Staphylococci are a circular-shaped family of bacteria that often inhabit the skin. Staph aureus is noted by The Merck Manuals Online Medical Library to be a dangerous species of bacteria within the family. The Merck Manuals note that the Staph aureus bacteria reside within the nose and on the skin of some people and that their residence is transient, or temporary, in most people but permanent in about 20 to 30 percent of the population. These people are called carriers and the infection is contagious. Staph aureus infections can vary in their severity and can cause skin, bloodstream, heart valve, bone and lung infections.
Beta-Lactamase Stable Penicillins
Staphylococcus aureus is a common class of bacteria. Justly so, S. aureus has been commonly treated with the first and most common class of antibiotic drugs, the penicillins. Penicillins, according to Susan M. Turley, author of "Understanding Pharmacology for Health Professions," were discovered in 1940. Over the last 70 years, many strains of Staphylococcus aureus species have developed a strategy to outlive the effects of antibiotics. One such strategy has allowed the bacteria to render the antibiotic ineffective, according to a 2003 "Podiatry Today" magazine article by Mark Kosinski, DPM.
The penicillin drug class is known by its consistent structure, a beta-lactam ring, also known as a penicillin ring. Staph aureus species have evolved to create an enzyme to destroy this characteristic ring and thus cause the drug to not work. This enzyme is known as the beta-lactamase or penicillinase enzyme. In a 2003 article in "Podiatry Today" magazine, by Mark Kosinski, DPM, he explains that all penicillins used to treat Staph aureus must be beta-lactamase stable. The synthetically derived antibiotics that meet this specification and are able to treat S. aureus infections are known as nafcillin, oxacillin, dicloxacillin and methicillin.
The older penicillins that could not work because of the bacteria's evolved ability to resist them were the commonly used amoxicillin and ampicillin. To overcome this resistance, Susan Turley, author of "Understanding Pharmacology for Health Professions," notes that an ingenious idea to combine these old penicillins with a new drug class that would work around the malfunction came into fruition. The new class of drugs was known as beta-lactamase inhibitors and they worked to block the ability of the S. aureus bacteria to destroy the distinctive penicillin ring structure. The new combination drugs that are effective against Staphylococcus aureus infections are amoxicillin/clauvulante, ampicillin/sublactam, piperacillin/tazobactam and ticarcillin/clavulanate.
When the beta-lactamase stable penicillins like methicillin were first derived in the laboratory, their success rates of treating the newly resistant strains of S. aureus infections were excellent. However, with consecutive use and dependence, even this group of antibiotics had resistant strains grow against them. The new strains of bacteria known to inhibit the beta-lactamase stable group are collectively known as methicillin resistant Staphylococcus aureus, or MRSA, bacteria. MRSA infections can be acquired in the hospital or community, notes Kosinski.
When people are infected with this class of resistant S. aureus bacteria, they may have to rely on antibiotics that Kosinski notes may have varying degrees of activity. They are not penicillins, do not have beta-lactam rings and are therefore more qualified to deal with this type of infection. MedlinePlus notes that MRSA antibiotics include clindamycin, daptomycin, doxycycline, linezolid, minocycline, tetracycline, trimethoprim-sulfamethoxazole and vancomycin.
- The Merck Manuals Online Medical Library: Staphylococcus Aureus Infections
- "Podiatry Today"; How to Choose Antibiotics for Staph Aureus Infections; Mark Kosinksi, DPM; 2003
- "Understanding Pharmacology for Health Professions, 4th Edition"; Susan M. Turley; 2009
- MedlinePlus: MRSA