Characterization of Veterinary Hospital-Associated Isolates of Enterococcus Species in Korea
Characterization of Veterinary Hospital-Associated Isolates of Enterococcus Species in Korea
Journal of Microbiology and Biotechnology. 2014. Mar, 24(3): 386-393
Copyright © 2014, The Korean Society For Microbiology And Biotechnology
  • Received : October 24, 2013
  • Accepted : November 24, 2013
  • Published : March 28, 2014
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About the Authors
Yeon Soo Chung
Department of Veterinary Microbiology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Ka Hee Kwon
Department of Veterinary Microbiology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Sook Shin
Department of Veterinary Microbiology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Jae Hong Kim
Department of Veterinary Microbiology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Yong Ho Park
Department of Veterinary Microbiology, College of Veterinary Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Jang Won Yoon
College of Veterinary Medicine, Kangwon National University, Chuncheon 200-701, Republic of Korea

Possible cross-transmission of hospital-associated enterococci between human patients, medical staff, and hospital environments has been extensively studied. However, limited information is available for veterinary hospital-associated Enterococcus isolates. This study investigated the possibility of cross-transmission of antibiotic-resistant enterococci between dog patients, their owners, veterinary staff, and hospital environments. Swab samples ( n = 465) were obtained from five veterinary hospitals in Seoul, Korea, during 2011. Forty-three Enterococcus strains were isolated, representing seven enterococcal species. E. faecalis and E. faecium were the most dominant species (16 isolates each, 37.2%). Although slight differences in the antibiotic resistance profiles were observed between the phenotypic and the genotypic data, our antibiogram analysis demonstrated high prevalence of the multiple drug-resistant (MDR) isolates of E. faecalis (10/16 isolates, 62.5%) and E. faecium (12/16 isolates, 75.0%). Pulsed-field gel electrophoretic comparison of the MDR isolates revealed three different clonal sets of E. faecalis and a single set of E. faecium , which were isolated from different sample groups or dog patients at the same or two separate veterinary hospitals. These results imply a strong possibility of cross-transmission of the antibiotic-resistant enterococcal species between animal patients, owners, veterinary staff, and hospital environments.
Enterococci are saprophytic, Gram-positive, facultative anaerobes that often occur in pairs or short chains. As part of commensal inhabitants that belong to the normal gastrointestinal microflora of humans and animals [1] , the microorganisms are known to be commonly isolated from several food sources, including meats and milk products, as well as from various natural environments [12] . Thus, they were originally considered harmless to humans [10] . However, enterococci have recently emerged and been recognized as one of the leading causative agents of nosocomial infections, especially for species that have multiple drug resistance (MDR) [7 , 30] .
Human infections caused by enterococci are frequently associated with bacteremia, urinary tract infections, endocarditis, and meningitis [15 , 27] . Moreover, the microorganisms can easily acquire antibiotic resistance by either genetic mutation or horizontal gene transfer via certain mobile genetic elements such as transposons, bacteriophages, and plasmids [13 , 20 , 25] . As a result, they possess intrinsic or acquired antibiotic resistance properties against several antibiotics, including glycopeptides, β-lactams, fluoroquinolones, and high levels of aminoglycosides, including gentamicin and streptomycin [6] . Recently, the development of MDR among enterococcal species has become a major public health issue worldwide, partially driven by the overuse or abuse of antibiotics in both human and veterinary practices.
Enterococci thrive well in harsh environments. They can persist on various ex vivo environments, such as medical equipment and/or dry hospital surfaces, aided by their tolerance to heat, chlorine, and alcohol [5 , 11 , 13] . Thus, it has been hypothesized that enterococci are widely disseminated in hospital environments. Supporting this notion, hospital-acquired enterococcal infections have been extensively reported in human health care units [2 , 31] . Indeed, it has been reported that enterococcal isolates are ranked as the second most important pathogens among the intensive care unit-acquired bloodstream infections in Europe [2] . However, much less attention has been given to companion animal patients and their contribution to the cross-transmission of the antibiotic-resistant enterococci within and/or between veterinary hospitals. Only a few studies have reported on the possibility of cross-transmission of antibiotic-resistant bacteria or some pathogenic clones between companion animals and hospital environments in small animal clinics [11] .
In this study, veterinary hospital-associated Enterococcus species were isolated and identified from samples acquired from dog patients, their owners, veterinary staff, and hospital environments in five veterinary hospitals in Seoul, Korea, during 2011. The antibiotic resistance profiles and molecular fingerprints of the isolates were determined to compare their clonality.
Materials and Methods
- Sampling
A total of 465 swab samples were collected from four private small veterinary clinics and one veterinary teaching hospital in Seoul, Korea, throughout 2011. All the individual samples from 171 dog patients (external auditory meatus, 43 samples; medial canthus, 43 samples; interdigital cleft, 42 samples; nasal cavity, 2 samples; skin, 1 sample; anus, 40 samples), 123 pet owners (external auditory meatus, 41 samples; nasal cavity, 41 samples; medial side of a rms, 4 0 samples; medial c anthus, 1 sample), 1 50 v eterinary staff members (external auditory meatus, 50 samples; nasal cavity, 50 samples; medial side of arms, 50 samples), and 21 hospital environments (tables, otoscopes, stethoscopes, elephones, computer keyboards, floor, and sinks; 3 samples each) were aseptically obtained, immediately placed into the individual sterile collection tubes containing Amies transport medium (Yu-Han Lab Tech, Korea), and transported on ice to the laboratory within 6 h after collection. Each human sample was routinely taken from the external auditory meatus, nasal cavity, medial side of the arms, and medial canthus. Each animal sample was routinely acquired from the external auditory meatus, medial canthus, interdigital cleft, nasal cavity, skin, and anus. Each environmental sample was routinely taken from tables, otoscopes, stethoscopes, telephones, computer keyboards, floors, and sinks in the veterinary hospitals.
- Isolation and Identification of Enterococcus Species
All the swab samples were streaked on 5% sheep blood agar plates (Komed, Seongnam, Korea) and incubated at 37℃ for 24 h. Putative Enterococcus spp. were isolated according to a standard protocol previously established in our laboratory [24] . For species differentiation, both the genus-specific polymerase chain reaction (PCR) identification method [23] and the VITEK 2 bacterial identification system (BioMerieux, Craponne, France) were carried out based on the manufacturer’s instructions. For further confirmation, E. faecalis and E. faecium were identified by species-specific PCR [14] , whereas the other Enterococcus spp. were identified by 16S ribosomal RNA sequencing [14 , 16] . The PCR primers in this study are shown in Table 1 .
- Antibiotic Resistance Profiling
Antibiotic susceptibility was determined by a standard disk diffusion test [29] with the following antibiotic disks (Becton Dickinson, Sparks, MD, USA): tetracycline (TE, 30 μg), chloramphenicol (C, 30 μg), erythromycin (E, 15 μg), quinupristin/dalfopristin (SYN, 15 μg), ciprofloxacin (CIP, 5 μg), ampicillin (AM, 10 μg), vancomycin (VA, 30 μg), high-level gentamicin (HLG, 120 μg), high-level streptomycin (HLS, 300 μg), teicoplanin (TEC, 30 μg), and linezolid (LZD, 30 μg). The interpretation of antibiotic resistance, intermediate resistance, or susceptibility was done as described by the Clinical and Laboratory Standards Institute guidelines [29] . E. faecalis ATCC 29212 (American Type Culture Collection, Manassas, VA, USA) was used as the reference strain. The MDR isolates were defined as Enterococcus isolates resistant to three or more different categories of the evaluated antibiotics [22] .
- Detection of the Antibiotic Resistance Genes
To determine the mechanisms of antimicrobial resistance among the antibiotic-resistant Enterococcus isolates, all the isolates resistant to vancomycin, erythromycin, tetracycline, chloramphenicol, high-level gentamicin, and high-level streptomycin were PCR-screened for the presence of the following six resistance genes; vancomycin ( vanA and vanB ), erythromycin ( ermB ), tetracycline ( tetM and tetL ) [26] , chloramphenicol ( cat ), high-level gentamicin ( aac6' -Ie- aph2" -Ia), and high-level streptomycin ( ant6 -Ia) [21] . The PCR primers specific to the individual target genes are listed in Table 1 .
Oligonucleotide sequences used in this study.
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Oligonucleotide sequences used in this study.
- Molecular Fingerprinting
The genetic relatedness among the antibiotic-resistant Enterococcus isolates was determined by standard pulsed-field gel electrophoresis (PFGE) using CHEF MAPPER (Bio-Rad, Hercules, CA, USA) as described by the manufacture. In brief, bacterial cells from an overnight culture in 3 ml of Tryptic Soy Broth (Becton Dickinson) were pelleted at 13,000 rpm for 5 min. The pelleted cells were embedded in 1.6% agarose plugs and lysed by lysozyme (Sigma-Aldrich, St. Louis, MO, USA) and proteinase K (Sigma-Aldrich). Lysed plugs were then digested overnight with 40 U of Sma I (New England Biolabs, Waltham, MA, USA) at 25℃. Digested plugs were placed on 1.2% SeaKem Gold agarose (Lonza, Allendale, NJ, USA) and PFGE was carried out at 6.0 V for 19 h with a ramped pulse time of 1-20 sec in 0.5× Tris-Borate-EDTA (TBE) buffer at 14℃. BioNumerics software (Applied Maths, Sint-Martens-Latem, Belgium) was used to establish a DNA similarity matrix using the Dice coefficient (0.5% optimization, 1.0% tolerance) and the un-weighted pair group method (UPGMA). All statistical comparisons were performed using the chi-square test and the SPSS ver. 12 software (SPSS, Chicago, IL, USA).
Results and Discussion
In this study, 43 veterinary hospital-associated Enterococcus strains from five veterinary hospitals in Seoul, Korea, were isolated, speciated, and characterized for their antibiotic resistance profiles as well as molecular fingerprints to determine genetic similarities between those isolates. Our results imply a strong possibility of cross-transmission between dog patients, their owners, veterinary staff, and hospital environments within and/or among veterinary hospitals in Korea.
- Prevalence of Enterococcus spp. from the Veterinary Hospital-Associated Swab Samples
Among the 465 veterinary hospital-associated swab samples analyzed, 43 Enterococcus spp. (9.2%) were isolated and further differentiated into seven different species: E. faecalis, E. faecium, E. hirae, E. gallinarum, E. casseliflavus, E. canintestini, and E. dispar ( Table 2 ). Our results showed that both E. faecalis (16/43 isolates; 37.2%) and E. faecium (16/43; 37.2%) were the most dominant Enterococcus spp., collectively accounting for 74.4% of the total Enterococcus isolates ( Table 2 ). Interestingly, both E. faecalis and E. faecium are also known as the predominant species involved in human infections [28] . Other Enterococcus spp. were also isolated but seemed to be rare [23] , which included E. hirae (4/43 isolates; 8.5%), E. gallinarum (3/43; 6.4%), E. canintestini (2/43; 4.7%), E. casseliflavus (1/43; 2.3%), and E. dispar (1/43; 2.3%) ( Table 2 ). Notably, a higher prevalence of Enterococcus spp. in the samples of dog patients (33/171 isolates; 19.3%) and hospital environment (3/21; 14.3%) was observed than those of pet owners (3/123; 2.4%) and veterinary staff (4/150; 2.7%). Taken together, our results demonstrate that E. faecalis and E. faecium were most prevalent among the veterinary hospital-associated Enterococcus spp. in Korea, which is consistent with previous studies in Portugal and the United States [18 , 30] .
Prevalence ofEnterococcusspp. from veterinary hospitals in Korea, 2011.
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aIncludes E. casseliflavus, E. canintestini, and E. dispar. bSamples from veterinary hospital environments.
- Phenotypic Characterization of Antibiotic Resistance Among E. faecalis and E. faecium Isolates
The antibiotic resistance profiles were examined for all the E. faecalis and E. faecium isolates because they were the most predominant Enterococcus spp. related with veterinary hospitals in Korea ( Table 2 ). None of the 32 isolates displayed vancomycin resistance using a standard disk diffusion test ( Table 3 ). Similar to our observation, previous studies have reported very rare detection of vancomycin-resistant Enterococcus (VRE) isolates from veterinary medical equipment or domestic animals, such as dogs and cats, in small animal clinics [19 , 23] . Therefore, it appears that VRE strains are not yet prevalent in veterinary hospitals or environments, unlike in human hospitals or environments. The glycopeptide antibiotic avoparcin can induce cross-resistance with vancomycin [6] . In Korea, however, the use of avoparcin in feed and feed additives has been banned since 1998. The absence of VRE in the veterinary hospitals examined in this study might be directly or indirectly related with the governmental ban on the use of avoparcin.
As shown in Table 3 , however, our antibiogram analyses revealed that the antibiotic resistance rates of the E. faecalis isolates were 68.8% and 56.3% for tetracycline (11/16 isolates) and erythromycin (9/16), respectively, which were followed by 37.6% for chloramphenicol 6/16) and 6.25% for both high-level gentamicin and high-level streptomycin (1/16 each). Although limited information has been available, a recent study in the United States revealed that resistance to enrofloxacin (73.0%), erythromycin (53.9%), ampicillin (51.0%), and doxycycline (42.9%) was detected among 115 E. faecium isolates from small animal clinics [23] , suggesting that the resistance profiles are similar to those in Korea. Since their intrinsic resistance against quinupristin/dalfopristin has been well established [3 , 9] , we originally decided to exclude evaluation of quinupristin/dalfopristin resistance among the E. faecalis isolates. However, a recent study demonstrated that some clinical strains of E. faecalis carry premature stop codons in the lsa gene responsible for quinupristin/dalfopristin resistance [8] . In support of the latter observation, four E. faecalis isolates were susceptible to quinupristin/dalfopristin, implying that such a nonsense mutation might be increased among strains of E. faecalis . In comparison, the antibiotic resistance rates of the E. faecium isolates were 81.3% for tetracycline and ampicillin (13/16 isolates each), followed by 68.8% for erythromycin and ciprofloxacin (11/16 each), 56.3% for high-level gentamicin (9/16), and 37.5% for high-level streptomycin (6/16) ( Table 3 ). It is noteworthy that most of the E. faecalis and E. faecium isolates were resistant to tetracycline (24/32 isolates; 75.0%) and erythromycin (20/32; 62.5%) ( Table 3 ).
It is known that enterococci are intrinsically resistant to several antibiotics and can readily accumulate certain genetic mutations and exogenous genes that confer additional resistance [1 , 4] . In support of this observation, 68.8% of the E. faecalis and E. faecium isolates displayed the MDR phenotypes; 10/16 isolates (62.5%) for E. faecalis and 12/16 (75.5%) for E. faecium . The 10 MDR isolates of E. faecalis were resistant to three (5 isolates; 50%) or four (5 isolates; 50%) different antibiotics evaluated, whereas the 12 MDR isolates of E. faecium were resistant to four (3 isolates; 25.0%) or five (9 isolates; 75.0%) different antibiotics. All the E. faecalis and E. faecium isolates were susceptible to linezolid and teicoplanin (data not shown).
- Detection of the Antibiotic Resistance Genes Among the Resistant E. faecalis and E. faecium Isolates
To evaluate the presence of appropriate antibiotic resistance genes in the resistant E. faecalis and E. faecium isolates ( Table 3 ), PCR was carried out with the previously established primers ( Table 1 ) specific to individual resistance genes: vanA and vanB for resistance to vancomycin, ermB for erythromycin, tetM and tetL for tetracycline, cat for chloramphenicol, aac6' -Ie- aph2" -Ia for high-level gentamicin, and ant6 -Ia for high-level streptomycin. As summarized in Table 4 , almost all the resistant E. faecalis and E. faecium isolates carried the appropriate resistance genes with minor exceptions, implying the existence of alternative resistance mechanisms. In agreement with the disk diffusion assay results, vanA and vanB genes were not detected (data not shown).
Antibiotic resistance profiling of theE. faecalisandE. faeciumisolates.
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aAbbreviations: VA (Vancomycin), E (Erythromycin), TE (Tetracycline), C (Chloramphenicol), HLG (High-level gentamicin), HLS (High-level streptomycin), AM (Ampicillin), CIP (Ciprofloxacin), SYN (quinupristin/dalfopristin), TEC (teicoplanin), LZD (linezolid), and MDR (Multiple drug resistance). bSamples from veterinary hospital environments.
Among the 11 E. faecalis and 13 E. faecium isolates resistant to tetracycline, 23 isolates (95.8%) harbored the tetM gene. Not surprisingly, the 13 tetracycline-resistant and tetM -positive isolates (13/23; 56.5%) also possessed the tetL gene ( Table 4 ). The ermB gene was widely distributed among the erythromycin-resistant isolates (18/20; 90.0%) ( Table 4 ). Almost all the high-level gentamicin (9/10; 90.0%)- or high-level streptomycin-resistant isolates (6/7; 85.7%) carried the bifunctional gentamicin resistance gene ( aac6' -Ie- aph2" -Ia) or the streptomycin resistance gene ( ant6 -Ia) ( Table 4 ). Interestingly, there was a significant difference in the presence of the aac6' -Ie- aph2" -Ia gene between E. faecalis and E. faecium isolates ( Table 4 ; p < 0.05). However, such a difference between E. faecalis and E. faecium would not be a species-specific pattern because the same resistance gene has been detected among the gentamicin-resistant E. faecalis isolates from dog and cats in the US [17 , 18] .
Detection of the antibiotic resistance genes among the resistant isolates ofE. faecalisandE. faecium.
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aermB, erythromycin resistance gene; tetM & tetL, tetracycline resistance gene; cat, chloramphenicol resistance gene; aac6'-Ie-aph2"-Ia, high-level gentamicin resistance gene; ant6-Ia, high-level streptomycin resistance gene.
- Genetic Relatedness Between the Antibiotic-Resistant Isolates of E. faecalis or E. faecium
To determine the genetic relatedness between the veterinary hospital-associated Enterococcus isolates, 27 antibiotic-resistant E. faecalis and E. faecium isolates were analyzed by PFGE (see Materials and Methods) because of their clinical importance. The analysis with the 13 E. faecalis isolates revealed three different sets (Type A to C), which were almost identical in their molecular patterns ( Fig. 1 A). Types A and C originated at the same veterinary hospital from different sample groups (Type A) or dog patients (Type C) ( Fig. 1 A). They also shared their own antibiogram profiles ( Fig. 1 A). These results indicate that Type A or C might be the same clonal sets. PFGE analysis with the 14 E. faecium isolates showed the single identical set in their molecular patterns (Type D; Fig. 1 B); Type D was isolated from the different sample groups at the same veterinary hospital and showed a slight difference in antibiogram profiles ( Fig. 1 B).
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PFGE analysis of the 13 E. faecalis (A) and 14 E. faecium (B) isolates resistant to antibiotics. All the genomic DNAs were digested with SmaI followed by standard PFGE analysis (see Materials and Methods). Levels of similarity were determined using Dice coefficient (0.5% optimization, 1.0% tolerance) and the unweighted pair group method. Individual PFGE patterns are summarized with their antibiotic resistance profiles, sample groups, veterinary hospitals where the samples were collected, and sample sources. Abbreviations: E, erythromycin; TE, tetracycline; C, chloramphenicol; HLG, high-level gentamicin; HLS, high-level streptomycin; AM, ampicillin; CIP, ciprofloxacin; SYN, quinupristin/dalfopristin.
In conclusion, our experimental analysis revealed a low contamination of enterococci among veterinary hospital-associated swab samples in Korea. Although no VRE isolates were identified, 68.8% of the E. faecalis and E. faecium isolates displayed the MDR phenotypes. More importantly,the PFGE data strongly indicate the possibility for cross-transmission of antibiotic-resistant Enterococcus clones among veterinary hospital-associated environments, such as dog patients, their owners, veterinary staff, and hospital environments. To the best of our knowledge, this is the first report on the existence of a potential clonal set of the antibiotic-resistant E. faecalis isolates from different sample groups, namely dog patients and veterinary staff, at the same animal hospital in Korea. Proper hygiene, effective infection control, and restricted movement of companion animal patients in veterinary hospitals would be prudent.
This study was supported by a grant (Z-AD13-2011-11-06) from the Animal and Plant Quarantine Agency, Ministry of Food, Agriculture, Forestry, and Fisheries, Republic of Korea in 2011.
Arias CA , Murray BE 2012 The rise of the Enterococcus: beyond vancomycin resistance. Nat. Rev. Microbiol. 10 266 - 278    DOI : 10.1038/nrmicro2761
Bohme H , Konigsmark C , Klare I , Zischka M , Werner G 2012 Cross-transmission rates of enterococcal isolates among newborns in a neonatal intensive care unit. Pediatr. Rep. 4 e15 -    DOI : 10.4081/pr.2012.e15
Bozdogan B , Leclercq R 1999 Effects of genes encoding resistance to streptogramins A and B on the activity of quinupristin-dalfopristin against Enterococcus faecium. Antimicrob. Agents Chemother. 43 2720 - 2725
Cauwerts K , Decostere A , De Graef EM , Haesebrouck F , Pasmans F 2007 High prevalence of tetracycline resistance in Enterococcus isolates from broilers carrying the erm(B) gene. Avian Pathol. 36 395 - 399    DOI : 10.1080/03079450701589167
Cetinkaya Y , Falk P , Mayhall CG 2000 Vancomycinresistant enterococci. Clin. Microbiol. Rev. 13 686 - 707    DOI : 10.1128/CMR.13.4.686-707.2000
Clark NC , Cooksey RC , Hill BC , Swenson JM , Tenover FC 1993 Characterization of glycopeptide-resistant enterococci from U.S. hospitals. Antimicrob. Agents Chemother. 37 2311 - 2317    DOI : 10.1128/AAC.37.11.2311
Clewell DB 1990 Movable genetic elements and antibiotic resistance in enterococci. Eur. J. Clin. Microbiol. Infect. Dis. 9 90 - 102    DOI : 10.1007/BF01963632
Dina J , Malbruny B , Leclercq R 2003 Nonsense mutations in the lsa-like gene in Enterococcus faecalis isolates susceptible to lincosamides and streptogramins A. Antimicrob. Agents Chemother. 47 2307 - 2309    DOI : 10.1128/AAC.47.7.2307-2309.2003
Duh RW , Singh KV , Malathum K , Murray BE 2001 In vitro activity of 19 antimicrobial agents against enterococci from healthy subjects and hospitalized patients and use of an ace gene probe from Enterococcus faecalis for species identification. Microb. Drug Resist. 7 39 - 46    DOI : 10.1089/107662901750152765
Dupre I , Zanetti S , Schito AM , Fadda G , Sechi LA 2003 Incidence of virulence determinants in clinical Enterococcus faecium and Enterococcus faecalis isolates collected in Sardinia (Italy). J. Med. Microbiol. 52 491 - 498    DOI : 10.1099/jmm.0.05038-0
Fisher K , Phillips C 2009 The ecology, epidemiology and virulence of Enterococcus. Microbiology 155 1749 - 1757    DOI : 10.1099/mic.0.026385-0
Ghosh A , Kukanich K , Brown CE , Zurek L 2012 Resident cats in small animal veterinary hospitals carry multi-drug resistant enterococci and are likely involved in crosscontamination of the hospital environment. Front Microbiol. 3 62 -    DOI : 10.3389/fmicb.2012.00062
Giraffa G 2002 Enterococci from foods. FEMS Microbiol. Rev. 26 163 - 171    DOI : 10.1111/j.1574-6976.2002.tb00608.x
Hummel A , Holzapfel WH , Franz CM 2007 Characterisation and transfer of antibiotic resistance genes from enterococci isolated from food. Syst. Appl. Microbiol. 30 1 - 7    DOI : 10.1016/j.syapm.2006.02.004
Huycke MM , Sahm DF , Gilmore MS 1998 Multiple-drug resistant enterococci: the nature of the problem and an agenda for the future. Emerg. Infect. Dis. 4 239 - 249    DOI : 10.3201/eid0402.980211
Jackson CR , Fedorka-Cray PJ , Barrett JB 2004 Use of a genus- and species-specific multiplex PCR for identification of enterococci. J. Clin. Microbiol. 42 3558 - 3565    DOI : 10.1128/JCM.42.8.3558-3565.2004
Jackson CR , Fedorka-Cray PJ , Davis JA , Barrett JB , Brousse JH , Gustafson J , Kucher M 2010 Mechanisms of antimicrobial resistance and genetic relatedness among enterococci isolated from dogs and cats in the United States. J. Appl. Microbiol. 108 2171 - 2179
Jackson CR , Fedorka-Cray PJ , Davis JA , Barrett JB , Frye JG 2009 Prevalence, species distribution and antimicrobial resistance of enterococci isolated from dogs and cats in the United States. J. Appl. Microbiol. 107 1269 - 1278    DOI : 10.1111/j.1365-2672.2009.04310.x
Jensen LB , Frimodt-Moller N , Aarestrup FM 1999 Presence of erm gene classes in gram-positive bacteria of animal and human origin in Denmark. FEMS Microbiol. Lett. 170 151 - 158    DOI : 10.1111/j.1574-6968.1999.tb13368.x
Ke D , Picard FJ , Martineau F , Menard C , Roy PH , Ouellette M , Bergeron MG 1999 Development of a PCR assay for rapid detection of enterococci. J. Clin. Microbiol. 37 3497 - 3503
Kobayashi N , Alam M , Nishimoto Y , Urasawa S , Uehara N , Watanabe N 2001 Distribution of aminoglycoside resistance genes in recent clinical isolates of Enterococcus faecalis, Enterococcus faecium and Enterococcus avium. Epidemiol. Infect. 126 197 - 204    DOI : 10.1017/S0950268801005271
Kos VN , Desjardins CA , Griggs A , Cerqueira G , Van Tonder A , Holden MT 2012 Comparative genomics of vancomycin-resistant Staphylococcus aureus strains and their positions within the clade most commonly associated with methicillin-resistant S. aureus hospital-acquired infection in the United States. MBio. 3    DOI : 10.1128/mBio.00112-12
KuKanich KS , Ghosh A , Skarbek JV , Lothamer KM , Zurek L 2012 Surveillance of bacterial contamination in small animal veterinary hospitals with special focus on antimicrobial resistance and virulence traits of enterococci. J. Am. Vet. Med. Assoc. 240 437 - 445    DOI : 10.2460/javma.240.4.437
Kwon KH , Hwang SY , Moon BY , Park YK , Shin S , Hwang CY , Park YH 2012 Occurrence of antimicrobial resistance and virulence genes, and distribution of enterococcal clonal complex 17 from animals and human beings in Korea. J. Vet. Diagn. Invest. 24 924 - 931    DOI : 10.1177/1040638712455634
Magiorakos AP , Srinivasan A , Carey RB , Carmeli Y , Falagas ME , Giske CG 2012 Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin. Microbiol. Infect. 18 268 - 281    DOI : 10.1111/j.1469-0691.2011.03570.x
Malhotra-Kumar S , Lammens C , Piessens J , Goossens H 2005 Multiplex PCR for simultaneous detection of macrolide and tetracycline resistance determinants in streptococci. Antimicrob. Agents Chemother. 49 4798 - 4800    DOI : 10.1128/AAC.49.11.4798-4800.2005
Marothi YA , Agnihotri H , Dubey D 2005 Enterococcal resistance - an overview. Indian J. Med. Microbiol. 23 214 - 219
Murray BE 1990 The life and times of the Enterococcus. Clin. Microbiol. Rev. 3 46 - 65
NCCLS 2009 Performance Standards for Antimicrobial Susceptibility Testing, Nineteenth Informational Supplement. CLSI document M100-S19 NCCLS Wayne, PA.
Poeta P , Costa D , Rodrigues J , Torres C 2006 Antimicrobial resistance and the mechanisms implicated in faecal enterococci from healthy humans, poultry and pets in Portugal. Int. J. Antimicrob. Agents 27 131 - 137    DOI : 10.1016/j.ijantimicag.2005.09.018
Top J , Willems R , van der Velden S , Asbroek M , Bonten M 2008 Emergence of clonal complex 17 Enterococcus faecium in The Netherlands. J. Clin. Microbiol. 46 214 - 219    DOI : 10.1128/JCM.01351-07