title: Cephalosporinases associated with outer membrane vesicles released by Bacteroides spp. protect gut pathogens and commensals against β-lactam antibiotics.
abstract: OBJECTIVE
  To identify β-lactamase genes in gut commensal Bacteroides species and to assess the impact of these enzymes, when carried by outer membrane vesicles (OMVs), in protecting enteric pathogens and commensals.
  
  
  METHODS
  A deletion mutant of the putative class A β-lactamase gene (locus tag BT_4507) found in the genome of the human commensal Bacteroides thetaiotaomicron was constructed and a phenotypic analysis performed. A phylogenetic tree was built from an alignment of nine Bacteroides cephalosporinase protein sequences, using the maximum likelihood method. The rate of cefotaxime degradation after incubation with OMVs produced by different Bacteroides species was quantified using a disc susceptibility test. The resistance of Salmonella Typhimurium and Bifidobacterium breve to cefotaxime in liquid culture in the presence of B. thetaiotaomicron OMVs was evaluated by measuring bacterial growth.
  
  
  RESULTS
  The B. thetaiotaomicron BT_4507 gene encodes a β-lactamase related to the CepA cephalosporinase of Bacteroides fragilis. OMVs produced by B. thetaiotaomicron and several other Bacteroides species, except Bacteroides ovatus, carried surface-associated β-lactamases that could degrade cefotaxime. β-Lactamase-harbouring OMVs from B. thetaiotaomicron protected Salmonella Typhimurium and B. breve from an otherwise lethal dose of cefotaxime.
  
  
  CONCLUSIONS
  The production of membrane vesicles carrying surface-associated β-lactamases by Bacteroides species, which constitute a major part of the human colonic microbiota, may protect commensal bacteria and enteric pathogens, such as Salmonella Typhimurium, against β-lactam antibiotics.
authors.affiliation: Gut Health and Food Safety Programme, Institute of Food Research, Norwich NR4 7UA, UK regis.stentz@ifr.ac.uk.
authors.forename: Régis
authors.initials: R
authors.lastname: Stentz
authors.affiliation: Gut Health and Food Safety Programme, Institute of Food Research, Norwich NR4 7UA, UK.
authors.forename: Nikki
authors.initials: N
authors.lastname: Horn
authors.affiliation: Analytical Sciences Unit, Institute of Food Research, Norwich NR4 7UA, UK.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Cross
authors.affiliation: Analytical Sciences Unit, Institute of Food Research, Norwich NR4 7UA, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Salt
authors.affiliation: School of Biological Sciences, The University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Charles
authors.initials: C
authors.lastname: Brearley
authors.affiliation: Norwich Medical School, The University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Livermore
authors.affiliation: Gut Health and Food Safety Programme, Institute of Food Research, Norwich NR4 7UA, UK Norwich Medical School, The University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Simon R
authors.initials: SR
authors.lastname: Carding
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001439:Bacteroides / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D001644:Bifidobacterium / Q000187:drug effects / Q000254:growth & development; D001711:Biotransformation; D002510:Cephalosporinase / Q000235:genetics / Q000378:metabolism*; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D055354:Exosomes / Q000201:enzymology*; D041981:Gastrointestinal Tract / Q000382:microbiology; D006801:Humans; D006868:Hydrolysis; D056265:Microbial Interactions; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D010802:Phylogeny; D012486:Salmonella typhimurium / Q000187:drug effects / Q000254:growth & development; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D047090:beta-Lactams; D002510:Cephalosporinase
keywords: Salmonella; gut microbiota; protective effect; β-lactamases