Vergleichende Untersuchung zum Resistenzverhalten ausgewählter Bakterien von Legehennen und Eiern aus konventionellen und ökologischen Haltungssystemen

By investigating the resistance characteristics of bacteria from
organic and conventional keeping systems of laying hens, it was to
be determined to what extent different rearing systems influence
bacterial resistance patterns. For this purpose, samples from 10
organic and 10 conventional flocks were investigated 4 times
between January 2004 and April 2005. In total, 799 cloacal swabs
and 800 egg samples were taken and examined. The isolation and
identification of Salmonella spp., Listeria spp., E.
coli/Coliforms, Campylobacter spp., and Enterococcus spp. was
performed with standardized, cultural methods. Selected isolates of
the genera Salmonella (n = 44), Listeria (n = 13), Campylobacter
(C. jejuni, n = 218; C. coli, n = 46), Escherichia (E. coli, n =
545; E. fergusonii n = 18; E. hermanii n = 1 ) Citrobacter
(Citrobacter freundii n = 9), Enterobacter (Enterobacter cloacae n
= 5; Enterobacter sakazakii n = 3; Enterobacter gergoviae n = 2;
Enterobacter asburiae n = 1), Pantoea (Pantoea agglomerans n = 2)
and Enterococcus (E. faecalis, n = 361; E. faecium, n = 57; other
enterococci [E. nonfaecalis/nonfaecium], n = 569) were tested for
their resistance behaviour with respect to 29 different antibiotics
by means of microdilution. During the bacteriological investigation
of the cloacal swabs, prevalences were found for all bacteria
groups in the same order of magnitude in the different rearing
systems (Salmonella spp. 3.5 % (organic [org.]) vs. 1.8 %
(conventional [con.]); Listeria spp.: 1.3 % (org.) vs. 1.6 %
(con.); Campylobacter spp : 34.8 % (org.) or 29.0 % (con.); E.
coli: 66.4 % (org.) vs. 72.0 % (con.); Enterococcus spp.: 95.5 %
(org.) vs. 97.5 % (con.). Eggs were generally infected with less
bacteria, most of which were of the genera Enterococcus and
Escherichia, whereas Listeria, Salmonella and Campylobacter were
only rarely isolated from the samples. Salmonella of the serovar
type S. Typhimurium were resistant to up to nine antibiotics;
Salmonella of the serogroup B were resistant to up to 6 different
antibiotics. All Salmonella isolates proved to be resistant towards
spectinomycin. A high percentage of C. jejuni and C. coli isolates
showed resistance to flourquinolones; a similar resistance was
observed in the case of ampicillin and doxycycline. The Listeria
isolates were mostly sensitive towards the tested antibiotics, and
only a few strains showed resistance to clindamycin and imipenem.
E. coli isolates showed a high resistance prevalence to ß-lactames,
doxycycline, streptomycin, and cefaclor. High percentages (54.8 %)
of E. faecalis were found to be resistant to doxycycline;
macrolides were also only marginally effective. The investigated E.
faecium isolates proved to have high resistance rates to
clindamycin, fosfomycin and erythromycin, while a significant
percentage (9.1 %) of E. faecium had already been classified as
resistant to the reserve antibiotic synercid. Other enterococci
showed higher resistance rates to doxycycline, erythromycin,
fosfomycin, and rifampicine. There were no glykopeptide-resistant
enterococci. The analysis of the prevalence rates of sensitive and
resistant isolates depending on the keeping system showed a
correlation between rearing system and resistance rates: In the
case of E. faecalis, a significantly lower prevalence of resistance
to tylosin, streptomycin and doxycycline was determined among
isolates from organic farms, while significantly higher amounts of
isolates were found to be sensitive to enrofloxacin and
ciprofloxacin; however, when tested on rifampicin and imipenem, E.
faecalis behaved contrary to this. E. coli isolates from organic
layers showed significantly lower resistance rates or significantly
higher amounts of sensitive isolates with regard to nine agents,
while in the case of E. coli from conventional rearing systems,
these results could only be observed for two antibiotics. In the
case of C. jejuni, significantly better rates were observed for
isolates from organic flocks with regard to imipenem and
amoxicillin/clavulanic acid, whereas fosfomycin favoured isolates
from conventional layer flocks. In the case of 8 antibiotics, the
amounts of sensitive and resistant enterococci of the E.
nonfaecalis/nonfaecium group originating from organic farms were
found to be higher and lower respectively compared to the isolates
from conventional farms. Overall, the comparison of the amounts of
sensitive and resistant bacteria isolates and the mean MIC values
showed that the isolates from organic layer rearing systems scored
much better statistically than those from conventional systems. The
results show that organic layer flocks reduce the amount of
bacteria resistant to antibiotics, as both the resistance rates of
the selected bacteria to certain antibiotics as well as the mean
MIC values for certain antibiotic agents were lower in organic
systems than in conventional ones. Thus, organic livestock farming
contributes towards securing the continued effectiveness of
anti-infectives.