Biofilm Production by Critical Antibiotic-Resistant Pathogens from an Equine Wound

Abstract

As in human medicine, in veterinary medicine, chronic wounds are often related to polymicrobial infections and the presence of a biofilm, which compromises the effectiveness of therapeutic approaches. In this study, a Lusitano mare presented a 21-day-old chronic wound that was only being treated with an antiseptic. A swab sample was collected, and three isolates of Staphylococcus aureus and one of Pseudomonas aeruginosa were isolated. S. aureus did not show resistance to a panel of antibiotics. However, the P. aeruginosa isolate showed a resistance profile to carbapenems and fluoroquinolones, which may suggest a cross-resistance between antiseptic and antibiotics, given that no antibiotic therapy was applied to the wound or the mare in the previous year. Further experiments were conducted to assess the ability of the isolates to form biofilms, and to ascertain their susceptibility to gentamicin. The results demonstrated that the isolates produced biofilms. Gentamicin at the minimum inhibitory concentration (MIC) and 10× MIC caused biofilm removal between 59.3% and 85.7%, with the highest removal percentage being obtained for the P. aeruginosa isolate (at 10× MIC concentration). This study reveals that an equine wound was colonized by antibiotic resistant bacteria, and that all the wound colonizers could form biofilms, demonstrating the relevance of an adequate diagnosis and treatment when there is a suspicion of a biofilm-infected wound. It also highlights the possibility of resistance transmission between animals, animals and humans, or animals and the environment.

In Vitro Effect of Eucalyptus Essential Oils and Antiseptics (Chlorhexidine Gluconate and Povidone-Iodine) against Bacterial Isolates from Equine Wounds

“…Blank disks impregnated with an equivalent volume of sodium chloride (NaCl 0.9%) were included as the negative control, and disks with gentamicin (10 µg/disk) (Oxoid, England, UK)) were used as the positive control, according to the antibiotic susceptibility test conducted previously for these isolates ( Tables S3 and S4 ). The antibiotic susceptibility test methodology was the same followed by [ 9 ], where the Vitek ® 2 Compact System (BioMerieux, Paris, France) was used, and the antimicrobial resistance results were automatically evaluated by Vitek ® 2 software, which follows the Clinical and Laboratory Standards Institute (CLSI) guidelines. After incubation, the diameters of the inhibitory zones around the disks were recorded.…”

“…One of the main goals of wound medical management is to prevent infection, creating an appropriate environment for epithelial recovery and tissue repair [ 6 , 7 ]. To achieve this purpose, topical antimicrobials are often used, sometimes in an indiscriminate way and without proper knowledge of their effectiveness, a practice that strongly contributes to AMR development [ 8 , 9 , 10 , 11 ]. Fortunately, most equine practitioners are leaving this kind of approach, and mainly for acute wounds, the first steps include wound cleansing and antiseptic application [ 5 , 12 ].…”