Lack of upward creep of glycopeptide MICs for methicillin-resistant Staphylococcus aureus (MRSA) isolated in the UK and Ireland 2001-07.

OBJECTIVES: There have been several reports of upward creep in vancomycin MICs for Staphylococcus aureus [predominantly methicillin-resistant S. aureus (MRSA)] over recent years, but only in single centres or using contemporaneous results. We aimed to test the hypothesis of MIC creep in a multicentre study, testing all the isolates concurrently. METHODS: Nineteen laboratories in the UK and Ireland contributed isolates from blood to the BSAC Bacteraemia Resistance Surveillance Programme every year between 2001 and 2007. MICs for 271 MRSA from these sites were re-measured at a single central laboratory during a single week by the BSAC agar dilution method, but with √2-fold instead of conventional 2-fold dilutions. Re-test results were compared with the original results obtained each year at the same central laboratory. RESULTS: The re-test results were much less variable than the original results and avoided the confounding of experimental variation with year of collection. They demonstrated statistically significant but very slow downward trends in MICs of vancomycin and teicoplanin, at 0.027 and 0.055 doubling dilutions/year, respectively. The original results had suggested more rapid trends in MICs, upward for vancomycin and downward for teicoplanin. The proportion of EMRSA-16 fell from 21% to 9% over the study period, while EMRSA-15 rose from 76% to 85%. CONCLUSIONS: Historical data can give a misleading impression of trends in MIC values because of experimental variation between tests conducted at different times. There was no upward creep in glycopeptide MICs for MRSA in the UK and Ireland between 2001 and 2007.

Harmonisation of in-silico next-generation sequencing based methods for diagnostics and surveillance.

Improvements in cost and speed of next generation sequencing (NGS) have provided a new pathway for delivering disease diagnosis, molecular typing, and detection of antimicrobial resistance (AMR). Numerous published methods and protocols exist, but a lack of harmonisation has hampered meaningful comparisons between results produced by different methods/protocols vital for global genomic diagnostics and surveillance. As an exemplar, this study evaluated the sensitivity and specificity of five well-established in-silico AMR detection software where the genotype results produced from running a panel of 436 Escherichia coli were compared to their AMR phenotypes, with the latter used as gold-standard. The pipelines exploited previously known genotype-phenotype associations. No significant differences in software performance were observed. As a consequence, efforts to harmonise AMR predictions from sequence data should focus on: (1) establishing universal minimum to assess performance thresholds (e.g. a control isolate panel, minimum sensitivity/specificity thresholds); (2) standardising AMR gene identifiers in reference databases and gene nomenclature; (3) producing consistent genotype/phenotype correlations. The study also revealed limitations of in-silico technology on detecting resistance to certain antimicrobials due to lack of specific fine-tuning options in bioinformatics tool or a lack of representation of resistance mechanisms in reference databases. Lastly, we noted user friendliness of tools was also an important consideration. Therefore, our recommendations are timely for widespread standardisation of bioinformatics for genomic diagnostics and surveillance globally.

Distinct bacteriophages encoding Panton-Valentine leukocidin (PVL) among international methicillin-resistant Staphylococcus aureus clones harboring PVL.

Genetically diverse community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) can harbor a bacteriophage encoding Panton-Valentine leukocidin (PVL) lysogenized into its chromosome (prophage). Six PVL phages (ΦPVL, Φ108PVL, ΦSLT, ΦSa2MW, ΦSa2USA, and ΦSa2958) are known, and single-nucleotide polymorphisms (SNPs) in the PVL genes have been reported. We sought to determine the distribution of lysogenized PVL phages among MRSA strains with PVL (PVL-MRSA strains), the PVL gene sequences, and the chromosomal phage insertion sites in 114 isolates comprising nine clones of PVL-MRSA that were selected for maximal underlying genetic diversity. The six PVL phages were identified by PCR; ΦSa2USA was present in the highest number of different lineages (multilocus sequence type clonal complex 1 [CC1], CC5, CC8, and sequence type 93 [ST93]) (n = 37 isolates). Analysis of 92 isolates confirmed that PVL phages inserted into the same chromosomal insertion locus in CC22, -30, and -80 but in a different locus in isolates of CC1, -5, -8, -59, and -88 and ST93 (and CC22 in two isolates). Within the two different loci, specific attachment motifs were found in all cases, although some limited inter- and intralineage sequence variation occurred. Overall, lineage-specific relationships between the PVL phage, the genes that encode the toxin, and the position at which the phage inserts into the host chromosome were identified. These analyses provide important insights into the microepidemiology of PVL-MRSA, will prove a valuable adjunct in outbreak investigation, and may help predict the emergence of new strains.

Clinical and molecular epidemiology of ciprofloxacin-susceptible MRSA encoding PVL in England and Wales.

We aimed to enhance our case ascertainment of meticillin-resistant Staphylococcus aureus encoding Panton-Valentine leucocidin (PVL-MRSA), determine the patient demographic, risk factor and disease associations, and define the clonal diversity amongst isolates referred to the UK Health Protection Agency's Staphylococcus Reference Unit. PVL-MRSA collected during 2005-6 from community-based and hospitalised patients located across England and Wales were identified by polymerase chain reaction (PCR). Representative geographically and temporally unrelated isolates were characterised via toxin gene profiling, SCCmec, spa and agr typing, multilocus sequence typing (MLST) and minimum inhibitory concentration (MIC) determinations. PVL-MRSA were identified from 275 patients. Affected individuals were <1 to 95 years of age (mean 30, median 27 years). Forty-five isolates were from 18 household or community-based clusters and 23 isolates were from outbreaks in healthcare settings. Overall, 58% (n = 161) had skin and soft tissue infections and 9% (n = 25) presented with or developed more serious disease, including eight patients (3%) with necrotising pneumonia, five of whom subsequently died. PVL-MRSA were genetically diverse and harboured SCCmecIV or V(T)/VII. Representatives of MLST clonal complexes (CCs) 8, 30 and 80 were identified the most often. The 275 PVL-MRSA included internationally disseminated community-associated MRSA (CA-MRSA) strains, as well as other minor lineages, and were associated with typical risk factors and disease presentations.

Factors that impact on the burden of Escherichia coli bacteraemia: multivariable regression analysis of 2011-2015 data from West London.

BACKGROUND: The incidence of Escherichia coli bacteraemia in England is increasing amid concern regarding the roles of antimicrobial resistance and nosocomial acquisition on burden of disease. AIM: To determine the relative contributions of hospital-onset E. coli bloodstream infection and specific E. coli antimicrobial resistance patterns to the burden and severity of E. coli bacteraemia in West London. METHODS: Patient and antimicrobial susceptibility data were collected for all cases of E. coli bacteraemia between 2011 and 2015. Multivariable logistic regression was used to determine the association between the category of infection (hospital or community-onset) and length of stay, intensive care unit admission, and 30-day all-cause mortality. FINDINGS: E. coli bacteraemia incidence increased by 76% during the study period, predominantly due to community-onset cases. Resistance to quinolones, third-generation cephalosporins, and aminoglycosides also increased over the study period, occurring in both community- and hospital-onset cases. Hospital-onset and non-susceptibility to either quinolones or third-generation cephalosporins were significant risk factors for prolonged length of stay, as was older age. Rates of mortality were 7% and 12% at 7 and 30 days, respectively. Older age, a higher comorbidity score, and bacteraemia caused by strains resistant to three antibiotic classes were all significant risk factors for mortality at 30 days. CONCLUSION: Multidrug resistance, increased age, and comorbidities were the main drivers of adverse outcome. The rise in E. coli bacteraemia was predominantly driven by community-onset infections, and initiatives to prevent community-onset cases should be a major focus to reduce the quantitative burden of E. coli infection.

Virulence factors in Escherichia coli with CTX-M-15 and other extended-spectrum beta-lactamases in the UK.

OBJECTIVES: Multiresistant Escherichia coli with CTX-M-15 extended-spectrum beta-lactamase (ESBL) are widespread in the UK. We examined their phylogenetic groups and virulence factors. METHODS: Clinical E. coli isolates (n = 114), collected between 2003 and 2006, were phylogenetically grouped and screened by PCR for 33 virulence factor genes. They included representatives of the five major UK epidemic E. coli strains with CTX-M-15 enzyme, as well as non-clonal isolates with CTX-M or other types of ESBLs. RESULTS: All representatives of the epidemic E. coli strains belonged to the virulent extra-intestinal phylogenetic group B2, as did 60% (34/56) of the non-clonal isolates with CTX-M-15-like enzymes and 75% (15/20) of those with non-CTX-M ESBLs. Half of those with CTX-M-9-like enzymes belonged to virulence group D. Within phylogenetic group B2, the prevalence of most virulence factors was comparable among clonal and non-clonal isolates with CTX-M enzymes, and among those with non-CTX-M ESBLs. The most frequent virulence genes were PAI, fimH, fyuA, iutA, kpsMTII, K5, traT, uidA and usp. Among the five epidemic clones, afa/draBC was specific to strain A, whereas P fimbriae were only detected in strain D, and only representatives of the B-C-E group specifically harboured sfaS, kpsMTII and K5. However, afa/draBC was also found in 30% of non-clonal isolates with CTX-M ESBLs, and no virulence gene was unique to the epidemic strains. CONCLUSIONS: Most E. coli with CTX-M ESBLs belonged to virulent phylogenetic groups, mainly B2. The successful epidemic strains did not appear more virulent, but iutA and fyuA were significantly more prevalent among these than in non-clonal isolates also belonging to phylogenetic group B2. The most successful clone with CTX-M-15 enzyme (A) differed from other epidemic clones in harbouring afa/draBC, but this was also found in non-clonal isolates with CTX-M-15 enzyme.

Author Correction: Rapid susceptibility profiling of carbapenem-resistant Klebsiella pneumoniae.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

The emergence of antibiotic resistance by mutation.

The emergence of mutations in nucleic acids is one of the major factors underlying evolution, providing the working material for natural selection. Most bacteria are haploid for the vast majority of their genes and, coupled with typically short generation times, this allows mutations to emerge and accumulate rapidly, and to effect significant phenotypic changes in what is perceived to be real-time. Not least among these phenotypic changes are those associated with antibiotic resistance. Mechanisms of horizontal gene spread among bacterial strains or species are often considered to be the main mediators of antibiotic resistance. However, mutational resistance has been invaluable in studies of bacterial genetics, and also has primary clinical importance in certain bacterial species, such as Mycobacterium tuberculosis and Helicobacter pylori, or when considering resistance to particular antibiotics, especially to synthetic agents such as fluoroquinolones and oxazolidinones. In addition, mutation is essential for the continued evolution of acquired resistance genes and has, e.g., given rise to over 100 variants of the TEM family of beta-lactamases. Hypermutator strains of bacteria, which have mutations in genes affecting DNA repair and replication fidelity, have elevated mutation rates. Mutational resistance emerges de novo more readily in these hypermutable strains, and they also provide a suitable host background for the evolution of acquired resistance genes in vitro. In the clinical setting, hypermutator strains of Pseudomonas aeruginosa have been isolated from the lungs of cystic fibrosis patients, but a more general role for hypermutators in the emergence of clinically relevant antibiotic resistance in a wider variety of bacterial pathogens has not yet been proven.

High diversity of Panton-Valentine leukocidin-positive, methicillin-susceptible isolates of Staphylococcus aureus and implications for the evolution of community-associated methicillin-resistant S. aureus.

In total, 100 Staphylococcus aureus isolates from diverse cases of skin and soft-tissue infection at a university hospital in Saxony, Germany, were characterised using diagnostic microarrays. Virulence factors, including Panton-Valentine leukocidin (PVL), were detected and the isolates were assigned to clonal groups. Thirty isolates were positive for the genes encoding PVL. Only three PVL-positive methicillin-resistant S. aureus (MRSA) isolates were found, two of which belonged to European clone ST80-MRSA IV and one to USA300 strain ST8-MRSA IV. The remaining methicillin-susceptible PVL-positive isolates belonged to a variety of different multilocus sequence types. The predominant strains were agrI/ST22, agrII/CC5, agrIII/CC30 and agrIV/ST121. In order to check for possible bias caused by regional or local outbreak strains, an additional 18 methicillin-susceptible, PVL-positive isolates from the UK were tested. Approximately two-thirds of the UK isolates belonged to types that also comprised approximately two-thirds of the isolates from Saxony. Some methicillin-susceptible PVL-positive isolates (agrI/ST152, agrIII/ST80 and agrIII/ST96) closely resembled known epidemic community-acquired MRSA (CaMRSA) strains. These findings indicate that the current rise in PVL-positive CaMRSA could be caused by the dissemination of novel SCCmec elements among pre-existing PVL-positive strains, rather than by the spread of PVL phages among MRSA strains.

Carriage of extended-spectrum beta-lactamase-producing Enterobacteriaceae in HIV-infected children in Zimbabwe.

BACKGROUND: Antimicrobial resistance is an emerging global health issue. Data on the epidemiology of multidrug-resistant organisms are scarce for Africa, especially in HIV-infected individuals who often have frequent contact with healthcare. We investigated the prevalence of extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) carriage in stool among HIV-infected children attending an HIV outpatient department in Harare, Zimbabwe. METHODS: We recruited children who were stable on antiretroviral therapy (ART) attending a HIV clinic from August 2014 to June 2015. Information was collected on antibiotic use and hospitalization. Stool was tested for ESBL-E through combination disc diffusion. API20E identification and antimicrobial susceptibility was performed on the positive samples followed by whole genome sequencing. RESULTS: Stool was collected from 175/202 (86.6 %) children. Median age was 11 [inter-quartile range (IQR) 9-12] years. Median time on ART was 4.6 years (IQR 2.4-6.4). ESBL-Es were found in 24/175 samples (13.7 %); 50 % of all ESBL-Es were resistant to amoxicillin-clavulanate, 100 % to co-trimoxazole, 45.8 % to chloramphenicol, 91.6 % to ceftriaxone, 20.8 % to gentamicin and 62.5 % to ciprofloxacin. ESBL-Es variously encoded CTX-M, OXA, TEM and SHV enzymes. The odds of ESBL-E carriage were 8.5 times (95 % CI 2.2-32.3) higher in those on ART for less than one year (versus longer) and 8.5 times (95 % CI 1.1-32.3) higher in those recently hospitalized for a chest infection. CONCLUSION: We found a 13.7 % prevalence of ESBL-E carriage in a population where ESBL-E carriage has not been described previously. Antimicrobial resistance (AMR) in Africa merits further study, particularly given the high HIV prevalence and limited diagnostic and therapeutic options available.

Rapid susceptibility profiling of carbapenem-resistant Klebsiella pneumoniae.

The expanding global distribution of multi-resistant Klebsiella pneumoniae demands faster antimicrobial susceptibility testing (AST) to guide antibiotic treatment. Current ASTs rely on time-consuming differentiation of resistance and susceptibility after initial isolation of bacteria from a clinical specimen. Here we describe a flow cytometry workflow to determine carbapenem susceptibility from bacterial cell characteristics in an international K. pneumoniae isolate collection (n = 48), with a range of carbapenemases. Our flow cytometry-assisted susceptibility test (FAST) method combines rapid qualitative susceptible/non-susceptible classification and quantitative MIC measurement in a single process completed shortly after receipt of a primary isolate (54 and 158 minutes respectively). The qualitative FAST results and FAST-derived MIC (MICFAST) correspond closely with broth microdilution MIC (MICBMD, Matthew's correlation coefficient 0.887), align with the international AST standard (ISO 200776-1; 2006) and could be used for rapid determination of antimicrobial susceptibility in a wider range of Gram negative and Gram positive bacteria.

The role of whole genome sequencing in antimicrobial susceptibility testing of bacteria: report from the EUCAST Subcommittee.

Whole genome sequencing (WGS) offers the potential to predict antimicrobial susceptibility from a single assay. The European Committee on Antimicrobial Susceptibility Testing established a subcommittee to review the current development status of WGS for bacterial antimicrobial susceptibility testing (AST). The published evidence for using WGS as a tool to infer antimicrobial susceptibility accurately is currently either poor or non-existent and the evidence / knowledge base requires significant expansion. The primary comparators for assessing genotypic-phenotypic concordance from WGS data should be changed to epidemiological cut-off values in order to improve differentiation of wild-type from non-wild-type isolates (harbouring an acquired resistance). Clinical breakpoints should be a secondary comparator. This assessment will reveal whether genetic predictions could also be used to guide clinical decision making. Internationally agreed principles and quality control (QC) metrics will facilitate early harmonization of analytical approaches and interpretive criteria for WGS-based predictive AST. Only data sets that pass agreed QC metrics should be used in AST predictions. Minimum performance standards should exist and comparative accuracies across different WGS laboratories and processes should be measured. To facilitate comparisons, a single public database of all known resistance loci should be established, regularly updated and strictly curated using minimum standards for the inclusion of resistance loci. For most bacterial species the major limitations to widespread adoption for WGS-based AST in clinical laboratories remain the current high-cost and limited speed of inferring antimicrobial susceptibility from WGS data as well as the dependency on previous culture because analysis directly on specimens remains challenging. For most bacterial species there is currently insufficient evidence to support the use of WGS-inferred AST to guide clinical decision making. WGS-AST should be a funding priority if it is to become a rival to phenotypic AST. This report will be updated as the available evidence increases.

Development of high-level ceftazidime resistance via single-base substitutions of blaCTX-M-3 in hyper-mutable Escherichia coli.

Mutations can increase the ceftazidimase activity of CTX-M-3 beta-lactamase, as seen with its widespread variant CTX-M-15. This study compared the frequencies of emerging ceftazidime resistance in isogenic wild-type and hyper-mutable mutS CTX-M-3-producing Escherichia coli strains, and sequenced the mutant bla(CTX-M) alleles selected. Ceftazidime resistance emerged more readily in the hyper-mutable background than in the wild-type strain. All selected CTX-M mutants, in both the wild-type and the mutS derivatives, had single amino-acid changes at position 167, including a novel Pro167Gln substitution. These data emphasise the potential for further diversification of CTX-M enzymes.

Development of extended-spectrum activity in TEM beta-lactamases in hyper-mutable, mutS Escherichia coli.

TEM-1 and TEM(pUC19)beta-lactamases can gain activity against ceftazidime and other expanded-spectrum cephalosporins via point mutation. The frequency of emergent resistance to ceftazidime at 4 x MIC was elevated >or= 250-fold in hyper-mutable, MutS-deficient Escherichia coli harbouring these beta-lactamase genes on high- or low-copy plasmids. Moreover, although ceftazidime-resistant mutants, or those with reduced susceptibility, were selected in both the wild-type and mutS hosts, many more mutants in the mutS host showed ceftazidimase-type extended-spectrum beta-lactamase (ESBL) activity. This correlated with a G-A point mutation at position 484 in the bla(TEM-1) and bla(TEM-pUC19) genes, conferring the Arg164His amino-acid substitution found in the TEM-29 ESBL. Non-ESBL mutants lacked changes in bla(TEM).

Identification of genetic variation exclusive to specific lineages associated with Staphylococcus aureus bacteraemia.

BACKGROUND: Meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia cases have declined since 2003, and have mostly been due to two epidemic (E) strains, E15 (multi-locus sequence type clonal complex CC22) and E16 (CC30). By contrast, the incidence of meticillin-susceptible S. aureus (MSSA) bacteraemia has remained largely unchanged and our understanding of these isolates has remained poor. AIM: To investigate the distribution and nucleotide sequence of heterogeneous regions between successful lineages using the 2009 British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Resistance Surveillance Programme collection of S. aureus. METHODS: S. aureus isolates (N = 202) comprised of 103 MRSA and 99 MSSA isolates were analysed using fluorescent amplified fragment length polymorphism (FAFLP) to detect nucleotide variations due to lineage-specific sequence motifs as well as differences in the distribution of mobile genetic elements between lineages. FINDINGS: E15 and E16 MRSA strains comprised 79% and 6% of the collection in 2009 respectively. Six lineages, including CC22 and CC30, were associated with MRSA bacteraemia in the UK and Ireland. MSSA isolates were more diverse with 19 different lineages detected. FAFLP revealed lineage-specific sequence variations in loci encoding factors such as proteases or factors involved in haem biosynthesis, both of which may affect the success of major S. aureus lineages. Proteins encoded on certain mobile genetic elements or involved in cobalamin biosynthesis were found to be exclusive to CC8, CC22, or CC30. CONCLUSION: Overall, the genetic diversity among regions of the core genome and mobile genetic elements may alter antimicrobial resistance and the production of virulence or fitness factors that may be linked to strain success.

Failure of acute intravascular volume expansion to alter plasma vasopressin in the nonhuman primate, Macaca fascicularis.

Experiments were carried out in the anesthetized monkey to determine the influence of acute hypervolemia on plasma vasopressin (ADH) concentration. The administration of an isotonic-isooncotic high molecular weight dextran infusion in two steps, each in an amount equal to 15% of the estimated blood volume, produced substantial elevations of left ventricular end diastolic pressure (17.1 cm H2O); however, no consistent change in mean plasma ADH concentration or mean arterial pressure occurred. The results support the position that in the primate, arterial blood pressure rather than blood volume is the major modulator of ADH secretion when blood volume is increased isoosmotically.

Molecular diversity within clonal complex 22 methicillin-resistant Staphylococcus aureus encoding Panton-Valentine leukocidin in England and Wales.

Panton-Valentine leukocidin (PVL)-positive methicillin-resistant Staphylococcus aureus (MRSA) that are multi-locus sequence type clonal complex 22 (CC22) comprise a significant public health problem in the UK. In the present study we sought to determine the genetic diversity, and the respective patient demographics, among 47 PVL-MRSA with a CC22 pulsotype that occurred sporadically or in clusters in community and healthcare settings in eight of nine geographic regions in England and Wales between January 2005 and September 2007. Patient demographics and disease presentations were typical for PVL-S. aureus infections (mostly skin and soft tissue infections in individuals <40 years old); one patient with community-acquired pneumonia died. Although the isolates were closely genotypically related by spa typing and pulsed field gel electrophoresis, at least two variant groups were suggested. PCR detections demonstrated that the majority of the CC22 PVL-MRSA identified (n = 42; 89%) harboured SCCmecIVc, three had SCCmecIVd, one had SCCmecIV but was non-subtypeable, and one isolate harboured SCCmecV. At least three different PVL-encoding phages were detected: ФPVL, Ф108PVL and an unidentified icosahedral phage. Agar dilution MIC determinations showed that the CC22 PVL-MRSA identified were typically resistant to gentamicin and trimethoprim (43 of 47 isolates) and ciprofloxacin resistance was also noted in six isolates. In conclusion, the CC22 PVL-MRSA tested were geographically disseminated but highly genetically related. The observed variances in acquired elements (most notably SCCmec and PVL-encoding phages) suggested that CC22 PVL-MRSA in England and Wales have evolved on multiple occasions.

Panton-Valentine leukocidin-encoding bacteriophage and gene sequence variation in community-associated methicillin-resistant Staphylococcus aureus.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) often produce Panton-Valentine leukocin (PVL), which is encoded by two co-transcribed genes located on lysogenized bacteriophages. Six PVL-encoding temperate phages have been described and single nucleotide polymorphisms (SNPs) in the PVL genes have been reported. In the present study, 22 PVL-positive CA-MRSA isolates were chosen to reflect the diversity of multilocus sequence type (MLST) clonal complexes (CC) identified in our hospital. Isolates were characterized by antimicrobial resistance profile, staphylococcal cassette chromosome mec (SCCmec) and spa type, pulsed-field gel electrophoresis profile and MLST. Primers were designed to sequence the lukSF-PV genes. PVL-encoding phages were characterized using a PCR-based assay. SNPs were identified at seven locations in the lukSF-PV genes, which varied with S. aureus MLST lineage. One SNP was nonsynonymous. All CC80 and some CC1 isolates carried PhiSa2mw; CC8, CC88 and CC154 isolates harboured PVL-encoding elongated head-type phages; and some CC59 isolates harboured a PhiSa2958-like phage. Novel or variant phages were present in CC5 and some CC1 and CC59 isolates. The PVL gene sequence and the PVL-encoding phage varied with lineage. Further work is required to determine whether PVL sequence and/or phage variations result in biological differences.