Salmonella Strain's Path to Virulence Uncovered
Published: April 21, 2009
Source : USDA Agricultural Research Service
Agricultural Research Service (ARS) scientists have uncovered genetic evidence about the evolutionary path that transformed Salmonella enteritidis from an innocuous bacterium into a virulent pathogen.
S. enteritidis, like many bacteria, reproduces very quickly--every 20 minutes in optimal conditions, according to veterinary medical officer Jean Guard-Bouldin in the ARS Egg Safety and Quality Research Unit in Athens, Ga.
"To reduce current levels of infection, we're studying how S. enteritidis evolves and infects hens on the farm," says Guard-Bouldin. "Using mutational changes in the Salmonella genome as a sort of 'breadcrumb trail,' we've tried to determine the first time this bacterium became capable of getting inside the egg from hen reproductive organs."
"To reduce current levels of infection, we're studying how S. enteritidis evolves and infects hens on the farm," says Guard-Bouldin. "Using mutational changes in the Salmonella genome as a sort of 'breadcrumb trail,' we've tried to determine the first time this bacterium became capable of getting inside the egg from hen reproductive organs."
Such a fast reproductive pace allows the organism to accumulate genetic variations. Only healthy competitors go on to reproduce, survive and develop the mechanisms needed to infect the egg. Using DNA analysis, Guard-Bouldin is looking at evolutionary evidence to determine how some S. enteritidis strains became pathogenic. Studying how S. enteritidis evolves and infects hens on the farm may someday help reduce levels of infection.
Guard-Bouldin and her colleagues found S. enteritidis strains to be so similar genetically that they appear identical, yet they may behave differently inside the hen. To distinguish between the apparently identical genomes, researchers must use a technique called "whole-genome mutational mapping" to analyze multiple strains.
Guard-Bouldin and her colleagues found S. enteritidis strains to be so similar genetically that they appear identical, yet they may behave differently inside the hen. To distinguish between the apparently identical genomes, researchers must use a technique called "whole-genome mutational mapping" to analyze multiple strains.
Through these analyses, the researchers developed a timeline of when S. enteritidis first became capable of getting inside the egg from hen reproductive organs--approximately 36 years ago. It appears that a large-scale swap of DNA between strains, in association with the emergence of egg contamination, created a hybrid strain of S. enteritidis.
This hybrid strain had the ability to contaminate the internal contents of eggs. Later, it also split very quickly into two lineages, each carrying one virus. Both of the newly split lineages continued to evolve and eventually began to vary in their ability to contaminate eggs and to survive on the farm.
The data from this research is being entered into a publicly available database by the National Center for Biotechnology Information, part of the National Institutes of Health.
"This information about differences between genomes could help streamline the process of finding out how human disease organisms evolve to become more virulent," says Guard-Bouldin. "The main focus for us now is to continue sequencing entire genomes and searching for more genetic changes that help us understand the Salmonella organism.
"Up until recently, genomic techniques for delving this deeply into the genetic code of multiple Salmonella strains weren't available or cost effective.
"If we can understand how Salmonella evolved to become pathogenic, perhaps we can apply the same principles to other foodborne pathogens and begin to study foodborne illness the way influenza is being monitored-with equal emphasis on the importance of small, as well as large, genetic changes."
According to the Centers for Disease Control and Prevention, about 40,000 cases of salmonellosis are reported in the United States every year. Most result in diarrhea, fever, and abdominal cramps lasting 4 to 7 days, but severe cases caused about 70 deaths in 2000. Adequate cooking eliminates the risk of infection from eggs.
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Meriden Animal Health Limited
16 de junio de 2009
There is direct evidence that antimicrobial use in animals selects for antimicrobial-resistant non-typhoid salmonella serotypes. These bacteria have been transmitted to humans in food or through direct contact with animals. Antimicrobial resistance limits the therapeutic options available to veterinarians and physicians for the subset of clinical cases of non-typhoid salmonella which require treatment.
A recent example is a clone of S. typhimurium DT104, resistant to ampicillin, tetracycline, streptomycin, chloramphenicol and sulphonamides, which has become prevalent in many countries including the UK, Germany and the USA.
Following the introduction of fluoroquinolones for use in food-producing animals, the emergence of salmonella serotypes with reduced susceptibility to fluoroquinolones in humans has become a cause for particular concern. This phenomenon has been observed in countries such as France, Germany, Ireland, the Netherlands, the Russia Federation, Spain and the UK.
Many industry experts have realised that certain essential oils have antimicrobial effects and have tried to apply this knowledge to salmonellosis control in poultry farms. Amongst the various essential oils available as feed additives, natural phytobiotics such as oregano essential oils stand out, as they have been found to assist in controlling and preventing salmonellosis in poultry farms. This was recently proven in an experiment by Penalver et al. (2005), who studied the antimicrobial activity of five different essential oils against origin strains of the Enterobacteriaceae family described as follows.
An in vitro assay measuring the antimicrobial activity of essential oils of Coridothymus capitatus (Spanish origanum), Satureja montana, Thymus mastichina (Spanish Origanum majorana), Thymus zygis (Spanish variety of Thymus vulgaris) and Origanum vulgare (Orego-Stim®) was carried out against poultry origin strains of Escherichia coli, Salmonella enteritidis and Salmonella essen, and pig origin strains of enterotoxigenic Escherichia coli (ETEC), Salmonella choleraesuis and Salmonella typhimurium.
The essential oil that showed the highest antimicrobial activity against the four strains of salmonella was Origanum vulgare such as that found in Orego-Stim®.
The results of this work confirm the antimicrobial activity of Origanum vulgare as well as its potential application in the treatment and prevention of poultry and pig diseases caused by salmonella.
Reference:
Penalver P, Huerta B, Borge C, Astorga R, Romero R, Perea A. Antimicrobial activity of five essential oils against animal origin strains of the Enterobacteriaceae family. APMIS 2005113:1–6.
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Jadeed Group
22 de abril de 2009
The occurence of salmonella in live poultry and poultry products is a common challenge the farmers and then the consumers are facing.
The research has defined the organism very well; however much is to be defined yet, as this is a typical organism of poultry.
Dr. Saadat Ali Changezi
D.V.M.
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