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Image Credit: Scarisoara Ice Cave, 2006, photo by Cristian Bortes (Flickr)

Remember the classic chases where Wile E. Coyote tries to catch Roadrunner but is often outsmarted? It turns out that bacteria have to survive their own epic chases, in a way. They are constantly developing new ways to outwit their old enemy: antibiotics. Antibiotics have been around long before modern medicine because they are naturally produced by other microbes, plants, and animals, so bacteria have had time to develop resistance before humans introduced synthetic drugs.

You may have heard of antibiotic resistance, which occurs when bacteria are successful at defeating drugs that are designed to kill them. Those bacteria reproduce and create more bacteria that are also resistant to these drugs. While this may be good for the surviving bacteria, it can be really harmful to human health. An infection caused by one of these antibiotic-resistant “superbugs” may be hard or even impossible to treat. Understanding how bacteria evolve antibiotic resistance gives us insight into how to develop drugs that they can’t beat.

To beat antibiotic resistance, researchers have been looking far and wide for insight into this problem. Recently, a team of scientists was able to collect bacteria from 13,000-year-old cut-out cylinders of ice, which are called ice cores. They drilled out the cores carefully, using fire to sterilize the drill and keeping the cores fully frozen to prevent any modern bacteria from contaminating the samples. Much like how tree rings can tell us how old a tree is, ice cores act as a snapshot of Earth’s history.

The ice cores in the study were collected from the Scarisoara Ice Cave located in Romania. This ice cave is unique due to its constant cold environment and holds some of the world’s oldest and largest year-round ice blocks. This marked the first time that bacteria were collected from ice that was from the Late Glacial period, which happened over 11,000 years ago! The scientists grew colonies from 68 individual bacteria from the ice cores and discovered that 17 of the bacteria types were new and unclassified.

The bacteria collected in this study had two different outer structures. The first structure belongs to bacteria that have a thin but very impenetrable outer layer, like a bulletproof vest. These are called gram-negative bacteria. They are highly antibiotic-resistant and very resilient due to their outer membrane made of phospholipids. E. coli is one example of gram-negative bacteria that live in our gut and help us digest food.

The second type of structure belongs to bacteria that have a very thick outer layer, like a slab of drywall that protects the bacteria. It is made of layers of amino acids, making it thicker but more penetrable than the layer around gram-negative bacteria. These are called gram-positive bacteria. For example, the rare bacterial infection called “botulism” is caused by a gram-positive bacterium.

Structures of Gram positive and Gram negative bacteria

The differences between Gram positive and Gram negative bacteria. (These are cross sections of their membranes) From Wikimedia Commons.

In this study, the team were able to identify the types of bacteria present by sequencing the DNA of each colony and searching for matches using databases of DNA sequences belonging to known species. The gram-negative bacteria the scientists found showed greater signs of antibiotic resistance than the gram-positive bacteria they collected. More than 50% of the bacteria collected showed high resistance to 17 of the most commonly used antibiotics in medicine and laboratory research. The gram-negative bacteria called Bacteroidetes showed the highest resistance rate of 100% resistance to all 17 antibiotics.

The ice that these bacteria were found in had been completely untouched by humans before it was collected, which means that the bacteria developed antibiotic resistance thousands of years before man-made antibiotics were invented. By looking into unexplored old habitats, we are able to get a glimpse into the evolution of antibiotic resistance. This may also lead to the discovery of new antibiotics in nature that doctors could use to treat infections.

The scientists also expressed concern that antibiotic-resistant bacteria like the ones found in this study pose a potential threat if they are reintroduced to the environment, which could happen as ice melts due to global warming. The resistant genes from these preserved bacteria may possibly make modern bacteria even more antibiotic-resistant as new resistant genes are added to the gene pool. While this is no coyote and roadrunner chase, there is a microscopic battle going on between bacteria and the antibiotics that are heavily prescribed to us across the world.

 

Study Information

Original study: First report on antibiotic resistance and antimicrobial activity of bacterial isolates from 13,000-year old cave ice core

Study published on: January 12, 2021

Study author(s): Victoria I. Paun, Paris Lavin, Mariana C. Chifiriuc & Cristina Purcarea

The study was done at: Institute of Biology (Romania), Universidad de Antofagasta (Chile), University of Bucharest (Romania)

The study was funded by: This study was financially supported by the H2020 EraNet-LAC ELAC2014/DCC0178 Joint Program and PN-III-P2-2.1-PED2019-2461.

Raw data availability: The partial 16S rRNA gene sequences of the bacterial isolates from cave ice core were deposited in GenBank database under accession numbers MG642093-MG642131, MG642137-MG642141, MG680928, MG680933-MG680934, MH321580-MH321599, MH321601-MH321603, MN577392-MN577395, MN577397, MN577399, MN577401, MN577406, MN577408.

Featured image credit: Scarisoara Ice Cave, 2006, photo by Cristian Bortes (Flickr)