Comparative Analysis of Antibiotic Resistance Characteristics of Gram‐negative Bacteria Isolated from Laying Hens and Eggs in Conventional and Organic Keeping Systems in Bavaria, Germany

Abstract

By investigating the prevalence and resistance characteristics of Gram-negative bacteria from organic and conventional kept laying hens against 31 (Campylobacter: 29) different antibiotics using the microdilution method, we determined to what extent different keeping systems influence bacterial resistance patterns. For this purpose, samples from 10 organic and 10 conventional flocks in Bavaria (Germany) were investigated four times between January 2004 and April 2005. Altogether, 799 cloacal swabs and 800 eggs (contents and shells) were examined. The bacterial investigation performed with standardized cultural methods showed prevalence for all bacteria groups in about the same order of magnitude in the two different keeping systems: Salmonella spp. 3.5% (organic ([org])) versus 1.8% (conventional ([con])); Campylobacter spp. 34.8%(org) versus 29.0%(con) and E. coli 64.4%(org) versus 69.0%(con). Coliforms (Citrobacter, Enterobacter, Pantoea) were only isolated in single cases. In eggs, generally less bacteria were detected, predominantly Escherichia; Salmonella and Campylobacter were only scarcely isolated. Salmonella enterica ssp. enterica serovar Typhimurium (n=10) were resistant to up to nine, S. of the serogroup B (n=4) up to six antibiotics. All tested Salmonella (n=23) proved to be resistant to spectinomycin. Escherichia coli (n=257(org) and 276(con)) from organic layers showed significant lower resistance rates and higher rates of susceptible isolates to nine agents, namely amoxicillin/clavulanic acid, ampicillin, cefaclor, cefoxitin, cefuroxime, doxycycline, mezlocillin, neomycin and piperacillin. In contrast, only two antibiotics turned out to be more effective in conventional isolates (gentamicin and tobramycin). In the case of Campylobacter jejuni (n=118(org) and 99(con)), statistically significantly better rates were observed for isolates from organic flocks concerning imipenem and amoxicillin/clavulanic acid, whereas fosfomycin was more potent in strains from conventional flocks. Results of this study indicate that both resistance rates and mean minimum inhibitory concentrations of bacteria isolated from organic keeping systems have lower values than those from conventional ones, particularly recognizable for E. coli. Thus, organic livestock farming with its restrictions and additional requirements contributes to further effectiveness of antibiotics.

Antimicrobial resistance ofEscherichia coliandEnterococcus faecalisin housed laying-hen flocks in Europe

“…This is in contrast to the studies of Schwaiger et al [17,18] who found significantly lower levels of antimicrobial resistance in E. coli and faecal enterococci in free-range organic laying hens compared to laying hens housed in conventional battery cages. There are several possible explanations for the ambiguous association between the non-cage housing types and the level of MDR.…”

“…This is in accord with previous studies in laying hens [17,18,29]. The overall limited antimicrobial usage in egg-producing laying hens, as shown in the results, could play a role in this observation since it is generally accepted that the use of antimicrobials is one of the major risk factors for the development and spread of antimicrobial resistance [30,31].…”

“…Presently it is not clear whether the different housing and management systems for laying hens will influence the occurrence of antimicrobial resistance. Recent reports indicate that both in poultry and other animal species the move from conventional indoor production towards free-range and organic production exerts a beneficial effect on the levels of antimicrobial resistance in zoonotic and indicator bacteria [16][17][18][19]. On the other hand it has been shown that this move to non-cage housing systems resulted in an increased incidence of bacterial diseases [20,21], which could potentially lead to increased antimicrobial usage.…”

Scientific Opinion on the public health risks of table eggs due to deterioration and development of pathogens

“…This pathogen can also be found in laying hen farms (Doyle, 1984;Rasschaert et al, 2007;Sulonen et al, 2007;Schwaiger et al, 2008;Cox et al, 2009;Messelhäusser et al, 2011). The prevalence of Campylobacter in laying hen farms varies among studies and countries from 35 % (Rasschaert et al, 2007) to 84 % (Sulonen et al, 2007).…”

“…Eggshell contamination by Campylobacter has not been widely investigated. Some studies have reported that the presence of Campylobacter on eggshells is uncommon despite flock infection (Doyle, 1984;Shane et al, 1986;Jones and Musgrove, 2007;Schwaiger et al, 2008;Widdicombe et al, 2009). Shane et al (1986) demonstrated that C. jejuni cannot survive more than 16 hours in a dry environment.…”