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Staphylococcus AG structure?

Staphylococcus AG structure?


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I found this statement in my study materials in the section of Staphylococcus

The AG structure:

  • protein AG (species specific);
  • polysaccharide AG (serotype specific).

I know what is Protein A/G, a recombinant fusion protein that combines IgG binding domains of both Protein A and Protein G.

What is the point of this AG structure thing in the contex of Staphylococcus? Can we say that staphylococcus have AG structure? I think it has properties related to protein AG and also to polysaccharide AG. I know very little about polysaccharide AG and not sure how it is related to serotype specificity in the context of staphylococcus.

Extension to the question

Antigenic structure of Steptococcus pyogenes: the group AG is unique, placing streptococcus in group A.

What is the AG here?


After puzzling over this for a while I think I have the answer . It's nothing to do with protein A or protein G. I think that whoever wrote your study materials meant Ag which is a common abbreviation for 'antigen'. I guess this was in the context of immune responses, or strain typing.

Looking back over your last few questions, it seems that you are at the mercy of a teacher who specialises in ambiguity.


22A: Identification of Staphylococcus Species

Staphylococcus is a genus of Gram +, nonspore-forming cocci belonging to the family Micrococcaceaethat are often found as normal human microbiota of the skin and nasal cavity. There are five organisms to consider as potential human pathogens in this genus: S. aureus, S. epidermidis, S. saprophiticus, S. haemolyticus, and S. hominisbut the first three are the most common isolates. S.aureusis often considered to be the most problematic of the three pathogens and is distinguished from the other two by being the only one able to coagulate plasma. S. aureusisable to cause many superficial pyogenic (pus-forming) infections of the dermis and underlying tissues as well as serious systemic infections. It can produce a range of toxins including enterotoxins (food poisoning), cytotoxins (general systemic toxins), and toxic shock superantigens. The other coagulase-negative staphylococci(S. epidermidisand S. saprophiticus) are much less frequently found as pathogens but are occasionally associated with endocarditis, prosthetic joint infections,and wound infections, just to name a few.

This exercise gives you the opportunity to use selective media, in this case based on high sodium chloride (MSA and SM1 10 are both selective media for the isolation of Staphylococci- 7.5% NaCl). A selective medium has an inhibitory agent which favors the growth of certain bacteria by inhibiting others. MSA contains an additional indicator for monitoring mannitol fermentation, which makes it a differential media also. Of the bacteria which can grow in the presence of high NaCl, some are halophilic (requiring a certain concentration of salt to grow) while other are haloduric (do not use the salt, but can tolerate it). Staphylococcusisnot halophilic, but rather haloduric, in that it can live in or endure high NaCl concentrations. The high salt content in SM1 10 and MSA inhibits other common skin microorganisms. The other media being used in this exercise are for differentiating pathogenic Staphylococcus from nonpathogenic, and for identification of the species.

Not only salt resistant, Staphylococcusis always facultatively anaerobic. When stained, it will be seen in small clusters (staphylo = cluster). Staphylococcus is usually either beta hemolytic or not hemolytic at all (called gamma hemolysis). Pathogenic Staphylococcican produce a variety of virulence factors, including toxins,coagulase, leucocidins, and hydrolytic enzymes that can damage host tissues.

Blood agar (BAP) is made with 5% sheep blood. It is a common medium used to culture bacteria because:

  1. It is a great enrichment medium for fastidious bacteria.
  2. Hemolysis of blood cells can be very useful as an identification test.

CNA agar is a type of blood agar. The only difference is that CNA has an antibiotic, naladixic acid, that inhibits gram - bacteria.

Hemolysis is the breakdown of red blood cells. Hemolysins are enzymes produced by some bacteria and are released into the medium around the bacterial colony. It can be a complete breakdown of the cells, with the release of hemoglobin and a clearing of the red from the surrounding medium around the colony. Or the hemolysis can be a partial breakdown, resulting in a greenish or green-yellow zone around the colony.


Objective 1: Importance of Staphylococcus aureus to humans

The importance of Staphylococcus aureus to humans would be outlined by a review of its cell structure, cell physiology and environmental niches, followed by the medical implications of Staphylococcus as a result of these properties.

Cell structure

As a member of the Bacteria domain, it is expected that Staphylococcus has bacterial cell structure. In other words, it lacks nucleus and membrane-bound organelles. The structural elements in a cell of Staphylococcus should include a cell membrane, cell wall, ribosome and nucleoid (6).

Moreover, being one of the five genera from the family of Staphylococcaceae, Staphylococcus possesses specific cellular properties that are unique to this family. In particular, it is a cocci and gram-positive bacterium and this indicates that its cell wall is essentially composed of a thick layer of peptidoglycan (21).

In addition to the above structures, Staphylococcus aureus possesses some special cellular structures that distinguish it from other species in the genus. This includes the possession of surface proteins that help attachment to proteins such as the fibronectin and fibrinogen-binding proteins involved in blood clotting (3). This cellular property may explain the pathogenic nature of Staphylococcus aureus, as infections might be caused by invasion via wounds.

On the other hand, it is worthwhile to note that Staphylococcus does not have flagella and spores (16). That is to say, Staphylococcus aureus is non-motile.

Cell physiology

The cell physiology of Staphylococcus covers temperature, pH and oxygen requirements.

Most Staphylococcus can grow at 45°C, but it is reasonable to predict that its optimal temperature for metabolism would be close to the body temperature of humans, which is 37°C (5).

Concerning the optimum pH for metabolism, the enzymes in Staphylococcus work best in slightly alkaline medium, with a pH range of 7.4 to 7.6 (16).

As for oxygen requirement, Staphylococcus is facultative anaerobic (21). This implies that Staphylococcus can grow regardless of the presence of oxygen, but the presence of oxygen would be more favorable.

In the presence of oxygen, Staphylococcus utilizes glucose to carry out cellular respiration to generate energy for metabolism. Oxygen performs the role of a terminal electron acceptor and it is completely reduced to water (8).

When oxygen is lacking or absent, Staphylococcus may undergo fermentation and lactic acid is the usual product (21). In the process, glucose is converted into substrate pyruvate, followed by its binding to the cofactor Nicotinamide Adenine Dinucleotide (NAD+) to produce lactic acid (6).

Moving on the ways Staphylococcus metabolize, as light is not readily available on skin surface and mucous membranes, it is proposed that Staphylococcus obtain energy via organic chemical compounds. Hence it is regarded as a chemotroph (21). The facultative anaerobic property of Staphylococcus may lead to a deduction that it utilizes organic carbon as the source of electron when oxygen is present. Though some Staphylococcus may use reduced forms of inorganic nitrates to generate electrons, its preference towards an aerobic atmosphere should define it as an organotroph (21). When comes to carbon source, Staphylococcus is a heterotrophy (12). That is to say, it attains its carbon source by utilization of organic substances such as sucrose for synthesis of metabolites (19). To summarize, Staphylococcus should be one of the members of the microbial group, Chemo-organotrophic heterotrophs.

Environmental niches

The environmental niches of Staphylococcus can be addressed by its interactions with the environment as to where it is found, the type of relationship it forms with other organisms and its capability of undergoing mutation.

Staphylococcus is commonly found on the skin and mucous membranes of animals with stable body temperatures, including humans (15). Typically, the skin temperature of humans is approximately 32°C, which is reasonably close to the optimal temperature of 37oC (22). This enhances the growth of this microbe on skin. Moreover, the salty environment along skin surface due to the production of sweat may also account for the abundance of Staphylococcus in humans, since its enzymatic activity is optimal at more alkaline pH (17).

Staphylococcus aureus specifically colonizes in nasal cavity, larynx and on the skin surface of humans (2). The colonization of Staphylococcus aureus is principally achieved by fibrinogen-binding proteins adhering to the epithelial cells of the humans and thus this may outline a host-parasitic relationship between Staphylococcus and humans (10).

The interactions of Staphylococcus with the environment may also be underlined by mutation, which often occurs with Staphylococcus aureus. An example would be Methicillin-resistant Staphylococcus aureus (MRSA), a Staphylococcus aureus that is resistant particularly to the antibiotic, Methicillin (21). The mutation is caused by an alteration of the methicillin-resistance gene (mec A) coding for a penicillin-binding protein (4). This results in failure of antibiotics to cure infections caused by Staphylococcus aureus, which will be addressed in the medical implication section.

Medical implications of Staphylococcus

The features as in the cell structure, cell physiology and environmental niches of Staphylococcus can pose a great diversity of medical implications, which presents the importance of this bacterial genus.

Statistics show that Staphylococcus aureus is present in 79% of healthy people (14). Though Staphylococcus may colonize on the skin surface of the host without causing any harms, its ubiquity can still present various medical issues. The MRSA mentioned previously would be one of the problems associated with Staphylococcus. Apart from methicillin, MRSA could show resistance against many other antibiotics such as penicillin and amoxicillin (1). The ineffectiveness of existing antibiotics to cure MRSA infections has resulted in fatality, and it is usually characterized by the incidence of septic shock and pneumonia (11). A rapid increase of MRSA infections has been observed over the decades. The rate of hospitalized MRSA infections was only 2% in 1974 but this figure increases dramatically to approximately 40% in 1997 (13). Consequently, this causes deaths of 19000 in the United States of America annually (11).

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As Staphylococcus colonies on skin surfaces and mucous membrane, skin infections and diseases associated with mucous membranes could be another medical implication. It is known that Staphylococcus aureus may cause Scalded Skin and Toxic Shock syndromes. Moreover, it may cause urinary tract infections and food poisoning (9).


Staphylococcus

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Staphylococcus, (genus Staphylococcus), group of spherical bacteria, the best-known species of which are universally present in great numbers on the mucous membranes and skin of humans and other warm-blooded animals. The term staphylococcus, generally used for all the species, refers to the cells’ habit of aggregating in grapelike clusters. Staphylococci are microbiologically characterized as gram-positive (in young cultures), non-spore-forming, nonmotile, facultative anaerobes (not requiring oxygen).

Of significance to humans are various strains of the species S. aureus and S. epidermidis. While S. epidermidis is a mild pathogen, opportunistic only in people with lowered resistance, strains of S. aureus are major agents of wound infections, boils, and other human skin infections and are one of the most common causes of food poisoning. S. aureus also causes meningitis, pneumonia, urinary tract infections, and mastitis, an infection of the breast in women or of the udder in domestic animals. In addition, local staphylococcal infections can lead to toxic shock syndrome, a disease associated with the liberation of a toxin into the bloodstream from the site of infection.

One strain that is of great concern to humans is methicillin-resistant S. aureus ( MRSA), which is characterized by the presence of a single mutation that renders it resistant to methicillin, a semisynthetic penicillin used to treat staphylococcus infections that are resistant to mold-derived penicillin. This strain of S. aureus was first isolated in the early 1960s, shortly after methicillin came into wide use as an antibiotic. Today methicillin is no longer used, but the strain of MRSA to which it gave rise is commonly found on the skin, in the nose, or in the blood or urine of humans. Some 50 million people worldwide are believed to carry MRSA, which is readily passed by skin contact but rarely causes infection in healthy individuals. However, very young children and elderly or ill patients in hospitals and nursing homes are particularly susceptible to MRSA infection, which is difficult to treat because of its resistance to most antibiotics. The treatment of MRSA infections with vancomycin, an antibiotic often considered as a last line of defense against MRSA, has led to the emergence of vancomycin-resistant S. aureus (VRSA), against which few agents are effective. In 2005 in the United States, deaths from MRSA (approximately 18,000) surpassed deaths from HIV/AIDS (approximately 17,000), underscoring the need for improved surveillance to prevent and control the spread of this potentially lethal organism.

This article was most recently revised and updated by Kara Rogers, Senior Editor.


Staphylococcus Aureus Morphology

The morphology of Staphylococcus aureus – the shape of the bacteria – if shown under a microscope shows purple clusters of round bacteria. The purple color is not a natural phenomenon but the result of a Gram-stain that colors the thick peptidoglycan membrane of any gram-positive bacteria purple. The natural color of a colony of S. aureus is yellow in fact, the word aureus means golden. Even though Gram-negative bacteria are traditionally considered to be more harmful, S. aureus kills approximately 20,000 Americans every year.

Unlike other staphylococci, most S. aureus bacteria produce an enzyme called coagulase. This enzyme reacts in the blood to produce another chemical called staphylothrombin. Staphylothrombin might make S. aureus even more difficult to kill by adding a layer of clotted protein to the bacterium membrane. You just have to look at the image below to see how thick the peptidoglycan membrane of Gram-positive bacteria is – an additional layer would make it very hard for a bactericide drug to enter the cell and destroy it.

S. aureus grows both aerobically (with oxygen) or anaerobically (without) at temperatures of between 64.5°F (18°C) and 104°F (40 °C). MRSA strain chromosomes carry a mec gene that can be detected in the laboratory this test is carried out very early on so that the correct treatment can be immediately started. Early treatment is essential in Staphylococcus aureus infections.


Staphylococcus ribosome structure researched by KFU Structural Biology Lab

The results were published in Nucleic Acids Research. This paper was announced as the best of May 2017 by FSBMB.

Bacterial ribosome is a macromolecular complex containing 3 RNA molecules and about 50 individual proteins. Before this KFU research the structure of gram-negative bacteria's ribosomes had been researched in atomic definition only through X-ray crystallography, and cryo-electron microscopy had given medium definition results.

Marat Yusupov, Head of the Structural Biology Lab and Head of the Ribosome Structure Lab at IGBMC, commented in 2016, "In our work we used modern biophysical and biochemical methods the Lab staff is inter-Institute. It includes biologists and physicists, and chemists are expected to join as well. Currently our work is mostly conducted together with the Biochemistry Lab NMR is used. The main constraint of this project now is that KFU doesn't have cryo-electron microscopy which would allow researching frozen specimens and discover the structure of macromolecular complexes with very high precision, basically on the molecular level. X-ray crystallography allows studying protein structure on its chemical atomic level, when each atom can be positioned in 3D which gives the opportunity to predict which inhibitors and small molecules can deactivate the protein. There are not many research centers which possess all the three technologies, as well as not many of those who study ribosome structures. The problem is both in the object and in the research methods".

By presenting the Staphylococcus ribosome structure in HD cryo-electron microscopy the researchers have significantly advanced in their work - the one which is of great significance for medicine, starting from mild skin diseases and ending with lethal infections like pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock, and septicemia.

The scientists try to find a way to «disable» protein synthesis in Staphylococcus cells and thus a way to kill it.

There are many drug-resistant strains of Staphylococcus circulating in the population, so this research can lead to saving millions of lives in the long run.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


NMR structure-based optimization of Staphylococcus aureus sortase A pyridazinone inhibitors

Staphylococcus aureus is a leading cause of hospital-acquired infections in the USA and is a major health concern as methicillin-resistant S. aureus and other antibiotic-resistant strains are common. Compounds that inhibit the S. aureus sortase (SrtA) cysteine transpeptidase may function as potent anti-infective agents as this enzyme attaches virulence factors to the bacterial cell wall. While a variety of SrtA inhibitors have been discovered, the vast majority of these small molecules have not been optimized using structure-based approaches. Here we have used NMR spectroscopy to determine the molecular basis through which pyridazinone-based small molecules inhibit SrtA. These inhibitors covalently modify the active cysteine thiol and partially mimic the natural substrate of SrtA by inducing the closure of an active site loop. Computational and synthetic chemistry methods led to second-generation analogues that are

70-fold more potent than the lead molecule. These optimized molecules exhibit broad-spectrum activity against other types of class A sortases, have reduced cytotoxicity, and impair SrtA-mediated protein display on S. aureus cell surface. Our work shows that pyridazinone analogues are attractive candidates for further development into anti-infective agents, and highlights the utility of employing NMR spectroscopy and solubility-optimized small molecules in structure-based drug discovery.

Keywords: NMR Staphylococcus aureus Sortase SrtA molecular docking molecular dynamics protein structure protein-inhibitor complex transpeptidase.


Abstract

Staphylococcus epidermidis is frequently implicated in human infections associated with indwelling medical devices due to its ubiquity in the skin flora and formation of robust biofilms. The accessory gene regulator (agr) quorum sensing (QS) system plays a prominent role in the establishment of biofilms and infection by this bacterium. Agr activation is mediated by the binding of a peptide signal (or autoinducing peptide, AIP) to its cognate AgrC receptor. Many questions remain about the role of QS in S. epidermidis infections, as well as in mixed-microbial populations on a host, and chemical modulators of its agr system could provide novel insights into this signaling network. The AIP ligand provides an initial scaffold for the development of such probes however, the structure–activity relationships (SARs) for activation of S. epidermidis AgrC receptors by AIPs are largely unknown. Herein, we report the first SAR analyses of an S. epidermidis AIP by performing systematic alanine and d -amino acid scans of the S. epidermidis AIP-I. On the basis of these results, we designed and identified potent, pan-group inhibitors of the AgrC receptors in the three S. epidermidis agr groups, as well as a set of AIP-I analogs capable of selective AgrC inhibition in either specific S. epidermidis agr groups or in another common staphylococcal species, S. aureus. In addition, we uncovered a non-native peptide agonist of AgrC-I that can strongly inhibit S. epidermidis biofilm growth. Together, these synthetic analogs represent new and readily accessible probes for investigating the roles of QS in S. epidermidis colonization and infections.


The Problem

The incidence of disease caused by MRSA bacteria is increasing worldwide. Thirty years ago, MRSA accounted for 2 percent of staph infections. By 2003, 64 percent of staph infections were caused by MRSA. According to a report by the Centers for Disease Control and Prevention (CDC) in the United States in 2005, more 94,000 people developed life-threatening infections caused by MRSA nearly 19,000 people died during hospital stays related to these MRSA infections. The majority of MRSA cases, 85 percent, were associated with healthcare facilities, while approximately 14 percent occurred in individuals with no known exposure to healthcare.

The staph bacterium continues to evolve and is beginning to show resistance to additional antibiotics. In 2002 the first staph strains were found that are resistant to vancomycin, an antibiotic that is one of the few available treatments used as a last resort against MRSA. Although vancomycin-resistant staph strains are currently still quite rare, it is feared that these strains will become more widespread over time and further reduce the limited number of antibiotics that are effective against MRSA.

The rising problem of resistance of staph bacteria to methicillin and other antibiotics is part of a larger issue that greatly concerns healthcare professionals. The emergence of antimicrobial-resistant organisms is making it more difficult to treat a variety of infectious diseases. Besides MRSA, the treatment of other diseases complicated by drug resistance include HIV, tuberculosis, influenza, and malaria.

Drug resistance occurs because microbes, such as staph bacteria, need to reproduce to ensure their survival. When this ability is threatened, as when they are exposed to antibiotics, microbes adapt and evolve to overcome the block to their reproduction. This can occur naturally, and microbes become genetically altered in ways which allow them to survive in the presence of antimicrobial drugs. However, drug resistance adaptations can be accelerated by human actions, particularly by the overuse and inappropriate use of antibiotics. The escalating use of antimicrobials in humans, animals, and agriculture is increasing the problem of drug resistance.

The consequences of antimicrobial resistance pose a significant concern to scientists and medical professionals. Infection with drug-resistant organisms can lead to increased and longer hospital stays, more complicated treatment, more deaths, and higher healthcare costs.


Staphylococcus AG structure? - Biology

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Tag words: Staphylococcus aureus, Staphylococcus, staph, staphylococcal, S. aureus, MRSA , MRSA , CA-MRSA , superbug , staph infection, wound infection, food poisoning, toxic shock syndrome, antibiotic resistance, Staph epidermidis, normal flora, skin bacteria, bacteriology, microbiology

Staphylococcus aureus

Kingdom: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Bacillales
Family: Staphylococcaceae
Genus: Staphylococcus
Species: S. aureus


Common References: Staphylococcus, Staph, MRSA , Superbug




Staphylococcus aureus and Staphylococcal Disease (page 1)

Staphylococcus aureus Electron micrograph from Visuals Unlimited, with permission.

Staphylococci (staph) are Gram-positive spherical bacteria that occur in microscopic clusters resembling grapes. Bacteriological culture of the nose and skin of normal humans invariably yields staphylococci. In 1884, Rosenbach described the two pigmented colony types of staphylococci and proposed the appropriate nomenclature: Staphylococcus aureus (yellow) and Staphylococcus albus (white). The latter species is now named Staphylococcus epidermidis. Although more than 20 species of Staphylococcus are described in Bergey's Manual (2001), only Staphylococcus aureus and Staphylococcus epidermidis are significant in their interactions with humans. S. aureus colonizes mainly the nasal passages, but it may be found regularly in most other anatomical locales, including the skin, oral cavity and gastrointestinal tract. S epidermidis is an inhabitant of the skin.

Taxonomically, the genus Staphylococcus is in the Bacterial family Staphylococcaceae, which includes three lesser known genera, Gamella, Macrococcus and Salinicoccus. The best-known of its nearby phylogenetic relatives are the members of the genus Bacillus in the family Bacillaceae, which is on the same level as the family Staphylococcaceae. The Listeriaceae are also a nearby family.

Staphylococcus aureus forms a fairly large yellow colony on rich medium S. epidermidis has a relatively small white colony. S. aureus is often hemolytic on blood agar S. epidermidis is non hemolytic. Staphylococci are facultative anaerobes that grow by aerobic respiration or by fermentation that yields principally lactic acid. The bacteria are catalase-positive and oxidase-negative. S. aureus can grow at a temperature range of 15 to 45 degrees and at NaCl concentrations as high as 15 percent. Nearly all strains of S. aureus produce the enzyme coagulase: nearly all strains of S. epidermidis lack this enzyme. S. aureus should always be considered a potential pathogen most strains of S. epidermidis are nonpathogenic and may even play a protective role in humans as normal flora. Staphylococcus epidermidis may be a pathogen in the hospital environment. Staphylococci are perfectly spherical cells about 1 micrometer in diameter. The staphylococci grow in clusters because the cells divide successively in three perpendicular planes with the sister cells remaining attached to one another following each successive division. Since the exact point of attachment of sister cells may not be within the divisional plane, and the cells may change position slightly while remaining attached, the result is formation of an irregular cluster of cells.

The shape and configuration of the Gram-positive cocci helps to distinguish staphylococci from streptococci. Streptococci are slightly oblong cells that usually grow in chains because they divide in one plane only, similar to a bacillus. Without a microscope, the catalase test is important in distinguishing streptococci (catalase-negative) from staphylococci, which are vigorous catalase-producers. The test is performed by adding 3% hydrogen peroxide to a colony on an agar plate or slant. Catalase-positive cultures produce O2 and bubble at once. The test should not be done on blood agar because blood itself contains catalase.

FIGURE 1. Gram stain of Staphylococcus aureus in pustular exudate


Table 1. Important phenotypic characteristics of Staphylococcus aureus

Gram-positive, cluster-forming coccus
nonmotile, nonsporeforming facultative anaerobe
fermentation of glucose produces mainly lactic acid
ferments mannitol (distinguishes from S. epidermidis)
catalase positive
coagulase positive
golden yellow colony on agar
normal flora of humans found on nasal passages, skin and mucous membranes
pathogen of humans, causes a wide range of suppurative infections, as well as food poisoning and toxic shock syndrome