Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a Gram positive coccus that is an important human and veterinary pathogen. Strains of MRSA have been classified into hospital-associated strains (typically multi-drug resistant and can cause septicemia and death) and community-associated strains (typically cause skin infections and are sensitive to many non-beta lactam antibiotics) using pulse-field gel electrophoresis.^1,2 Approximately 2% of healthy humans carry MRSA and this can be a risk factor for companion animals acquiring MRSA infections.^3,4

In dogs and cats, human associated strains are most common.³ MRSA isolates from horses are of varied genotypes, whereas food animals appear to have a unique MRSA lineage evolved recently from common human S. aureus clones.³ MRSA isolation from marine mammals has been described during surveillance of clinically normal animals from the wild and in collections.^4,5 There is one report of potential mortality associated with MRSA cultured from a lymph node and spleen of a harbor seal (Phoca vitulina) that died at a seal sanctuary in Ireland.^4-6

Here we document the isolation of MRSA from a weanling female harbor seal (Phoca vitulina), with a significant shark bite wound to the caudal body. At initial physical examination, the seal was lethargic, in poor body condition, and had a large open wound across the hip area. Initial treatment consisted of amoxicillin at 22 mg/kg, enrofloxacin at 5 mg/kg and carprofen at 4 mg/kg. For two weeks the patient ate well and the wound appeared to be healing. However, two weeks into treatment, the seal demonstrated decreased appetite, increased lethargy and the wound started to drain a purulent exudate. The exudate was cultured on blood agar at the University of California at Davis Microbiology Laboratory, producing MRSA, which was susceptible to many non-beta lactam antibiotics including doxycycline. Treatment was changed to doxycycline at 10 mg/kg and the animal improved within days.

The day wound culture results were received, the patient's nares, penmate's nares, the pool walls, floor of the enclosure and water in the pool they were housed in were swabbed and cultured. MRSA was isolated from all swabs of the enclosure and the patient's nares but not from the pool water or from the penmate's nares. The animals were moved, the pools were cleaned with dilute bleach and no MRSA was isolated on follow up swabs of the pen one week later.

Pulse-field gel electrophoresis was performed by the Centers for Disease Control and identified the strain as USA300, typical community associated MRSA found in the United States. We were unable to determine whether the patient acquired this isolate at TMMC or whether she was already colonized prior to admit, as the wound was not cultured until non-response to initial treatment. Doxycycline was discontinued after 18 days and the seal released one week later. This case demonstrates a zoonotic risk that caretakers must take into consideration when working with marine mammals, and highlights the need for further research into potential sources of antibiotic resistant bacteria in marine mammals.

Acknowledgments

The authors would like to thank Spencer Jang of The University of California Davis Veterinary Microbiology lab, Brandi Limbago and Gregory Fosheim of the Centers for Disease Control, Carlos Rios, Lauren Campbell, Deb Wickham, Michelle Blascow and all of the wonderful volunteers at The Marine Mammal Center-Sausalito.

References

1.  Johnson JK, Khoie T, Shurland S, Kreisel K, Stine OC, Roghmann MC. Skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus USA300 clone. Emerging Infectious Diseases 2007; 13:1195–1200.

2.  Tattevin P, An Diep B, Jula M, Remington FP. Methicillin-resistant Staphylococcus aureus USA300 clone in long-term care facility. Emerging Infectious Diseases 2009; 15: 953–955.

3.  Loeffler A, Lloyd DH. Companion animals: a reservoir for methicillin-resistant Staphylococcus aureus in the community? Epidemiol Infect 2010; 138: 595–605.

4.  Faires MC, Gehring E, Mergl J, Weese JS. Methicillin-resistant Staphylococcus aureus in marine mammals. Emerging Infectious Diseases 2009; 15:2071–2072.

5.  Schaefer AM, Goldstein JD, Reif JS, Fair PA, Bossart GD. Antibiotic-resistant organisms cultured from Atlantic bottlenose dolphins (Tursiops truncatus) inhabiting estuarine waters of Charleston, SC and Indian River Lagoon, FL. Ecohealth 2009; 6: 33–41.

6.  O'Mahony R, Abott Y, Leonard FC. Methicillin-resistant Staphylococcus aureus (MRSA) isolated from animals and veterinary personnel in Ireland. Veterinary Microbiology 2005; 109: 285–296.