TYPHOID

          

            Typhoid fever is a bacterial infection caused by Salmonella enterica. It is also termed as enteric fever. It is a highly contagious disease. Typhoid can be fatal if it is not attended too quickly.  It is transmitted by the ingestion of food or water contaminated with bacterium Salmonella. Typhoid is also transmitted through the feces of an infected person. Common symptoms include high or slow fever, profuse sweating and gastroenteritis. Typhoid fever is a common worldwide illness. It can affect any person irrespective of health, background and race. There are 1000 different types of typhoid bacteria. Various drugs used to treat typhoid are unsuccessful against resistant strains of typhoid bacteria. In developing country such as India, it is a great threat and a major cause of death. Typhoid disease mainly hit on children who are in school-going age. It is not very common in adults and older people.

         Bacteria of typhoid are survived in unhygienic conditions. These bacteria are spread by typhoid patients and carriers in large quantities through stools and vomit. The bacteria then travel to food, drinks and water through house-flies and other insects. Such foods are contaminated. When these contaminated food or drinks, are taken by healthy person, bacteria enter in to the body of person and causes typhoid fever. Person may get typhoid fever by consuming food or drink that has been carried by someone having the bacteria, or if sewage contaminated with S.typhi gets into water used for drinking or washing food. There are 107 different strains of this bacterium.

       Paratyphoid is caused by Salmonella enteritidis paratyphi A, B or C. It is generally a less infection than typhoid. A very low percent of typhoid patients remain chronic carriers regardless of treatment. Most common complications are intestinal bleeding and perforation. The source of fever is polluted water. In India, due to population explosion, water is polluted and this disease is matter of worry especially in disaster areas, where water supply and sewage disposal are disrupted. Raw vegetables grown on sewage fields also spread infection. The bacteria can survive in soil and water for several months. They grow rapidly in milk and milk-products.

         Typhoid cases are more common in developing countries due to unhygienic conditions. Early and most common symptoms include fever, malaise, abdominal pain and severe diarrhea which could worse conditions more. Other symptoms include abdominal tenderness, bloody stools, chills, confusion, nose bleeding, lethargic feeling and weakness.

         Salmonella causes three clinical syndromes in human being they are enteric fever, gastroenteritis and septicemia. Bacteria usually enters the body through mouth by the  contaminated food or water. Once bacteria resist host defense mechanism and manage to penetrate intestinal wall and multiplies in great number. Within 24 hours to 72 hours bacteria tries to enter into bloodstream causing septicemia and systemic infection.

           Salmonella multiplies in gall bladder abundantly and is discharged continuously into the intestine where it involves Peyers’s Patches and Lymphoid follicles. These become inflamed and undergo necrosis and slough off, leaving behind the characteristic typhoid ulcers. Ulceration of bowels leads to complication known as intestinal perforation and hemorrhage. Onset is usually gradual with headache, abdominal discomfort, lethargic etc. The typical feature is step ladder pyrexia.

         Apart from intestinal perforation and hemorrhage other complications involved is circulatory collapse. Some degree of bronchitis or bronchopneumonia is always found. Some develop psychoses, deafness or meningitis. Cholecystitis, abscesses, arthritis, periosteistis, nephritis, hemolytic anemia, venous thromboses and peripheral neuritis are other complications found. The number of such symptoms involved is quiet less but fatality rate is very high.

Treatment  

               As it is said for all diseases, prevention is the best remedy. For typhoid, proper antibiotics have to be used. There is a growing frequency of resistant strains of the bacteria. Other treatment is to reduce symptoms through drinking more fluids. This prevents the dehydration that results from a prolonged fever and diarrhea. If a patient is severely dehydrated, he may need to receive fluids intravenously. Patient must take a healthy diet. Typhoid fever in most cases is not fatal. Antibiotics, such as ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, amoxicillin and ciprofloxacin, have been commonly used to treat typhoid fever in microbiology. Even after treatment with antibiotics, some people who recover from typhoid fever continue to carry the bacteria in their intestinal tract or gallbladder for years. Such people called chronic carriers. They carry the bacteria in their feces and are capable of infecting others, although they no longer have signs or symptoms of the disease themselves.

GENE- what are they...???

        
         The children acquire the characteristic features of theirs parents. The inheritance of these hereditary characters can be explained on the basis of ancestral genes that are found to be arranged on chromosomes, and they make the total genetic make-up of the organism.

        But the question arises, What are gene? What are genes chemically composed of and their functions and how are they transmitted to the offspring's?

        The hereditary units which are transmitted from one generation to another are called genes. It is a fundamental biological unit which is called as functional factor of heredity.

        These characters are transmitted from parents to the offspring's during reproduction which forms the basis of maintaining continuity of a species. Genes responsible for transmission are located on chromosomes and through the gametes enter a diploid zygote cell which occurs in all sexually reproducing organisms. Thus, each offspring's receives 50% genes from male parent and the remaining 50% from the female parent during fusion of gametes to form zygote.

ON THE BASIS OF MODERN CONCEPT OF GENETIC KNOWLEDGE :

Genetics material of any organism is the substance that carries genetic information determining the properties of that organism. The genetic material is also responsible for transferring genetic material from parent to their offspring's.

CHARACTERISTICS OR PROPERTIES OF GENETIC MATERIAL :

Genes are linearly arranged segments of DNA molecule, which determines the inheritance and expression of particular hereditary characters. The principle criteria material should therefore:

1. Possesses the ability to store and express genetic information and also transmit as required.

2. Possesses the ability to make its own replica so that a copy of it may be transmitted to the offspring.

3. Possesses the ability to transfer its information from parent cell to daughter cells with least minimal error.

4. Maintains physical and chemical stability in order to prevent loss of genetic information.

5. Possesses the capability for genetic change without major loss of parental information which generates the biological variations essential for evolution.

IRON EATING BACTERIA CAN EAT ELECTRICITY INSTEAD

         

         Scientist have developed a way to grow iron oxidizing bacteria using electricity instead of iron, an advance that will allow them to better study the organism and could one day be used to turn electricity into fuel. The study will be published in mBio.


         The method, called electrochemical cultivation, supplies these bacteria with a steady supply of electrons that the bacteria use to respire or 'breathe'. It opens the possibility that one day electricity generated from the sources like wind or solar could be funneled to iron oxidising bacteria that combine it with carbon dioxide to create biofuels, capturing the energy as a useful, storable substances.


          "Its a new way to cultivate a microorganism that's been difficult to study. But the fact that these organisms can synthesize everything they need using only electricity," says Daniel Bond of the University of Minnesota.


           To 'breathe', iron oxidisers take electrons off of dissolved iron, called Fe (II) - a process that produces copious amounts of rust, called Fe (III). Iron oxidising bacteria are found around world. Scientist think these bacteria must carry out the iron oxidation step on their surfaces. If that's true, Bond reasoned, the outsides of the organisms should be covered with proteins that interact with Fe (II), so you should be able provide a stream of pure electrons to the outsides and get them to grow.


            Bond and his colleagues added the marine iron oxidiser Mariprofundus ferrooxydans PV -1, along with some nutrient medium, to an electrode carefully tuned to provide electrons at the same energy level, or potential, as Fe (II) would provide. The idea, says Bond, was to "fool the bacteria into thinking they're at the world's best buffet of Fe (II) atoms."


            It worked. The bacteria multiplied and formed a film on the electrode, Bond says, and eventually they were able to grow M ferrooxydans with no iron in the medium.


            "Bacteria are experts at the capture of carbon dioxide. They build cells and compounds" with the carbon, he says. They might one day be exploited as microscopic energy packagers : Bacteria like M ferrooxydans could capture electricity from an electrode, combine it with carbon dioxide and package it as a carbon rich compound we could use as fuel.

Article from MUMBAI MIRROR NEWSPAPER

AUSTRALIAN EXPERTS OFFER HOPE FOR AIDS CURE

Tweaking Virus Protein Can Shield Cells From Contracting HIV Infection

          In a break through, Australian researchers claim to have discovered how to modify a protein in Human Deficiency Virus ( HIV) which could lead to a potential cure for Acquired immunodeficiency Syndrome (AIDS).

         According to researcher David Harrich from Queensland Institute of Medical Research, the protein can be modified so that instead of replicating, it protects against the deadly infection.

          "I consider that this is fighting fire with fire. What we've actually done is taken a normal virus protein that the virus needs to grow, and we've changed this protein, so that instead of assisting the virus, it actually impedes virus replication and does it quite strongly," Harrich said.

         He added that modified protein cannot cure HIV but it has protected human cells from AIDS in the laboratory.

       "This is therapy is potentially a cure for AIDS. So it's not a cure for HIV infection, but it potentially could end the disease," he said. Over 30,000 people have been diagnosed with HIV in Australia.

        If clinical trails are successful  one treatment could be effective enough to replace the multiple therapies they currently need.

        "Drug therapy targets individual enzymes or proteins and they have one drug, one protein. He added that they have to take two or three drugs, so this would be a single agent that essentially has the same effect. "So in that respect, this is world first agent at multiple steps of the virus life cycle," he added.

      He said that the new treatment has the potential to make big improvements in the quality of life for those carrying HIV. "I think what people are looking for is basically a means to go on and lives with as little intrusion as possible. You either have to eliminate the virus infection or alternatively you have to eliminate the disease process and that's what this could do, potentially for a very long time, Harrich said.

     Harrich added that animal rials are due to start this year and early indications are positive.

NEW TECH HELPS SPOT CANCER SPREAD

IT  WILL  ALLOW  SURGEONS  TO  REMOVE  TUMOURS  &  SAVE HEALTHY  CELLS  IN  PATIENTS

            Researchers have developed a new technique that will allow surgeons to identify how far the tumour has spread and help them decide which tissue to remove in order to save healthy cells in cancer patients.

          "With molecular-targeted imaging, surgeons can avoid unnecessary removal of healthy lymph nodes which is better long-term for patients." said Quyen T Nguyen, associate professor at University of California, San Diego School of Medicine. "The range of the surgeon's visual field is greatly enhanced by a molecular tool that can help achieve accurate surgical margins and detection of metastases so that no tumour is left behind," Nguyen said.

         Lymph nodes, located throughout the body, serve as filters that contain immune cells to fight infection and clean the blood. When cancer cells break away from a tumour, the cells can travel through the lymph system and hide in these tiny organs. 

        Surgeons remove the nodes to determine if a cancer has spread. However, human nodes, only half a centimeter in size, are difficult to discern among the surrounding issue during surgery.

       Furthermore, even when surgeons are able to map the location of the nodes, there is no current technique that indicates whether or not the lymph nodes contain cancer, requiring removal of more lymph nodes than necessary.

        "This research is significant because it shows real time intra-operative detection of cancer metastases in mice. In the future, surgeons will be better able to detect and stage cancer that has spread to the patient's lymph nodes using molecules that were designed and developed at UC San Diego," he said.

          The fluorescently labelled molecules, know as ratiometric activatable cell-penetrating peptides (RACPP), are injectable. When used in mouse models, surgeons could see where the cancer had spread with high sensitivity and specificity even when the metastatic sites were only a few millimeters in size. 

WHAT IS MICROBIOLOGY...???

Actually this should have been my first post but never the less. I am sharing this so that many would know what is MICROBIOLOGY.

             

         Microbiology is the study of living organism about microscopic size, which includes bacteria, fungi, algae  protozoa and the infectious agents at the borderline of life that are called as viruses. The field is concerned with their form, structure, classification, metabolism, physiology and their distribution in environment.  To relate each of organism with each other, with environment, with other species and of-course with plants, animals and humans. The field  notes the physical, chemical and biological changes in environment.

          Microorganism have a major role to play with human health and its welfare. When various organism are taken into consideration, some organisms have beneficial effect while some have harmful effect. Organisms which are involved in making of cheese, beer, wine, vinegar, antibiotic production, curd etc are beneficial organisms. While microorganism which are responsible for food spoilage, diseases or deteriorating things like iron pipes, lenses, wood etc are harmful organisms.

         Most of microorganisms are unicellular i.e. one single cell. All the metabolism, processes for living are performed by a single cell.When compared to any multicellular organism, they have different organs and tissues which are specific for various functions. Thus one cell is capable of performing all activities necessary for its survival. Thus complexity in cell functioning is too high.

         The word cell was first used more than two centuries ago by an Englishman ROBERT HOOKE ( 1635-1703 ). Later the concept of the cell as the structural unit of life - The Cell Theory_ is credited to two Germans _ MATTHIAS SCHLEIDEN & THEODOR SCHWANN, who in 1838-1839 describe cells as the basic structural and functional unit of all organisms.

          Any kind of organisms may be present, either unicellular or multicellular, all biological system have the following characteristics in common- 1. The ability to reproduce, 2. The ability to ingest or assimilate food substances and metabolize them for energy and growth, 3.The ability to excrete waste products, 4. The ability to react to changes in the environment and 5. Susceptibility to mutation.

         Thus, a microbiologist work is large and on many parameters. As it is said "THE NEXT SMALL THING IS BIG"...!!!

PLANT CELL

HOPE OF TREATING CANCER

SCIENTISTS CREATE TUMOUR-KILLING CELLS WHICH CAN BE DIRECTLY INJECTED INTO PATIENTS

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         In a breakthrough, scientists have for the first time created cancer-killing cells which can be directly injected into patients. Researchers in Japan have created cancer-specific killer T-cell, the cells naturally occur in small numbers, but it is hoped injecting huge quantities back into a patient could turbo-charge the immune system.

         Researchers at the RIKEN Research Centre for Allergy and Immunology revealed they have succeeded for the first time in creating cancer-specific, immune system cells called killer T lymphocytes.

        To create these, the team first had to reprogramme T lymphocytes specialized in killing a certain type of cell called induced pluripotent stem cell (iPS cells). These iPS cells then generated fully active, cancer-specific T lymphocytes. These lymphocytes regenerated from iPS cells could potentially serve as cancer therapy in the future, researchers believe.

        Previous research has shown that killer T lymphocytes produced in the lab using conventional methods are inefficient in killing cancer cells mainly because they have a very short life-span, which limits their use as treatment for cancer.

        To overcome the problems, Japanese researchers, led by Hiroshi Kawamoto reprogrammed mature human killer T lymphocytes into iPS cells and investigated how these cells differentiate. The team induced killer T lymphocytes specific for a certain type of skin cancer to reprogram into iPs cells by exposing the lymphocytes to the “Yamanaka factors” – a group of compounds that induce cells to revert to a non specialized, stage.

        The iPS cells obtained were then grown in the lab and induced to differentiate into killer T lymphocytes again. This new batch of T lymphocytes was shown to be specific for the same type of skin cancer as the original lymphocytes.

        They maintained the genetic reorganization, enabling them to express the cancer-specific receptor on their surface. The new T lymphocytes were also shown to be active and to produce an anti-tumour compound.

“We have succeeded in the expansion of antigen-specific T cells by making iPS cells and differentiating them back into functional T cells.” Kawamoto said.

DENGUE IN CITY...BE AWARE...

APART FROM TUBERCULOSIS AND MALARIA....SOMETHING IS MORE  AROUND YOU.

TRY TO KNOW AND BE AWARE, AND FOLLOW BASIC PREVENTION METHODS.

http://www.sharemicro.blogspot.in/search/label/medical

IN GENERAL -- ABOUT ANTI-MICROBIAL AGENTS

DENGUE - THE CURRENT PROBLEM

           Dengue is a tropical disease which is caused by dengue virus. Dengue is transmitted by mosquitoes especially with genus Aedes i.e. Aedes aegypti. In very rare cases the disease is life threatening while many a times the symptoms are asymptomatic or only have mild symptoms. As such there is no commercially vaccine.

ABOUT VIRUS :- Dengue fever virus is a RNA type virus belongs to family of Flaviviridae and genus Flavivirus. Transmission of virus is through arthropods i.e. via arbovirus ( arthropod borne virus ). Genome of virus contain about 11,000 nucleotide base which is coding for different types of proteins that are C, prM and E, together comprise the viral particle. Four strains of the virus present in atmosphere are DENV-1/ D-1, DENV-2/ D-2, DENV-3/D-3, DENV-4/ D-4.

TRANSMISSION:- Primarily the virus is transmitted through Aedes aegypti. While other species involved in transmitting the disease are A.scutellaris, A.albopictus, A.polynesiensis. Mosquito bite is generally during day time, particularly in early morning or evening. Humans are primary host. Yet many a times primates are also infected. Usually single bit is enough to contract the disease. Virus transmission is also possible through vertical transmission ( from mother to child ) and during organ transplant.

             Female mosquito takes a blood from a person who infected with dengue fever and then becomes itself infected with the virus. About 8–10 days later, the virus spreads to other tissues including the salivary glands of mosquito and is subsequently present its saliva. With contact with human/primates the virus is released inside the host. The virus seems to have no harmful effect on the mosquito, which remains infected for life. 

             
         Once virus enters the host, it binds to cell lining and enters white blood cells, It reproduces inside the cells while they move throughout the body. The white blood cells respond to virus by producing a number of signaling proteins, such as interferon, which are responsible for many of the general symptoms, such a fever, flu-like symptoms and the severe pains. In severe infection occurs , the virus multiplication inside the body is greatly increased, and many more organs can be affected. Furthermore, dysfunction of the bone marrow leads to reduced numbers of platelets, which are necessary for effective blood clotting; this increases the risk of bleeding, the other major complication of dengue fever.

              Once inside the skin, dengue virus binds to Langerhans cells. (a population of dendritic cells.). The dendritic cell moves to the nearest lymph node. Meanwhile, the virus genome is translated in membrane-bound vesicles on the cell's endoplasmic reticulum. Here cell's protein synthesis apparatus produces new viral proteins that replicate the viral RNA and begin to form viral particles. Immature virus particles are transported to the Golgi apparatus and complete mature particle is formed. Mature new viruses bud on the surface of the infected cell and are released through exocytosis. 

              The incubation period (time between exposure and onset of symptoms) ranges from 3–14 days. And therefore, travelers returns from endemic areas show likely symptoms are unlikely to have dengue. Children often experience symptoms similar to those of the common cold and gastroentritis and, though initial symptoms are generally mild but include high fever. Symptoms ignored in children’s or old people can give rise to severe dengue infection which can be life threatening and thus preliminary precautions has to be taken.

SIGNS AND SYMPTOMS:-

                       The general characteristic symptoms of dengue are sudden-onset fever, headache  muscle and joint pains, and a rash. The alternative name for dengue, "break-bone fever", comes from the associated muscle and joint pains. The course of infection is divided into three phases: febrile, critical, and recovery. Phases are associated with pain headache for  3 to 6 days while may a times vomiting is seen due to abdominal discomfort. Measles like rashes are prominently visible, this symptoms should be confused with measles. The fever itself is classically biphasic in nature, breaking and then returning for one or two days, although there is wide variation in how often this pattern actually happens.

                    In some people, the disease proceeds to a critical phase. During this phase there may be significant fluid accumulation in the chest and abdominal cavity due to increased capillary permeability and leakage. This leads to depletion of fluid from the circulation and decreased blood supply to vital organs. During this phase, organ dysfunction and severe bleeding, typically from the gastrointestinal tract, may occur. Shock (dengue shock syndrome) and hemorrhage (dengue hemorrhagic fever) occur in less than 5% of all cases of dengue, however those who have previously been infected with other serotypes of dengue virus ("secondary infection") are at an increased risk.

 DIAGNOSIS:-

             The diagnosis of dengue is typically made clinically, on the basis of reported symptoms and physical examination; this kind of diagnosis is especially carried in endemic areas. However, early disease can be difficult to differentiate from other viral infections. General diagnosis is based on the findings of fever  nausea and vomiting, rash, generalized pains, low white blood cell count, positive tourniquet test, in someone who lives in anendemic area. The diagnosis should be considered in anyone who develops a fever within two weeks of being in the tropics or subtropics. It can be difficult to distinguish dengue fever and chikungunya, as both the viral infection shares many symptoms and occurs in similar parts of the world to dengue. Often, investigations are performed to exclude other conditions that cause similar symptoms, such as malaria, leptospirosis, viral hemorrhagic fever, typhoid fever,  measles, and influenza.

                The earliest change detectable in laboratory testing is a low white blood cell count, which may then be followed by low platelets and metabolic acidosis. A moderately elevated level of aminotransferase from the liver is commonly associated with low platelets and white blood cells. 

             Dengue fever may be diagnosed by microbiological laboratory testing. This can be done by virus isolation in cell cultures, nucleic acid detection by PCR, viral antigen detection or specific antibodies. Virus isolation and nucleic acid detection are more accurate than antigen detection, but these tests are not widely available due to their greater cost.

             Tests for dengue virus-specific antibodies, types IgG and IgM, can be useful in confirming a diagnosis in the later stages of the infection. Both IgG and IgM are produced after 5–7 days. The highest levels of IgM are detected following a primary infection. After a primary infection the IgG reaches peak levels in the blood after 14–21 days. Both IgG and IgM provide protective immunity to the infecting serotype of the virus.

PREVENTION AND CONTROL:- 

- There are no approved vaccines for the dengue virus. 

-Prevention thus depends on control and protection from the bites of the mosquito that transmits it. 

-Elimination of stagnant water at home, schools and work place to avoid breeding of mosquitoes. 

-Using insect repellents over the exposed parts of the body.Using mosquito screens or nets in non – air-conditioned rooms. 

-Wearing the long sleeved clothes like long trousers of a light shade for protection against mosquitoes.

-Properly covering all water tanks so that mosquitoes cannot get in. Getting rid of any container capable of retaining water in the outdoor surroundings (used tyres, food cans, garbage, saucers under flower pots, etc).

- Renew water in flower vases at least once a week. Aedes species is the main target of control. Source reduction of breeding sites of mosquitoe. 

-Requires community involvement to keep the water storage containers free of mosquitoes. Eliminate other breeding places in and around houses. 

-Introduction of larvivorous fish, namely Gambusia and Guppy in water tanks and other water sources. -

-The organophosphorous insecticide ABATE is being used in a large scale. ABATE can prevent breeding upto 3 months when applied to sand granules. It does not affect man or the taste of water. 

-Educate community about the disease, mode of its transmission, availability of treatment and adoption of control measures.

-Changes in practice of storage of water and personal protection should be encouraged. They should also be reassured that this a preventable disease. 

-Community should be advised to cooperate in fogging. Take measures for eliminating breeding places. Special campaigns may be carried out involving mass media including local vernacular newspapers/magazines, radio and TV as well outdoor publicity like hoardings, miking, drum beating, rallies etc. 

-Health education materials should be developed and widely disseminated in the form of posters, pamphlets, handbills. 

-Interpersonal communication through group meetings, traditional/folk media particularly must be optimally utilized.

EPIDEOMOLOGY :-

DIFFERENT CELL WALL STRUCTURE

Gram-Positive Cell Walls

           

  Normally the thick, homogeneous cell wall of gram-positive bacteria is composed primarily of peptidoglycan, which often contains a peptide interbridge. However gram-positive cell walls usually also contain large amounts of teichoic acids, polymers of glycerol or ribitol joined by phosphate groups. Amino acids such as D-alanine or sugars like glucose are attached to the glycerol and ribitol groups.

The teichoic acids are connected to either the peptidoglycan itself by a covalent bond with the six hydroxyl of N-acetylmuramic acid or to plasma membrane lipids; in the latter case they are called lipoteichoic acids. Teichoic acids appear to extend to the surface of the peptidoglycan, and, because they are negatively charged, help give the gram-positive cell wall its negative charge. The functions of these molecules are still unclear, but they may be important in maintaining the structure of the wall. Teichoic acids are not present in gram negative bacteria.

 Gram-Negative Cell Walls

Gram-negative cell walls are much more complex than gram-positive walls. The thin peptidoglycan layer next to the plasma membrane may constitute not more than 5 to 10% of the wall weight. In E. coli it is about 2 nm thick and contains only one or two layers or sheets of peptidoglycan. The outer membrane lies outside the thin peptidoglycan layer. The most abundant membrane protein is Braun’s lipoprotein, a small lipoprotein covalently joined to the underlying peptidoglycan and embedded in the outer membrane by its hydrophobic end. The outer membrane and peptidoglycan are so firmly linked by this 
lipoprotein that they can be isolated as one unit.

Another structure that may strengthen the gram-negative wall and hold the outer membrane in place is the adhesion site. The outer membrane and plasma membrane appear to be in direct contact at many locations in the gram-negative wall. Possibly the most unusual constituents of the outer membrane are its lipopolysaccharides (LPSs). These large, complex molecules contain both lipid and carbohydrate, and consist of three parts: (1) lipid A, (2) the core polysaccharide, and (3) the O side chain. The LPS from Salmonella typhimurium has been studied most, and its general structure is described. The lipid A region contains two glucosamine sugar derivatives, each with three fatty acids and phosphate or pyrophosphate attached. It is buried in the outer membrane and the remainder of the LPS molecule projects from the surface. The core polysaccharide is joined to lipid A. In Salmonella it is constructed of 10 sugars, many of them unusual in structure. The O side chain or O antigen is a polysaccharide chain extending outward from the core. It has several peculiar sugars and varies in composition between bacterial strains.

            LPS has many important functions. As a major constituent of the exterior leaflet of the outer membrane, lipid A also helps in stabilizing outer membrane structure. LPS may contribute to bacterial attachment to surfaces and aids in creating a permeability barrier. LPS restrict the entry of bile salts, antibiotics and other toxic substances. Apart from protecting, LPS is a potent antigen which can elicits an immune response in host e.g. O side chain of LPS.

taken from,

Microbiology book- Prescott, Harley and Klein's Microbiology, McGraw Hill International Edition.