Bacteraemia caused by Enterobacteriaceae (EB) producing extended-spectrum β-lactamase (ESBL+) has been associated with higher mortality compared with non-ESBL-producing (ESBL–) EB bacteraemia in observational studies. We conducted a systematic review and meta-analysis of these studies to assess how adjusting for confounding in multivariate analyses affects the pooled estimate, and whether multivariate analyses that include intermediates in the causal pathway of outcome (sepsis severity and inadequate empirical therapy) have lower estimates of attributable mortality.

PubMed search on 23 November 2010 followed by manually searching reference lists of included studies.

Cohort studies published in English with separate mortality rates for ESBL+ and ESBL– EB bacteraemia.

Random-effects pooling of unadjusted and adjusted ORs followed by subgroup analyses to explore effects of adjustment procedures on adjusted ORs.

The pooled OR for the unadjusted mortality associated with ESBL production was 2.35 (95% CI 1.90–2.91, I² = 42%, 32 studies). The pooled adjusted OR was 1.52 (95% CI 1.15–2.01, I² = 32%, 15 studies). Adjustment for more intermediates was associated with decreasing ORs. The pooled OR for the analyses adjusting for inadequate empirical therapy was 1.37 (95% CI 1.04–1.82).

ESBL production in EB bacteraemia is associated with a higher mortality compared with bacteraemia with ESBL– EB, although the estimate of this association is affected by adjustment procedures. Adjustment for inadequate empirical therapy leads to a reduction in ORs, indicating that higher mortality is likely to be mediated through this phenomenon.

To characterize the mechanisms responsible for elevated MICs of ceftaroline for methicillin-resistant Staphylococcus aureus (MRSA).

During the 2008 Assessing Worldwide Antimicrobial Resistance Evaluation (‘AWARE’) surveillance programme, four S. aureus collected from separate patients in Athens, Greece, demonstrated ceftaroline MICs of 4 mg/L. These isolates were clonally related and one strain (13101) was selected for further characterization. Two strains (4981 and 4977) displaying ceftaroline MICs of 1 and 2 mg/L, respectively, were included for comparison. All strains originated from the same hospital. Penicillin-binding protein (PBP) affinities for ceftaroline and comparators were determined. Strains were typed by single-locus typing (i.e. spa typing), multilocus sequence typing (‘MLST’) and by multiple-locus variable-number tandem repeat fingerprinting (MLVF). The presence of Pantone–Valentine leucocidin and the staphylococcal cassette chromosome mec types was assessed. We also performed nucleotide sequencing of the mecA (encoding PBP2a) promoter and ribosomal binding site (rbs) regions and mecR1.

Ceftaroline demonstrated the highest PBP2a affinity with strain 4981 (ST5-MRSA-II) (IC₅₀ 0.06 mg/L; MIC 1 mg/L). Strains 4977 and 13101 (both ST239-MRSA-III) showed indistinguishable MLVF profiles. Ceftaroline PBP2a binding affinity in strains 4977 (IC₅₀ 0.25 mg/L; MIC 2 mg/L) and 13101 (IC₅₀ 1 mg/L; MIC 4 mg/L) was 4- and 16-fold lower than 4981, respectively. Strain 4981 contains a wild-type PBP2a, while strains 4977 and 13101 have N₁₄₆K and E₁₅₀K alterations in the non-penicillin-binding domain. Additionally, 13101 has one substitution (H₃₅₁N) in the transpeptidase domain. Alterations in the mecR1, mecA promoter or rbs regions were not observed.

Increased ceftaroline MICs were associated with decreased PBP2a binding affinity and reflected alterations in PBP2a.

Denmark and several other countries experienced the first epidemic of methicillin-resistant Staphylococcus aureus (MRSA) during the period 1965–75, which was caused by multiresistant isolates of phage complex 83A. In Denmark these MRSA isolates disappeared almost completely, being replaced by other phage types, predominantly only penicillin resistant. We investigated whether isolates of this epidemic were associated with a fitness cost, and we employed a mathematical model to ask whether these fitness costs could have led to the observed reduction in frequency.

Bacteraemia isolates of S. aureus from Denmark have been stored since 1957. We chose 40 S. aureus isolates belonging to phage complex 83A, clonal complex 8 based on spa type, ranging in time of isolation from 1957 to 1980 and with varyous antibiograms, including both methicillin-resistant and -susceptible isolates. The relative fitness of each isolate was determined in a growth competition assay with a reference isolate.

Significant fitness costs of 2%–15% were determined for the MRSA isolates studied. There was a significant negative correlation between number of antibiotic resistances and relative fitness. Multiple regression analysis found significantly independent negative correlations between fitness and the presence of mecA or streptomycin resistance. Mathematical modelling confirmed that fitness costs of the magnitude carried by these isolates could result in the disappearance of MRSA prevalence during a time span similar to that seen in Denmark.

We propose a significant fitness cost of resistance as the main bacteriological explanation for the disappearance of the multiresistant complex 83A MRSA in Denmark following a reduction in antibiotic usage.

Staphylococcus epidermidis is a harmless commensal, but it can become a human pathogen, mainly in the hospital environment. In order to clarify strategies used by these bacteria to adapt to the hospital environment, we compared the population structure and staphylococcal cassette chromosome mec (SCCmec) content of S. epidermidis from the community and hospital.

S. epidermidis were collected from nasal swabs of both healthy military draftees (192 isolates) and patients (94 isolates) recovered in the same time period and geographical region. S. epidermidis were characterized by PFGE, multilocus sequence typing and SCCmec typing.

Clonal complex 5 was predominant in the hospital (100%) and the community (58%), but some clonal types were specific to each environment and others were found in both (C/H clones). The methicillin-resistant S. epidermidis (MRSE) colonization rate in the community was very low (7%) when compared with the hospital (30%; P < 0.05). Community-associated MRSE carried mostly SCCmec IV and V [Simpson's index of diversity (SID) = 57.52%; 95% CI 38.35–76.69], whereas hospital-associated MRSE carried 17 SCCmec structures (SID = 82.67%; 95% CI 77.38–87.96). Isolates of the same PFGE type had a much higher number of different SCCmec types when collected in the hospital than in the community.

Our data suggest that the S. epidermidis population is composed of hospital-associated clonal types, community-associated clonal types and types that are able to survive in both environments. Moreover, adaptation to the hospital environment in S. epidermidis appears to promote an increase in the frequency and diversification of SCCmec.

To determine the context and location of the bla_OXA-23 carbapenem-resistance gene and the structure of the resistance island in the chromosomal comM gene in a representative Australian global clone 2 (GC2) Acinetobacter baumannii isolate.

Long-range PCR was used to link genes and determine the organization of the resistance island. PCR amplicons were sequenced, and bioinformatic analysis identified features. Multilocus sequence typing (MLST) was performed.

The GC2 isolate A91 is sequence type (ST) ST92 (Oxford MLST scheme). It includes a 37 kb genomic resistance island, Tn6167, in the comM gene. At one end, Tn6167 carries Tn60221 interrupted by a novel insertion sequence, ISAba17. The sul2 (sulphonamide resistance) and strA-strB (streptomycin resistance) genes and tet(B) tetracycline resistance determinant are at the other end in the configuration ISAba1-sul2-CR2-tetA(B)-tetR(B)-CR2-strB-strA with part of the tni end of a Tn6022-related transposon preceding them and an orf4 end following them. Transposon Tn2006 carrying bla_OXA-23 was found in an 11 kb region located between Tn60221 and the other resistance genes. The 17.6 kb Tn6166 from the GC2 reference strain A320/RUH134 can be derived from Tn6167 via a single deletion arising adjacent to Tn60221 and causing loss of a large central segment.

The transposons found in comM in the GC2 isolates A91 and A320 differ substantially from AbaR3-type islands, found predominantly in global clone 1 (GC1) isolates, in both resistance gene content and organization. However, the A. baumannii GC1 and GC2 clones have both acquired antibiotic resistance genes via their association with transposons that target comM.

To determine the pattern and antimicrobial resistance genes of cephalosporin resistance in Shigella flexneri and Shigella dysenteriae over 9 years.

Isolates of Shigella (S. flexneri, n = 119 and S. dysenteriae, n = 24) were tested for resistance to ceftriaxone and cefepime by disc diffusion, for MIC by Etest and for extended-spectrum β-lactamase (ESBL) and AmpC production. The presence of antimicrobial resistance genes was investigated by PCR using specific primers for bla_TEM, bla_OXA-1, bla_CTX-M-15, bla_SHV and bla_CMY-2 for all the isolates.

Twenty (16.8%) S. flexneri isolates were resistant/intermediately susceptible to ceftriaxone/cefepime, while all S. dysenteriae were susceptible. In S. flexneri isolates, the MIC₅₀ values of ceftriaxone and cefepime were found to be 0.032 and 0.125 mg/L, respectively, while their MIC₉₀ values were 12 and 8 mg/L, respectively. The MIC₅₀ and MIC₉₀ for S. dysenteriae were below 1 mg/L for ceftriaxone; however, for cefepime the MIC₉₀ was found to be 4 mg/L. Of the 20 resistant/intermediately susceptible S. flexneri isolates, 9 were positive for ESBL production and 4 for AmpC production by phenotypic tests. All 20 isolates were found to be positive for bla_TEM, 10 for bla_CTX-M-15, 8 for bla_OXA and 7 for bla_CMY-2; none was positive for bla_SHV.

We report a high level of cephalosporin resistance with high MICs and ESBL- and AmpC-mediated antibiotic resistance in Shigella from north India.

Ceftaroline + avibactam (NXL104) is a novel inhibitor combination active against Enterobacteriaceae with class A and C β-lactamases. We investigated its risk of mutational resistance.

Single- and multi-step mutants were sought and characterized from Enterobacteriaceae with extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases and KPC β-lactamases.

Overgrowth occurred on agar with low MIC multiples of ceftaroline + avibactam, but frequencies for single-step mutants were <10^–9. Most mutants were unstable, with only three remaining resistant on subculture. For one, from an CTX-M-15-positive Escherichia coli, the ceftaroline + avibactam MIC was raised, but the organism had reduced resistance to ceftaroline and lost resistance to other oxyimino-cephalosporins, with this profile retained when the mutant bla_CTX-M-15 was cloned into E. coli DH5α. Sequencing identified a Lys237Gln substitution in the CTX-M-15 variant. The other two stable single-step mutants were from an AmpC-derepressed Enterobacter cloacae strain; these had unaltered or slightly reduced resistance to other β-lactams. Both had amino acids 213–226 deleted from the loop of AmpC. Further stable mutants were obtained from AmpC-inducible and -derepressed E. cloacae in multi-step selection, and these variously had reduced expression of OmpC and OmpF, and/or Asn366His/Ile substitutions in AmpC.

Stable resistant mutants were difficult to select. Those from AmpC-derepressed E. cloacae had porin loss or AmpC changes, including loop deletions. A Lys237Gln substitution in CTX-M-15 conferred resistance, but largely abolished ESBL activity.

To investigate the occurrence and molecular mechanisms associated with carbapenemases in carbapenem-resistant Gram-negative isolates from Canadian cases.

Twenty hospital sites across Canada submitted isolates for a 1 year period starting 1 September 2009. All Enterobacteriaceae with MICs ≥2 mg/L and Acinetobacter baumannii and Pseudomonas aeruginosa with MICs ≥16 mg/L of carbapenems were submitted to the National Microbiology Laboratory (NML) where carbapenem MICs were confirmed by Etest and isolates were characterized by PCR for carbapenemase genes, antimicrobial susceptibilities, PFGE and plasmid isolation.

A total of 444 isolates (298 P. aeruginosa, 134 Enterobacteriaceae and 12 A. baumannii) were submitted to the NML of which 274 (61.7%; 206 P. aeruginosa, 59 Enterobacteriaceae and 9 A. baumannii) met the inclusion criteria as determined by Etest. Carbapenemase genes were identified in 30 isolates: bla_GES-5 (n = 3; P. aeruginosa), bla_KPC-3 (n = 7; Enterobacteriaceae), bla_NDM-1 (n = 2; Enterobacteriaceae), bla_VIM-2 and bla_VIM-4 (n = 8; P. aeruginosa) bla_SME-2 (n = 1; Enterobacteriaceae) and bla_OXA-23 (n = 9; A. baumannii). PFGE identified a cluster in each of Enterobacteriaceae, P. aeruginosa and A. baumannii corresponding to isolates harbouring carbapenemase genes. Three KPC plasmid patterns (IncN and FllA) were identified where indistinguishable plasmid patterns were identified in unrelated clinical isolates.

Carbapenemases were rare at the time of this study. Dissemination of carbapenemases was due to both dominant clones and common plasmid backbones.

To investigate the occurrence and characteristics of extended-spectrum β-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae isolates in clinical samples of companion animals and horses and compare the results with ESBL/AmpC-producing isolates described in humans.

Between October 2007 and August 2009, 2700 Enterobacteriaceae derived from clinical infections in companion animals and horses were collected. Isolates displaying inhibition zones of ≤25 mm for ceftiofur and/or cefquinome by disc diffusion were included. ESBL/AmpC production was confirmed by combination disc tests. The presence of resistance genes was identified by microarray, PCR and sequencing, Escherichia coli genotypes by multilocus sequence typing and antimicrobial susceptibility by broth microdilution.

Sixty-five isolates from dogs (n = 38), cats (n = 14), horses (n = 12) and a turtle were included. Six Enterobacteriaceae species were observed, mostly derived from urinary tract infections (n = 32). All except 10 isolates tested resistant to cefotaxime and ceftazidime by broth microdilution using clinical breakpoints. ESBL/AmpC genes observed were bla_{CTX-M-1, -2, -9, -14, -15,} bla_TEM-52, bla_CMY-2 and bla_CMY-39. bla_CTX-M-1 was predominant (n = 17). bla_CTX-M-9 occurred in combination with qnrA1 in 3 of the 11 Enterobacter cloacae isolates. Twenty-eight different E. coli sequence types (STs) were found. E. coli carrying bla_CTX-M-1 belonged to 13 STs of which 3 were previously described in Dutch poultry and patients.

This is the first study among a large collection of Dutch companion animals and horses characterizing ESBL/AmpC-producing isolates. A similarity in resistance genes and E. coli STs among these isolates and isolates from Dutch poultry and humans may suggest exchange of resistance between different reservoirs.