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The distinction between Gram-positive and Gram-negative bacteria is based upon the Gram staining method, that reflects the bacterial wall physical properties. However, this classification involves also a large number of differences between them. For example, the endospore formation usually occurs in Gram-positive bacteria and also the quorum sensing mechanism is different.
So what are those differences? Which of them are due to the cell wall thickness and membrane(s) composition and which instead to evolutionary divergences?
I didn't know there were distinct differences between gram-positive and gram-negative bacteria when it came to quorum sensing, but it seems as though there are:
In gram negative bacteria, acyl-homoserine lactone type molecules serve as the main signalling molecules while lipid, peptide, and amino acid based signalling molecules infrequently serve as signalling molecules. Furthermore, in gram-negative bacteria, there is one well conserved mechanism for controlling quorum response. Gram-positive bacteria, on the other hand, use peptides or modified peptides as the primary means of signaling; and also differing from gram-negative bacteria, there are several different mechanisms found within the class which are used to gain quorum responses.
In G+ bacteria, the two main quorum sensing mechanisms are apparently as follows:
Two-component signal transduction, in which the peptide signal works by binding to a sensor protein, histidine kinase, located in the cell membrane of the bacterium. The activation of the histidine kinase leads to phosphorylation of response-regulating protein, and interaction with another regulatory protein facilitates transcriptional activation.
Internalization, in which the signal molecules are transported into the responder cell to interact with intracellular effectors.
G- bacteria on the other hand, synthesize autoinducers, effector molecules that can diffuse freely through the cell membrane and trigger cell response when a certain concentration threshold is reached. I do not know how or if these differences are related to cell wall structure.
When it comes to endospore formation, all I know of the difference between the two is that this is by far most common in gram-positive bacteria.
Gram-positive vs. Gram-negative Bacteria
Danish scientist Hans Christian Gram devised a method to differentiate two types of bacteria based on the structural differences in their cell walls. In his test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria. In contrast, Gram-negative bacteria do not retain the violet dye and are colored red or pink. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall. These bacteria have a wide variety of applications ranging from medical treatment to industrial use and Swiss cheese production.
Difference Between Gram Positive and Gram Negative Bacteria
Gram staining is the first stage in identification of the bacteria. It differentiates the bacteria on the basis of chemical properties of their Cell Wall. Hans Christian Gram was the inventor of Gram staining. Please note that NOT all bacteria can be classified by this technique and only those bacteria which can be classified by using this technique are called Gram variable. Otherwise they are called Gram indeterminate.
How does Gram Staining work?
The staining distinct two types of bacteria viz. Gram positive and Gram negative denoted by G+ and G-. The primary stain used in the technique is crystal violet. Crystal violet is followed by use of a trapping agent (Gram Iodine) and after that alcohol is used to decolorize and finally Safranin / Basic fushcin is used to counter stain. The crystal violet gets dissociated in CV+ and Cl- ions in water and these ions penetrate the cell walls.
The cell wall which is made up of Peptidoglycan as well as lipids gets violet due to the reaction of the CV+. After the decolorization with alcohol, the lipids gets dissolved and the bacteria with higher Peptidoglycan remain violet. These are called Gram Positive bacteria. The bacteria which lose the violet color are called Gram negative bacteria.
It includes form, elevation, and margin of the bacterial colony.
Form of the bacterial colony: – The form refers to the shape of the colony. These forms represent the most common colony shapes you are likely to encounter. e.g. circular, irregular, filamentous, rhizoid, etc.
Elevation of the bacterial colony: It gives information about, how much does the colony rise above the agar. This describes the “side view” of a colony. These are the most common elevations e.g. flat, raised, umbonate (having a knobby protuberance), crateriform, convex, pulvinate (cushion-shaped).
Margin of bacterial colony: The margin or edge of a colony may be an important characteristic in identifying organisms. Common examples are entire (smooth), irregular, undulate (wavy), lobate, curled, filiform, etc.
Colonies that are irregular in shape and/or have irregular margins are likely to be motile organisms. Highly motile organisms swarmed over the culture media, such as Proteus spp.
Peptidoglycan layer is the outermost covering of the Gram-positive cell wall. It constitutes as much as 90% of the cell wall of Gram-positive. Many Gram-positive bacteria have several sheets of peptidoglycan stacked one upon another and cross-linked by glycan strands. Many gram-positive bacteria have teichoic acids (polymers of glycerol phosphate or ribitol phosphate) covalently bonded to muramic acid in the wall peptidoglycan or membrane lipids (lipoteichoic acids).
The gram-negative cell wall is chemically complex than gram-positive and consists of at least two layers. Outer membrane (lipopolysaccharide layer, LPS in short) is the outermost covering of the Gram-negative cell wall. Beneath it lies a thin sheet of peptidoglycan which constitutes only 10% of the cell wall of Gram-negative. Outer membrane contains a lipid bilayer bonded with polysaccharides (hence the name lipopolysaccharide).
Spheroplasts: Gram-negative bacteria with the intact cytoplasmic membrane of the protoplast plus the outer membrane (LPS layer) of the cell wall, after peptidoglycan layer is destroyed by lysozyme or its synthesis inhibited by antibiotics.
Protoplasts: Cells whose walls have been completely remove and are incapable of normal growth and division.
What is the Difference Between Gram Positive and Gram Negative Bacteria?
The major difference between gram positive and gram negative bacteria is that gram positive bacteria have a thick peptidoglycan layer in their cell wall while gram negative bacteria have a thin peptidoglycan layer in their cell wall. Apart from the peptidoglycan layer, gram negative bacteria possess an outer membrane and it is absent in gram positive bacteria. Hence, this is also a difference between gram positive and gram negative bacteria. Furthermore, gram negative bacteria have a periplasmic space and two layers in the cell wall while gram positive bacteria lack a periplasmic space and they have a single layered rigid and even cell wall.
The following infographic describes more facts regarding the difference between gram positive and gram negative bacteria.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
This work was supported by a grant from the NIAID, NIH (grant # R01 A1099451 to LJS, AV, and GR) and federal funds appropriated to the Ohio Agricultural Research and Development Center (OARDC) of The Ohio State University. The authors thank Dr. J. Hanson, R. Wood, and J. Ogg, J. Chepngeno, and K. Scheuer for their technical assistance.
- Bacteria and viruses differ in their structure and their response to medications.
- Bacteria are single-celled, living organisms. They have a cell wall and all the components necessary to survive and reproduce, although some may derive energy from other sources.
- Viruses are not considered to be &ldquoliving&rdquo because they require a host cell to survive long-term, for energy, and to reproduce. Viruses consist of only one piece of genetic material and a protein shell called a capsid. They survive and reproduce by &ldquohijacking&rdquo a host cell, and using its ribosomes to make new viral proteins.
- Less than 1% of bacteria cause disease. Most are beneficial for our good health and the health of Earth&rsquos ecosystems. Most viruses cause disease.
- Antibiotics may be used to treat some bacterial infections, but they do not work against viruses. Some severe bacterial infections may be prevented by vaccination.
- Vaccination is the primary way to prevent viral infections however, antivirals have been engineered that can treat some viral infections, such as Hepatitis C or HIV. Antivirals are not effective against bacteria.
What are bacteria?
Bacteria are simple, single celled organisms, called prokaryotes, which means their DNA is contained within a certain area of the cell called the nucleoid, but not enclosed. Bacteria are one of the oldest living things on earth, having been in existence for at least 3.5 billion years. A microscope is needed to see them.
Bacteria come in many shapes and sizes, including spheres, cylinders, threads, rods, or chains. They can be aerobic (those that require oxygen to survive), anaerobic (those that die when exposed to oxygen), and those that prefer oxygen but can live without it. Bacteria that create their energy through light or chemical reactions are called autotrophs, and those that have to consume and break down complex organic compounds to obtain energy are called heterotrophs.
Bacteria are enclosed by a rigid cell wall, which can vary widely in its composition, helping to distinguish between different species of bacteria. When exposed to a dye called a gram stain, gram positive bacteria trap the dye due to the structure of their walls, while gram negative bacteria release the dye readily, because their cell wall is thin. Inside the cell wall sits all the components necessary for bacteria to grow, metabolize, and reproduce.
Bacteria may also have protrusions, these are known as pili (help bacteria to attach to certain structures, such as teeth or intestines) or flagella (which help bacteria to move).
Although some bacteria can cause disease, less than one percent make us sick. Many beneficial species are essential for our good health and the overall health of most of Earth&rsquos ecosystems. Inside our bodies, we have tens of trillions of bacteria making up our gut microbiome, and trillions more living, usually harmlessly, on our skin. Many chronic diseases, such as cancer and heart disease, are associated with poor oral health often because of an imbalance of bacteria within our mouth. Infections caused by bacteria include strep throat, tuberculosis, and urinary tract infections (UTI).
The primary way to prevent bacterial infections is by giving antibiotics however, because of resistance, antibiotics are usually only used for severe infections, because the immune system of most people is usually strong enough to overcome the infection.
For some severe bacterial infections, such as diphtheria, meningococcal disease, pertussis, or tetanus, vaccinations have been developed and these are the most effective way to prevent against infection.
What are viruses?
Viruses consist of a piece of genetic material, such as DNA or RNA (but not both) surrounded by a protein shell called a capsid.
Sometimes this shell is surrounded by an envelope of fat and protein molecules, and out of this envelope may project glycoprotein protrusions, called peplomers, which can be triangular, spiked, or shaped like a mushroom. These protrusions bind only to certain receptors on a host cell and determine what type of hosts or host cell a virus will infect and how infectious that virus will be.
A microscope is required to see viruses and they are 10 to 100 times smaller than the smallest bacteria.
Because viruses MUST infect a host cell to carry out life-sustaining functions or to reproduce, they are not considered living organisms, although some can survive on surfaces for long periods. Viruses are essentially like a parasite, relying on a host cell to reproduce and survive.
When a virus infects a host cell, it uses its genetic material to &ldquohijack&rdquo the ribosomes in the host cell. These are the cell structures that make protein. So instead of protein being made that can be used by the host cell, viral proteins are made.
The virus also takes advantage of other components within the host cell, such as ATP (adenosine triphosphate) for energy, and amino acids and fats to make new capsids and assemble new viruses. Once enough new viruses have been made, they burst out of the cell in a process called lysis, which kills the host cell. This is called viral replication and it is the way viruses reproduce.
Once new viruses have been made, they can go on to infect new host cells, and new hosts.
Most viruses cause disease, and they are usually quite specific about the area of the body that they attack, for example, the liver, the respiratory tract, or the blood. Common viruses include herpes zoster, HIV, influenza, the common cold, and the rabies virus. Viruses can also cause pneumonia or sinusitis. The new coronavirus SARs-CoV-2 that causes COVID-19 is also a virus.
As well as humans and animals, viruses can also infect plants, although virtually all plant viruses are transmitted by insects or other organisms that feed on plant walls.
The primary way to prevent viral infections is by vaccination however, antivirals have been engineered that can treat some viral infections, such as Hepatitis C or HIV. Antibiotics do not treat a viral infection.
Virus vs bacteria: Any difference in symptoms?
Symptoms usually reflect the area of the body infected, and the infecting organism. For example, a bacterial infection of the skin may cause a discharge, swelling, pain and redness in a certain area, whereas a viral infection, such as hepatitis C may cause abdominal pain, joint pain, nausea or vomiting, and yellowing of the skin or eyes.
Some illnesses can be caused by either a virus or bacteria, for example pneumonia, meningitis, or diarrhea, and symptoms may be similar, reflecting the body trying to rid itself of the infecting organism, and may include:
What does Low G+C mean?
Scanning electron micrograph of Mycoplasma mobile. White scale bar, lower right, represents 100nm.
The DNA of all living things is made up of four nucleotide bases Adenine (A), Cytosine (C), Guanine (G) and Thymidine (T). In a double helix of DNA, Adenine pairs with Thymidine and Guanine pairs with Cytosine. Therefore the number of Cytosine bases equals the number of Guanine bases and likewise A=T. The percentage of G+C is one of many general features used to characterize bacterial genomes
Most Firmicutes have cell walls, and these bacteria can be found in a great variety of habitats. They are grouped in the Class Bacilli or Class Clostridia. Diverse Firmicutes include Staphylococcus, Micrococcus, Streptococcus and Lactobacillus. Some staphylococci and micrococci are commonly found on human skin and mucosal surfaces. Streptococcus is most famous for causing "strep throat" but many benign streptococci are normally found in the mouth and throat. Lactobacillus is common in the making of yogurt and cheese products. Some Lactobacillus species are associated with mucosal surfaces of humans. These resident Lactobacillus species help maintain our health by preventing colonization by disease-associated bacteria.
Some Firmicutes can form an endospore, a resistant differentiated cell produced under special, usually stressful, conditions. Endospore-forming bacteria such as Bacillus and Clostridium species can be classified by their aerotolerance. Many anaerobic organisms fall under the Clostridium banner. These organisms have very diverse ways of getting energy without using oxygen, but almost all are fermenters. Some Clostridium species are used by industry to produce solvents, an end product of their fermentation activity. Others produce toxins. One famous application of a Clostridium toxin is the use of Clostridium botulinum toxin, also known as BoTox, to paralyze muscles of the face to reduce skin wrinkles. Epulopiscium is closely related to Clostridium species.
Bacilli prefer to live in oxygen-rich environments but some are capable of survival without it. Members of this group are commonly found in soil. Some are responsible for the disease anthrax while others produce antibiotics or insecticides. Bacillus subtilis is one of the primary model organisms used by researchers to understand topics ranging from cell differentiation to iron storage and DNA replication.
The organisms described above represent only a tiny part of the diversity found within the group of Firmicutes. Their huge impact on fields as diverse as agriculture, medicine, food production and ecology make them a vital subject of inquiry.
Difference Between Pathogenic and Nonpathogenic Bacteria
The main difference between pathogenic and nonpathogenic bacteria is that the pathogenic bacteria can cause diseases while the nonpathogenic bacteria are harmless. Moreover, pathogenic bacteria possess several genes that endow the capacity to cause diseases while nonpathogenic bacteria lack such genes. Another difference between pathogenic and nonpathogenic bacteria is that the pathogenic bacteria invades the cells of the body while nonpathogenic bacteria live outside the body cells.
Pathogenic and nonpathogenic bacteria are the two main types of bacteria other organisms are in contact with. The distinction between the two can be made based on the Koch’s Postulates. However, some pathogenic bacteria may be present in normal individuals without causing a disease. Moreover, nonpathogenic bacteria may also cause diseases, becoming opportunistic pathogens in an immune-compromised host.
Key Areas Covered
Bacterial Diseases, Nonpathogenic Bacteria, Pathogenic Bacteria, Pathogenic Factors, Useful Bacteria
Low G+C Gram-positive Bacteria
The low G+C gram-positive bacteria have less than 50% guanine and cytosine in their DNA, and this group of bacteria includes a number of genera of bacteria that are pathogenic.
Clinical Focus: Sharnita, Part 3
Based on her symptoms, Sharnita’s doctor suspected that she had a case of tuberculosis. Although less common in the United States, tuberculosis is still extremely common in many parts of the world, including Nigeria. Sharnita’s work there in a medical lab likely exposed her to Mycobacterium tuberculosis, the bacterium that causes tuberculosis.
Sharnita’s doctor ordered her to stay at home, wear a respiratory mask, and confine herself to one room as much as possible. He also said that Sharnita had to take one semester off school. He prescribed isoniazid and rifampin, antibiotics used in a drug cocktail to treat tuberculosis, which Marsha was to take three times a day for at least three months.
We’ll conclude Sharnita’s example later in this page.
One large and diverse class of low G+C gram-positive bacteria is Clostridia. The best studied genus of this class is Clostridium. These rod-shaped bacteria are generally obligate anaerobes that produce endospores and can be found in anaerobic habitats like soil and aquatic sediments rich in organic nutrients. The endospores may survive for many years.
Figure 2. Clostridium difficile, a gram-positive, rod-shaped bacterium, causes severe colitis and diarrhea, often after the normal gut microbiota is eradicated by antibiotics. (credit: modification of work by Centers for Disease Control and Prevention)
Clostridium spp. produce more kinds of protein toxins than any other bacterial genus, and several species are human pathogens. C. perfringens is the third most common cause of food poisoning in the United States and is the causative agent of an even more serious disease called gas gangrene. Gas gangrene occurs when C. perfringens endospores enter a wound and germinate, becoming viable bacterial cells and producing a toxin that can cause the necrosis (death) of tissue. C. tetani, which causes tetanus, produces a neurotoxin that is able to enter neurons, travel to regions of the central nervous system where it blocks the inhibition of nerve impulses involved in muscle contractions, and cause a life-threatening spastic paralysis. C. botulinum produces botulinum neurotoxin, the most lethal biological toxin known. Botulinum toxin is responsible for rare but frequently fatal cases of botulism. The toxin blocks the release of acetylcholine in neuromuscular junctions, causing flaccid paralysis. In very small concentrations, botulinum toxin has been used to treat muscle pathologies in humans and in a cosmetic procedure to eliminate wrinkles. C. difficile is a common source of hospital-acquired infections (Figure 2) that can result in serious and even fatal cases of colitis (inflammation of the large intestine). Infections often occur in patients who are immunosuppressed or undergoing antibiotic therapy that alters the normal microbiota of the gastrointestinal tract. Taxonomy of Clinically Relevant Microorganisms lists the genera, species, and related diseases for Clostridia.
The order Lactobacillales comprises low G+C gram-positive bacteria that include both bacilli and cocci in the genera Lactobacillus, Leuconostoc, Enterococcus, and Streptococcus. Bacteria of the latter three genera typically are spherical or ovoid and often form chains.
Streptococcus, the name of which comes from the Greek word for twisted chain, is responsible for many types of infectious diseases in humans. Species from this genus, often referred to as streptococci, are usually classified by serotypes called Lancefield groups, and by their ability to lyse red blood cells when grown on blood agar.
S. pyogenes belongs to the Lancefield group A, β-hemolytic Streptococcus. This species is considered a pyogenic pathogen because of the associated pus production observed with infections it causes (Figure 3). S. pyogenes is the most common cause of bacterial pharyngitis (strep throat) it is also an important cause of various skin infections that can be relatively mild (e.g., impetigo) or life threatening (e.g., necrotizing fasciitis, also known as flesh eating disease), life threatening.
Figure 3. (a) A gram-stained specimen of Streptococcus pyogenes shows the chains of cocci characteristic of this organism’s morphology. (b) S. pyogenes on blood agar shows characteristic lysis of red blood cells, indicated by the halo of clearing around colonies. (credit a, b: modification of work by American Society for Microbiology)
The nonpyogenic (i.e., not associated with pus production) streptococci are a group of streptococcal species that are not a taxon but are grouped together because they inhabit the human mouth. The nonpyogenic streptococci do not belong to any of the Lancefield groups. Most are commensals, but a few, such as S. mutans, are implicated in the development of dental caries.
S. pneumoniae (commonly referred to as pneumococcus), is a Streptococcus species that also does not belong to any Lancefield group. S. pneumoniae cells appear microscopically as diplococci, pairs of cells, rather than the long chains typical of most streptococci. Scientists have known since the 19th century that S. pneumoniae causes pneumonia and other respiratory infections. However, this bacterium can also cause a wide range of other diseases, including meningitis, septicemia, osteomyelitis, and endocarditis, especially in newborns, the elderly, and patients with immunodeficiency.
The name of the class Bacilli suggests that it is made up of bacteria that are bacillus in shape, but it is a morphologically diverse class that includes bacillus-shaped and cocccus-shaped genera. Among the many genera in this class are two that are very important clinically: Bacillus and Staphylococcus.
Bacteria in the genus Bacillus are bacillus in shape and can produce endospores. They include aerobes or facultative anaerobes. A number of Bacillus spp. are used in various industries, including the production of antibiotics (e.g., barnase), enzymes (e.g., alpha-amylase, BamH1 restriction endonuclease), and detergents (e.g., subtilisin).
Two notable pathogens belong to the genus Bacillus. B. anthracis is the pathogen that causes anthrax, a severe disease that affects wild and domesticated animals and can spread from infected animals to humans. Anthrax manifests in humans as charcoal-black ulcers on the skin, severe enterocolitis, pneumonia, and brain damage due to swelling. If untreated, anthrax is lethal. B. cereus, a closely related species, is a pathogen that may cause food poisoning. It is a rod-shaped species that forms chains. Colonies appear milky white with irregular shapes when cultured on blood agar (Figure 4). One other important species is B. thuringiensis. This bacterium produces a number of substances used as insecticides because they are toxic for insects.
Figure 4. (a) In this gram-stained specimen, the violet rod-shaped cells forming chains are the gram-positive bacteria Bacillus cereus. The small, pink cells are the gram-negative bacteria Escherichia coli. (b) In this culture, white colonies of B. cereus have been grown on sheep blood agar. (credit a: modification of work by “Bibliomaniac 15″/Wikimedia Commons credit b: modification of work by Centers for Disease Control and Prevention)
Figure 5. This SEM of Staphylococcus aureus illustrates the typical “grape-like” clustering of cells. (credit: modification of work by Centers for Disease Control and Prevention)
The genus Staphylococcus also belongs to the class Bacilli, even though its shape is coccus rather than a bacillus. The name Staphylococcus comes from a Greek word for bunches of grapes, which describes their microscopic appearance in culture (Figure 5). Staphylococcus spp. are facultative anaerobic, halophilic, and nonmotile. The two best-studied species of this genus are S. epidermidis and S. aureus.
S. epidermidis, whose main habitat is the human skin, is thought to be nonpathogenic for humans with healthy immune systems, but in patients with immunodeficiency, it may cause infections in skin wounds and prostheses (e.g., artificial joints, heart valves). S. epidermidis is also an important cause of infections associated with intravenous catheters. This makes it a dangerous pathogen in hospital settings, where many patients may be immunocompromised.
Strains of S. aureus cause a wide variety of infections in humans, including skin infections that produce boils, carbuncles, cellulitis, or impetigo. Certain strains of S. aureus produce a substance called enterotoxin, which can cause severe enteritis, often called staph food poisoning. Some strains of S. aureus produce the toxin responsible for toxic shock syndrome, which can result in cardiovascular collapse and death.
Many strains of S. aureus have developed resistance to antibiotics. Some antibiotic-resistant strains are designated as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA). These strains are some of the most difficult to treat because they exhibit resistance to nearly all available antibiotics, not just methicillin and vancomycin. Because they are difficult to treat with antibiotics, infections can be lethal. MRSA and VRSA are also contagious, posing a serious threat in hospitals, nursing homes, dialysis facilities, and other places where there are large populations of elderly, bedridden, and/or immunocompromised patients. Taxonomy of Clinically Relevant Microorganisms lists the genera, species, and related diseases for bacilli.
Although Mycoplasma spp. do not possess a cell wall and, therefore, are not stained by Gram-stain reagents, this genus is still included with the low G+C gram-positive bacteria. The genus Mycoplasma includes more than 100 species, which share several unique characteristics. They are very small cells, some with a diameter of about 0.2 μm, which is smaller than some large viruses. They have no cell walls and, therefore, are pleomorphic, meaning that they may take on a variety of shapes and can even resemble very small animal cells. Because they lack a characteristic shape, they can be difficult to identify. One species, M. pneumoniae, causes the mild form of pneumonia known as “walking pneumonia” or “atypical pneumonia.” This form of pneumonia is typically less severe than forms caused by other bacteria or viruses.
Table 3 summarizes the characteristics of notable genera low G+C Gram-positive bacteria.
|Table 3. Bacilli: Low G+C Gram-Positive Bacteria|
|Example Genus||Microscopic Morphology||Unique Characteristics|
|Bacillus||Large, gram-positive bacillus||Aerobes or facultative anaerobes form endospores B. anthracis causes anthrax in cattle and humans, B. cereus may cause food poisoning|
|Clostridium||Gram-positive bacillus||Strict anaerobes form endospores all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis|
|Enterococcus||Gram-positive coccus forms microscopic pairs in culture (resembling Streptococcus pneumoniae)||Anaerobic aerotolerant bacteria, abundant in the human gut, may cause urinary tract and other infections in the nosocomial environment|
|Lactobacillus||Gram-positive bacillus||Facultative anaerobes ferment sugars into lactic acid part of the vaginal microbiota used as probiotics|
|Leuconostoc||Gram-positive coccus may form microscopic chains in culture||Fermenter, used in food industry to produce sauerkraut and kefir|
|Mycoplasma||The smallest bacteria appear pleomorphic under electron microscope||Have no cell wall classified as low G+C Gram-positive bacteria because of their genome M. pneumoniae causes “walking” pneumonia|
|Staphylococcus||Gram-positive coccus forms microscopic clusters in culture that resemble bunches of grapes||Tolerate high salt concentration facultative anaerobes produce catalase S. aureus can also produce coagulase and toxins responsible for local (skin) and generalized infections|
|Streptococcus||Gram-positive coccus forms chains or pairs in culture||Diverse genus classified into groups based on sharing certain antigens some species cause hemolysis and may produce toxins responsible for human local (throat) and generalized disease|
|Ureaplasma||Similar to Mycoplasma||Part of the human vaginal and lower urinary tract microbiota may cause inflammation, sometimes leading to internal scarring and infertility|
Think about It
- Name some ways in which streptococci are classified.
- Name one pathogenic low G+C gram-positive bacterium and a disease it causes.
Clinical Focus: Sharnita, Resolution
This example concludes Sharnita’s story that started in Prokaryote Habitats, Relationships, and Microbiomes, Proteobacteria, and above
Marsha’s sputum sample was sent to the microbiology lab to confirm the identity of the microorganism causing her infection. The lab also performed antimicrobial susceptibility testing (AST) on the sample to confirm that the physician has prescribed the correct antimicrobial drugs.
Figure 6. M. tuberculosis grows on Löwenstein-Jensen (LJ) agar in distinct colonies. (credit: Centers for Disease Control and Prevention)
Direct microscopic examination of the sputum revealed acid-fast bacteria (AFB) present in Marsha’s sputum. When placed in culture, there were no signs of growth for the first 8 days, suggesting that microorganism was either dead or growing very slowly. Slow growth is a distinctive characteristic of M. tuberculosis.
After four weeks, the lab microbiologist observed distinctive colorless granulated colonies (Figure 6). The colonies contained AFB showing the same microscopic characteristics as those revealed during the direct microscopic examination of Marsha’s sputum. To confirm the identification of the AFB, samples of the colonies were analyzed using nucleic acid hybridization, or direct nucleic acid amplification (NAA) testing. When a bacterium is acid-fast, it is classified in the family Mycobacteriaceae. DNA sequencing of variable genomic regions of the DNA extracted from these bacteria revealed that it was high G+C. This fact served to finalize Marsha’s diagnosis as infection with M. tuberculosis. After nine months of treatment with the drugs prescribed by her doctor, Marsha made a full recovery.
Biopiracy and Bioprospecting
In 1969, an employee of a Swiss pharmaceutical company was vacationing in Norway and decided to collect some soil samples. He took them back to his lab, and the Swiss company subsequently used the fungus Tolypocladium inflatum in those samples to develop cyclosporine A, a drug widely used in patients who undergo tissue or organ transplantation. The Swiss company earns more than $1 billion a year for production of cyclosporine A, yet Norway receives nothing in return—no payment to the government or benefit for the Norwegian people. Despite the fact the cyclosporine A saves numerous lives, many consider the means by which the soil samples were obtained to be an act of “biopiracy,” essentially a form of theft. Do the ends justify the means in a case like this?
Nature is full of as-yet-undiscovered bacteria and other microorganisms that could one day be used to develop new life-saving drugs or treatments.  Pharmaceutical and biotechnology companies stand to reap huge profits from such discoveries, but ethical questions remain. To whom do biological resources belong? Should companies who invest (and risk) millions of dollars in research and development be required to share revenue or royalties for the right to access biological resources?
Compensation is not the only issue when it comes to bioprospecting. Some communities and cultures are philosophically opposed to bioprospecting, fearing unforeseen consequences of collecting genetic or biological material. Native Hawaiians, for example, are very protective of their unique biological resources.
For many years, it was unclear what rights government agencies, private corporations, and citizens had when it came to collecting samples of microorganisms from public land. Then, in 1993, the Convention on Biological Diversity granted each nation the rights to any genetic and biological material found on their own land. Scientists can no longer collect samples without a prior arrangement with the land owner for compensation. This convention now ensures that companies act ethically in obtaining the samples they use to create their products.
Key Concepts and Summary
- Gram-positive bacteria are a very large and diverse group of microorganisms. Understanding their taxonomy and knowing their unique features is important for diagnostics and treatment of infectious diseases.
- Gram-positive bacteria are classified into high G+C gram-positive and low G+C gram-positive bacteria, based on the prevalence of guanine and cytosine nucleotides in their genome
- Actinobacteria is the taxonomic name of the class of high G+C gram-positive bacteria. This class includes the genera Actinomyces, Arthrobacter, Corynebacterium, Frankia, Gardnerella, Micrococcus, Mycobacterium, Nocardia, Propionibacterium, Rhodococcus, and Streptomyces. Some representatives of these genera are used in industry others are human or animal pathogens.
- Examples of high G+C gram-positive bacteria that are human pathogens include Mycobacteriumtuberculosis, which causes tuberculosis M. leprae, which causes leprosy (Hansen’s disease) and Corynebacteriumdiphtheriae, which causes diphtheria.
- Clostridia spp. are low G+C gram-positive bacteria that are generally obligate anaerobes and can form endospores. Pathogens in this genus include C.perfringens (gas gangrene), C. tetani (tetanus), and C. botulinum (botulism).
- Lactobacillales include the genera Enterococcus, Lactobacillus, Leuconostoc, and Streptococcus. Streptococcus is responsible for many human diseases, including pharyngitis (strep throat), scarlet fever, rheumatic fever, glomerulonephritis, pneumonia, and other respiratory infections.
- Bacilli is a taxonomic class of low G+C gram-positive bacteria that include rod-shaped and coccus-shaped species, including the genera Bacillus and Staphylococcus. B. anthracis causes anthrax, B. cereus may cause opportunistic infections of the gastrointestinal tract, and S.aureus strains can cause a wide range of infections and diseases, many of which are highly resistant to antibiotics.
- Mycoplasma spp. are very small, pleomorphic low G+C gram-positive bacteria that lack cell walls. M. pneumoniae causes atypical pneumonia.
Which of the following bacterial species is classified as high G+C gram-positive?