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Shortly after the introduction of fluoroquinolones into human and animal therapy an acquired resistance to these compounds was described in many bacterial species. The primary type of the resistance generally involves multiple point mutations in the genes encoding the quinolone target enzymes: gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE). The frequency of occurrence of Salmonella strains conferring quinolone resistance has recently increased significantly. Moreover, novel plasmid-mediated resistance mechanisms that can spread horizontally were reported. These include the production of enzyme protecting peptides encoded by several alleles of qnr gene (qnrA, qnrB, qnrS, qnrD) and their variants, quinolone efflux pump (qep), and finally ciprofloxacin modification by a variant of aminoglycoside acethyltransferase (aac(6’)-Ib-cr). The paper presents the background of resistance mechanisms as well as the occurrence and global spread of quinolone resistant Salmonella.
Salmonella spp. is one of the most common causes of foodborne diseases. Infections are mainly caused by the consumption of food of animal origin contaminated with Salmonella. To date, over 2,610 serotypes have been recognised, but only several show epidemiological importance. The number of human cases caused by Salmonella 1,4,[5],12:i:- has increased over the last decade, and they have become one of the most frequent serovars in many countries. The paper presents current knowledge on the spread, epidemiology, antimicrobial resistance and pathogenicity of Salmonella 1,4,[5],12:i:-, also known as monophasic Salmonella Typhimurium strains. Special attention was paid to diagnostic issues related to this particular Salmonella variant.
Salmonella strains were isolated from 24.1 % of wastes, sewage sludge and compost samples. The strains belongcd to serovars widely identified among human, animal, food and animal feeding stuffs isolates and showed high resistance to antimicrobials. Therefore Salmonella contamination of the environment should be controlled to protect human and animal health.
The aim of the study was the microbiological quality assessment of feed materials produced and used in animal feeding in Poland. Examinations were conducted in all regional laboratories dealing with animal feedstuff testing. Prevalence of Salmonella sp. and Clostridium sp. were assessed, as well as mesophilic aerobic bacteria, Enterobacteriaceae and fungi counts. The following materials were examined: 9 389 samples in the year 2003, 5 716 samples in 2004, 4 490 samples in 2005 and 6 905 samples feed materials in 2006. Assays were done following Polish standards harmonized with European standards and/or international (ISO) standards. Most often Salmonella sp. were detected in extracted oil seed meal samples, and the percentage of positive samples, depending on the examined materials, ranged from 1.5 to 7.7. The number of Enterobacteriaceae in most of the examined meat and bone meal samples did not exceed 10 cfu/g, and in oil seed meals 100 cfu/g. The highest level of contamination by Enterobacteriaceae confirmed in plant feed materials reached the level 10⁴ cfu/g. The most often confirmed level of contamination by aerobic bacteria ranged from 10² to 10⁶ cfu/g. In the mycological studies performed more than 10⁵ fungi per gram were detected in 0.8% of oil seed meal samples and more than 2% of cereal samples. The highest level of contamination by aerobic bacteria and fungi were detected in the cereal samples examined. Most examined feed material samples showed Clostridium sp. presence in titre from 0.01 to less than 0.1. Clostridium species occurred in meat and bone meal samples more often than in oil seed meal and cereal samples. The results obtained indicate an urgent need for the verification of previous microbiological criteria established for feed materials.
The globalization of trade and travel contributes to the spread of food-borne pathogens over long distance and across borders. Contemporary epidemiology and disease control need a new approach to identify the source and route of infection, especially when it originates in a different country than where the illness is originally observed. PulseNet is an international network of laboratories operating in different parts of the world and is dedicated to the molecular surveillance and outbreak detection of food-borne infections. The network was originally initiated by the Centers for Disease Control and Prevention located in Atlanta, USA, as well as several state health departments, in 1996. The goal of PulseNet was to facilitate the molecular subtyping of bacterial food-borne pathogens for epidemiologic purposes. The network began as a national program involving 10 laboratories typing a single pathogen (Escherichia coli O157:H7). Today, PulseNet USA includes over 70 participants from state, city and county public health laboratories and federal regulatory agencies. Currently, six food-borne pathogens: E coli 0157:H7; Salmonella, Listeria monocytogenes, Campylobacter, Shigella and Vibrio cholerae are being subtyped, and other bacterial, viral and parasitic organisms will be added soon. PulseNet International was established with the objective of creating worldwide regional networks utilizing molecular subtyping methods and sharing information in real-time to provide an early warning on food-borne disease outbreaks, emerging food-borne infections, and acts of food bioterrorism. From 1999 to 2006, 5 PulseNet international networks were progressively established worldwide (in chronological order): PulseNet Canada, PulseNet Europe, PulseNet Asia Pacific, PulseNet Latin America and PulseNet Middle East. These regional PulseNet networks collaborate under the umbrella of PulseNet International. PulseNet Europe gathers 61 veterinary, food and public health laboratories from 30 countries and, besides PulseNet USA and PulseNet Canada, it is the first international network with a functional central database gathering profiles of Salmonella, Listeria monocytogenes and verocytoxin-producing Escherichia coli genomic DNA. Real time sharing of typing results among participating laboratories facilitates the timely recognition of either national or international food-borne outbreaks. Routine fingerprinting enables the identification of clusters of cases that were not initially recognized as outbreaks using the classical epidemiological methods. It also defines the diversity of the micro-organism within space, its source, and time frames. Participants cooperate to modernize and elaborate new typing techniques, as well as to improve interpretative criteria used in epidemiological investigations. These goals are achievable because of the defined rules and common tools that are established throughout the network. The basic PulseNet tools are: harmonized and standardized PFGE protocols for DNA macrorestriction, common endonucleases and molecular weight markers, and a PulseNet-customized software used for image analysis, which allows the electronic sharing of results among participants’ local databases and the submission of these results to the central database. The database is accessible only by certified participants in order to insure the quality of the results. The long-term goal of PulseNet Europe, as well as that of other PulseNet international networks, is the improvement of food safety worldwide by means of enhancing surveillance of food-borne diseases and cooperation among food regulatory agencies and industry.
An efficient method for cephalosporin resistance screening in E. coli isolated from healthy farm animals has been described. One hundred and twenty nine rectal swabs were streaked on MacConkey agar and selective medium supplemented with cefotaxime. Antimicrobial resistance was tested with broth microdilution and E. coli resistant to either/or cefotaxime and ceftazidime were further tested with Etest. The observed synergy of the compounds allowed confirming the presence of defined cephalosporin resistance phenotypes. The sensitivity of cephalosporin detection by the procedure with MacConkey culture reached merely 16.7% compared to the method with selective supplement medium. Extended spectrum of beta-lactamase producing isolates was found in strains isolated from 15 samples taken from turkeys, broilers, laying hens, and pigs. The ampC-type resistance was noted in E. coli from 33 samples originating from the same animal species. None of the resistance phenotypes was observed in cattle isolates. Attention is drawn to possible public health implications of slaughtered farm animals colonised with beta-lactam resistant E. coli.
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