TABLE 1

E. coli strains used in this study

StrainSerovarPhylogenetic groupaSequence typebCharacteristic(s)cAntibiotic resistance profiledDairy originReference(s)
FAM19195O8:H21B1Heat resistantstrRaw milk cheese15, 16
FAM21805O68:H14AHeat resistantRaw milk cheese15, 16
FAM21807O68:H14AHeat resistantstrRaw milk cheese15
FAM21808O11:H11AHeat resistantstrRaw milk cheese15
FAM21843O178:H12AHeat resistantSTR, TMPRaw milk cheese15, 16
FAM21845O68:H14AST1434Heat resistantGEN, KAN, STR, TET, TMP, SXT, AMPRaw milk cheese15
FAM22636AHeat resistantstrRaw milk cheese18
FAM22639AHeat resistantstrRaw milk cheese18
FAM22791AHeat resistantRaw milk cheese18
FAM22808AHeat resistantRaw milk cheese18
FAM22891B1Heat resistantGEN, KAN, STR, CHL, TET, TMP, SXT, AMPRaw milk cheese18
FAM22936AHeat resistantstrRaw milk cheese18
FAM22940B1Heat resistantamp, cefRaw milk cheese18
FAM22947AHeat resistantRaw milk cheese18
FAM22954AHeat resistantRaw milk cheese18
FAM22961AHeat resistantRaw milk cheese18
FAM22962AHeat resistantRaw milk cheese18
FAM22963AHeat resistantRaw milk cheese18
FAM23012AHeat resistantTETRaw milk cheese18
FAM23014AHeat resistantstrRaw milk cheese18
FAM23016AHeat resistantstrRaw milk cheese18
FAM23030AHeat resistantRaw milk cheese18
FAM23031AHeat resistantstrRaw milk cheese18
FAM23078AHeat resistantstrRaw milk cheese18
FAM23092AHeat resistantTETRaw milk cheese18
FAM23093AHeat resistantTETRaw milk cheese18
FAM23101AHeat resistantGEN, KAN, TET, TMP, SXT, AMPRaw milk cheese18
FAM23106AHeat resistantstrRaw milk cheese18
FAM23109AHeat resistantSTR, TET, AMPRaw milk cheese18
FAM23113AHeat resistantKAN, STR, CHL, TET, AMP, cef, amcRaw milk cheese18
FAM21846O16:H21AHeat sensitiveRaw milk cheesePresent study
FAM22942B1Heat sensitiveSTR, CHL, TET, AMP, cefRaw milk cheesePresent study
FAM22956B1Heat sensitivestrRaw milk cheesePresent study
FAM22996AHeat sensitiveTET, AMPRaw milk cheesePresent study
FAM22321AST4483Heat-sensitive, ESBL phenotype; TEM-1, CTX-M-14GEN, KAN, STR, CHL, TET, NAL, CIP, TMP, SXT, AMP, CEF, CXM, CTX, atmRaw milk18
FAM22871EST69, STC69Heat-sensitive, ESBL phenotype; TEM-1, CTX-M-15GEN, KAN, STR, TET, AMP, CEF, CXM, CTX, ATMRaw milk18
K-12 MG1655Heat sensitive; DSM 18039
K-12 MG1655 NALr RIFrHeat sensitive; spontaneous resistant mutantNAL, RIF95
  • 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).