Bacteria are unicellular, self-propagating micro-organisms that multiply through growth in bacterial cell size and the subsequent division of the cell. Bacteria can be broadly classified into two categories based upon the composition of their cell walls: Gram-positive or Gram-negative. Many antibacterial drugs that are effective against Gram-positive bacteria are less effective or ineffective against Gram-negative bacteria, and vice versa. Antibacterial drugs that are active against a large number of both classes of bacteria are often referred to as “broad-spectrum” anti bacterials or antibiotics.
Bacteria adapt remarkably well to their surroundings due to the high level of variation found within bacterial DNA and the ability of bacteria to reproduce rapidly. Replication of bacterial DNA is often error prone and can result in a high frequency of mutations. Because the bacterial reproductive cycle is very short, ranging from minutes to several days, a mutation that helps a bacterium survive exposure to an antibiotic drug may quickly become dominant throughout the population. Additionally, bacteria can acquire segments of DNA from other bacteria and organisms, which can also convey drug resistance.
Bacterial Resistance Driving Need for New Medications
One of the most common pathogenic bacteria is the Gram-positive bacterium Staphylococcus aureus, or S. aureus, also referred to simply as “Staph.” S. aureus can cause serious infections of the skin, bloodstream, bones or joints. In 2002, 57% of S. aureus infections in the hospital were with strains of S. aureus that were resistant to methicillin, part of a commonly used class of antibiotics. Frequently, these methicillin-resistant S. aureus strains, commonly referred to as MRSA, are also resistant to other classes of antibacterials such as cephalosporins and quinolones. Consequently, MRSA is commonly used to refer to multi-drug-resistant bacteria associated with serious infections. The increasing difficulty in treating MRSA and other multi-drug-resistant hospital-based infections has led to higher morbidity and mortality rates, as well as increasing health care expenditures.