Characterisation of staphylococcus aureus circulating in Portugal

  • Ana Isabel Rodrigues Pereira de Castro (Student)

Student thesis: Doctoral Thesis


Staphylococcus aureus is a pathogen responsible for skin infections and invasivediseases such as meningitis or pulmonary infection and staphylococcal food poisoning(SFP). The main goal of this study was to increase knowledge on S. aureus circulatingin Portugal mainly concerning their virulence characteristics and antimicrobialresistance. According to EFSA-ECDC, Portugal is considered to have one of the highestlevels of methicillin-resistant S. aureus (MRSA) from bacteraemia in Europe.The frequency of occurrence of S. aureus from different origins was determined. Swabsamples were collected from hands and nose of health care professionals and foodhandlers - noses and hands are niches where S. aureus are likely to be present in humans- and particularly noses of children (3 to 6 years). Presence of S. aureus in food sampleswas also determined. Collected isolates were further characterized phenotypically andgenomically.Nasal carriage of S. aureus was higher in children (48.6%) compared to health careprofessionals (39.6%) and food handlers (19.8%). The occurrence of S. aureus on thehands of health care professionals and food handlers was 8.9% and 11.1%, respectively.Globally, higher S. aureus occurrence rates were obtained for nasal carriage.The first case of Methicillin-Resistant Staphylococcus aureus (MRSA) was reported in1961. Since then, it has been considered the leading cause of nosocomial infections,responsible for causing serious morbidity and mortality rates, worldwide. Globally, theoccurrence of MRSA strains was higher in hospital health care professionals; no MRSAstrains were detected in food handlers, children presented a carriage of 9.7% of MRSAand low occurrence rates were detected in the analysed food samples (between 0.68 and5.5 %).Other virulence factors have been reported for S. aureus strains including antibioticresistance and presence of enterotoxins, Panton-Valentine Leukocidin (PVL),haemolysins, exfoliative toxins and numerous factors involved in invasion of host cellsamong others.In the present study, resistance to oxacillin, penicillin and ampicillin and to antibioticsof classes other than betalactams, namely ciprofloxacin, gentamicin, rifampicinn,vancomycin, tetracycline, erythromycin, nitrofurantoin and chloramphenicol wasinvestigated. As expected, high levels of resistance to ß-lactams were observed. Testedstrains showed low resistance rates to gentamicin, chloramphenicol and rifampicin.Regardless of the source of isolates, resistance to erythromycin was evident.Enterotoxin genes sea - sej and tst were evaluated by multiplex PCR. Although sea isconsidered the most prevalent enterotoxin gene reported all over the world, in thepresent study this was not verified. tst gene was detected in children, hospital healthcare professionals and food handlers. PVL genes were analysed in all the MRSA strainscollected from various origins, but only one food strain showed the presence of thesegenes.Typing by SCCmec has been performed and revealed the presence of type IV and V.SCCmec type IV is associated worldwide with PVL positive strains, but which was notverified in this study. PFGE typing was performed on S. aureus strains isolated from handsand from nose of the same individual of the health care professionals and food handlers; 60and 30% of the individuals, respectively, presented the same S. aureus strain on hands andnose.
Date of Award27 Feb 2017
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorPaula Teixeira (Supervisor) & Joana Gabriela Laranjeira Silva (Co-Supervisor)


  • Doutoramento em Biotecnologia

Cite this