title: Effects of exposure to quaternary-ammonium-based biocides on antimicrobial susceptibility and tolerance to physical stresses in bacteria from organic foods.
abstract: In the present study, a collection of 76 biocide-sensitive bacterial strains isolated from organically produced food were adapted by repeated exposure to increasing concentrations of the quaternary ammonium compounds (QACs) benzalkonium chloride (BC) and hexadecylpyridinium chloride (HDP). The sensitivity of both wildtype strains and their corresponding QAC-adapted strains to other biocides and to antibiotics was studied. QAC tolerance increased in 88.2% of strains for BC and in 30.3% of strains for HDP, with increases in minimum inhibitory concentrations between 2 and over 100 fold. Adaptive resistance was stable after 20 subcultures in biocide-free medium for 7 and 5 of the BC- and HDP-adapted strains, respectively. Adaptation to BC and HDP also reduced the susceptibility to other biocides, mainly hexachlorophene (CF), didecyldimethylammonium bromide (AB), triclosan (TC) and chlorhexidine (CH). BC-adapted strains showed increased antibiotic resistance to ampicillin (AM) followed by sulfamethoxazol (SXT) and cefotaxime (CTX), and some showed increased sensitivity to ceftazidime (CAZ), CTX, AM and STX. Changes in antibiotic resistance in HDP-adapted strains were more heterogeneous and strain-dependent. Main efflux pump genes detected in QAC-adapted strains were acrB, sugE, norC, qacE and qacH, as well as antibiotic resistance genes aac(6_)-Ie-aph(2_)-Ia, aph(2_)-Ic, ant(4_)-Ia, lsa, mrsA/B, ereA, ermB and cat. Membrane anisotropy experiments revealed that QAC adaptation induced an increase in membrane rigidity in the case of BC, while response to HDP was more heterogeneous and strain-dependent. Growth capacity was significantly higher in some QAC-adapted strains and strain-dependent changes in heat tolerance were also detected in QAC-adapted strains. Gastric acid or bile resistances do not seem to be influenced by QAC adaptation.
authors.affiliation: Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Rebeca
authors.initials: R
authors.lastname: Gadea
authors.affiliation: Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Miguel Ángel
authors.initials: MÁ
authors.lastname: Fernández Fuentes
authors.affiliation: Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: Pérez Pulido
authors.affiliation: Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain. Electronic address: agalvez@ujaen.es.
authors.forename: Antonio
authors.initials: A
authors.lastname: Gálvez
authors.affiliation: Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Ortega
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D001548:Benzalkonium Compounds / Q000494:pharmacology; D004202:Disinfectants / Q000737:chemistry / Q000494:pharmacology*; D004352:Drug Resistance, Microbial / Q000235:genetics; D005516:Food Microbiology; D058870:Food, Organic / Q000382:microbiology*; D008560:Membrane Fluidity / Q000187:drug effects; D026901:Membrane Transport Proteins / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics; D008826:Microbial Sensitivity Tests; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D001548:Benzalkonium Compounds; D004202:Disinfectants; D026901:Membrane Transport Proteins; D000644:Quaternary Ammonium Compounds
keywords: Adaptation; Antibiotics; Biocides; Quaternary ammonium compounds; Resistance