In bacteriology, 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 type of cell wall.
Gram-negative bacteria are bacteria that unlike gram-positive bacteria do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is their cell envelope, which consists of a thin peptidoglycan cell wall sandwiched between an inner (cytoplasmic) membrane and an outer membrane. These bacteria are found in all environments that support life on Earth.
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like layer (sacculus) that surrounds the bacterial cytoplasmic membrane. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Attached to the N-acetylmuramic acid is an oligopeptide chain made of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer. Peptidoglycan serves a structural role in the bacterial cell wall, giving structural strength, as well as counteracting the osmotic pressure of the cytoplasm. This repetitive linking results in a dense peptidoglycan layer which is critical for maintaining cell form and withstanding high osmotic pressures, and it is regularly replaced by peptidoglycan production. Peptidoglycan hydrolysis and synthesis are two processes that must occur in order for cells to grow and multiply, a technique carried out in three stages: clipping of current material, insertion of new material, and re-crosslinking of existing material to new material.
Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally, and ecologically diverse. Applications of bacteriocins are being tested to assess their application as narrow-spectrum antibiotics.
Linezolid is an antibiotic used for the treatment of infections caused by Gram-positive bacteria that are resistant to other antibiotics. Linezolid is active against most Gram-positive bacteria that cause disease, including streptococci, vancomycin-resistant enterococci (VRE), and methicillin-resistant Staphylococcus aureus (MRSA). The main uses are infections of the skin and pneumonia although it may be used for a variety of other infections including drug-resistant tuberculosis. It is used either by injection into a vein or by mouth.
Nisin is a polycyclic antibacterial peptide produced by the bacterium Lactococcus lactis that is used as a food preservative. It has 34 amino acid residues, including the uncommon amino acids lanthionine (Lan), methyllanthionine (MeLan), didehydroalanine (Dha), and didehydroaminobutyric acid (Dhb). These unusual amino acids are introduced by posttranslational modification of the precursor peptide. In these reactions a ribosomally synthesized 57-mer is converted to the final peptide. The unsaturated amino acids originate from serine and threonine, and the enzyme-catalysed addition of cysteine residues to the didehydro amino acids result in the multiple (5) thioether bridges.
Lantibiotics are a class of polycyclic peptide antibiotics that contain the characteristic thioether amino acids lanthionine or methyllanthionine, as well as the unsaturated amino acids dehydroalanine, and 2-aminoisobutyric acid. They belong to ribosomally synthesized and post-translationally modified peptides.
Ceftazidime, sold under the brand name Fortaz among others, is a third-generation cephalosporin antibiotic useful for the treatment of a number of bacterial infections. Specifically it is used for joint infections, meningitis, pneumonia, sepsis, urinary tract infections, malignant otitis externa, Pseudomonas aeruginosa infection, and vibrio infection. It is given by injection into a vein, muscle, or eye.
Cefaclor, sold under the trade name Ceclor among others, is a second-generation cephalosporin antibiotic used to treat certain bacterial infections such as pneumonia and infections of the ear, lung, skin, throat, and urinary tract. It is also available from other manufacturers as a generic.
Piperacillin is a broad-spectrum β-lactam antibiotic of the ureidopenicillin class. The chemical structure of piperacillin and other ureidopenicillins incorporates a polar side chain that enhances penetration into Gram-negative bacteria and reduces susceptibility to cleavage by Gram-negative beta lactamase enzymes. These properties confer activity against the important hospital pathogen Pseudomonas aeruginosa. Thus piperacillin is sometimes referred to as an "anti-pseudomonal penicillin".
Tigecycline, sold under the brand name Tygacil, is a tetracycline antibiotic medication for a number of bacterial infections. It is a glycylcycline class drug that is administered intravenously. It was developed in response to the growing rate of antibiotic resistant bacteria such as Staphylococcus aureus, Acinetobacter baumannii, and E. coli. As a tetracycline derivative antibiotic, its structural modifications has expanded its therapeutic activity to include Gram-positive and Gram-negative organisms, including those of multi-drug resistance.
Imipenem is a synthetic β-lactam antibiotic belonging to the carbapenems chemical class. developed by Merck scientists Burton Christensen, William Leanza, and Kenneth Wildonger in the mid-1970s. Carbapenems are highly resistant to the β-lactamase enzymes produced by many multiple drug-resistant Gram-negative bacteria, thus playing a key role in the treatment of infections not readily treated with other antibiotics. It is usually administered through intravenous injection.
Ampicillin/sulbactam is a fixed-dose combination medication of the common penicillin-derived antibiotic ampicillin and sulbactam, an inhibitor of bacterial beta-lactamase. Two different forms of the drug exist. The first, developed in 1987 and marketed in the United States under the brand name Unasyn, generic only outside the United States, is an intravenous antibiotic. The second, an oral form called sultamicillin, is marketed under the brand name Ampictam outside the United States, and generic only in the United States. Ampicillin/sulbactam is used to treat infections caused by bacteria resistant to beta-lactam antibiotics. Sulbactam blocks the enzyme which breaks down ampicillin and thereby allows ampicillin to attack and kill the bacteria.
Dicloxacillin is a narrow-spectrum β-lactam antibiotic of the penicillin class. It is used to treat infections caused by susceptible (non-resistant) Gram-positive bacteria. It is active against beta-lactamase-producing organisms such as Staphylococcus aureus, which would otherwise be resistant to most penicillins. Dicloxacillin is available under a variety of trade names including Diclocil (BMS).
Boromycin is a bacteriocidal polyether-macrolide antibiotic. It was initially isolated from the Streptomyces antibioticus, and is notable for being the first natural product found to contain the element boron. It is effective against most Gram-positive bacteria, but is ineffective against Gram-negative bacteria. Boromycin kills bacteria by negatively affecting the cytoplasmic membrane, resulting in the loss of potassium ions from the cell. Boromycin has not been approved as a drug for medical use.
Beta-lactamases are a family of enzymes involved in bacterial resistance to beta-lactam antibiotics. In bacterial resistance to beta-lactam antibiotics, the bacteria have beta-lactamase which degrade the beta-lactam rings, rendering the antibiotic ineffective. However, with beta-lactamase inhibitors, these enzymes on the bacteria are inhibited, thus allowing the antibiotic to take effect. Strategies for combating this form of resistance have included the development of new beta-lactam antibiotics that are more resistant to cleavage and the development of the class of enzyme inhibitors called beta-lactamase inhibitors. Although β-lactamase inhibitors have little antibiotic activity of their own, they prevent bacterial degradation of beta-lactam antibiotics and thus extend the range of bacteria the drugs are effective against.
Cefodizime is a 3rd generation cephalosporin antibiotic with broad spectrum activity against aerobic gram positive and gram negative bacteria. Clinically, it has been shown to be effective against upper and lower respiratory tract infections, urinary tract infections, and gonorrhea. Cefodizime is a bactericidal antibiotic that targets penicillin-binding proteins (PBPs) 1A/B, 2, and 3 resulting in the eventual death of the bacterial cell. In vivo experimental models of infection showed that bacterial clearance by this drug is at least as effective compared with other 3rd generation cephalosporins. It has similar adverse effect profile to other 3rd generation cephalosporins as well, mainly being limited to gastrointestinal or dermatological side effects.
Bactoprenol also known as dolichol-11 and C55-isoprenyl alcohol (C55-OH) is a lipid first identified in certain species of lactobacilli. It is a hydrophobic alcohol that plays a key role in the growth of cell walls (peptidoglycan) in Gram-positive bacteria.
Cephalosporins are a broad class of bactericidal antibiotics that include the β-lactam ring and share a structural similarity and mechanism of action with other β-lactam antibiotics. The cephalosporins have the ability to kill bacteria by inhibiting essential steps in the bacterial cell wall synthesis which in the end results in osmotic lysis and death of the bacterial cell. Cephalosporins are widely used antibiotics because of their clinical efficiency and desirable safety profile.
Lipid II is a precursor molecule in the synthesis of the cell wall of bacteria. It is a peptidoglycan, which is amphipathic and named for its bactoprenol hydrocarbon chain, which acts as a lipid anchor, embedding itself in the bacterial cell membrane. Lipid II must translocate across the cell membrane to deliver and incorporate its disaccharide-pentapeptide "building block" into the peptidoglycan mesh. Lipid II is the target of several antibiotics.
