SummaryReasons for performing study: Sepsis is an important cause of death in foals. Knowledge of which pathogens are likely to be involved is important for selection of antimicrobial drugs for initial treatment. Objectives: To identify temporal trends in prevalence of bacteria isolated from foals with sepsis between 1979 and 2010. Study design: Retrospective review of medical records. Methods: All foals ≤30 days of age presented to the Veterinary Medical Teaching Hospital (VMTH) at the University of California, Davis between 1979 and 2010, with a diagnosis of sepsis confirmed by culture of bacteria from blood or internal organs (antemortem or at necropsy), were included in the study. Conventional microbiological methods were used to identify isolated organisms. The Cochran-Armitage trend test was used for statistical analysis. Results:The percentage of Gram-positive isolates increased significantly over the years. The percentage Enterobacteriacea, and Klebsiella spp. in particular, decreased over time. Enterococcus spp. isolates were cultured more often in recent years. Conclusions: Whereas Gram-negative bacteria, particularly Enterobacteriaceae, remain the most common isolates from neonatal foals with sepsis, the prevalence of Gram-positive bacteria is increasing. This trend underlines the importance of including antimicrobial drugs active against both Gram-positive and Gram-negative bacteria in treatment protocols while awaiting the results of bacteriological culture and susceptibility tests. The increased prevalence of Enterococcus spp. is of concern because antimicrobial susceptibility patterns for enterococci are unpredictable and enterococci can also act as donors of antimicrobial resistance genes to other bacteria.

SummaryReasons for performing the study: Monitoring the development of antimicrobial resistance is important for the rational selection of appropriate antimicrobial drugs to initiate treatment of foals with sepsis. Objectives: To identify temporal trends in antimicrobial susceptibility patterns of bacteria isolated from foals with sepsis. Study design: Retrospective review of medical records. Methods: Foals aged <30 days with a diagnosis of sepsis, confirmed by culture of bacteria, were included. Susceptibility data, expressed as minimum inhibitory concentrations (MICs) (MIC50, MIC90, MIC range) and percent of isolates that were susceptible to a particular antimicrobial drug, were compared for bacteria isolated from foals during 3 different time periods: 1979-1990, 1991-1997 and 1998-2010. The Cochran-Armitage trend test and the Jonckheere-Terpstra test were used for statistical analysis. Results: A total of 1091 bacterial isolates were cultured from 588 foals. Enterobacteriaceae, Actinobacillus spp. and β-haemolytic Streptococcus spp. showed a decrease in percent of isolates susceptible to gentamicin over time. Enterobacteriaceae, Actinobacillus spp. and β-haemolytic Streptococcus spp. showed an increase in MIC values for amikacin. Enterobacteriaceae showed a decrease in percent of isolates susceptible to ceftiofur. Enterococcus spp. and Pseudomonas spp. showed increased MIC values to ceftiofur. Enterobacteriaceae showed increased MIC values to ceftizoxime. Enterococcus spp. became more resistant to imipenem and showed increased MIC values to ticarcillin/clavulanic acid. In contrast, several trends in increased susceptibility were also seen. Conclusions: Based on these in vitro results, the combination of amikacin and ampicillin remains an appropriate choice for initiating treatment of sepsis in foals while awaiting culture and susceptibility test results, although increasing development of resistance to amikacin was demonstrated. The decrease in in vitro activity of ceftiofur against Enterobacteriaceae is of concern. Similarly, the development of resistance of Enterococcus spp. to imipenem is an important finding that warrants monitoring in the future. Judicious use of antimicrobials is therefore crucial.

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Background Antimicrobial treatment protocols for foals with sepsis that do not improve clinically often are adjusted based on bacteriological and antimicrobial susceptibility testing results from samples collected at hospital admission. Objectives To evaluate whether hospitalization for ≥48 hours affects bacteriological and antimicrobial susceptibility testing results. Animals Two‐hundred sixty‐seven foals <30 days of age admitted to a neonatal intensive care unit and diagnosed with sepsis. Methods Medical records were reviewed retrospectively to identify foals with sepsis and positive bacteriological cultures. Results from samples collected at hospital admission were compared to those collected ≥48 hours after admission. Logistic regression for clustered data and exact logistic regression were used for statistical analysis. Results Three‐hundred fifty‐three unique bacterial isolates were obtained from 231 foals at hospital admission and 92 unique bacterial isolates were obtained from 57 foals after ≥48 hours of hospitalization. Relative isolation frequency after ≥48 hours of hospitalization increased for Acinetobacter spp., 0.6% versus 3.3% (odds ratio [OR], 7.63; 95% confidence interval [CI], 1.28‐45.45); Enterococcus spp., 4.8% versus 19.6% (OR, 5.37; 95% CI, 2.64‐10.90); Klebsiella spp., 5.1% versus 10.9% (OR, 2.27; 95% CI, 1.05‐4.89); Pseudomonas spp., 3.0% versus 7.6% (OR, 3.49; 95% CI, 3.49‐240.50); and Serratia spp., 3.0% versus 5.4% (OR, 20.23; 95% CI, 2.20‐186.14). Bacteria isolated after ≥48 hours of hospitalization were less susceptible to all tested antimicrobial drugs, except for imipenem. Conclusions and Clinical Importance Decreased antimicrobial susceptibility of bacteria isolated after ≥48 hours of hospitalization provides a rationale for repeated bacteriological culture and susceptibility testing in hospitalized foals with sepsis.

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