Carbapenem-resistant Klebsiella pneumoniae strain 1756 was isolated from a pus specimen from a Taiwanese patient. Here, the complete genome sequence of strain 1756 is presented. Copyright © 2017 Kao et al.
An atypically large outbreak of Elizabethkingia anophelis infections occurred in Wisconsin. Here we show that it was caused by a single strain with thirteen characteristic genomic regions. Strikingly, the outbreak isolates show an accelerated evolutionary rate and an atypical mutational spectrum. Six phylogenetic sub-clusters with distinctive temporal and geographic dynamics are revealed, and their last common ancestor existed approximately one year before the first recognized human infection. Unlike other E. anophelis, the outbreak strain had a disrupted DNA repair mutY gene caused by insertion of an integrative and conjugative element. This genomic change probably contributed to the high evolutionary rate of the outbreak strain and may have increased its adaptability, as many mutations in protein-coding genes occurred during the outbreak. This unique discovery of an outbreak caused by a naturally occurring mutator bacterial pathogen provides a dramatic example of the potential impact of pathogen evolutionary dynamics on infectious disease epidemiology.
Klebsiella pneumoniae is a major human pathogen responsible for high morbidity and mortality rates. The emergence and spread of strains resistant to multiple antimicrobial agents and documented large nosocomial outbreaks are especially concerning. To develop new therapeutic strategies for K. pneumoniae, it is imperative to understand the population genomic structure of strains causing human infections. To address this knowledge gap, we sequenced the genomes of 1,777 extended-spectrum beta-lactamase-producing K. pneumoniae strains cultured from patients in the 2,000-bed Houston Methodist Hospital system between September 2011 and May 2015, representing a comprehensive, population-based strain sample. Strains of largely uncharacterized clonal group 307 (CG307) caused more infections than those of well-studied epidemic CG258. Strains varied markedly in gene content and had an extensive array of small and very large plasmids, often containing antimicrobial resistance genes. Some patients with multiple strains cultured over time were infected with genetically distinct clones. We identified 15 strains expressing the New Delhi metallo-beta-lactamase 1 (NDM-1) enzyme that confers broad resistance to nearly all beta-lactam antibiotics. Transcriptome sequencing analysis of 10 phylogenetically diverse strains showed that the global transcriptome of each strain was unique and highly variable. Experimental mouse infection provided new information about immunological parameters of host-pathogen interaction. We exploited the large data set to develop whole-genome sequence-based classifiers that accurately predict clinical antimicrobial resistance for 12 of the 16 antibiotics tested. We conclude that analysis of large, comprehensive, population-based strain samples can assist understanding of the molecular diversity of these organisms and contribute to enhanced translational research. IMPORTANCEKlebsiella pneumoniae causes human infections that are increasingly difficult to treat because many strains are resistant to multiple antibiotics. Clonal group 258 (CG258) organisms have caused outbreaks in health care settings worldwide. Using a comprehensive population-based sample of extended-spectrum beta-lactamase (ESBL)-producing K. pneumoniae strains, we show that a relatively uncommon clonal type, CG307, caused the plurality of ESBL-producing K. pneumoniae infections in our patients. We discovered that CG307 strains have been abundant in Houston for many years. As assessed by experimental mouse infection, CG307 strains were as virulent as pandemic CG258 strains. Our results may portend the emergence of an especially successful clonal group of antibiotic-resistant K. pneumoniae. Copyright © 2017 Long et al.
Staphylococcus aureus MRSA strains belonging to the clonal complex 398 (CC398) are highly prevalent in livestock and companion animals but may also cause serious infections in humans. CC398 strains in livestock usually do not possess well-known virulence factors that can be frequently found in other MRSA sequence types (ST). Since many staphylococcal virulence genes are residing on the genomes of temperate phages, the question arises why livestock-associated (LA-) CC398 strains are only rarely infected by those phages. We isolated and characterized four temperate phages (P240, P282, P630 and P1105) containing genes of the immune evasion cluster (IEC) and/or for the Panton-Valentine leucocidin (PVL). Sequence analysis of the phage genomes showed that they are closely related to known phages and that the DNA region encoding lysis proteins, virulence factors and the integrase exhibits numerous DNA repeats which may facilitate genomic rearrangements. All phages lysed and lysogenized LA-CC398 strains. Integration of IEC phage P282 was detected at ten sites of the hosts’ chromosome. The prophages were stably inherited in LA-CC398 and enterotoxin A, staphylokinase and PVL toxin were produced. The data demonstrate that lysogenic conversion of LA-CC398 strains by virulence-associated phages may occur and that new pathotypes may emerge by this mechanism.
Clostridium perfringens is an opportunistic human pathogen that causes necrotic enteritis, mild diarrhea, clostridial myonecrosis or gas gangrene, sepsis, etc. In this study, we aim to determine the pathogenesis of this bacterium at the genomic level. The genome of strain CBA7123 was sequenced, and a comparative genomic analysis between strain CBA7123 and four other related C. perfringens strains was performed.The genome of strain CBA7123 consisted of one circular chromosome and one plasmid that were 3,088,370 and 46,640 bp long with 28.5 and 27.1 mol% G+C content, respectively. The genomic DNA was predicted to contain 2798 open reading frames (ORFs), 10 rRNA genes, and 94 tRNA genes. The genomic comparison analysis between the five strains revealed the distinctive virulence properties of strain CBA7123 by highlighting certain strain-specific genes.In this study, the C. perfringens CBA7123 genome was sequenced and compared with other C. perfringens genomes. Among the various genes sequenced, the detection of antimicrobial resistance genes and those encoding various virulence factors may extend the understanding of the pathogenesis of C. perfringens strains.
USA300 is a predominant community-associated methicillin-resistant Staphylococcus aureus strain causing significant morbidity and mortality. We present here the full annotated genome of a USA300 hypervirulent clinical strain, USA300-C2406, isolated from a patient with a lethal case of necrotizing pneumonia, to gain a better understanding of USA300 hypervirulence. Copyright © 2017 McClure and Zhang.
In this study, we sequenced the complete genome of the multidrug-resistant Escherichia coli strain E28, which was used as an indicator strain for phage therapy in vivo We used a combination of single-molecule real-time and Illumina sequencing technology to reveal the presence of a spontaneously inducible prophage. Copyright © 2017 Schmidt et al.
The emergence of the plasmid-mediated mcr colistin resistance gene in the community poses a potential threat for treatment of patients, especially when hospitalized. The aim of this study was to determine the prevalence of all currently known mcr mediated colistin resistance gene in fecal samples of patients attending a tertiary care hospital. From November 2014 until July 2015, fecal samples of patients attending the Leiden University Medical Center were collected and screened for presence of mcr using real-time PCR. Two of 576 patients were positive for mcr-1, resulting in a prevalence of 0.35%, whereas no mcr-2 was found. One of these samples was culture negative, the second sample contained a blaCMY-2 and mcr-1 containing E.coli. This strain belonged to Sequence Type 359 and serotype O177:H21. The mcr-1 containing E.coli was phenotypically susceptible to colistin with a MIC of = 0.25mg/l, due to a 1329bp transposon IS10R inserted into the mcr-1 gene as identified by WGS. This prevalence study shows that mcr-1 is present in low levels patients out of the community attending a hospital. Furthermore the study underlines the importance of phenotypical confirmation of molecular detection of a mcr-1 gene.
We tested the biofilm formation potential of 30 heat-resistant and 6 heat-sensitive Escherichia coli dairy isolates. Production of curli and cellulose, static biofilm formation on polystyrene (PS) and stainless steel surfaces, biofilm formation under dynamic conditions (Bioflux), and initial adhesion rates (IAR) were evaluated. Biofilm formation varied greatly between strains, media, and assays. Our results highlight the importance of the experimental setup in determining biofilm formation under conditions of interest, as correlation between different assays was often not a given. The heat-resistant, multidrug-resistant (MDR) strain FAM21845 showed the strongest biofilm formation on PS and the highest IAR and was the only strain that formed significant biofilms on stainless steel under conditions relevant to the dairy industry, and it was therefore fully sequenced. Its chromosome is 4.9 Mb long, and it harbors a total of five plasmids (147.2, 54.2, 5.8, 2.5, and 1.9 kb). The strain carries a broad range of genes relevant to antimicrobial resistance and biofilm formation, including some on its two large conjugative plasmids, as demonstrated in plate mating assays.IMPORTANCE In biofilms, cells are embedded in an extracellular matrix that protects them from stresses, such as UV radiation, osmotic shock, desiccation, antibiotics, and predation. Biofilm formation is a major bacterial persistence factor of great concern in the clinic and the food industry. Many tested strains formed strong biofilms, and especially strains such as the heat-resistant, MDR strain FAM21845 may pose a serious issue for food production. Strong biofilm formation combined with diverse resistances (some encoded on conjugative plasmids) may allow for increased persistence, coselection, and possible transfer of these resistance factors. Horizontal gene transfer may conceivably occur in the food production setting or the gastrointestinal tract after consumption. Copyright © 2017 Marti et al.
Staphylococcus aureus sequence type 398 (ST398) is a rapidly emerging livestock-associated strain causing zoonotic disease in humans. The course of pathogen evolution remains unclear, prompting whole-genome comparative studies in attempts to elucidate this issue. We present the full, annotated genomes of five newly isolated representative ST398 strains from five major sequence heterogeneity groups of our diverse isolate collection. Copyright © 2017 McClure and Zhang.
Several lines of evidence indicate that the most primitive staphylococcal species, those of the Staphylococcus sciuri group, were involved in the first stages of evolution of the staphylococcal cassette chromosome mec (SCCmec), the genetic element carrying the ß-lactam resistance gene mecA However, many steps are still missing from this evolutionary history. In particular, it is not known how mecA was incorporated into the mobile element SCC prior to dissemination among Staphylococcus aureus and other pathogenic staphylococcal species. To gain insights into the possible contribution of several species of the Staphylococcus sciuri group to the assembly of SCCmec, we sequenced the genomes of 106 isolates, comprising S. sciuri (n = 76), Staphylococcus vitulinus (n = 18), and Staphylococcus fleurettii (n = 12) from animal and human sources, and characterized the native location of mecA and the SCC insertion site by using a variety of comparative genomic approaches. Moreover, we performed a single nucleotide polymorphism (SNP) analysis of the genomes in order to understand SCCmec evolution in relation to phylogeny. We found that each of three species of the S. sciuri group contributed to the evolution of SCCmec: S. vitulinus and S. fleurettii contributed to the assembly of the mec complex, and S. sciuri most likely provided the mobile element in which mecA was later incorporated. We hypothesize that an ancestral SCCmec III cassette (an element carried by one of the most epidemic methicillin-resistant S. aureus clones) originated in S. sciuri possibly by a recombination event in a human host or a human-created environment and later was transferred to S. aureus. Copyright © 2017 American Society for Microbiology.
We report here the complete genome sequence of the livestock-associated methicillin-resistant Staphylococcus aureus strain 08S00974 from sequence type 398 (ST398 LA-MRSA) isolated from a fatting pig at a farm in Germany. Copyright © 2017 Makarova et al.
Burkholderia pseudomallei Bp1651 is resistant to several classes of antibiotics that are usually effective for treatment of melioidosis, including tetracyclines, sulfonamides, and ß-lactams such as penicillins (amoxicillin-clavulanic acid), cephalosporins (ceftazidime), and carbapenems (imipenem and meropenem). We sequenced, assembled, and annotated the Bp1651 genome and analyzed the sequence using comparative genomic analyses with susceptible strains, keyword searches of the annotation, publicly available antimicrobial resistance prediction tools, and published reports. More than 100 genes in the Bp1651 sequence were identified as potentially contributing to antimicrobial resistance. Most notably, we identified three previously uncharacterized point mutations in penA, which codes for a class A ß-lactamase and was previously implicated in resistance to ß-lactam antibiotics. The mutations result in amino acid changes T147A, D240G, and V261I. When individually introduced into select agent-excluded B. pseudomallei strain Bp82, D240G was found to contribute to ceftazidime resistance and T147A contributed to amoxicillin-clavulanic acid and imipenem resistance. This study provides the first evidence that mutations in penA may alter susceptibility to carbapenems in B. pseudomallei Another mutation of interest was a point mutation affecting the dihydrofolate reductase gene folA, which likely explains the trimethoprim resistance of this strain. Bp1651 was susceptible to aminoglycosides likely because of a frameshift in the amrB gene, the transporter subunit of the AmrAB-OprA efflux pump. These findings expand the role of penA to include resistance to carbapenems and may assist in the development of molecular diagnostics that predict antimicrobial resistance and provide guidance for treatment of melioidosis. Copyright © 2017 American Society for Microbiology.
Acinetobacter baumannii is an increasingly common multidrug-resistant pathogen in health care settings. Although the genetic basis of antibiotic resistance mechanisms has been extensively studied, much less is known about how genetic variation contributes to other aspects of successful infections. Genetic changes that occur during host infection and treatment have the potential to remodel gene expression patterns related to resistance and pathogenesis. Longitudinal sets of multidrug-resistant A. baumannii isolates from eight patients were analyzed by RNA sequencing (RNA-seq) to identify differentially expressed genes and link them to genetic changes contributing to transcriptional variation at both within-patient and population levels. The number of differentially expressed genes among isolates from the same patient ranged from 26 (patient 588) to 145 (patient 475). Multiple patients had isolates with differential gene expression patterns related to mutations in the pmrAB and adeRS two-component regulatory system genes, as well as significant differences in genes related to antibiotic resistance, iron acquisition, amino acid metabolism, and surface-associated proteins. Population level analysis revealed 39 genetic regions with clade-specific differentially expressed genes, for which 19, 8, and 3 of these could be explained by insertion sequence mobilization, recombination-driven sequence variation, and intergenic mutations, respectively. Multiple types of mutations that arise during infection can significantly remodel the expression of genes that are known to be important in pathogenesis. IMPORTANCE Health care-associated multidrug-resistant Acinetobacter baumannii can cause persistent infections in patients, but bacterial cells must overcome host defenses and antibiotic therapies to do so. Genetic variation arises during host infection, and new mutations are often enriched in genes encoding transcriptional regulators, iron acquisition systems, and surface-associated structures. In this study, genetic variation was shown to result in transcriptome remodeling at the level of individual patients and across phylogenetic groups. Differentially expressed genes include those related to capsule modification, iron acquisition, type I pili, and antibiotic resistance. Population level transcriptional variation reflects genome dynamics over longer evolutionary time periods, and convergent transcriptional changes support the adaptive significance of these regions. Transcriptional changes can be attributed to multiple types of genomic change, but insertion sequence mobilization had a predominant effect. The transcriptional effects of mutations that arise during infection highlight the rapid adaptation of A. baumannii during host exposure. Copyright © 2017 Wright et al.
M92 is a methicillin-resistant Staphylococcus aureus (MRSA) colonizing strain belonging to ST239-MRSA-III. It frequently shows local nasal colonization in our hospital staff, but has never been associated with infection. We sequenced the complete genome of M92, in order to compare it to highly virulent MRSA strains to gain insight into MRSA virulence factors. Copyright © 2017 McClure and Zhang.
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