Staphylococcus aureus

Staphylococcus aureus is a facultative anaerobic gram-positive coccus, and is the most common cause of staph infections. It is commonly part of the skin flora found in the nose and on skin. Around 20% of the human population is long-term carriers. It gets its golden color due to its carotenoid pigment staphyloxanthin. The pigment acts as a virulence factor with an antioxidant action that allows the microbe to evade death by reactive oxygen species used by the host immune system. Staphylococci which lack the pigment are more easily killed by host defenses.

It can cause a range of illnesses from minor skin infections to life-threatening diseases such as pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock syndrome, chest pain, and sepsis. It is one of the five most common causes of nosocomial infections and it often causes post-surgical wound infections. S. aureus should not be confused with the similarly named and similarly dangerous species of the genus Streptococcus.

Sir Alexander Ogston discovered S. aureus in Scotland in 1880. Around 500,000 patients in America hospitals contract staphylococcal infections each year. A recent study showed that almost half of the meat and poultry in the U.S. grocery stores were contaminated with S. aureus.

S. aureus is facultatively anaerobic, gram-positive coccus which shows up as a grape-like cluster in the microscope. It is catalase-positive which makes it capable of converting hydrogen peroxide to water and oxygen. Strains can create enterotoxin and pathogenicity which can cause food poisoning.

S. aureus can occur as a commensal on skin, in the nose, and less commonly in the throat. Occurrence of S. aureus under does not always indicate infection and therefore does not always require treatment. It can survive on domesticated animals and can survive hours, weeks, or months on dry environmental surfaces depending on the strain. It can infect other tissues when barriers have been breached which leads to furuncles and carbuncles.

It can spread through contact with pus from an infected wound, skin-to-skin contact, and contacts with objects such as towels, sheets, clothing, or athletic equipment used by an infected person. Deeply penetrating S. aureus infections can be severe.

S. aureus is extremely prevalent in atopic dermatitis patients who are less resistant to it other than people. It can cause complications and is most often found in fertile active places, including the armpits, hair, and scalp. Some strains that produce exotoxin are the causative agents of toxic shock syndrome. Other strains produce enterotoxin that is the causative agent of S. aureus gastroenteritis.

It is one of the causal agents of mastitis in dairy cows. It reproduces asexually and starts doing that by reproducing its DNA. The cells form a hollow space that eventually divides into two new cells. The new cell wall does not fully separate from the existing cell wall, which is why the cells are observed in clusters. The cell will eventually reproduce, and cells will attach to it.

Protein A is anchored to staphylococcal peptidoglycan pentaglycine brides by the transpeptidase sortase A. Certain drugs designed to inhibit the bacteria’s production of the staphlyoxanthin may weaken it and renew its susceptibility to antibiotics. It is similar to the way human cholesterol works and thus some drugs developed for cholesterol lowering have been shown to block S. aureus pigmentation and disease progression in a mouse infection model.

Depending on the infection present a specimen is obtained and sent to the laboratory for definitive identification by using biochemical or enzyme-based tests. A gram stain is performed which would show Gram-positive bacteria in clusters. For other differentiation on the species level catalase, coagulase, DNAse, lipase, and phosphatase tests are done. Diagnostic microbiology laboratories and reference laboratories are a key in identifying outbreaks and new strains of S. aureus. Genetic advances have allowed for reliable and rapid techniques for the identification and characterization of clinical isolates of S. aureus in real time. These help support infection control strategies that limit bacterial spread and ensure the appropriate use of antibiotics.

General treatment is penicillin, in most countries, though there are penicillin-resistant strains. To treat serious infections combination therapy with gentamicin may be used although this method does provide a high risk of damage to the kidneys. Resistance to methicillin is mediated via the mec operon. Kanamycin, gentamicin, streptomycin, and other aminoglycoside antibiotics were once effective against staphlyococal infections until strains evolved ways to inhibit the aminoglycosides’ action. The vanA gene is used to mediate resistance to Glycopeptide.

S. aureus has become resistant to many commonly used antibiotics. Only 2% of all S. aureus isolates are sensitive to penicillin in the UK as well as everywhere else. Generally thought to spread through human-to-human contact although recently some veterinarians have discovered the infection can be spread through pets with environmental contamination thought to play a relatively unimportant part.

There have been a myriad of reported cases of S. aureus in hospitals across America. The pathogen has had facilitated transportation in medical facilities mainly because of insufficient healthcare worker hygiene. Ethanol is an effective topical sanitizer against MRSA.