The main goal of this work was to identify the mechanisms responsible for carbapenem resistance in 61 Chilean clinical isolates of Enterobacteriaceae (Enterobacter spp., Serratia marcescens, Morganella morganii, Escherichia coli and Klebsiella pneumoniae) with reduced susceptibility to at least one carbapenem (ertapenem, imipenem or meropenem). All of the isolates were analysed for the presence of carbapenemases, extended spectrum β-lactamases (ESBLs), AmpC enzymes and outer-membrane proteins. None of the isolates exhibited carbapenemase activity nor did they have any of the carbapenemase genes that were screened for. Most of the 61 strains produced at least one ESBL and/or one AmpC enzyme and either lost their porins or had altered porins according to sequence analysis. The distribution of ESBLs and AmpC enzymes was different among the species studied. Resistance in K. pneumoniae and E. coli isolates was associated with ESBLs; in M. morganii isolates, resistance was attributed to overexpression of an AmpC enzyme; and in Enterobacter spp. isolates, resistance was associated with both types of enzymes. In K. pneumoniae isolates, porin integrity was more a determinant of carbapenem resistance than the presence of ESBLs, whereas in isolates of Enterobacter spp., M. morganii and S. marcescens, the presence of an overexpressed AmpC enzyme was associated with higher imipenem and meropenem MIC values. Therefore, carbapenem resistance in Chilean isolates is not due to true carbapenemases but rather to a combination of porin loss/alteration and β-lactamase activity. The fact that carbapenemases were not detected in this study is unique, given that many countries in the region have already reported the presence of these enzymes.
Doménech-SánchezA.,
Martínez-MartínezL.,
Hernández-AllésS.,
del Carmen ConejoM.,
PascualA.,
TomásJ. M.,
AlbertíS.,
BenedíV. J.2003; Role of Klebsiella pneumoniae OmpK35 porin in antimicrobial resistance. Antimicrob Agents Chemother 47:3332–3335 [View Article][PubMed]
DoumithM.,
EllingtonM. J.,
LivermoreD. M.,
WoodfordN.2009; Molecular mechanisms disrupting porin expression in ertapenem-resistant Klebsiella and Enterobacter spp. clinical isolates from the UK. J Antimicrob Chemother 63:659–667 [View Article][PubMed]
HutsulJ. A.,
WorobecE.1997; Molecular characterization of the Serratia marcescens OmpF porin, and analysis of S. marcescens OmpF and OmpC osmoregulation. Microbiology 143:2797–2806 [View Article][PubMed]
LobosS. R.,
MoraG. C.1991; Alteration in the electrophoretic mobility of OmpC due to variations in the ammonium persulfate concentration in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electrophoresis 12:448–450 [View Article][PubMed]
MitsuyamaJ.,
HirumaR.,
YamaguchiA.,
SawaiT.1987; Identification of porins in outer membrane of Proteus, Morganella, and Providencia spp. and their role in outer membrane permeation of β-lactams. Antimicrob Agents Chemother 31:379–384[PubMed][CrossRef]
PagèsJ. M.,
JamesC. E.,
WinterhalterM.2008; The porin and the permeating antibiotic: a selective diffusion barrier in Gram-negative bacteria. Nat Rev Microbiol 6:893–903 [View Article][PubMed]
PasteranF.,
MendezT.,
GuerrieroL.,
RapoportM.,
CorsoA.2009; Sensitive screening tests for suspected class A carbapenemase production in species of Enterobacteriaceae
. J Clin Microbiol 47:1631–1639 [View Article][PubMed]
PeiranoG.,
SekiL. M.,
Val PassosV. L.,
PintoM. C.,
GuerraL. R.,
AsensiM. D.2009; Carbapenem-hydrolysing β-lactamase KPC-2 in Klebsiella pneumoniae isolated in Rio de Janeiro, Brazil. J Antimicrob Chemother 63:265–268 [View Article][PubMed]
RadiceM.,
PowerP.,
GutkindG.,
FernándezK.,
VayC.,
FamigliettiA.,
RicoverN.,
AyalaJ. A.2004; First class A carbapenemase isolated from Enterobacteriaceae in Argentina. Antimicrob Agents Chemother 48:1068–1069 [View Article][PubMed]
SeniorB. W.,
VörösS.1990; Protein profile typing – a new method of typing Morganella morganii strains. J Med Microbiol 33:259–264 [View Article][PubMed]
SmetA.,
MartelA.,
PersoonsD.,
DewulfJ.,
HeyndrickxM.,
CatryB.,
HermanL.,
HaesebrouckF.,
ButayeP.2008; Diversity of extended-spectrum β-lactamases and class C β-lactamases among cloacal Escherichia coli isolates in Belgian broiler farms. Antimicrob Agents Chemother 52:1238–1243 [View Article][PubMed]
StruyvéM.,
MoonsM.,
TommassenJ.1991; Carboxy-terminal phenylalanine is essential for the correct assembly of a bacterial outer membrane protein. J Mol Biol 218:141–148 [View Article][PubMed]
VillegasM. V.,
LolansK.,
CorreaA.,
SuarezC. J.,
LopezJ. A.,
VallejoM.,
QuinnJ. P.the Colombian Nosocomial Resistance Study Group2006; First detection of the plasmid-mediated class A carbapenemase KPC-2 in clinical isolates of Klebsiella pneumoniae from South America. Antimicrob Agents Chemother 50:2880–2882 [View Article][PubMed]
WoodfordN.,
TiernoP. M.Jr,
YoungK.,
TysallL.,
PalepouM. F.,
WardE.,
PainterR. E.,
SuberD. F.,
ShunguD.other authors2004; Outbreak of Klebsiella pneumoniae producing a new carbapenem-hydrolyzing class A β-lactamase, KPC-3, in a New York medical center. Antimicrob Agents Chemother 48:4793–4799 [View Article][PubMed]