Abstract: Continuing introduction of multi-drug resistant, zoonotic pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) in horse clinics challenges the biosafety of employees and animal patients. This study was aimed to determine the occurrence of mobile genetic elements facilitating survival in the early stages of invasive infection in different host species, including humans and horses, in MRSA carried by equine patients admitted to a large horse clinic. A total of 341 equine patients were investigated for carriage of MRSA by hygiene screening directly at hospital admission. MRSA were further investigated by antimicrobial susceptibility testing, whole-genome sequencing and genomic composition, including virulence factors involved in immune evasion and host adaption. From a total of 340 validated specimens from equine nostrils, 3.5% yielded positive results for MRSA. All MRSA were found to be closely related belonging to sequence type (ST) 398_t011 with up to four additional antimicrobial resistances. All MRSA harbored a specific Staphylococcal Pathogenicity Island (SaPIbov5) involved in facilitating survival in ruminant and equine plasma. Moreover, a β-hemolysin (hlb) converting ΦSa3 phage encoding the human-specific Immune Evasion Cluster (IEC) was present in 72% of the isolates. An equid-specific leukotoxin encoded by a further temperate phage (Saeq1) was only rarely detected (22%). Despite the absence of β-hemolysin production for all IEC-positive ST398, a prominent hemolysis zone was demonstrable on sheep blood agar. Thus, IEC might remain undetected among the ST398 lineage, since the presence of IEC is commonly associated with reduction of hemolysis in S. aureus belonging to other genetic backgrounds. Here we describe MRSA-ST398 harboring different mobile genetic elements encoding variants of immune evasion factors and toxins previously shown to contribute to S. aureus invasive diseases in specific host species or ecologic niches. We suggest these combinations contribute to the adaptation of MRSA belonging to ST398 with respect to epidemic spread across different habitats and hosts, and may therefore confer a host "generalist" phenotype.
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The research article discusses the investigation into the presence of Methicillin-Resistant Staphylococcus Aureus (MRSA) in horse patients in a clinic, their genetic composition, and how these might contribute to the bacteria’s adaptation in different hosts.
Study Procedure
The researchers collected samples from 341 horse patients admitted to a large horse clinic upon their arrival.
The aim was to check if these samples were carriers of MRSA, a type of bacteria resistant to several antibiotics.
The samples were subjected to antimicrobial susceptibility testing, whole-genome sequencing, and evaluation of their genomic composition.
The researchers were specifically interested in investigating the prevalence of virulence factors involved in immune evasion and adaptation to the host.
Findings
Out of the 340 validated samples, around 3.5% tested positive for MRSA.
All the tested MRSA were found to belong to the sequence type (ST) 398_t011.
These MRSA were additionally resistant to approximately four other types of antimicrobial drugs.
The researchers detected the presence of a specific Staphylococcal Pathogenicity Island (SaPIbov5) in all the MRSA tested. This genetic element facilitates survival of the bacteria within the blood of ruminants and horses.
Furthermore, a phage called ΦSa3, encoding the human-specific Immune Evasion Cluster (IEC), was present in 72% of the samples. The presence of IEC is usually linked with reduced hemolysis (destruction of red blood cells), but this was not the case in the tested samples.
A horse-specific leukotoxin was detected only rarely (in 22% of the samples).
Implications
The investigators hypothesize that the variety of immune evasion factors and toxins, encoded by mobile genetic elements, could contribute to the bacteria’s ability to cause invasive diseases in different hosts and ecological niches.
The presence of such genetic elements might confer a “generalist” phenotype to the ST398 lineage of MRSA, enabling them to adapt and spread across diverse habitats and hosts.
This discovery could imply increased risks to the health of both animal patients and human caregivers and on-site staff at animal clinics, indicating the importance of continued attention to hygiene practices.
Cite This Article
APA
Walther B, Klein KS, Barton AK, Semmler T, Huber C, Merle R, Tedin K, Mitrach F, Lübke-Becker A, Gehlen H.
(2018).
Equine Methicillin-Resistant Sequence Type 398 Staphylococcus aureus (MRSA) Harbor Mobile Genetic Elements Promoting Host Adaptation.
Front Microbiol, 9, 2516.
https://doi.org/10.3389/fmicb.2018.02516
Centre for Infection Medicine, Institute of Microbiology and Epizootics, Freie Universität Berlin, Berlin, Germany.
Advanced Light and Electron Microscopy (ZBS4), Robert Koch Institute, Berlin, Germany.
Klein, Katja-Sophia
Equine Clinic, Surgery and Radiology, Freie Universität Berlin, Berlin, Germany.
Barton, Ann-Kristin
Equine Clinic, Surgery and Radiology, Freie Universität Berlin, Berlin, Germany.
Semmler, Torsten
Microbial Genomics (NG1), Robert Koch Institute, Berlin, Germany.
Huber, Charlotte
Microbial Genomics (NG1), Robert Koch Institute, Berlin, Germany.
Merle, Roswitha
Institute for Veterinary Epidemiology and Biostatistics, Freie Universität Berlin, Berlin, Germany.
Tedin, Karsten
Centre for Infection Medicine, Institute of Microbiology and Epizootics, Freie Universität Berlin, Berlin, Germany.
Mitrach, Franziska
Faculty of Environment and Natural Sciences, Institute of Biotechnology, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus, Germany.
Lübke-Becker, Antina
Centre for Infection Medicine, Institute of Microbiology and Epizootics, Freie Universität Berlin, Berlin, Germany.
Gehlen, Heidrun
Equine Clinic, Surgery and Radiology, Freie Universität Berlin, Berlin, Germany.
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