Bacteria Genomes - STAPHYLOCOCCUS AUREUS

Staphylococcus aureus is a bacterium commonly found on the skin and in the nose of healthy people. The major habitats of the pathogen are the nasal membrane and skin of warm-blooded animals. It is one of the major causes of community-acquired and hospital-acquired infections.

Occasionally, staphylococci cause infections that are minor (such as pimples, boils, and other skin conditions) or serious and sometimes fatal (such as blood infections, carditis, meningitis, or pneumonia). It produces numerous toxins including superantigens that cause unique disease entities such as toxic-shock syndrome and staphylococcal scarlet fever, and has acquired resistance to practically all antibiotics.

The onset of symptoms in staphylococcal food poisoning is usually rapid and in many cases acute, depending on individual susceptibility to the toxin, the amount of contaminated food eaten, the amount of toxin in the food ingested, and the general health of the victim. Recovery generally takes two days, However, it us not unusual for complete recovery to take three days and sometimes longer in severe cases.

Although food handlers are usually the main source of food contamination in food poisoning outbreaks, equipment and environmental surfaces can also be sources of contamination with S. aureus . Human intoxication is caused by ingesting enterotoxins produced in food by some strains of S. aureus, usually because the food has not been kept hot enough (60C, 140F, or above) or cold enough (7.2C, 45F, or below).

Staphylococcus aureus is highly vulnerable to destruction by heat treatment and nearly all sanitising agents. Thus, the presence of this bacterium or its enterotoxins in processed foods or on food processing equipment is generally an indication of poor sanitation.

S. aureus is a spherical bacterium (coccus) which on microscopic examination appears in pairs, short chains, or bunched, grape-like clusters. These organisms are Gram-positive.

Over the past 50 years, S. aureus has undergone incremental changes in genetic complement that have resulted in the emergence of strains that are antibiotic-resistant and that appear to be successful at transmission and causing disease in the hospital setting. More recently, MRSA (Methicillin resistant Staphylococcus aureus) strains appear to have become established within the community. Staphylococcus aureus is an important nosocomial and community-acquired pathogen. Its genetic plasticity has facilitated the evolution of many virulent and drug-resistant strains, presenting a major and constantly changing clinical challenge. Recently, two disease-causing S. aureus strains isolated from distinct clinical settings have been sequenced and their genomic data compared to explore the mechanisms of evolution and to identify regions affecting virulence and drug resistance: a recent hospital-acquired representative of the epidemic methicillin-resistant S. aureus EMRSA-16 clone (MRSA252), a clinically important and globally prevalent lineage; and a representative of an invasive community-acquired methicillin-susceptible S. aureus clone (MSSA476). A better understanding of the features that make MSSA (methicillin-susceptible S. aureus) and MRSA strains successful in both community and hospital settings is urgently needed. Further sequencing of diverse S. aureus strains will facilitate description of the full range of putative pathogenic determinants carried by this species and provide a basis for predicting rates of horizontal gene transfer.

References:

http://vm.cfsan.fda.gov/~mow/chap3.html
http://www.sanger.ac.uk/Projects/S_aureus/
Lancet 2001, 357 (9264):1225-40
Lancet 359:1819-1827(2002)
Proc. Natl. Acad. Sci. USA 101 (26): 9786-9791 .