Salmonella contamination of laying-hen flocks in two regions of Algeria

A preliminary epidemiological study of Salmonella contamination in laying-hen flocks was carried out in the regions of Annaba and Eltarf, Algeria, from March to October 2008 and March to November 2009. Our objectives were (i) to estimate the prevalence of infection by Salmonella spp. in seven pooled samples during the hens' laying period (ii) to identify the serotypes and antimicrobial resistance phenotypes of isolates, and (iii) to characterize the factors that may be related to Salmonella contamination in Algerian henhouses. For this purpose, 18 out of 22 operational laying-hen houses were sampled one to three times during these periods: once at the start of laying (pullets aged 22–31weeks), once in the middle of laying (47–60week) and once at the end of laying prior to depopulation (70–86week). The flocks'Salmonella status was assessed by collecting 2754 environmental samples that were analyzed according to the ISO 6579 method. The antibiotic resistance of Salmonella strains was tested as per the guidelines of the Clinical and Laboratory Standards Institute (CLSI). The relationship between each potential risk factor and the Salmonella status of laying-hen flocks was evaluated by calculating the relative risk with 95% confidence intervals. Eight flocks tested positive for Salmonella spp., with a higher prevalence at the end of laying than at either the beginning or middle. Only 19 isolates were recovered from the 2754 samples analyzed and nine different serotypes identified. S. enteritidis (n=4) was the most prevalent serovar, along with S. Kentucky and S. Hadar (n=3), followed by S. Heidelberg, S. Manhattan and S. Virchow (n=2), whereas S. Dublin, S. Typhimurium and S. Albany were found only once. Thirteen isolates were resistant to at least one antimicrobial agent. Of these, six were resistant to at least three different antimicrobial classes. Salmonella serovar Kentucky isolates were resistant to fluoroquinolones with ciprofloxacin MIC≥8mg/L. Six risk indicators were identified as potentially related to the Salmonella status of layer houses. ► Salmonella was detected in eight out of eighteen laying hen flocks that were sampled. ► Only nineteen samples were positive among 2754 analyzed. ► Nine serovars were identified. ► Thirteen isolates were resistant to antibiotic and six were multi-resistant. ► Six risk factors with a relative risk over 2 were identified as relevant.