Athanassios Tsakris

Harokopion University of Athens, Athínai, Attica, Greece

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Publications (166)629.95 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: Previous studies have reported very different rates of human rhinovirus (HRV) and respiratory syncytial virus (RSV) genome detection in nasal and sputum samples, but not in bronchoalveolar lavage (BAL) and bronchial biopsy samples. Our study aimed to investigate the presence of HRV and RSV in the lungs of 31 consecutive patients with stable COPD (11 GOLD stage I, 11 II, and 9 III) and 22 control subjects (12 current or past smokers, and 10 non-smokers), who underwent diagnostic (e.g., lung cancer) and/or therapeutic (e.g., hemoptysis) fibreoptic bronchoscopy in a university hospital in Athens, Greece. Viral RNA of HRV and RSV were not detected in any of the samples of COPD patients or control subjects after being processed with real-time PCR.
    Preview · Article · Dec 2016 · Respiratory research
  • [Show abstract] [Hide abstract] ABSTRACT: • Tigecycline still remains relatively active among Enterobacteriaceae.
    No preview · Article · May 2016
  • [Show abstract] [Hide abstract] ABSTRACT: OXA-48-like carbapenemases have only recently emerged in Europe. OXA-162 is a rare OXA-48 variant usually co-expressed with extended-spectrum β-lactamases. We aim to report the identification of the first OXA-162 carbapenemase-producing Klebsiella pneumoniae isolates which co-expressed an AmpC cephalosporinase (DHA-1) retrieved from a patient in Greece. They belonged to a single sequence type (ST11) and caused the first documented community-onset urinary tract infections attributable to an OXA-48 like-producing Enterobacteriaceae strain.
    No preview · Article · Dec 2015 · Antimicrobial Agents and Chemotherapy
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    [Show abstract] [Hide abstract] ABSTRACT: Acinetobacter baumannii is a pathogen of increasing concern, commonly causing outbreaks in the hospital environment. Of particular concern, A. baumannii strains exhibiting resistance to carbapenems, which were previously considered the treatment of choice for infected patients, have dramatically increased worldwide, leaving a few antibacterial choices. Tigecycline, a broad-spectrum modified minocycline derivative, isconsidered as a last resort drug against multidrug-resistant A. baumannii. Though, resistance to tigecycline has emerged and is growing notably following increasing tigecycline usage. Comparative evaluation of the tigecycline resistance rates reported worldwide is challenging due to the absence of official interpretative criteria for in vitro susceptibility testing and the discrepancies among the different susceptibility methodologies used, with broth microdilution being considered the reference method. Tigecycline resistance is mainly associated with resistance-nodulation-cell division (RND)-type transporters, mainly the AdeABC, AdeFGH and AdeIJK efflux pumps, but other resistance mechanisms have also been implicated. Tigecycline is still an attractive choice for A. baumannii , but further investigations are warranted so that treatment of MDR Α. baumannii could be guided by validated in vitro data.
    Full-text · Article · Nov 2015 · Advances in Experimental Medicine and Biology
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    [Show abstract] [Hide abstract] ABSTRACT: Background: The overuse of antimicrobials is one of the main factors responsible for the development and spread of antimicrobial resistance, together with other causes, such as intra- and inter-hospital spread of resistant microorganisms and infection control policies and practices. The objective of the present study is to report the trends of Klebsiella pneumoniae and Acinetobacter baumannii antimicrobial resistance indicators in an Italian intensive care unit (ICU) during a six-year period, from 2008 to 2013. Methods: Susceptibility data and annual antibiotic consumptions in the ICU were retrospectively obtained from the clinical laboratory and the pharmacy. Trends over time of resistance rates (RRs) and of incidence densities of resistant isolates were determined by linear regression. Results: Isolation density of A. baumannii increased significantly from 2008 (20.4 per 1,000 patient-days) to 2013 (58.1 per 1,000 patient-days) and of K. pneumoniae from 2010 (22.3 per 1,000 patient-days) to 2013 (55.9 per 1,000 patient-days). RRs of third-generation cephalosporins (3GCs)-resistant K. pneumoniae (from 2010: 41.9 %, to 2012: 87.0 %), of carbapenem-resistant K. pneumoniae (from 2008: 0 %, to 2013: 59.2 %), and of carbapenem-resistant A. baumannii (from 2008: 87.5 %, to 2013: 96.6 %) showed significant increasing trends. Carbapenems was the main antibiotic class consumed (24.9 % of the total antimicrobial usage density), followed by 3GCs (21.0 %), fluoroquinolones (20.6 %), aminoglycosides (17.3 %), penicillins (15.1 %) and glycopeptides (1.1 %). Carbapenems consumption decreased from 2008 to 2012 and then increased in 2013. Glycopeptides consumption decreased from 2008 to 2011 and then increased in 2013. Aminoglycosides consumption decreased from 2008 to 2010 and increased from 2012 to 2013. Finally, 3GC, penicillins and fluoroquinolones consumptions decreased from 2012 to 2013. Conclusions: RRs of carbapenem-resistant A. baumannii and of carbapenem- and 3GC-resistant K. pneumoniae were higher than those for Europe. Our findings highlight the necessity to implement an integrated system for monitoring not only consumption of antibiotics and resistance profiles but also the clonality of alert microorganisms in the ICU for effective infection control.
    Full-text · Article · Nov 2015
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    [Show abstract] [Hide abstract] ABSTRACT: The identification of immunodominant B-cell epitopes within surface pneumococcal virulence proteins (PnVPs) in paediatric patients with invasive pneumococcal disease (IPD) is a valuable approach to define novel vaccine candidates. To this aim, we evaluated sera from children with IPD and age-matched controls against 141 twenty-mer synthetic peptides covering the entire sequence of major antigenic fragments within PnVPs, namely the choline-binding protein D (CbpD), the pneumococcal histidine-triad proteins (PhtD, PhtE), the pneumococcal surface protein A (PspA), the plasminogen and fibronectin binding protein B (PfbB) and the zinc metalloproteinase B (ZmpB). Ten immunodominant B-cell epitopes were identified: CbpD-pep4 [aa291-310], PhtD-pep11 [aa88-107], PhtD-pep17 [aa172-191], PhtD-pep19 [aa200-219], PhtE-pep32 [aa300-319], PhtE-pep40 [aa79-98], PfbB-pep76 [aa180-199], PfbB-pep79 [aa222-241], PfbB-pep90 [aa484-503] and ZmpB-pep125 [aa431-450]. All epitopes were highly conserved among different pneumococcal serotypes and 4 of them were located within the functional zinc-binding domain of histidine triad proteins phtD and PhtE. Peptides CbpD-pep4, PhtD-pep19 and PhtE-pep40 were broadly recognized by IPD patients` sera with prevalence 96.4%, 92.9% and 71.4% respectively, while control sera exhibited only minor reactivities(<10.7%). Their specificity for IPD was 93.3%, 95% and 96.7%, their sensitivity was 96.4%, 92.9% and 71.4% and their positivity likelihood ratio for IPD was 14.5, 18.6 and 21.4 respectively. Furthermore, purified antibodies against CbpD-pep4, PhtD-pep19 and PhtE-pep40 readily bound on the surface of different pneumococcal serotypes, as assessed by FACS and immunofluorescence analysis. The identified immunodominant B-cell epitopes provide a better understanding of immune response in IPD and are worth evaluation in additional studies as potential vaccine candidates.
    Full-text · Article · Sep 2015 · Journal of Biological Chemistry
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    [Show abstract] [Hide abstract] ABSTRACT: The mec and bla systems, among other genetic factors, are critical in regulating the expression of methicillin resistance in Staphylococcus aureus. We examined by WGS a naturally occurring oxacillin-susceptible mecA-positive S. aureus isolate to identify the mechanism conferring oxacillin susceptibility. The mecA-positive oxacillin-susceptible S. aureus isolate GR2 (penicillin and oxacillin MICs 0.094 and 1 mg/L, respectively), belonging to clonal complex 80, was characterized. DNA fragment libraries were sequenced on Roche 454 and Illumina MiSeq sequencers and de novo assembly of the genome was generated using SeqMan NGen software. Plasmid curing was conducted by SDS treatment. Expression of mecA was quantified without/with β-lactam pressure. The genome of GR2 consisted of a 2 792 802 bp chromosome and plasmids pGR2A (28 895 bp) and pGR2B (2473 bp). GR2 carried SCCmec type IV, with a truncated/non-functional mecR1 gene and no mecI. A single copy of the bla system, with an organization unique for S. aureus, was found, harboured by plasmid pGR2A. Particularly, the blaZ gene was orientated like its regulatory genes, blaI and blaR1, and a gene encoding transposase IS66 was integrated between blaZ and the regulatory genes deleting the 5'-end of blaR1; blaI, encoding blaZ/mecA repressor, was intact. After plasmid loss, GR2 became penicillin and oxacillin resistant (MICs 0.5 and 6 mg/L, respectively). We can conclude that after exposure to β-lactams, the non-functional BlaR1 does not cleave the mecA repressor BlaI, derepression does not occur and mecA is not efficiently expressed. Removal of the bla system after curing of pGR2A allows constitutive expression of mecA, resulting in oxacillin and penicillin resistance. © The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail:
    Full-text · Article · Jul 2015 · Journal of Antimicrobial Chemotherapy
  • [Show abstract] [Hide abstract] ABSTRACT: As MRSA are considered Staphylococcus aureus isolates with oxacillin minimum inhibitory concentration (MIC) of ≥4 mg/L or harboring the mecA gene. However, the presence of mecA does not necessarily lead to oxacillin resistance and mecA gene-carrying isolates may have oxacillin MIC within the susceptible range (≤2 mg/L). During the last few years it has become apparent that oxacillin-susceptible (OS) mecA-positive S. aureus isolates (commonly called OS-MRSA) are rather commonly detected worldwide and may remain undiagnosed using phenotypic susceptibility testing methods. This review will summarize the current reports on OS-MRSA isolations and the underlying mechanisms regulating the expression of oxacillin resistance and also oxacillin susceptibility in mecA-positive S. aureus isolates. As MRSA commonly cause severe infections against which effective therapies are limited, understanding of these mechanisms could enable the identification of new targets for the treatment or reversion of the MRSA phenotype.
    No preview · Article · Mar 2015 · Current pharmaceutical design
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    Full-text · Dataset · Feb 2015
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    Full-text · Dataset · Feb 2015
  • [Show abstract] [Hide abstract] ABSTRACT: Here we describe an outbreak caused by a pandrug-resistant Providencia stuartii strain involving 15 critically ill patients in a Greek intensive care unit (ICU) during September-November 2011. All isolates harboured the blaVIM-1 gene and a class 1 integron structure of 1913 bp as well as blaSHV-5 and blaTEM-1. Pulsed-field gel electrophoresis (PFGE) demonstrated that isolates from all 15 patients belonged to a single P. stuartii clonal type. As all of the infected patients were hospitalised during overlapping time periods, horizontal intra-ICU transmission was considered as the main route for the dissemination of the outbreak strain. The outbreak ended following reinforcement of infection control measures, including implementation of additional barrier precautions for infected patients. Copyright © 2015 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.
    No preview · Article · Feb 2015 · International Journal of Antimicrobial Agents
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    [Show abstract] [Hide abstract] ABSTRACT: The current phenotypic methods for detecting carbapenemase-producing Enterobacteriaceae (CPE) allow differentiation between class A and B carbapenemases but they cannot confirm in a single test class D OXA-48 carbapenemase producers. In this study we evaluated a new phenotypic test, the OXA-48 disk test, which is based on an imipenem disk and two blank disks loaded with the tested strain and impregnated with EDTA and EDTA plus phenyl boronic acid (PBA), respectively. The evaluation of the OXA-48 disk test was performed with 81 genotypically confirmed OXA-48-producing Enterobacteriaceae (41 ESBL producers, 3 AmpC producers and 37 non-ESBL, non-AmpC producers). To measure the specificity of the test, 173 genotypically confirmed OXA-48-negative Enterobacteriaceae isolates (57 KPC producers, 34 VIM producers, 23 KPC/VIM producers, 22 NDM producers, 37 AmpC or ESBL producers and porin deficient) that were non-susceptible to at least one carbapenem were chosen for testing. Using imipenem disk and the distortion of the inhibition halo around both blank disks containing EDTA and EDTA/PBA, the test differentiated all but three of the 81 OXA-48 producers (sensitivity 96.3%). The test was negative for OXA-48 production in all but four of the 173 carbapenem-non-susceptible isolates producing other carbapenemases, AmpCs or ESBLs (specificity 97.7%). This evaluation shows that OXA-48 disk test is a useful phenotypic method for the accurate differentiation of OXA-48-producing Enterobacteriaceae. Its use along with combined-disk tests employing inhibitor-supplemented carbapenem disks could allow the differentiation of the currently known carbapenemase types in Enterobacteriaceae species and provide important infection control information. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Full-text · Article · Feb 2015 · Journal of Clinical Microbiology
  • [Show abstract] [Hide abstract] ABSTRACT: Molecular typing data on antimicrobial-resistant Propionibacterium strains are limited in the literature. We examined antimicrobial resistance profiles and the underlying resistance mechanisms in Propionibacterium spp. isolates recovered from patients with moderate to severe acne vulgaris in Greece. The clonallity of the resistant Propionibacterium acnes isolates was also investigated. Propionibacterium spp. isolates were detected using Tryptone-Yeast Extract-Glucose (TYG) agar plates supplemented with 4% furazolidone. Erythromycin, clindamycin, vancomycin, penicillin, co-trimoxazole, doxycycline, minocycline and ciprofloxacin MICs were determined using the gradient strip method. Erythromycin, clindamycin and tetracycline mechanisms of resistance were determined using PCR and sequencing of the domain V of 23S rRNA and 16S rRNA, as well as the presence of the ermX gene. Typing was performed using the multi locus sequence typing (MLST) methodology. Seventy nine isolates from 76 patients were collected. Twenty-three isolates (29.1%) exhibited resistance to erythromycin and clindamycin, while two additional isolates (2.5%) were resistant only to erythromycin. Resistance to tetracycline was not detected. The underlying molecular mechanisms were point mutations A2059G and A2058G. MLST typing of the P. acnes resistant isolates revealed that lineage type IA1 (ST-1, 3 and 52) prevailed (12/18; 66.7%), whilst lineage type IA2 (ST-2 and 22) accounted for five more isolates (27.8%). Susceptible isolates were more evenly distributed between ST types. Propionibacterium spp. from moderate to severe acne vulgaris in Greece are frequently resistant to erythromycin/clindamycin but not to tetracyclines, mainly due to the point mutations A2059G and A2058G. P. acnes resistant isolates were more clonally related than susceptible ones and belonged to a limited number of MLST types. Copyright © 2014 Elsevier Ltd. All rights reserved.
    No preview · Article · Nov 2014 · Anaerobe
  • [Show abstract] [Hide abstract] ABSTRACT: Influenza human infections are considered as a persistent global public health issue. Whereas vaccination is important for prevention, given its limitations, antiviral therapy is at the forefront of treatment, while it also plays a significant role in prevention. Currently, two classes of drugs, adamantanes (M2 blockers) and neuraminidase inhibitors (NAIs), are available for treatment and chemoprophylaxis of influenza infections. Given the resistance patterns of circulating influenza strains, adamantanes are not currently recommended. The current review mainly focuses on the development of resistance to NAIs among A and B subtypes of influenza virus strains over the last 5 years. 'Permissive' drift mutations and reassortment of viral gene segments have resulted in NAI oseltamivir-resistant A/(H1N1) variants that rapidly became predominant worldwide in the period 2007-2009. However, the prevalence of antiviral resistance to NAI zanamivir remains relatively low. In addition, the recently developed NAIs, peramivir and laninamivir, while licensed in certain countries, are still under evaluation and only a few reports have described resistance to peramivir. Although in 2014, the majority of circulating human influenza viruses remains susceptible to all NAIs, the emergence of oseltamivir-resistant influenza variants that could retain viral transmissibility, highlights the necessity for enhanced epidemiological and microbiological surveillance and clinical assessment of antiviral resistance.
    No preview · Article · Nov 2014 · Expert Review of Anti-infective Therapy
  • [Show abstract] [Hide abstract] ABSTRACT: ABSTRACT Aim: The bacterial and atypical etiology of acute exacerbations of chronic obstructive pulmonary disease was investigated and the diagnostic techniques used were compared among 92 hospitalized patients. Sputum specimens were investigated using culture and PCR, serological status evaluation was performed and the inflammatory profile was associated with the microbiological results. The majority of the patients (65.2%) had very severe airway obstruction. The most common bacteria were Haemophilus influenzae and Pseudomonas aeruginosa (23.9 and 14.1%, respectively). Acinetobacter baumannii- and P. aeruginosa-positive cultures were associated with prolonged hospitalization and severe airway obstruction (p = 0.03 and 0.031, respectively). Chlamydia pneumoniae or Mycoplasma pneumoniae infection was diagnosed in four and two patients, respectively. Discrepant results were detected between PCR and serology, especially regarding C. pneumoniae.
    No preview · Article · Nov 2014 · Future Microbiology
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    [Show abstract] [Hide abstract] ABSTRACT: The effects of doxycycline-streptomycin-rifampin versus a standard doxycycline-streptomycin regimen on residual Brucella DNA were compared in 36 acute brucellosis patients. At admission, all patients given triple (n = 22) and double (n = 14) regimens had detectable Brucella DNA with similar mean loads (P = 0.982). At follow-up, 14 to 20 months postpresentation, significantly more patients receiving triple than double regimens had undetectable Brucella DNA (P = 0.026). The doxycycline-streptomycin-rifampin regimen eliminates Brucella DNA more efficiently than doxycycline-streptomycin, which may result in superior long-term clearance of Brucella.
    Full-text · Article · Sep 2014 · Antimicrobial Agents and Chemotherapy
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    [Show abstract] [Hide abstract] ABSTRACT: Serological, molecular and phylogenetic analyses of a recently imported case of Middle East respiratory syndrome coronavirus (MERS-CoV) in Greece are reported. Although MERS-CoV remained detectable in the respiratory tract secretions of the patient until the fourth week of illness, viraemia was last detected 2 days after initiation of triple combination therapy with pegylated interferon, ribavirin and lopinavir/ritonavir, administered from Day 13 of illness. Phylogenetic analysis of the virus showed close similarity with other human MERS-CoVs from the recent Jeddah outbreak in Saudi Arabia. Immunoglobulin G (IgG) titres peaked 3 weeks after the onset of illness, whilst IgM levels remained constantly elevated during the follow-up period (second to fifth week of illness). Serological testing confirmed by virus neutralisation assay detected an additional case that was a close contact of the patient.
    Full-text · Article · Sep 2014 · International Journal of Antimicrobial Agents
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    Full-text · Article · Sep 2014 · Immunology Letters
  • [Show abstract] [Hide abstract] ABSTRACT: Linezolid-dependent growth was recently reported in Staphylococcus epidermidis clinical strains carrying mutations associated with linezolid resistance. To investigate this unexpected behavior at the molecular level, we isolated active ribosomes from one of the linezolid-dependent strains and we compared them with ribosomes isolated from a wild-type strain. Both strains were grown in the absence and presence of linezolid. Detailed biochemical and structural analyses revealed essential differences in the function and structure of isolated ribosomes which were assembled in the presence of linezolid. The catalytic activity of peptidyltransferase was found to be significantly higher in the ribosomes derived from the linezolid-dependent strain. Interestingly, the same ribosomes exhibited an abnormal ribosomal subunit dissociation profile on a sucrose gradient in the absence of linezolid, but the profile was restored after treatment of the ribosomes with an excess of the antibiotic. Our study suggests that linezolid most likely modified the ribosomal assembly procedure, leading to a new functional ribosomal population active only in the presence of linezolid. Therefore, the higher growth rate of the partially linezolid-dependent strains could be attributed to the functional and structural adaptations of ribosomes to linezolid.
    No preview · Article · Jul 2014 · Antimicrobial Agents and Chemotherapy
  • [Show abstract] [Hide abstract] ABSTRACT: Enteroviruses are important human pathogens, causing a broad spectrum of diseases from minor common colds to fatal myocarditis. However, certain disease syndromes are caused by one or few serotypes. Serotype identification is difficult due to the laborious neutralization tests that lack of sensitivity, while in commercial ELISAs homotypic antibodies' activities are largely masked by the recognition of genera-specific by heterotypic antibodies. In the present study homotypic assays were developed with the ability to discriminate different enterovirus serotypes. Seventy three children sera, positive for IgM antibodies against enterovirus genus and 49 healthy children were examined for the presence of antibodies against 14 synthetic peptides derived from a non-conserved region of the VP1 protein of coxsackieviruses B2, B3, B4, B5, A9, A16, A24, echoviruses 6, 7, 9, 11, 30, enterovirus 71 and parechovirus 1. 50% of the anti-enterovirus IgM positive sera (>150 BU) reacted with the peptides with the majority of them to preferentially recognize one of them, supporting the homotypic nature of our assay. Inhibition studies yielded homologous inhibition rates 67% - 95% suggesting that specific peptide recognition actually occurred. The diagnostic value of our assay was tested in blood samples drawn over a 1.5 year period from a five-year old patient. The anti-enterovirus reactivity was clearly attributed to echovirus serotype 11. The IgM/IgG antibody ratio was reversed 4 months later and subsequently IgM antibodies dropped below the cutoff point. In this paper we demonstrate that our assay can be used to discriminate between antibodies targeting different enterovirus serotypes.
    No preview · Article · Jun 2014 · Peptides