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Increase of β-lactam-resistant invasive Haemophilus influenzae in Sweden, 1997 to 2010.


The proportions of Haemophilus influenzae resistant to ampicillin and other β-lactam antibiotics have been low in Sweden compared to other countries in the Western world. However, a near-doubled proportion of nasopharyngeal Swedish H. influenzae isolates with resistance to β-lactams has been observed in the last decade. In the present study, the epidemiology and mechanisms of antimicrobial resistance of H. influenzae isolates from blood and cerebrospinal fluid in southern Sweden from 1997 to 2010 (n = 465) were studied. Antimicrobial susceptibility testing was performed using disk diffusion, and isolates with resistance to any tested β-lactam were further analyzed in detail. We identified a significantly increased (P = 0.03) proportion of β-lactam-resistant invasive H. influenzae during the study period, which was mainly attributed to a significant recent increase of β-lactamase-negative β-lactam-resistant isolates (P = 0.04). Furthermore, invasive β-lactamase-negative β-lactam-resistant H. influenzae isolates from 2007 and onwards were found in higher proportions than the corresponding proportions of nasopharyngeal isolates in a national survey. Multiple-locus sequence typing (MLST) of this group of isolates did not completely separate isolates with different resistance phenotypes. However, one cluster of β-lactamase-negative ampicillin-resistant (BLNAR) isolates was identified, and it included isolates from all geographical areas. A truncated variant of a β-lactamase gene with a promoter deletion, bla(TEM-1)-PΔ dominated among the β-lactamase-positive H. influenzae isolates. Our results show that the proportions of β-lactam-resistant invasive H. influenzae have increased in Sweden in the last decade.


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    Medical Microbiology, Department of Laboratory Medicine Malmö, Lund University, Sweden.

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    Antimicrobial agents and chemotherapy 56:8 2012 Aug pg 4408-15


    Base Sequence
    Genetic Variation
    Haemophilus Infections
    Haemophilus influenzae
    Microbial Sensitivity Tests
    Multilocus Sequence Typing
    Promoter Regions, Genetic
    Sequence Analysis, DNA
    beta-Lactam Resistance

    Pub Type(s)

    Journal Article
    Research Support, Non-U.S. Gov't



    PubMed ID