Wound swabs versus biopsies to detect methicillin resistant Staphylococcus aureus in experimental equine wounds

Abstract

Objective: To compare: (1) the load and diversity of cultivatable bacterial species isolated from tissue biopsies with cultures from surface swabs, and (2) the ability of each technique to detect methicillin-resistant Staphylococcus aureus (MRSA) in a model of MRSA-infected equine wounds. Study design: Experimental in vivo study.Animals: Three light-breed adult horses.Methods: Four 2.5 Â 2.5 cm full-thickness skin wounds were created on the dorsolateral aspect of each forelimb. Five days later, each wound was inoculated with a pure culture of MRSA (ATCC 43300). One hundred microlitres of 0, 5 Â 10 8 , 5 Â 10 9 or 5 Â 10 10 colony forming units (CFU)/ml was used to inoculate each wound. Surface swabs (Levine technique) and tissue biopsy samples (3 mm punch biopsy) were obtained at 2, 7, 14, and 21 days after inoculation. Quantitative aerobic culture was performed using routine clinical techniques. Results: A similar bacterial profile was identified from the culture of each wound-sampling technique and there was moderate correlation (R = 0.49, P < .001) between the bacterial bioburdens. Agreement was fair (κ = 0.31; 95% CI, 0.129-0.505) between the sampling techniques in identification of MRSA.Methicillin-resistant Staphylococcus aureus was isolated more frequently (P = .016) from cultures of tissue biopsies (79%; 76/96) than from surface swabs (62%; 60/96). Conclusion: Bacterial load and diversity did not differ between sampling techniques but MRSA was detected more often from the cultures of tissue biopsies. Clinical significance: Tissue biopsy should be preferred to culture swab in wounds where MRSA is suspected.

Review of the role of biofilms in equine wounds: Clinical indications and treatment strategies

“…However, several publications have supported that tissue samples, while being more invasive to collect, are more likely to yield reliable culture results compared with swabs and to detect antimicrobial‐resistant bacteria in wounds (Esposito et al., 2017; Freeman et al., 2009; Haalboom et al., 2018; Huang et al., 2016; Reddy et al., 2012; Westgate et al., 2011). Specific to horses, wound surface swabs (Levine technique) were recently compared with tissue biopsies to detect methicillin‐resistant Staphylococcus aureus (MRSA) in experimental equine wounds, concluding that bacterial load and diversity did not differ between techniques, but MRSA was more frequently detected from cultures of tissue biopsies versus swabs (Brock et al., 2022). Ideally, submission of tissue samples should be performed prior to beginning or altering antimicrobial protocols; however, if considered necessary to collect samples while horses are currently receiving antimicrobials, it is recommended to notify the receiving laboratory of the horse's current regimen and when the most recent dose was received in relation to sample collection (Orsini et al., 2017).…”