Staphylococcus aureus is a aerobic gram positive bacterium that usually forms clusters which resemble grapes when viewed with a microscope. Staphylococcus bacteria were first observed by Robert Koch in 1878, followed by Louis Pasteur in 1880. In 1884 Rosenbach proposed the classifications of S. aureus for Staphylococcus that formed yellow colonies, and S. albus (now called Staphylococcus epidermidis) for white colonies. At least fifteen strains of S. aureus are infectious to humans. These bacteria can infect virtually any human tissue or organ causing boils, endocarditis, pneumonia (usually a complication of influenza), toxic shock syndrome, is the most common cause of septicaemia in intensive care units worldwide, but it is most commonly known for its role in food poisoning.
Characteristics of S. aureus:
- Survives at temperatures of 7-45oC
- Tolerates pH in the range of 4.5 to 9.3
- Little resistance to heat, killed by pasteurization
- Have inherent and aquired resistance to antibiotics1 including penicillin, methicillin, erythromycin, streptomycin, tetracycline, and chloramphenicol. There are isolated reports of resistance to vancomycin (Really bad news!)
- Exists in air, dust, sewage, water, milk, food/food processing equipment, and in the nasal passages/throat/hair/skin of more than 50% of healthy humans
- Surface proteins promote colonization of host tissues
- Produce invasins that promote spread of infection (leukocidin, kinases, and hyaluronidase)
- Surface factors (microcapsule, Protein A) inhibit phagocytic engulfment to some extent
- Carotenoids and catalase production ehance survival of S.aureus in phagocytes
- Produce hemolysins, leukotoxin, and leukocidin, toxins which lyse eukaryotic cell membranes
- Produce exotoxins such as toxic shock syndrome toxin and superantigen staphylococcal enterotoxins A through G
Food poisoning caused by S. Aureus appears anywhere from 1 to 10 hours after ingesting contaminated food. Symptoms include vomiting, nausea, diarrhea, abdominal pain, headache, fever, chills, dizziness and weakness. The infection lasts from 1 to 88 hours, with the average infection lasting just over a day. About 10% of patients require fluid replacement because of severe diarrhea or vomiting. In rare cases acute gastritis or enterocolitis may occur. The overall fatality rate for people infected by S. aureus is 0.03%, but more than 4% of children and elderly patients die. This microbe is estimated to cause 14% of food poisoning cases in the United States. Most cases occur during the summer (food sitting out at picnics and such), with a second spike in November and December (usually linked to improper handling of leftovers from holiday meals). Foods commonly involved in S. aureus food poisoning include custard and cream-filled baked goods, chicken/tuna/ham/potato/egg salad, meats (especially ham for some reason), canned corned beef2, dairy products, and boiled eggs (contaminated during cooling). S. aureus is easily destroyed by heat treatment and most sanitizing agents, so its presence in processed food or food processing equipment is almost always caused by poor sanitation. The effects of staphylococcal food poisoning are caused by enterotoxins produced by the organisms. It takes less than 1 microgram of these toxins to cause symptoms.
1Although resistant to many antibiotics, one strain of S. aureus is commonly used for microbial assays specified in the United States Pharmacopeia (General Chapter <81>)for measuring potency of antibiotics including amikacin, cephalothin, cephapirin, chlorotetracycline, cloxacillin, cycloserine, democlocycline, doxycycline, kanamycin, methacycline, nafcillin, oxytetracycline, penicillin G, rolitetracycline, tetracycline, tobramycin, and tylosin. I just love having live bacteria in the lab.
2Canned corned beef is not inherently dangerous, but the seams of the cans can fail during cooling.
Sources:
http://www.msu.edu/course/fsc/840/lect-16.pdf -- Lecture for "Advanced Foodborne Disease" by Elliot Ryser, Michigan State University
USP25/NF20
http://vm.cfsan.fda.gov/~mow/chap3.html -- Part of the "Bad Bug Book"
http://vm.cfsan.fda.gov/~ebam/bam-12.html -- more info from the FDA
http://www.cdc.gov/ncidod/hip/aresist/visa.html -- Info from the Centers for Disease Control and Prevention
http://www.bac.wisc.edu/Bact330/lecturestaph -- Lecture by Kenneth Todar, University of Wisconsin-Madison
http://www.ewi.med.uu.nl/enare/topics/Methicillin_resistant_Staphylococcus_aureus_and_Staphylococcus_epidermidis.html -- by Mark E. Jones
If anyone has a reference for info about Rosenbach, especially one with his first name, please /msg me!
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