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Comparative analysis of extended-spectrum-ß-lactamase CTX-M-65-producing Salmonella enterica serovar Infantis isolates from humans, food animals, and retail chickens in the United States.

Antimicrobial agents and chemotherapy
61, e00488-17


Abstract +

We sequenced the genomes of ten Salmonella enterica serovar Infantis containing blaCTX-M-65 isolated from chicken, cattle, and human sources collected between 2012 and 2015 in the United States through routine NARMS surveillance and product sampling programs. We also completely assembled the plasmids from four of the isolates. All isolates had a D87Y mutation in the gyrA gene and harbored between 7 and 10 resistance genes (aph (4)-Ia, aac (3)-IVa, aph(3' )-Ic, blaCTX-M-65, fosA3, floR, dfrA14, sul1, tetA, aadA1) located in two distinct sites of a megaplasmid (~316-323kb) similar to that described in a blaCTX-M-65-positive S. Infantis isolated from a patient in Italy. High-quality single nucleotide polymorphism (hqSNP) analysis revealed that all U.S. isolates were closely related, separated by only 1 to 38 pairwise high quality SNPs, indicating a high likelihood that strains from humans, chicken, and cattle recently evolved from a common ancestor. The U.S. isolates were genetically similar to the blaCTX-M-65-positive S. Infantis isolate from Italy, with a separation of 34 to 47 SNPs. This is the first report of the blaCTX-M-65 gene and the pESI-like megaplasmid from S. Infantis in the United States, and illustrates the importance of applying a global One Health, human and animal perspective to combat antimicrobial resistance. Copyright © 2017 American Society for Microbiology.

Comparative genomic analysis and virulence differences in closely related Salmonella enterica serotype Heidelberg isolates from humans, retail meats, and animals.

Genome biology and evolution
6, 1046-1068


Abstract +

Salmonella enterica subsp. enterica serovar Heidelberg (S. Heidelberg) is one of the top serovars causing human salmonellosis. Recently, an antibiotic-resistant strain of this serovar was implicated in a large 2011 multistate outbreak resulting from consumption of contaminated ground turkey that involved 136 confirmed cases, with one death. In this study, we assessed the evolutionary diversity of 44 S. Heidelberg isolates using whole-genome sequencing (WGS) generated by the 454 GS FLX (Roche) platform. The isolates, including 30 with nearly indistinguishable (one band difference) Xbal pulsed-field gel electrophoresis patterns (JF6X01.0032, JF6X01.0058), were collected from various sources between 1982 and 2011 and included nine isolates associated with the 2011 outbreak. Additionally, we determined the complete sequence for the chromosome and three plasmids from a clinical isolate associated with the 2011 outbreak using the Pacific Biosciences (PacBio) system. Using single-nucleotide polymorphism (SNP) analyses, we were able to distinguish highly clonal isolates, including strains isolated at different times in the same year. The isolates from the recent 2011 outbreak clustered together with a mean SNP variation of only 17 SNPs. The S. Heidelberg isolates carried a variety of phages, such as prophage P22, P4, lambda-like prophage Gifsy-2, and the P2-like phage which carries the sopE1 gene, virulence genes including 62 pathogenicity, and 13 fimbrial markers and resistance plasmids of the incompatibility (Inc)I1, IncA/C, and IncHI2 groups. Twenty-one strains contained an IncX plasmid carrying a type IV secretion system. On the basis of the recent and historical isolates used in this study, our results demonstrated that, in addition to providing detailed genetic information for the isolates, WGS can identify SNP targets that can be utilized for differentiating highly clonal S. Heidelberg isolates.

Genomic Analysis of Emerging Florfenicol-Resistant Campylobacter coli Isolated from the Cecal Contents of Cattle in the United States.



Abstract +

Genomic analyses were performed on florfenicol-resistant (FFNr) Campylobacter coli isolates recovered from cattle, and the cfr(C) gene-associated multidrug resistance (MDR) plasmid was characterized. Sixteen FFNrC. coli isolates recovered between 2013 and 2018 from beef cattle were sequenced using MiSeq. Genomes and plasmids were found to be closed for three of the isolates using the PacBio system. Single nucleotide polymorphisms (SNPs) across the genome and the structures of MDR plasmids were investigated. Conjugation experiments were performed to determine the transferability of cfr(C)-associated MDR plasmids. The spectrum of resistance encoded by the cfr(C) gene was further investigated by agar dilution antimicrobial susceptibility testing. All 16 FFNr isolates were MDR and exhibited coresistance to ciprofloxacin, nalidixic acid, clindamycin, and tetracycline. All isolates shared the same resistance genotype, carrying aph (3')-III, hph, ?aadE (truncated), blaOXA-61, cfr(C), and tet(O) genes plus a mutation of GyrA (T86I). The cfr(C), aph (3')-III, hph, ?aadE, and tet(O) genes were colocated on transferable MDR plasmids ranging in size from 48 to 50?kb. These plasmids showed high sequence homology with the pTet plasmid and carried several Campylobacter virulence genes, including virB2, virB4, virB5, VirB6, virB7, virB8, virb9, virB10, virB11, and virD4 The cfr(C) gene conferred resistance to florfenicol (8 to 32?µg/ml), clindamycin (512 to 1,024?µg/ml), linezolid (128 to 512?µg/ml), and tiamulin (1,024?µg/ml). Phylogenetic analysis showed SNP differences ranging from 11 to 2,248 SNPs among the 16 isolates. The results showed that the cfr(C) gene located in the conjugative pTet MDR/virulence plasmid is present in diverse strains, where it confers high levels of resistance to several antimicrobials, including linezolid, a critical drug for treating infections by Gram-positive bacteria in humans. This report highlights the power of genomic antimicrobial resistance surveillance to uncover the intricacies of transmissible coresistance and provides information that is needed for accurate risk assessment and mitigation strategies.IMPORTANCECampylobacter is a leading cause of foodborne diarrheal illness worldwide, with more than one million cases each year in the United States alone. The global emergence of antimicrobial resistance in this pathogen has become a growing public health concern. Florfenicol-resistant (FFNr) Campylobacter has been very rare in the United States. In this study, we employed whole-genome sequencing to characterize 16 multidrug-resistant Campylobacter coli isolates recovered from cattle in the United States. A gene [cfr(C)] was found to be responsible for resistance not only to florfenicol but also to several other antimicrobials, including linezolid, a critical drug for treating infections by Gram-positive bacteria in humans. The results showed that cfr(C) is located in a conjugative pTet MDR/virulence plasmid. This report highlights the power of antimicrobial resistance surveillance to uncover the intricacies of transmissible coresistance and provides information that is needed for accurate risk assessment and mitigation strategies.

Comparative Genomic Analysis of Virulence, Antimicrobial Resistance, and Plasmid Profiles of Salmonella Dublin Isolated from Sick Cattle, Retail Beef, and Humans in the United States.

Microbial drug resistance
ePub ahead of print


Abstract +

Salmonella enterica serovar Dublin is a host-adapted serotype associated with typhoidal disease in cattle. While rare in humans, it usually causes severe illness, including bacteremia. In the United States, Salmonella Dublin has become one of the most multidrug-resistant (MDR) serotypes. To understand the genetic elements that are associated with virulence and resistance, we sequenced 61 isolates of Salmonella Dublin (49 from sick cattle and 12 from retail beef) using the Illumina MiSeq and closed 5 genomes using the PacBio sequencing platform. Genomic data of eight human isolates were also downloaded from NCBI (National Center for Biotechnology Information) for comparative analysis. Fifteen Salmonella pathogenicity islands (SPIs) and a spv operon (spvRABCD), which encodes important virulence factors, were identified in all 69 (100%) isolates. The 15 SPIs were located on the chromosome of the 5 closed genomes, with each of these isolates also carrying 1 or 2 plasmids with sizes between 36 and 329?kb. Multiple antimicrobial resistance genes (ARGs), including blaCMY-2, blaTEM-1B, aadA12, aph(3')-Ia, aph(3')-Ic, strA, strB, floR, sul1, sul2, and tet(A), along with spv operons were identified on these plasmids. Comprehensive antimicrobial resistance genotypes were determined, including 17 genes encoding resistance to 5 different classes of antimicrobials, and mutations in the housekeeping gene (gyrA) associated with resistance or decreased susceptibility to fluoroquinolones. Together these data revealed that this panel of Salmonella Dublin commonly carried 15 SPIs, MDR/virulence plasmids, and ARGs against several classes of antimicrobials. Such genomic elements may make important contributions to the severity of disease and treatment failures in Salmonella Dublin infections in both humans and cattle.

Genotypes and phenotypes of Enterococci isolated from broiler chickens

Frontiers in sustainable food systems
2, 83


Abstract +

The objective of this study was to compare the resistance phenotypes to genotypes of enterococci from broiler and to evaluate the persistence and distribution of resistant genotypes in broiler fed bambermycin (BAM), penicillin (PEN), salinomycin (SAL), bacitracin (BAC) or a salinomycin/bacitracin combination (SALBAC) for 35 days. A total of 95 enterococci from cloacal (n=40), cecal (n=38) and litter collected on day 36 (n=17) samples were isolated weekly from day 7 to 36. All isolates were identified by API-20 Strep and their antimicrobial susceptibilities were evaluated using the Sensititre system with the commercially available NARMS’s plates of Gram positive bacteria. Whole genome sequencing (WGS) was used to assess their intra- and inter-genetic variability, with a focus on virulence and antibiotic resistance characteristics. All isolates were further characterized for hemolysin production (HEM), bile salt hydrolysis (BSH) and gelatinase (GEL) activities. Of the 95 isolates, E. faecium (n = 58) and E. faecalis (n = 24) were the most common Enterococcus species identified. Significant differences in the level of resistance for the E. faecium isolates to ciprofloxacin, macrolide, penicillin and tetracycline were observed among treatments. The bcrR, mefA and aac(6) genes were higher in BAM treatment than the other groups whereas bcrR, ermA, ermB, aphA(3) and tetL were more prevalent in PEN and BAC treatments. Overall, E. faecium isolates showed higher prevalence of antimicrobial resistance, but E. faecalis from litter also exhibited a significant level of resistance. A range of 4 to 15 different virulence genes was detected in E. faecalis. All isolates from litter but one (94.1%) showed BSH activities while 52.9% of them produced GEL. HEM activity was observed only in isolates collected on Day 7 (n= 9) and Day 14 (n= 1). This study confirmed that genetically diverse antimicrobial resistant enterococci harboring virulence factors can be promoted by the use of certain antimicrobials in feed and such enterococci could persist in broiler chickens and their litter, potentially contaminating the soil upon land application. This study underscores the need for ongoing monitoring the AMR enterococci.

Novel linezolid resistance plasmids in Enterococcus from food animals in the USA.

The Journal of antimicrobial chemotherapy
73, 3254-3258


Abstract +

To sequence the genomes and determine the genetic mechanisms for linezolid resistance identified in three strains of Enterococcus isolated from cattle and swine caecal contents as part of the US National Antimicrobial Resistance Monitoring System (NARMS) surveillance programme.Broth microdilution was used for in vitro antimicrobial susceptibility testing to assess linezolid resistance. Resistance mechanisms and plasmid types were identified from data generated by WGS on Illumina® and PacBio® platforms. Conjugation experiments were performed to determine whether identified mechanisms were transmissible.Linezolid resistance plasmids containing optrA were identified in two Enterococcus faecalis isolates and one Enterococcus faecium. The E. faecium isolate also carried the linezolid resistance gene cfr on the same plasmid as optrA. The linezolid resistance plasmids had various combinations of additional resistance genes conferring resistance to phenicols (fexA), aminoglycosides [spc and aph(3')-III] and macrolides [erm(A) and erm(B)]. One of the plasmids was confirmed to be transmissible by conjugation, resulting in linezolid resistance in the transconjugant.To the best of our knowledge, this is the first identification of linezolid resistance in the USA in bacteria isolated from food animals. The oxazolidinone class of antibiotics is not used in food animals in the USA, but the genes responsible for resistance were identified on plasmids with other resistance markers, indicating that there may be co-selection for these plasmids due to the use of different antimicrobials. The transmissibility of one of the plasmids demonstrated the potential for linezolid resistance to spread horizontally. Additional surveillance is necessary to determine whether similar plasmids are present in human strains of Enterococcus.

Identification and characterization of conjugative plasmids that encode ciprofloxacin resistance in Salmonella.

Antimicrobial agents and chemotherapy
72, e00575-18


Abstract +

This study aimed to characterize novel conjugative plasmids that encode transferrable ciprofloxacin resistance in Salmonella In this study, 157 non-duplicated Salmonella isolates were recovered from food products, 55 out of which were found to be resistant to ciprofloxacin. Interestingly, 37 out of the 55 (67%) CipRSalmonella isolates did not harbor any mutations in the Quinolone resistance determine regions (QRDR). Interestingly, six Salmonella isolates were shown to carry two novel types of conjugative plasmids that could transfer ciprofloxacin resistance phenotype to E. coli J53 (AziR). The first type belonged to the ~110kb IncFIB type conjugative plasmid carrying qnrB-bearing and aac(6')-Ib-cr-bearing mobile elements. Transfer of the plasmid between E. coli or Salmonella could confer CIP MIC to 1 to 2µg/ml. The second type of conjugative plasmid belonged to ~240kb IncH1/IncF plasmids carrying a single PMQR gene, qnrS Importantly, this type of conjugative ciprofloxacin resistance plasmids could be detected in clinical isolates of Salmonella Dissemination of these conjugative plasmids that confer ciprofloxaicn resistance poses serious public health impact and Salmonella infection control. Copyright © 2018 American Society for Microbiology.

Sequence analysis of IncA/C and IncI1 plasmids isolated from multidrug-resistant Salmonella Newport using Single-Molecule Real-Time Sequencing.

Foodborne pathogens and disease
15, 361-371


Abstract +

Multidrug-resistant (MDR) plasmids play an important role in disseminating antimicrobial resistance genes. To elucidate the antimicrobial resistance gene compositions in A/C incompatibility complex (IncA/C) plasmids carried by animal-derived MDR Salmonella Newport, and to investigate the spread mechanism of IncA/C plasmids, this study characterizes the complete nucleotide sequences of IncA/C plasmids by comparative analysis. Complete nucleotide sequencing of plasmids and chromosomes of six MDR Salmonella Newport strains was performed using PacBio RSII. Open reading frames were assigned using prokaryotic genome annotation pipeline (PGAP). To understand genomic diversity and evolutionary relationships among Salmonella Newport IncA/C plasmids, we included three complete IncA/C plasmid sequences with similar backbones from Salmonella Newport and Escherichia coli: pSN254, pAM04528, and peH4H, and additional 200 draft chromosomes. With the exception of canine isolate CVM22462, which contained an additional IncI1 plasmid, each of the six MDR Salmonella Newport strains contained only the IncA/C plasmid. These IncA/C plasmids (including references) ranged in size from 80.1 (pCVM21538) to 176.5?kb (pSN254) and carried various resistance genes. Resistance genes floR, tetA, tetR, strA, strB, sul, and mer were identified in all IncA/C plasmids. Additionally, blaCMY-2 and sugE were present in all IncA/C plasmids, excepting pCVM21538. Plasmid pCVM22462 was capable of being transferred by conjugation. The IncI1 plasmid pCVM22462b in CVM22462 carried blaCMY-2 and sugE. Our data showed that MDR Salmonella Newport strains carrying similar IncA/C plasmids clustered together in the phylogenetic tree using chromosome sequences and the IncA/C plasmids from animal-derived Salmonella Newport contained diverse resistance genes. In the current study, we analyzed genomic diversities and phylogenetic relationships among MDR Salmonella Newport using complete plasmids and chromosome sequences and provided possible spread mechanism of IncA/C plasmids in Salmonella Newport Lineage II.

Comparative sequence analysis of multidrug-resistant IncA/C plasmids from Salmonella enterica

Frontiers in microbiology
8, 1459


Abstract +

Determinants of multidrug resistance (MDR) are often encoded on mobile elements, such as plasmids, transposons, and integrons, which have the potential to transfer among foodborne pathogens, as well as to other virulent pathogens, increasing the threats these traits pose to human and veterinary health. Our understanding of MDR among Salmonella has been limited by the lack of closed plasmid genomes for comparisons across resistance phenotypes, due to difficulties in effectively separating the DNA of these high-molecular weight, low-copy-number plasmids from chromosomal DNA. To resolve this problem, we demonstrate an efficient protocol for isolating, sequencing and closing IncA/C plasmids from Salmonella sp. using single molecule real-time sequencing on a Pacific Biosciences (Pacbio) RS II Sequencer. We obtained six Salmonella enterica isolates from poultry, representing six different serovars, each exhibiting the MDR-Ampc resistance profile. Salmonella plasmids were obtained using a modified mini preparation and transformed with Escherichia coli DH10Br. A Qiagen Large-Construct kit™ was used to recover highly concentrated and purified plasmid DNA that was sequenced using PacBio technology. These six closed IncA/C plasmids ranged in size from 104 to 191 kb and shared a stable, conserved backbone containing 98 core genes, with only six differences among those core genes. The plasmids encoded a number of antimicrobial resistance genes, including those for quaternary ammonium compounds and mercury. We then compared our six IncA/C plasmid sequences: first with 14 IncA/C plasmids derived from S. enterica available at the National Center for Biotechnology Information (NCBI), and then with an additional 38 IncA/C plasmids derived from different taxa. These comparisons allowed us to build an evolutionary picture of how antimicrobial resistance may be mediated by this common plasmid backbone. Our project provides detailed genetic information about resistance genes in plasmids, advances in plasmid sequencing, and phylogenetic analyses, and important insights about how MDR evolution occurs across diverse serotypes from different animal sources, particularly in agricultural settings where antimicrobial drug use practices vary.

Salmonella enterica serovar Enteritidis strains recovered from human clinical cases between 1949 and 1995 in the United States.

Genome announcements
6, e01406-17


Abstract +

Salmonella enterica serovar Enteritidis is one of the most commonly isolated foodborne pathogens and is transmitted primarily to humans through consumption of contaminated poultry and poultry products. We are reporting completely closed genome and plasmid sequences of historical S. Enteritidis isolates recovered from humans between 1949 and 1995 in the United States.

Complete sequences of six IncA/C plasmids of multidrug-resistant Salmonella enterica subsp. enterica serotype Newport.

Genome announcements
3, e00027-15


Abstract +

Multidrug-resistant (MDR) Salmonella enterica subsp. enterica serotype Newport has been a long-standing public health concern in the United States. We present the complete sequences of six IncA/C plasmids from animal-derived MDR S. Newport ranging from 80.1 to 158.5 kb. They shared a genetic backbone with S. Newport IncA/C plasmids pSN254 and pAM04528. Copyright © 2015 Cao et al.

Complete genome sequence of a multidrug-resistant Salmonella enterica serovar Typhimurium var. 5- strain isolated from chicken breast.

Genome announcements
2, e01068-13


Abstract +

Salmonella enterica subsp. enterica serovar Typhimurium is a leading cause of salmonellosis. Here, we report a closed genome sequence, including sequences of 3 plasmids, of Salmonella serovar Typhimurium var. 5- CFSAN001921 (National Antimicrobial Resistance Monitoring System [NARMS] strain ID N30688), which was isolated from chicken breast meat and shows resistance to 10 different antimicrobials. Whole-genome and plasmid sequence analyses of this isolate will help enhance our understanding of this pathogenic multidrug-resistant serovar.


CannMed 2020

September 20, 2020-September 22, 2020


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