Fighting antimicrobial resistance in foal sepsis

Abstract

General introductionChapter 1 may lead to excessive inflammation and bacterial translocation into the bloodstream, resulting in sepsis. It has been suggested this is the most common route for development of sepsis in foals. While many foals admitted to equine hospitals show clinical signs consistent with 'suspected sepsis', definite diagnosis of sepsis is complicated. Blood cultures are considered the gold standard. However, up to 40% of blood cultures collected from foals with sepsis were found to be false negative in a study comparing blood culture results to samples collected at necropsy 18 . False negatives can result from samples collected after antimicrobial treatment has started or if low blood volumes are used 19 . Blood cultures can also be false positive, in case of sample contamination or potential transient bacteremia without clinical implications 20 . Therefore, it is important that blood culture results are interpreted in the light of presence of clinical signs suggestive of sepsis. A weighted sepsis scoring system is therefore often used as a diagnostic tool for sepsis in neonatal foals, but this has a relatively low sensitivity and specificity 21, 22 . Progression of sepsis is often rapid and sepsis can lead to multiple organ dysfunction syndrome (MODS), multiple organ failure syndrome (MOFS), septic shock and ultimately the death of the foal within hours 15 . Culture and antimicrobial susceptibility testing results are usually not available until at least 48 hours after submission of the sample. The rapid clinical deterioration in foals with sepsis is a challenge to the treating veterinarian and warrants immediate initiation of (antimicrobial) treatment, while awaiting culture and susceptibility testing results. TREATMENT OF SEPSIS IN FOALS: THE IMPORTANCE OF ANTIMICROBIALSThe most common form of sepsis in foals is bacterial sepsis 23 . Therefore, in attempt to control the infection, antimicrobials are the cornerstone of treatment in foals with sepsis. Other important aspects of treatment of sepsis in foals are anti-inflammatory treatment, cardiovascular support, respiratory support and nutritional support 15 . Because of the immature immune system and the large variation in bacteria that can cause sepsis in foals, initial antimicrobial treatment should be bactericidal and broad-spectrum. Drug selection is often based on historic data of causative organisms and their susceptibility patterns. Most studies until now have identified Escherichia coli as the most common causative organism isolated from foals with sepsis. Prevalence of other bacteria such as Enterococcus spp., Streptococcus spp., Actinobacillus spp., Enterobacter spp., Staphylococcus spp. and Klebsiella spp. vary widely between studies conducted in different geographic locations and in different time periods. 8, 13,[23][24][25][26][27] . Temporal trends in prevalence of bacteria causing sepsis in foals have been identified 23 . A decrease in enteric gram-negative organisms, Salmonella spp. and Actinobacillus spp. isolated from blood...