|Gram-negative bacterial infection|
|Gram-negative cell wall|
|Specialty|| Infectious disease |
Gram-negative bacterial infection refers to a disease caused by gram-negative bacteria. One example is E. coli.
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane.
It is important to recognize that this class is defined morphologically (by the presence of a bacterial outer membrane), and not histologically (by a pink appearance when stained), though the two usually coincide.
The bacterial outer membrane is found in gram-negative bacteria. Its composition is distinct from that of the inner cytoplasmic cell membrane - among other things, the outer leaflet of the outer membrane of many gram-negative bacteria includes a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and in some bacteria such as E. coli it is linked to the cell's peptidoglycan by Braun's lipoprotein.
One reason for this division is that the outer membrane is of major clinical significance: it can play a role in the reduced effectiveness of certain antibiotics,and it is the source of endotoxin.
The gram status of some organisms is complex or disputed:
Mycoplasma are a mollicute genus of bacteria that lack a cell wall around their cell membranes. This characteristic makes them naturally resistant to many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans, including M. pneumoniae, which is an important cause of atypical pneumonia and other respiratory disorders, and M. genitalium, which is believed to be involved in pelvic inflammatory diseases. Mycoplasma species are the smallest bacterial cells yet discovered, can survive without oxygen, and come in various shapes. For example, M. genitalium is flask-shaped, while M. pneumoniae is more elongated. Hundreds of mycoplasma species infect animals.
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi but rarely in other eukaryotes including animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters.
Gram stain or Gram staining, also called Gram's method, is a method of staining used to distinguish and classify bacterial species into two large groups. The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique.
Gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their cell wall.
Nongonococcal urethritis (NGU) is an inflammation of the urethra that is not caused by gonorrheal infection.
Gardnerella is a genus of Gram-variable-staining facultative anaerobic bacteria of which Gardnerella vaginalis is the only species. The organisms are small non-spore-forming, nonmotile coccobacilli.
Atypical pneumonia, also known as walking pneumonia, is the type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease it is called primary atypical pneumonia (PAP).
Teichoic acids are bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydrates linked via phosphodiester bonds.
The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the periplasmic space in gram-negative bacteria. Using cryo-electron microscopy it has been found that a much smaller periplasmic space is also present in gram-positive bacteria.
The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is absent.
Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer more generally to any organic molecule that contains amino sugar substructures. Aminoglycoside antibiotics display bactericidal activity against Gram-negative aerobes and some anaerobic bacilli where resistance has not yet arisen but generally not against Gram-positive and anaerobic Gram-negative bacteria.
Polymyxins are antibiotics. Polymyxins B and E are used in the treatment of Gram-negative bacterial infections. They work mostly by breaking up the bacterial cell membrane. They are part of a broader class of molecules called nonribosomal peptides.
Bacterial pneumonia is a type of pneumonia caused by bacterial infection.
Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules. They are present in the outer membrane of gram-negative bacteria and some gram-positive Mycobacteria, the outer membrane of mitochondria, and the outer chloroplast membrane.
Clue cells are epithelial cells of the vagina that get their distinctive stippled appearance by being covered with bacteria. The etymology behind the term "clue" cell derives from the original research article from Gardner and Dukes describing the characteristic cells. The name was chosen for its brevity in describing the sine qua non of bacterial vaginosis.
The Nugent Score is a Gram stain scoring system for vaginal swabs to diagnose bacterial vaginosis. The Nugent score is calculated by assessing for the presence of large Gram-positive rods, small Gram-variable rods, and curved Gram-variable rods. A score of 7 to 10 is consistent with bacterial vaginosis without culture. The Nugent Score is now rarely used by physicians due to the time it takes to read the slides and requires the use of a trained microscopist. Bacterial vaginosis diagnosis is done by evaluating the pH, the presences of Lactobacillus spp. versus a mixed flora consisting of Gardnerella vaginalis, Bacteroides spp, Mobiluncus spp, and Mycoplasma hominis. Nugent's test for bacterial vaginosis is performed by measuring the pH, evaluating the presence of clue cells, white discharge an odor of amines after mixing with KOH. Prior to the development of Nugent's test, assessment of bacterial vaginosis was based on culturing G. vaginalis, examining a gram stain of vaginal discharge and gas chromatography.
Bactericidal/permeability-increasing protein (BPI) is a 456-residue (~50kDa) protein that is part of the innate immune system. It belongs to family of lipid-binding serum glycoproteins.
In bacteriology, a fimbria, also referred to as an "attachment pilus" by some scientists, is an appendage that can be found on many Gram-negative and some Gram-positive bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long. Fimbriae are used by bacteria to adhere to one another and to adhere to animal cells and some inanimate objects. A bacterium can have as many as 1,000 fimbriae. Fimbriae are only visible with the use of an electron microscope. They may be straight or flexible.
Mobiluncus is a genus of Gram-negative, anaerobic, rod-shaped bacteria. While this species possesses a cell wall with structural similarity to other Gram-positive cell walls, upon Gram stain, these bacteria may be stained either Gram-negative or Gram-variable.
Mycoplasma adleri is a species of bacteria in the genus Mycoplasma. This genus of bacteria lacks a cell wall around their cell membrane. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. Mycoplasma are the smallest bacterial cells yet discovered, can survive without oxygen and are typically about 0.1 µm in diameter. It is found in goats where it causes infection. The type strain is strain G145 = ATCC 27948 = CIP 105676. Its genome has been determined. M. adleri is gram negative and appears round or coccobacillary in form. Individual cells vary in diameter from 300 to 600 nm, and each is surrounded by a single cytoplasmic membrane. The cell has a ‘fried-egg’ resemblance on a variety of growth media. It is anaerobic.
Mycoplasma spumans is a species of bacteria in the genus Mycoplasma. This genus of bacteria lacks a cell wall around their cell membrane. Without a cell wall, pathogenic species in this genus are unaffected by many antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. Mycoplasma are the smallest bacterial cells yet discovered, can survive without oxygen and are typically about 0.1 µm in diameter.