Gram Positive Bacteria

8 Key excerpts on "Gram Positive Bacteria"

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  eBook - ePub

  Microbial Food Safety

  A Food Systems Approach

  • Charlene Wolf-Hall, William Nganje(Authors)
  • 2017(Publication Date)
  • CAB International

    (Publisher)

  6 Gram-Positive Bacteria

  Key Questions

  •   Which Gram-positive bacteria are of most concern for microbial food safety?

  •   What are the mechanisms by which these Gram-positive bacteria cause illness?

  •   What are the hazards these Gram-positive bacteria present to consumers?

  •   What controls are available to prevent foodborne illness due to these Gram-positive bacteria?

  The Difference Between Gram-Positive and Gram-Negative Bacteria

  Hans Christian Gram was the Danish scientist who, in 1884, published a method for a staining technique to help better see bacteria in tissue samples under the microscope. An unanticipated result of this technique was a way to differentiate two major groups of bacteria based on their cell wall compositions.

  Bacterial cell membranes that contain thick layers of peptidoglycan are able to retain the crystal violet stain used in the method, resulting in purple- or violet-stained cells that are described as Gram positive. Bacteria that contain less peptidoglycan in their cell membranes are unable to retain the crystal violet stain after the destaining step of the procedure, and as a result of counter-staining with safranin dye appear red or pink, and are described as Gram negative. As with all microbiological testing methods, there are limitations and some bacterial species may produce Gram-variable results, indicating an ability to stain with either reaction result and not provide a clear distinctive result.

  Gram staining is a preliminary test used on bacterial cultures to give clues to the identity of the species. The Gram reaction is a first clue, and then other clues like the microscopic cell morphology or shape and placement can provide other clues. The remainder of this chapter will focus on those bacterial pathogens of most concern in foods that fall under the category of Gram positive, and Chapter 7

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  Ocular Infection

  Investigation and Treatment in Practice

  • David V. Seal, Uwe Pleyer(Authors)
  • 2007(Publication Date)
  • CRC Press

    (Publisher)

  TWO Microbiology BACTERIOLOGY Cell Wall Bacteria are divided into Gram-positive and Gram-negative groups based on their cell wall structure. The bacterial cell wall is a rigid structure surrounding a flexible cell membrane. The cell wall maintains the shape of the cell: its rigid wall compensates for the innate flexibility of the phospholipid membrane and also maintains the cell’s integrity when the intracellular osmotic gradient is unfavorable. The wall is also responsible for attachment: teichoicacids attached to the outer surface of the wall serve as attachment sites for bacteriophages. Flagella, fimbriae, and pili all emanate from the wall. The composition of the Gram-positive cell wall is 90% peptidoglycan polymer made of alternating sequences of N-acetylglucosamine (NAG) and N-acetyl-muraminic acid (NAMA) with each layer cross-linked by an amino acid bridge. The peptidoglycan polymer imparts thickness to the Gram-positive cell wall. In contrast, peptidoglycan makes up only 20% of the Gram-negative cell wall. Periplasmic space and an outer membrane also diffe]rentiate the Gram-negative organism and contain proteins that destroy potentially dangerous foreign matter. The outer membrane, composed of lipid, protein, and lipopolysaccharide (LPS), is porous because porin proteins allow free passage of small molecules. The lipid portion of LPS also contains lipid A, a toxic substance, which imparts the pathogenic virulence associated with some Gram-negative bacteria. Gram stain was the innovation of Hans Christian Joaquim Gram, a Danish physicist, who sought to distinguish bacterial organisms based on their different cell wall structures. The crystal violet primary stain in Gram stain preferentially binds peptidoglycan. Because the cell wall of Gram-negative bacteria is low in peptidoglycan content and high in lipid content, the primary crystal violet stain is washed out when the decolorizer (acetone) is added.

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  High Value Fermentation Products, Volume 1

  Human Health

  • Saurabh Saran, Vikash Babu, Asha Chaubey, Saurabh Saran, Vikash Babu, Asha Chaubey(Authors)
  • 2019(Publication Date)
  • Wiley-Scrivener

    (Publisher)

  Figure 3.1 shows representation of the arrangement of components in the cell walls of Gram-positive bacteria. Gram-positive cell walls have an open, hydrophilic structure that retains the cell shape during isolation and purification. The key component of cell wall is peptidoglycan, that covered 50% of the weight of the wall. Linear anionic polymers, termed teichoic or teichuronic acids, are covalently associated to the peptidoglycan, giving the wall a net negative charge. Teichoic acids are linear polymers of repeating units of ribitol or glycerol units linked by phosphodiesters. Teichuronic acids do not contain any phosphate; in its place, they are made up from linear chains of sugar units containing uronic acid residues. Additional key form of teichoic acid found in the Gram-positive cell wall is lipoteichoic acid (LTA). LTA is a glycerolphosphate teichoic acid chain linked covalently to a glycolipid (typically a glycosyl diglyceride) situated on the external face of the cytoplasmic membrane. The glycerophosphate chain extends over the cellwall and is exposed on the cell surface. A number of functionally major proteins are also found both covalently and noncovalently linked to peptidoglycan. These mediate interactions between cells and their environment. Many pathogens cooperate precisely with host cells and tissues in infections by creating surface exposed proteins that bind to host proteins. Some Gram Positive Bacteria generate capsular polysaccharides, that are loosely connected to the cell wall. Capsules form an additional barricade around the cells, protecting against engulfment by predatory cells in natural environments and by host phagocytic cells in infection [5].

  Figure 3.1

  Cell wall structural morphology of Gram Positive Bacteria.

  Actinomyces spp plays a significant role in nature in which some are human pathogens. A few of them are opportunistic pathogens which caused infectious diseases in the human mouth, i.e., periodontitis (inflammation of the gums) and oral abscesses. Genus Mycobacterium causes a diverse group of infectious diseases in which M. tuberculosis is the causative agent of tuberculosis. Another pathogenic species, M. leprae, is the cause of Hansen’s disease (leprosy). C. diphtheria is the causative agent of diphtheria. Genus Gardnerella, contains only one species, G. vaginalis which causes vaginosis in women [6].

  Although recent global consideration is paying attention to the concern of multi-drug resistance (MDR) in Gram-negative bacteria, Gram-positive AMR is also a serious concern. Methicillin-resistant Staphylococcus aureus (MRSA) is perhaps the paradigm example, and is of high global importance as a cause of community-acquired and healthcare-associated infection. MRSA is a pathogen of concern due to its inherent resistance to almost all β-lactam antimicrobials (i.e., penicillins, cephalosporins and carbapenems) [7].

  There are various species of pathogenic Gram Positive Bacteria in nature which cause various diseases in humans and very few drugs are available in the market to cure such diseases. The major drawback associated with the antibiotic use is bacterial drug resistance which has created a chaotic situation in the whole world. Therefore, scientists have a great challenge to discover novel antibiotics which have less tendency to get resisted as well as with high efficiency. Out of the various antibiotics available in the market, few are specific for Gram Positive Bacteria. They are categorized on the basis of their structure which has been discussed further.

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  Gram-Positive Pathogens

  • Vincent A. Fischetti, Richard P. Novick, Joseph J. Ferretti, Daniel A. Portnoy, Mirian Braunstein, Julian I. Rood, Vincent A. Fischetti, Richard P. Novick, Joseph J. Ferretti, Daniel A. Portnoy, Mirian Braunstein, Julian I. Rood(Authors)
  • 2019(Publication Date)
  • ASM Press

    (Publisher)

  The Gram-Positive Bacterial Cell Wall

  Manfred Rohde 1

  HISTORICAL BACKGROUND

  In 1884, the Danish bacteriologist Hans Christian Gram developed a staining procedure to view stained bacteriaunder the light microscope (1 ). His staining method, nowadays simply called Gram staining, discriminated between a Gram-positive and Gram-negative bacterial cell wall. He introduced a dye, gentian violet, which penetrates the cell wall and cytoplasmic membrane, thus staining the cytoplasm of the heat-fixed bacteria. After addition of iodine, an insoluble complex is formed which is retained by the Gram-positive bacterial cell wall upon addition of a decolorizer such as ethanol. Therefore, Gram-positive bacteria appear almost purple, while Gram-negative bacteria retain the dye to a lesser extent or not at all and have to be counterstained with a second dye, safranin or fuchsine, appearing pink or reddish. It is noteworthy that some mycobacteria showed an indifferent staining behavior when Gram stained, suggesting that the cell wall of mycobacteria might be somehow different from the other two types. In the following decades, it became obvious that cell walls/cell envelopes are more diverse and that Gram staining alone often could lead to misinterpretations of the cell wall composition.

  Before the early 1950s, when the chemical composition of bacterial cell walls was not known, it was speculated that chitin or cellulose, polymers recognized as providing rigid structures to other organisms, might also represent the building material of the bacterial cell wall. In 1951, experiments with a phenol-insoluble material from Corynebacterium diphtheria (2 ) revealed glucosamine and diaminopimelic acid as components of the bacterial cell wall which are associated with polysaccharides. Chemical examination of streptococcal cell wall layers highlighted the presence of amino acids and hexosamines in the cell wall extract, as well as rhamnose as a main component in Gram-positive bacteria (3 , 4 ). Systematic analyses of a number of Gram-positive bacteria identified the hexosamines glucosamine and muramic acid as major components together with three prevalent amino acids, namely, d-alanine, lysine or diaminopimelic acid, and glutamic acid. By then, a typical basic basal unit in Gram-positive cell walls was also recognized in which glucosamine and muramic acid are linked with three amino acids via a peptide bond (5 , 6 ). Gram-negative bacteria express the identical basal unit. Numerous analyses of other bacteria revealed that each bacterial genus or even species is often characterized by a distinctive pattern of amino acids, amino sugars, and sugars connected to the basic basal unit. It was believed that these differences should provide a valuable pattern to discriminate between bacterial genera/species (7 , 8 ). Over the following years other compounds of the Gram-positive cell wall were recognized, such as teichoic acids (TAs), which are polyribitol phosphates (9

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  The Nobel Prize Winning Discoveries in Infectious Diseases

  • David Rifkind, Geraldine Freeman(Authors)
  • 2005(Publication Date)
  • Academic Press

    (Publisher)

  Bacteria are of about one micron in size – 25 000 per inch – and can be visualized only with a relatively high-powered light microscope. To be visible under the microscope bacteria must first be stained, and the most common technique used is the Gram stain, which was devised in 1884 by Hans Christian Joachim Gram, a Danish microbiologist. In this procedure bacteria are fixed on to a microscope slide, treated with the purple dye ‘crystal violet’, plus iodine, and then washed with alcohol. Those bacteria that retain the stain after the alcohol wash are termed Gram-positive, whilst those not retaining the stain are termed Gram-negative. The unique importance and utility of this simple staining procedure is not just that it provides ready visualization of the organisms but rather that it correlates with important biological features of the species of bacteria – most notably the types of disease produced and patterns of their susceptibility to the various antibiotics.

  Most bacteria can be killed by heating to 150°F for thirty minutes or 161°F for fifteen seconds – the procedure used in pasteurization of milk. However, some important bacteria, notably the clostridia (which cause tetanus, gas gangrene and botulism) produce resistant spores that require steaming under increased pressure for inactivation (250°F for fifteen minutes).

  Some bacteria, like cells of higher organisms, require oxygen for growth; these bacteria are the aerobes . Others, however, the anerobes, will only grow in the absence of oxygen – a unique characteristic first described by Pasteur.

  Bacteria can be cultivated in various liquid media and on media solidified with agar, a polysaccharide derived from seaweed. The unique feature of culture on solid medium is that each individual colony which develops is derived from a single bacterial cell in the inoculum – that is, the colony is a clone .

  Bacteria multiply by simple binary fission, an asexual process in which a single bacterial cell divides in two. By the application of genetic techniques Joshua Lederberg showed that a sexual process of recombination between two different bacterial cells can occur. This discovery was recognized by a share of the Nobel Prize for Physiology or Medicine in 1958.

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  Bacterial Physiology

  • C. H. Werkman, P. W. Wilson, C. H. Werkman, P. W. Wilson(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  Differ- ent structures of the same cell may give a different gram reaction or may differ in the degree of gram positiveness: For instance, in Thiobacillus thiooxidans the protoplasm is gram negative, but the content of the vacuole in mature cultures is gram positive; several common members of Bacillus in actively growing cultures often show a negative cytoplasm 16 GEORGES KNAYSI and a strongly positive cytoplasmic membrane when stained by Burke's method; when a positive cell is decolorized slowly, the cytoplasmic membrane is the last one to lose its color; the vegetative cells of strain C 2 of Bacillus mycoides, when developed from the spore in a nitrogen- free medium, are predominently negative and contain moderately posi- tive nuclei. There is a general correspondence between the gram reaction and certain important properties of bacteria (Churchman, 1928). Gram- negative bacteria are readily plasmolyzable by ordinary means; they have a higher apparent isoelectric point, and are less susceptible to halogens, triphenylmethane dyes, and common antibodies than are gram- positive bacteria. A number of other differences as in susceptibility to phagocytosis, bacteriolytic agents, and digestibility of the killed cells by proteolytic enzymes were also reported. This explains why the mechanism of the reaction has been the object of many investigations. Obviously, the true mechanism of the reaction would account for a number of observations made both on the bacteria and on the technique. When growing in ordinary culture media, negative bacteria from a mature culture may be plasmolyzed by 2 or 3 % KN0 3 ; positive bacteria are not plasmolyzed even by several times this concentration and, indeed, the conditions under which they may be regularly plasmolyzed are not yet known and deserve investigation. However, there is no structural difference between the two types as was believed by Churchman.

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  Scott-Brown's Otorhinolaryngology and Head and Neck Surgery

  Volume 1: Basic Sciences, Endocrine Surgery, Rhinology

  • John Watkinson, Ray Clarke, John C Watkinson, Ray W Clarke, John Watkinson, Ray Clarke, John C Watkinson, Ray W Clarke(Authors)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Microbiology

  CHAPTER 19

  Microorganisms

  Ursula Altmeyer, Penelope Redding and Nitish Khanna

  Introduction Basic concepts in microbiology Classification of bacterial organisms References

  SEARCH STRATEGY

  This chapter collates basic consensus knowledge of bacteriology. Laboratory practices described are based on Public Health England’s Standards for Microbiology Investigations (SMI). Data in this chapter may be updated by a PubMed search using the keywords: basic concepts in microbiology; classification of bacteria based on gram staining; gram positive; gram negative; staphylococci, streptococci, enterobacteriaceae, anaerobes; mycobacteriae; spirochetes.

  INTRODUCTION

  The human body is a habitat that supports single-cell microorganisms in numbers that by far exceed the number of its own cells. Most of these organisms have evolved over millions of years in close association with our own species, forming what is referred to as the human microbiome.

  Contained in their ecological niche, these bacteria can be essential for the survival of the host body, although if given the opportunity to leave their niche, for example through injury or surgery, their presence may equally lead to disease. Some of these beneficial, or at least harmless, tenants also have the potential to cause opportunistic infections in host organisms that are particularly susceptible, whether that be due to overall poor health, extremes of age, or constitutional or iatrogenic immunosuppression.

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  An Introduction to Microbiology

  Pharmaceutical Monographs

  • W. B. Hugo, J. B. Stenlake(Authors)
  • 2014(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  CHAPTER 1 THE BACTERIAL CELL The present detailed knowledge of the anatomy of the bacterial cell represents the cumulation of a century of research. Early information was gathered by careful microscopic study using light (as distinct from electron) microscopy and a variety of special staining techniques. One of these, discovered in 1884 by Gram (page 29), divided bacteria into two groups dependent on whether they remained stained (Gram-positive) or not (Gram-negative) on washing with ethanol. This difference was later found to be linked with other general differences in properties within the two groups. More recently the study of bacteria by electron microscopy has confirmed and extended the findings of the early workers. It is now possible to cut sections of bacteria thin enough for examination by electron microscopy, while scanning electron microscopy is play-ing an increasingly important role in the study of microbial anatomy. In addition much information has been gained by the fragmen-tation of bacteria by mechanical or chemical methods followed by separation of components by differential centrifugation. These components have been subsequently examined in the electron and scanning electron microscope and also subjected to chemical analysis. SHAPE AND MORPHOLOGY The bacteria are unicellular organisms and it is important when considering bacterial cells to gain first an impression of their shape and size. The true bacteria exist in two main morphological variants, as rod-shaped cells with rounded or sometimes pointed ends, and as spherical or almost spherical cells called cocci. Four variants of the rod-shaped form are found : rods with one convolution (Vibrio), rods with several convolutions (Spirillum), rods which tend to form chains with the cells arranged end to end (some lactobacilli) and those that may show branched forms as seen amongst some of the Actinomycetales. Variants of the coccoid form depend on the degree and manner of aggregation of the cells 1

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