34th Annual Scientific Meeting proceedings

Introduction
Antimicrobial resistance (AMR) increases morbidity, mortality and costs in human and veterinary healthcare. AMR bacteria readily colonise veterinary environments. These include meticillin-resistant staphylococci (MRS), ESBL- & AmpC-E. coli, and multi-drug resistant (MDR) Enterococcus faecium, Pseudomonas aeruginosa, Acinetobacter baumannii and Serratia marcescens etc. MRS are declining, but MDR Gram-negative and environmental bacterial infections are increasing.

Avoid unnecessary antibiotic therapy
Prevention is always easier than cure but great care should be taken to avoid relying antibiotics to prevent infections. Systemic antibiotics “treat” the whole microbiota and not just the surgical or infected sites. Therefore, treatment may be effective for the current infection but selects for AMR carriage in other bacteria. In a recent case, the likely cause of the dog’s MDR E. faecium post-operative wound infection was the multiple previous courses of amoxicillin-clavulanate for skin and urinary tract infections. Antibiotics select for resistance – their use must therefore be justified in terms of the likely benefit and risks. When necessary, treatment should be based on good empirical evidence or antimicrobial susceptibility tests (ASTs) using the lowest tier and most narrow spectrum drug appropriate to each patient. Overly long courses of treatment must be avoided.

Use high standards of infection control and hospital care
A thorough understanding of the most important nosocomial infections and how they occur is necessary to implement effective infection control policies. Physical separation of patients, hand washing, gloving and other PPE, and cleaning and hygiene are essential baseline measures. Consideration should be given to aerosols and other debris from air conditioning, urine, vomit and diarrhoea, clipping, scrubbing and bathing, clinical procedures, and cleaning etc. Effective hand washing, cleaning and disinfection are the most important ways to prevent nosocomial infections. However, visual cleanliness is misleading and practices must consider the invisible microbiological risks. Adopting regular protocols and procedures helps ensure microbiological cleanliness.

Fomite or vehicle borne common source infections are an important in veterinary healthcare and other animal care. They can result in serious outbreaks affecting multiple animals. Examples include contamination of shared equipment, soaps, shampoos, diluted antiseptics & cleaning solutions, multidose vials, water and food, and IV fluids etc. Clinical audit will identify clusters of infection suggestive of common source infections and targets for testing/intervention.

Patient risk factors for nosocomial infections

Pre-operative risk factors
Most nosocomial infections involve opportunistic pathogens. Patient risk factors must be considered when planning consultations, procedures and care. Pre-existing conditions can compromise skin/mucosal integrity and/or facilitate dysbiosis and colonisation. For example, atopic dermatitis affects 10-15% of dogs and involves poor skin barrier function, hyper-reactive skin, and secondary staphylococcal and Malassezia infections. Clipping and skin preparation triggers inflammation and expression of adhesion molecules for Staphylococcus pseudintermedius. Therefore, managing atopic dermatitis with topical or systemic glucocorticoids, oclacitinib or ciclosporin reduces the risk of post-operative infections. In other conditions, pre-& post-operative care should maximise innate and adaptive barriers to infection.

Peri- & post-operative risk factors
Wherever possible, surgery should be delayed until the patient is well enough to undergo the procedure with the least risk of complications. This could include managing pre-existing problems (see above), optimising nutrition and body condition, minimising stress, and using high standards of supportive care before and after surgery (especially if hospitalised).

Minimally traumatic clipping and skin preparation will preserve stratum corneum and skin microbiome integrity, reducing colonisation with potential pathogens. Over-clipping and scrubbing rapidly induces physical and thermal trauma and potential pathogens such as coagulase-positive staphylococci (CoPS; e.g. S. aureus & S. pseudintermedius) colonise inflamed skin before other commensal bacteria (including coagulase negative staphylococci/CoNS that regulate CoPS populations).

Good surgical techniques are essential. Breaks in asepsis, tissue trauma, vascular disruption, inappropriate materials and poor patient care are all drivers for infection.

Pre-, peri- and post-operative antibiotics must only be given if indicated. Treatment should follow evidence-based guidelines using drugs appropriate to the risk and most likely bacteria. Similarly, appropriate use of antimicrobial-impregnated materials (e.g. sutures, implants, cement, catheter patches etc.) can be effective but practices shouldn’t become over-reliant on these and should avoid using them in situations where there is likely to be little to no advantage over standard care.

Care must be taken if CoNS are cultured from patients pre-operatively or from post-operative infections. CoNS are only rarely associated with infections. Their clinical significance must be established using clinical signs and cytology alongside the AST results. CoNS frequently exhibit AMR with meticillin-resistance seen in 40-50% of isolates from healthy dogs. Therefore treatment may not only be unnecessary but will involve inappropriate 2^nd or 3^rd line antibiotics.

Biofilms should be suspected in all nosocomial infections, especially with implants or other devices. Standard cultures and ASTs may give false negative results and/or overestimate susceptibility. N-acetyl cysteine (NAC) can damage biofilms and enhance antibiotic efficacy. Anti-biofilm measures should be considered where there is a risk or suspicion that biofilms may complicate treatment. However, biofilm-associated implant infections usually require revision surgery and implant removal.

Conclusions
Antibiotics are life-savers that enable modern veterinary and human healthcare. Many surgical techniques would be impossible without antibiotics. However, antibiotic treatment selects for AMR – using them has consequences. We must therefore use antibiotics wisely to preserve their efficacy. Antibiotics must not to used to mask deficiencies in patient care, surgical technique and infection control. This needs a holistic approach that includes: identifying and managing clinic- and patient-associated risk factors; high standards of hospital care & infection control; good surgical technique; and following evidence-based guidelines for pre-, peri- and post-operative antibiotic treatment.