Ethanolamine metabolism through two genetically distinct loci enables Klebsiella pneumoniae to bypass nutritional competition in the gut.

Successful microbial colonization of the gastrointestinal (GI) tract hinges on an organism's ability to overcome the intense competition for nutrients in the gut between the host and the resident gut microbiome. Enteric pathogens can exploit ethanolamine (EA) in the gut to bypass nutrient competition. However, Klebsiella pneumoniae (K. pneumoniae) is an asymptomatic gut colonizer and, unlike well-studied enteric pathogens, harbors two genetically distinct ethanolamine utilization (eut) loci. Our investigation uncovered unique roles for each eut locus depending on EA utilization as a carbon or nitrogen source. Murine gut colonization studies demonstrated the necessity of both eut loci in the presence of intact gut microbiota for robust GI colonization by K. pneumoniae. Additionally, while some Escherichia coli gut isolates could metabolize EA, other commensals were incapable, suggesting that EA metabolism likely provides K. pneumoniae a selective advantage in gut colonization. Molecular and bioinformatic analyses unveiled the conservation of two eut loci among K. pneumoniae and a subset of the related taxa in the K. pneumoniae species complex, with the NtrC-RpoN regulatory cascade playing a pivotal role in regulation. These findings identify EA metabolism as a critical driver of K. pneumoniae niche establishment in the gut and propose microbial metabolism as a potential therapeutic avenue to combat K. pneumoniae infections.

Deciphering the gastrointestinal carriage of Klebsiella pneumoniae.

Bacterial infections pose a significant global health threat, accounting for an estimated 7.7 million deaths. Hospital outbreaks driven by multi-drug-resistant pathogens, notably Klebsiella pneumoniae (K. pneumoniae), are of grave concern. This opportunistic pathogen causes pneumonia, urinary tract infections, and bacteremia, particularly in immunocompromised individuals. The rise of hypervirulent K. pneumoniae adds complexity, as it increasingly infects healthy individuals. Recent epidemiological data suggest that asymptomatic gastrointestinal carriage serves as a reservoir for infections in the same individual and allows for host-to-host transmission via the fecal-oral route. This review focuses on K. pneumoniae's gastrointestinal colonization, delving into epidemiological evidence, current animal models, molecular colonization mechanisms, and the protective role of the resident gut microbiota. Moreover, the review sheds light on in vivo high-throughput approaches that have been crucial for identifying K. pneumoniae factors in gut colonization. This comprehensive exploration aims to enhance our understanding of K. pneumoniae gut pathogenesis, guiding future intervention and prevention strategies.

Klebsiella pneumoniae l-Fucose Metabolism Promotes Gastrointestinal Colonization and Modulates Its Virulence Determinants.

Colonization of the gastrointestinal (GI) tract by Klebsiella pneumoniae is generally considered asymptomatic. However, gut colonization allows K. pneumoniae to either translocate to sterile site within the same host or transmit through the fecal-oral route to another host. K. pneumoniae gut colonization is poorly understood, but knowledge of this first step toward infection and spread is critical for combatting its disease manifestations. K. pneumoniae must overcome colonization resistance (CR) provided by the host microbiota to establish itself within the gut. One such mechanism of CR is through nutrient competition. Pathogens that metabolize a broad range of substrates have the ability to bypass nutrient competition and overcome CR. Herein, we demonstrate that in response to mucin-derived fucose, the conserved fucose metabolism operon (fuc) of K. pneumoniae is upregulated in the murine gut, and we subsequently show that fucose metabolism promotes robust gut colonization. Growth studies using cecal filtrate as a proxy for the gut lumen illustrate the growth advantage that the fuc operon provides K. pneumoniae. We further show that fucose metabolism allows K. pneumoniae to be competitive with a commensal Escherichia coli isolate (Nissle). However, Nissle is eventually able to outcompete K. pneumoniae, suggesting that it can be utilized to enhance CR. Finally, we observed that fucose metabolism positively modulates hypermucoviscosity, autoaggregation, and biofilm formation but not capsule biogenesis. Together, these insights enhance our understanding of the role of alternative carbon sources in K. pneumoniae gut colonization and the complex relationship between metabolism and virulence in this species.

MgrB-Dependent Colistin Resistance in Klebsiella pneumoniae Is Associated with an Increase in Host-to-Host Transmission.

Due to its high transmissibility, Klebsiella pneumoniae is one of the leading causes of nosocomial infections. Here, we studied the biological cost of colistin resistance, an antibiotic of last resort, in this opportunistic pathogen using a murine model of gut colonization and transmission. Colistin resistance in K. pneumoniae is commonly the result of the inactivation of the small regulatory protein MgrB. Without a functional MgrB, the two-component system PhoPQ is constitutively active, leading to an increase in lipid A modifications and subsequent colistin resistance. Using an isogenic mgrB deletion mutant (MgrB-), we demonstrate that the mutant's colistin resistance is not associated with a fitness defect under in vitro growth conditions. However, in our murine model of K. pneumoniae gastrointestinal (GI) colonization, the MgrB- colonizes the gut poorly, allowing us to identify a fitness cost. Moreover, the MgrB- mutant has higher survival outside the host compared with the parental strain. We attribute this enhanced survivability to dysregulation of the PhoPQ two-component system and accumulation of the master stress regulator RpoS. The enhanced survival of MgrB- may be critical for its rapid host-to-host transmission observed in our model. Together, our data using multiple clinical isolates demonstrate that MgrB-dependent colistin resistance in K. pneumoniae comes with a biological cost in gut colonization. However, this cost is mitigated by enhanced survival outside the host and consequently increases its host-to-host transmission. Additionally, it underscores the importance of considering the entire life cycle of a pathogen to determine the actual biological cost associated with antibiotic resistance. IMPORTANCE The biological cost associated with colistin resistance in Klebsiella pneumoniae was examined using a murine model of K. pneumoniae gut colonization and fecal-oral transmission. A common mutation resulting in colistin resistance in K. pneumoniae is a loss-of-function mutation of the small regulatory protein MgrB that regulates the two-component system PhoPQ. Even though colistin resistance in K. pneumoniae comes with a fitness defect in gut colonization, it increases bacterial survival outside the host enabling it to transmit more effectively to a new host. The enhanced survival is dependent upon the accumulation of RpoS and dysregulation of the PhoPQ. Hence, our study expands our understanding of the underlying molecular mechanism contributing to the transmission of colistin-resistant K. pneumoniae.

Animal Model To Study Klebsiella pneumoniae Gastrointestinal Colonization and Host-to-Host Transmission.

An important yet poorly understood facet of the life cycle of a successful pathogen is host-to-host transmission. Hospital-acquired infections (HAI) resulting from the transmission of drug-resistant pathogens affect hundreds of millions of patients worldwide. Klebsiella pneumoniae, a Gram-negative bacterium, is notorious for causing HAI, with many of these infections difficult to treat, as K. pneumoniae has become multidrug resistant. Epidemiological studies suggest that K. pneumoniae host-to-host transmission requires close contact and generally occurs through the fecal-oral route. Here, we describe a murine model that can be utilized to study mucosal (oropharynx and gastrointestinal [GI]) colonization, shedding within feces, and transmission of K. pneumoniae through the fecal-oral route. Using an oral route of inoculation, and fecal shedding as a marker for GI colonization, we showed that K. pneumoniae can asymptomatically colonize the GI tract in immunocompetent mice and modifies the host GI microbiota. Colonization density within the GI tract and levels of shedding in the feces differed among the clinical isolates tested. A hypervirulent K. pneumoniae isolate was able to translocate from the GI tract and cause hepatic infection that mimicked the route of human infection. Expression of the capsule was required for colonization and, in turn, robust shedding. Furthermore, K. pneumoniae carrier mice were able to transmit to uninfected cohabitating mice. Lastly, treatment with antibiotics led to changes in the host microbiota and development of a transient supershedder phenotype, which enhanced transmission efficiency. Thus, this model can be used to determine the contribution of host and bacterial factors toward K. pneumoniae dissemination.

The fission yeast MTREC and EJC orthologs ensure the maturation of meiotic transcripts during meiosis.

Meiosis is a highly regulated process by which genetic information is transmitted through sexual reproduction. It encompasses unique mechanisms that do not occur in vegetative cells, producing a distinct, well-regulated meiotic transcriptome. During vegetative growth, many meiotic genes are constitutively transcribed, but most of the resulting mRNAs are rapidly eliminated by the Mmi1-MTREC (Mtl1-Red1 core) complex. While Mmi1-MTREC targets premature meiotic RNAs for degradation by the nuclear 3'-5' exoribonuclease exosome during mitotic growth, its role in meiotic gene expression during meiosis is not known. Here, we report that Red5, an essential MTREC component, interacts with pFal1, an ortholog of eukaryotic translation initiation factor eIF4aIII in the fission yeast Schizosaccharomyces pombe In mammals, together with MAGO (Mnh1), Rnps1, and Y14, elF4AIII (pFal1) forms the core of the exon junction complex (EJC), which is essential for transcriptional surveillance and localization of mature mRNAs. In fission yeast, two EJC orthologs, pFal1 and Mnh1, are functionally connected with MTREC, specifically in the process of meiotic gene expression during meiosis. Although pFal1 interacts with Mnh1, Y14, and Rnps1, its association with Mnh1 is not disrupted upon loss of Y14 or Rnps1. Mutations of Red1, Red5, pFal1, or Mnh1 produce severe meiotic defects; the abundance of meiotic transcripts during meiosis decreases; and mRNA maturation processes such as splicing are impaired. Since studying meiosis in mammalian germline cells is difficult, our findings in fission yeast may help to define the general mechanisms involved in accurate meiotic gene expression in higher eukaryotes.

Battery power comparison to charge medical devices in developing countries.

Many people in developing countries cannot afford or rely on certain modes of electricity. We establish the reasonability of relying on lead-acid batteries, 9 V alkaline batteries, and lithium-ion batteries for charging low-voltage medical equipment. Based on the research and tests we conducted, we determined that using these battery types to charge medical devices truly is a reasonable solution.