Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/3849
Antimicrobial resistance is a growing problem in human as well as veterinary medicine. Antimicrobial resistance rates of bacteria from production animals and their food products are available for many countries but until now little has been known about the prevalence in Iceland. The main objective of this study was to determine the prevalence of antimicrobial resistant bacteria (Salmonella spp., Campylobacter spp. and Escherichia coli) in production animals in Iceland and if these resistant bacteria were transferred from animals to humans, possibly through food.
A total of 163 Salmonella strains and 362 Campylobacter strains, isolated from broilers and pigs in the national Salmonella and Campylobacter surveillance programmes in the years 2001-2005, were available for study. A total of 482 E. coli isolates from healthy pigs, broiler chicken, pork, broiler meat, broiler feed, slaughterhouse personnel and outpatients in the years 2005-2008 were collected and tested. Isolates were tested for antimicrobial susceptibility using a microbroth dilution method (VetMIC) and resistant strains were compared using Pulsed Field Gel Electrophoresis (PFGE), Randomly Amplified Polymorphic DNA (RAPD) and phage typing.
The overall prevalence of resistance among Salmonella spp. was 13.6% in chickens and 12.8% in pigs. Twenty one isolates (12.8%) were resistant to one or more antimicrobials, 19 S. Typhimurium strains, one S. Infantis strain and one S. Worthington strain. Of the 19 resistant S. Typhimurium strains, 16 were multiresistant (to ≥3 antimicrobial agents) and of these 15 had identical or closely related PFGE patterns and were of phage type DT 104.
The prevalence of resistance among Campylobacter isolates was 6.9%, although none were multiresistant. Resistance to ampicillin was most commonly observed (3.6%) followed by resistance to enrofloxacin (3%), nalidixic acid (1.9%) and oxytetracyclin (0.3%), with cross-resistance between enrofloxacin and nalidixic acid. Resistance rates among C. coli isolates (53.8%) were much higher than among C. jejuni isolates (5.2%) and resistance patterns differed. Macrorestriction with SmaI and KpnI restriction enzymes yielded 13 different pulsotypes, none of wich indicated a predominant genotype. Specific pulsotypes with uniform resistance patterns arising on geographically separated farms indicates clonal dissemination.
The resistance rates among E. coli isolates were 54.1% and 28% (cecal and meat samples) among pigs, 33.6% and 52% (cecal and meat samples) among broilers, 31.8% in broiler feed, 39.1% among slaughterhouse personnel and 23.1% among outpatients. Prevalence of resistance to ciprofloxacin and nalidixic acid increased significantly between sampling in 2005-2007 and in 2008 (p<0.0001) but decreased for other antimicrobials. The majority (78.6%) of the resistant E. coli isolates was genotypically diverse based on PFGE fingerprint analyses and clustering was limited. The same resistance pattern and pulsotype was found among isolates from broiler meat and a slaughterhouse worker and closely related isolates were found in humans, broilers, broiler meat and broiler feed.
The prevalence of antimicrobial resistance in Salmonella spp. and Campylobacter spp. in pigs and poultry in Iceland is low. However we found a multiresistant S. Typhimurium clone that causes concern. Prevalence of antimicrobial resistant E. coli from production animals and their food products in Iceland was moderate to high, especially in broilers and broiler meat. Of notice was resistance to quinolones, particularly among broiler and broiler meat isolates as there is no known antimicrobial selection pressure in the broiler production in Iceland. There was some clustering of isolates of different origin, indicating spread of antimicrobial resistant E. coli from animals to humans. Diverse resistance patterns and pulsotypes suggest the presence of a large population of resistant E. coli in production animals in Iceland. Data presented in this thesis support the hypothesis that feed is a source of antimicrobial resistant bacteria in chicken and that chicken and their products may be a source of fluoroquinolone resistant E. coli in humans. Continuous resistance surveillance in Iceland is important and further research on the source of resistant clones and possible transmission to humans is needed.