Evaluation of resazurin-based rapid test to detect colistin resistance in Acinetobacter baumannii isolates.

Acinetobacter baumannii primarily causes colonization, yet it can be an opportunistic pathogen associated with hospital-acquired infections. Many countries report rapid spread of carbapenem-resistant Acinetobacter baumannii (CRAb) which limits treatment options, with colistin frequently being the last line treatment option. The aim of our study was to evaluate a recently developed rapid method, namely the Rapid ResaPolymyxin test, for detection of colistin resistance (ColR) in Acinetobacter baumannii. This test was used for rapid screening of colistin resistance in a clinical setting where there is endemicity of CRAb isolates. A total of 82 A. baumannii clinical isolates were included in the evaluation. The majority of them were resistant to carbapenems (75/82, 91.5%). A total of 37 isolates (45.1%) were resistant to colistin, all being resistant to carbapenems. None of the ColR isolates carried the plasmid-mediated mcr-1 to -5 genes. The Rapid ResaPolymyxin NP test reached a 95.1% categorical agreement with results of reference broth microdilution method, with 93.3% sensitivity and specificity, and positive and negative predictive values being respectively at 92.3% and 97.7%. The Rapid ResaPolymyxin NP test performed well on our collection of clinical and surveillance CRAb isolates from the Central Slovenia region. The test is inexpensive and easy to integrate into laboratory workflow. The main value of the test is rapid categorization of susceptibility and resistance which has important implications with respect to the treatment strategy as well as the infection control measures.

High prevalence of division II (cfiA positive) isolates among blood stream Bacteroides fragilis in Slovenia as determined by MALDI-TOF MS.

Bacteroides fragilis can be classified into division I (cfiA negative) and division II (cfiA positive) isolates. Division II isolates have a silent chromosomal carbapenemase gene (cfiA) that can become overexpressed by an insertion of a mobile genetic element and thus develop a phenotypic resistance to carbapenems. Aims of our study were (i) to determine the prevalence of B. fragilis division II (cfiA positive) isolates among blood stream and non-blood stream isolates from two major Slovenian tertiary-care hospitals and (ii) to assess its influence on phenotypic resistance to imipenem. Consecutive non-duplicate B. fragilis isolates from blood stream and non-blood stream specimens were included in the analysis from 2015 to 2017 period. Data from laboratory information system were matched with mass spectra obtained with Microflex LT instrument and MALDI Biotyper 3.1 software (Bruker Daltonik, Bremen, Germany). All mass spectra were reanalyzed using Bruker taxonomy library. Spectra with a log(score) > 2.0 were further analyzed with cfiA library that separates B. fragilis division I and II isolates based on a log(score) value difference of >0.3. Minimal inhibitory concentrations (MICs) for imipenem were determined with Etest (bioMérieux, Marcy l'Étoile, France), using supplemented Brucella agar and EUCAST breakpoints (S ≤ 2 mg/L, R > 8 mg/L). Altogether 623 consecutive B. fragilis isolates were included in the analysis; 47 (7.5%) were isolated from blood stream and 576 (92.5%) from non-blood stream specimens. Among all study isolates, 51 (8.2%) proved to belong to division II (cfiA positive). The proportions of division II isolates among blood stream and non-blood stream isolates were 14.9% and 7.6%, respectively (p = 0.081, ns). In total, 1.3% (n = 8) were non-susceptible to imipenem (MIC >2 mg/L); 4.3% (n = 2) among blood stream and 1% (n = 6) among non-blood stream isolates. All imipenem resistant isolates belonged to division II. Modal MICs (MIC range) were 0.064 mg/L (0.016 mg/L-2 mg/L) and 0.125 mg/L (0.064 mg/L-≥32 mg/L) for division I and II isolates, respectively.

Should we consider faecal colonisation with extended-spectrum ß-lactamase-producing Enterobacteriaceae in empirical therapy of community-onset sepsis?

In patients colonised with extended-spectrum ß-lactamase-producing Enterobacteriaceae (ESBL-E), the preference for carbapenems (CRBs) over non-CRB antibiotics for empirical therapy of sepsis is questionable from an ecologic perspective. Moreover, how well colonisation predicts an ESBL-E aetiology of infection has been poorly investigated. The purpose of this retrospective observational study was to determine the positive predictive value (PPV) of ESBL-E faecal colonisation for ESBL-E sepsis aetiology and the impact of empirical therapy on treatment outcome. The study included 653 ESBL-E carriers with community-onset sepsis hospitalised at a single medical centre during a 5-year period. The PPV of ESBL-E colonisation for ESBL-E sepsis aetiology was significantly higher (62.6%) when sepsis originated from a urinary tract infection (UTI) than from a respiratory tract infection (24.5%), other known origins (27.1%) or an unidentified origin (21.4%). Among the 653 patients, 177 (27.1%) received CRBs empirically and 476 received non-CRBs, predominantly ß-lactam/ß-lactamase inhibitor combinations. Although univariate analysis suggested a higher 30-day mortality in the non-CRB versus CRB group (26.7% vs. 19.2%; OR = 1.53; P = 0.049), the estimated association was much smaller and was not significant (OR = 1.11, 95% CI 0.66-1.87; P = 0.68) in the multiple regression analysis adjusted for age, sex, Charlson comorbidity index, and severity, origin or aetiology of sepsis. The subgroup of 240 patients with unidentified sepsis aetiology also did not benefit from empirical CRB treatment. In non-critically ill ESBL-E carriers with community-onset sepsis, CRB-sparing empirical therapy seems appropriate, particularly if sepsis originates from a site other than a UTI.