Screening of benzalkonium chloride resistance in Listeria monocytogenes strains isolated during cold smoked fish production.
OBJECTIVE
To determine the susceptibility to disinfectants and cross-resistance to antibiotics in Listeria monocytogenes strains isolated from fish products and the fish-processing environment.


RESULTS
Minimal inhibitory concentration assessment, using the agar dilution method, showed 108 of 255 L. monocytogenes isolates with low susceptibility to benzalkonium chloride (BC), commonly used in food industries. Most of them are from raw products of farmed fish during processing, while the remaining resistant isolates were mainly from the environment and finished products irrespective of the fish species. Two BC-resistant isolates were resistant to ethidium bromide (EB). The conservation of resistance after plasmid curing suggested that the resistance genes are not plasmid associated. EB accumulation assays demonstrated that the two BC(R) EB(R) isolates used an efflux pump to expel these substrates whereas a different mechanism was probably used by the majority of the strains with BC(R) EB(S) pattern. No cross-resistance was found with antibiotics.


CONCLUSIONS
This study highlights the difference in susceptibilities to BC for L. monocytogenes strains isolated from fish-processing plants and in resistance mechanisms to BC developed by these bacteria.


CONCLUSIONS
The presence of BC resistant L. monocytogenes strains could contribute to their adaptation and so explained their survival and persistence in the fish-processing environment.
Soumet
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C
Agence Française de Sécurité Sanitaire des Aliments (AFSSA), Laboratoire d'études et de recherches sur les médicaments vétérinaires et les désinfectants, La Haute Marche, Fougères. c.soumet@afssa.fr
Ragimbeau
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C
Maris
P
P
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001548:Benzalkonium Compounds / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004996:Ethidium / Q000494:pharmacology; D005396:Fish Products / Q000382:microbiology*; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000187:drug effects
D000900:Anti-Bacterial Agents; D001548:Benzalkonium Compounds; D004996:Ethidium