Gram-Negative Bacteria (GnR) are a group of microorganisms which include Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Klebsiella oxytoca and others. They are known to cause various types of infections including urinary tract infection, bloodstream infections, skin and soft tissue infections, respiratory disease and food poisoning.
The term “gram negative” was first used in the 1930s by Professor Hans Christian Joachim Gram, the developer of a simple and rapid method of staining bacteria which still bears his name.
The staining method involves dipping bacteria in a solution containing a substance called crystal violet.
The bacteria are then exposed to a solution of iodine before being washed with a sodium carbonate solution.
The result is that the bacteria absorb the iodine and appear purple.
The remainder of the stain washes away and the bacteria are left surrounded by a thin line of purplecoloured crystals of iodine.
These bacteria can then be treated with a solution of fluorescent dye.
As the dye attaches itself to the outside of the cell wall, the bacteria take on a pink colour and can be seen under a special light microscope.
These bacteria are known as Gram-negative because of this process.
Other types of bacteria, those that have a thicker cell wall surrounding the cell membrane, resist the stains used and remain colourless under the microscope. These are known as Gram-positive because they resist the Gram stain.
These are not necessarily more “positive” or “negative” than Gram-negative bacteria. It is just a description of how they appear when stained.
Gram staining is not a foolproof method of identification. Sometimes bacteria that appear Gram-negative under the microscope will turn out to be Gram-positive after further testing.
The term “gram negative” is not a specific name for any single group of organisms.
It is just a way of describing the staining reaction of certain bacteria.
Gram-negative bacteria can be found in several different groups, including the following.
Gram-negative Bacteria and Antibiotic Resistance
One particularly worrying development in the medical field is the increase in the number of diseases caused by antibiotic resistant strains of bacteria.
Gram-negative bacteria are known to be resistant to a wide variety of antibiotics.
One example is the Acinetobacter baumannii, which causes pneumonia and infections in wounds.
This particular pathogen is resistant to nearly all first-line antibiotics.
Antibiotic resistance is not unique to Gram-negative bacteria.
However, the high incidence of antibiotic resistance within the Gram-negative group means that treatment options are severely limited in many cases.
Antibiotic Resistance and Gram-Negative Bacteria
The rise in antibiotic resistance within the Gram-negative group of bacteria is due to several factors.
One of the main reasons is the excessive use of antibiotics by humans.
Since antibiotics have been over-used, pathogens have evolved to survive and these resistant strains are then passed on from person to person.
Antibiotics are also widely used in the livestock and poultry industries.
This overuse promotes the development of resistance by the pathogenic bacteria within these animals.
The antibiotics are excreted in the faeces of the animals and get into the soil.
Resistant strains can then infect humans through food or water contaminated with these faeces.
This can be a major cause of the resistance to antibiotics such as tetracycline, erythromycin and clindamycin.
Recent evidence suggests that soil-based organisms are developing resistance to macrolide, lincosamide and tetraphosphonate antibiotics.
This can affect the treatment of tuberculosis in humans.
These drugs are also used in agriculture and it is thought that soil bacteria are becoming resistant as a result.
This is an alarming development since tuberculosis is normally treated with multiple antibiotics.
Without effective drugs to combat the disease, it can become fatal once again.
Gram-negative bacteria occur in the soil and water.
They are found in most ecosystems on Earth, including in the bodies of animals and humans.
Some are pathogens and some are commensals.
Commensals are organisms like the bacteria that live in our digestive system and provide some benefit to us.
Usually, a commensal bacterium will not cause disease unless something changes in the environment or its host.
Gram-negative bacteria are known to grow and reproduce quickly.
This enables them to cause disease more easily than other types of pathogen.
For example, the Gram-negative bacteria E. coli are found in the digestive system of healthy humans and animals.
However, some strains such as E. coli O157:H7 cause illness by releasing toxins that poison the human body.
Inflammation and cell destruction can occur on a large scale, leading to symptoms such as bloody diarrhoea.
The NDM-1 enzyme was recently discovered in a strain of bacteria called the New Delhi metallo-beta-lactamase.
This was found in a patient who had been hospitalised in New Delhi, hence the name NDM-1.
This enzyme makes bacteria resistant to the antibiotic known as carbapenem.
Carbapenems are considered to be a last resort drug when no other treatment works.
The NDM-1 enzyme makes these “last resort” drugs useless.
This is a significant problem since there are few options for treating patients infected with the bacteria that produce the NDM-1 enzyme.
These patients suffer from extreme bacterial infections when most antibiotics no longer work.
Antibiotics are one of the greatest advances of science.
However, the improper use of these drugs has been a major contributor to the rise of antibiotic-resistant superbugs.
In September 2011, the United Nations General Assembly held a meeting about the danger of antibiotic resistance.
The World Health Organisation is involved in an international effort to address this problem.
The WHO has created the “Global Strategy for Containment of Antimicrobial Resistance”.
This involves research into new drugs and changes in medical practices.
For example, the guidelines advise that doctors should prescribe antibiotics only when necessary.
This would prevent unnecessary exposure to antibiotics and could slow down the development of resistance.
Antibiotic resistance is a global problem that will affect everyone at some point in their lives.
To make matters worse, very few new antibiotics are in the process of being developed.
It is now more important than ever to practice proper hygiene to prevent the spread of infection.
When people are sick they should also not go to school or work until they are feeling better.
This will prevent the spread of infection to others who may not be as healthy and more susceptible to disease.
Also, people should not expect doctors to provide a cure-all for every disease.
When sick, people should seek proper medical attention and take all the antibiotics they are given.
Also, people should not save their leftover antibiotics since this will promote antibiotic resistance in bacterial strains.
Once a bacterial population becomes resistant to an antibiotic it is almost impossible to change that.
Use of antibiotics should be limited as much as possible to slow the development of resistance.
Forgotten antibiotics should be discarded instead of saved for later use.
People who do not need antibiotics should not demand them from their doctors.
Antibiotic resistance is a serious problem that affects everyone.
By practicing proper hygiene, not demanding unnecessary prescription drugs, and speaking out against the improper use of antibiotics, everyone can do their part to slow the development of resistance.
Sources & references used in this article:
- Improved broad-host-range plasmids for DNA cloning in gram-negative bacteria (NT Keen, S Tamaki, D Kobayashi, D Trollinger – Gene, 1988 – Elsevier)
- The complete general secretory pathway in gram-negative bacteria. (AP Pugsley – Microbiology and Molecular Biology Reviews, 1993 – Am Soc Microbiol)
- Multidrug efflux pumps of gram-negative bacteria. (H Nikaido – Journal of bacteriology, 1996 – ncbi.nlm.nih.gov)