A multilocus sequence typing (MLST) scheme based on seven housekeeping genes was used to investigate the epidemiology and population structure of Enterococcus faecalis. MLST of 110 isolates from different sources and geographic locations revealed 55 different sequence types that grouped into four major clonal complexes (CC2, CC9, CC10, and CC21) by use of eBURST. Two of these clonal complexes, CC2 and CC9, are particularly fit in the hospital environment, as CC2 includes the previously described BVE clonal complex identified by an alternative MLST scheme and CC9 includes exclusively isolates from hospitalized patients. Identical alleles were found in genetically diverse isolates with no linkage disequilibrium, while the different MLST loci gave incongruent phylogenetic trees. This demonstrates that recombination is an important mechanism driving genetic variation in E. faecalis and suggests an epidemic population structure for E. faecalis. Our novel MLST scheme provides an excellent tool for investigating local and short-term epidemiology as well as global epidemiology, population structure, and genetic evolution of E. faecalis.Although classically considered a commensal of the gastrointestinal tracts of humans and animals rather than a specialized human pathogen, enterococci have become extremely relevant in hospital-acquired infections. Their ability to acquire specific genetic traits, such as virulence and antibiotic resistance determinants that could increase their fitness in such a complex ecosystem, has been recognized (18). The paradigm of this evolutionary development is the emergence and spread of vancomycin-resistant enterococci (VRE) (20).Among enterococcal species, Enterococcus faecalis is responsible for most human infections in both community and hospital settings. Though resistance to vancomycin and penicillins is very rare, E. faecalis seems to harbor a broader repertoire of potential virulence traits than E. faecium (34). However, little is known about the relationship between the population structure and global epidemiology of E. faecalis. Different molecular typing methods have been developed to analyze E. faecalis epidemiology (3,11,19,36,37,40). Pulsed-field gel electrophoresis (PFGE) is considered a practical "gold standard" due to its high discriminatory abilities (3, 37), but the most important limitation of PFGE is its low interlaboratory reproducibility and its unsuitability for both global and long-term epidemiology studies or for phylogenetic or population structure studies.For many different bacterial species, the most appropriate technique for global and long-term epidemiology studies is multilocus sequence typing (MLST) (38). MLST provides an unambiguous nomenclature for genotypes, and clones and data are easily stored in databases that can be exchanged between different laboratories via the Internet (1). For E. faecium, the development of an MLST scheme has been critical in the understanding of global epidemiology, genetic evolution, and population structure (14,41). A previous ML...

Seventeen multiple-antibiotic-resistant nonpathogenic Escherichia coli strains of human, animal, and food origins showed a wide variety of antibiotic resistance genes, many of them carried by class 1 and class 2 integrons. Amino acid changes in MarR and mutations in marO were identified for 15 and 14 E. coli strains, respectively.

Colonization by Campylobacter strains was investigated in human, broiler, and pig fecal samples from 1997-1998, as well as in foods of animal origin, and antibiotic susceptibility testing was carried out for these strains. Campylobacter strains were isolated in the foods of animal origin (55 of 101 samples; 54.4%), intestinal samples from broilers (85 of 105; 81%), and pigs (40 of 45; 88.9%). A total of 641 Campylobacter strains were isolated from 8,636 human fecal samples of clinical origin (7.4%). Campylobacter jejuni was the most frequently isolated species from broilers (81%) and humans (84%), and Campylobacter coli was most frequently isolated from pigs (100%). An extremely high frequency of ciprofloxacin resistance was detected among Campylobacter strains, particularly those isolated from broilers and pigs (99%), with a slightly lower result for humans (72%); cross-resistance with nalidixic acid was almost always observed. A higher frequency of resistance to erythromycin (81.1%), ampicillin (65.7%), gentamicin (22.2%), and amikacin (21.6%) was detected in C. coli strains isolated from pigs compared to those isolated from humans (34.5, 29.3, 8.6, and 0%, respectively). A low frequency of erythromycin resistance was found in C. jejuni or C. coli isolated from broilers. A greater resistance to ampicillin and gentamicin (47.4 and 11.9%, respectively) was detected in C. jejuni isolated from broilers than in human strains (38 and 0.4%, respectively). ␤-Lactamase production was found in 81% of the Campylobacter strains tested, although 44% of them were characterized as ampicillin susceptible. The increasing rates of Campylobacter resistance make advisable a more conservative policy for the use of antibiotics in farm animals.

The blaESBL and blaAmpC genes in Enterobacteriaceae are spread by plasmid-mediated integrons, insertion sequences, and transposons, some of which are homologous in bacteria from food animals, foods, and humans. These genes have been frequently identified in Escherichia coli and Salmonella from food animals, the most common being blaCTX-M-1, blaCTX-M-14, and blaCMY-2. Identification of risk factors for their occurrence in food animals is complex. In addition to generic antimicrobial use, cephalosporin usage is an important risk factor for selection and spread of these genes. Extensive international trade of animals is a further risk factor. There are no data on the effectiveness of individual control options in reducing public health risks. A highly effective option would be to stop or restrict cephalosporin usage in food animals. Decreasing total antimicrobial use is also of high priority. Implementation of measures to limit strain dissemination (increasing farm biosecurity, controls in animal trade, and other general postharvest controls) are also important.

Enterococci are natural inhabitants of the intestinal tract in humans and many animals, including food-producing and companion animals. They can easily contaminate the food and the environment, entering the food chain. Moreover, is an important opportunistic pathogen, especially the species and , causing a wide variety of infections. This microorganism not only contains intrinsic resistance mechanisms to several antimicrobial agents, but also has the capacity to acquire new mechanisms of antimicrobial resistance. In this review we analyze the diversity of enterococcal species and their distribution in the intestinal tract of animals. Moreover, resistance mechanisms for different classes of antimicrobials of clinical relevance are reviewed, as well as the epidemiology of multidrug-resistant enterococci of animal origin, with special attention given to beta-lactams, glycopeptides, and linezolid. The emergence of new antimicrobial resistance genes in enterococci of animal origin, such as and , is highlighted. The molecular epidemiology and the population structure of and isolates in farm and companion animals is presented. Moreover, the types of plasmids that carry the antimicrobial resistance genes in enterococci of animal origin are reviewed.