"Long before it's in the papers"
January 27, 2015


Slimy bacterial colonies may have met their match

Aug. 1, 2012
Courtesy of Harvard University
and World Science staff

Slimy, wily bac­te­ri­al col­o­nies that have been out­smart­ing hu­man at­tempts to wipe them out may no long­er have a ground to stand on. Sci­en­tists say they have de­vel­oped a way to pre­vent the trou­ble­some bac­te­ri­al com­mun­i­ties, called bio­films, from form­ing.

Biofilms are popula­t­ions of bac­te­ria that are ex­tremely hard to de­stroy be­cause the germs cling to­geth­er, mu­tu­ally sup­port each oth­er chem­ic­ally, and shield them­selves with pro­tec­tive coat­ings that fend off an­ti­bi­otics. They stick to just about eve­ry­thing, from cop­per pipes to steel ship hulls to glass catheters. 

The word “S­LIPS” is coat­ed with the SLIPS tech­nol­o­gy to show its abil­i­ty to re­pel liq­uids and solids and even pre­vent ice or frost from form­ing. The slip­pery dis­cov­ery has now been shown to pre­vent more than 99 per­cent of harm­ful bac­te­ri­al slime from form­ing on sur­faces. (Im­age cour­te­sy of Jo­an­na Aizen­berg, Re­bec­ca Belisle, and Tak-Sing Wong)

More than just a nui­sance, they re­sult in de­creased en­er­gy ef­fi­cien­cy, con­tamina­t­ion of wa­ter and food, and per­sist­ent in­fec­tions. Even ca­vi­ties in teeth are the un­wel­come re­sult of bac­te­ri­al col­o­nies.

But in a new study pub­lished in the jour­nal Pro­ceed­ings of the Na­t­ional Acad­e­my of Sci­ences, Har­vard Uni­vers­ity re­search­ers say they have found a so­lu­tion. They coat­ed sol­id sur­faces with an “im­mo­bi­lized liq­uid film” to trick the bac­te­ria in­to think­ing they had no­where to at­tach and grow.

“Peo­ple have tried all sorts of things… tex­tured sur­faces, chem­ical coat­ings, and an­ti­bi­otics, for ex­am­ple,” said Jo­an­na Aizen­berg, a ma­te­ri­als sci­ent­ist at Har­vard. “In all those cases, the so­lu­tions are short-lived at best. The sur­face treat­ments wear off, be­come cov­ered with dirt, or the bac­te­ria even de­pos­it their own coat­ings on top of the coat­ing in­tend­ed to pre­vent them. In the end, bac­te­ria man­age to set­tle and grow on just about any sol­id sur­face we can come up with.”

The re­search­ers used a new tech­nol­o­gy dubbed SLIPS (slip­per­y-liq­uid-infused po­rous sur­faces) to ef­fec­tively cre­ate a sur­face that is smooth and slip­pery due to a liq­uid lay­er that is fixed on­to it. First de­scribed in the Sept. 22, 2011, is­sue of the jour­nal Na­ture, the super-slip­pery sur­faces have been found to re­pel both wa­ter- and oil-based liq­uids and even to pre­vent ice or frost from form­ing.

This de­prives bac­te­ria of the sol­id sur­face “they need to get a grip and grow to­geth­er,” said Al­ex­an­der Ep­stein, a re­cent doc­tor­al grad­u­ate who worked in Aizen­berg’s lab at the time of the stu­dy. “In es­sence, we turned a once bac­te­ri­a-friendly sol­id sur­face in­to a liq­uid one. As a re­sult, biofilms can­not cling to the ma­te­ri­al, and even if they do form, they easily slip off,” added col­la­bo­ra­tor Tak-Sing Wong.

Aizen­berg and col­leagues re­ported that SLIPS re­duced by 96 to 99 per­cent the forma­t­ion of three of the most no­to­ri­ous, disease-causing biofilms — Pseu­dom­o­nas aerug­i­nosa, Esch­e­rich­ia coli, and Staph­y­lo­coc­cus au­re­us — over a se­ven-day pe­ri­od.

This may be the first suc­cess­ful test of a non­toxic syn­thet­ic sur­face that can al­most com­pletely pre­vent the forma­t­ion of biofilms for a long time, the re­search­ers said. They pro­pose the ap­proach may find ap­plica­t­ions in med­i­cal, in­dus­t­ri­al, and con­sum­er prod­ucts and set­tings.

“Biofilms have been amaz­ing at out­smart­ing us. And even when we can at­tack them, we of­ten make the situa­t­ion worse with tox­ins or chem­icals. With some very cool, nature-inspired de­sign tricks, we are ex­cit­ed about the pos­si­bil­ity that biofilms may have fi­nally met their match,” said Aizen­berg.

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Slimy, wily bacterial colonies that have been outsmarting human attempts to wipe them out may no longer have a ground to stand on. Scientists say they have developed a way to prevent the troublesome bacterial communities, biofilms, from forming. Biofilms are populations of bacteria that are extremely hard to destroy because they cling together, mutually support each other chemically, and shield themselves with protective coatings that fend off antibiotics. They stick to just about everything, from copper pipes to steel ship hulls to glass catheters. More than just a nuisance, they result in decreased energy efficiency, contamination of water and food, and persistent infections. Even cavities in teeth are the unwelcome result of bacterial colonies. But in a new study published in the journal Proceedings of the National Academy of Sciences, Harvard University researchers say they have found a solution. They coated solid surfaces with an “immobilized liquid film” to trick the bacteria into thinking they had nowhere to attach and grow. “People have tried all sorts of things… textured surfaces, chemical coatings, and antibiotics, for example,” said Joanna Aizenberg, a materials scientist at Harvard. “In all those cases, the solutions are short-lived at best. The surface treatments wear off, become covered with dirt, or the bacteria even deposit their own coatings on top of the coating intended to prevent them. In the end, bacteria manage to settle and grow on just about any solid surface we can come up with.” Taking a new approach, the researchers used their recently developed technology, dubbed SLIPS (slippery-liquid-infused porous surfaces) to effectively create a surface that is smooth and slippery due to a liquid layer that is fixed onto it. First described in the Sept. 22, 2011, issue of the journal Nature, the super-slippery surfaces have been found to repel both water- and oil-based liquids and even to prevent ice or frost from forming. This deprives bacteria of the solid surface “they need to get a grip and grow together,” said Alexander Epstein, a recent doctoral graduate who worked in Aizenberg’s lab at the time of the study. “In essence, we turned a once bacteria-friendly solid surface into a liquid one. As a result, biofilms cannot cling to the material, and even if they do form, they easily ‘slip’ off under mild flow conditions,” added collaborator Tak-Sing Wong. Aizenberg and colleagues reported that SLIPS reduced by 96 to 99 percent the formation of three of the most notorious, disease-causing biofilms — Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus — over a seven-day period. This may be the first successful test of a nontoxic synthetic surface that can almost completely prevent the formation of biofilms over an extended period of time, the researchers said. They propose the approach may find applications in medical, industrial, and consumer products and settings. “Biofilms have been amazing at outsmarting us. And even when we can attack them, we often make the situation worse with toxins or chemicals. With some very cool, nature-inspired design tricks, we are excited about the possibility that biofilms may have finally met their match,” said Aizenberg.