Uncoupling between core genome and virulome in extraintestinal pathogenic Escherichia coli.

Extraintestinal pathogenic Escherichia coli (ExPEC) are among the most frequently isolated bacterial pathogens in hospitals. They are considered opportunistic pathogens and are found mostly in urinary and bloodstream infections. They are genetically diverse, and many studies have sought associations between genotypes or virulence genes and infection site, severity, or outcome, with varied, often contradictory, results. To understand these difficulties, we have analyzed the diversity patterns in the core genomes and virulomes of more than 500 ExPEC isolates from 5 different collections. The core genome was analyzed using a multilocus sequence type-based single-nucleotide polymorphism (SNP) pyrosequencing approach, while the virulence gene content (the virulome) was studied by polymerase chain reaction detection of 25 representative genes. SNP typing showed a similar population structure in the different collections: half of the isolates belong to a few sequence types (5 to 8), while the other half is composed of a large diversity of sequence types that are found once or twice. Sampling analysis by rarefaction plots of SNP profiles showed saturation curves indicative of a limited diversity. Contrary to this, the virulome shows an extremely high diversity, with almost as many gene profiles as isolates, and linear, nonsaturating, rarefaction plots, even within sequence types. These data show that genetic exchange rates are very heterogeneous along the chromosome, being much higher in the virulome fraction of the genome than in the core genome.

Point-of-care system for detection of Mycobacterium tuberculosis and rifampin resistance in sputum samples.

Early detection of Mycobacterium tuberculosis complex (MTBC) and markers conveying drug resistance can have a beneficial impact on preventive public health actions. We describe here a new molecular point-of-care (POC) system, the Genedrive, which is based on simple sample preparation combined with PCR to detect MTBC and simultaneously detect mutation markers in the rpoB gene directly from raw sputum sample. Hybridization probes were used to detect the presence of the key mutations in codons 516, 526, and 531 of the rpoB gene. The sensitivities for MTBC and rpoB detection from sputum samples were assessed using model samples spiked with known numbers of bacteria prepared from liquid cultures of M. tuberculosis. The overall sensitivities were 90.8% (95% confidence interval [CI], 81, 96.5) for MTBC detection and 72.3% (95% CI, 59.8, 82.7) for rpoB detection. For samples containing ≥1,000 CFU/ml, the sensitivities were 100% for MTBC and 85.7% for rpoB detection, while for samples containing ≤100 CFU/ml, the sensitivities were 86.4% and 65.9% for MTBC and rpoB detection, respectively. The specificity was shown to be 100% (95% CI, 83.2, 100) for MTBC and rpoB. The clinical sputum samples were processed using the same protocol and showed good concordance with the data generated from the model. Tuberculosis-infected subjects with smear samples assessed as scanty or negative were detectable by the Genedrive system. In these paucibacillary patients, the performance of the Genedrive system was comparable to that of the GeneXpert assay. The characteristics of the Genedrive platform make it particularly useful for detecting MTBC and rifampin resistance in low-resource settings and for reducing the burden of tuberculosis disease.

Infections caused by OXA-48-producing Klebsiella pneumoniae in a tertiary hospital in Spain in the setting of a prolonged, hospital-wide outbreak.

OBJECTIVES: We describe clinical and microbiological features of infections caused by OXA-48-producing Klebsiella pneumoniae (O48KP) in the setting of a prolonged, hospital-wide outbreak detected in January 2011. METHODS: Clinical, demographic and microbiological data of patients with growth of O48KP in clinical specimens were collected until December 2011. PCR was used to detect carbapenemase and ß-lactamase genes. The genetic relationships were determined by automated repetitive-sequence-based PCR. RESULTS: Seventy-one patients with clinically guided cultures showing growth of O48KP were identified. Nine were considered to be colonizing rather than causing infection. The most frequent source of infection was the urinary tract (22/62), followed by surgical site infections (17/62). Blood cultures were positive in 23/62 patients. Many patients had significant comorbidity and prolonged hospital stays. In-hospital mortality among patients with O48KP infections was 43.5%. The MIC(90)s of ertapenem, imipenem and meropenem were >32, 16 and 16 mg/L, respectively. No single antimicrobial was active against all the isolates. The antibiotics most active against O48KP were amikacin (97.2% susceptible), colistin (90.1%), tigecycline (73%) and fosfomycin (66.2%). Although eight clones were identified, a predominant clone caused 73.2% of the infections. Multilocus sequence typing (MLST) of the predominant clone gave sequence type (ST) 405 and bla(TEM-1), bla(SHV-76), bla(CTX-M-15) and bla(OXA-1) genes and the insertion sequence IS1999 of the Tn1999 transposon were associated with bla(OXA-48) in this clone. CONCLUSIONS: To our knowledge, this is the largest reported series of infections caused by O48KP in the setting of a single-centre outbreak and provides further input on the clinical relevance of infections caused by O48KP and the difficulties associated with its detection and control.

Impact of virulence genes on sepsis severity and survival in Escherichia coli bacteremia.

Extraintestinal pathogenic Escherichia coli (ExPEC) are a frequent cause of bacteremia and sepsis, but the role of ExPEC genetic virulence factors (VFs) in sepsis development and outcome is ill-defined. Prospective study including 120 adult patients with E. coli bacteremia to investigate the impact of bacterial and host factors on sepsis severity and mortality. Patients' clinical and demographic data were registered. Phylogenetic background of E. coli isolates was analyzed by SNP pyrosequencing and VFs by PCR. The E. coli isolates presented an epidemic population structure with 6 dominant clones making up to half of the isolates. VF gene profiles were highly diverse. Multivariate analysis for sepsis severity showed that the presence of cnf and blaTEM genes increased the risk of severe illness by 6.75 (95% confidence interval [CI] 1.79-24.71) and 2.59 (95% CI 1.04-6.43) times respectively, while each point in the Pitt score increased the risk by 1.34 (95% CI 1.02-1.76) times. Multivariate analysis for mortality showed that active chemotherapy (OR 17.87, 95% CI 3.35-95.45), McCabe-Jackson Index (OR for rapidly fatal category 120.15, 95% CI 4.19-3446.23), Pitt index (OR 1.78, 95% CI 1.25-2.56) and presence of fyuA gene (OR 8.05, 95% CI 1.37-47.12) were associated to increased mortality while the presence of P fimbriae genes had a protective role (OR 0.094, 95%IC 0.018-0.494). Bacteremic E. coli had a high diversity of genetic backgrounds and VF gene profiles. Bacterial VFs and host determinants had an impact on disease evolution and mortality.

Use of multiplex PCR in diagnosis of bloodstream infections in kidney patients.

The LightCycler® SeptiFast Test (Roche Diagnostics GmbH, Mannheim, Germany) was prospectively compared with the standard blood culture technique in a series of 86 kidney patients. The sensitivity of the PCR compared with the culture was 71%, and the specificity was 88%. All the species identified by culture in these patients were in the SeptiFast panel. The median time to results was 1 day for the PCR, 3 days for positive cultures, and 5 days for negative cultures.

Outcome of bacteraemia due to extended-spectrum ß-lactamase-producing Escherichia coli: impact of microbiological determinants.

OBJECTIVES: To investigate the impact of virulence factors (VF) and other microbiological determinants on the outcome of patients with invasive infections due to extended-spectrum ß-lactamase-producing Escherichia coli (ESBLEC). METHODS: A prospective multicentre cohort including 191 patients with bacteraemia due to ESBLEC from 13 hospitals in Spain was studied. Phylogroups and 25 genes encoding for putative VF were studied by PCR. Main outcome variable was 30-day mortality; presentation with severe sepsis or septic shock was also assessed. Logistic regression was used to performed multivariate analyses. RESULTS: After controlling for patient comorbidity, source, and empirical antimicrobial therapy, ibeA (OR = 3.41; 95% CI: 0.96-12.10) and amoxicillin-clavulanate resistance (OR = 2.38; 95% CI: 1.07-5.26) were independently associated with increased mortality, while papGII showed a protective effect (OR = 0.18; 95% CI: 0.04-0.87). When these 3 variables were deleted from the multivariate model, the area under the ROC curve decreased only from 0.83 to 0.77. papGII also showed a protective effect for presentation with severe sepsis or septic shock (adjusted OR = 0.34; 95% CI: 0.10-1.14). CONCLUSION: Some pathogen-associated determinants showed a significant although limited impact on outcome in bacteraemic infections due to ESBLEC, and should be further studied as potential therapeutic or preventive targets.

Virulence profiles of bacteremic extended-spectrum ß-lactamase-producing Escherichia coli: association with epidemiological and clinical features.

There is scarce data about the importance of phylogroups and virulence factors (VF) in bloodstream infections (BSI) caused by extended-spectrum ß-lactamase-producing Escherichia coli (ESBLEC). A prospective multicenter Spanish cohort including 191 cases of BSI due to ESBLEC was studied. Phylogroups and 25 VF genes were investigated by PCR. ESBLEC were classified into clusters according to their virulence profiles. The association of phylogropus, VF, and clusters with epidemiological features were studied using multivariate analysis. Overall, 57.6%, 26.7%, and 15.7% of isolates belonged to A/B1, D and B2 phylogroups, respectively. By multivariate analysis (adjusted OR [95% CI]), virulence cluster C2 was independently associated with urinary tract source (5.05 [0.96-25.48]); cluster C4 with sources other than urinary of biliary tract (2.89 [1.05-7.93]), and cluster C5 with BSI in non-predisposed patients (2.80 [0.99-7.93]). Isolates producing CTX-M-9 group ESBLs and from phylogroup D predominated among cluster C2 and C5, while CTX-M-1 group of ESBL and phylogroup B2 predominantes among C4 isolates. These results suggest that host factors and previous antimicrobial use were more important than phylogroup or specific VF in the occurrence of BSI due to ESBLEC. However, some associations between virulence clusters and some specific epidemiological features were found.

Epidemic population structure of extraintestinal pathogenic Escherichia coli determined by single nucleotide polymorphism pyrosequencing.

We have developed an MLST-based scheme for typing Escherichia coli isolates using pyrosequencing of single nucleotide polymorphic positions (SNP). The SNP sequences are converted into allelic patterns and analyzed using the same approach used for MLST analyses. We have tested the method in two unselected collections of clinical isolates of E. coli obtained from blood and urine cultures. The two collections had a similar structure, 25% of the profiles (representing 68% of the isolates) were common to both, and 62% of the profiles (nearly 20% of the isolates) were unique. The four major profiles accounted for 44% of the isolates, and among these the most frequent one was related to the pandemic ST131 clone. The method is easy to implement and might be useful for typing large microbial collections.