Functional definition of NrtR, a remnant regulator of NAD+ homeostasis in the zoonotic pathogen Streptococcus suis.

NAD+ is an enzyme cofactor required for the 3 domains of life. However, little is known about the NAD+ biosynthesis and salvage pathways in the opportunistic pathogen Streptococcus suis. A genome-wide search allows us to identify the NAD+ salvage pathway encoded by an operon of nadR-pnuC-nrtR (from SSU05_1973 to SSU05_1971 on the reverse strand) in the S. suis 05ZYH33 that causes streptococcal toxin shock-like syndrome. The regulator of this pathway is Nudix-related transcriptional regulator (NrtR), a transcription regulator of the Nudix family comprising an N-terminal Nudix-like effector domain, and a C-terminal DNA-binding winged helix-turn-helix-like domain. Intriguingly, the S. suis NrtR naturally contains a single amino acid substitution (K92E) in the catalytic site of its Nudix domain that renders it catalytically inactive but does not influence its ability to bind DNA. Despite its lack of enzymatic activity, DNA-binding activity of NrtR is antagonized by the effector ADP-ribose. Furthermore, nrtR knockout in S. suis serotype 2 reduces its capacity to form biofilms and attenuates its virulence in a mouse infection model. Genome mining indicates that nrtR appears in a strain-specific manner whose occupancy is correlated to bacterial infectivity. Unlike the paradigmatic member of NrtR family having 2 unrelated functions (Nudix hydrolase and DNA binding), S. suis 2 retains a single regulatory role in the modulation of NAD+ salvage. This control of NAD+ homeostasis contributes to S. suis virulence.-Wang, Q., Hassan, B. H., Lou, N., Merritt, J., Feng, Y. Functional definition of NrtR, a remnant regulator of NAD+ homeostasis in the zoonotic pathogen Streptococcus suis.

Genomic surveillance indicates clonal replacement of hypervirulent Klebsiella pneumoniae ST881 and ST29 lineage strains in vivo.

The emergence of hypervirulent Klebsiella pneumoniae (hvKp) poses a significant public health threat, particularly regarding its carriage in the healthy population. However, the genomic epidemiological characteristics and population dynamics of hvKp within a single patient across distinct infection episodes remain largely unknown. This study aimed to investigate the clonal replacement of hvKp K2-ST881 and K54-ST29 lineage strains in a single patient experiencing multiple-site infections during two independent episodes. Two strains, designated EDhvKp-1 and EDhvKp-2, were obtained from blood and cerebrospinal fluid during the first admission, and the strain isolated from blood on the second admission was named EDhvKp-3. Whole-genome sequencing, utilizing both short-read Illumina and long-read Oxford Nanopore platforms, was conducted. In silico multilocus sequence typing (MLST), identification of antimicrobial resistance and virulence genes, and the phylogenetic relationship between our strains and other K. pneumoniae ST881 and ST29 genomes retrieved from the public database were performed. Virulence potentials were assessed through a mouse lethality assay. Our study indicated that the strains were highly susceptible to multiple antimicrobial agents. Plasmid sequence analysis confirmed that both virulence plasmids, pEDhvKp-1 (166,008 bp) and pEDhvKp-3 (210,948 bp), belonged to IncFIB type. Multiple virulence genes, including rmpA, rmpA2, rmpC, rmpD, iroBCDN, iucABCD, and iutA, were identified. EDhvKp-1 and EDhvKp-2 showed the closest relationship to strain 502 (differing by 51 SNPs), while EDhvKp-3 exhibited 69 SNPs differences compared to strain TAKPN-1, which all recovered from Chinese patients in 2020. In the mouse infection experiment, both ST881 EDhvKp-1 and ST29 EDhvKp-3 displayed similar virulence traits, causing 90 and 100% of the mice to die within 72 h after intraperitoneal infection, respectively. Our study expands the spectrum of hvKp lineages and highlights genomic alterations associated with clonal switching between two distinct lineages of hvKP that successively replaced each other in vivo. The development of novel strategies for the surveillance, diagnosis, and treatment of high-risk hvKp is urgently needed.

Chasing the landscape for intrahospital transmission and evolution of hypervirulent carbapenem-resistant Klebsiella pneumoniae.

The spread of hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKP) is a global health concern. Here, we report the intrahospital colonization and spread of Hv-CRKP isolates in a tertiary hospital from 2017 to 2022. Analyses of 90 nonredundant CRKP isolates from 72 patients indicated that Hv-CRKP transferability relies on the dominant ST11-K64 clone. Whole-genome sequencing of 11 representative isolates gave 31 complete plasmid sequences, including 12 KPC-2 resistance carriers and 10 RmpA virulence vehicles. Apart from the binary vehicles, we detected two types of fusion plasmids, favoring the cotransfer of RmpA virulence and KPC-2 resistance. The detection of ancestry/relic plasmids enabled us to establish genetic mechanisms by which rare fusion plasmids form. Unexpectedly, we found a total of five rmpA promoter variants (P9T-P13T) exhibiting distinct activities and varying markedly in their geographic distributions. CRISPR/Cas9 manipulation confirmed that an active PT11-rmpA regulator is a biomarker for the "high-risk" ST11-K64/CRKP clone. These findings suggest clonal spread and clinical evolution of the prevalent ST11-K64/Hv-CRKP clones. Apart from improved public awareness of Hv-CRKP convergence, our findings might benefit the development of surveillance (and/or intervention) strategies for the dominant ST11-K64 lineage of the Hv-CRKP population in healthcare sectors.

Structure and mechanism for streptococcal fatty acid kinase (Fak) system dedicated to host fatty acid scavenging.

Staphylococcus and Streptococcus, two groups of major human pathogens, are equipped with a fatty acid kinase (Fak) machinery to scavenge host fatty acids. The Fak complex is contains an ATP-binding subunit FakA, which interacts with varied FakB isoforms, and synthesizes acyl-phosphate from extracellular fatty acids. However, how FakA recognizes its FakB partners and then activates different fatty acids is poorly understood. Here, we systematically describe the Fak system from the zoonotic pathogen, Streptococcus suis. The crystal structure of SsFakA complexed with SsFakB2 was determined at 2.6 Å resolution. An in vitro system of Fak-PlsX (phosphate: acyl-ACP transacylase) was developed to track acyl-phosphate intermediate and its final product acyl-ACP. Structure-guided mutagenesis enabled us to characterize a mechanism for streptococcal FakA working with FakB partners engaged in host fatty acid scavenging. These findings offer a comprehensive description of the Fak kinase machinery, thus advancing the discovery of attractive targets against deadly infections with Streptococcus.