An Animal Model to StudyKlebsiella pneumoniaeGastro-Intestinal Colonization and Host-to-Host Transmission

Abstract

42An important yet poorly understood facet in the life cycle of a successful pathogen is the host-to-43 host transmission. Hospital-acquired infections (HAI) resulting from the transmission of drug-44 resistant pathogens affect hundreds of millions of patients worldwide. Klebsiella pneumoniae 45 (Kpn), a gram-negative bacterium, is notorious for causing HAI, with many of these infections 46 difficult to treat as Kpn has become multi-drug resistant. Epidemiological studies suggest that 47 Kpn host-to-host transmission requires close contact and generally occurs through the fecal-oral 48 route. Herein, we describe a murine model that can be utilized to study mucosal (oropharynx and 49 gastrointestinal [GI]) colonization, shedding within feces, and transmission of Kpn through the 50 fecal-oral route. Using an oral route of inoculation, and fecal shedding as a marker for GI 51 colonization, we show that Kpn can asymptomatically colonize the GI tract of immunocompetent 52 mice, and modifies the host GI microbiota. Colonization density within the GI tract and levels of 53 shedding in the feces differed among the clinical isolates tested. A hypervirulent Kpn isolate was 54 able to translocate from the GI tract and cause hepatic infection that mimicked the route of 55 human infection. Expression of the capsule was required for colonization and, in turn, robust 56 shedding. Furthermore, Kpn carrier mice were able to transmit to uninfected cohabitating mice. 57 Lastly, treatment with antibiotics led to changes in the host microbiota and development of a 58 transient super-shedder phenotype, which enhanced transmission efficiency. Thus, this model 59 can be used to determine the contribution of host and bacterial factors towards Kpn 60 dissemination. 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77Introduction. 79Host-to-host transmission of pathogens is the primary source of nosocomial infections, 80 which are considered a serious threat to patient's health and also a significant burden on the 81 healthcare system (1, 2). Hospital-acquired infections (HAI) account for ~100,000 deaths in the 82 United States alone (3). A leading cause of these hospital-acquired infections and multiple 83 outbreaks in hospitals around the world is Klebsiella pneumoniae (K. pneumoniae; Kpn), a 84 member of the Enterobacteriaceae family that frequently causes pneumonia, bacteremia, 85 pyogenic liver abscesses, and urinary tract infections (4), with most of these infections generally 86 occuring in immunocompromised patients. With the rampant use of antibiotics Kpn isolates have 87 become extensively drug-resistant, and some are now even considered pan-drug resistant, 88 making the infections they cause extremely difficult to treat (5-7). For this reason, WHO 89 lists Klebsiella pneumoniae as a critical pathogen for which new antibiotics and other therapies 90are urgently required to address this growing healthcare problem (8, 9). Further exacerbating 91 treatment of Kpn infections is the recent identification of isolates termed "hyperv...