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      Comparative Genomics of Multidrug Resistance in Acinetobacter baumannii


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          Acinetobacter baumannii is a species of nonfermentative gram-negative bacteria commonly found in water and soil. This organism was susceptible to most antibiotics in the 1970s. It has now become a major cause of hospital-acquired infections worldwide due to its remarkable propensity to rapidly acquire resistance determinants to a wide range of antibacterial agents. Here we use a comparative genomic approach to identify the complete repertoire of resistance genes exhibited by the multidrug-resistant A. baumannii strain AYE, which is epidemic in France, as well as to investigate the mechanisms of their acquisition by comparison with the fully susceptible A. baumannii strain SDF, which is associated with human body lice. The assembly of the whole shotgun genome sequences of the strains AYE and SDF gave an estimated size of 3.9 and 3.2 Mb, respectively. A. baumannii strain AYE exhibits an 86-kb genomic region termed a resistance island—the largest identified to date—in which 45 resistance genes are clustered. At the homologous location, the SDF strain exhibits a 20 kb-genomic island flanked by transposases but devoid of resistance markers. Such a switching genomic structure might be a hotspot that could explain the rapid acquisition of resistance markers under antimicrobial pressure. Sequence similarity and phylogenetic analyses confirm that most of the resistance genes found in the A. baumannii strain AYE have been recently acquired from bacteria of the genera Pseudomonas, Salmonella, or Escherichia. This study also resulted in the discovery of 19 new putative resistance genes. Whole-genome sequencing appears to be a fast and efficient approach to the exhaustive identification of resistance genes in epidemic infectious agents of clinical significance.


          The bacterial species Acinetobacter baumannii is a major cause of hospital-acquired infection throughout the world, and it is an increasing public health concern due to its increasing resistance to antibiotic treatment. Coincidently, a high incidence of multidrug-resistant A. baumannii bloodstream infections was recently reported in US Army service members injured during Afghanistan and Iraq/Kuwait military operations. A. baumannii exhibits a remarkable ability to rapidly develop antibiotic resistance, which led from fully susceptible to multidrug-resistant strains within three decades. The authors used whole-genome sequencing and bioinformatic analyses to identify the complete repertoire of resistance genes exhibited by the multidrug-resistant A. baumannii strain AYE, which is epidemic in France, and to investigate the mechanisms of their acquisition by comparison with the fully susceptible A. baumannii strain SDF, which is associated with human body lice. This study led to the discovery in the AYE genome of an 86-kb region called a resistance “island”—the largest identified to date—that contains a cluster of 45 resistance genes. The homologous location in the susceptible strain, curiously, exhibited a 20-kb genomic island that is devoid of resistance markers. This ability to “switch” its genomic structure probably explains the unmatched speed at which A. baumannii captures resistance markers when under antibacterial pressure, such as is found in hospital intensive care units.

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          Extensive mosaic structure revealed by the complete genome sequence of uropathogenic Escherichia coli.

          We present the complete genome sequence of uropathogenic Escherichia coli, strain CFT073. A three-way genome comparison of the CFT073, enterohemorrhagic E. coli EDL933, and laboratory strain MG1655 reveals that, amazingly, only 39.2% of their combined (nonredundant) set of proteins actually are common to all three strains. The pathogen genomes are as different from each other as each pathogen is from the benign strain. The difference in disease potential between O157:H7 and CFT073 is reflected in the absence of genes for type III secretion system or phage- and plasmid-encoded toxins found in some classes of diarrheagenic E. coli. The CFT073 genome is particularly rich in genes that encode potential fimbrial adhesins, autotransporters, iron-sequestration systems, and phase-switch recombinases. Striking differences exist between the large pathogenicity islands of CFT073 and two other well-studied uropathogenic E. coli strains, J96 and 536. Comparisons indicate that extraintestinal pathogenic E. coli arose independently from multiple clonal lineages. The different E. coli pathotypes have maintained a remarkable synteny of common, vertically evolved genes, whereas many islands interrupting this common backbone have been acquired by different horizontal transfer events in each strain.
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              Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18.

              Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis.

                Author and article information

                Role: Editor
                PLoS Genet
                PLoS Genetics
                Public Library of Science (San Francisco, USA )
                January 2006
                13 January 2006
                : 2
                : 1
                : e7
                [1 ] Information Génomique et Structurale, Institute for Structural Biology and Microbiology, IBSM, Marseille, France
                [2 ] Génoscope, Centre National de Séquençage and CNRS UMR8030, Evry, France
                [3 ] Département de Bactériologie-Virologie, Hôpital de Bicêtre, Le-Kremlin-Bicêtre, France
                [4 ] Unité des Rickettsies, CNRS UMR6020, Faculté de Médecine, Université de la Méditerranée, Marseille, France
                INSERM U571, France
                Author notes
                * To whom correspondence should be addressed. E-mail: Pierre-Edouard.Fournier@ 123456univmed.fr (PEF); Jean-Michel.Claverie@ 123456igs.cnrs-mrs.fr (JMC)

                ¤ Current address: Unité des Rickettsies, Faculté de Médecine, Université de la Méditerranée, Marseille, France

                05-PLGE-RA-0296R2 plge-02-01-04
                Copyright: © 2006 Fournier et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                : 26 September 2005
                : 6 December 2005
                Page count
                Pages: 11
                Research Article
                Infectious Diseases
                Genetics/Gene Discovery
                Genetics/Comparative Genomics
                Acinetobacter Baumannii
                Antibiotic Resistancenosocomial Infection
                Genome Sequence
                Custom metadata
                Fournier PE, Vallenet D, Barbe V, Audic S, Ogata H, et al. (2006) Comparative genomics of multidrug resistance in Acinetobacter baumannii. PLoS Genet 2(1): e7.



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