Clinical insights: Antimicrobials in an age of resistance

Abstract

Antimicrobial-resistant bacteria cause at least 700,000 human deaths per year according to the World Health Organization [1]. The veterinary field remains a relatively minor contributor to the development of antimicrobial resistance, and significant morbidity and mortality associated with antimicrobial resistance remains relatively limited in companion and food animals. However, the risk of antimicrobial-resistant determinants travelling among bacteria, animals and humans through the food chain, direct contact and environmental contamination has made the issue of judicious antimicrobial use in the veterinary field a trending topic both among lawmakers and human healthcare professionals. Reliable estimates for equine morbidity and mortality relating to infection with antimicrobial-resistant bacteria are not yet available. However, cases doubtless occur and the most significant threat to both human and equine populations is multidrug-resistant (MDR) pathogens, including methicillin resistant Staphylococcus aureus (MRSA), extended spectrum betalactamase (ESBL) producing Escherichia coli, MDR Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecium, and rising MDR strains of Salmonella spp. and Clostridium difficile. Veterinarians and their staff carry a higher risk of MRSA colonisation compared to the general population, and nosocomial MRSA infections have been reported in equine hospitals resulting in patient morbidity and significant financial losses [2]. In an analysis of 12,695 antibiograms in France between 2012 and 2016, the highest proportion (22.5%) of MDR-resistant isolates was S. aureus [3]. Carriage and isolation of ESBL E. coli strains that are resistant to all available antimicrobial classes has increased markedly in horses, and are being seen as a rising cause of nosocomial disease in equine hospitals [2]. In a sampling of healthy adult horses at 41 premises in France in 2015, 44% of horses sampled shed MDR-resistant E. coli, with 29% of premises shedding ESBL isolates [4]. Resistance to even 'reserved' classes of antimicrobials has been reported in equine and canine Salmonella isolates, such as the fluoroquinolone-resistant serovar ST198 as well as ESBL and ceftiofur-resistant strains [2]. Macrolide and rifampicin-resistant strains of R. equi have been demonstrated in farms in the United States, and an increasing prevalence has been noted in Kentucky over the period of 2007-2017 compared with the period 1995-2006 [5]. Antimicrobial use is critical to the practice of veterinary medicine and safeguarding animal welfare; however, inappropriate antimicrobial use in equine and companion animal practice may lead the industry to face legislative regulations on par with food animal practices. The World Health Organization has identified five classes of antimicrobials, later generation cephalosporins, glycopeptides, macrolides, polymyxins and quinolones, as being critically important, and therefore reserved, antimicrobials in human medicine [1]. In a recent review of prescribing behaviour of three '...

Audit of antimicrobial use in eleven equine practices over a five‐year period (2014–2018)

“…Around 700,000 people die of resistant infections every year, and it has been estimated that by 2050, 10 million lives a year are at risk due to the rise of drug‐resistant infections if we do not find proactive solutions now to slow down the rise of drug resistance (O’Neill 2016). Although the companion animal veterinary field is likely to be a relatively minor contributor to the development of AMR, and significant morbidity and mortality associated with AMR in horses remains limited (Isgren 2018), there are significant risks of antimicrobial‐resistant determinants travelling among bacteria, animals and humans through the food chain, direct contact and environmental contamination (Mercer and Davies 2019). The UK’s Department of Health set out a national 5‐year action plan to tackle AMR in 2019, which included a focus on veterinary antimicrobial prescribing and stated “responsible prescribing and use of antimicrobials in pets and horses is especially important because of the close relationship they have with their owners” (Department of Health 2019).…”

Current Trends in Understanding and Managing Equine Rhodococcosis

“…The most important problems in treating Rhodococcus equi infections are the limited number of effective antimicrobial drugs ( Table 1 ) and an increasing resistance. Generally, the number of antibiotic groups used in equine medicine is very restricted and antimicrobial resistance has grown significantly over the last decades [ 39 , 40 , 41 ]. Recommendations for treatment strategy were settled a few decades ago but prior to the 2000s reports on resistance were very rare [ 42 ].…”

“…The combination of a macrolide with rifampicin remains the recommended therapy for foals with clinical signs of infection caused by R. equi for about 40 years. However, the most recent papers suggest that combining rifampicin with some macrolides like clarithromycin or one of the newest, semi-synthetic macrolide tulathromycin can allow for lowering the effective concentration of rifampicin’s in bronchoalveolar cells [ 40 , 44 , 47 ]. There are also papers suggesting that the use of macrolide as the only antimicrobial treatment (azithromycin or gamithromycin) may be at least equally effective as a standard combination of antibiotics [ 4 , 46 ].…”