Comparison of methods for the microbiological identification and typing of Cronobacter species in infant formula.

Cronobacter species represent an emerging opportunistic foodborne pathogen associated with meningitis and necrotizing enterocolitis in infants. Current evidence indicates that powdered infant formula (PIF) is the main source of Cronobacter contamination. A total of 75 strains of Cronobacter spp. from different geographic regions, as well as from PIF processing environments, were identified and typed with different methods, including biochemical profiling by the API 20E system (bioMérieux, Marcy l'Etoile, France), protein profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and genotypic profiling by ribotype. Analysis by MALDI-TOF MS and biochemical identification was more accurate compared with ribotype analysis. However, MALDI-TOF MS typing and ribotype analysis showed more discriminatory ability compared with biochemical phenotyping. In conclusion, MALDI-TOF MS is a rapid and reliable tool to identify Cronobacter spp. in PIF and has the potential to trace dissemination of Chronobacter along the production chain.

Cloning and sequencing of mammalian glutathione reductase cDNA.

The molecular cloning of a partial cDNA to mouse glutathione reductase mRNA and of a full-length cDNA to the mRNA of the human enzyme is described. An initial cDNA clone designated lambda GRM-B11 was isolated by plaque-screening of an induced mouse cDNA expression library in the lambda gt11 vector with a rabbit antibody probe to human glutathione reductase. 125Iodine-labelled whole anti-rabbit immunoglobulin was used as second antibody. EcoRI digestion of the lambda GRM-B11 clone released a 720-bp fragment which was identified as a partial mouse glutathione reductase cDNA by the following techniques. (a) Escherichia coli Y1089 lysogenized with lambda GRM-B11 could be induced to synthesize a recombinant polypeptide whose antigenicity to anti-(glutathione reductase) serum was established by SDS/polyacrylamide gel electrophoresis and subsequent immunoblotting. (b) The GRM-B11 sequence, recloned in the Bluescript vector to give the plasmid pGRM-B11, was found to code for a polypeptide consisting of 242 amino acid residues exhibiting 82% identities with the known amino acid sequence of the human glutathione reductase from position 77 to 318. The insert of the pGRM-B11 plasmid was used as a bona fide nucleic acid probe to screen mouse and human cDNA libraries prepared in the lambda gt11 or in the lambda gt10 vector. The first full-length cDNA clone (lambda GRH-Mev10) was identified in a human cDNA library based on RNA of human placental cells. Its insert was composed of three EcoRI fragments of 720, 613 and 336 bp. The three fragments were recloned in the Bluescript vector and sequenced. The largest fragment (pGRH-B) is colinear with the mouse sequence cloned in the pGRM-B11 plasmid. The fragment of intermediate size (pGRH-CT) comprises the 3' end of the mRNA and the poly(A) tail while the short fragment (pGRH-NT) corresponds to the 5' region of the mRNA. The amino acid sequence deduced from the nucleotide sequences of the three subclones is identical with the known sequence of the mature glutathione reductase from human erythrocytes in all 478 positions.