In vitro evaluation of double-carbapenem combinations against OXA-48-producing Klebsiella pneumoniae isolates using time-kill studies.

Purpose. The aim of this study was to evaluate the in vitro activity of double-carbapenem combinations against OXA-48-producing Klebsiella pneumoniae clinical isolates.Methodology. Double combinations of ertapenem, meropenem and imipenem were evaluated for synergy and bactericidal activity using the time-kill methodology. All antibiotics were tested at 10 mg l-1 and at a sub-inhibitory concentration of 0.5× minimum inhibitory concentration (MIC) for isolates with a carbapenem MIC≤8 mg l-1. Synergy was defined as a ≥2log10 colony-forming units (c.f.u.) ml-1 decrease of viable colonies at 24 h compared to the most active carbapenem alone.Results. Ten distinct K. pneumoniae clinical isolates were tested. All carried bla OXA-48 and bla CTX-M-15, and exhibited an MIC range of 64-128, 4-32 and 1-32 mg l-1 for ertapenem, meropenem and imipenem, respectively. Out of 48 isolate-combinations, synergy was observed in 9 (18.8 %) and cidal activity was observed in 13 (27.1 %). In vitro synergistic activity was noted for 5 out of 29 (17.2 %) ertapenem-, 6 out of 29 (20.7 %) meropenem- and 7 out of 38 (18.4 %) imipenem-containing combinations. No combination exhibited antagonism. Bactericidal activity was observed in 7 (24.1 %) ertapenem-, 8 (27.6 %) meropenem- and 11 (28.9 %) imipenem-containing combinations. Among the sub-inhibitory concentration combinations, three (15 %) ertapenem-, four (20 %) meropenem- and three (15 %) imipenem-containing ones showed synergistic interaction.Conclusion. Dual combinations of carbapenems, including those containing sub-inhibitory concentrations of antibiotics, were synergistic against multidrug-resistant (MDR) and extensively drug-resistant (XDR) K. pneumoniae isolates harbouring bla OXA-48.

Plasmid-mediated quinolone resistance determinants among Gram-negative bacteraemia isolates: a hidden threat.

PURPOSE: The aim of the study was to investigate the prevalence of plasmid-mediated quinolone resistance (PMQR) genes in an unselected collection of bloodstream isolates recovered over an 18-month period in a laboratory affiliated to a university hospital in Athens, Greece, and to assess their impact on the in vitro activity of ciprofloxacin and levofloxacin. METHODS: Eight PMQR genes were screened by PCR and sequencing. All PMQR-positive isolates were submitted to isoelectric focusing for ß-lactamase detection, conjugation or transformation, time-kill assays, mutant prevention concentrationand inoculum effect evaluation. PCR and sequencing of gyrA and parC were performed for detection of chromosomal mutations. RESULTS: Among 96 Gram-negative isolates, 7 (7.3 %) carried one or more PMQR genes. qnrS1 was the most prevalent (5.2 %), followed by aac(6')-Ib-cr (4.2 %) and their combination (2 %). Cloning was successful for three isolates. The presence of a single PMQR determinant without any target modification was not associated with quinolone resistance with one exception, Stenotrophomonasmaltophilia carrying qnrS1, which was resistant to norfloxacin and ciprofloxacin, but in this isolate, additional mechanisms of quinolone resistance cannot be excluded. All PMQR-positive isolates showed a significant inoculum effect. The mutant prevention concentrations of ciprofloxacin against the quinolone-susceptible clinical isolates ranged from 0.38 to 32 mg l-1 and those of levofloxacin from 1 to 32 mg l-1. CONCLUSIONS: PMQRs compromised the bactericidal activity of ciprofloxacin and levofloxacin when expressed in Enterobactercloacae, S. maltophilia or Klebsiellapneumoniae and when more than one co-existed. PMQR determinants represent an unrecognized threat, capable to compromise the in vitro activity of quinolones if expressed in a favourable genetic environment and to favour selection of resistant mutants by widening the mutant selection window of these agents.

Calprotectin as a diagnostic tool for inflammatory bowel diseases.

Inflammatory bowel diseases (IBD) are chronic intestinal disorders caused by a number of factors, including external influences, intestinal microbiota and genetics. The two major clinically defined types of IBD are Crohn's disease and ulcerative colitis, each of which is characterized by relapses in the clinical course, thus patients must be under constant observation via regular endoscopies. As endoscopy, which has been used for direct evaluation and diagnosis of IBD, requires uncomfortable and expensive bowel preparation, a non-invasive test was required to reduce the number of patients undergoing unnecessary endoscopy. Calprotectin is a protein occurring in the cytosol of inflammatory cells and is released by the activation of leukocytes. As it is elevated and stable in the faeces of patients with IBD and can be reliably detected in faecal samples of <5 g, it may serve as an inexpensive, non-invasive diagnostic method for IBD. This is explored in the following review.