Since penicillin was identified in 1941 and gained consistent use as an antibiotic, resistance to treatment began to appear. Bacteria acquire DNA sequences from other bacteria that they come into contact with, sharing genes for resistance to drugs that compromise bacterial replication and survival. For example, if methicillin-resistant bacteria (such as Staphylococcus aureus) come into contact with vancomycin-resistant bacteria (such as Enterococcus faecalis), they can both potentially become double resistant to both antibiotics and replicate into a double resistant strain upon circulation. Today, only vancomycin is effective against methicillin resistant Staph strains. However, in 2002 vancomycin resistant methicillin resistant strains were identified in two U.S. states, and a third instance occurred in a long-term care facility in NY a year later. Some evidence in scientific journals indicates that the cocolonization of patients with both bacteria (Staph and Enterococci) is currently occurring, which does not bode well for the future of antibiotics.
Antibiotic-resistant bacteria, and drug-resistant disease in general, are becoming more common as mutations allow the pathogens to survive amidst human medical advances. S. aureus usually colonizes the skin. The skin surface of a third of all people is colonized by S. aureus. Open wounds and surgical incisions can allow the bacterium to enter and gain access to the internal organs or bloodstream, leading to sepsis. Antibiotics are used to treat infections, most of which stay confined to the skin because the bacteria does not have an opportunity to spread. Methicillin-resistant S. aureus (MRSA) is usually seen in those who have invasive surgery or reduced immunity.
There are currently two types of MRSA, nosocomial, or hospital-acquired, and community, one circulating among the population. Nosocomial infections tend to be more invasive than community strains. The first community strains were seen in intravenous drug users in 1981 at the same time that MRSA was becoming rampant in hospitals, and the first deaths attributed to a community MRSA strain were four schoolchildren in Minnesota in 1997.
According to a 2007 report from the U.S. Centers for Disease Control (CDC) evaluating infection data from eight metropolitan areas in 2005, there are approximately 19,000 deaths in the U.S each year from MRSA, 15% of which are estimated to be due to a community strain. The CDC cautions that the figure may be higher than the actual number of deaths due to the population density of the monitored areas, but the information suggests that the MRSA-associated death rate doubled in only 5 years.
And Then There Were Two
At a New York Academy of Science meeting on emerging and re-emerging microbial diseases in late 2004, Dr. Barry Kreiswirth from the Public Health Research Institute presented information about MRSA infections. Of particular concern were the first cases of vancomycin-resistant MRSA (VR-MRSA) seen by researchers in 2002. This is a form of MRSA that is also resistant to another antibiotic, vancomycin, once again reducing treatment options and increasing the survival of the bacteria versus the survival of its human host.
The elderly and those who stay in the hospital often are at a higher risk of suffering from antibiotic resistant infections, because the more virulent strains often circulate in the healthcare system. Based on information from the CDC, approximately 65% of hospital-based S. aureus infections were methicillin resistant in 2003, and 8.2% of nosocomial bacterial infections can be expected to be MRSA. Three-fourths of all nosocomial infections are estimated to be drug resistant, and hospital-acquired infections result in 100,000 deaths annually. A return to basic hygiene consciousness, more diligent hand-washing and sterilization, may be able to cut the numbers.
Furuno, et al. Methicillin-resistant Staphylococcus aureus and Vancomycin-resistant enterococci Co-colonization. Emerging Infectious Diseases 11(10);1539-1544, 2005.
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