MICROGLOSSARY



Campylobacter- Campylobacter are gram negative, microaerophilic bacteria with a respiratory type of metabolism. These curved rods are actively motile with darting, corkscrew-like motion. They have replaced Shigella as the second leading cause of gastroenteritis in the U.S. Improved methods of isolation and identification is the likely reason for this change. They are part of the intestinal microbiota of cattle and poultry. Cows showing no illness may secrete them in their milk. C. jejuni, which causes gastroenteritis, is catalase positive and oxidase positive. Infection is often associated with fever, cramping and diarrhea with blood and mucus in the feces.


Cyanobacteria- The aerobic, autotrophic, nitrogen fixing species of cyanobacteria (left) can be enriched by adding the source of bacteria to a mineral medium and incubate under a fluorescent light (500-600 nm)at 35 C.The medium is devoid of combined nitrogen and the higher temperature eliminates the algae. In the absence of nitrates the filamentous cyanobacteria produce specialized cells, heterocysts, that fix nitrogen. The image at the right shows the thick-walled structure which is responsible for nitrogen fixation. The purpose of the thick walls is to exclude oxygen which poisons the nitrogen fixation enzyme.




Escherichia coli- Gram negative, rod, catalase positive, oxidase negative; common inhabitant of the human gut; Produces vitamin K for the body. Strain 0157:H7 was the cause of the food poison outbreak associated with Jack-in-the-Box food chain several years ago. This is the most highly studied bacterium and is the model for gram negative bacterial studies and prokaryotic, in general.






Rhodospirillum- Many purple non-sulfur bacteria, such as Rhodospirillum_, can be found in pond water. The growth of Rhodospirillum_ is favored by providing an organic acid, (such as acetate) as an electron donor and carbon source, an incandescent light source of 600 and 900 nm in wavelength, and a temperature of 35¡ C. The culture vessel should be filled to the top with medium and sealed to exclude oxygen. This enriches the pond water sample for Rhodospirillum_ because few other phototrophs can grow under anoxic conditions, and other anaerobic bacteria don't grow as fast as the phototrophic Rhodospirillum_




Salmonella- Salmonella are gram negative straight rods like the other Enterobacteriaceae.They are facultatively anaerobic,oxidase negative and catalase positive.Salmonellosis or Salmonella gastroenteritis is the result of a bacterial infection and usually has a longer incubation period than (12 hours- 2 weeks) bacterial intoxications.There is fever,nausea,abdominal pain,cramps and diarrhea.Recovery is usually complete in a few days but many individuals will shed the organisms in their feces for as long as 6 months.This food born disease in underreported with the 50,000 cases easch year being only 1-10% of the actual total.Sources of these organisms in the intestinal tract of many animals with meat poultry,eggs and egg products often the contaminated food.Diagnosis depends on isolation of the organism from the patients stool of from leftover food.Faster methods depend on DNA probe kits and ELISA-type kits that use monoclonal antibodies.


Shigella- Shigella are gram negative straight rods like the other Enterobacteriaceae. They are non motile and facultatively anaerobic with both respiratory and fermentative metabolism. Most are catalase positive and all are oxidase negative. They ferment sugars without forming gas. These organisms may be ingested with contaminated water, eggs, vegetables, shellfish and dairy products. They are intestinal pathogens of man and other primates. Most cases have symptoms of watery diarrhea and are termed shigellosis. Toxins produced by the microorganisms often causes death. Severe abdominal cramps with blood and mucus in the stools is diagnosed as bacillary dysentery and may require rehydration. Antibiotics tend to be ineffective as many strains are resistant due to R factors.


Staphylococcus- Staphylococcus are gram positive cocci arranged in clusters,singles and pairs.They are facultative anaerobes but growth is best under aerobic conditions.Catalase is produced by cells growing aerobically.Metabolism is repiratory and fermentative.S aureus is a potential pathogen causing a wide range of infections including impetigo,pneumonia, boils,carbuncles,osteomyelitis,meningitis,encocarditis,bacteremia,food poisoning(via enterotoxin),enterocolitis,urogenital infection and toxic shock syndrome. Cells are resistant to heat(60C),drying,radiation and high osmotic pressure.They are common inhabitants of the nasal passages from which they contaminate the hands and thus enter foods.If the organisms incubate in the food they grow and release enterotoxin.Toxin production is highly correlated with coagulase positive reactions.High risk foods are ham,custards and cream pies.The toxin is heat stable(30 min of boiling) and triggers vomiting.Cramps and diarrhea usually follow quickly./Organisms can be recovered from the food or a test for thermostable nuclease in which an extract of the food is allowed to react with DNA is evidence that there was a population large enough to produce toxin enough for illness.