Functional and molecular characterization of pSE34 encoding a type IV secretion system inSalmonella entericaserotype Enteritidis phage type 34

Temperature-Regulated IncX3 Plasmid Characteristics and the Role of Plasmid-Encoded H-NS in Thermoregulation

Carbapenem-resistant Enterobacteriaceae (CRE) are a critical public health problem worldwide. Globally, IncX3-type plasmids have emerged as the predominant vehicles carrying the metallo-β-lactamase gene bla NDM. Although bla NDM-bearing IncX3 plasmids have been found in various hosts from diverse environments, whether their transfer and persistence properties vary under different conditions and what factors influence any variation is unknown. By observing the effects of different temperatures on IncX3 plasmid conjugation rates, stability, and effects on host fitness in Escherichia coli, we demonstrate that temperature is an important determinant of plasmid phenotypes. The IncX3 plasmid pGZIncX3 transferred at highest frequencies, was most stable and imposed lower fitness costs at 37°C. Temperature-regulated variation in pGZIncX3 properties involved a thermoregulated plasmid-encoded H-NS-like protein, which was produced at higher levels at 30°C and 42°C and inhibited the expression of type IV secretion system genes involved in conjugation. These findings suggest that bla NDM-bearing IncX3 plasmids are adapted to carriage by enterobacteria that colonize mammalian hosts and could explain the rapid dissemination of these plasmids among human-associated species, particularly in hospital settings.

Microbiological and genomic investigations of invasive Salmonella enterica serovar Panama from a large outbreak in Taiwan

BACKGROUND/PURPOSE

Salmonella Panama was considered an invasive non-typhoidal Salmonella (iNTS) serovar. Comprehensive clinical, microbiological, and genomic studies on S. Panama are scarce. We aimed to characterize the clinical and microbiological characteristics of S. Panama infection. Virulence mechanism of S. Panama and other iNTS serovars were also examined.

METHODS

Based on data from the longitudinal surveillance system for Salmonella deployed in Taiwan since 2004, a case-control study was undertaken to evaluate clinical characteristics of S. Panama infection during an outbreak in 2015-2016. Cellular experiments were conducted to compare pathogenicity of S. Panama and other iNTS with S. Typhimurium.

RESULTS

Most patients (41/44, 93.2%) infected by S. Panama were <5 years old (median, 1.3 years). The case-control study showed that 28 out of the 41 (68.3%) manifested as bacteremia, compared to S. Typhimurium (11.1%). Patients infected by S. Panama had longer durations of fever (P = 0.005) and hospitalization (P < 0.001). Genomic analyses split the isolates into three clades: two clones caused the outbreak, whereas another one accounted for the sporadic infections before 2015. Cellular experiments revealed that S. Panama and other iNTS serovars showed higher monolayer penetration and intracellular survival within macrophages, compared to S. Typhimurium.

CONCLUSION

This study confirmed that S. Panama is a clinically invasive serovar. Different iNTS serovars express common virulence phenotypes, but they may acquire invasiveness through distinct expression or combinations of virulence genes.

Impact of Plasmid-Encoded H-NS-like Protein on blaNDM-1-Bearing IncX3 Plasmid in Escherichia coli

BACKGROUND

This study was performed to assess the role of the histone-like nucleoid-structuring (H-NS)-like protein, carried by blaNDM-1-encoding IncX3-type plasmids, in the dissemination of IncX3 plasmids.

METHODS

The blaNDM-1-encoding IncX3 plasmids were analyzed using southern blot, conjugation, and competition assays. Virulence was evaluated with a Galleria mellonella infection model. An hns-knockout IncX3 plasmid was also constructed to identify the functions of plasmid-borne H-NS-like protein in Escherichia coli.

RESULTS

The assasys detected blaNDM-1-encoding IncX3-type plasmids with similar fingerprint patterns in all New Delhi metallo-β-lactamase (NDM) 1-producing carbapenem-resistant Enterobacteriaceae. The IncX3 plasmid conferred a fitness advantage to E. coli J53 but had no effect on host virulence. Moreover, the transconjugation frequency of the hns-null IncX3 plasmid pHN330-△hns was increased by 2.5-fold compared with the wild type. This was caused by up-regulation of conjugation-related plasmid-borne genes and the partition-related gene, in the J330-pHN330-△hns strain. In addition, decreased virulence was detected with this variant.

CONCLUSIONS

Our results highlight the important role of IncX3 plasmids in the dissemination of blaNDM-1 in south China. Plasmid-encoded H-NS-like protein can inhibit plasmid conjugation, partition, and the expression of related genes, in addition to promoting virulence in the host.

Salmonella secretion systems: Differential roles in pathogen-host interactions

The bacterial genus Salmonella includes a large group of food-borne pathogens that cause a variety of gastrointestinal or systemic diseases in hosts. Salmonella use several secretion devices to inject various effectors targeting eukaryotic hosts, or bacteria. In the past few years, considerable progress has been made towards understanding the structural features and molecular mechanisms of the secretion systems of Salmonella, particularly regarding their roles in host-pathogen interactions. In this review, we summarize the current advances about the main characteristics of the Salmonella secretion systems. Clarifying the roles of the secretion systems in the process of infecting various hosts will broaden our understanding of the importance of microbial interactions in maintaining human health and will provide information for developing novel therapeutic approaches.

Towards a Low-Cost and Portable Photoacoustic Microscope for Point-of-Care and Wearable Applications

Several breakthrough applications in biomedical imaging have been reported in the recent years using advanced photoacoustic microscopy imaging systems. While two photon and other optical microscopy systems have recently emerged in portable and wearable form, there is much less work reported on the portable and wearable photoacoustic microscopy (PAM) systems. Working towards this goal, we report our studies on a low-cost and portable photoacoustic microscopy system that uses a custom fabricated 2.5 mm diameter ring ultrasound transducer integrated with a fiber-coupled laser diode. The ultrasound transducer is centered at 17.25 MHz, and shows ~ 45% and ~ 100% fractional bandwidths for ultrasound pulse-echo and photoacoustic A-line signals respectively. To achieve overall system portability, besides the imaging head, other backend imaging system components need to be readily portable as well. In this direction, we have studied the potential use of compact pre-amplifiers, scanning stages and microcontroller based data acquisition and reconstruction for photoacoustic imaging. The portable PAM system is validated by imaging phantoms embedded with light absorbing targets. Future directions that will likely help achieve a completely portable and wearable photoacoustic microscopy system are discussed.

Discovery of an Isothiazolinone-Containing Antitubercular Natural Product Levesquamide

Antitubercular agent levesquamide is a new polyketide-nonribosomal peptide (PK-NRP) hybrid marine natural product isolated from Streptomyces sp. RKND-216. The structure contains a rare isothiazolinone moiety which has only been reported in collismycin SN. Structure elucidation by NMR spectroscopy was a significant challenge due to a deficiency of protons in this aromatic moiety. Therefore, the genome of Streptomyces sp. RKND-216 was sequenced to identify the levesquamide biosynthetic gene cluster (BGC). Analysis of the BGC provided structural insights and guided stable-isotope labeling experiments, which led to the assignment of the fused pyridine-isothiazolinone moiety. The BGC and the labeling experiments provide further insights into the biosynthetic origin of isothiazolinones. Levesquamide exhibited antimicrobial activity in the microplate alamarBlue assay (MABA) and low oxygen recovery assay (LORA) against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) values of 9.65 and 22.28 μM, respectively. Similar activity was exhibited against rifampicin- and isoniazid-resistant M. tuberculosis strains with MIC values of 9.46 and 9.90 μM, respectively. This result suggests levesquamide has a different mode of action against M. tuberculosis compared to the two first-line antitubercular drugs rifampicin and isoniazid. Furthermore, levesquamide shows no cytotoxicity against the Vero cell line, suggesting it may have a useful therapeutic window.

IncX4 Plasmid Carrying the New mcr-1.9 Gene Variant in a CTX-M-8-Producing Escherichia coli Isolate Recovered From Swine

We studied a commensal colistin-resistant Escherichia coli isolated from a swine cecum sample collected at a slaughter, in Portugal. Antimicrobial susceptibility phenotype of E. coli LV23529 showed resistance to colistin at a minimum inhibitory concentration of 4 mg/L. Whole genome of E. coli LV23529 was sequenced using a MiSeq system and the assembled contigs were analyzed for the presence of antibiotic resistance and plasmid replicon types using bioinformatics tools. We report a novel mcr-1 gene variant (mcr-1.9), carried by an IncX4 plasmid, where one-point mutation at nucleotide T1238C leads to Val413Ala substitution. The mcr-1.9 genetic context was characterized by an IS26 element upstream of the mcr-pap2 element and by the absence of ISApl1. Bioinformatic analysis also revealed genes conferring resistance to β-lactams, sulphamethoxazole, trimethoprim, chloramphenicol and colistin, corresponding to the phenotype noticed. Moreover, we highlight the presence of mcr-1.9 plus bla_CTX-M-8, a bla_ESBL gene rarely detected in Europe in isolates of animal origin; these two genes were located on different plasmids with 33,303 and 89,458 bp, respectively. MCR-1.9-harboring plasmid showed high identity to other X4-type mcr-1-harboring plasmids characterized worldwide, which strongly suggests that the presence of PMCR-encoding genes in food-producing animals, such as MCR-1.9, represent a potential threat to humans, as it is located in mobile genetic elements that have the potential to spread horizontally.

Plasmid with Colistin Resistance Gene mcr-1 in Extended-Spectrum-β-Lactamase-Producing Escherichia coli Strains Isolated from Pig Slurry in Estonia

A plasmid carrying the colistin resistance gene mcr-1 was isolated from a pig slurry sample in Estonia. The gene was present on a 33,311-bp plasmid of the IncX4 group. mcr-1 is the only antibiotic resistance gene on the plasmid, with the other genes mainly coding for proteins involved in conjugative DNA transfer (taxA, taxB, taxC, trbM, and the pilX operon). The plasmid pESTMCR was present in three phylogenetically very different Escherichia coli strains, suggesting that it has high potential for horizontal transfer.

Development of a new molecular subtyping tool for Salmonella enterica serovar Enteritidis based on single nucleotide polymorphism genotyping using PCR

The lack of a sufficiently discriminatory molecular subtyping tool for Salmonella enterica serovar Enteritidis has hindered source attribution efforts and impeded regulatory actions required to disrupt its food-borne transmission. The underlying biological reason for the ineffectiveness of current molecular subtyping tools such as pulsed-field gel electrophoresis (PFGE) and phage typing appears to be related to the high degree of clonality of S. Enteritidis. By interrogating the organism's genome, we previously identified single nucleotide polymorphisms (SNP) distributed throughout the chromosome and have designed a highly discriminatory PCR-based SNP typing test based on 60 polymorphic loci. The application of the SNP-PCR method to DNA samples from S. Enteritidis strains (n = 55) obtained from a variety of sources has led to the differentiation and clustering of the S. Enteritidis isolates into 12 clades made up of 2 to 9 isolates per clade. Significantly, the SNP-PCR assay was able to further differentiate predominant PFGE types (e.g., XAI.0003) and phage types (e.g., phage type 8) into smaller subsets. The SNP-PCR subtyping test proved to be an accurate, precise, and quantitative tool for evaluating the relationships among the S. Enteritidis isolates tested in this study and should prove useful for clustering related S. Enteritidis isolates involved in outbreaks.

Evaluation of Gram-negative bacterial infection by a stable and conjugative bioluminescence plasmid in a mouse model

Background

The green fluorescence protein (GFP)-associated fluorescence method and the luciferase-associated bioluminescence method are the two major methods for IVIS imaging system to investigate the bacterial infection in animal models. The aim of this study was to evaluate the infection route of Gram-negative bacteria carrying a stable and broad range of conjugative bioluminescence plasmid pSE-Lux1 in a mouse model.

Results

Both encapsulated and non-encapsulated Gram-negative bacteria were used as hosts to evaluate conjugation efficiency and plasmid stability of pSE-Lux1, a recombinant of pSE34 and luxABCDE operon. The plasmid conjugation efficiencies of pSE-Lux1 ranged from 10⁻³ to 10⁻⁷ in various Gram-negative bacteria. Plasmid pSE-Lux1 maintained in Escherichia coli, Klebsiella pneumoniae, and Salmonella enterica serovars Choleraesues (abbreviated S. Choleraesuis) and Typhimurium (S. Typhimurium), than in Acinetobacter baumannii and Serratia marcescens, was shown to be of better stability for at least four days. To investigate systemic bacterial infections, K. pneumoniae strain CG354 was intravenously injected, and then was clearly observed to be non-pathogenic to Balb/c mice for a long-term bioluminescence monitoring for 6 days. For examining dynamic distributions of gastrointestinal tract infection, the invasion protein SipB-deficient mutant OU5045△sipB and OU5046△sipB of S. serovar Typhimurium constructed in this study, compared to wild-type strain OU5045 and its virulence plasmid-less strain OU5046, were of less virulence to mice.

Conclusions

This is the first study to evaluate the conjugative and stable bioluminescence vehicle system of pSE-Lux1 in a wide range of Gram-negative bacteria, a system that can provide a useful reporter approach to trace systemic and gastrointestinal bacterial infections in a mouse model.

Conjugative transfer of an IncA/C plasmid-borne blaCMY-2 gene through genetic re-arrangements with an IncX1 plasmid

Background

Our observation that in the Mexican Salmonella Typhimurium population none of the ST19 and ST213 strains harbored both the Salmonella virulence plasmid (pSTV) and the prevalent IncA/C plasmid (pA/C) led us to hypothesize that restriction to horizontal transfer of these plasmids existed. We designed a conjugation scheme using ST213 strain YU39 as donor of the bla_CMY-2 gene (conferring resistance to ceftriaxone; CRO) carried by pA/C, and two E. coli lab strains (DH5α and HB101) and two Typhimurium ST19 strains (SO1 and LT2) carrying pSTV as recipients. The aim of this study was to determine if the genetic background of the different recipient strains affected the transfer frequencies of pA/C.

Results

YU39 was able to transfer CRO resistance, via a novel conjugative mechanism, to all the recipient strains although at low frequencies (10^-7 to 10^-10). The presence of pSTV in the recipients had little effect on the conjugation frequency. The analysis of the transconjugants showed that three different phenomena were occurring associated to the transfer of bla_CMY-2: 1) the co-integration of pA/C and pX1; 2) the transposition of the CMY region from pA/C to pX1; or 3) the rearrangement of pA/C. In addition, the co-lateral mobilization of a small (5 kb) ColE1-like plasmid was observed. The transconjugant plasmids involving pX1 re-arrangements (either via co-integration or ISEcp1-mediated transposition) obtained the capacity to conjugate at very high levels, similar to those found for pX1 (10^-1). Two versions of the region containing bla_CMY-2 were found to transpose to pX1: the large version was inserted into an intergenic region located where the “genetic load” operons are frequently inserted into pX1, while the short version was inserted into the stbDE operon involved in plasmid addiction system. This is the first study to report the acquisition of an extended spectrum cephalosporin (ESC)-resistance gene by an IncX1 plasmid.

Conclusions

We showed that the transfer of the YU39 bla_CMY-2 gene harbored on a non- conjugative pA/C requires the machinery of a highly conjugative pX1 plasmid. Our experiments demonstrate the complex interactions a single strain can exploit to contend with the challenge of horizontal transfer and antibiotic selective pressure.