Search

Gram-negative bacteremia is a major cause of global morbidity involving three phases of pathogenesis: initial site infection, dissemination, and survival in the blood and filtering organs.Klebsiella pneumoniaeis a leading cause of bacteremia and pneumonia is often the initial infection. In the lung,K. pneumoniaerelies on many factors like capsular polysaccharide and branched chain amino acid biosynthesis for virulence and fitness. However, mechanisms directly enabling bloodstream fitness are unclear. Here, we performed transposon insertion sequencing (TnSeq) in a tail-vein injection model of bacteremia and identified 58K. pneumoniaebloodstream fitness genes. These factors are diverse and represent a variety of cellular processes.In vivovalidation revealed tissue-specific mechanisms by which distinct factors support bacteremia. ArnD, involved in Lipid A modification, was required across blood filtering organs and supported resistance to soluble splenic factors. The purine biosynthesis enzyme PurD largely enhanced liver fitness and was required for replication in serum. PdxA, a member of the endogenous vitamin B6 biosynthesis pathway, optimized replication in serum and lung fitness. The stringent response regulator SspA was required for splenic fitness yet was dispensable in the liver. In a bacteremic pneumonia model that incorporates initial site infection and dissemination, splenic fitness defects were enhanced, and DsbA, SspA, and PdxA increased fitness across bacteremia phases. SspA and PdxA enhancedK. pnuemoniaeresistance to oxidative stress. SspA specifically resists oxidative stress produced by NADPH oxidase Nox2 in the lung, spleen, and liver, as it was a fitness factor in wild-type but not Nox2-deficient (Cybb−/−) mice. These results identify site-specific fitness factors that act during the progression of Gram-negative bacteremia. DefiningK. pneumoniaefitness strategies across bacteremia phases could illuminate therapeutic targets that prevent infection and sepsis.Author SummaryGram-negative bacteremia is a deadly family of infections that initiate sepsis, a leading cause of global morbidity and mortality. Only a small number of Gram-negative species contribute to the majority of clinical bacteremia.Klebsiella pneumoniaeis the second leading cause of Gram-negative bacteremia, and the third leading cause of overall bloodstream infection.K. pneumoniaeis highly linked to hospital-associated infection with increasing antimicrobial resistance, endangering the most vulnerable patients. It is critical to understand the pathogenesis ofK. pneumoniaebacteremia to better develop targets for future therapies that can prevent these deadly infections. Here, we define over 50K. pneumoniaegenes that support bloodstream fitness. These factors are diverse, support tissue-specific fitness, and increase bacterial resistance to oxidative stress. Our study is the first to systematically defineK. pneumoniaefactors enhancing bacteremia in a mammalian system. These results illuminate host-pathogen interactions duringK. pneumoniaebacteremia that may be extended to additional Gram-negative species.

Healthcare-acquired infections are a leading cause of disease in patients that are hospitalized or in long-term-care facilities. Klebsiella pneumoniae (Kp) is a leading cause of bacteremia, pneumonia, and urinary tract infections in these settings. Previous studies have established that the ter operon, a genetic locus that confers tellurite oxide (K 2 TeO 3 ) resistance, is associated with infection in colonized patients.

Healthcare-acquired infections are a leading cause of disease in patients that are hospitalized or in long-term care facilities.Klebsiella pneumoniae(Kp) is a leading cause of bacteremia, pneumonia, and urinary tract infections in these settings. Previous studies have established that theteroperon, a genetic locus that confers tellurite oxide (K2TeO3) resistance, is associated with infection in colonized patients. Rather than enhancing fitness during infection, theteroperon increases Kp fitness during gut colonization; however, the biologically relevant function of this operon is unknown. First, using a murine model of urinary tract infection, we demonstrate a novel role for theteroperon protein TerC as a bladder fitness factor. To further characterize TerC, we explored a variety of functions, including resistance to metal-induced stress, resistance to ROS-induced stress, and growth on specific sugars, all of which were independent of TerC. Then, using well-defined experimental guidelines, we determined that TerC is necessary for tolerance to ofloxacin, polymyxin B, and cetylpyridinium chloride. We used an ordered transposon library constructed in a Kp strain lacking theteroperon to identify genes required to resist K2TeO3− and polymyxin B-induced stress, which suggested that K2TeO3-induced stress is experienced at the bacterial cell envelope. Finally, we confirmed that K2TeO3disrupts the Kp cell envelope, though these effects are independent ofter. Collectively, the results from these studies indicate a novel role for theteroperon as stress tolerance factor, therefore explaining its role in enhancing fitness in the gut and bladder.

Klebsiella frequently colonizes the gut and colonization is associated with subsequent infection. To identify genes associated with progression from colonization to infection, we undertook a case-control comparative genomics study. Concordant cases (N = 85), where colonizing and invasive Klebsiella isolates were identical strain types, were matched to asymptomatically colonizing controls (N = 160). Thirty-seven genes were significantly associated with infection, 27 of which remained significant following adjustment for patient variables and bacterial phylogeny. Infection-associated genes were not previously characterized virulence factors, but instead a diverse group of stress resistance, regulatory and antibiotic resistance genes, despite careful adjustment for antibiotic exposure. Many infection-associated genes were plasmid borne, and for some, the relationship with infection was mediated by gut dominance. Five infection-associated genes were validated in a geographically independent cohort of colonized patients. This study identifies novel genes that are reproducibly associated with progression to infection in patients colonized by diverse Klebsiella.

Klebsiella pneumoniae (Kp) is an important cause of healthcare-associated infections, which increases patient morbidity, mortality, and hospitalization costs. Gut colonization by Kp is consistently associated with subsequent Kp disease, and patients are predominantly infected with their colonizing strain. Our previous comparative genomics study, between disease-causing and asymptomatically colonizing Kp isolates, identified a plasmid-encoded tellurite (TeO3-2)-resistance (ter) operon as strongly associated with infection. However, TeO3-2 is extremely rare and toxic to humans. Thus, we used a multidisciplinary approach to determine the biological link between ter and Kp infection. First, we used a genomic and bioinformatic approach to extensively characterize Kp plasmids encoding the ter locus. These plasmids displayed substantial variation in plasmid incompatibility type and gene content. Moreover, the ter operon was genetically independent of other plasmid-encoded virulence and antibiotic resistance loci, both in our original patient cohort and in a large set (n = 88) of publicly available ter operon-encoding Kp plasmids, indicating that the ter operon is likely playing a direct, but yet undescribed role in Kp disease. Next, we employed multiple mouse models of infection and colonization to show that 1) the ter operon is dispensable during bacteremia, 2) the ter operon enhances fitness in the gut, 3) this phenotype is dependent on the colony of origin of mice, and 4) antibiotic disruption of the gut microbiota eliminates the requirement for ter. Furthermore, using 16S rRNA gene sequencing, we show that the ter operon enhances Kp fitness in the gut in the presence of specific indigenous microbiota, including those predicted to produce short chain fatty acids. Finally, administration of exogenous short-chain fatty acids in our mouse model of colonization was sufficient to reduce fitness of a ter mutant. These findings indicate that the ter operon, strongly associated with human infection, encodes factors that resist stress induced by the indigenous gut microbiota during colonization. This work represents a substantial advancement in our molecular understanding of Kp pathogenesis and gut colonization, directly relevant to Kp disease in healthcare settings., Author summary The bacterial pathogen Klebsiella pneumoniae is of substantial public health concern due to its ability to cause serious antibiotic-resistant infections. These infections frequently occur in healthcare settings, especially in patients with detectable gut colonization by K. pneumoniae. Importantly, infectious K. pneumoniae strains are often detected in the gut of patients with K. pneumoniae disease, indicating that the gut is a reservoir of infectious K. pneumoniae. Our previous work interrogating the genetic underpinnings of K. pneumoniae disease in colonized patients identified a strong association between K. pneumoniae infection and the presence of an enigmatic genetic locus known as the ter operon. We found that this operon is not needed for pneumonia and bacteremia, and therefore, we explored the importance of the ter operon in the gut. K. pneumoniae lacking ter function was at a disadvantage in the gut, thus explaining the connection between the ter operon and infection in hospitalized patients. Interestingly, the advantage conferred by the ter operon in the gut was associated with the presence of specific indigenous gut microbiota and the presence of short-chain fatty acids, which are metabolized by the host and gut microbiota. This work demonstrates that the ter operon is a microbiome-dependent gut fitness factor and suggests that indigenous gut bacteria may limit colonization by infectious K. pneumoniae.

Introductory paragraphGut colonization by the pathogen Klebsiella pneumoniae (Kp) is consistently associated with subsequent Kp disease1-5, and patients are predominantly infected with their colonizing strain1,2. However, colonizing strains likely vary in their potential to cause infection. We previously identified the plasmid-encoded tellurium resistance (ter) operon as highly associated with infection when compared to asymptomatic colonization in hospitalized patients1. The ter operon bestows resistance to the toxic compound tellurite oxide (TeO3−2), but this is unlikely to be its physiological function, as tellurium and TeO3−2 are exceedingly rare. Here we show that terC is necessary and terZABCDEF is sufficient for phenotypic TeO3−2 resistance. Next, we demonstrate that ter is encoded on a diverse group of plasmids without known plasmid-encoded virulence genes, suggesting an independent role in infection. Finally, our studies indicate that ter is a gut fitness factor, and its fitness advantage is conferred only when specific gut microbiota constituents are present. Collectively, these data reveal the Kp ter operon that is highly associated with human infection likely acts early in pathogenesis as a horizontally-transferrable fitness factor promoting robust gut colonization in the presence of the indigenous microbiota.