Athanassios Tsakris

Harokopion University of Athens, Athínai, Attica, Greece

Are you Athanassios Tsakris?

Claim your profile

Publications (275)1034.24 Total impact

  • [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:
    Journal of Antimicrobial Chemotherapy 07/2015; DOI:10.1093/jac/dkv210 · 5.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Group A streptococcus (GAS) is an important cause of morbidity and mortality worldwide. Surveillance of emm types have important implications as they can serve as baseline information for possible implementation of vaccination. A total of 1349 GAS pediatric isolates were collected during a 7-year period (2007-2013). emm typing was completed in 1282 pharyngeal (84%) or non-pharyngeal (16%) isolates and emm-clusters and temporal changes were analyzed. Thirty five different emm types including 14 sub-types were identified. The most prevalent emm types identified were 1(16.7%), 12(13.6%), 77(10.9%), 4(10.8%), 28(10.4%), 6(6.8%) 3(6.6%) and 89(6.6%) accounting for 82.3% of total isolates. Rheumatogenic emm types comprised 16.3% of total isolates. emm types 12, 4 and 77 were more prevalent among pharyngeal isolates and emm1, 89, 6, 75 and 11 among non-pharyngeal. The emm types identified belong to 13 emm-clusters and the 8 most prevalent clusters comprise 97% of all isolates. There was statistically significant decrease in prevalence of emm types 12, 4, 5 and 61 and increase in emm89, 75 and 11 comparing with the period 2001-2006. Proposed 30-valent GAS vaccine, currently in preclinical studies, encompasses 97.2% of emm types detected in our study and 97.4% of erythromycin resistant strains. In addition, it includes 93.3% of emm types involved in bacteremia. A much greater diversity of GAS emm types was identified in our area than previously described. Seasonal fluctuations and introduction of new emm types was observed. Continuous surveillance of emm types is needed in order to evaluate the possible benefit of an M protein based GAS vaccine. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Journal of clinical microbiology 04/2015; 53(7). DOI:10.1128/JCM.00301-15 · 4.23 Impact Factor
  • [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.
  • Source
  • Source
  • [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.
    International Journal of Antimicrobial Agents 02/2015; 45(5). DOI:10.1016/j.ijantimicag.2014.12.030 · 4.26 Impact Factor
  • [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.
    Journal of Clinical Microbiology 02/2015; 53(4). DOI:10.1128/JCM.03318-14 · 4.23 Impact Factor
  • [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.
    Anaerobe 11/2014; 31. DOI:10.1016/j.anaerobe.2014.10.007 · 2.36 Impact Factor
  • [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.
    Expert Review of Anti-infective Therapy 11/2014; 12(11):1325-36. DOI:10.1586/14787210.2014.966083 · 2.28 Impact Factor
  • [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.
    Future Microbiology 11/2014; 9(11):1251-60. DOI:10.2217/fmb.14.90 · 3.82 Impact Factor
  • [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.
    Antimicrobial Agents and Chemotherapy 09/2014; 58(12). DOI:10.1128/AAC.03841-14 · 4.45 Impact Factor
  • Source
    [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.
    International Journal of Antimicrobial Agents 09/2014; 44(6). DOI:10.1016/j.ijantimicag.2014.07.026 · 4.26 Impact Factor
  • Source
    Immunology Letters 09/2014; 161(1). DOI:10.1016/j.imlet.2014.04.013 · 2.37 Impact Factor
  • [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.
    Antimicrobial Agents and Chemotherapy 07/2014; 58(8):4651-4656. DOI:10.1128/AAC.02835-14 · 4.45 Impact Factor
  • [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.
    Peptides 06/2014; DOI:10.1016/j.peptides.2014.04.017 · 2.61 Impact Factor
  • European journal of dermatology: EJD 06/2014; 24(4). DOI:10.1684/ejd.2014.2376 · 1.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Antimicrobial susceptibility testing (AST) and conclusive assessment of minimal inhibitory concentrations (MICs) of highly pathogenic bacteria is difficult due to a lack of (consensus) standards and incomplete breakpoint definitions. Standards are available from the Clinical and Laboratory Standards Institute (CLSI) and furthermore, from WHO only for Bacillus anthracis and Francisella tularensis. The CLSI M45‐A2 document provides recommendations for testing conditions (microdilution), but the available breakpoints are not for all relevant substances and often only for the category "susceptible". Furthermore, during external quality assurance (EQA) exercises of the European joint action Quality Assurance Exercises and Networking on the Detection of Highly Infectious Pathogens (QUANDHIP) several discrepancies in AST were observed among the participants. Therefore, a working group from six European laboratories was established to identify one AST method appropriate for all highly pathogenic bacteria to standardize this method and to evaluate it in consecutive QUANDHIP EQAs.
    ECCMID 2014, Barcelona, Spain.; 05/2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: On 18 April 2014, a case of Middle East Respiratory Syndrome coronavirus (MERS-CoV) infection was laboratory confirmed in Athens, Greece in a patient returning from Jeddah, Saudi Arabia. Main symptoms upon initial presentation were protracted fever and diarrhoea, during hospitalisation he developed bilateral pneumonia and his condition worsened. During 14 days prior to onset of illness, he had extensive contact with the healthcare environment in Jeddah. Contact tracing revealed 73 contacts, no secondary cases had occurred by 22 April.
    Eurosurveillance: bulletin europeen sur les maladies transmissibles = European communicable disease bulletin 04/2014; Euro Surveill(19 (16)):20782. DOI:10.2807/1560-7917.ES2014.19.16.20782 · 4.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Despite the fact that the NDM-1 carbapenemase has successfully disseminated worldwide, outbreaks remain uncommon in the European region. We describe the characteristics of the first outbreaks caused by NDM-1-producing Klebsiella pneumoniae clonal isolates in Greece. Between January 2010 and June 2013, 132 non-repetitive carbapenem-resistant Enterobacteriaceae isolates, which gave a positive modified Hodge test and were phenotypically suspected of metallo-β-lactamase production, were recovered from patients hospitalized at Ioannina University Hospital. Resistance genes were identified by PCR and sequencing. Plasmid profiling, conjugation experiments, enterobacterial repetitive intergenic consensus PCR, PFGE and multilocus sequence typing (MLST) were performed. Patient records were retrieved to access patterns of acquisition. Molecular testing verified the presence in 78 K. pneumoniae isolates, collected from 71 patients, of the blaNDM-1 gene. The blaCTX-M-15, blaOXA-1 and blaTEM-1 genes were also present in most isolates. The blaNDM-1 gene was located on a narrow host range IncFII-type plasmid, of ∼95 kb, flanked upstream by a non-truncated ISAba125 element and downstream by the bleMBL gene. Genotyping clustered all K. pneumoniae isolates into a single clonal type with one subtype and MLST assigned them to sequence type 11. Two outbreaks were noted, the first between November and December 2011 involving four patients and the second initiated in May 2012 and ongoing, involving the remaining patients. All but two cases were characterized as hospital acquired. No links to immigration or travel history to endemic areas were established. This survey highlights the successful undetected dissemination of yet another carbapenemase in Greece and strengthens the hypothesis of a latent NDM-1 cluster in the Balkan region.
    Journal of Antimicrobial Chemotherapy 04/2014; 69(8). DOI:10.1093/jac/dku105 · 5.44 Impact Factor
  • Source
    Eurosurveillance: bulletin europeen sur les maladies transmissibles = European communicable disease bulletin 04/2014; 19(13). DOI:10.2807/1560-7917.ES2014.19.13.20758 · 4.66 Impact Factor

Publication Stats

4k Citations
1,034.24 Total Impact Points


  • 2008–2014
    • Harokopion University of Athens
      Athínai, Attica, Greece
  • 2004–2014
    • National and Kapodistrian University of Athens
      • • Department of Medicine
      • • Division of Microbiology
      Athínai, Attica, Greece
  • 2013
    • Κωνσταντοπούλειο νοσοκομείο Νέας Ιωνίας (Η Αγία Όλγα)
      Athínai, Attica, Greece
    • Hellenic Center for Disease Control and Prevention
      Saloníki, Central Macedonia, Greece
  • 2012
    • Γενικό Νοσοκομείο Σάμου Αγίου Παντελεήμονα
      Vathy, North Aegean, Greece
    • University of Kragujevac
      Krabujevac, Central Serbia, Serbia
  • 2009–2012
    • University of Thessaly
      • School of Medicine
      Iolcus, Thessaly, Greece
  • 2011
    • Tzaneio General Hospital of Piraeus
      Le Pirée, Attica, Greece
    • National Technical University of Athens
      Athínai, Attica, Greece
    • Azienda Ospedaliera Cannizzaro
      Catania, Sicily, Italy
  • 2009–2011
    • Γενικό Νοσοκομείο Σερρών
      Seres, Central Macedonia, Greece
  • 2010
    • Aglaia Kyriakou Children's Hospital
      Athínai, Attica, Greece
    • National Academy of Medical Sciences of Nepal
      Kantipura, Central Region, Nepal
  • 2007
    • Aghia Sophia Children’s Hospital
      Athínai, Attica, Greece
  • 2006
    • Metaxa Cancer Hospital
      Le Pirée, Attica, Greece
  • 2001–2006
    • Hippokration General Hospital, Thessaloniki
      Saloníki, Central Macedonia, Greece
  • 1994–2005
    • AHEPA University Hospital
      Saloníki, Central Macedonia, Greece
  • 1997–2003
    • Aristotle University of Thessaloniki
      • Laboratory of General Microbiology
      Saloníki, Central Macedonia, Greece
  • 1992
    • Hippokration General Hospital, Athens
      Athínai, Attica, Greece
  • 1991
    • North Middlesex University Hospital NHS Trust
      Londinium, England, United Kingdom