RESUMO
Dioecy (i.e. having separate sexes) is a rather rare breeding system in flowering plants. Such rareness may result from a high probability of extinction in dioecious species because of less efficient dispersal and the costs of sexual selection, which are expected to harm dioecious species' survival on the long term. These handicaps should decrease the effective population size (Ne) of dioecious species, which in turn should reduce the efficacy of selection. Moreover, sexual selection in dioecious species is expected to specifically affect some genes, which will evolve under positive selection. The relative contribution of these effects is currently unknown and we tried to disentangle them by comparing sequence evolution between dioecious and non-dioecious species in the Silene genus (Caryophyllaceae), where dioecy has evolved at least twice. For the dioecious species in the section Melandrium, where dioecy is the oldest, we found a global reduction of purifying selection, while on some, male-biased genes, positive selection was found. For section Otites, where dioecy evolved more recently, we found no significant differences between dioecious and non-dioecious species. Our results are consistent with the view that dioecy is an evolutionary dead end in flowering plants, although other scenarios for explaining reduced Ne cannot be ruled out. Our results also show that contrasting forces act on the genomes of dioecious plants, and suggest that some time is required before the genome of such plants bears the footprints of dioecy.
Assuntos
Evolução Molecular , Silene/genética , Regulação da Expressão Gênica de Plantas , Genes de Plantas/genética , Filogenia , Reprodução , Seleção Genética , Silene/classificaçãoRESUMO
The occurrence of staphylococci and enterococci expressing increased resistance to erythromycin (ERY) and, in particular, to macrolide-lincosamide-streptogramin B (MLS(B) ) antibiotics was investigated in dairy cattle, pigs and turkeys. Three hundred rectal (cloacal) swabs of each animal species were examined. A total of 120 and 71 staphylococci and enterococci, respectively, with increased resistance to ERY were identified. These were most frequent in turkeys (42.3% of positive animals), followed by pigs and dairy cattle (6.7% and 6.0% of positive animals, respectively). Similarly, MLS(B) -resistant isolates colonized predominantly turkeys (29.7% of animals), while their occurrence in pigs and dairy cattle was only sporadic (0.8% of animals). At least one of the erm genes encoding for MLS(B) resistance was found in 56.7% and 69.0% of staphylococci and enterococci, respectively. The erm(C) gene prevailed in staphylococci while the erm(B) gene was predominant in enterococci. Macrolide efflux genes msr(A) and msr(C) were also frequent in staphylococci and enterococci, respectively. Macrolide inactivation gene mph(C) occurred mainly in staphylococci. In staphylococci, methicillin resistance was rarely detected (7.5% of isolates), but resistance to telithromycin (ketolides) was frequent in both staphylococci and enterococci (89.2% and 47.9% of isolates, respectively). This study showed that turkeys represent an important source of ERY (MLS(B) )-resistant cocci. In addition, resistance to ketolides was also frequent.
Assuntos
Antibacterianos/farmacologia , Farmacorresistência Bacteriana/genética , Enterococcus/efeitos dos fármacos , Enterococcus/genética , Eritromicina/farmacologia , Staphylococcus/efeitos dos fármacos , Staphylococcus/genética , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bovinos , Enterococcus/isolamento & purificação , Genes Bacterianos/efeitos dos fármacos , Genótipo , Lincosamidas/farmacologia , Macrolídeos/farmacologia , Testes de Sensibilidade Microbiana , Fenótipo , Doenças das Aves Domésticas , Prevalência , Infecções Estafilocócicas/tratamento farmacológico , Infecções Estafilocócicas/epidemiologia , Staphylococcus/isolamento & purificação , Estreptogramina B/farmacologia , Suínos , PerusRESUMO
Geographically related Staphylococcus epidermidis isolates from human patients (n=30), dairy farms (farmers and individual raw milk from cattle, n=36) and a dairy plant (n=55) were examined for epidemiological relatedness by pulsed-field gel electrophoresis and, using in vitro methods, for the ability to produce biofilm and antimicrobial resistance. Methicillin-resistant isolates (MRSE) were also identified and characterized. Isolates from farmers and dairy cattle were found to be genetically related, while isolates from human patients were highly diverse. Some dairy plant isolates (18.2%) were closely related to those from dairy farms. Biofilm production and resistance to antimicrobial agents were most typical for isolates from human patients, of which 76.7% were MRSE. Methicillin resistance was also widespread in farm-related isolates (61.1%). This study indicates the possible transmission of S. epidermidis between cattle and farmers. Dairy products were not proven to be an important source of either human infections or methicillin-resistant strains.
