title: Presence of AmpC beta-lactamases, CSA-1, CSA-2, CMA-1, and CMA-2 conferring an unusual resistance phenotype in Cronobacter sakazakii and Cronobacter malonaticus.
abstract: Here we describe the presence of two very similar but unusual variants of AmpC cephalosporinase in each Cronobacter sakazakii and C. malonaticus isolates conferring resistance exclusively to first generation cephalosporins. During a survey on the antibiotic resistance patterns of C. sakazakii and C. malonaticus strains isolated from a milk powder production facility, originally two different phenotypes regarding the susceptibility/resistance for the two beta-lactam antibiotics ampicillin (amp) and cephalothin (ceph) were observed: (i) isolates being susceptible for both antibiotics (amp(S)/ceph(S)), and (ii) strains exhibiting susceptibility to ampicillin but resistance to cephalothin (amp(S)/ceph(R)). The latter phenotype (amp(S)/ceph(R)) was observed in the majority of the environmental strains from the facility. Analysis of whole genome sequences of C. sakazakii revealed a gene putatively coding for an AmpC beta-lactamase. Consequently, the ampC genes from both species and both phenotypes were subjected to a cloning approach. Surprisingly, when expressed in Escherichia coli, all transformants exhibited the amp(S)/ceph(R) phenotype regardless of (i) the phenotypic backgrounds or (ii) the AmpC amino acid sequences of the original strains from which the clones were derived. The novel AmpC beta-lactamases were designated CSA-1 and CSA-2 (from C. sakazakii) and CMA-1 and CMA-2 (from C. malonaticus). The observed variations in the minimum inhibitory concentration (MIC) levels for cephalothin (wt compared to transformants) suggest that this feature is a target of a yet unknown regulatory mechanism present in the natural Cronobacter background but absent in the neutral E. coli host.
authors.affiliation: Institute for Food Safety and Hygiene, Vetsuisse Faculty, University of Zurich , Zurich, Switzerland .
authors.forename: Andrea
authors.initials: A
authors.lastname: Müller
authors.forename: Herbert
authors.initials: H
authors.lastname: Hächler
authors.forename: Roger
authors.initials: R
authors.lastname: Stephan
authors.forename: Angelika
authors.initials: A
authors.lastname: Lehner
mesh_terms: D000667:Ampicillin / Q000378:metabolism / Q000627:therapeutic use; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002417:Cattle; D002512:Cephalothin / Q000378:metabolism / Q000627:therapeutic use; D059126:Cronobacter / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D044083:Cronobacter sakazakii / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005612:Freeze Drying; D015870:Gene Expression; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000382:microbiology; D008969:Molecular Sequence Data; D010957:Plasmids / Q000737:chemistry*; D011208:Powders; D013045:Species Specificity; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D007527:Isoenzymes; D011208:Powders; D000667:Ampicillin; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; D002512:Cephalothin