Antibiotic-Resistant Bacteria.
The fight against frequent and inappropriate use of antibiotics. The human body petri-dish.
Modern medicine often depends on antibiotics to kill bacterial pathogens. Failure to treat infections due to the evolution of antibiotic resistance in bacteria is a problem that continues to increase every year in the United States. A problem that the World Health Organization describes as “one of the top three threats to global health.”
The heavy use of antibiotics and lack of antibiotic knowledge enhances the chances of developing antibiotic resistance. Without effective antibiotics, common infections such as strep throat, staph, or sexually transmitted diseases pose a significant threat to humans. Many common healthcare interventions and procedures such as surgeries could become too risky or even near impossible to undertake. By identifying the evolutionary tradeoffs whereby the bacteria becomes resistant to a drug at a cost that scientists may be able to exploit.
Antibiotics are natural products produced by bacteria and fungi. These drugs are usually enzyme inhibitors but their mechanism includes cell wall damage, inhibition of transcription, inhibition of translation, or inhibition of DNA replication. Since the first discovery of antibiotics, bacteria have evolved to become resistant to antibiotics.
“It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them, and the same thing has occasionally happened in the body. The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant.”
- Alexander Fleming
Penicillin
In 1928, Scottish bacteriologist Sir Alexander Fleming discovered the first antibiotic, accidentally while working at the St. Mary’s Hospital, located in Paddington, London. Fleming examined his culture plate and noted a secretion from Penicillium notatum. This secretion was observed to have destroyed the colonies of the bacterium Staphylococcus sp. This secretion was named an antibiotic. Further clinical trials that were taken to commercialize the production of antibiotics did not occur until World War II.
The upper-middle colony that appears on this culture plate is Penicillium notatum. There appears to be a zone of inhibition around the Penicillium, inhibiting Staphylococcus growth. Within this zone of inhibition are Staphylococci undergoing lysis. Below this zone of inhibition is the normal Staphylococcal colony.
Understanding Broad Spectrum and Narrow Spectrum Antibiotics
Antibiotics may be Broad or Narrow Spectrum. Broad-spectrum antibiotics kill all bacterial types well. Usually by the inhibition of enzymes found in all bacteria.
Broad-spectrum antibiotics kill both (and everything in between) gram-positive and gram negatives bacteria. Neosporin is an example of first aid, a broad-spectrum antibiotic ointment, typically used to treat mild skin infections.
Narrow spectrum antibiotics kill only some bacteria but not others as it is usually an inhibitor of enzymes that are found in certain bacteria. Narrow-spectrum antibiotics often kill only gram-negative, or only gram-positive bacteria, as they are made possible to only kill one species. Vancomycin is an example of a narrow-spectrum antibiotic typically used to treat nosocomial infections (Libretexts 2020, April 24).
In a clinical setting, narrow-spectrum antibiotics are favored/administered first over broad-spectrum antibiotics. Broad-spectrum antibiotics target several infectious diseases and therefore would mostly be used in the scenario where the infection cannot be diagnosed with certainty. If an oral broad-spectrum was taken, this puts the individual at risk of killing their good microflora, however, the risk-to-benefit ratio deems this necessary as the origin of the infection is unknown or when there are multiple infections taking place.
In cases where drug-resistant bacteria do not respond to narrow-spectrum antibiotics — superinfection — a broad-spectrum antibiotic will be administered (Libretexts 2020, April 24).
In addition, the disruption of normal bacterial flora leads to opportunistic infections — such as Candida albicans (yeast) infections which can result in Clostridium difficile (C. diff): infections of the intestine.
This figure indicates that a gram-positive cell wall contains a thick peptidoglycan layer with teichoic acids whereas, a gram-negative cell wall consists of a thin peptidoglycan layer surrounded by an outer membrane (Dr. Samanthi, 2018, June 07).
This figure is significant because the inhibitors of enzymes that are found in bacteria are not humans. Human cells are significantly different enough to be able to take antibiotics — without damage to an individual’s own cell. Humans do not have cell walls, cannot make folate, and have differences in transcription, RNA, ribosomal and etc, (University of Utah, Retrieved May 28, 2022).
Understanding Bacteria Growth Curve
Lag phase: Bacteria are metabolically active — adapting to the new growth/environment conditions and not adapting.
Log phase/Exponential phase: Bacteria double in population with each generation.
Stationary phase: Growth of the bacteria plateaus due to the depletion of nutrients ensuing growth-limiting
factors. Where the rate of cell division and death are roughly equal.
Death phase: Exponential declines due to a lack of resources, bad conditions, or toxins/ethanol. During this phase, more cells are dying than new cells are being produced — and the number of cells decreases rapidly.
Bacteria cells divide at a constant rate by binary fission during the log/exponential phase. During this phase, metabolic activity is high. It is in this growth phase that antibiotics and disinfectants are most effective as antibiotics will typically target bacteria cell walls, and processes that generate division — such as the protein synthesis processes of DNA transcription or RNA translation.
This figure is significant because antibiotics and disinfectants usually affect exponentially growing populations. Theoretically, if antibiotics were taken inconsistently — if the antibiotics were not taken consistently through the exponential phase, a death phase would not occur, for the resources necessary in the human body (host) are not limited. This may lead to resistance to the antibiotic that was administered and taken inconsistently.
Evolution of Bacterial Resistance
A Kishony Lab at HMS and Technion (www.technion.ac.il/en/) scientist designed an experiment to study bacterial movement as they become impervious to drugs — by observation of how bacteria maneuvers through a petri dish as they encounter increasingly high doses of antibiotic.
The color lines indicate the difference and number of bacterial colonies on the petri dish and the plots/points indicate the point of adaptation to survive and thrive in them.
The petri dish agar is separated into 9 sections, each with a different amount of antibiotic. The outside contains zero antibiotics and increases by one then by tens until the middle of the petri dish is met with an equal number — as shown below.
Interpreting this experiment is important because through the progression of this petri dish suggests mutations, selections, and trade-offs occur within the bacteria as a means of survival.
At zero antibiotics, the bacteria grow to the point where they can no longer survive — when met with the first dose of antibiotics. Then a mutation appears within a bacterial cell, spreads, and competes with other mutants surrounding it. This early low-resistance mutant will soon give rise to other moderately resistant mutants.
This process will continue and ultimately in intermediate bacterial cells that will spawn highly resistant strains. By the end of this experiment, Figure 4 indicates strains that are able to overcome a dose of trimethoprim high as 1,000. The final result of this experiment is a bacteria that is 1,000 times more resistant than their ancestors. From this experience, one could infer that in order to avoid resistance, initial high dosages and a long duration of treatment are necessary.
Recovery Time
Letter (A) of this figure represents the recovery time by cell density over time. The time that the cell population requires to return to the initial density after exposure to a dose of antibiotic.
Letter (B) Indicates that each dose of antibiotic/concentration includes a recovery time. To capture both Time and concentration is a dependent relationship between the given bacterial population and the antibiotic. The recovery time may be measured in four different ranges of antibiotic concentration. The curves represent the concentration of antibiotics as 1–4 from weakest to most substantial.
Letter (C) Indicates the recovery time each pathogen requires per antibiotic. The recovery time is represented by the curve that is seen increasing by recovery time over the initial/given antibiotic. The recovery time for each range of antibiotic concentrations represents an interaction between a pathogen and a particular antibiotic from one of the given ranges in concentration.
This figure is significant as it supports the experiment conducted by the Kishony Lab at HMS and Technion. This study represents a metric to guide proper antibiotic dosing protocols. This experiment intends to optimize treatment efficacy for any antibiotic and pathogen combination. One could infer that in order to avoid resistance, proper dosages and duration of treatment based on recovery time are necessary.
Relevancy to Nosocomial Infection
The increasing incidence of healthcare-acquired infections marks hospitals, facilities, and intensive care units as a breeding ground for the development and spread of antibiotic-resistant pathogens. This is the consequence of heavy antibiotics as a result of excessive antibiotic prescription and the interplay of microorganisms in a high-density patient population — met with frequent contact from health staff — increases morbidity and mortality.
MRSA caused by staphylococcus aureus is indicated to be increasingly resistant to Methicillin. VRE an enterococci is indicated to be increasingly resistant to Vancomycin. FQRP/fluoroquinolone-resistant Pseudomonas aeruginosa. Multidrug-resistant Gram-negative rods like Acinetobacter baumannii (famously known as Iraqibacter)
Work Cited:
Bacterial growth. (2022, May 01). Retrieved May 28, 2022, from https://en.wikipedia.org/wiki/Bacterial_growth#/media/File:Bacterial_growth_en.svg
Bacterial temporal dynamics enable optimal design of antibiotic treatment. (n.d.). Retrieved May 28, 2022, from https://journals.plos.org/ploscompbiol/article/figure?id=10.1371%2Fjournal.pcbi.1004201.g002
CDC’s antibiotic resistance threats report, 2019 — hhs.gov. (n.d.). Retrieved May 29, 2022, from https://www.hhs.gov/sites/default/files/michael-craig-cdc-talk-thursday-am-508.pdf
Dr.Samanthi. (2018, June 07). Difference between gram-positive and gram-negative cell wall. Retrieved May 28, 2022, from https://www.differencebetween.com/difference-between-gram-positive-and-gram-negative-cell-wall/
Harvardmedicalschool. (2016, September 09). The evolution of bacteria on a “mega-plate” Petri dish (kishony lab). Retrieved May 28, 2022, from https://www.youtube.com/watch?v=plVk4NVIUh8
Libretexts. (2020, April 24). 7.1.4: Spectrum of antimicrobial activity. Retrieved May 28, 2022, from https://bio.libretexts.org/Courses/Northwest_University/MKBN211%3A_Introductory_Microbiology_(Bezuidenhout)/07%3A_Antimicrobial_Drugs/7.01%3A_Overview_of_Antimicrobial_Therapy/7.1.04%3A_Spectrum_of_Antimicrobial_Activity#:~:text=Narrow%20spectrum%20antibiotics%20act%20against,negative%20bacteria%2C%20for%20example%20amoxicillin.
Sir Alexander Fleming’s laboratory by St Mary’s Hospital Medical School/Science Photo Library. (n.d.). Retrieved May 28, 2022, from https://fineartamerica.com/featured/sir-alexander-flemings-laboratory-st-marys-hospital-medical-schoolscience-photo-library.html
University of Utah. (n.d.). What is an Antibiotic? Retrieved May 28, 2022, from https://learn.genetics.utah.edu/content/microbiome/antibiotics#:~:text=Antibiotics%20work%20by%20affecting%20things,many%20types%20of%20bacteria%20do.
Van Staa, T., Palin, V., Li, Y., Welfare, W., Felton, T., Dark, P., & Ashcroft, D. (2020, March 02). The effectiveness of frequent antibiotic use in reducing the risk of infection-related hospital admissions: Results from two large population-based cohorts — BMC medicine. Retrieved May 28, 2022, from https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-020-1504-5