Salmonella Detection and Identification Methods
Key Characteristics
•The genus Salmonella contains only two species, but includes around 2,500 ‘serovars’, many of which can cause human illness, often food borne
•Traditional detection and confirmation methods are long established and typically take 3-5 days to obtain a result
•Rapid detection and confirmation methods are widely available and are capable of reducing detection times to 48 hours or less
Introduction
As well as being the cause of enteric (typhoid) fever, an important infectious disease, Salmonella is perhaps best known as a cause of bacterial food poisoning. Although typhoid fever has been largely eradicated in the developed world, Salmonella food poisoning has long been, and continues to be, an important global public health problem. In much of Europe and North America, Campylobacter is now the most frequent cause of foodborne human infections, but Salmonella remains a very important and widespread pathogen. It is a major cause of concern for the food industry, where its control is vital for products ranging from cooked meats to chocolate and from fresh produce to peanut butter.
Given the long history of foodborne salmonellosis, it is not surprising that the need for microbiological testing of food ingredients and food products is very significant. A substantial number of methods, both traditional and rapid, have been developed over the years for the detection and identification of Salmonella.
Salmonella enterica
Bacteria of the genus Salmonella are Gram-negative, facultatively anaerobic, non-spore forming, usually motile rods belonging to the family Enterobacteriaceae and primarily associated with animals. The genus currently contains just two species, Salmonella enterica (including six subspecies) and Salmonella bongori. Most of the Salmonella isolates from cases of human infection belong to Salmonella enterica subspecies enterica. The genus is also further subdivided into approximately 2,500 serovars (or serotypes), characterised on the basis of their somatic (O) and flagellar (H) antigens.
Until recently, individual serovars were referred to as if they were species, for example Salmonella typhimurium. However the current convention is to refer to this serovar as Salmonella enterica subsp. enterica serovar Typhimurium. Fortunately, it is customary to shorten this to Salmonella Typhimurium. The commonest serovars associated with human disease are S. Typhimurium and S. Enteritidis, but many others have been shown to cause disease, notably S. Infantis, S. Virchow and S. Newport.
Individual serovars can be further characterised (typed) by a number of methods, including phage typing and antibiotic resistance profiles. The most severe form of Salmonella infection is typhoid fever caused by serovars adapted to a human host, such as S. Typhi and S. Paratyphi. But infection by non-typhoid salmonellae is much more common and usually causes gastroenteritis, with symptoms including diarrhoea, abdominal pain, nausea and vomiting lasting from 1-7 days. Healthy adults rarely suffer other symptoms and the mortality rate is
Salmonella Detection and Identification Methods
Key Characteristics
•The genus Salmonella contains only two species, but includes around 2,500 ‘serovars’, many of which can cause human illness, often food borne
•Traditional detection and confirmation methods are long established and typically take 3-5 days to obtain a result
•Rapid detection and confirmation methods are widely available and are capable of reducing detection times to 48 hours or less
Introduction
As well as being the cause of enteric (typhoid) fever, an important infectious disease, Salmonella is perhaps best known as a cause of bacterial food poisoning. Although typhoid fever has been largely eradicated in the developed world, Salmonella food poisoning has long been, and continues to be, an important global public health problem. In much of Europe and North America, Campylobacter is now the most frequent cause of foodborne human infections, but Salmonella remains a very important and widespread pathogen. It is a major cause of concern for the food industry, where its control is vital for products ranging from cooked meats to chocolate and from fresh produce to peanut butter.
Given the long history of foodborne salmonellosis, it is not surprising that the need for microbiological testing of food ingredients and food products is very significant. A substantial number of methods, both traditional and rapid, have been developed over the years for the detection and identification of Salmonella.
Salmonella enterica
Bacteria of the genus Salmonella are Gram-negative, facultatively anaerobic, non-spore forming, usually motile rods belonging to the family Enterobacteriaceae and primarily associated with animals. The genus currently contains just two species, Salmonella enterica (including six subspecies) and Salmonella bongori. Most of the Salmonella isolates from cases of human infection belong to Salmonella enterica subspecies enterica. The genus is also further subdivided into approximately 2,500 serovars (or serotypes), characterised on the basis of their somatic (O) and flagellar (H) antigens.
Until recently, individual serovars were referred to as if they were species, for example Salmonella typhimurium. However the current convention is to refer to this serovar as Salmonella enterica subsp. enterica serovar Typhimurium. Fortunately, it is customary to shorten this to Salmonella Typhimurium. The commonest serovars associated with human disease are S. Typhimurium and S. Enteritidis, but many others have been shown to cause disease, notably S. Infantis, S. Virchow and S. Newport.
Individual serovars can be further characterised (typed) by a number of methods, including phage typing and antibiotic resistance profiles. The most severe form of Salmonella infection is typhoid fever caused by serovars adapted to a human host, such as S. Typhi and S. Paratyphi. But infection by non-typhoid salmonellae is much more common and usually causes gastroenteritis, with symptoms including diarrhoea, abdominal pain, nausea and vomiting lasting from 1-7 days. Healthy adults rarely suffer other symptoms and the mortality rate is
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