The link between phylogeny and virulence in Escherichia coli extraintestinal infection

Previous studies suggesting a link between Escherichia coli phylogenetic groups and extraintestinal virulence have been hampered by the difficulty in establishing the intrinsic virulence of a bacterial strain. Indeed, unidentified virulence factors do exist, and the susceptibility of the host to infection is highly variable. To overcome these difficulties, we have developed a mouse model of extraintestinal virulence to test the virulence of the strains under normalized conditions. We then assessed the phylogenetic relationships compared to the E. coli reference (ECOR) collection, the presence of several known virulence determinants, and the lethality to mice of 82 human adult E. coli strains isolated from normal feces and during the course of extraintestinal infections. Commensal strains belong mainly to phylogenetic groups A and B1, are devoid of virulence determinants, and do not kill the mice. Strains exhibiting the same characteristics as the commensal strains can be isolated under pathogenic conditions, thus indicating the role of host-dependent factors, such as susceptibility linked to underlying disease, in the development of infection. Some strains of phylogenetic groups A, B1, and D are able to kill the mice, their virulence being most often correlated with the presence of virulence determinants. Lastly, strains of the B2 phylogenetic group represent a divergent lineage of highly virulent strains which kill the mice at high frequency and possess the highest level of virulence determinants. The observed link between virulence and phylogeny could correspond to the necessity of virulence determinants in a genetic background that is adequate for the emergence of a virulent clone, an expression of the interdependency of pathogenicity and metabolic activities in pathogenic bacteria.

Myostatin and the skeletal muscle atrophy and hypertrophy signaling pathways

Myostatin, a member of the transforming growth factor-β superfamily, is a potent negative regulator of skeletal muscle growth and is conserved in many species, from rodents to humans. Myostatin inactivation can induce skeletal muscle hypertrophy, while its overexpression or systemic administration causes muscle atrophy. As it represents a potential target for stimulating muscle growth and/or preventing muscle wasting, myostatin regulation and functions in the control of muscle mass have been extensively studied. A wealth of data strongly suggests that alterations in skeletal muscle mass are associated with dysregulation in myostatin expression. Moreover, myostatin plays a central role in integrating/mediating anabolic and catabolic responses. Myostatin negatively regulates the activity of the Akt pathway, which promotes protein synthesis, and increases the activity of the ubiquitin-proteasome system to induce atrophy. Several new studies have brought new information on how myostatin may affect both ribosomal biogenesis and translation efficiency of specific mRNA subclasses. In addition, although myostatin has been identified as a modulator of the major catabolic pathways, including the ubiquitin-proteasome and the autophagy-lysosome systems, the underlying mechanisms are only partially understood. The goal of this review is to highlight outstanding questions about myostatin-mediated regulation of the anabolic and catabolic signaling pathways in skeletal muscle. Particular emphasis has been placed on (1) the cross-regulation between myostatin, the growth-promoting pathways and the proteolytic systems; (2) how myostatin inhibition leads to muscle hypertrophy; and (3) the regulation of translation by myostatin.

Phylogenetic and genomic diversity of human bacteremic Escherichia coli strains

Background

Extraintestinal pathogenic Escherichia coli (ExPEC) strains represent a huge public health burden. Knowledge of their clonal diversity and of the association of clones with genomic content and clinical features is a prerequisite to recognize strains with a high invasive potential. In order to provide an unbiased view of the diversity of E. coli strains responsible for bacteremia, we studied 161 consecutive isolates from patients with positive blood culture obtained during one year in two French university hospitals. We collected precise clinical information, multilocus sequence typing (MLST) data and virulence gene content for all isolates. A subset representative of the clonal diversity was subjected to comparative genomic hybridization (CGH) using 2,324 amplicons from the flexible gene pool of E. coli.

Results

Recombination-insensitive phylogenetic analysis of MLST data in combination with the ECOR collection revealed that bacteremic E. coli isolates were highly diverse and distributed into five major lineages, corresponding to the classical E. coli phylogroups (A+B1, B2, D and E) and group F, which comprises strains previously assigned to D. Compared to other strains of phylogenetic group B2, strains belonging to MLST-derived clonal complexes (CCs) CC1 and CC4 were associated (P < 0.05) with a urinary origin. In contrast, no CC appeared associated with severe sepsis or unfavorable outcome of the bacteremia. CGH analysis revealed genomic characteristics of the distinct CCs and identified genomic regions associated with CC1 and/or CC4.

Conclusion

Our results demonstrate that human bacteremia strains distribute over the entire span of E. coli phylogenetic diversity and that CCs represent important phylogenetic units for pathogenesis and comparative genomics.

Commensal Escherichia coli isolates are phylogenetically distributed among geographically distinct human populations

An intraspecies phylogenetic grouping of 168 human commensal Escherichia coli strains isolated from the stools of three geographically distinct human populations (France, Croatia, Mali) was generated by triplex PCR. The distributions of seven known extraintestinal virulence determinants (ibeA, pap, sfa/foc, afa, hly, cnf1, aer) were also determined by PCR. The data from the three populations were compiled, which showed that strains from phylogenetic groups A (40%) and B1 (34%) were the most common, followed by phylogenetic group D strains (15%). Strains of the phylogenetic group B2 were rare (11%). However, a significant specific distribution for strains of groups A, B1 and B2 within each population was observed, which may indicate the influence of (i) geographic/climatic conditions, (ii) dietary factors and/or the use of antibiotics or (iii) host genetic factors on the commensal flora. Virulence determinants were rarely detected, with only 25.6% of the strains harbouring at least one of the virulence genes tested. The strains with virulence factors most frequently belonged to phylogenetic group B2. The commensal strains of phylogenetic groups A, B1 and D had fewer virulence determinants than pathogenic strains of the corresponding groups when these data were compared with those for previous collections of virulent extraintestinal infection strains studied using the same approach. However, the virulence patterns of commensal and pathogenic B2 phylogenetic group strains were the same. The data thus suggest that strains of the A, B1 and D phylogenetic groups predominate in the gut flora and that these strains must acquire virulence factors to become pathogenic. In contrast, commensal phylogenetic group B2 strains are rare but appear to be potentially virulent.

Extraintestinal virulence is a coincidental by-product of commensalism in B2 phylogenetic group Escherichia coli strains

The selective pressures leading to the evolution and maintenance of virulence in the case of facultative pathogens are quite unclear. For example, Escherichia coli, a commensal of the gut of warm-blooded animals and humans, can cause severe extraintestinal diseases, such as septicemia and meningitis, which represent evolutionary dead ends for the pathogen as they are associated to rapid host death and poor interhost transmission. Such infectious process has been linked to the presence of so-called "virulence genes." To understand the evolutionary forces that select and maintain these genes, we focused our study on E. coli B2 phylogenetic group strains that encompass both commensal and pathogenic (extra- and intraintestinal) strains. Multilocus sequence typing (MLST), comparative genomic hybridization of the B2 flexible gene pool, and quantification of extraintestinal virulence using a mouse model of septicemia were performed on a panel of 60 B2 strains chosen for their genetic and ecologic diversity. The phylogenetic history of the strains reconstructed from the MLST data indicates the emergence of at least 9 subgroups of strains. A high polymorphism is observed in the B2 flexible gene pool among the strains with a good correlation between the MLST-inferred phylogenetic history of the strains and the presence/absence of specific genomic regions, indicating coevolution between the chromosomal background and the flexible gene pool. Virulence in the mouse model is a highly prevalent and widespread character present in all subgroups except one. Association studies reveal that extraintestinal virulence is a multigenic process with a common set of "virulence determinants" encompassing genes involved in transcriptional regulation, iron metabolism, adhesion, lipopolysaccharide (LPS) biosynthesis, and the recently reported peptide polyketide hybrid synthesis system. Interestingly, these determinants can also be viewed as intestinal colonization and survival factors linked to commensalism as they can increase the fitness of the strains within the normal gut environment. Altogether, these data argue for an ancestral emergence of the extraintestinal virulence character that is a coincidental by-product of commensalism. Furthermore, the phenotypic and genotypic markers identified in this work will allow further epidemiological studies devoted to test the niche specialization hypothesis for the B2 phylogenetic subgroups.

Phylogenetic analysis of Escherichia coli strains causing neonatal meningitis suggests horizontal gene transfer from a predominant pool of highly virulent B2 group strains

Phylogenetic relationships of 69 neonatal meningitis Escherichia coli strains isolated worldwide were studied. Restriction fragment length polymorphism of rrn operons (rrn RFLP) in these isolates was compared with that of the 72 strains of the ECOR reference collection. Distributions of K1 antigen, of polymerase chain reaction-detected ibe10 gene, pap, afa, sfa/foc, hly, and aer operons, and of a 14.9-kb rrn-containing HindIII fragment previously associated with neonatal meningitis were compared. Oligoclonality was observed for the meningitis strains. Factorial analysis of correspondence on the rrn RFLP data showed a frequency gradient of meningitis strains from the phylogenetic B2 group (68%) to the A group (6%), via the D and B1 groups (26%). The distribution of the virulence determinants argues for their horizontal transfer during the evolution of E. coli. Analysis of the status of some neonates further suggests that neonatal meningitis results from a balance between bacterial genes of virulence and host factors.

Isolation of a 7S particle from Xenopus laevis oocytes: a 5S RNA-protein complex

Previtellogenic oocytes of Xenopus laevis contain a free 5S RNA-protein complex sedimentating at 7 S. This particle consists of one molecule of 5S RNA and one 45,000-dalton protein. The protein of the 7S particle and the protein that is released in association with 5S RNA when the ribosome is treated with EDTA are unrelated. Because the 5S RNA accumulated by small oocytes in storage particles is incorporated into the ribosome later in oogenesis, we conclude that 5S RNA is succesively associated with two proteins during the life span of the oocyte.

Large-scale population structure of human commensal Escherichia coli isolates

The study of several Escherichia coli intestinal commensal isolates per individual in 265 healthy human subjects belonging to seven populations distributed worldwide showed that the E. coli population is highly structured, with major differences between the tropical and temperate populations.

Effect of human vicinity on antimicrobial resistance and integrons in animal faecal Escherichia coli

OBJECTIVES

To determine the level of antimicrobial resistance and the occurrence of class 1, 2 and 3 integrons in faecal Escherichia coli from several animal populations variously exposed to human contact.

METHODS

A collection of 341 faecal E. coli isolates was constituted from several animal populations subject to various degrees of exposure to humans: 18 animals never exposed to humans (living in the Antarctic or Gabon), 71 wild animals living in a low human density area (mountainous region of the Pyrenees, France), 61 wild animals living in a higher human density area (Fontainebleau forest near Paris, France), and 128 extensively reared farm animals and 42 pet dogs, both living in the Pyrenees. Resistance to antimicrobial agents was determined by the method of disc diffusion and quantified using the resistance score of BE Murray, JJ Mathewson, HL DuPont, CD Ericsson and RR Reves (Antimicrobial Agents and Chemotherapy 1990; 34: 515-18). Integrons were characterized by triplex real-time PCR and sequencing. The absence of epidemiologic clones was confirmed by PCR-based methods.

RESULTS

A gradient of resistance ranging from absence to high prevalence (resistance score of 18.7%) and a gradual increase in the prevalence of class 1 integrons (from 0% to 16%), both correlated with the increase in exposure to humans, were observed. In wild animals with little contact with humans, resistance, when present, was not mediated by integrons.

CONCLUSIONS

Our findings firmly establish that the current prevalence of antimicrobial resistance found in animal faecal bacteria, as well as the prevalence of integrons, is clearly anthropogenic. The presence of integrons may constitute an adaptive process to environments whose antimicrobial pressure exceeds a certain threshold.

Identification of forces shaping the commensal Escherichia coli genetic structure by comparing animal and human isolates

To identify forces shaping the Escherichia coli intraspecies ecological structure, we have characterized in terms of phylogenetic group (A, B1, D and B2) belonging, presence/absence of extraintestinal virulence genes (pap, sfa, hly and aer) and intra-host phylotype diversity a collection of 1898 commensal isolates originating from 387 animals (birds and mammals) sampled in the 1980s and the 2000s. These data have been compared with 760 human commensal isolates, sampled from 152 healthy subjects in the 2000s, and analysed with the same approach. The prevalence of the E. coli phylogenetic groups in birds, non-human mammals and humans is clearly different with a predominance of D/B1, A/B1 and A/B2 strains respectively. A major force shaping the ecological structure is the environment with a strong effect of domestication and the year of sampling followed by the climate. Host characteristics, as the diet and body mass, also influence the ecological structure. Human microbiota are characterized by a higher prevalence of virulence genes and a lower intra-host diversity than the non-human mammal ones. This work identifies for the first time a group of strains specific to the animals, the B1 phylogenetic group strains exhibiting the hly gene. In conclusion, a complex network of factors seems to shape the ecological structure of commensal E. coli, with anthropogenic factors playing a major role and perturbing natural niche equilibrium.

Surveillance network for herpes simplex virus resistance to antiviral drugs: 3-year follow-up

Herpes simplex virus (HSV) infections are very common in the general population and among immunocompromised patients. Acyclovir (ACV) is an effective treatment which is widely used. We deemed it essential to conduct a wide and coordinated survey of the emergence of ACV-resistant HSV strains. We have formed a network of 15 virology laboratories which have isolated and identified, between May 1999 and April 2002, HSV type 1 (HSV-1) and HSV-2 strains among hospitalized subjects. The sensitivity of each isolate to ACV was evaluated by a colorimetric test (C. Danve, F. Morfin, D. Thouvenot, and M. Aymard, J. Virol. Methods 105:207-217, 2002). During this study, 3900 isolated strains among 3357 patients were collected; 55% of the patients were immunocompetent. Only six immunocompetent patients excreted ACV-resistant HSV strains (0.32%), including one female patient not treated with ACV who was infected primary by an ACV-resistant strain. Among the 54 immunocompromised patients from whom ACV-resistant HSV strains were isolated (3.5%), the bone marrow transplantation patients showed the highest prevalence of resistance (10.9%), whereas among patients infected by human immunodeficiency virus, the prevalence was 4.2%. In 38% of the cases, the patients who excreted the ACV-resistant strains were treated with foscarnet (PFA), and 61% of them developed resistance to PFA. The collection of a large number of isolates enabled an evaluation of the prevalence of resistance of HSV strains to antiviral drugs to be made. This prevalence has remained stable over the last 10 years, as much among immunocompetent patients as among immunocompromised patients.

Animal and human pathogenic Escherichia coli strains share common genetic backgrounds

Escherichia coli is a versatile species encompassing both commensals of the digestive tracts of many vertebrates, including humans, and pathogenic strains causing various intra- and extraintestinal infections. Despite extensive gene flow between strains, the E. coli species has a globally clonal population structure, consisting of distinct phylogenetic groups. Little is known about the relationships between phylogenetic groups and host specificity. We therefore used multilocus sequence typing (MLST) to investigate phylogenetic relationships and evaluated the virulence gene content of 35 E. coli strains representative of the diverse diseases encountered in domestic animals. We compared these strains with a panel of 101 human pathogenic and 98 non-human and human commensal strains representative of the phylogenetic and pathovar diversity of this species. A global factorial analysis of correspondence indicated that extraintestinal infections were caused mostly by phylogenetic group B2 strains, whereas intraintestinal infections were caused mostly by phylogenetic group A/B1/E strains, with strains responsible from extraintestinal or intraintestinal infections having specific virulence factors. It was not possible to distinguish between strains of human and animal origin. A detailed phylogenetic analysis of the MLST data showed that numerous pathogenic animal and human strains are very closely related, and had a number of virulence genes in common. However, a set of specific adhesins was identified in animal non-B2 group strains of all pathotypes. In conclusion, human and animal pathogenic strains share common genetic backgrounds, but non-B2 strains of different origins seem to have different sets of adhesins that could be involved in host specificity.

Genetic background of Escherichia coli and extended-spectrum beta-lactamase type

ESBL-producing E. coli may arise from interactions between ESBL type, strain genetic background, and selective pressures in various ecologic niches.

To assess the implication of the genetic background of Escherichia coli strains in the emergence of extended-spectrum-β-lactamases (ESBL), 55 TEM-, 52 CTX-M-, and 22 SHV-type ESBL-producing clinical isolates involved in various extraintestinal infections or colonization were studied in terms of phylogenetic group, virulence factor (VF) content (pap, sfa/foc, hly, and aer genes), and fluoroquinolone resistance. A factorial analysis of correspondence showed that SHV type, and to a lesser extent TEM type, were preferentially observed in B2 phylogenetic group strains that exhibited numerous VFs but were fluoroquinolone-susceptible, whereas the newly emerged CTX-M type was associated with the D phylogenetic group strains that lacked VF but were fluoroquinolone-resistant. Thus, the emergence of ESBL-producing E. coli seems to be the result of complex interactions between the type of ESBL, genetic background of the strain, and selective pressures in ecologic niches.

High frequency of mutator strains among human uropathogenic Escherichia coli isolates

By using a panel of 603 commensal and pathogenic Escherichia coli and Shigella isolates, we showed that mutation rates of strains vary considerably among different ecotypes. Uropathogenic strains had the highest frequency of mutators, while strains from patients with bacteremia had the lowest mutation rates. No correlation between the mutation rates and antibiotic resistance was observed among the studied strains.

Experimental mouse lethality of Escherichia coli isolates, in relation to accessory traits, phylogenetic group, and ecological source

BACKGROUND

Whether accessory traits, phylogenetic background, or ecological source best predicts extraintestinal virulence within Escherichia coli is undefined.

METHODS

A total of 90 E. coli strains (18 fecal isolates and 72 extraintestinal-infection isolates) were characterized for 55 accessory traits and phylogenetic group (A, B1, B2, or D). Bacterial traits and ecological source were compared with experimental mouse lethality.

RESULTS

Of the 90 strains, 41% were "killers" (i.e., killed > or =90% of mice). By univariate analysis, multiple group B2-associated traits (including malX [pathogenicity-island marker], pap [P fimbriae] elements, usp [uropathogenic-specific protein], and fyuA [yersiniabactin system]) were most closely associated with killer status, followed by group B2 (or non-group A) status and then by nonfecal origin. Stepwise multivariate analysis identified pap, malX, usp, fyuA, and B2 (all of which were positive predictors) and ireA (which was a negative predictor) as significant predictors of killer status. Killer strains segregated significantly from nonkiller strains, according to accessory-trait profiles. Factorial analysis of correspondence placed group B2 among the traits most closely associated with killer status, but not as the closest.

CONCLUSIONS

Specific group B2-associated accessory traits are more potent predictors of experimental virulence among E. coli isolates than is either phylogenetic background or ecological source. Molecular typing can estimate an E. coli isolate's extraintestinal virulence potential, regardless of source.

Coronavirus-related nosocomial viral respiratory infections in a neonatal and paediatric intensive care unit: a prospective study

The incidence of nosocomial viral respiratory infections (NVRI) in neonates and children hospitalized in paediatric and neonatal intensive care units (PNICU) is unknown. Human coronaviruses (HCoV) have been implicated in NVRI in hospitalized preterm neonates. The objectives of this study were to determine the incidence of HCoV-related NVRI in neonates and children hospitalized in a PNICU and the prevalence of viral respiratory tract infections in staff. All neonates (age< or =28 days) and children (age>28 days) hospitalized between November 1997 and April 1998 were included. Nasal samples were obtained by cytological brush at admission and weekly thereafter. Nasal samples were taken monthly from staff. Virological studies were performed, using indirect immunofluorescence, for HCoV strains 229E and OC43, respiratory syncytial virus (RSV), influenza virus types A and B, paramyxoviruses types 1, 2 and 3 and adenovirus. A total of 120 patients were enrolled (64 neonates and 56 children). Twenty-two samples from 20 patients were positive (incidence 16.7%). In neonates, seven positive samples, all for HCoV, were detected (incidence 11%). Risk factors for NVRI in neonates were: duration of hospitalization, antibiotic treatment and duration of parenteral nutrition (P<0.01). Monthly prevalence of viral infections in staff was between 0% and 10.5%, mainly with HCoV. In children, 15 samples were positive in 13 children at admission (seven RSV, five influenza and three adenovirus) but no NVRI were observed. In spite of a high rate of community-acquired infection in hospitalized children, the incidence of NVRI with common respiratory viruses appears low in neonates, HCoV being the most important pathogen of NRVI in neonates during this study period. Further research is needed to evaluate the long-term impact on pulmonary function.

Yersinia high-pathogenicity island contributes to virulence in Escherichia coli causing extraintestinal infections

The Yersinia high-pathogenicity island (HPI) encodes an iron uptake system mediated by the siderophore yersiniabactin (Ybt) and confers the virulence of highly pathogenic Yersinia species. This HPI is also widely distributed in human pathogenic members of the family of Enterobacteriaceae, above all in extraintestinal pathogenic Escherichia coli (ExPEC). In the present study we demonstrate a highly significant correlation of a functional HPI and extraintestinal virulence in E. coli. Moreover, using a mouse infection model, we show for the first time that the HPI contributes to the virulence of ExPEC.

Identification of a clone of Escherichia coli O103:H2 as a potential agent of hemolytic-uremic syndrome in France

In a French multicenter study, six verocytotoxin-producing Escherichia coli strains were isolated from the stools of 6 of 69 children suffering from hemolytic-uremic syndrome. All strains belonged to serotype O103:H2, a serotype commonly associated with diarrhea in weaned rabbits in France. To determine whether the strains from humans and rabbits were genetically related, they were compared by analyzing their esterase electropherotypes and the restriction fragment length polymorphisms of the ribosomal DNA regions. A common clonal origin of these pathogenic strains was suggested by their identical esterase electropherotypes and their identical ribotypes, in addition to their identical serotypes. However, strains from humans, which are cytotoxic for HeLa cells through the production of verocytotoxin type 1, do not show adhesion in vitro to HeLa 229 cells and cannot infect rabbits. On the other hand, strains from rabbits do not carry the verocytotoxin type 1 gene, are not cytotoxic for Hela cells, and adhere to ileal villi and HeLa 229 cells because of the expression of their 32-kDa adhesin. Our results therefore identify a clone of verocytotoxin-producing E. coli O103:H2 as a potential agent of hemolytic uremic syndrome in France. They further suggest that clones from humans and rabbits probably have a common origin but that adaptation to the two species occurred by different mechanisms. Thus, they eliminate the hypothesis that the species is horizontally transmitted between rabbits and humans.

Sex in Escherichia coli does not disrupt the clonal structure of the population: evidence from random amplified polymorphic DNA and restriction-fragment-length polymorphism

Analysis of the Escherichia coli population by multilocus enzyme electrophoresis (MLEE) has established its clonal organization, but there is increasing evidence that horizontal DNA transfer occurs in E. coli. We have assessed the genetic structure of the species E. coli and determined the extent to which recombination can affect the clonal structure of bacteria. A panel of 72 E. coli strains from the ECOR collection was characterized by random amplified polymorphic DNA (RAPD) and restriction-fragment-length polymorphism (RFLP) of the ribosomal RNA gene (rrn) regions. These strains have been characterized by MLEE and are assumed to reflect the range of genotypic variation in the species as a whole. Statistical analysis, including factorial analysis of correspondence (FAC) and hierarchical classifications, established that the data obtained with the three genetic markers are mutually corroborative, thus providing compelling evidence that horizontal transfer does not disrupt the clonal organization of the population. However, there is a gradient of correlation between the different classifications which ranges from the highly clonal structure of B2 group strains causing extraintestinal infections in humans to the less-stringent structure of B1 group strains that came mainly from nonprimate mammals. This group (B1) appears to be the framework from which the remaining non-A group strains have emerged. These results indicate that RAPD analysis is well suited to intraspecies characterization of E. coli. Lastly, treating the RAPD data by FAC allowed description of subgroup-specific DNA fragments which can be used, in a strategy comparable to positional cloning, to isolate virulence genes.

Identification and functional characterization of arylamine N-acetyltransferases in eubacteria: evidence for highly selective acetylation of 5-aminosalicylic acid

Arylamine N-acetyltransferase activity has been described in various bacterial species. Bacterial N-acetyltransferases, including those from bacteria of the gut flora, may be involved in the metabolism of xenobiotics, thereby exerting physiopathological effects. We characterized these enzymes further by steady-state kinetics, time-dependent inhibition, and DNA hybridization in 40 species, mostly from the human intestinal microflora. We report for the first time N-acetyltransferase activity in 11 species of Proteobacteriaceae from seven genera: Citrobacter amalonaticus, Citrobacter farmeri, Citrobacter freundii, Klebsiella ozaenae, Klebsiella oxytoca, Klebsiella rhinoscleromatis, Morganella morganii, Serratia marcescens, Shigella flexneri, Plesiomonas shigelloides, and Vibrio cholerae. We estimated apparent kinetic parameters and found that 5-aminosalicylic acid, a compound efficient in the treatment of inflammatory bowel diseases, was acetylated with a catalytic efficiency 27 to 645 times higher than that for its isomer, 4-aminosalicylic acid. In contrast, para-aminobenzoic acid, a folate precursor in bacteria, was poorly acetylated. Of the wild-type strains studied, Pseudomonas aeruginosa was the best acetylator in terms of both substrate spectrum and catalytic efficiency. DNA hybridization with a Salmonella enterica serovar Typhimurium-derived probe suggested the presence of this enzyme in eight proteobacterial and four gram-positive species. Molecular aspects together with the kinetic data suggest distinct functional features for this class of microbial enzymes.

Molecular characterization of addiction systems of plasmids encoding extended-spectrum beta-lactamases in Escherichia coli

OBJECTIVES

Escherichia coli producing CTX-M-type extended-spectrum beta-lactamases (ESBLs) are spreading worldwide. The aim of this work was to investigate the addiction systems carried by the replicons involved in the emergence and spread of ESBLs in relation to ESBL and replicon types.

METHODS

A collection of 125 TEM, SHV and CTX-M ESBL-producing E. coli isolates and their 125 transconjugants or transformants was analysed. Five plasmid protein antitoxin-regulated systems and three plasmid antisense RNA-regulated systems were sought by PCR.

RESULTS

Two hundred and ninety-eight plasmid addiction systems were detected in the parental strains (mean 2.38, range 0-6 per strain) and 86 were detected in the recipient strains (mean 0.69, range 0-5 per strain). PemKI, CcdAB, Hok-Sok and VagCD were the most frequently represented systems in both recipient and parental strains. The parental SHV and CTX-M ESBL-producing strains had more addiction systems than the TEM ESBL producers. In the recipient strains, the frequency of addiction systems was significantly higher in IncF plasmids. Among the IncF replicons carrying CTX-M-type enzymes, the frequency of addiction systems was significantly higher in IncF plasmids carrying CTX-M-15 (mean 3.5) or CTX-M-9 (mean 4) than in those carrying CTX-M-14 (mean 0.6).

CONCLUSIONS

In E. coli producing CTX-M-15 or CTX-M-9 ESBLs, plasmids bearing the bla(CTX-M) gene have multiple addiction systems that could contribute to their maintenance in host strains.

Phylogenetic, virulence and antibiotic resistance characteristics of commensal strain populations of Escherichia coli from community subjects in the Paris area in 2010 and evolution over 30 years

It is important to study commensal populations of Escherichia coli because they appear to be the reservoir of both extra-intestinal pathogenic E. coli and antibiotic resistant strains of E. coli. We studied 279 dominant faecal strains of E. coli from 243 adults living in the community in the Paris area in 2010. The phylogenetic group and subgroup [sequence type complex (STc)] of the isolates and the presence of 20 virulence genes were determined by PCR assays. The O-types and resistance to 18 antibiotics were assessed phenotypically. The B2 group was the most frequently recovered (34.0 %), followed by the A group (28.7 %), and other groups were more rare. The most prevalent B2 subgroups were II (STc73), IV (STc141), IX (STc95) and I (STc131), with 22.1, 21.1, 16.8 and 13.7 %, respectively, of the B2 group strains. Virulence factors (VFs) were more common in B2 group than other strains. One or more resistances were found in 125 strains (44.8 % of the collection) but only six (2.2 % of the collection) were multiresistant; no extended-spectrum beta-lactamase-producing strain was isolated. The C phylogroup and clonal group A strains were the most resistant. No trade-off between virulence and resistance was evidenced. We compared these strains with collections of strains gathered under the same conditions 30 and 10 years ago. There has been a parallel and linked increase in the frequency of B2 group strains (from 9.4 % in 1980, to 22.7 % in 2000 and 34.0 % in 2010) and of VFs. Antibiotic resistance also increased, from 22.6 % of strains resistant to at least one antibiotic in 1980, to 31.8 % in 2000 and 44.8 % in 2010; resistance to streptomycin, however, remained stable. Commensal human E. coli populations have clearly evolved substantially over time, presumably reflecting changes in human practices, and particularly increasing antibiotic use.

Escherichia coli strains from pregnant women and neonates: intraspecies genetic distribution and prevalence of virulence factors

To determine the extent to which the vagina, endocervix, and amniotic fluid screen the Escherichia coli strains responsible for neonatal infections, we studied the genetic relationships among 105 E. coli strains isolated from all of the ecosystems involved in this infectious process. Twenty-four strains were isolated from the intestinal flora, and 25 strains were isolated from the vaginas of pregnant women. Twenty-seven strains were isolated from the amniotic fluid, blood, and cerebrospinal fluid (CSF) of infected neonates. The intraspecies genetic characteristics of all of the isolates were determined by random amplified polymorphic DNA (RAPD) analysis, PCR ECOR (E. coli reference) grouping, and PCR virulence genotyping. A correlation was found between the intraspecies distributions of the strains in the A, B1, B2, and D ECOR groups and in the two major RAPD groups (I and II). Nevertheless, the distribution of the E. coli strains in the RAPD groups according to their anatomical origins was more significant than their distribution in the ECOR groups. This may be explained by the existence of an E. coli subpopulation, defined by the RAPD I group, within the ECOR B2 group. This RAPD I group presents a major risk for neonates: 75% of the strains isolated from patients with meningitis and 100% of the strains isolated from patients with bacteremia were in this group. The vagina and the amniotic fluid are two barriers that favor colonization by highly infectious strains. Indeed, only 17% of fecal strains belonged to the RAPD I group, whereas 52% of vaginal strains and 67% of amniotic fluid strains belonged to this subpopulation. The ibeA and iucC genes were significantly associated with CSF strains, whereas the hly and sfa/foc genes were more frequent in blood strains. These findings could serve as a basis for developing tools to recognize vaginal strains, which present a high risk for neonates, for use in prophylaxis programs.