Antibacterial Drugs

Diagnosis of Infectious Disease Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites . Doctors suspect an infection based on the person's symptoms, physical examination results, and risk factors. First, doctors confirm that the person has an infection rather than another type of illness. For example, a person with a cough and difficulty breathing may have pneumonia (a lung infection). However, the person may have asthma or heart failure. In such a person, a chest x-ray can help doctors distinguish pneumonia from the other possible disorders. Once doctors confirm that the person has an infection, they usually need to know which specific microorganism is causing the infection. Many different microorganisms can cause a given infection. For example, pneumonia can be caused by viruses, bacteria, or, rarely, fungi. The treatment is different for each microorganism. Many different types of laboratory tests can identify microorg...

Gram staining  or  Gram stain ,    also called  Gram's method , is a method of  staining used to differentiate  bacterial  species into two large groups ( gram-positive  and  gram-negative ). The name comes from the Danish  bacteriologist   Hans Christian Gram , who developed the technique. Gram staining differentiates bacteria by the chemical and physical properties of their  cell walls  by detecting  peptidoglycan , which is present in the cell wall of Gram-positive bacteria. Gram-negative cells also contain peptidoglycan, but a very small layer of it that is dissolved when the alcohol is added. This is why the cell loses its initial colour from the primary stain. Gram-positive bacteria retain the  crystal violet dye , and thus are stained violet, while the Gram-negative bacteria do not; after washing, a counterstain is added (commonly  safranin  or  fuchsine ) that will stain these Gra...

Gram-negative bacteria Gram-negative bacteria  are a group of 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. Gram-negative bacteria are spread worldwide, in virtually all environments that support life. The gram-negative bacteria include the model organism  Escherichia coli , as well as many pathogenic bacteria, such as  Pseudomonas aeruginosa ,  Neisseria gonorrhoeae ,  Chlamydia trachomatis , and  Yersinia pestis . Several classes of antibiotics target gram-negative bacteria specifically, including aminoglycosides and carbapenems.

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. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Gram-negative bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, caus...

Nalidixic acid is used for: Treating urinary tract infections caused by certain bacteria. Nalidixic acid is an antibacterial. It works by killing sensitive bacteria in the urinary tract by stopping the production of essential proteins needed by the bacteria to survive. Nalidixic acid  (tradenames  Nevigramon ,  Neggram ,  Wintomylon  and  WIN 18,320 ) is the first of the synthetic quinolone antibiotics. In a technical sense, it is a naphthyridone, not a quinolone: its ring structure is a 1,8-naphthyridine nucleus that contains two nitrogen atoms, unlike quinoline, which has a single nitrogen atom. Synthetic quinolone antibiotics were discovered by George Lesher and coworkers as a byproduct of chloroquine manufacture in the 1960s. Used clinically from 1967. Nalidixic acid is effective primarily against gram-negative bacteria, with minor anti-gram-positive activity. In lower concentrations, it acts in a bac...

What is the difference between bacteriostatic and bactericidal drugs? Bactericidal  antibiotics kill bacteria directly, and  bacteriostatic  antibiotics stop bacteria from growing. Another important thing to remember about antibiotics is that they don't all work against all types of bacteria. Bactericidal Drugs Bactericidal agents is a one type of antibiotic which kills bacteria directly. The antibiotic polymyxin B injures the plasma membrane of bacteria, allowing their contents to leak out. Bactericides includes disinfectants, antibiotics or antiseptics. The distinction between bactericidal and bacteriostatic agents appears to be clear according to the basic/clinical definition, but this only applies under strict laboratory conditions and it is important to distinguish microbiological and clinical definitions. Bacteriostatic agents have been effectively used for treatment that are considered to require bactericidal activity.Antibiotic...