MRSA
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MRSA – an emerging zoonotic agent or a pathogen in edible clothing?

The gram-positive organism Staphylococcus aureus is recognized as both an important human pathogen and a commensal . This adaptable organism has been shown to be responsible for nosocomial (hospital) infections, with methicillin-resistant S. aureus (MRSA) strains presenting particular treatment problems in hospitals worldwide.



Recently, there have been several reports of MRSA in both domestic and companion animals. The isolation of MRSA from animals was first reported in 1972 following its detection in milk from mastitic cows (cows with inflamed udders) (Devriese et al., 1972), and since then, occasional publications have reported MRSA infection in domestic animals including dogs, cats, cattle, sheep, chickens, rabbits and horses with the literature suggesting that the rate of isolation has being increasing (Devriese and Hommez, 1975; Hartmann et al., 1997; Pak et al., 1999; Tomlin et al., 1999; Lee, 2003; Goni et al., 2004; Rich and Roberts, 2004; Weese and Rousseau, 2005). For instance, Kitai et al. (2005), reported MRSA strains possessing SCCmec type IV, (a genotypic characteristic prevalent in community acquired-MRSA isolates), isolated from retail samples of chickens in Japan, and over a period of two years in the UK, 285 strains of MRSA were isolated from a variety of animals including cats and dogs (Rich et al., 2005). MRSA is now widely recognized as an important risk factor in veterinary medicine, with a number of practices screening animals for MRSA prior to operative procedures. Indeed, MRSA-positive animal patients can be treated using barrier nursing methods to effect isolation from other patients (Pfeiffer et al. 2005; Leonard et al. 2006; Moodley et al 2006).

However, we may be witnessing a further niche exploitation by this organism in terms of reports of detection in raw meat products. Reports to date have indicated the presence of MRSA in a number of food-producing animals such as chicken (Kwon et al., 2006, Lee 2006) cattle (Lee, 2006) and rabbits (Rodriguez-Calleja et al., 2006). Interestingly, Kwon and co-workers (2006) reported that, in their study, chicken, bovine milk and animal hospital isolates were closely related using multilocus sequence typing. In the study by Lee (2006) it is reported that whilst both chicken and cattle samples showed the presence of MRSA, the pork samples under examination did not. Preliminary studies (Agyirey-Kwakye et al. unpublished data) undertaken on 150 samples of chicken and pork giving rise to 26 S. aureus isolates from which two phenotypic MRSA isolates were detected, one from pork and one from chicken. Reports have suggested that the presence of MRSA in raw meat products may constitute a health hazard to some consumers despite the rate of isolation being low (Kitai et al., 2005). It is acknowledged that there is a surprising paucity of data relating to the isolation of MRSA from foodstuffs, (Lee, 2003; Kitai et al., 2005).

With this in mind it is clear that there is a need to establish the relevance of these disparate findings. It is now evident that S. aureus isolates derived from animals and/or raw meat/meat products appear to harbour resistance to antimicrobials commonly used in human medicine, including methicillin. Several studies have shown a low, but potentially important level of methicillin resistance appearing in animals and the food chain within Europe and the US and these findings concur with the findings of others for East and Southeast Asia (Kitai et al., 2005, Lee, 2003, 2006; Kwon et al., 2006). However, it is unclear whether the isolates cultured from these food items are colonizers of the source animal or contaminants from the food-processing agents therefore any inference of these findings from a zoonotic potential is at present uncertain. The dearth of data from Europe and the US points towards the requirement for a co-ordinated surveillance programme to be carried out to determine the epidemiology of S. aureus and MRSA in the food chain from clone tracing through to monitoring of antibiogram profiles to ascertain the importance of this versatile pathogen in a potentially new role. The collated data will contribute to the understanding of the natural biology of the organism. Importantly, we hope to assess whether we have a risk that needs to be properly assessed or whether a change in handling practices will be sufficient to control the apparent spread a microorganism harbouring human drug resistances.

Mark D. Fielder
School of Life Sciences, Kingston University, Penrhyn Road, Kingston-Upon-Thames, Surrey KT1 2EE, UK

Agar plate showing antibiotic resistance
Petri dish showing resistance to certain antimicrobial agents. A disk with no clear zone indicates that the bacteria are resistant.

References

Devriese, L.A., Hommez, J. Res. Vet. Sci. 1975; 19:23–27.

Devriese, L.A., Vandamme, L.R., Fameree, L. Zbl. Vet. B, 1972; 19:598–605.

Goni, P., Vergara, Y., Ruiz, J., et al. Int. J. Antimicrob. Agents 23:268–272.

Hartmann, F. A., Trostle, S.S., Klohnen, A.A. J. Am. Vet. Med. Assoc. 1997; 211:590–592.

Kitai S., Shimizu A., Kawano J., et al. J Vet Med Sci. 2005; 67(1):107–10.

Kwon N.H, Park K.T, Jung W.K, et al. Vet Microbiol. 2006 31;117(2–4):304–12.

Lee, J.H. Appl. Environ. Microbiol. 2003; 69:6489–6494.

Lee J.H. Vet Microbiol. 2006 16; 114(1–2):155–9.

Leonard F.C., Abbott Y., Rossney A., et al. Vet Rec. 2006; 158(5):155–9.

Moodley A., Stegger M., Bagcigil A.F., et al. J Antimicrob Chemother. 2006; 58: 1118–1123.

Pak, S.I., Han, H.R., Shimizu, J. Vet. Med. Sci. 1999; 61:1013–1018.

Pfeiffer D., Lloyd D., Loeffler A., et al. Vet Rec. 2005; 157(6):179–80.

Rich, M., Roberts, L. Vet. Rec. 2004; 154:310.

Rich M., Deighton L., Roberts L., Vet Microbiol. 2005;111(3–4):237–40.

Rodriguez-Calleja J.M., Garcia-Lopez I., Santos J.A., Ortero, A., Garcia-Lopez, M.-L. Res Microbiol. 2006 ; 157(5) :496–502.

Tomlin, J., Pead, M. J., Lloyd, D.H., et al. Vet. Rec. 1999; 144:60 – 64.

Weese J.S., Rousseau J., Equine Vet J. 2005 Nov;37(6):510-4.

 
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 Page Contact: Jennie Drew - Last modified: 2007-01-17