When penicillin came into use in the first half of the 20th century, it was hailed as a miracle drug, and it remains one of the scientific marvels of the 20th century. The bacteria it used to effortlessly conquer gradually built up defenses, however, eroding the power of penicillin and its many antibiotic cousins. In the 1960s, methicillin-resistant S. aureus emerged, creating a serious public health problem that was immune to conventional antibiotics. We have never fully recovered the upper hand in this battle. Rather than constantly developing new antibiotics in an ultimately futile molecular arms race, scientists at the University of South Carolina posited a different approach: why not give existing antibiotics a new lease on life by pairing them with a protective polymer? The technique is viable because of the molecular structure of penicillin and its derivatives, and the way in which bacteria nullify their effects.
The greatest strength of penicillin is its molecular core, a cyclic four-membered amide ring termed a beta-lactam, explains Steven Powell, who wrote about the research on Phys.org. The beta-lactam structure hinders the ability of bacteria to multiply, and so "chemists have for years spent time making molecules that all contain the beta-lactam structural motif, but differ in the surrounding molecular 'shrubbery,'" notes Powell.
One of the most effective bacterial defenses against this structure is an enzyme called beta-lactamase, which chews up the beta-lactam structure. Some bacteria, such as MRSA, have developed the ability to biosynthesize and release beta-lactamase when needed. Researchers at the university figured that shielding penicillin before sending it into battle might give it a fighting chance to prevail.
Graduate student Jiuyang Zhang prepared a cobaltocenium metallopolymer that greatly slowed the destructiveness of beta-lactamase on a model beta-lactam molecule (nitrocefin) in lab tests. The research also showed that the antimicrobial effectiveness was modestly enhanced against two strains of bacteria but that it was quite aggressive against hospital-associated MRSA.
The metallopolymer by itself demonstrated antimicrobial properties, lysing bacterial cells while leaving human red blood cells unaffected, reports Phys.org.
|Antimicrobial properties of conjugates of a beta-lactam antibiotic with a metallopolymer were enhanced compared
with the antibiotic alone, especially with hospital-associated MRSA (left). Image courtesy Journal of the American