RESUMEN
A significant part of horizontal gene transfer is facilitated by genomic islands. Haemophilus influenzae genomic island ICEHin1056 is an archetype of a genomic island that accounts for pandemic spread of antibiotics resistance. ICEHin1056 has modular structure and harbors modules involved in type IV secretion and integration. Previous studies have shown that ICEHin1056 encodes a functional type IV secretion system; however, other modules have not been characterized yet. Here we show that the module on the 5' extremity of ICEHin1056 consists of 15 genes that are well conserved in a number of related genomic islands. Furthermore by disrupting six genes of the investigated module of ICEHin1056 by site-specific mutagenesis we demonstrate that in addition to type IV secretion system module, the investigated module is also important for the successful conjugal transfer of ICEHin1056 from donor to recipient cells.
Asunto(s)
Conjugación Genética/genética , Redes Reguladoras de Genes/genética , Transferencia de Gen Horizontal/genética , Genes Bacterianos/genética , Islas Genómicas/genética , Haemophilus/genética , Secuencia de Bases , Biología Computacional , Replicación del ADN/genética , Inestabilidad Genómica/genética , Haemophilus influenzae/genética , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Análisis de Secuencia de ADNRESUMEN
BACKGROUND: A major part of horizontal gene transfer that contributes to the diversification and adaptation of bacteria is facilitated by genomic islands. The evolution of these islands is poorly understood. Some progress was made with the identification of a set of phylogenetically related genomic islands among the Proteobacteria, recognized from the investigation of the evolutionary origins of a Haemophilus influenzae antibiotic resistance island, namely ICEHin1056. More clarity comes from this comparative analysis of seven complete sequences of the ICEHin1056 genomic island subfamily. RESULTS: These genomic islands have core and accessory genes in approximately equal proportion, with none demonstrating recent acquisition from other islands. The number of variable sites within core genes is similar to that found in the host bacteria. Furthermore, the GC content of the core genes is similar to that of the host bacteria (38% to 40%). Most of the core gene content is formed by the syntenic type IV secretion system dependent conjugative module and replicative module. GC content and lack of variable sites indicate that the antibiotic resistance genes were acquired relatively recently. An analysis of conjugation efficiency and antibiotic susceptibility demonstrates that phenotypic expression of genomic island-borne genes differs between different hosts. CONCLUSION: Genomic islands of the ICEHin1056 subfamily have a longstanding relationship with H. influenzae and H. parainfluenzae and are co-evolving as semi-autonomous genomes within the 'supragenomes' of their host species. They have promoted bacterial diversity and adaptation through becoming efficient vectors of antibiotic resistance by the recent acquisition of antibiotic resistance transposons.
Asunto(s)
Genoma Bacteriano , Haemophilus/genética , Secuencia de Bases , ADN Bacteriano , Farmacorresistencia Microbiana/genética , Evolución Molecular , Transferencia de Gen Horizontal , Datos de Secuencia Molecular , Homología de Secuencia de Ácido Nucleico , Especificidad de la EspecieRESUMEN
OBJECTIVE: To assess the effect of community prescribing of an antibiotic for acute respiratory infection on the prevalence of antibiotic resistant bacteria in an individual child. STUDY DESIGN: Observational cohort study with follow-up at two and 12 weeks. SETTING: General practices in Oxfordshire. PARTICIPANTS: 119 children with acute respiratory tract infection, of whom 71 received a beta lactam antibiotic. MAIN OUTCOME MEASURES: Antibiotic resistance was assessed by the geometric mean minimum inhibitory concentration (MIC) for ampicillin and presence of the ICEHin1056 resistance element in up to four isolates of Haemophilus species recovered from throat swabs at recruitment, two weeks, and 12 weeks. RESULTS: Prescribing amoxicillin to a child in general practice more than triples the mean minimum inhibitory concentration for ampicillin (9.2 microg/ml v 2.7 microg/ml, P=0.005) and doubles the risk of isolation of Haemophilus isolates possessing homologues of ICEHin1056 (67% v 36%; relative risk 1.9, 95% confidence interval 1.2 to 2.9) two weeks later. Although this increase is transient (by 12 weeks ampicillin resistance had fallen close to baseline), it is in the context of recovery of the element from 35% of children with Haemophilus isolates at recruitment and from 83% (76% to 89%) at some point in the study. CONCLUSION: The short term effect of amoxicillin prescribed in primary care is transitory in the individual child but sufficient to sustain a high level of antibiotic resistance in the population.