TABLE 1

E. coli strains used in this study

StrainSerovarPhylogenetic groupaSequence typebCharacteristic(s)cAntibiotic resistance profiledDairy originReference(s)
FAM19195O8:H21B1 Heat resistantstrRaw milk cheese 15, 16
FAM21805O68:H14A Heat resistant Raw milk cheese 15, 16
FAM21807O68:H14A Heat resistantstrRaw milk cheese 15
FAM21808O11:H11A Heat resistantstrRaw milk cheese 15
FAM21843O178:H12A Heat resistantSTR, TMPRaw milk cheese 15, 16
FAM21845O68:H14AST1434Heat resistantGEN, KAN, STR, TET, TMP, SXT, AMPRaw milk cheese 15
FAM22636 A Heat resistantstrRaw milk cheese 18
FAM22639 A Heat resistantstrRaw milk cheese 18
FAM22791 A Heat resistant Raw milk cheese 18
FAM22808 A Heat resistant Raw milk cheese 18
FAM22891 B1 Heat resistantGEN, KAN, STR, CHL, TET, TMP, SXT, AMPRaw milk cheese 18
FAM22936 A Heat resistantstrRaw milk cheese 18
FAM22940 B1 Heat resistantamp, cefRaw milk cheese 18
FAM22947 A Heat resistant Raw milk cheese 18
FAM22954 A Heat resistant Raw milk cheese 18
FAM22961 A Heat resistant Raw milk cheese 18
FAM22962 A Heat resistant Raw milk cheese 18
FAM22963 A Heat resistant Raw milk cheese 18
FAM23012 A Heat resistantTETRaw milk cheese 18
FAM23014 A Heat resistantstrRaw milk cheese 18
FAM23016 A Heat resistantstrRaw milk cheese 18
FAM23030 A Heat resistant Raw milk cheese 18
FAM23031 A Heat resistantstrRaw milk cheese 18
FAM23078 A Heat resistantstrRaw milk cheese 18
FAM23092 A Heat resistantTETRaw milk cheese 18
FAM23093 A Heat resistantTETRaw milk cheese 18
FAM23101 A Heat resistantGEN, KAN, TET, TMP, SXT, AMPRaw milk cheese 18
FAM23106 A Heat resistantstrRaw milk cheese 18
FAM23109 A Heat resistantSTR, TET, AMPRaw milk cheese 18
FAM23113 A Heat resistantKAN, STR, CHL, TET, AMP, cef, amcRaw milk cheese 18
FAM21846O16:H21A Heat sensitive Raw milk cheesePresent study
FAM22942 B1 Heat sensitiveSTR, CHL, TET, AMP, cefRaw milk cheesePresent study
FAM22956 B1 Heat sensitivestrRaw milk cheesePresent study
FAM22996 A Heat sensitiveTET, AMPRaw milk cheesePresent study
FAM22321 AST4483Heat-sensitive, ESBL phenotype; TEM-1, CTX-M-14GEN, KAN, STR, CHL, TET, NAL, CIP, TMP, SXT, AMP, CEF, CXM, CTX, atmRaw milk 18
FAM22871 EST69, STC69Heat-sensitive, ESBL phenotype; TEM-1, CTX-M-15GEN, KAN, STR, TET, AMP, CEF, CXM, CTX, ATMRaw milk 18
K-12 MG1655 Heat sensitive; DSM 18039
K-12 MG1655 NALr RIFr Heat sensitive; spontaneous resistant mutantNAL, RIF 95
  • a Determined by quadruplex and group C- and E-specific PCRs (76).

  • b Determined by use of a 7-allele multilocus sequence typing scheme (MLST Database at UoW) (77).

  • c All strains tested positive for catalase activity. Heat resistant, clpK and orfI positive by PCR and phenotypically heat resistant (<1-log reduction in CFU after 30 min of incubation at 55°C) (18).

  • d Antimicrobial resistances were determined according to CLSI guidelines (78). Capital and lowercase letters indicate resistant and intermediate phenotypes, respectively. Antimicrobials tested were gentamicin (GEN), kanamycin (KAN), streptomycin (STR), chloramphenicol (CHL), tetracycline (TET), nalidixic acid (NAL), ciprofloxacin (CIP), trimethoprim (TMP), sulfamethoxazole-trimethoprim (19:1) (SXT), ampicillin (AMP), cefoxitin (FOX), cephalothin (CEF), cefuroxime (CXM), cefotaxime (CTX), cefepime (FEP), aztreonam (ATM), amoxicillin-clavulanic acid (20:10) (AMC), and ertapenem (ETP).