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Hu L, Zhang XT, Zeng X, Xiong LX, Ai Q, Liu CJ, Yang WW, Wu Y, Guo X, Li GQ, Liu L. ISAba1 mediated intrinsic chromosomal oxacillinase amplification confers carbapenem resistance in Acinetobacter baumannii. Int J Antimicrob Agents 2024:107258. [PMID: 38914142 DOI: 10.1016/j.ijantimicag.2024.107258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Revised: 05/19/2024] [Accepted: 06/17/2024] [Indexed: 06/26/2024]
Abstract
Tandem amplification of carbapenemase genes increases gene copy number and enhances carbapenem resistance. These amplifications are often heterogeneous, transient, and located on plasmids, which also contribute to heteroresistance. Amplification of encoding genes is especially important for enzymes with low hydrolysis activity, which are often overlooked. Here, we reported an intrinsic oxacillinase oxaAb amplification flanked by ISAba1. The amplification is in the chromosome and contains up to twenty-five repeats. We provided genomic, transcriptomic, and proteomic evidence that the amplification resulted in oxacillinase overproduction. Notably, no point mutations of oxaAb were found during the amplification process. Strains of A. baumannii with intrinsic amplified or external transformed ISAba1-oxaAb exhibited higher meropenem hydrolysis activity. Furthermore, the number of repeats in the amplification decreased gradually over a period of 21 days cultured with carbapenem withdrawal. However, upon re-exposure to meropenem, the ISAba1 flanked oxaAb responded rapidly, with repeat numbers reaching or exceeding pre-carbapenem withdrawal levels within 24 hours. Taken together, these findings suggest that ISAba1-mediated gene amplification and overproduction of intrinsic low-activity oxacillinase oxaAb resulted in carbapenem resistance.
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Affiliation(s)
- Limiao Hu
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China
| | - Xiao-Tuan Zhang
- Department of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
| | - Xi Zeng
- Department of Gastroenterology, the First Affiliated Hospital of Shaoyang University, Shaoyang, 422000, China
| | - Lu-Xi Xiong
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China
| | - Qi Ai
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China
| | - Cai-Juan Liu
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China
| | - Wei-Wei Yang
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China
| | - Yuan Wu
- Department of Clinical Laboratory Medicine, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China.
| | - Xuemin Guo
- Meizhou People's Hospital, Meizhou, 514031, China; Guangdong Provincial Key Laboratory of Precision Medicine and Clinical Translation Research of Hakka Population, Meizhou, 514031, China.
| | - Guo-Qing Li
- Department of Gastroenterology, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China; Hunan Provincial Key Laboratory of Basic and Clinical Pharmacological Research for Gastroenterological Tumors, Hengyang, 421001, China.
| | - Logen Liu
- Hunan Provincial Key Laboratory of Basic and Clinical Pharmacological Research for Gastroenterological Tumors, Hengyang, 421001, China; Clinical Research Center, The Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, 421001, China;.
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Harmer CJ, Hall RM. IS 26 and the IS 26 family: versatile resistance gene movers and genome reorganizers. Microbiol Mol Biol Rev 2024:e0011922. [PMID: 38436262 DOI: 10.1128/mmbr.00119-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2024] Open
Abstract
SUMMARYIn Gram-negative bacteria, the insertion sequence IS26 is highly active in disseminating antibiotic resistance genes. IS26 can recruit a gene or group of genes into the mobile gene pool and support their continued dissemination to new locations by creating pseudo-compound transposons (PCTs) that can be further mobilized by the insertion sequence (IS). IS26 can also enhance expression of adjacent potential resistance genes. IS26 encodes a DDE transposase but has unique properties. It forms cointegrates between two separate DNA molecules using two mechanisms. The well-known copy-in (replicative) route generates an additional IS copy and duplicates the target site. The recently discovered and more efficient and targeted conservative mechanism requires an IS in both participating molecules and does not generate any new sequence. The unit of movement for PCTs, known as a translocatable unit or TU, includes only one IS26. TU formed by homologous recombination between the bounding IS26s can be reincorporated via either cointegration route. However, the targeted conservative reaction is key to generation of arrays of overlapping PCTs seen in resistant pathogens. Using the copy-in route, IS26 can also act on a site in the same DNA molecule, either inverting adjacent DNA or generating an adjacent deletion plus a circular molecule carrying the DNA segment lost and an IS copy. If reincorporated, these circular molecules create a new PCT. IS26 is the best characterized IS in the IS26 family, which includes IS257/IS431, ISSau10, IS1216, IS1006, and IS1008 that are also implicated in spreading resistance genes in Gram-positive and Gram-negative pathogens.
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Affiliation(s)
- Christopher J Harmer
- School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia
| | - Ruth M Hall
- School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia
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Zeng S, Huang Y, Zhang X, Fu L, Sun Z, Li X. Molecular characterization of IncFII plasmid carrying blaNDM-5 in a Salmonella enterica serovar Typhimurium ST34 clinical isolate in China. mSphere 2023; 8:e0048023. [PMID: 37909767 PMCID: PMC10732066 DOI: 10.1128/msphere.00480-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 09/26/2023] [Indexed: 11/03/2023] Open
Abstract
IMPORTANCE In this study, an IncFII plasmid pIncFII-NDM5 carrying blaNDM-5 was found in carbapenem-resistant Salmonella enterica serovar Typhimurium (S. enterica serovar Typhimurium), which has conjugative transferability and carried blaNDM-5, bleMBL, mph(A), and blaTEM-1 four resistance genes that can mediate resistance to multiple antibiotics including cephalosporins, beta-lactamase inhibitor combinations, carbapenems, and macrolides. Phylogenetic analysis showed that 1104-65 and 1104-75 were closely related to other S. enterica serovar Typhimurium in this area. The above-mentioned S. enterica serovar Typhimurium chromosome carries blaCTX-M-55, qnrS1, and tet(A) genes, so the antibiotic resistance of isolates will be further enhanced after obtaining the pIncFII_NDM5-like plasmid. Meanwhile, we discovered a novel genetic structure of blaNDM-5 mediated by the IS26 composite transposon, which will expand our understanding of the emergence and spread of carbapenem-resistance genes. Altogether, the presence of the IncFII plasmid pIncFII-NDM5 further underscores the need for vigilant surveillance and appropriate infection control measures to mitigate the impact of carbapenem-resistant S. enterica serovar Typhimurium in clinical settings.
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Affiliation(s)
- Shihan Zeng
- Department of Clinical Laboratory, Fifth Affiliated Hospital, Southern Medical University, Guangzhou, China
| | - Yulan Huang
- Department of Clinical Laboratory, Fifth Affiliated Hospital, Southern Medical University, Guangzhou, China
| | - Xiwei Zhang
- Department of Clinical Laboratory, Fifth Affiliated Hospital, Southern Medical University, Guangzhou, China
| | - Liang Fu
- Department of Clinical Laboratory, Fifth Affiliated Hospital, Southern Medical University, Guangzhou, China
| | - Zhaohui Sun
- Department of Laboratory Medicine, General Hospital of Southern Theater Command, Guangzhou, China
| | - Xiaoyan Li
- Department of Clinical Laboratory, Fifth Affiliated Hospital, Southern Medical University, Guangzhou, China
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Duplication of bla CTX-M-1 and a class 1 integron on the chromosome enhances antimicrobial resistance in Escherichia coli isolated from racehorses in Japan. J Glob Antimicrob Resist 2021; 27:225-227. [PMID: 34655811 DOI: 10.1016/j.jgar.2021.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 09/21/2021] [Accepted: 10/04/2021] [Indexed: 11/24/2022] Open
Abstract
OBJECTIVES Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae have become a cause for great concern. Although some studies have reported the prevalence of ESBL-producing bacteria and ESBL-encoding genes in horses worldwide, the genetic structure surrounding the ESBL gene has not been analysed in detail. In the present study, we isolated two ESBL-producing Escherichia coli strains from diseased racehorses in Japan and demonstrated the mechanisms underlying the acquisition of their antimicrobial resistance (AMR) genes. METHODS Two ESBL-producing E. coli strains (E148 and E189) were isolated from the heart and liver of horses with endocarditis and sepsis in 2014 and 2016, respectively, in Japan. Complete genomic sequences of the two strains were analysed using a PacBio RSII sequencer. Antimicrobial susceptibility testing was performed by the agar dilution method. RESULTS The two isolates possessed a chromosomal AMR gene cluster containing blaCTX-M-1 that was similar to the pEQ1 plasmid found in E. coli isolated from a racehorse in the Czech Republic. In one of the two strains, tandem duplication of the 16-kb region containing blaCTX-M-1 and a class 1 integron, which occurred via IS26-mediated recombination, increased minimum inhibitory concentrations (MICs) associated with the duplicated AMR genes. CONCLUSION Chromosomal blaCTX-M-1 possibly derived from the pEQ1 or pEQ1-like plasmid was found in Japanese equine E. coli isolates. In Japanese strains, many AMR genes containing blaCTX-M-1 and the class 1 integron are highly accumulated in one region on the chromosome, and the AMR of E. coli was enhanced via the IS26-mediated duplication of the AMR gene cluster.
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Fang LX, Li XP, Li L, Chen MY, Wu CY, Li LL, Liao XP, Liu YH, Sun J. IS Ecp1-mediated transposition of chromosome-borne blaCMY-2 into an endogenous ColE1-like plasmid in Escherichia coli. Infect Drug Resist 2018; 11:995-1005. [PMID: 30087569 PMCID: PMC6061673 DOI: 10.2147/idr.s159345] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Background CMY-2 is the most prevalent pAmpC β-lactamase, but the chromosomal blaCMY-2 gene transfer via horizontal transmission has been seldom reported. This study aimed to describe an ISEcp1-mediated transposition of a chromosomal blaCMY-2 gene from Escherichia coli into a small endogenous ColE1-like plasmid, resulting in elevated resistance to extended-spectrum cephalosporins. Methods Three ESCs-resistant ST641 E. coli strains EC6413, EC4103 and EC5106 harbored the blaCMY-2 gene. S1-PFGE, I-ceu I-PFGE, Southern blotting and electroporation experiments were performed to investigate the location and transferability of blaCMY-2. The genetic context and gene expression of blaCMY-2 in the original isolates and the corresponding electroporants were explored by PCR mapping, primer walking strategy and RT-qPCR. Results The blaCMY-2-containing region (ISEcp1-blaCMY-2-∆blc-∆yggR-∆tnp1-orf7-orf8-orf9-∆tnp2-∆hsdR) was transposed into endogenous ColE1-like plasmid pSC137 in the process of electroporation at very low frequencies (10-8-10-9). The transpositions resulted in novel larger blaCMY-2-harboring ColE1-like plasmids with size of 14,845 bp, enabling increase in MICs of 2 to 8-fold for cefotaxime, ceftiofur, and ceftazidime in recipient strains over their respective original counterparts. Transcriptional level analysis revealed that the increased blaCMY-2 expression was correlated with elevated MIC values of cephalosporins. The blaCMY-2 transposition unit was identical to that in a clinical isolate E. coli TN44889 from France isolated in 2004. Conclusions Our results firstly demonstrated that ISEcp1 mediated a transposition of chromosome-borne blaCMY-2 into an endogenous ColE1-like plasmid by electroporation. Amplification of the blaCMY-2 gene facilitates the strain adaptation to a changed environment with an elevated antibiotic pressure.
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Affiliation(s)
- Liang-Xing Fang
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Xing-Ping Li
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Liang Li
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Mu-Ya Chen
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Cai-Yan Wu
- Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou, People's Republic of China
| | - Lu-Lu Li
- Institute of Animal Science and Veterinary Medicine, Shandong Academy of Agricultural Sciences, Jinan, People's Republic of China
| | - Xiao-Ping Liao
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Ya-Hong Liu
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
| | - Jian Sun
- National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China, .,Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China,
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De Meur Q, Deutschbauer A, Koch M, Wattiez R, Leroy B. Genetic Plasticity and Ethylmalonyl Coenzyme A Pathway during Acetate Assimilation in Rhodospirillum rubrum S1H under Photoheterotrophic Conditions. Appl Environ Microbiol 2018; 84:e02038-17. [PMID: 29180364 PMCID: PMC5772224 DOI: 10.1128/aem.02038-17] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 11/16/2017] [Indexed: 02/07/2023] Open
Abstract
Purple nonsulfur bacteria represent a promising resource for biotechnology because of their great metabolic versatility. Rhodospirillum rubrum has been widely studied regarding its metabolism of volatile fatty acid, mainly acetate. As the glyoxylate shunt is unavailable in Rs. rubrum, the citramalate cycle pathway and the ethylmalonyl-coenzyme A (CoA) pathway are proposed as alternative anaplerotic pathways for acetate assimilation. However, despite years of debate, neither has been confirmed to be essential. Here, using functional genomics, we demonstrate that the ethylmalonyl-CoA pathway is required for acetate photoassimilation. Moreover, an unexpected reversible long-term adaptation is observed, leading to a drastic decrease in the lag phase characterizing the growth of Rs. rubrum in the presence of acetate. Using proteomic and genomic analyses, we present evidence that the adaptation phenomenon is associated with reversible amplification and overexpression of a 60-kb genome fragment containing key enzymes of the ethylmalonyl-CoA pathway. Our observations suggest that a genome duplication and amplification phenomenon is not only involved in adaptation to acute stress but can also be important for basic carbon metabolism and the redox balance.IMPORTANCE Purple nonsulfur bacteria represent a major group of anoxygenic photosynthetic bacteria that emerged as a promising resource for biotechnology because of their great metabolic versatility and ability to grow under various conditions. Rhodospirillum rubrum S1H has notably been selected by the European Space Agency to colonize its life support system, called MELiSSA, due to its capacity to perform photoheterotrophic assimilation of volatile fatty acids (VFAs), mainly acetate. VFAs are valuable carbon sources for many applications, combining bioremediation of contaminated environments with the generation of added-value products. Acetate is one of the major volatile fatty acids generated as a by-product of fermentation processes. In Rs. rubrum, purple nonsulfur bacteria, the assimilation of acetate is still under debate since two different pathways have been proposed. Here, we clearly demonstrate that the ethylmalonyl-CoA pathway is the major anaplerotic pathway for acetate assimilation in this strain. Interestingly, we further observed that gene duplication and amplification, which represent a well-known phenomenon in antibiotic resistance, also play a regulatory function in carbon metabolism and redox homeostasis.
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Affiliation(s)
- Quentin De Meur
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Adam Deutschbauer
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Matthias Koch
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Ruddy Wattiez
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Baptiste Leroy
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
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Lee KI, Morita-Ishihara T, Iyoda S, Ogura Y, Hayashi T, Sekizuka T, Kuroda M, Ohnishi M. A Geographically Widespread Outbreak Investigation and Development of a Rapid Screening Method Using Whole Genome Sequences of Enterohemorrhagic Escherichia coli O121. Front Microbiol 2017; 8:701. [PMID: 28473825 PMCID: PMC5397494 DOI: 10.3389/fmicb.2017.00701] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 04/05/2017] [Indexed: 11/13/2022] Open
Abstract
From 2014 to 2015, we investigated a suspected nationwide outbreak of enterohemorrhagic Escherichia coli serogroup O121. However, similar pulsed field gel electrophoresis (PFGE) profiles and the lack of epidemiological links between the isolates made detection of the outbreak difficult. To elucidate a more precise genetic distance among the isolates, whole genome sequence (WGS) analyses were implemented in the investigation. The WGS-based single nucleotide polymorphism (SNP) analysis showed that 23 out of 44 isolates formed a distinct cluster (the number of intra-cluster SNPs was ≤8). Specific genomic regions in the clustered isolates were used to develop a specific PCR analysis. The PCR analysis detected all the clustered isolates and was suitable for rapid screening during the outbreak investigation. Our results showed that WGS analyses were useful for the detection of a geographically widespread outbreak, especially for isolates showing similar PFGE profiles and for the development of a rapid and cost-effective screening method.
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Affiliation(s)
- Ken-Ichi Lee
- Department of Bacteriology I, National Institute of Infectious DiseasesTokyo, Japan
| | | | - Sunao Iyoda
- Department of Bacteriology I, National Institute of Infectious DiseasesTokyo, Japan
| | - Yoshitoshi Ogura
- Department of Bacteriology, Faculty of Medical Sciences, Kyushu UniversityFukuoka, Japan
| | - Tetsuya Hayashi
- Department of Bacteriology, Faculty of Medical Sciences, Kyushu UniversityFukuoka, Japan
| | - Tsuyoshi Sekizuka
- Laboratory of Bacterial Genomics, Pathogen Genomics Center, National Institute of Infectious DiseasesTokyo, Japan
| | - Makoto Kuroda
- Laboratory of Bacterial Genomics, Pathogen Genomics Center, National Institute of Infectious DiseasesTokyo, Japan
| | - Makoto Ohnishi
- Department of Bacteriology I, National Institute of Infectious DiseasesTokyo, Japan
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Corrected Genome Annotations Reveal Gene Loss and Antibiotic Resistance as Drivers in the Fitness Evolution of Salmonella enterica Serovar Typhimurium. J Bacteriol 2016; 198:3152-3161. [PMID: 27621280 DOI: 10.1128/jb.00545-16] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Accepted: 09/02/2016] [Indexed: 11/20/2022] Open
Abstract
Horizontal acquisition of novel chromosomal genes is considered to be a key process in the evolution of bacterial pathogens. However, the identification of gene presence or absence could be hindered by the inconsistencies in bacterial genome annotations. Here, we performed a cross-annotation of omnipresent core and mosaic accessory genes in the chromosome of Salmonella enterica serovar Typhimurium across a total of 20 fully assembled genomes deposited into GenBank. Cross-annotation resulted in a 32% increase in the number of core genes and a 3-fold decrease in the number of genes identified as mosaic genes (i.e., genes present in some strains only) by the original annotation. Of the remaining noncore genes, the vast majority were prophage genes, and 255 of the nonphage genes were actually of core origin but lost in some strains upon the emergence of the S Typhimurium serovar, suggesting that the chromosomal portion of the S Typhimurium genome acquired a very limited number of novel genes other than prophages. Only horizontally acquired nonphage genes related to bacterial fitness or virulence were found in four recently sequenced isolates, all located on three different genomic islands that harbor multidrug resistance determinants. Thus, the extensive use of antimicrobials could be the main selection force behind the new fitness gene acquisition and the emergence of novel Salmonella pathotypes. IMPORTANCE Significant discrepancies in the annotations of bacterial genomes could mislead the conclusions about evolutionary origin of chromosomal genes, as we demonstrate here via a cross-annotation-based analysis of Salmonella Typhimurium genomes from GenBank. We conclude that despite being able to infect a broad range of vertebrate hosts, the genomic diversity of S Typhimurium strains is almost exclusively limited to gene loss and the transfer of prophage DNA. Only nonphage chromosomal genes acquired after the emergence of the serovar are linked to the genomic islands harboring multidrug resistance factors. Since the fitness factors could lead to increased virulence, this poses an important research question: could overuse or misuse of antimicrobials act as selection forces for the emergence of more pathogenic strains of Salmonella?
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