Volume 2, December 2016, Pages 11–17
Open Access
Abstract
A total of 272 methicillin-resistant Staphylococcus aureus
(MRSA) from equine infections originating from 17 equine hospitals and
39 veterinary practices in Germany as well as 67 isolates from personnel
working at equine clinics were subjected to molecular typing. The
majority of isolates from horses was attributed to clonal complex (CC)
398 (82.7%). Within CC398, 66% of isolates belonged to a subpopulation
(clade) of CC398, which is associated with equine clinics.
MRSA attributed to CC8 (ST254, t009, t036, SCCmecIV; ST8, t064, SCCmecIV)
were less frequent (16.5%). Single isolates were attributed to ST1,
CC22, ST130, and ST1660. The emergence of MRSA CC22 and ST130 in horses
was not reported so far. Nasal MRSA colonization was found in 19.5% of
veterinary personnel with occupational exposure to horses. The typing
characteristics of these isolates corresponded to isolates from equine
infections.
Comparing typing characteristics of equine
isolates with those of a substantial number of isolates from human
infections typed at the German Reference Center for Staphylococci and
Enterococci (2006–2014; n = 10864) yielded that the proportion of
isolates exhibiting characteristics of MRSA from equine medicine is very
low (< 0.5%). As this low proportion was also found among MRSA
originating from nasal screenings of human carriers not suffering from a
staphylococcal infection (n = 5546) transmission of MRSA from equine
clinics to the community seems to be rare so far.
Keywords
- MRSA;
- Equine clinic associated MRSA;
- Zoonotic transmission;
- Host specificity
Introduction
Staphylococcus aureus becomes methicillin resistant by acquisition of the mec genes (mecA and homologues) contained by staphylococcal cassette chromosome mec (SCCmec) elements from which at least 11 basic types are known so far. S. aureus
shows a rather clonal population structure; typing of isolates by
relevant methods reveals allocation to certain clonal types, in
particular multilocus-sequence typing (MLST) and spa-typing are used as standard methodologies [1] and [2].
MRSA is globally prevalent in nosocomial settings as
hospital-associated MRSA (HA-MRSA), which is mainly due to intra- and
interhospital spread of epidemic clonal lineages [3], [4] and [5]. In addition, MRSA emerged in the community without any relation to healthcare facilities (CA-MRSA, [6]).
The first MRSA in animals was reported from cases of mastitis in dairy
cattle in 1972, followed by sporadic observations of infections in
various animals including postsurgical wound infections in horses [7].
Since 2006 MRSA attributed to clonal complex CC398 received specific
attention since these so-called livestock-associated MRSA (LA-MRSA) is
widely disseminated among various livestock animals mainly as an
asymptomatic nasal colonizer [8] and [9].
Because of its capacity to cause a variety of infections in humans such
as skin and soft-tissue infections, surgical wound and joint
infections, invasive device infections (catheter, endoprostheses),
ventilator-associated pneumonia, and septicemia [10], [11] and [12] MRSA CC398 became a public health issue.
Furthermore,
MRSA raised attention as nosocomial pathogens in companion animals and
equine medicine. For companion animals, such as cats and dogs, clusters
of MRSA infections in veterinary facilities were observed [13], [14] and [15].
Several studies have provided evidence of hospital-associated (HA)-MRSA
HA-MRSA transmission from humans to small animals in veterinary
facilities and vice versa. Molecular typing of the isolates suggested an
origin in human hospitals [16] and [17]. The first report of an outbreak of MRSA infections in horses in a veterinary hospital came from the United States in 1999 [18], and was followed by descriptions of clusters of MRSA infections in equine hospitals in Canada [19] and [20] and in Central Europe a few years later [21] and [22].
The majority of the Canadian MRSA isolates from horses and staff, as
reported by previous studies, has typically been identified as Canadian
epidemic MRSA-5, equivalent to “USA500”, a putatively equine clinic
associated strain, which accounted for nearly 10% of MRSA in Canadian
hospitals by the end of the 1990 [23]. It exhibits MLST ST8, spa type t064 (corresponds to spa type 7 according to the Kreiswirth nomenclature), and contains SCCmecIV [20]. This strain type was also reported for MRSA isolates from horses from the United States and from Ireland [24] and [25]. In a Canadian veterinary hospital a cluster of skin and soft tissue infections in humans working there was also observed [26]. At this time the central European MRSA isolates from nosocomial infections in horses exhibited ST254, t036, and SCCmecIVh [21] and [22].
Meanwhile, MRSA CC398 is prevalent as a nosocomial pathogen in
veterinary clinics, particularly in those for horses in Austria [22] and [27], Belgium [28] and [29], Germany [30], the Netherlands [31], Switzerland [32], and the United Kingdom [17]. Furthermore, nasal colonization of veterinary personnel attending horses was reported [22], [31], [32] and [33].
The majority of MRSA CC398 isolates from horse clinics exhibited a
typical pattern of characteristics when subjected to typing: spa type t011, more rarely t6867, SCCmecIVa, and phenotypic resistance to gentamicin based on the aacA-aphD gene [22], [31] and [32].
A more detailed analysis of the population-structure through mutation
discovery at 97 loci revealed that MRSA CC398 from horse clinics
exhibiting the above mentioned characteristics represent a particular
subpopulation (clade) of LA-MRSA CC398 [34].
The
significance of MRSA from colonization and infections in horses for
infections in humans has not been assessed in more detail so far.
Therefore, the objective of this study was to determine the proportion
of typical equine MRSA clones among the MRSA from human infections based
on a comparative analysis of typing characteristics.
