title: Tigecycline susceptibility in Klebsiella pneumoniae and Escherichia coli causing neonatal septicaemia (2007-10) and role of an efflux pump in tigecycline non-susceptibility.
abstract: OBJECTIVE
  To investigate the trend of tigecycline susceptibility and mechanisms behind tigecycline non-susceptibility in Klebsiella pneumoniae and Escherichia coli isolates causing neonatal septicaemia (2007-10).
  
  
  METHODS
  MICs of tigecycline for the isolates were determined. The isolates were evaluated for β-lactamases and carbapenemases. Molecular typing of the tigecycline-resistant isolates was performed. Expression of efflux pump genes (acrA, acrB and tolC) and regulators (soxS and ramA) was examined by real-time RT-PCR and western blotting. Sequencing of the ramA and ramR genes was carried out to identify mutations within these genes.
  
  
  RESULTS
  Tigecycline susceptibility was evaluated in all K. pneumoniae (n = 57) and E. coli (n = 19) blood isolates. The prevalence of extended-spectrum β-lactamase (ESBL)-producing organisms was high, but tigecycline non-susceptibility remained low in these isolates. Though MIC values of tigecycline remained in the susceptible range, there was a 2-fold increase in the value of MIC90 from 2007 to 2010. Over the 4 year period K. pneumoniae showed higher MIC values of tigecycline in comparison with E. coli. Tigecycline non-susceptibility was not observed among carbapenem-resistant isolates. Only two ESBL-producing clonally distinct K. pneumoniae isolates showed tigecycline resistance with overexpression of ramA and the AcrAB-TolC pump. No mutations were present within the ramA and ramR genes that might enhance the expression of the pump.
  
  
  CONCLUSIONS
  The study showed for the first time the trend of tigecycline susceptibility in E. coli and K. pneumoniae causing neonatal septicaemia. Tigecycline still has potent antimicrobial effects against most ESBL- or carbapenemase-producing K. pneumoniae and E. coli, but the increasing MIC values make it essential to be vigilant.
authors: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, P33, CIT Road, Scheme XM, Beliaghata, Kolkata 700010, India.
authors: Subhasree
authors: S
authors: Roy
authors: Saswati
authors: S
authors: Datta
authors: Rajlakshmi
authors: R
authors: Viswanathan
authors: Arun K
authors: AK
authors: Singh
authors: Sulagna
authors: S
authors: Basu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015153:Blotting, Western; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000145:classification / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology*; D020869:Gene Expression Profiling; D006801:Humans; D007231:Infant, Newborn; D007710:Klebsiella Infections / Q000382:microbiology*; D007711:Klebsiella pneumoniae / Q000145:classification / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D026901:Membrane Transport Proteins / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D058889:Molecular Typing; D050505:Mutant Proteins / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018805:Sepsis / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D000078304:Tigecycline; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D026901:Membrane Transport Proteins; D050505:Mutant Proteins; D000078304:Tigecycline; D001618:beta-Lactamases; D008911:Minocycline