You can teach old pathogens new tricks: the zoonotic potential of Escherichia coli, Clostridium difficile, Staphylococcus aureus, and enterococci, or from Noah's Ark to Pandora's Box

Abstract

Think of your typical infectious disease agent of major morbidity and mortality today: you will probably think of Escherichia coli and other Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecium and Enterococcus faecalis, Klebsiella spp., Pseudomonas aeruginosa, or Acinetobacter baumannii. You will probably think of antimicrobial resistance, of hospital-acquired infections, of intensive-care or surgical units, of the need for implementation of strict institutional measures for avoiding the spread of resistance, of resistance genes and plasmids travelling around the world and necessitating the urgent development of novel antimicrobials, or the ideal public health policies for avoiding resistance becoming entrenched in a healthcare setting. From this perspective, you will rarely think of a community-acquired infection, except perhaps for MRSA. But are we missing the whole picture? Random, but consistent, evidence has been accumulating in recent decades, constructing a complex framework, and underlining the existence of an overlooked infectious disease reservoir of uncertain significance: animals. The extent and burden of typical zoonotic infections has been the subject of a past theme issue in this journal, but the zoonotic nature of MRSA, E. coli and enterococci is increasingly being recognized. On the other hand, A. baumannii has not been implicated in zoonotic transmission: there have been observations of an increased prevalence of A. baumannii in the human body louse [1La Scola B Raoult D Acinetobacter baumannii in human body louse.Emerg Infect Dis. 2004; 10: 1671-1673Crossref PubMed Scopus (79) Google Scholar], but whether the pathogen utilizes the humans as reservoirs for the infection of lice or vice versa has not been adequately clarified. The present issue hosts four reviews that discuss the zoonotic potential and significance of three of the classic pathogens (E. coli, MRSA, and enterococci), as well as of an emerging public health infectious threat, that of Clostridium difficile. These exhaustive reviews summarize the diverse epidemiological, clinical and experimental knowledge that is gradually accumulating: the zoonotic gene transfer risks of Enterococcus faecium and the potential zoonotic nature of Enterococcus faecalis are highlighted in the review by Annette Hammerum [2Hammerum AM Enterococci of animal origin and their significance for public health.Clin Microbiol Infect. 2012; 18: 619-625Abstract Full Text Full Text PDF PubMed Scopus (178) Google Scholar]; the importance of the zoonotic MRSA reservoir, referring both to companion animals and to the food-chain industry, and the characteristics of the human-animal interaction are discussed by Iris Spiliopoulou and Efthimia Petinaki [3Petinaki E Spiliopoulou I Methicillin-resistant Staphylococcus aureus among companion and food-chain animals: impact of human contacts.Clin Microbiol Infect. 2012; 18: 626-634Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar]; the significance for humans of the circumstantial presence of a C. difficile type in pigs and calves is reviewed by Marjolein Hensgens and colleagues[4Hensgens MPM Keessen EC Squire MM et al.Clostridium difficile infection in the community: a zoonotic disease?.Clin Microbiol Infect. 2012; 18: 635-645Abstract Full Text Full Text PDF PubMed Scopus (233) Google Scholar] in a Netherlands-Australia collaborative work; and the extremely complex situation of the presence of extended-spectrum β-lactamase (ESBL)-producing E. coli strains is thoroughly presented by Christa Ewers and colleagues [5Ewers C Bethe A Semmler T Guenther S Wieler LH Extended-spectrum β-lactamase-producing and AmpC-producing Escherichia coli from livestock and companion animals and their putative impact on public health: a global perspective.Clin Microbiol Infect. 2012; 18: 646-655Abstract Full Text Full Text PDF PubMed Scopus (473) Google Scholar]. These reviews tell us that we are far from fully understanding the complete extent of the actual zoonotic nature of these pathogens, but also that we are obliged to investigate this nature in detail. A recent research article published in this journal [6Leverstein-van Hall MA Dierikx CM Cohen Stuart J et al.Dutch patients, retail chicken meat and poultry share the same extended-spectrum β-lactamase genes, plasmids, and strains.Clin Microbiol Infect. 2011; 17: 873-880Abstract Full Text Full Text PDF PubMed Scopus (546) Google Scholar] demonstrated persuasively that a percentage of the ESBL-producing E. coli-related human disease in The Netherlands can be attributed directly to an ESBL-producing strain of animal origin. Similar observations are being continuously published; in some studies, methodology may be an issue, regarding the need to exclude the possibility that humans may serve as reservoirs for animal colonization. However, there is a need to see the big picture, and to understand that our close relationship with animals, directly in our Noah's Ark, or indirectly through the food chain, may actually open a Pandora's Box with hitherto non-quantified consequences. No conflict of interest.