995. A Murine Model of Klebsiella pneumoniae Gastrointestinal Colonization with Parenteral Vancomycin Administration

Background As a leading cause of nosocomial infections, Klebsiella pneumoniae poses a significant threat due to its propensity to acquire resistance to many classes of antibiotics, including carbapenems. Gastrointestinal (GI) colonization by K. pneumoniae is a risk factor for subsequent infection as well as transmission to other patients. To study this crucial step in pathogenesis, we developed a mouse model of K. pneumoniae GI colonization using a clinically relevant parenteral antibiotic regimen. Methods To improve the clinical relevance of our model, we elected to use intraperitoneal injections of vancomycin, one of the most highly utilized antibiotics in the United States. Results To optimize dosage in C57bl/6 mice, we injected 20mg/kg, 350mg/kg, or vehicle (PBS) for three days prior to gastric gavage with 108 colony forming units (CFU) of a low-resistance strain of K. pneumoniae. The mice who received 350mg/kg (a mouse equivalent of a human dose of 1g/day calculated through the FDA guidelines for estimating safe dosing) shed about 107 CFU/g of feces at Day 7 while those receiving the lower dose or vehicle shed 104 CFU/g. Next, we compared 3- or 5-day pre-treatments with vancomycin prior to inoculation with an ST258 (epidemic carbapenem-resistant) strain. At Day 7 post-inoculation, mice who received 5 days shed 1010 CFU/g feces while those who received vancomycin for 3 days or vehicle for 5 days (PBS) shed 106 or 104 CFU/g feces respectively. Thus, we chose 5 days of 350mg/kg vancomycin injection as our regimen for inducing robust GI colonization in mice. Finally, we tested the durability of colonization by following fecal shedding in mice up to Day 60 post-inoculation with a second ST258 strain. Shedding during the first 7 days occurs at about 1010 CFU/g feces, and from day 14 to day 60 fecal loads are stable around 107 CFU/g feces. Results are comparable between male and female mice. Conclusion In conclusion, we have developed a mouse model of robust, prolonged GI colonization with multiple strains of K. pneumoniae using controlled dosing of a clinically relevant antibiotic. This model may be used to study a key step in K. pneumoniae pathogenesis and infection prevention in the future. Disclosures All Authors: No reported disclosures

Carbapenemase-Producing Klebsiella pneumoniae Colonization and Infection in Solid Organ Transplant Recipients: A Single-Center, Retrospective Study

Carbapenemase-KPC producing Klebsiella pneumoniae (CP-Kp) infection represents a serious threat to solid organ transplant (SOT). All patients admitted between 1 May 2011 and 31 August 2014 undergoing SOT were included in the retrospective study. The primary outcomes included a description of the association of enteric colonization and invasive infections by CP-Kp with one-year mortality. Secondary outcomes were the study of risk factors for colonization and invasive infections by CP-Kp. Results: A total of 5.4% (45/828) of SOT recipients had at least one positive rectal swab for CP-Kp, with most (88.9%) occurring after transplantation. 4.5% (35/828) of patients developed a CP-Kp-related invasive infection, with 68.6% (24/35) being previously colonized. The 1-year mortality was 31.1% in patients with enteric colonization with CP-Kp and, it was 51.4% among patients with CP-Kp-related invasive infections. At univariate analysis, colonization, invasive infections, sepsis, severe sepsis, and septic shock were significantly associated with 1-year mortality. At multivariate analysis, only invasive infections and the combination of sepsis, severe sepsis, or septic shock were significantly associated with 1-year mortality, whereas gastrointestinal colonization was significantly associated with survival. In this population, the 1-year mortality was significantly associated with invasive infections; otherwise, gastrointestinal colonization was not associated with increased 1-year mortality.

From Klebsiella pneumoniae Colonization to Dissemination: An Overview of Studies Implementing Murine Models

Klebsiella pneumoniae is a Gram-negative pathogen responsible for community-acquired and nosocomial infections. The strains of this species belong to the opportunistic group, which is comprised of the multidrug-resistant strains, or the hypervirulent group, depending on their accessory genome, which determines bacterial pathogenicity and the host immune response. The aim of this survey is to present an overview of the murine models mimicking K. pneumoniae infectious processes (i.e., gastrointestinal colonization, urinary, pulmonary, and systemic infections), and the bacterial functions deployed to colonize and disseminate into the host. These in vivo approaches are pivotal to develop new therapeutics to limit K. pneumoniae infections via a modulation of the immune responses and/or microbiota.

Neonatal Immune System Ontogeny: The Role of Maternal Microbiota and Associated Factors. How Might the Non-Human Primate Model Enlighten the Path?

Interactions between the immune system and the microbiome play a crucial role on the human health. These interactions start in the prenatal period and are critical for the maturation of the immune system in newborns and infants. Several factors influence the composition of the infant’s microbiota and subsequently the development of the immune system. They include maternal infection, antibiotic treatment, environmental exposure, mode of delivery, breastfeeding, and food introduction. In this review, we focus on the ontogeny of the immune system and its association to microbial colonization from conception to food diversification. In this context, we give an overview of the mother–fetus interactions during pregnancy, the impact of the time of birth and the mode of delivery, the neonate gastrointestinal colonization and the role of breastfeeding, weaning, and food diversification. We further review the impact of the vaccination on the infant’s microbiota and the reciprocal case. Finally, we discuss several potential therapeutic interventions that might help to improve the newborn and infant’s health and their responses to vaccination. Throughout the review, we underline the main scientific questions that are left to be answered and how the non-human primate model could help enlighten the path.

Candida albicans Colonizes and Disseminates to the Gastrointestinal Tract in the Presence of the Microbiota in a Severe Combined Immunodeficient Mouse Model

Candida albicans is the leading cause of candidemia or other invasive candidiasis. Gastrointestinal colonization has been considered as the primary source of candidemia. However, few established mouse models that mimic this infection route are available. In the present study, we established a mouse model of disseminated candidiasis developed through the translocation of Candida from the gut. In this study, we developed a novel C. albicans GI colonization and dissemination animal model by using severe combined immunodeficient Rag2–/–IL2γc–/– (Rag2γc) mice, which lack functional T, B, NK cells, and IL2γc-dependent signaling. Rag2γc mice were highly susceptible to C. albicans gastrointestinal infection even in the presence of the gut microbiota. Within 4 weeks post infection, Rag2γc mice showed dose-dependent weight loss and disseminated candidiasis in more than 58% (7/12) of moribund mice. Histological analysis demonstrated abundant hyphae penetrating the mucosa, with significant neutrophilic infiltration in mice infected with wild-type C. albicans but not a filamentation-defective mutant. In moribund Rag2γc mice, the necrotic lesions and disrupted epithelial cells were associated with C. albicans hyphae. Notably, removal of the gut microbiota by antibiotics exacerbated the severity of fungal infection in Rag2γc mice, as demonstrated by elevated fungal burdens and accelerated weight loss and death. Furthermore, higher fungal burden and IL-1β expression were prominently noted in the stomach of Rag2γc mice. In fact, a significant increase in circulating proinflammatory cytokines, including IL-6, TNF-α, and IL-10, indicative of a septic response, was evident in infected Rag2γc mice. Additionally, Rag2γc mice exhibited significantly lower levels of IL-22 but not IFN-γ or IL-17A than wild-type B6 mice, suggesting that IL-22 plays a role in C. albicans gastrointestinal infection. Collectively, our analysis of the Rag2γc mouse model revealed features of C. albicans gastrointestinal colonization and dissemination without the interference from antibiotics or chemotherapeutic agents, thus offering a new investigative tool for delineating the pathogenesis of C. albicans and its cross-talk with the gut microbiota.

Homology analysis between clinically isolated extraintestinal and enteral Klebsiella pneumoniae among Neonates

Background: Klebsiella pneumoniae is a leading cause of hospital-associated (HA) infections. It has been reported that gastrointestinal colonization (GI) is likely to be a common and significant reservoir for the transmission and infections of K. pneumoniae in both adults and neonates. However, the homologous relationship between clinically isolated extraintestinal and enteral K. pneumoniae in neonates hasn’t been characterized yet.Results: 43 isolates from 21 neonatal patients were collected in this study. The proportion of carbapenem resistance was 62.8%. There were 12 patients (12/21, 57.4%) whose antibiotic resistance phenotypes, genotypes, and ST types (STs) were concordant. Six sequence types were detected using MLST, with ST37 and ST54 being the dominant types. The results of MLST were consist with the results of PFGE.Conclusions: These data showed that there might be a close homologous relationship between extraintestinal K. pneumoniae (EXKP) and enteral K. pneumoniae (EKP) in neonates，indicating that the K. pneumoniae from the GI tract is possibly to be a significant reservoir for causing extraintestinal infections.

Potency of gastrointestinal colonization and virulence of Candida auris in a murine endogenous candidiasis

Background Candida auris infections have recently emerged worldwide, and this species is highly capable of colonization and is associated with high levels of mortality. However, strain-dependent differences in colonization capabilities and virulence have not yet been reported. Objectives In the present study, we aimed to clarify the differences between clinically isolated invasive and non-invasive strains of C. auris. Methods We evaluated colonization, dissemination, and survival rates in wild C57BL/6J mice inoculated with invasive or non-invasive strains of C. auris under cortisone acetate immunosuppression, comparing with those of Candida albicans and Candida glabrata infections. We also evaluated the potency of biofilm formation. Results Stool fungal burdens were significantly higher in mice inoculated with the invasive strains than in those infected with the non-invasive strain. Along with intestinal colonization, liver and kidney fungal burdens were also significantly higher in mice inoculated with the invasive strains. In addition, histopathological findings revealed greater dissemination and colonization of the invasive strains. Regarding biofilm-forming capability, the invasive strain of C. auris exhibited a significantly higher capacity of producing biofilms. Moreover, inoculation with the invasive strains resulted in significantly greater loss of body weight than that noted following infection with the non-invasive strain. Conclusions Invasive strains showed higher colonization capability and rates of dissemination from gastrointestinal tracts under cortisone acetate immunosuppression than non-invasive strains, although the mortality rates caused by C. auris were lower than those caused by C. albicans.

Homology analysis between clinically isolated extraintestinal and enteral Klebsiella pneumoniae among Neonates

Background: Klebsiella pneumoniae is a leading cause of hospital-associated (HA) infections . It has been reported that gastrointestinal colonization (GI) is likely to be a common and significant reservoir for the transmission and infections of K. pneumoniae in both adults and neonates. However, the homologous relationship between clinically isolated extraintestinal and enteral K. pneumoniae in neonates hasn’t been characterized yet. Results: 43 isolates from 21 neonatal patients were collected in this study. The proportion of carbapenem resistance was 62.8%. There were 12 patients (12/21, 57.4%) whose antibiotic resistance phenotypes, genotypes, and ST types (STs) were concordant. Six sequence types were detected using MLST, with ST37 and ST54 being the dominant types. The results of MLST were consist with the results of PFGE. Conclusions: These data showed that there might be a close homologous relationship between EXKP and EKP in neonates，indicating that the K. pneumoniae from the GI tract is possibly to be a significant reservoir for causing extraintestinal infections.