Carbapenemase-producing Enterobacterales (CPE) can colonize the gut and are of major clinical concern. Identification of CPE colonization is problematic; there is no gold-standard detection method, ...and the effects of antibiotic exposure and microbiota dysbiosis on detection are unknown.
Based on a national survey we selected four CPE screening assays in common use. We used a clinically reflective in vitro model of human gut microbiota to investigate the performance of each test to detect three different CPE strains under different, clinically relevant antibiotic exposures.
Twelve gut models were seeded with a pooled faecal slurry and exposed to CPE either before, after, concomitant with, or in the absence of piperacillin-tazobactam (358 mg/L, 3 × daily, seven days). Total Enterobacterales and CPE populations were enumerated daily. Regular screening for CPE was performed using Cepheid Xpert® Carba-R molecular test, and with Brilliance™ CRE, Colorex™ mSuperCARBA and CHROMID® CARBA SMART agars.
Detection of CPE when the microbiota are intact is problematic. Antibiotic exposure disrupts microbiota populations and allows CPE proliferation, increasing detection. The performances of assays varied, particularly with respect to different CPE strains. The Cepheid assay performed better than the three agar methods for detecting a low level of CPE within an intact microbiota, although performance of all screening methods was comparable when CPE populations increased in a disrupted microbiota.
CPE strains differed in their dynamics of colonization in an in vitro gut model and in their subsequent response to antibiotic exposure. This affected detection by molecular and screening methods, which has implications for the sensitivity of CPE screening in healthcare settings.
Extra-intestinal pathogenic
Escherichia coli
are a significant cause of urinary tract infection and bacteraemia within the UK. We sought to identify the serogroups of 658
E. coli
isolates collected ...in the UK between January 2011 and March 2012, to better understand the ExPEC population and understand the relevance of serogroups in this pathotype. Isolates were typed and serogroup identified using established phenotypic and molecular methods. Sixty-two serogroups were identified; 54 among urinary isolates and 35 among bloodstream isolates. However, serogroups O25, O6, and O2 dominated both infection types. These serogroups were linked to the major ExPEC STs as follows: ST131-O25, ST73-O6, ST127-O6, and ST95-O2. The serogroup data from this study have increased our understanding of the ExPEC population in the UK, but also highlighted key ST–serogroup relationships within the major ExPEC clones. These data can be used to guide vaccine design and in the development of laboratory diagnostic tests targeting the ExPEC population.
The multidrug-resistant ST131-O25b clone of Escherichia coli is well established as a significant cause of extra-intestinal infections worldwide. However, there have been only two small regional ...studies comparing ST131 isolates from the UK. Therefore, we characterized 143 ST131 E. coli (38 urinary, 105 bloodstream) collected between January 2011 and March 2012 from 38 centres located across the UK and Republic of Ireland. Phenotypic and genotypic characterization of clonal isolates revealed high rates of resistance to amoxicillin-clavulanate (56 %), cefotaxime (32 %), ciprofloxacin (79 %), temocillin (69 %, bloodstream isolates only), gentamicin (67 %) and trimethoprim-sulfamethoxazole (59 %). The most frequently detected extended-spectrum beta-lactamase was CTX-M-15 (87 %), predominantly encoded on IncF plasmids, although it was also associated with IncU plasmids in two isolates. The majority of UK ST131 clonal isolates possessed the O25b antigen (97 %) and the H30 fimH allele (92 %), but three serogroups (O19a, O136 and O153) novel to ST131 were identified among our strains. Contrary to previous reports, UK ST131-O16 isolates were typically susceptible to ciprofloxacin and lacked beta-lactamase genes (n = 12/12). In summary, ST131 strains of E. coli circulating in the UK possess characteristic clonal features, but are becoming more diverse than other international ST131 populations.
Objectives: During 2003, the Health Protection Agency's Antibiotic Resistance Monitoring and Reference Laboratory began to receive isolates of Escherichia coli for confirmation of extended-spectrum ...β-lactamase production with a phenotype implying a CTX-M-type β-lactamase, i.e. MICs of cefotaxime ≥8-fold higher than MICs of ceftazidime. Many were referred as being from community patients. We examined 291 CTX-M-producing isolates from the UK and investigated the genetic basis of their phenotype. Methods: PCR was used to detect alleles encoding CTX-M enzymes and to assign these to their blaCTX-M phylogenetic groups. Selected alleles were sequenced. Producers were compared by analysis of banding patterns generated by pulsed-field gel electrophoresis of XbaI-digested genomic DNA. MICs were determined by an agar dilution method or by Etest. Results: Of 291 CTX-M-producing E. coli isolates studied from 42 UK centres, 70 (24%) were reportedly from community patients, many of whom had only limited recent hospital contact. Community isolates were referred by 12 centres. Two hundred and seventy-nine (95.9%) producers contained genes encoding group 1 CTX-M enzymes and 12 contained blaCTX-M-9-like alleles. An epidemic CTX-M-15-producing strain was identified, with 110 community and inpatient isolates referred from six centres. Representatives of four other major strains also produced CTX-M-15, as did several sporadic isolates examined. Most producers were multi-resistant to fluoroquinolones, trimethoprim, tetracycline and aminoglycosides as well as to non-carbapenem β-lactams. Conclusions: CTX-M-producing E. coli are a rapidly developing problem in the UK, with CTX-M-15 particularly common. The diversity of producers and geographical scatter of referring laboratories indicates wide dissemination of blaCTX-M genes. Because of the public health implications, including for the treatment of community-acquired urinary tract infections, the spread of these strains—and CTX-M-15 β-lactamase in particular—merits close monitoring.
A density functional theory (DFT) and atoms-in-molecules (AIM) analysis has been applied to the intramolecular hydrogen bonding in the enol conformers of malonaldehyde and its fluoro-, chloro-, ...cyano-, and nitro-substituted derivatives. With the B3LYP/6-311++G(2d,p) method, good agreement between the DFT geometries and published experimental structures has been found. The donor−acceptor distance was also varied in a series of constrained optimizations in order to determine if energetic, structural, and topological trends associated with intermolecular hydrogen bonding remain valid in the intramolecular case. At very short donor−acceptor distances (<2.24 Å), the hydrogen is symmetrically located between donor and acceptor; at distances longer than this, the hydrogen bonding is no longer symmetric. The AIM methodology has been applied to explore the topology of the electron density in the intramolecular hydrogen bonds of the chosen model systems. Most AIM properties for intramolecular hydrogen bond distances longer than 2.24 Å show smooth trends, consistent with intermolecular hydrogen bonds. Integrated AIM properties have also been used to explore the phenomenon of resonance-assisted hydrogen bonding (RAHB). It is shown that as the donor−acceptor distance is varied, π-electron density is redistributed among the carbon atoms in the intramolecular hydrogen bond ring; however, contrary to prior studies, the integrated atomic charges on the donor−acceptor atoms were found to be insensitive to variation of hydrogen-bonding distance.
Background TR-700 is the active moiety of TR-701 (DA-7157), a new oral/intravenous oxazolidinone prodrug. We examined its activity against linezolid-susceptible and -resistant staphylococci and ...enterococci. Methods MICs were determined by the CLSI agar dilution method. Results MICs of TR-700 were tightly clustered around 0.5 mg/L for linezolid-susceptible staphylococci and enterococci compared with 2 mg/L for linezolid. MICs for 52 linezolid-resistant isolates were raised, but only exceeded 4 mg/L for two Enterococcus faecium isolates homozygous for the G2576T 23S rRNA mutation and for one with an unknown mechanism of linezolid resistance. Conclusions TR-700 is 4- to 16-fold more active than linezolid and overcame most linezolid resistance in vitro.
Objectives We investigated the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii from a Taiwanese hospital and determined the mechanisms responsible for resistance. Methods ...Ninety-two consecutive meropenem-resistant A. baumannii isolates collected between January 2005 and June 2007 were screened for genes encoding OXA carbapenemases, metallo-β-lactamases and for the carO gene encoding an outer membrane protein. PFGE was used to define clonal relatedness. PCR mapping was used to examine the linkage of insertion sequences and blaOXA genes. Southern hybridization of plasmid extracts and I-CeuI-restricted chromosomal DNA was used to locate blaOXA-24-like genes. Sequences of selected blaOXA-24-like and carO genes were determined and loss of CarO expression was confirmed by SDS–PAGE. Results Most (70/92, 76%) isolates belonged to one of three PFGE pulsotypes, indicating clonal spread. Fifty-nine isolates, including the majority of those of pulsotypes I and III, produced OXA-72 carbapenemase. The blaOXA-72 gene was located on a 54 kb plasmid in selected isolates. Thirty-three (36%) isolates, including all 16 of pulsotype II, had ISAba1 preceding the blaOXA-51-like gene, promoting its expression. In addition to OXA-72 carbapenemase, two pulsotype I and three pulsotype III isolates did not produce CarO protein as the carO gene was disrupted by insertion of an ISAba1 element. Two isolates of a minor pulsotype had a blaOXA-58-like gene and a single PFGE-unique isolate had a blaOXA-23-like gene. Conclusions Although diverse mechanisms were identified, production of OXA-72 carbapenemase was the most common mechanism of carbapenem resistance in A. baumannii from this Taiwanese hospital. The plasmidic location of the gene had facilitated its spread to multiple strains.
The antimicrobial treatment of
Stenotrophomonas maltophilia
infections is complicated by intrinsic multidrug resistance and a lack of reliable susceptibility data. We assessed the activity of ...colistin (COL), rifampicin (RIF) and tigecycline (TGC) alone and in combination using a range of in vitro susceptibility testing methodologies and a simple invertebrate model of
S. maltophilia
infection (
Galleria mellonella
). Synergy fractional inhibitory concentration indices (FICIs) ≤0.5 between COL and either RIF or TGC was observed against 92 % and 88 % of 25
S. maltophilia
isolates, respectively, despite resistance to one or another of the single agents alone. In time–kill assays, COL combined with either RIF or TGC was superior to single agents, but only the COL/RIF regimen was reliably bactericidal. The in vitro findings correlated with treatment outcomes in
G. mellonella
, with heightened survival observed for larvae treated with COL/RIF or COL/TGC compared with COL, RIF or TGC alone. COL combined with RIF was the most effective combination overall in both in vitro and in vivo (
p
< 0.05) assays. Given the difficulty in selecting appropriate therapy for
S. maltophilia
infections, regimens consisting of COL combined with RIF or TGC could be considered for clinical use.
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