[Molecular biology characteristics of ESBL-positive strains of Klebsiella pneumoniae collected in the Neonatal Unit of the Teaching Hospital in Olomouc]

Abstract

Background: One of the problems of contemporary medicine is an increasing number of bacterial strains with hazardous phenotypes of resistance. This is also true for neonatal units where nosocomial infections caused by multiresistant bacteria pose a serious threat to newborns. The feared bacterial pathogens include Klebsiella pneumoniae strains producing AmpA Extended-Spectrum Beta-Lactamases. The study focused on the molecular biology characteristics of ESBL-positive strains of K. pneumoniae collected in the Neonatal Unit of the Teaching Hospital in Olomouc (THO).

Materials and methods: Clinical material from newborns hospitalized in the THO Neonatal Unit between January and June 2004 was used to isolate and determine K. pneumoniae strains by standard identification procedures. Their susceptibility to antibiotics was tested using a dilution micromethod. A Double-Disk Synergy Test was used for phenotype determination of ESBL production. The bla gene coding ESBL production was demonstrated by PCR. Molecular biology characteristics of ESBL-positive strains utilized the genomic DNA isolation, XbaI restrictase digestion and PFGE differentiation. The acquired restriction maps of individual isolates were compared using the GelCompare software and their relationship was determined. The selection pressure of antimicrobial agents was assessed according to the absolute number of defined daily doses of individual antibiotics.

Results: During the monitored period, 112 K. pneumoniae strains were isolated in total. In 22 of them (19.6%), the TEM-type ESBL production was determined. ESBL-positive strains were only observed in upper respiratory tract and rectal swabs collected from newborns with no signs of infection. The molecular biology analysis showed that 21 ESBL-positive strains had an identical restriction profile, i.e. they were very likely to be identical. The selection pressure of third- and fourth-generation cephalosporins was very low over the observed period and their consumption accounted for 1.9 % of all administered antimicrobial agents.

Conclusion: The results presented above suggest that ESBL-positive strains of K. pneumoniae occurred in the THO Neonatal Unit due to clonal and horizontal spread from an unidentified source.