Increase Over Time in Prevalence of Multiple Antibiotic Resistance in Listeria from Poultry in Spain

Similar Listeria contamination rates were observed in 1993 and 2006 but multiple drug-resistance was more common in 2006, according to new research from the University on León in Spain.
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The aim of this study was to determine and compare the antibiotic resistance profiles of Listeria monocytogenes isolates obtained from poultry in north-western Spain in 1993 and 2006, explain Alicia Alonso-Hernando and colleagues at the University of León in Spain in a paper published online in the journal, Food Control. The prevalence of Listeria spp. and L. monocytogenes was also investigated.

A total of 202 samples were analysed (100 in 1993 and 102 in 2006). Samples taken in 1993 and 2006 showed a similar (P>0.05) prevalence for both Listeria spp. (95.0 per cent and 92.1 per cent, respectively) and L. monocytogenes (32.0 per cent and 24.5 per cent). In both 1993 and 2006 the species most frequently detected was Listeria innocua, followed by L. monocytogenes. Other species isolated were Listeria welshimeri, Listeria grayi and Listeria ivanovii.

L. monocytogenes isolates (68) were tested by disc diffusion assay for their resistance to 15 drugs currently used in veterinary and human therapy. All isolates displayed resistance to at least one antibiotic. Excluding nalidixic acid, to which most strains are intrinsically resistant, 37.2 per cent of strains in 1993 and 96.0 per cent in 2006 showed resistance to at least one antibiotic.

Multi-resistance, i.e. resistance to two or more antibiotics, was less common in 1993 than in 2006 (18.6 per cent and 84.0 per cent, respectively; P<0.001).

The average number of antibiotics to which the strains were resistant was lower (P<0.001) in 1993 (1.6) than in 2006 (4.2).

An increase (P<0.05) in the percentage of resistant strains was observed between 1993 and 2006 for six different drugs: gentamicin, streptomycin, neomycin, enrofloxacin, ciprofloxacin and furazolidone.

In this research, the prevalence and the antibiotic susceptibility of L. monocytogenes in poultry samples from the same origin in North-Western Spain in the 1990s and the 2000s were compared for the first time, according to the researchers in León.

They explain that the increase in antibiotic resistance from 1993 to 2006 constitutes a matter for concern and confirms a general worldwide pattern among many groups of bacteria.

The high prevalence of L. monocytogenes in poultry suggests the crucial role of food handlers in preventing listeriosis in consumers, concluded Alonso-Hernando and colleagues. They also highlighted the need to reduce the prevalence of L. monocytogenes in poultry and prevent the emergence or selection of antibiotic-resistant strains.


Alonso-Hernando A., M. Prieto, C. García-Fernández, C. Alonso-Calleja and R. Capita. 2011. Increase over time in the prevalence of multiple antibiotic resistance among isolates of Listeria monocytogenes from poultry in Spain. Food Control (article in press) doi:10.1016/j.foodcont.2011.06.006

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August 2011
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