Investigating Bacterial Bloodstream Infections in Dogs and Cats: A 4-Year Surveillance in an Italian Veterinary University Hospital

In small animal practice, blood cultures (BCs) are essential for diagnosing bacterial bloodstream infections (BSIs) and guiding targeted antimicrobial therapy, particularly in relation to the rise of multidrug-resistant (MDR) pathogens. This study analyzed 96 positive BCs from dogs and cats at the Veterinary University Hospital (VUH) of Bologna (2020-2024), assessing bacterial prevalence, antimicrobial resistance, and associated risk factors. <i>Escherichia coli</i> was the most common isolate (29/96), followed by <i>Streptococcus canis</i> (11/96). MDR percentage was 29.2% (28/96), with Gram-negatives associated with higher rates (<i>p</i> = 0.040). Nearly half of the cases (46.9%, 45/96) were suspected healthcare-associated infections (HAIs) significantly associated with the number of invasive devices used (<i>p</i> = 0.008) and with the absence of co-positive samples (<i>p</i> = 0.012). Empirical antibiotic therapy was administered in 94.8% (91/96) of cases, with ampicillin-sulbactam and marbofloxacin as the most used drugs. In vitro empirical therapy appropriateness was 76.9% (70/91). MDR was associated with inappropriate empirical therapy (<i>p</i> < 0.001). Mortality within 30 days was 36.5% (35/96), significantly linked to antibiotic escalation (<i>p</i> = 0.006). The findings highlight the need for systematic BC surveillance in veterinary settings to optimize treatment strategies (especially in countries with restrictions on antibiotic use in animals) to mitigate MDR spread and to protect public health.