High prevalence of faecal carriage of ESBL-producing Enterobacteriaceae in Norwegian patients with gastroenteritis

We conducted a cross-sectional study to examine the prevalence of faecal carriage of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in patients with gastroenteritis. During April 2011, all faecal samples submitted to our hospital laboratory were examined for ESBL-producing Enterobacteriaceae. Isolates expressing an ESBL phenotype were investigated for the presence of genes encoding broad-spectrum beta-lactamases, ESBLs, carbapenemases, and plasmid-mediated AmpC. Information on age, gender, and travel history was extracted from the laboratory records. In total 273 faecal samples were included. The overall carrier rate in the study population was 15.8%. The ESBL carrier rate among patients with no history of recent travel, or where this information was missing, was 10.3%. In contrast, the carrier rate was 56.3% (odds ratio 16.3, p < 0.001) among patients with a record of travel to Asia. Two ESBL-producing isolates were identified as enteropathogenic Escherichia coli. Co-resistance between third-generation cephalosporins, trimethoprim-sulfamethoxazole, and fluoroquinolones was seen in 49% of isolates. No carbapenemase-producers were found.

Large IncHI2-plasmids encode extended-spectrum β-lactamases (ESBLs) in Enterobacter spp. bloodstream isolates, and support ESBL-transfer to Escherichia coli

We investigated the prevalence of extended-spectrum β-lactamases (ESBLs) in Enterobacter spp. bloodstream isolates from 19 hospital laboratories in Norway during 2011. A total of 62/230 (27%) isolates were resistant to third-generation cephalosporins and four (1.7%) were ESBL-positive; blaCTX -M-15 (n = 3) and blaSHV -12 (n = 1). This is comparable to the prevalence of ESBLs in clinical isolates of Escherichia coli and Klebsiella pneumoniae in Norway during the same period. All ESBL-positive isolates were multidrug resistant (MDR) and harboured plasmid-mediated quinolone resistance. Three isolates supported transfer of large IncHI2-plasmids harbouring ESBL- and MDR-encoding genes to E. coli recipients by in vitro conjugation.

Evaluation of ROSCO Neo-Sensitabs for phenotypic detection and subgrouping of ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae

The increasing prevalence of ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae necessitates reliable phenotypic tests for detection and categorization. The main objective of this study was to evaluate ROSCO Neo-Sensitabs with different β-lactam-β-lactam inhibitor combinations for phenotypic detection and categorization of β-lactamases in Enterobacteriaceae. Using standard CLSI/EUCAST methodology, differences in zones of inhibitions between a β-lactam alone compared with the combination with a β-lactamase inhibitor as well as subjective synergy observations were determined for 172 well characterized Enterobacteriaceae strains with defined resistance mechanisms. The results showed that for all ESBL-positive strains (n = 66), combinations of clavulanic acid synergy with cefotaxime, ceftazidime or cefepime, were observed. All acquired AmpC β-lactamases (n = 17) were detected using cloxacillin combined with cefotaxime and/or ceftazidime (both combinations were required). Carbapenemase producers (n = 59) with the exception of one KPC-producer were correctly grouped using the combination of meropenem ± aminophenylboronic acid (APBA) or dipicolinic acid (DPA). Ethylene diamine tetraacetic acid (EDTA) also inhibited all metallo-β-lactamases, but as with DPA, one false positive result was observed. Based upon these data, we propose a tablet layout for 14 cm agar plates, which could be used as a whole or in a targeted approach for detection and categorizing of relevant acquired β-lactamases in Enterobacteriaceae.

Structural and computational investigations of VIM-7: insights into the substrate specificity of vim metallo-β-lactamases

The presence of metallo-β-lactamases (MBLs) in many clinically important human bacterial pathogens limits treatment options, as these enzymes efficiently hydrolyze nearly all β-lactam antibiotics. VIM enzymes are among the most widely distributed MBLs, but many of the individual VIM subtypes remain poorly characterized. Pseudomonas aeruginosa VIM-7 is the most divergent among VIM-type MBLs in terms of amino acid sequence. Here we present crystal structures of VIM-7 as the native enzyme, with Cys221 oxidized (VIM-7-Ox), and with a sulfur atom bridging the two active-site zinc ions (VIM-7-S). Comparison with VIM-2 and VIM-4 structures suggests an explanation for the reduced catalytic efficiency of VIM-7 against cephalosporins with a positively charged cyclic substituent at the C3 position (e.g., ceftazidime). Kinetic variations are attributed to substitutions in residues 60-66 (that form a loop adjacent to the active site previously implicated in substrate binding) and to the disruption of two hydrogen-bonding clusters through substitutions at positions 218 and 224. Furthermore, the less negatively charged surface of VIM-7 (compared to VIM-2) may also contribute to the reduced hydrolytic efficiency. Docking of the cephalosporins ceftazidime and cefotaxime into the VIM-2 and VIM-7 structures reveals that amino acid substitutions may cause the mode of substrate binding to differ between the two enzymes. Our structures thus provide new insights into the variation in substrate specificity that is evident across this family of clinically important enzymes.

Molecular epidemiology of metallo-beta-lactamase-producing Pseudomonas aeruginosa isolates from Norway and Sweden shows import of international clones and local clonal expansion

Scandinavia is considered a region with a low prevalence of antimicrobial resistance. However, the number of multidrug-resistant (MDR) Gram-negative bacteria is increasing, including metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa. In this study MBL-producing P. aeruginosa isolates identified in Norway (n = 4) and Sweden (n = 9) from 1999 to 2007 were characterized. Two international clonal complexes (CC), CC111 (n = 8) and CC235 (n = 2), previously associated with MBL-producing isolates, were dominant. CC111 isolates (ST111/229; serotype O12; bla(VIM-2)) included clonally related isolates identified in Skåne County, Sweden (n = 6), and two isolates associated with importation from Greece and Denmark. In all CC111 isolates, bla(VIM-2) was located in integron In59.2 or In59 variants. The two CC235 isolates (ST235/ST230; serotype O11; bla(VIM-4)) were imported from Greece and Cyprus, were possibly clonally related, and carried bla(VIM-4) in two different integron structures. Three isolates imported from Ghana (ST233; serotype O6; bla(VIM-2)), Tunisia (ST654; serotype O11; bla(VIM-2)), and Thailand (ST260; serotype O6; bla(IMP-14)) were clonally unrelated. ST233 was part of a new CC (CC233) that included other MBL-producing isolates, while ST654 could also be part of a new CC associated with MBL producers. In the isolates imported from Ghana and Tunisia, bla(VIM-2) was part of unusual integron structures lacking the 3' conserved segment and associated with transposons. The bla(VIM) gene was found to be located on the chromosome in all isolates. Known risk factors for acquisition of MBL were reported for all patients except one. The findings suggest that both import of successful international clones and local clonal expansion contribute to the emergence of MBL-producing P. aeruginosa in Scandinavia.

[Broad-spectrum beta-lactamases in Gram-negative bacteria]

BACKGROUND

beta-lactams are our most valuable and frequently used antibiotics. Resistance towards them, in both Gram-positive and Gram-negative bacteria, challenges their antimicrobial effect. beta-lactamases are the most important resistance mechanism against beta-lactams in Gram-negative bacteria.

MATERIAL AND METHODS

This review is based on literature retrieved through a non-systematic search of Pubmed (with the terms "ESBL", "AmpC", and "carbapenemases"), as well as the authors' own research experience.

RESULTS AND INTERPRETATION

We now observe a global dissemination of particularly broad spectrum beta-lactamases; extended-spectrum beta-lactamases (ESBLs), plasmid-mediated AmpC, and carbapenemases. These beta-lactamases are hosted by multidrug-resistant clones of Enterobacteriaceae, Pseudomonas aeruginosa with few, if any, therapeutic alternatives. We have observed that this pandemic has reached Norway with an increase in ESBL-producing Escherichia coli in particular, but also pan-resistant carbapenemase-producing K. pneumoniae, P. aeruginosa OG A. baumannii during the last years. The latter ones have been associated with import after hospitalization abroad, but this situation may change due to the epidemic potential of these resistant clones. Rapid diagnostic service and targeted infection control measures are important to prevent them from spreading.

(+)-agelasine D: improved synthesis and evaluation of antibacterial and cytotoxic activities

An improved synthesis of (+)-agelasine D (10) from (+)-manool is reported together with cytotoxic and antibacterial data for agelasine D and structurally close synthetic analogues. These compounds display a broad spectrum of antibacterial activities including effects on M. tuberculosis and Gram-positive and Gram-negative bacteria (both aerobes and anaerobes). They exhibit profound cytotoxic activity against several cancer cells, including a multidrug-resistant cell line. (+)-Agelasine D (10) has been isolated earlier from a marine sponge (Agelas sp.).

Staphylococcus aureus small colony variants are resistant to the antimicrobial peptide lactoferricin B

OBJECTIVES

To determine whether Staphylococcus aureus small colony variants (SCVs) are resistant to the antimicrobial peptide lactoferricin B. To assess if deficiency in transmembrane potential, a common characteristic of SCVs that are haemin- or menadione-auxotrophs, affects the uptake of the peptide into the bacterial cytoplasm.

METHODS

A broth microdilution technique was used for susceptibility testing to determine the MIC of lactoferricin B for SCVs with three different auxotrophisms (haemin, menadione or thymidine) and their isogenic parent strains. Both clinical isolates and genetically defined mutants were used. The internalization of lactoferricin B in a hemB mutant and the respective parent strain was studied using transmission electron microscopy and immunogold labelling.

RESULTS

All SCVs showed reduced susceptibility to lactoferricin B irrespective of their auxotrophy compared with their isogenic parent strains. The MIC for all SCVs was >256 mg/L, whereas the MICs for the parent strains ranged from 16-256 mg/L. Surprisingly, the hemB mutant contained significantly more lactoferricin B intracellularly than the respective parent strain.

CONCLUSIONS

The resistance mechanism of SCVs towards the antimicrobial peptide lactoferricin B is presumably caused by the metabolic changes present in SCVs rather than by a changed transmembrane potential of SCVs or reduced uptake of the peptide.

Induced resistance to the antimicrobial peptide lactoferricin B inStaphylococcus aureus

This study was designed to investigate inducible intrinsic resistance against lactoferricin B in Staphylococcus aureus. Serial passage of seven S. aureus strains in medium with increasing concentrations of peptide resulted in an induced resistance at various levels in all strains. The induced resistance was unstable and decreased relatively rapidly during passages in peptide free medium but the minimum inhibitory concentration remained elevated after thirty passages. Cross-resistance to penicillin G and low-level cross-resistance to the antimicrobial peptides indolicidin and Ala(8,13,18)-magainin-II amide [corrected] was observed. No cross-resistance was observed to the human cathelicidin LL-37. In conclusion, this study shows that S. aureus has intrinsic resistance mechanisms against antimicrobial peptides that can be induced upon exposure, and that this may confer low-level cross-resistance to other antimicrobial peptides.