The Cell Wall-Targeting Antibiotic Stimulon of Enterococcus faecalis

Abstract

Enterococcus faecalis is an opportunistic nosocomial pathogen that is highly resistant to a variety of environmental insults, including an intrinsic tolerance to antimicrobials that target the cell wall (CW). With the goal of determining the CW-stress stimulon of E. faecalis, the global transcriptional profile of E. faecalis OG1RF exposed to ampicillin, bacitracin, cephalotin or vancomycin was obtained via microarrays. Exposure to the β-lactams ampicillin and cephalotin resulted in the fewest transcriptional changes with 50 and 192 genes differentially expressed 60 min after treatment, respectively. On the other hand, treatment with bacitracin or vancomycin for 60 min affected the expression of, respectively, 377 and 297 genes. Despite the differences in the total number of genes affected, all antibiotics induced a very similar gene expression pattern with an overrepresentation of genes encoding hypothetical proteins, followed by genes encoding proteins associated with cell envelope metabolism as well as transport and binding proteins. In particular, all drug treatments, most notably bacitracin and vancomycin, resulted in an apparent metabolic downshift based on the repression of genes involved in translation, energy metabolism, transport and binding. Only 19 genes were up-regulated by all conditions at both the 30 and 60 min time points. Among those 19 genes, 4 genes encoding hypothetical proteins (EF0026, EF0797, EF1533 and EF3245) were inactivated and the respective mutant strains characterized in relation to antibiotic tolerance and virulence in the Galleria mellonella model. The phenotypes obtained for two of these mutants, ΔEF1533 and ΔEF3245, support further characterization of these genes as potential candidates for the development of novel preventive or therapeutic approaches.

Identification and Characterization of a Bacitracin Resistance Network in Enterococcus faecalis

“…As mentioned above, operons for two such transporters were previously identified in the genome of E. faecalis by a comparative genomics study, namely, EF2050-2049 and EF2752-2751 (16). Although our proteomic study identified only the former transporter, both loci were found to be upregulated in response to bacitracin by transcriptome analysis (8). We therefore decided to investigate these two transporters in more detail, regarding both their role in bacitracin resistance and their regulation.…”

“…In accordance with the need for a better understanding of the response of E. faecalis to antibiotics that inhibit cell wall synthesis, a recent transcriptomic study identified a large number of genes that were upregulated after exposure to ampicillin, cephalothin, vancomycin, and bacitracin (8). Of these compounds, bacitracin elicited the broadest response, affecting genes with functions in cell wall maintenance, metabolism, and transport processes.…”

“…One strategy can be alterations in the cell's surface charge, for example, by alanylation of teichoic acids catalyzed by the DltABCD system (6,7). Accordingly, in a recent study, the dlt operon of E. faecalis was shown to be upregulated in response to bacitracin and vancomycin (8). Alternatively, upregulation of the enzyme inhibited by the antibiotic, e.g., in the case of bacitracin, undecaprenyl-pyrophosphate phosphatases, can confer resistance, as has been shown for Bacillus subtilis and E. faecalis (2,9).…”

Chlorhexidine Induces VanA-Type Vancomycin Resistance Genes in Enterococci

“…The VanH dehydrogenase converts pyruvate into Other highly upregulated genes have previously been implicated in the enterococcal extracytoplasmic stress response (Table 2; see also Data Set S1). We identified overlap between the H-CHG transcriptomic response in E. faecium 1,231,410 with the transcriptomic response of E. faecalis OG1RF to the cell wall-active antibiotics ampicillin, bacitracin, cephalothin, and vancomycin (38) and with the E. faecalis OG1X response to the plasmid-encoded Fst toxin, which likely interacts with the OG1X cell membrane, causing stress (39,40). Further, mutations in four genes in our data set are associated with daptomycin nonsusceptibility in E. faecalis and E. faecium (41)(42)(43)(44).…”

The antibacterial activities of some plant-derived triterpenes

“…B. cereus is normally associated with food poisoning that is characterized by either diarrhoea and abdominal distress or nausea and vomiting (Senesi and Ghelardi, 2010). It is also an opportunistic pathogen in immunocompromised patients causing severe endophthalmitis, bacteremia, septicemia, endocarditis, pneumonia, meningitis, gastritis, and cutaneous infections (Senesi and Ghelardi, 2010); Vibrio bacteria is incriminated in mostly gastrointestinal and extra-intestinal diseases in man (Health protection agency, 2007); Enterococcus bacteria are common causes of nosocomial infections (Arias et al, 2010), such as catheter-associated urinary tract infections, endocarditis as well as surgical and burn wound infections (Abranches et al, 2013) ; E. coli bacteria, mostly the shiga toxin producing serotypes cause mild to bloody diarrhoea, haemorrhagic colitis, and hemolytic-uremic syndrome (HUS) (Brooks et al, 2005). Treatment of these various bacterial infections is, however, being hindered by the prevalence of antibiotic resistant strains (Furtula et …”