Abstract
Antibiotic resistance has turned into a global public health issue. Enterococci are intrinsically resistant to many antimicrobials groups. These bacteria colonize dairy and meat products and integrate the autochthonous microbiota of mammal’s gastrointestinal tract. Over the last decades, detection of vanA genotype in Enterococcus faecium from animals and from food of animal origin has been reported. Vancomycin-resistant E. faecium has become a prevalent nosocomial pathogen. Hospitalized patients are frequently treated with broad-spectrum antimicrobials and this leads to an increase in the presence of VanA or VanB vancomycin-resistant enterococci in patients’ gastrointestinal tract and the risk of invasive infections. In humans, E. faecium is the main reservoir of VanA and VanB phenotypes. Acquisition of high-level aminoglycoside resistance is a significant therapeutic problem for patients with severe infections because it negates the synergistic effect between aminoglycosides and a cell-wall-active agent. The aac(6′)-Ie-aph (2″)-Ia gene is widely spread in E. faecalis and has been detected in strains of human origin and in the food of animal origin. Enzyme AAC(6′)-Ie-APH(2″)-Ia confers resistance to available aminoglycosides, except to streptomycin. Due to the fast dissemination of this genetic determinant, the impact of its horizontal transferability among enterococcal species from different origin has been considered. The extensive use of antibiotics in food-producing animals contributes to an increase in drug-resistant animal bacteria that can be transmitted to humans. Innovation is needed for the development of new antibacterial drugs and for the design of combination therapies with conventional antibiotics. Nowadays, semi-purified bacteriocins and probiotics are becoming an attractive alternative to the antibiotic in animal production. Therefore, a better understanding of a complex and relevant issue for Public Health such as high-level vancomycin and gentamicin resistance in enterococci and their impact is needed. Hence, it is necessary to consider the spread of vanA E. faecium and high-level gentamicin resistant E. faecalis strains of different origin in the environment, and also highlight the potential horizontal transferability of these resistance determinants to other bacteria.
Highlights
Enterococci are resistant to diverse physicochemical conditions and are widespread in nature
The microbiological and ecological factors that contribute with intestinal colonization are unknown, even though up to 108 CFU/g of enterococci have been found in human feces
Despite the use of antibiotics as growth promoters has been forbidden in many countries, worldwide, foods supplemented with antimicrobials are freely acquired in several countries with no veterinarian control, including in Argentina
Summary
Enterococci are resistant to diverse physicochemical conditions and are widespread in nature. Despite the use of antibiotics as growth promoters has been forbidden in many countries, worldwide, foods supplemented with antimicrobials are freely acquired in several countries with no veterinarian control, including in Argentina. This leads to bacterial exposure to subtherapeutic concentrations of antibiotics and, it may promote the expression of antibiotic resistance (Andersson and Hughes, 2014). The concentration of antimicrobials used for growth promotion has often been lower than that used for therapy and prophylaxis These sub-therapeutic doses of antibiotics often create an auspicious condition for selecting antibiotic resistant bacteria (Van Immerseel et al, 2004; Dibner and Richards, 2005). Enterococci, due to their characteristics of gastrointestinal colonization, environmental persistence, natural and acquired resistance to different antimicrobials and their availability to transfer genes horizontally, can be used as biomarkers of antimicrobial resistance in intensive husbandry
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