Hans Christian Gram developed his staining method in the 1880s. It became important because it could distinguish between two large groups of bacteria, both of which can cause diseases in humans. It is still used to screen bacteria quickly, while more time-consuming tests are performed to further identify the organisms. Gram-negative infections are more of a problem in immunocompromised patients in hospitals. Gram-positives can infect otherwise healthy people.
Gram-negatives include bacteria such as E. coli, Klebsiella and Acinetobacter. Gram-positives include Staphylococcus, Streptococcus and Enterococcus. The extra membrane of Gram-negatives prevents large molecules like antibiotics from entering and penetrating to the bacterial cell, making infections difficult to treat by drugs. The membrane contains peptidoglycan, a polymer that consists of lipopolysaccharides (LPS) linked to peptide chains. The inner cell wall is thinner than that of Gram-positive bacteria.
The thicker cell wall of Gram-positive bacteria, which is also composed of peptidoglycan, can take up more stain. Beginning with penicillin, many antibiotics have been introduced to treat these bacteria, but they are notorious for developing drug resistance, which is not dependent on the presence of an outer membrane. Researchers continue to develop new drugs against Gram-positives. Colistin and polymyxin B, antibiotics that were introduced in the 1940s, are among the drugs that can effectively treat Gram-negatives.
Infections caused by Gram-negative bacteria have started to spread outside the hospital environment, as they are also becoming more resistant to the drugs that work against them. Health officials are especially concerned because there are so few drugs available to treat Gram-negative infections. If larger doses become necessary, the likelihood of adverse drug effects increase. Colistin and polymyxin B are known to damage the nerves and kidneys.