[Species identification and molecular epidemiology of bacteria belonging to Ochrobactrum genus]

Carbonyl Cyanide 3-Chloro Phenyl Hydrazone (CCCP) Restores the Colistin Sensitivity in Brucella intermedia

Brucella intermedia (formerly Ochrobactrum intermedium), a non-fermentative bacterium, has been isolated from animals and human clinical specimens. It is naturally resistant to polymyxins, including colistin (CO), and may cause opportunistic infections in humans. We isolated six Brucella intermedia strains from Senegalese monkey stool. In order to determine whether an efflux pump mechanism was involved in CO resistance in B. intermedia, we evaluated the effects of verapamil (VRP), reserpine (RSP), phe-arg β-naphthylamide dihydrochloride (PAβN) and carbonyl cyanide 3-chloro phenyl hydrazone (CCCP), four efflux pump inhibitors, on these colistin-resistant strains. Using the broth microdilution method, a CO and CCCP combination of 2 µg/mL and 10 µg/mL, respectively, significantly reduced the CO minimal inhibitory concentration (MIC) of B. intermedia, supporting an efflux pump mechanism. In contrast, VRP, PAβN and RSP did not restore CO susceptibility. A time kill assay showed a bactericidal effect of the CO-CCCP combination. Genomic analysis revealed a potential implication in the CO resistance mechanism of some conserved efflux pumps, such as YejABEF, NorM and EmrAB, as previously reported in other bacteria. An inhibitory effect of the CO-CCCP combination was observed on biofilm formation using the crystal violet method. These results suggest that the intrinsic CO resistance in Brucella intermedia is linked to an efflux pump mechanism and that the synergistic effect of CO-CCCP may open a new field to identify new treatments to restore antibiotic efficacy in humans.

Niches, population structure and genome reduction in Ochrobactrum intermedium: clues to technology-driven emergence of pathogens

Ochrobactrum intermedium is considered as an emerging human environmental opportunistic pathogen with mild virulence. The distribution of isolates and sequences described in literature and databases showed frequent association with human beings and polluted environments. As population structures are related to bacterial lifestyles, we investigated by multi-locus approach the genetic structure of a population of 65 isolates representative of the known natural distribution of O. intermedium. The population was further surveyed for genome dynamics using pulsed-field gel electrophoresis and genomics. The population displayed a clonal epidemic structure with events of recombination that occurred mainly in clonal complexes. Concerning biogeography, clones were shared by human and environments and were both cosmopolitan and local. The main cosmopolitan clone was genetically and genomically stable, and grouped isolates that all harbored an atypical insertion in the rrs. Ubiquitism and stability of this major clone suggested a clonal succes in a particular niche. Events of genomic reduction were detected in the population and the deleted genomic content was described for one isolate. O. intermedium displayed allopatric characters associated to a tendancy of genome reduction suggesting a specialization process. Considering its relatedness with Brucella, this specialization might be a commitment toward pathogenic life-style that could be driven by technological selective pressure related medical and industrial technologies.

Multilocus sequence-based analysis delineates a clonal population of Agrobacterium (Rhizobium) radiobacter (Agrobacterium tumefaciens) of human origin

The genus Agrobacterium includes plant-associated bacteria and opportunistic human pathogens. Taxonomy and nomenclature within the genus remain controversial. In particular, isolates of human origin were all affiliated with the species Agrobacterium (Rhizobium) radiobacter, while phytopathogenic strains were designated under the synonym denomination Agrobacterium tumefaciens. In order to study the relative distribution of Agrobacterium strains according to their origins, we performed a multilocus sequence-based analysis (MLSA) on a large collection of 89 clinical and environmental strains from various origins. We proposed an MLSA scheme based on the partial sequence of 7 housekeeping genes (atpD, zwf, trpE, groEL, dnaK, glnA, and rpoB) present on the circular chromosome of A. tumefaciens C58. Multilocus phylogeny revealed that 88% of the clinical strains belong to genovar A7, which formed a homogeneous population with linkage disequilibrium, suggesting a low rate of recombination. Comparison of genomic fingerprints obtained by pulsed-field gel electrophoresis (PFGE) showed that the strains of genovar A7 were epidemiologically unrelated. We present genetic evidence that genovar A7 may constitute a human-associated population distinct from the environmental population. Also, phenotypic characteristics, such as culture at 42°C, agree with this statement. This human-associated population might represent a potential novel species in the genus Agrobacterium.

Multilocus sequence typing supports the hypothesis that Ochrobactrum anthropi displays a human-associated subpopulation

Background

Ochrobactrum anthropi is a versatile bacterial species with strains living in very diverse habitats. It is increasingly recognized as opportunistic pathogen in hospitalized patients. The population biology of the species particularly with regard to the characteristics of the human isolates is being investigated. To address this issue, we proposed a polyphasic approach consisting in Multi-Locus Sequence Typing (MLST), multi-locus phylogeny, genomic-based fingerprinting by pulsed-field gel electrophoresis (PFGE) and antibiotyping.

Results

We tested a population of 70 O. anthropi clinical (n = 43) and environmental (n = 24) isolates as well as the type strain O. anthropi ATCC49188^T and 2 strains of Ochrobactrum lupini and Ochrobactrum cytisi isolated from plant nodules. A Multi-Locus Sequence Typing (MLST) scheme for O. anthropi is proposed here for the first time. It was based on 7 genes (3490 nucleotides) evolving mostly by neutral mutations. The MLST approach suggested an epidemic population structure. A major clonal complex corresponded to a human-associated lineage since it exclusively contained clinical isolates. Genomic fingerprinting separated isolates displaying the same sequence type but it did not detect a population structure that could be related to the origin of the strains. None of the molecular method allowed the definition of particular lineages associated to the host-bacteria relationship (carriage, colonisation or infection). Antibiotyping was the least discriminative method.

Conclusion

The results reveal a human-associated subpopulation in our collection of strains. The emergence of this clonal complex was probably not driven by the antibiotic selective pressure. Therefore, we hypothesise that the versatile species O. anthropi could be considered as a human-specialized opportunistic pathogen.

Genetic diversity and phylogenetic relationships of bacteria belonging to the Ochrobactrum-Brucella group by recA and 16S rRNA gene-based comparative sequence analysis

The genetic diversity and phylogenetic interrelationships among 106 Ochrobactrum strains (O. anthropi: 72, O. intermedium: 22, O. tritici: 5, O. oryzae: 2, O. grignonense: 2, O. gallinifaecis: 1, O. lupini: 2), the type strains of the eight Brucella species and other closely related taxa were studied by recA and rrs gene (16S rRNA) comparative sequence analysis. Both markers correctly delineated the various Ochrobactrum species; however, resolution at the subspecies level was considerably higher in the recA gene-based approach. Phylogenetic analyses using neighbor-joining, parsimony, and maximum likelihood algorithms generated trees with similar topologies but the overall branching order, and also the order of the subclades, were not stable in either assay, which could be explained by generally high recA and rrs sequence similarities. Ochrobactrum and Pseudochrobactrum formed separate clades distinct from other Alphaproteobacteria with Bartonella, Agrobacterium, and Rhizobium as the closest relatives. O. gallinifaecis was the most distinct member, when compared to the type species O. anthropi, with rrs and recA similarities of 96.2% and 81.4%. Brucella species were indistinguishable, exhibiting high rrs and recA gene similarities of 98.6% and 85.5% compared with Ochrobactrum intermedium. At the protein level, all RecA sequences among the various Ochrobactrum species and between Ochrobactrum and Brucella were highly similar with only a few amino acid substitutions. O. anthropi and O. tritici were indistinguishable by means of their RecA proteins. A set of initially biochemically classified strains did not cluster within their assigned species and they either grouped within other known species or grouped as potential novel Ochrobactrum species. In further investigations, these strains were reclassified and described as novel species. In summary, Ochrobactrum is a highly diverse genus comprising several novel species. We recommend recA- in addition to rrs gene-analysis for correct species allocation and subtyping of novel Ochrobactrum isolates.

Ochrobactrum pseudintermedium sp. nov., a novel member of the family Brucellaceae, isolated from human clinical samples

Three novel Gram-negative, non-fermenting aerobic bacilli were isolated from human clinical samples. They shared more than 99.8 % of the 16S rRNA gene nucleotide positions. The strains were related to Ochrobactrum intermedium with about 97.48 % 16S rRNA gene sequence similarity. In 16S rRNA gene-, dnaK- and rpoB-based phylogenies, the strains were grouped in a lineage that was distinct from other Ochrobactrum species in the family Brucellaceae. Fatty acid composition, polar lipids, quinone system, DNA-DNA relatedness, genome organization, and physiological and biochemical data differentiated these isolates from recognized species of the genus Ochrobactrum. The three clinical strains therefore represent a novel species within the genus Ochrobactrum, for which the name Ochrobactrum pseudintermedium sp. nov., is proposed. The type strain is ADV31(T) (=CIP 109116(T)=DSM 17490(T)). The DNA G+C content of strain ADV31(T) was 54.5 mol%.

Differentiation of mesophilic and thermophilic bacteria with fourier transform infrared spectroscopy

In the present study the characterization and differentiation of mesophilic and thermophilic bacteria were investigated by using Fourier transform infrared (FT-IR) spectroscopy. Our results showed significant differences between the FT-IR spectra of mesophilic and thermophilic bacteria. The protein-to-lipid ratio was significantly higher for thermophiles compared to mesophiles. The absorption intensity of the CH(3) asymmetric stretching vibration was higher in thermophilic bacteria, indicating a change in the composition of the acyl chains. The higher intensity/area observed in the CH(2) symmetric stretching mode at 2857 cm(-1), and the CH(2) bending vibration band at 1452 cm(-1), indicated a higher amount of saturated lipids in thermophilic bacteria. The lipid C=O stretching vibration at 1739 cm(-1), which was observed in the mesophilic group, was not observed clearly in the thermophilic group, indicating a difference in packing that is presumably due to the decreased proportion of unsaturated acyl chains in thermophilic bacteria. In addition, the carbonyl groups become hydrogen bonded and the cellular DNA content was lower in thermophilic bacteria. Moreover, in the 1000-400 cm(-1) frequency region, the spectra of each bacterial species belonging to both the mesophilic and thermophilic bacterial groups, showed characteristic differences that were discriminated via dendrogram using cluster analysis. The current study implies that FT-IR spectroscopy could be successfully applied for the rapid comparison of bacterial groups and species to establish either similarities or discrepancies, as well as to confirm biochemical or physiological characteristics.

Genotyping of Ochrobactrum anthropi by recA-based comparative sequence, PCR-RFLP, and 16S rRNA gene analysis

A recA-PCR restriction fragment length polymorphism assay was developed to study intraspecies variation among Ochrobactrum anthropi. Primers deduced from the known recA gene sequence of the genetically closely related genus Brucella allowed the specific amplification of a 1065 bp recA fragment from each of the 38 O. anthropi and the eight Brucella strains investigated. RecA was also amplified from the type strains of O. intermedium, O. tritici, and O. lupini but could not be generated from O. grignonense and O. gallinifaecis. Subsequent comparative recA sequence- and HaeIII-recA restriction fragment length polymorphism analysis identified nine different genospecies among the tested 38 O. anthropi isolates, whereas the recA sequences of the Brucella spp. were indistinguishable. Furthermore, Brucella spp., O. anthropi, O. intermedium, and O. tritici were clearly separated from each other by means of their recA sequences and HaeIII restriction patterns. Five strains of uncertain species status listed in the Culture Collection University of Göteborg bacterial culture collection as O. anthropi were characterized by recA analysis, and their phylogenetic position within the Brucella-Ochrobactrum group was determined. In summary, recA-sequence analysis provides a new reliable molecular subtyping tool to study the phylogeny of the Ochrobactrum taxon at both the inter- and intraspecies level.

Pulsed-field gel electrophoresis to study the diversity of whole-genome organization in the genus Ochrobactrum

The alpha-proteobacterial genus Ochrobactrum groups together organisms that display varied life-styles, such as free-living bacteria, members of rhizosphere and soil, nitrogen-fixing bacteria in plant nodules, xenobiotic-degrading bacteria, colonizers of nematodes and insects, and opportunistic human pathogens. The genomes of nine strains of Ochrobactrum anthropi and eight strains of Ochrobactrum intermedium were analyzed by pulsed-field gel electrophoresis of the whole genome and of I-CeuI digestion fragments. All isolates and type strains of O. anthropi and O. intermedium possessed two high-molecular-weight circular replicons identified as two independent chromosomes on the basis of 16S rDNA hybridization. The genome of the type strain of Ochrobactrum tritici, Ochrobactrum grignonense, and Ochrobactrum gallinifaecis also contained two circular chromosomes. The megaplasmid content was highly variable even among strains in the same species, leading to whole-genome sizes that ranged from 5.060 to 8.300 Mbp and from 4.690 to 7.680 Mbp for O. anthropi and O. intermedium, respectively. This exceptional level of genomic diversity could be related to the adaptability of Ochrobactrum spp. to various ecological niches.

Clinical and microbiological features of Inquilinus sp. isolates from five patients with cystic fibrosis

Patients with cystic fibrosis (CF) may be colonized with unusual gram-negative bacilli whose identification is difficult and clinical impact unclear. We describe the clinical and microbiological features of five colonizations with organisms belonging to the recently described genus Inquilinus in CF patients. Isolates were identified from Burkholderia cepacia selective medium by means of 16S rRNA analysis. All of them were resistant to colistin, penicillins, cephalosporins, and monobactams but exhibited a remarkable susceptibility to imipenem. One of the five patients was transiently colonized with a nonmucoid isolate, whereas the four other patients were persistently colonized over the period of follow-up (8 to 21 months) with mucoid isolates. Pulsed-field gel electrophoresis of SpeI-digested genomic DNA was powerful for strain genotyping and demonstrated the clonality of Inquilinus sp. colonization for the two patients tested. Clinical evolution after the onset of Inquilinus was heterogeneous, but for at least one patient the lung function worsened and eradication of Inquilinus sp. was unsuccessful despite several imipenem courses. Finally, Inquilinus spp. may represent a new threat for CF patients due to their mucoid characteristic, their multiresistant pattern to antibiotics, and their ability to persist in the respiratory tract.

[The genome of alpha-proteobacteria : complexity, reduction, diversity and fluidity]

The alpha-proteobacteria displayed diverse and often unconventional life-styles. In particular, they keep close relationships with the eucaryotic cell. Their genomic organization is often atypical. Indeed, complex genomes, with two or more chromosomes that could be linear and sometimes associated with plasmids larger than one megabase, have been described. Moreover, polymorphism in genome size and topology as well as in replicon number was observed among very related bacteria, even in a same species. Alpha-proteobacteria provide a good model to study the reductive evolution, the role and origin of multiple chromosomes, and the genomic fluidity. The amount of new data harvested in the last decade should lead us to better understand emergence of bacterial life-styles and to build the conceptual basis to improve the definition of the bacterial species.

Atypical 16S rRNA gene copies in Ochrobactrum intermedium strains reveal a large genomic rearrangement by recombination between rrn copies

Ochrobactrum intermedium is an opportunistic human pathogen belonging to the alpha 2 subgroup of proteobacteria. The 16S rDNA sequences of nine O. intermedium isolates from a collection of clinical and environmental isolates exhibited a 46-bp insertion at position 187, which was present in only one sequence among the 82 complete or partial 16S rDNA sequences of Ochrobactrum spp. available in data banks. Reverse transcription-PCR experiments showed that the 46-bp insertion remained in the 16S rRNA. The inserted sequence folded into a stem-loop structure, which took place in and prolonged helix H184 of the 16S rRNA molecule. Helix H184 has been described as conserved in length among eubacteria, suggesting the idiosyncratic character of the 46-bp insertion. Pulsed-field gel electrophoresis experiments showed that seven of the clinical isolates carrying the 46-bp insertion belonged to the same clone. Insertion and rrn copy numbers were determined by hybridization and I-CeuI digestion. In the set of clonal isolates, the loss of two insertion copies revealed the deletion of a large genomic fragment of 150 kb, which included one rrn copy; deletion occurred during the in vivo evolution of the clone. Determination of the rrn skeleton suggested that the large genomic rearrangement occurred during events involving homologous recombination between rrn copies. The loss of insertion copies suggested a phenomenon of concerted evolution among heterogeneous rrn copies.