The emergence of extended spectrum β-lactamase (ESBL)-producing Enterobacteriaceae represents a major challenge to public and animal health in many countries including Lebanon. Carriage of ESBLs confers resistance to β-lactam antibiotics and more than 200 different sub-types have been identified, all of which are primarily encoded by genes located on conjugative plasmids.
Despite the high prevalence of ESBLs, there is still a paucity of information regarding the impact of ESBL plasmid carriage on the host bacterium and how the spread of antibiotic resistance relates to antibiotic use in hospital environments. Therefore, the aim of this study was, firstly, to characterise the genetic and phenotypic properties of ESBL-producing Escherichia coli and Klebsiella pneumoniae isolated from a hospital in Lebanon. Secondly, to assess the fitness of isolates harbouring different sub-types of ESBLs in order to better understand the influence of the plasmid on the host bacterium, and thirdly, to correlate hospital antibiotic consumption data calculated using ABC Calc software (in defined daily doses (DDD) per 100 bed days), with antimicrobial susceptibility profiles obtained over a three year period.
A total of 140 isolates of E. coli and K. pneumoniae that were resistant to at least one 3rd- or 4th- generation cephalosporin were collected from the Centre Hospitalier Du Nord (CHN) in Lebanon, between 1st May 2011 and the 31st December 2012. ESBL-production was confirmed in all isolates using the double disk synergy assay and the E-test ESBL strip. Out of 140 isolates, 35 were also found to harbour a chromosomal AmpC β-lactamase, whereas none harboured the plasmidic gene. PCR analyses showed that all isolates harboured CTX-M type β-lactamase, with 74% also harbouring TEM and approximately 40% harbouring either SHV or OXA type β-lactamases. Most E. coli isolates belonged to phylogenetic group B2, and harboured genes important in iron uptake.
PFGE analysis of both E. coli and K. pneumoniae indicated significant clonal diversity amongst the isolates. Analysis of the β-lactamase-encoding plasmids from selected isolates revealed the plasmids were conjugative and bore similarities to pEC_L8 and Inc group types. Plasmid curing studies indicated that ESBL plasmids influenced bacterial host cell fitness through altered carbon metabolism and generation time. Both positive and negative correlations were found between antibiotic consumption and the susceptibility of E. coli and K. pneumoniae to different types of antibiotics.
This study highlights the diversity of ESBL-producing isolates found among members of the Enterobacteriaceae in Lebanon and supports the idea that horizontal transfer of CTX-M-15 harbouring ESBL plasmids, rather than clonal expansion of particular isolates, has occurred. Moreover, the use of β-lactam antibiotics and quinolones may promote their spread, and thus effective hospital infection control programs and more pragmatic antimicrobial usage is recommended
