Klebsiella pneumoniae is a frequent cause of opportunistic, often severe, infections in mammals, including sepsis, pneumonia and mastitis, which are commonly treated with antibiotics. K. pneumoniae infection in horses can lead to potentially life-threatening haemorrhagic pneumonia with high treatment costs, particularly for infections refractory to first-line antibiotics, where use of amikacin is required (Estell et al., 2016). The rise in multidrug resistance in K. pneumoniae is therefore a serious veterinary concern (Ewers et al., 2012). Early identification of infective types and adjunctive therapies to antibiotics could prove important aids for timely and effective treatment. Use of bacteriophages for pathogen tracking (Sechter et al., 2000) and as alternative antibacterial agents (Khan Mirzaei & Nilsson, 2015) is being actively pursed in the era of multidrug resistant superbugs, and better understanding of the dynamic interactions between pathogenic bacteria, phage and the mammalian host is crucial for successful therapeutic outcomes.
In this study, we tracked and characterised K. pneumoniae isolated from bronchial aspirates of a horse with severe respiratory infection using de novo isolated bacteriophages. Predominant K. pneumoniae clones in two bronchial specimens, collected five days apart, were isolated by standard microbiology and typed based on cross-susceptibility to bacteriophages raised de novo against each, and according to their antibiotic resistance phenotype. Bacterial isolates with unique profiles were further characterised by pulsed field gel electrophoresis (PFGE) and whole genome sequencing (WGS). Multiple distinct K. pneumoniae strains were identified in these specimens with unique PFGE profiles. Bacteria-phage interactions (susceptibility profiles) allowed for early discrimination between different types and showed that predominant clones changed over the course of infection, as confirmed by WGS analysis and antibiotic resistance profiles. Use of bacteriophage susceptibility testing can be an additional rapid and cheap method for tracking K. pneumoniae infection.