Surface-adherent Growth of Listeria monocytogenes is Associated with Increased Resistance to Surfactant Sanitizers and Heat

Abstract

Surface-adherent microcolonies of Listeria monocytogenes were obtained by growing cells on glass slides immersed in a low nutrient medium containing excess glucose. The susceptibility of the adherent populations to benzalkonium chloride (100, 400, and 800 ppm solutions), anionic acid sanitizer (200 and 400 ppm solutions), and heat (55 and 70°C) was determined. Adherent microcolony cells decreased by 2 to 3 log cycles immediately after exposure to the sanitizers. The remaining population of microcolony cells survived 20 min of exposure demonstrating resistance to both sanitizers at all concentrations. Adherent single cells exhibited an initial 3 to 5 log decline in numbers and reached undetectable levels after 12 to 16 min of exposure to the sanitizers. Planktonic cells were reduced to undetectable levels after 30 sec exposure to the lowest concentration of each sanitizer. Removing adherent cells from the surface increased their sanitizer susceptibility to near that of planktonic cells. Heating adherent microcolonies at 70°C for 5 min resulted in a less than 5-log decrease in population with a surviving population of over 10 cfu/sq cm. These results demonstrate the ability of L. monocytogenes to develop resistance to inactivating agents when exposed to specific growth environments.

Resistance mechanisms of bacteria to antimicrobial compounds

“…Compared with their planktonic counterparts, attached bacteria typically exhibit enhanced resistance to antimicrobial agents (Brown and Gilbert, 1993), biocides (Blenksinsopp et al, 1992), and heat (Frank and Koffi, 1990). Studies have demonstrated the resistance of biofilms of bacteria such as Escherichia coli towards cetrimide (Evans et al, 1990), or Burkholderia cepacia and Serratia marcescens towards biguanides (Marrie and Costerton, 1981;Pallent et al, 1983), isothiazolones and quaternary ammonium compounds (Costerton and Lashen, 1984).…”

Colonization of Tomatoes by Salmonella Montevideo Is Affected by Relative Humidity and Storage Temperature

“…A biofilm is an assemblage of microbial cells that is irreversibly associated with a surface and enclosed in a matrix of primarily polysaccharide material (7). It has been well documented that microorganisms colonizing surfaces as part of a biofilm are more resistant to environmental challenges than their planktonic counterparts in suspension (10).…”

Ocorrência de Escherichia coli 0157:H7 em vegetais e resistência aos agentes de desinfecção de verduras

“…Nessas condições, os resultados da literatura deixam claro que a eficácia dos desinfetantes, aplicados tanto à microbiota natural quanto à cepas de microrganismos artificialmente inoculadas em superfícies de frutas e verduras, é muito menor do que nos testes de suspensão. Além disso, mesmo que a característica de resistência das cepas aos diferentes princípios ativos dos desinfetantes seja similar, as diferenças nas características de adesividade e formação de biofilmes podem interferir na eficácia dos desinfetantes [1,13,20,23,27,29,35,37,45] Outro fator importante a considerar é o fato de desinfetantes com o mesmo princípio ativo, porém, de marcas comerciais distintas, apresentarem diferença na eficácia antimicrobiana [17]. Assim, é imprescindível o monitoramento periódico da qualidade dos produtos disponíveis no mercado, para garantir segurança dos tratamentos de desinfecção aplicados.…”