Nonetheless, transposons or integrative and conjugative elements can disseminate resistance determinants among streptococci. Besides providing key elements on the prevalence of resistance in streptococci from animals, this article will also largely consider the mechanisms and molecular epidemiology of the major types of resistance to antimicrobials encountered in the most important streptococcal species in veterinary medicine.

Bacteria of the Klebsiella pneumoniae species complex (KpSC) are ubiquitous, and K. pneumoniae is a leading cause of antibiotic-resistant infections in humans. Despite the urgent public health threat represented by K. pneumoniae , there is a lack of knowledge of the contribution of food sources to colonization and subsequent infection in humans.

Pseudomonas aeruginosa is a major human pathogen, which also affects animals. It is thought that P. aeruginosa has a non-clonal epidemic population structure, with distinct isolates found in humans, animals or the environment. However, very little is known about the structure of the P. aeruginosa population from diseased animals. Data on antimicrobial resistance are also scarce. Thirty-four already registered and 19 new MLST profiles were identified. Interestingly, a few clones were more prevalent, and clones associated to human outbreaks were also detected. Multidrug resistance phenotypes were overall rare. We highlight the non clonal structure of the population and show a higher prevalence of specific clones, possibly correlating with higher pathogenicity. The low proportion of antimicrobial resistance contrasts with the high resistance rate of human isolates.