In the scramble to find alternative ways to stem the rise of superbugs, scientists from many fields are looking everywhere for solutions, including revisiting one that was proposed over 80 years ago: identifying natural “lytic” enzymes in body fluids like tears and saliva and other sources, that are capable of attacking bacteria, especially antibiotic-resistant ones like MRSA.
Now a new US study, by a team from the Georgia Institute of Technology in Atlanta and the University of Maryland in Rockville, published on 4 October in the Institute of Physics journal Physical Biology, describes the results of a pioneering method that can identify which lytic enzymes are the most effective at killing unfriendly bacteria, including superbugs.
Lytic enzymes were first spotted by Alexander Fleming in 1923, five years before he discovered penicillin; he noticed that enzymes present in mucus samples was capable of killing bacteria. But then penicillin came along, laying the ground for what we now know as antibiotics, and lytic enzymes were quietly forgotten.
However, antibiotic-resistant superbugs now demand that we consider a different approach to the “one size fits all” therapy of current antibiotics, which is considered partly responsible for their rise in the first place.
An advantage of lytic enzymes is that each type targets a limited range of bacteria, so in theory it should be possible to find ones that kill undesirable bacteria while leaving the “friendly” ones alone.
Now study authors Joshua Weitz and Gabriel Mitchell, quantitative biologists at the Georgia Institute of Technology, and Daniel Nelson, a biochemist from the University of Maryland, have shown it is possible on a microscopic scale, to work out how powerful lytic enzymes are at destroying bacteria by finding the rate at which they pierce the bacterial cell walls (the process of “lysis”), thereby causing the organisms to explode to death under the force of their own internal pressure.
In their paper they explained how they observed light passing through a solution of bacteria in a similar way to astrophysicists observing light from far-away galaxies: by measuring the amount and properties of the light they could “infer processes at a far different scale”.
Previous attempts to characterize lytic enzymes have used techniques based on synthetic substrates: this has proved difficult because lytic enzymes “bind to the complex superstructure of intact cell walls”, wrote the researchers.
The new method developed by Weitz and colleagues, which they described as “based on turbidity assays”, allows them to predict the cell level processes of bacterial death by measuring the rate at which the lytic enzymes clear a “cloudy” (turbid) solution of living bacteria, without having to use a synthetic substrate.
The challenge, they wrote, is in how then to analyze the results so that it is possible to infer what is happening at the microscopic level and thus classify the power of different lytic enzymes in destroying the same bacteria.
What they came up with was a reaction rate constant for each type of enzyme they tested.
To do this they developed a model that integrates the “chemistry responsible for bond cleavage with the physical mechanisms leading to cell wall failure”, and then used a mathematical “inverse problem” approach to estimate the reaction rate constants and the susceptibility of the target cells to being pierced (lysis).
They then validated the model using simulated and experimental assays.
The researchers hope that using this method to estimate reaction rate constants for different lytic enzymes will help to classify them biologically in order to use them as new types of antimicrobial agents.
They wrote they believe it will eventually be possible to find more enzymes, choose the most effective, and then engineer them to be even more effective, so they can tackle a range of superbugs.
Their vision is that one day, this technology will allow new enzymes to be produced for clinical use at the push of a button; however, today, with the publication of their study, as Weitz explained to BBC Radio 4’s Today program on Monday, only the first step has been reached in that long process, which is:
“Mapping out what we can know about enzymes of interest.”
“Quantifying enzymatic lysis: estimating the combined effects of chemistry, physiology and physics.”
Gabriel J Mitchell, Daniel C Nelson, and Joshua S Weitz.
Physical Biology, Volume 7, Number 4, published online 4 October 2010.
Source: Institute of Physics, BBC.
Written by: Catharine Paddock, PhD