The new Eurosurveillance website is almost here.

Eurosurveillance is on the updated list of the Directory of Open Access Journals and in the SHERPA/RoMEO database. Read more here.

On 6 June 2017, the World Health Organization (WHO) published updates to its ‘Essential Medicines List’ (EML). Read more here.

Follow Eurosurveillance on Twitter: @Eurosurveillanc

In this issue

Home Eurosurveillance Monthly Release  2006: Volume 11/ Issue 1 Article 7
Back to Table of Contents
en es fr

Eurosurveillance, Volume 11, Issue 1, 01 January 2006
Surveillance report
Emergence of MRSA infections in horses in a veterinary hospital: strain characterisation and comparison with MRSA from humans

Citation style for this article: Cuny C, Kuemmerle J, Stanek C, Willey B, Strommenger B, Witte W. Emergence of MRSA infections in horses in a veterinary hospital: strain characterisation and comparison with MRSA from humans. Euro Surveill. 2006;11(1):pii=595. Available online:


C Cuny1, J Kuemmerle1, C Stanek1, B Willey2, B Strommenger³, W Witte3

1. Veterinary University Vienna, Department V, Clinic of Orthopaedics, Austria
2. Department of Microbiology, Mount Sinai Hospital, Toronto, Ontario, Canada
3. Robert Koch-Institut, Wernigerode Branch, Wernigerode, Germany


Methicillin-resistant Staphylococcus aureus (MRSA) has become an emerging public health problem worldwide, no longer only associated with healthcare-associated infections. With the exception of some recent reports concerning infections in cats, dogs and horses, infections with MRSA in companion animals have been infrequently reported. Here we submit findings for MRSA infections in horses in a central European university veterinary hospital.
Methicillin-resistant Staphylococcus aureus (MRSA) has become a worldwide public health problem [1,2]. Increasing prevalence of healthcare-associated MRSA infections is usually associated with a wide dissemination of particular epidemic clonal lineages of the S. aureus population [3]. Since the late 1990s, MRSA has emerged in many countries as a cause of invasive skin infections in the community, independently from the healthcare setting [4-8]. In this context, colonisation and infections with MRSA in domestic animals are of particular interest with regard to a mutual dissemination between humans and animals. The first communication on MRSA infections in domestic animals concerned mastitis cases in dairy cows in Belgium in 1972 [9]. Since that time there have been reports of sporadic cases of infection with MRSA in a variety of other domestic animal species such as horses, chickens, dogs and cats [10-13]. MRSA infections in horses associated with wide dissemination of a particular clonal lineage have been recently documented in Canada [14,15].
Here we report on emergence of MRSA in a university veterinary hospital and on an assessment of the relation of human and animal MRSA isolates by means of molecular typing. This includes SmaI macrorestriction patterns, multilocus sequence typing (MLST) for assessing the core genome of S. aureus and characterisation of SCCmec elements of which at least 5 different groups have so far been described [16]. SCCmec (staphylococcal cassette chromosome mec) elements contain the mecA gene that codes for methicillin resistance [17].

Materials and methods

Description of the setting:
The Veterinary University of Vienna [Veterinärmedizinische Universität Wien, (VUW)] consists of a large hospital with separate departments for small animals, horses, farm animals, reproduction and diagnostic imaging/laboratory diagnostics. On average, 23 000-24 000 domestic animals including horses, ruminants, pigs, dogs, cats and rodents are admitted to hospital for a variety of diseases each year. Within the equine department there are separate clinic buildings for orthopaedics, soft tissue surgery and internal medicine. When necessary for diagnostics and/or specialised treatment, animals are moved between different clinics. Furthermore, veterinarians undertaking postgraduate education are on duty in different departments, and move freely between the various clinic buildings.

Origin of MRSA from infections and nasal colonisation in horses
Clinical isolates (from 24 cases) were obtained from specimens for bacteriological diagnostics that were routinely submitted in cases of wound infections, infected joints and suspected infections of various organ systems from summer 2003 until spring 2005.
In order to investigate nasal colonisation, the both nostrils of 24 horses (4 with an MRSA infection, 20 without) that were treated by the orthopaedics department during the same time period in 2004 and 2005 were screened for MRSA by taking nasal swabs. Colonisation was found in only 1 of these animals.

MRSA from nasal colonisation of VUW staff and veterinarians:
Specimens originated from direct cultures of swabs taken from both nostril

Reference strains for healthcare-associated epidemic MRSA
These strains represent multilocus sequence types (ST) of the major clonal lineages of epidemic MRSA from Europe (ST22: 1678/96; ST05: 3391/02; ST247: 134/93; ST45: 1150/93, ST254: 993/93 and 1000/93).
The strains were initially isolated from outbreaks of healthcare-associated infections and were established by representative SmaI macrorestriction patterns and multilocus sequence types (MLST). These strains were included in the HARMONY collection of epidemic MRSA from Europe [18] and in the first MLST-based population study of MRSA from sources worldwide [3].
In the study described here, these reference strains were used for comparison of SmaI macrorestriction patterns.

Reference strains for community-acquired MRSA (CA-MRSA)
ST80: 3925/02; ST01: 2773/03; ST30: 1880/04.
These strains represent multilocus sequence types of community-acquired MRSA that are frequently isolated in central Europe [(6-8] and have been used in this study for comparison of SmaI macrorestriction patterns. They originate from deep-seated skin infections in the community without hospital association, and are positive for the Panton-Valentineleukocidin determinants (lukS-lukF).

Methodology of specimen processing
MRSA from infections in horses were obtained from direct cultures of swabs onto blood agar-plates. Colonies typical for S. aureus were subjected to species identification according to standard procedures [19] and were also evaluated for antimicrobial susceptibility [20]. Nasal colonisation swabs from the anterior of horses and of veterinary personnel were streaked onto blood agar plates and in parallel onto CHROM agar for MRSA from Becton-Dickinson. After incubation for 48 hours, at least five colonies that were suspected to be S. aureus were further subjected to species identification and antimicrobial susceptibility testing.

Susceptibility testing
First line testing in veterinary clinical microbiology was performed by disk diffusion assay [20]. All isolates exhibiting oxacillin resistance were subjected to microbroth assay for MIC determination [20] and to polymerase chain reaction (PCR) for the mecA gene.

Molecular typing
SmaI macrorestriction patterns were obtained by use of the standardised HARMONY protocol [18] with subsequent cluster analysis based on the soft ware
described by Claus et al [21]. For comparison of SmaI patterns, cluster analysis was performed by comparing gel images.
For multilocus sequence typing (MLST) primers used and conditions of the PCR reaction corresponded to those described by Enright et al [3]. Sequences were analysed by use of the MLST databank (

Characterisation of SCCmec elements by PCR
PCR for ccr-complexes, detection of type II and type III specific sequences and discrimination of type IV was performed as described by Witte et al [6].

Demonstration of antibiotic resistance and virulence associated genes by PCR
PCR for lukS-lukF was performed as described by Witte et al 2005 [5]. For PCR detection of genes conferring resistance to methicillin (mecA), oxytetracycline (tetK, tetM), macrolides (ermA, ermB, ermC) and gentamicin (aac6’-aph2”), primers used and conditions were as in previous studies (Braulke et al [22] and Werner et al [23]). For PCR for superantigen determinants (tst, eta, etb, etc) primers and conditions were used as described by Mehrotra et al 2000 [24].


Emergence of MRSA infections in horses:
In 2003 there were 344 equine cases from which clinical specimens were submitted for bacteriological, diagnostics. S.aureus was isolated in 47 (14%) of these cases including 19 infections with MRSA. In 2004 samples from each of 29 among 259 cases were positive for S.aureus (11%) with 3 of them confirmed as MRSA infection. From January 2005 until April 2005 there were 21 S.aureus infections among 165 equine cases (13%), 2 of them were MRSA infections.
The time course, type of infection with MRSA and clinical department affected are shown in Figure 1. The index case occurred in surgery in mid 2003. Investigation into the introduction of MRSA from the community into the hospital via this patient was unsuccessful.
Currently, we have no information regarding cases of MRSA infections from other veterinary institutions in Austria. In this country the frequency of MRSA among S. aureus from healthcare-associated infections in humans is approximately 10%. This represents a relatively low incidence of infections when compared to the situation in other European countries [1]. Overall, the incidence of infections at the VUW with MRSA appears low considering the number of about 5000 horses admitted in 2004 and 2005, that means about 4.8 cases with an MRSA infection MRSA per 1000 admissions.

Typing and comparative characterisation to MRSA from humans:
All 24 isolates from infections horses exhibited similar SmaI macrorestriction patterns with only minor variations that are still in the range of variability during the course of an epidemic (25). This pattern is consistent with intrahospital spread of one particular MRSA clone. These fragment patterns were different from those exhibited by healthcare-associated epidemic MRSA disseminated in Europe and from those of community-acquired MRSA [FIGURE 2].

Furthermore, there was no congruence when SmaI-patterns of MRSA from horses were compared to patterns of 3680 MRSA isolates from healthcare-associated and community-acquired infections that were sent for typing to the author’s laboratory as the German National Reference Center for Staphylococci at the Robert Koch Institute between 2001 and 2004.
Five horse MRSA isolates that were subjected to MLST were identified as ST254.
PCR for typing of SCCmec elements that was performed on 5 isolates from horses revealed type IVd whereas IVc was found for MRSA of ST254 from humans [TABLE ]. None of the investigated horse MRSA contained lukS-lukF, tst1, eta, etb or etc.

Transmission to human nasal colonisation of personnel and veterinarians:
During the time periods of emergence of MRSA infections in horses in the surgery and orthopaedic clinics in 2004 and 2005, nasal swabs from 43 people that were directly involved in treatment of animals (veterinarians, veterinary assistants, animal keepers) were investigated. Two veterinarians were revealed as long term carriers (massive colonisation demonstrated in both a first investigation and follow-up sample 3 weeks later). The MRSA isolates exhibited the same SmaI macrorestriction patterns as isolates from infections in horses and contained SCCmec IVd elements.

Nasal colonisation of horses:
Data from human medicine indicates that nasal colonisation is an important reservoir with regard to infections of the primary carrier and to further dissemination [26,27]. A temporary colonisation (negative in a second investigation) was detected in only one among 24 horses. The MRSA isolate exhibited the same SmaI macrorestriction pattern as the isolates from infections and also contained a SCCmec IVd element.


MRSA from infections in horses in a central European veterinary hospital exhibit MLST ST254. This type has also been identified in healthcare-associated epidemic MRSA. This strain was frequent in the 1990s but has subsequently decreased in prevalence [28]. Reference isolate 994/93 is a representative of ST254 that was disseminated in the hospitals of the Order of Holy Elisabeth in the south-west of Germany and west of Austria [28]. A direct relationship between human MRSA of ST254 to those from horses is however unlikely,as both exhibit different SmaI-macrorestriction patterns and contain different subtypes of SCCmec IV elements. Subtypes of SCCmec elements of type IV differ by various DNA sequences in the region downstream from mecA. At the present time, no acquisition or loss of these sequences has been observed during the time course of dissemination of epidemic MRSA. PCR typing based on subtype specific DNA sequences appears to be a reliable tool for discrimination of subtypes. Demonstration of different subtypes of SCCmec elements in the genomic background of ST254 does however, not exclude an exchange of MRSA between humans and horses in the past. Another possibility is that methicillin-susceptible S. aureus of ST254 that was already widely disseminated among humans [29] was transferred to horses and later acquired a SCCmec element that is different from those acquired by human MRSA of ST254.
Until now MRSA exhibiting typing patterns like those of ST254 from horses have not been detected among MRSA isolates from infections in humans. Furthermore, the human ST254 strain has so far only been associated with healthcare-associated infections and has not emerged in the community.
However, the finding of stable nasal colonisation of two veterinarians who had been in contact with animals affected by MRSA infections demands further investigation of potential animal to human transmission.

This is underlined by findings of MRSA among horses that were reported from Canada. In this report a single well-recognised MRSA clone exhibiting the so called CA-MRSA-05 typing pattern that previously had been identified in healthcare-associated settings from 5 different geographical sites in Canada was demonstrated to have the ability to colonise the nose of horses. This clone spread among both horses and humans on farms and among personnel in veterinary hospitals (14,15). When representative isolates of these MRSA strains were subjected to MLST, we found it to be ST 8 [TABLE]. MRSA strains exhibiting ST8 are widely disseminated in US hospitals and may also become more frequent in Canada since a population dynamics of S. aureus and in particular of MRSA is well known [30]. Furthermore, MRSA of this clonal lineage containing the lukS-lukF gene that confers enhanced virulence became prevalent as community-acquired MRSA in the US [31], and sporadic cases of infections in the community have also been reported from Norway [32].


Infections in horses with MRSA of MLST ST254 emerged independently of MRSA infections in humans. Although MRSA in horses may presently not represent a substantial reservoir for infections in humans in central Europe, further surveillance is needed with respect to human transmission and to emergence of new clonal lineages.

Acknowledgement: we are grateful to Magister Ewald Denner, Institute for Bacteriology at Vienna
Veterinary University, for proving MRSA isolates from 2003, and in part from 2004.


1. Tiemersma EW, Bronzwaer SL, Lyytikainen O, Degener JE, Schrijnemakers P, Bruinsma N, Monen J, Witte W, Grundman H, European Antimicrobial Resistance Surveillance System Participants (2004) Methicillin-resistant Staphylococcus aureus in Europe, 1999 – 2002. Emerg Infect Dis. 2004 Sep;10(9):1627-34...
2. Morgan M, Evans-Williams D, Salmon R, Hosein I, Looker DN, Howard A (2000) The population impact of MRSA in a country: the national survey of MRSA in Wales, 1997. J Hosp Infect. 2000 Mar;44(3):227-39..
3. Enright MC, Robinson DA, Randle G, Feil EJ, Grundmann H, Spratt BG. The evolutionary history of methicillin-resistant Staphylococcus aureus (MRSA). PNAS (2002);99:7687-7692.
4. Chambers HF. The changing epidemiology of Staphylococcus aureus? Emerg Infect Dis. 2001 Mar-Apr;7(2):178-82.
5. Vandenesch F, Naimi T, Enright MC, Lina G, Nimmo GR, Heffernan H, Liassine N, Bes M, Greenland T, Reverdy ME, Etienne J. Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: worldwide emergence. Emerg Infect Dis. 2003 Aug;9(8):978-84.
6. Witte W, Braulke C, Cuny C, Strommenger B, Werner G, Heuck D, Jappe U, Wendt C, Linde H-J, Harmsen D (2005) Emergence of methicillin-resistant Staphylococcus aureus with Panton-Valentine leukocidin genes in central Europe. Eur J Clin Microbiol Infect Dis. 2005 Jan;24(1):1-5.
7. Milasevics E, Haeggman S, Balode A, Sanchez B (2004) Report on the first PVL-positive community MRSA strains in Latvia. Euro Surveill. 2004 Nov;9(11):29-30.
8. Vourli S, Perimeni D, Makri A, Polemis M, Voyiatzi A, Vatopoulos A, (2005) Community acquired MRSA infections in a paediatric population in Greece. Euro Surveill. 2005 May;10(5):78-9..
9. Devriese LA, Vandamme LR, Fameree L. Methicillin (cloxacillin)- resistant Staphylococcus aureus strains isolated from bovine mastitis cases. Zbl. Veterinärmedizin Reihe. 1972; B19:598-605.
10. Kawano J, Shimizu A, Saitoh Y, Yagi M, Saito T, Okamoto R (1996) Isolation of methicillin-resistant coagulase-negative staphylococci from chickens. J Clin Microbiol. 1996 Sep;34(9):2072-7.
11. Hartmann FA, Trostle SS, Klohnen AAO. Isolation of methicillin-resistant Staphylococcus aureus from a postoperative wound infection in a horse. J Am Vet Med Assoc. 1997 Sep 1;211(5):590-2..
12. Gortel K, Campbell KL, Kakoma I, Whittem T, Schaeffer DJ, Weisiger RM. Methicillin resistance among staphylococci isolated from dogs Am J Vet Res. 1999 Dec;60(12):1526-30.
13. Seguin JC, Walker RD, Caron JP, Kloos WE, George CG, Hollis RJ, Jones RN, Pfaller MA. Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal transmission. J Clin Microbiol. 1999 May;37(5):1459-63.
14. Weese JS, Rousseau J, Traub-Dargatz JL, Willey BM, McGeer AJ, Low DE.. Community-associated methicillin-resistant Staphylococcus aureus in horses and humans who work with horses. J Am Vet Med Assoc. 2005 Feb 15;226(4):580-3.
15. Weese JS, Archambault M, Willey BM, Hearn P, Kreiswirth BN, Said-Salim B, McGeer A, Lishoshvay Y, Prescott JF, Low DE. Methicillin-resistant Staphylococcus aureus in horses and horse personnel, 2000-2002. Emerg Infect Dis. 2005 Mar;11(3):430-5.
16. Ito T, Ma XX, Takeuchi F, Okuma K, Yuzawa H, Hiramatsu K. Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC. Antimicrob Agents Chemother. 2004 Jul;48(7):2637-51.
17. Hiramatsu KI, Cui L, Kuroda M, Ito T. The emergence and evolution of methicillin-resistant Staphylococcus aureus. Trends Microbiol. 2001 Oct;9(10):486-93..
18. Murchan S, Kaufmann ME, Deplano A, de Ryck R, Struelens M, Elsberg Zin C, Fussing V, Salmenlina S, Vuopio-Varkila J, El Solh N, Cuny C, Witte W, Tassios PT, Legakis N, van Leeuwen W, van Belkum A, Vindel A, Laconcha I, Garaizar J, Haeggman S, Olson-Liljequist B, Ransjo U, Coombes G, Cookson B.Harmonization of pulsed-field gel electrophoresis protocols for epidemiological typing of strains of methicillin-resistant Staphylococcus aureus: a single approach developed by consensus in 10 European laboratories and its application for tracing the spread of related strains. J Clin Microbiol. 2003 Apr;41(4):1574-85.
19. Isenberg HD. Clinical Microbiology procedures handbook.. Identification of commonly isolated aerobic gram-positive bacteria. American Society for Microbiology, Washington D.C. Ed. 1992; Vol1: 1.20
20. National Committee for Clinical Laboratory Standards . Performance standards for antimicrobial susceptibility testing. Informational supplement. 2002;M100-S12. NCCLS, Villanova, PA.
21. Claus H, Cuny C, Pasemann B, Witte W. A database system for fragment patterns of genomic DNA of Staphylococcus aureus. Zentralbl Bakteriol. 1998 Jan;287(1-2):105-16.
22. Braulke C, Heuck D, Witte W. Ergebnisse der Tätigkeit des Nationalen Referenzzentrums für Staphylokokken im Jahr 1998. Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz. 1999;42:499-506.
23. Werner G, Cuny C, Schmitz FJ, Witte W. Methicillin-resistant, quinupristin-dalfopristin-resistant Staphylococcus aureus with reduced sensitivity to glycopeptides. J Clin Microbiol. 2001 Oct;39(10):3586-90.
24. Mehrotra M, Wang G, Johnson WM. Multiplex PCR for detection of genes for Staphylococcus aureus enterotoxins, exfoliative toxins, toxic shock syndrome toxin 1, and methicillin resistance. J Clin Microbiol. 2000 Mar;38(3):1032-5.
25. Tenover FC, Arbeit RD, Goering RV, Mickelsen PA, Murray BE, Persing DH, Swaminathan B. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J Clin Microbiol. 1995 Sep;33(9):2233-9..
26. Coello R, Glynn JR, Gaspar C, Picazo JJ, Fereres J. Risk factors for developing clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) amongst hospital patients initially only colonized with MRSA. J Hosp Infect. 1997 Sep;37(1):39-46.
27. Merrer J, Santoli F, Appere de Vecchi C, Tran B, De Jonghe B, Outin H. “Colonization pressure” and risk of acquisition of methicillin-resistant Staphylococcus aureus in a medical intensive care unit. Infect Control Hosp Epidemiol. 2000 Nov;21(11):718-23.
28. Witte W, Kresken M, Braulke C, Cuny C. Increasing incidence and widespread dissemination of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals in central Europe, with special reference to German hospitals. Clin Microbiol Infect. 1997 Aug;3(4):414-422.
29. Skov R, Larsen AR, Böcher S, Stegger M, Klennush T, Monnet D. National surveillance on methicillin resistant Staphylococcus aureus in Denmark, 1999-2003. Abstract 0264. 15th European Congress of Clinical Microbiology and Infectious Diseases. Copenhagen, April 2 – 5, 2005.
30. Strommenger B, Cuny C, Werner G, Witte W. Obvious lack of association between dynamics of epidemic methicillin-resistant Staphylococcus aureus in central Europe and agr specificity groups. Eur J Clin Microbiol Infect Dis. 2004 Jan;23(1):15-9.
31. Frazee BW, Lynn J, Charlebois ED, Lambert L, Lowery D, Perdreau-Remington F. High prevalence of methicillin-resistant Staphylococcus aureus in emergency department skin and soft tissue infections. Ann Emerg Med. 2005 Mar;45(3):311-20.
32. Hanssen AM, Fossum A, Mikalsen J, Halvorsen DS, Bukholm G, Sollid JU. dissemination of community-acquired methicillin-resistant Staphylococcus aureus clones in northern Norway: sequence types 8 and 80 predominate J Clin Microbiol. 2005 May;43(5):2118-24.


Back to Table of Contents
en es fr

The publisher’s policy on data collection and use of cookies.

Disclaimer: The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the editorial team or the institutions with which the authors are affiliated. Neither ECDC nor any person acting on behalf of ECDC is responsible for the use that might be made of the information in this journal. The information provided on the Eurosurveillance site is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her physician. Our website does not host any form of commercial advertisement. Except where otherwise stated, all manuscripts published after 1 January 2016 will be published under the Creative Commons Attribution (CC BY) licence. You are free to share and adapt the material, but you must give appropriate credit, provide a link to the licence, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

Eurosurveillance [ISSN] - ©2007-2016. All rights reserved

This website is certified by Health On the Net Foundation. Click to verify. This site complies with the HONcode standard for trustworthy health information:
verify here.