Plants- Animals Science News

Veterinary medical officer Jean Guard Bouldin, at the ARS Southeast Poultry Research Laboratory in Athens, Ga., found an interesting phenomenon--not only was Salmonella present inside chicken eggs, but other bacteria were there also. Since these bacteria are usually seen in eggs that have been contaminated through cracks in the shell, Bouldin theorized that poor eggshell quality allowed the bacteria to enter the egg.

Salmonella enteritidis is hard to detect in chickens because there are no symptoms. This poses a significant problem, because S. enteritidis, found inside the egg, is an important cause of human food-borne illness.

Bouldin and Jeff Buhr, of the ARS Poultry Processing and Meat Quality Research Unit in Athens, Ga., conducted tests in which chickens were inoculated with S. enteritidis. Eggs were then tested for hardness by compressing them until a hairline crack formed. Eggs from Salmonella-infected hens cracked easier than those from noninfected hens. Other research has shown that some strains of S. enteritidis seem to target the hen's reproductive tract, which appears to result in an egg with a less resilient shell, according to Bouldin.

At low-dose infection, Bouldin found that S. enteritidis actually stimulated egg production, particularly in older hens. This increased production may have stretched the limited eggshell material--calcium--a bit too thin, literally.

Other diseases of chickens can also decrease shell quality, but usually they result in a decrease in production and illness in hens. Changes to eggshell quality over the lifespan of a laying hen are to be expected, and thus a hen's age could be an additional risk factor.

ARS is the USDA's chief scientific research agency.

Agricultural Research Service (ARS) microbiologist Peter S. Holt and entomologist Christopher J. Geden found that the common housefly, Musca domestica, readily picks up bacteria from its surroundings. When the chickens eat the flies, the bacteria get inside the birds. Holt works in the Egg Safety and Quality Research Unit at the ARS Richard B. Russell Research Center in Athens, Ga., while Geden is at the ARS Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

In three experiments, Holt placed chickens in individual, adjacent laying cages. Geden delivered fly pupae just 48 hours short of hatching as flies; this timing ensures the flies aren't exposed to any microbe prior to emergence. The fly pupae were placed in an open box in the bird room. Three days later, hens were orally infected with Salmonella.

The researchers detected the bacteria in and on 45 to 50 percent of the flies within the first 48 hours of the flies' hatching.

Next, uninfected hens were exposed to the newly infected flies. Just being around the flies didn't cause healthy birds to become infected, but eating infected flies did. This showed that simple physical contact may not be the primary method of transfer of Salmonella bacteria to different surfaces in a poultry house. But, according to the researchers, a hen's eating of contaminated flies does seem to be the primary mechanism of transmission of Salmonella from flies to birds.

According to Holt, this shows that flies in poultry houses are not only a nuisance, but also a threat to the safety of poultry products.

http://www.ars.usda.gov/main/main.htm

Salmonella is increasingly resistant to antibiotics and can sometimes go undetected in animals, which increases the risk of the infection being spread to humans. The team tested the strains found in birds in the laboratory and found that antibiotics were able to kill off the bacteria.

Scientists believed that wild birds carried a variety of Salmonella strains and passed the infection on to livestock through their faeces. Scientists at Liverpool, however, have found that only two Salmonella strains are common in garden birds, neither of which is prevalent in livestock or humans.

Research showed that these strains were a fairly distinct population of bacteria and well adapted in garden birds. They were particularly common in finches - such as greenfinch, siskins and goldfinches - as well as house sparrows.

Dr Paul Wigley, from the National Centre for Zoonosis at the University of Liverpool, said: "Salmonella is a bacterium that causes intestinal infection in humans and can cause illness such as vomiting and diarrhoea - usually through contaminated food like meat or eggs. Symptoms in birds include weight loss, feather ruffling and lethargy. We have witnessed a number of deaths due to Salmonella infection in garden birds and so it was important that we investigated how the disease was being spread.

"We thought that wild birds were incubators for Salmonella but have now found that garden birds carry two strains of a group of Salmonella microorganisms, called Salmonella Typhimurium, itself only one of over 2,500 types of Salmonella. We screened Salmonella genes we knew to be involved in causing disease and found that they lacked a gene normally found in the human form of the infection.

"The work suggests that the infection will keep circulating in the same species, increasing the risk of further disease outbreaks. We now know that these Salmonella strains are not resistant to antibiotics but it would be inadvisable to use antibiotics in garden birds as this would inevitably lead to the development of antibiotic resistant bacteria within these populations. We also now need to explore other possible sources to understand the infection in livestock and humans."

The research, conducted as part of the Garden Bird Health Initiative led by the Institute of Zoology and in conjunction with the Health Protection Agency, is published in BMC Veterinary Research.


http://www.liv.ac.uk/

For the first time UK scientists have shown what the food poisoning bug Salmonella feeds on to survive as it causes infection: glucose.

Their discovery of Salmonella’s weakness for sugar could provide a new way to vaccinate against it. The discovery could also lead to vaccine strains to protect against other disease-causing bacteria, including superbugs.

“This is the first time that anyone has identified the nutrients that sustain Salmonella while it is infecting a host’s body,” says Dr Arthur Thompson from the Institute of Food Research.

The nutrition of bacteria during infection is an emerging science. This is one of the first major breakthroughs, achieved in collaboration with Dr. Gary Rowley at the University of East Anglia.

Salmonella food poisoning causes infection in around 20 million people worldwide each year and is responsible for about 200,000 human deaths. It also infects farm animals and attaches to salad vegetables.

During infection, Salmonella bacteria are engulfed by immune cells designed to kill them. But instead the bacteria multiply.

Salmonella must acquire nutrients to replicate. The scientists focused on glycolysis, the process by which sugars are broken down to create chemical energy. They constructed Salmonella mutants unable to transport glucose into the immune cells they occupy and unable to use glucose as food. These mutant strains lost their ability to replicate within immune cells, rendering them harmless

“Our experiments showed that glucose is the major sugar used by Salmonella during infection,” said Dr Thompson.

The mutant strains still stimulate the immune system, and the scientists have filed patents on them which could be used to develop vaccines to protect people and animals against poisoning by fully virulent salmonella.

Glycolysis occurs in most organisms including other bacteria that occupy host cells. Disrupting how the bacteria metabolise glucose could therefore be used to create vaccine strains for other pathogenic bacteria, including superbugs.

The harmless strains could also be used as vaccine vectors. For example, the flu gene could be expressed within the harmless Salmonella strain and safely delivered to the immune system.

The next stage of the research will be to test whether the mutants elicit a protective immune response in mice.

In Germany the nutrition of bacteria is the subject of a six-year priority programme of research to investigate why bacteria are able to multiply inside a host’s body to cause disease.

The IFR is an institute of the Biotechnology and Biological Sciences Research Council (BBSRC). This research was funded by a Core Strategic Grant from BBSRC.

http://www.ifr.ac.uk/