SciCombinator

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Concept: Enterococcus

163

Despite the increasing importance of Enterococcus as opportunistic pathogens, their virulence factors are still poorly understood. This study determines the frequency of virulence factors in clinical and commensal Enterococcus isolates from inpatients in Porto Alegre, Brazil. Fifty Enterococcus isolates were analysed and the presence of the gelE, asa1 and esp genes was determined. Gelatinase activity and biofilm formation were also tested. The clonal relationships among the isolates were evaluated using pulsed-field gel electrophoresis. The asa1, gelE and esp genes were identified in 38%, 60% and 76% of all isolates, respectively. The first two genes were more prevalent in Enterococcus faecalis than in Enterococcus faecium, as was biofilm formation, which was associated with gelE and asa1 genes, but not with the esp gene. The presence of gelE and the activity of gelatinase were not fully concordant. No relationship was observed among any virulence factors and specific subclones of E. faecalis or E. faecium resistant to vancomycin. In conclusion, E. faecalis and E. faecium isolates showed significantly different patterns of virulence determinants. Neither the source of isolation nor the clonal relationship or vancomycin resistance influenced their distribution.

Concepts: Protein, Bacteria, Antibiotic resistance, Linezolid, Vancomycin, Enterococcus, Enterococcus faecium, Enterococcus faecalis

160

To date there are no clear criteria to determine whether a microbe is susceptible to biocides or not. As a starting point for distinguishing between wild-type and resistant organisms, we set out to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) distributions for four common biocides; triclosan, benzalkonium chloride, chlorhexidine and sodium hypochlorite for 3319 clinical isolates, with a particular focus on Staphylococcus aureus (N = 1635) and Salmonella spp. (N = 901) but also including Escherichia coli (N = 368), Candida albicans (N = 200), Klebsiella pneumoniae (N = 60), Enterobacter spp. (N = 54), Enterococcus faecium (N = 53), and Enterococcus faecalis (N = 56). From these data epidemiological cut-off values (ECOFFs) are proposed. As would be expected, MBCs were higher than MICs for all biocides. In most cases both values followed a normal distribution. Bimodal distributions, indicating the existence of biocide resistant subpopulations were observed for Enterobacter chlorhexidine susceptibility (both MICs and MBCs) and the susceptibility to triclosan of Enterobacter (MBC), E. coli (MBC and MIC) and S. aureus (MBC and MIC). There is a concern on the potential selection of antibiotic resistance by biocides. Our results indicate however that resistance to biocides and, hence any potential association with antibiotic resistance, is uncommon in natural populations of clinically relevant microorganisms.

Concepts: Bacteria, Pneumonia, Staphylococcus aureus, Antibiotic resistance, Escherichia coli, Linezolid, Enterobacteriaceae, Enterococcus

149

Quinomycin G (1), a new analogue of echinomycin, together with a new cyclic dipeptide, cyclo-(l-Pro-4-OH-l-Leu) (2), as well as three known antibiotic compounds tirandamycin A (3), tirandamycin B (4) and staurosporine (5), were isolated from Streptomyces sp. LS298 obtained from a marine sponge Gelliodes carnosa. The planar and absolute configurations of compounds 1 and 2 were established by MS, NMR spectral data analysis and Marfey’s method. Furthermore, the differences in NMR data of keto-enol tautomers in tirandamycins were discussed for the first time. Antibacterial and anti-tumor activities of compound 1 were measured against 15 drug-sensitive/resistant strains and 12 tumor cell lines. Compound 1 exhibited moderate antibacterial activities against Staphylococcuse pidermidis, S. aureus, Enterococcus faecium, and E. faecalis with the minimum inhibitory concentration (MIC) values ranged from 16 to 64 μg/mL. Moreover, it displayed remarkable anti-tumor activities; the highest activity was observed against the Jurkat cell line (human T-cell leukemia) with an IC50 value of 0.414 μM.

Concepts: Cell, Cancer, Bacteria, Antibiotic resistance, NMR spectroscopy, Cell culture, Enterococcus, Enterococcus faecium

42

Serious bacterial infections in immunocompromised patients require highly effective antibacterial therapy for cure, and thus, this setting may reveal novel mechanisms by which bacteria circumvent antibiotics in the absence of immune pressure. Here, an infant with leukemia developed vancomycin-resistant Enterococcus faecium (VRE) bacteremia that persisted for 26 days despite appropriate antibiotic therapy. Sequencing of 22 consecutive VRE isolates identified the emergence of a single missense mutation (L152F) in relA, which constitutively activated the stringent response, resulting in elevated baseline levels of the alarmone guanosine tetraphosphate (ppGpp). Although the mutant remained susceptible to both linezolid and daptomycin in clinical MIC testing and during planktonic growth, it demonstrated tolerance to high doses of both antibiotics when growing in a biofilm. This biofilm-specific gain in resistance was reflected in the broad shift in transcript levels caused by the mutation. Only an experimental biofilm-targeting ClpP-activating antibiotic was able to kill the mutant strain in an established biofilm. The relA mutation was associated with a fitness trade-off, forming smaller and less-well-populated biofilms on biological surfaces. We conclude that clinically relevant relA mutations can emerge during prolonged VRE infection, causing baseline activation of the stringent response, subsequent antibiotic tolerance, and delayed eradication in an immunocompromised state.

Concepts: Immune system, Mutation, Bacteria, Microbiology, Antibiotic resistance, Vancomycin, Enterococcus, Vancomycin-resistant enterococcus

30

We studied the vanA-carrying vancomycin-resistant enterococci (VRE) isolated from American crows in the United States during the winter 2011/2012. Faecal samples from crows were cultured selectively for VRE and characterized. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were used to examine epidemiological relationships of vanA-containing VRE. Isolates were tested in vitro for their ability to horizontally transfer the vancomycin resistance trait. VRE with the vanA gene were found in 15 (2.5%) of 590 crows samples, from which we obtained 22 different isolates. Enterococcal species were Enterococcus faecium (14) and E. faecalis (8). One, two and 19 isolates originated from Kansas, New York State and Massachusetts, respectively. Based on MLST analysis, E. faecium isolates were grouped as ST18 (6 isolates), ST555 (2), and novel types ST749 (1), ST750 (3), ST751 (1), ST752 (1). Enterococcus faecalis isolates belonged to ST6 (1), ST16 (3) and ST179 (4). All isolates were able to transfer the vancomycin resistance trait via filter mating with very high transfer range. Clinically important enterococci with the vanA gene occur in faeces of wild American crows throughout the United States. These migrating birds may contribute to the dissemination of VRE in environment over large distances. [Correction added after first online publication on 06 August 2013: The number of E. faecium ST752 isolate is now amended to ‘1’, consistent with that shown in the ‘Results’ section and Figure 2.].

Concepts: United States, Antibiotic resistance, Linezolid, Vancomycin, Enterococcus, Vancomycin-resistant enterococcus, Enterococcus faecium, Enterococcus faecalis

30

The use of glyphosate modifies the environment which stresses the living microorganisms. The aim of the present study was to determine the real impact of glyphosate on potential pathogens and beneficial members of poultry microbiota in vitro. The presented results evidence that the highly pathogenic bacteria as Salmonella Entritidis, Salmonella Gallinarum, Salmonella Typhimurium, Clostridium perfringens and Clostridium botulinum are highly resistant to glyphosate. However, most of beneficial bacteria as Enterococcus faecalis, Enterococcus faecium, Bacillus badius, Bifidobacterium adolescentis and Lactobacillus spp. were found to be moderate to highly susceptible. Also Campylobacter spp. were found to be susceptible to glyphosate. A reduction of beneficial bacteria in the gastrointestinal tract microbiota by ingestion of glyphosate could disturb the normal gut bacterial community. Also, the toxicity of glyphosate to the most prevalent Enterococcus spp. could be a significant predisposing factor that is associated with the increase in C. botulinum-mediated diseases by suppressing the antagonistic effect of these bacteria on clostridia.

Concepts: Bacteria, Gut flora, Microbiology, Pathogen, Enterococcus, Clostridium, Firmicutes, Clostridium botulinum

28

To identify enterococci from the fermentation of milk for the production of nono, an African fermented dairy product, to determine the technological properties for suitability as starter cultures and safety as probiotics.

Concepts: Milk, Butter, Cattle, Dairy, Enterococcus, Pasteurization, Dairy product, Enterococcus faecium

28

Twenty-five years ago, isolation of vancomycin-resistant Enterococcus faecium (VREm) was reported both in the UK and in France. Since then, VREm has spread worldwide in hospitals. Hospital outbreaks appeared to be related to the evolution since the end of 1980s of a subpopulation of E. faecium highly resistant to ampicillin and fluoroquinolones (the so-called clonal complex CC17) that later acquired resistance to vancomycin. CC17 isolates are presumably better adapted than other E. faecium isolates to the constraints of the hospital environment and most contain mobile genetic elements, phage genes, genes encoding membrane proteins, regulatory genes, a putative pathogenicity island and megaplasmids. Colonization and persistence are major features of VREm. Inherent characteristics of E. faecium including a remarkable genome plasticity, in part due to acquisition of IS elements, in particular IS16, have facilitated niche adaptation of this distinct E. faecium subpopulation that is multiply resistant to antibiotics. Quinupristin/dalfopristin and linezolid are licensed for the treatment of VREm infections, with linezolid often used as a first-line treatment. However, the emergence of plasmid-mediated resistance to linezolid by production of a Cfr methyltransferase in Enterococcus faecalis is worrying. Daptomycin has not been extensively evaluated for the treatment of VREm infections and resistant mutants have been selected under daptomycin therapy. Although control of VRE is challenging, a laissez-faire policy would result in an increased number of infections and would create an irreversible situation. Although so far unsuccessful, dissemination of glycopeptide-resistant Staphylococcus aureus with van genes acquired from resistant enterococci cannot be ruled out.

Concepts: Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Linezolid, Vancomycin, Enterococcus, Vancomycin-resistant enterococcus, Enterococcus faecium

28

Vancomycin-resistant enterococcus (VRE) colonization and infection have increased at our hospital, despite adherence to standard VRE control guidelines.

Concepts: Antibiotic resistance, Vancomycin, Enterococcus, Vancomycin-resistant enterococcus

28

Five VanN-type vancomycin-resistant Enterococcus faecium strains were isolated from a sample of domestic chicken meat in Japan. All isolates showed low-level resistance to vancomycin (MIC, 12 mg/liter) and had the same pulsed-field gel electrophoresis profile. The vancomycin resistance was encoded on a large plasmid (160 kbp) and was expressed constitutively. The VanN-type resistance operon was identical to the first resistance operon to be reported, with the exception of a 1-bp deletion in vanT(N) and a 1-bp substitution in vanS(N).

Concepts: Antibiotic resistance, Linezolid, Vancomycin, Chicken, Meat, Enterococcus, Vancomycin-resistant enterococcus, Enterococcus faecium