Maite Ruiz

Reliability of the E-Test Method for Detection of Colistin Resistance in Clinical Isolates of Acinetobacter baumannii

ABSTRACT We compared the E-test to the broth microdilution method for testing the susceptibility of 115 clinical isolates of Acinetobacter baumannii to colistin. Twenty-two (19.1%) strains were resistant to colistin and 93 (80.8%) strains were susceptible according to the reference broth microdilution method. A categorical agreement of 98.2% was found, with only two (1.7%) very major errors. Agreement within 1 twofold dilution between the E-test and the broth microdilution was 16.5%. Complete agreement was found for the strains for which MICs fell within the range of 0.25 to 1 μg of colistin/ml. However, there was poor concordance, particularly in extreme dilutions with higher MICs by the E-test method.

Direct Detection of Rifampin- and Isoniazid-Resistant Mycobacterium tuberculosis in Auramine-Rhodamine-Positive Sputum Specimens by Real-Time PCR

ABSTRACT Our objective was to evaluate the feasibility of a molecular assay based on a real-time PCR technique, carried out with a LightCycler instrument (Roche Biochemicals), to identify Mycobacterium tuberculosis bacilli and to detect rifampin and isoniazid resistance in DNA extracts from sputum samples. We studied three genes: rpoB, which is associated with rifampin resistance, and katG and inhA, which are associated with isoniazid resistance. A total of 205 sputum samples collected from 108 patients diagnosed with pulmonary tuberculosis with positive auramine-rhodamine-staining (AR) sputum samples, were tested. The sensitivities of the LightCycler PCR assay for the positive AR specimens was 97.5% (200 of 205) for rpoB and inhA genes and 96.5% (198 of 205) for the katG gene. For the total number of patients tested, the sensitivity was 100% (108 of 108 patients) for rifampin, whereas the sensitivity was 98.1% (106 of 108 patients) for isoniazid. Full agreement was found with the Bactec MGIT 960 method and the genotype inferred from the LightCycler data for rifampin. The phenotypic method for isoniazid reported 13 resistant strains (≥0.1 μg/ml). In seven (53.8%) strains there was a concordance between both methods, but we found that six (46.2%) strains reported as resistant by the phenotypic method were determined to be susceptible by real-time PCR. For the 75 strains reported as susceptible by the phenotypic method, the concordance with the LightCycler data was 100%. Our results demonstrate that rifampin-resistant M. tuberculosis could be detected in DNA extracted from auramine-rhodamine-positive sputum samples in a single-tube assay that took less than 3 h to perform for a collection of auramine-rhodamine-positive specimens obtained from patients with culture-documented pulmonary tuberculosis. Similarly, this occurs in half of the isoniazid-resistant M. tuberculosis DNA extracted from auramine-rhodamine-positive specimens.

Improved real-time PCR for rapid detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis clinical isolates

In this study we designed two pairs of probes for the detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis with real-time PCR procedures. One pair of probes spans the region between codon 510 and 528 of the rpoB gene, and the other one screens for mutation at the regulatory region of the inhA gene. We have evaluated these probes in combination with two other pairs of probes previously described to detect mutations in 20 susceptible and 53 unique resistant M. tuberculosis clinical isolates. We were able to detect nine different mutations affecting five codons of the rpoB gene, two different mutations at codon 315 of the katG gene and a nucleotide substitution (C209T) in the regulatory region of the inhA gene within two hours turnaround.

Molecular detection and identification of Aspergillus spp. from clinical samples using real-time PCR.

The definite and rapid diagnosis of invasive aspergillosis is necessary because of the high mortality caused. The objective of this study was to evaluate a real‐time PCR assay to detect Aspergillus spp. in clinical samples, based on the Light Cycler technology. Specificity was assessed by using DNA extracted from pathogenic and non‐pathogenic bacteria/fungi from Spanish Collection including: two Aspergillus flavus, four Aspergillus fumigatus, two Aspergillus nidulans, two Aspergillus niger and two Aspergillus terreus isolates. The analytical sensitivity was evaluated with different inocula (101–105 conidia ml−1), and serially diluted DNA of A. fumigatus. To assess clinical applicability, samples from patients at risk were analysed. Species identification was determined by analysing the melting curves. Reactions using genomic DNA from other species of different genera than Aspergillus were negative (specificity: 100%). Analytical sensitivity was 60 fg using DNA and 5–20 conidia using conidial suspensions. The linear range was from 60 to 6 × 107 fg. The Tm ranged from 67.34 to 70.7 °C for the different Aspergillus spp. studied. Nine hundred and forty‐eight consecutive blood samples from 127 patients were processed. In total, 10 (1%) of 948 samples from blood samples were PCR‐positive. The real‐time PCR assay provides a high sensitivity and specificity for detection of fungal DNA and rapidly identifies most of clinically relevant Aspergillus species.

Infectious complications in 159 consecutive kidney transplant recipients

INTRODUCTION The incidence of infections has decreased in kidney transplant (KT) recipients owing to advances in the surgical techniques and clinical management of this population. Nevertheless, these complications continue to occur and the causes seem to be changing, in part because of the prophylactic strategies used. METHOD Prospective, observational study investigating infections occurring during the first 2 years post-transplantation in KT recipients who underwent surgery between July 2003 and December 2005 at Hospital Universitario Virgen del Rocío. Univariate and multivariate regression analysis was performed to determine risk factors associated with the development of infection. RESULTS The incidence of infection was 1.11 episodes per patient over 510+/-234 days. The most common infections were urinary tract infection (UTI) (46.6%), cytomegalovirus (CMV) infection (22.7%), and surgical site infection (8%). The causes were bacterial (50.4%), viral (45.9%), and fungal (3.6%) agents. The most frequent pathogens were CMV (36%), Escherichia coli (28%), extended-spectrum beta-lactamase (ESBL)-producers (26%), and coagulase-negative staphylococci (6.3%). Seventy-nine percent of infection episodes occurred in the 4 months following KT. One recipient died 30 days after the infection episode. In the infection group, patient and graft survival at the end of follow-up was 98% and 89%, respectively. CONCLUSIONS The most frequent syndromes were UTI, CMV infection and surgical site infection. The infections were mainly produced by bacteria, in particular gram-negative rods, and there was a high rate of ESBL E. coli.

In vitro susceptibilities of bloodstream isolates of Candida spp.: results from a multicenter active surveillance program in Andalusia.

OBJECTIVES The aim of this study was to determine the antifungal drug susceptibilities of Candida bloodstream isolates in Andalusia, obtained through a multicenter active laboratory-based surveillance between October 2005 and September 2006. METHODS One hundred and ninety-seven Candida isolates were collected. The MICs of amphotericin B, fluconazole, itraconazole and voriconazole were established using the Sensititre YeastOne panel. The MICs of posaconazole and caspofungin were determined by Etest. RESULTS C. albicans was the most frequently isolated species (49.2%), followed by C. parapsilosis (17.3%), C. tropicalis (15.2%), C. glabrata (13.7%) and C. krusei (3.6%). All strains were inhibited at MICs of </=1 mg/L of amphotericin B and 98.5% of isolates were inhibited at MICs of < or = 1 mg/L of posaconazole. A total of 8 isolates (4.1%) were classified as resistant to fluconazole (MIC > or = 64 mg/L) and 7 (3.6%) were considered resistant to itraconazole (MIC > or = 1 mg/L). All the isolates were susceptible to voriconazole and caspofungin. CONCLUSION In our study C. krusei and C. glabrata were identified in over 18% of cases of candidemia. Most clinical isolates of these species are resistant or susceptible-dose-dependent to fluconazole but susceptible to voriconazole and caspofungin. These agents must be used in the empiric treatment of candidemia rather than fluconazole.

Complicaciones infecciosas en 159 receptores de trasplante renal consecutivos

INTRODUCTION The incidence of infections has decreased in kidney transplant (KT) recipients owing to advances in the surgical techniques and clinical management of this population. Nevertheless, these complications continue to occur and the causes seem to be changing, in part because of the prophylactic strategies used. METHOD Prospective, observational study investigating infections occurring during the first 2 years post-transplantation in KT recipients who underwent surgery between July 2003 and December 2005 at Hospital Universitario Virgen del Rocío. Univariate and multivariate regression analysis was performed to determine risk factors associated with the development of infection. RESULTS The incidence of infection was 1.11 episodes per patient over 510+/-234 days. The most common infections were urinary tract infection (UTI) (46.6%), cytomegalovirus (CMV) infection (22.7%), and surgical site infection (8%). The causes were bacterial (50.4%), viral (45.9%), and fungal (3.6%) agents. The most frequent pathogens were CMV (36%), Escherichia coli (28%), extended-spectrum beta-lactamase (ESBL)-producers (26%), and coagulase-negative staphylococci (6.3%). Seventy-nine percent of infection episodes occurred in the 4 months following KT. One recipient died 30 days after the infection episode. In the infection group, patient and graft survival at the end of follow-up was 98% and 89%, respectively. CONCLUSIONS The most frequent syndromes were UTI, CMV infection and surgical site infection. The infections were mainly produced by bacteria, in particular gram-negative rods, and there was a high rate of ESBL E. coli.

Infectious diseases in 159 consecutive kidney transplant recipients.

INTRODUCTION The incidence of infections has decreased in kidney transplant (KT) recipients owing to advances in the surgical techniques and clinical management of this population. Nevertheless, these complications continue to occur and the causes seem to be changing, in part because of the prophylactic strategies used. METHOD Prospective, observational study investigating infections occurring during the first 2 years post-transplantation in KT recipients who underwent surgery between July 2003 and December 2005 at Hospital Universitario Virgen del Rocío. Univariate and multivariate regression analysis was performed to determine risk factors associated with the development of infection. RESULTS The incidence of infection was 1.11 episodes per patient over 510+/-234 days. The most common infections were urinary tract infection (UTI) (46.6%), cytomegalovirus (CMV) infection (22.7%), and surgical site infection (8%). The causes were bacterial (50.4%), viral (45.9%), and fungal (3.6%) agents. The most frequent pathogens were CMV (36%), Escherichia coli (28%), extended-spectrum beta-lactamase (ESBL)-producers (26%), and coagulase-negative staphylococci (6.3%). Seventy-nine percent of infection episodes occurred in the 4 months following KT. One recipient died 30 days after the infection episode. In the infection group, patient and graft survival at the end of follow-up was 98% and 89%, respectively. CONCLUSIONS The most frequent syndromes were UTI, CMV infection and surgical site infection. The infections were mainly produced by bacteria, in particular gram-negative rods, and there was a high rate of ESBL E. coli.

A prospective survey of Aspergillus spp. in respiratory tract samples: Species identification and susceptibility patterns

We analyzed the species distribution and susceptibility patterns of 433 strains of Aspergillus spp. isolated from respiratory samples of 419 in-patients included in multicenter prospective study (FUNGAE-IFI) between July 2014 and October 2015. Identification was carried out by conventional methods at each participating center and by molecular sequencing of a portion of the β-tubulin gene at one of the centers. In vitro susceptibility was evaluated by broth microdilution methods and using the E-test (for cryptic species). Species identified included 249 A. fumigatus sensu stricto, 60 A. terreus sensu stricto, 47 A. flavus sensu stricto, 44 A. tubingensis, 18 A. niger sensu stricto , five A. nidulans sensu stricto, three A. tamarii, two A. calidoustus, two A. carneus, one A. acuelatus, one A. carbonarius, and one A. sydowii. Cryptic species were found in 12.5% of isolates (n = 54). The frequency of non-wild-type isolates for amphotericin B was 3.4% (n = 15) of the isolates tested and for azoles 3% (n = 10). None of the Aspergillus spp. were non-wild type to echinocandins. Of the 54 cryptic species only two strains were non-wild-type strains by microdilution method (3.7%) (two A. tubingensis, one to amphotericin B and another one to voriconazole) and by E-test method five strains of A. tubingensis showed high minimal inhibitory concentration (MIC) to amphotericin B (11.4%) and five to azoles (12.1%), one A. calidoustus strain showed high MICs for three azoles (50%), A. carneus to itraconazole (100%) and A. sydowii to amphotericin B and itraconazole (100%). These results provide relevant information on susceptibility patterns, frequency, and epidemiology of species involved in respiratory tract samples and of the incidence of recently described cryptic species.

Prevalence and in vitro antifungal susceptibility of cryptic species of the genus Aspergillus isolated in clinical samples

INTRODUCTION The genus Aspergillus contains more than 300 species, which are divided into closely related groups called sections. Molecular studies have revealed numerous cryptic species within different sections of this genus, which have different profiles of antifungal susceptibility and lack diagnostic morphological features. However, there are few studies on the prevalence and in vitro antifungal susceptibility of the cryptic species of this genus. The aim of this study was to investigate the distribution of Aspergillus spp. among clinical samples, and to study their in vitro susceptibility to different antifungal drugs. METHOD Over a period of 2-years (2014-2015), a total of 379 strains of the genus Aspergillus were isolated. Most of the isolates were classified as respiratory colonizations; no cases of invasive aspergillosis were found. The strains were identified by MALDI-TOF mass spectrometry, and susceptibility testing was performed by the EUCAST reference procedure. RESULTS Twenty species belonging to 8 sections were identified, being A. fumigatus the most prevalent (44.1%). The prevalence of cryptic species was 15.3%, with a clear predominance of A. tubingensis. Among the tested antifungal drugs, amphotericin B was the less active in vitro, followed by triazole drugs and echinocandins. The cryptic species had minimun inhibitory concentrations (MICs) higher than the corresponding type species. CONCLUSIONS Accurate identification of the genus Aspergillus at the species level and in vitro antifungal susceptibility testing are necessary because, as it has been shown, some species of this genus may show resistance profiles against available antifungal drugs.