Enterococcus Faecalis, but Other Species Also Can Be Recovered
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Antibiotic resistant enterococci from food and clinical samples: microbiological characterization, molecular typing and genetic relation of strains Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Stefanie Petra Templer von Zürich Leiter der Arbeit: Dr. Andreas Baumgartner Bundesamt für Gesundheit Antibiotic resistant enterococci from food and clinical samples: microbiological characterization, molecular typing and genetic relation of strains Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Stefanie Petra Templer von Zürich Leiter der Arbeit: Dr. Andreas Baumgartner Bundesamt für Gesundheit Von der Philosophisch-naturwissenschaftlichen Fakultät angenommen. Bern, 19. Juni 2006 Der Dekan Prof. Dr. P. Messerli Table of Contents Table of Contents Introduction ................................................................................................................................2 1. Enterococci: a general overview ..................................................................................... 2 1.1 Historical perspective and genus definition................................................................. 2 2. Human and nonhuman reservoirs of enterococci ........................................................... 3 2.1 Host specificity of enterococci..................................................................................... 3 2.2 Distribution of enterococcal species in humans .......................................................... 4 2.3 Importance of animal reservoirs according to gene transfer to human enterococci... 5 2.4 Enterococci in Foods................................................................................................... 5 3. Enterococcal Virulence ................................................................................................... 7 3.1 Secreted Factors......................................................................................................... 7 3.2 Enterococcal Adhesins................................................................................................ 8 4. Acquired Antibiotic Resistances in Enterococci .............................................................. 9 4.1 β-lactam Resistance .................................................................................................. 10 4.2 Glycopeptide Resistance........................................................................................... 10 4.3 Macrolide Resistance................................................................................................ 11 4.4 Chloramphenicol Resistance..................................................................................... 11 4.5 Tetracycline Resistance ............................................................................................ 12 5. Conjugation and Genetic Exchange in Enterococci ...................................................... 12 5.1 Plasmids.................................................................................................................... 12 5.2 Transposons ............................................................................................................. 13 6. Enterococcal Disease and Treatment ........................................................................... 13 6.1 Clinical Disease......................................................................................................... 13 6.2 Treatment with antimicrobial agents.......................................................................... 14 Reference List Introduction ...................................................................................................... 15 Aim of the Work ....................................................................................................................... 21 Publications.............................................................................................................................. 22 Summary and Discussion ........................................................................................................ 68 Acknowledgments.................................................................................................................... 71 Curriculum Vitae ...................................................................................................................... 72 i Introduction INTRODUCTION 1. Enterococci: a general overview The enterococci are a complex and diverse group of bacteria in respect of their interactions with humans. Some enterococcal strains can be used in the production of fermented foods or as probiotics. At the same time, however, enterococci have been associated with a number of human and animal infections. Several virulence factors have been described and the number of vancomycin-resistant enterococci is increasing. However, enterococci occur ubiquitous and are prevailed in nearly everything we humans come into contact with. They are commonly found in the alimentary tracts of humans and other animals, in the soil and water, and in the foods. 1.1 Historical perspective and genus definition In 1899 Thiercelin et al. [62] described bacteria seen in pairs and short chains in human feces and called them “streptococcus of fecal origin”. Their publication is probably the first report on enterococci In the following years several researchers made discoveries of similar bacteria isolated from a cesspool or a case of acute endocarditis. In 1906, The name Streptococcus faecalis was used by Andrews and Horder [4] to identify an organism of fecal origin that clotted milk. Orla-Jensen [47] described a second organism of this group, Streptococcus faecium, which differed from the fermentation patterns of S. faecalis. In the following 30 years several other species came to the so called group “enterococcal streptococci” such as Streptococcus durans which was very similar to S. faecium but had less fermentation activity. In 1970, Kalina proposed that a genus for the enterococcal streptococci be established and suggested that, based on cellular arrangement and phenotypic characteristics, S. faecalis and S. faecium and their subspecies of these two taxons be named Enterococcus [38]. It took another 14 years, based on the publication of Schleifer and Klipper-Balz [53], until the genus Enterococcus has been generally accepted. Enterococci are gram-positive cocci that occur singly, in pairs, or as short chains. They are facultative anaerobes with an optimum growth temperature of 37°C and a growth range from 10 to 45°C. Growth also occurs in the presence of 6.5% NaCl, at pH 9.6, and enterococci survive heating at 60°C for 30 min. To date, 28 species have been added to the genus Enterococcus on the basis of phylogenetic evidence strengthened by 16S rRNA DNA sequencing and/or DNA – DNA hybridization studies. Characteristically, enterococci inhabit harsh environments like the intestinal tract of humans and animals. Growth under such hostile conditions demands metabolic flexibility. In 2 Introduction this respect, enterococci are capable of much more than simple sugar fermentation to produce lactic acid. These organisms readily catabolize a spectrum of energy sources including diverse carbohydrates, glycerol, lactate, malate, citrate, the diamino acids arginine and agmatibe, and many α-keto acids [35]. 2. Human and nonhuman reservoirs of enterococci Enterococci are a natural part of the intestinal flora in most mammals and birds. For almost a century, enterococci are used as indicators of fecal contamination of water and food for human consumption. The emergence of multiple antimicrobial-resistant strains worldwide, led to the awareness of enterococci being an important agent of human disease. Six years ago, an interdisciplinary federal team of researchers in Switzerland worked out a situation analysis with regard to antibiotic resistant microorganisms in human and veterinary medicine and in food [10]. They reasoned that the spread of antibiotic resistant microorganisms is in a first place retraced back to human medicine and the hospital environment, followed by the veterinary medicine. It was recognized that foods were important for the transfer of antibiotic resistance, but only in a third place. 2.1 Host specificity of enterococci Enterococci are ubiquitous and can therefore be found, aside the intestinal flora of mammals and birds, in soil, on plants, and in water. In water they are generally considered as fecal contaminants and belong mainly to the species Enterococcus faecium and Enterococcus faecalis, but other species also can be recovered. Some of the enterococcal species are typically associated with a certain environment or select animal species, which points to a moderate host specificity. Several enterococcal species, although identifiable in a number of hosts, can be divided into host-specific ecovars on the basis of phenotypic or genotypic characteristics. Phenotypically, E. faecium strains from poultry origin are frequently able to ferment raffinose, whereas this characteristic generally is not present in E. faecium strains from other origins [20]. Ahmed et al. recently published the results of a biochemical, phenotypic characterization of 4057 enterococcal isolates from surface water. Based on the biochemical phenotypes (BPTs), they traced the source of faecal contamination in a local creek. Furthermore, they were able to distinguish the enterococcal isolates between human and animal