Prokaryotic Microbes.pdf

THE PROKARYOTIC CELL AND MICROORGANISMS (Chapters 2.4, 3.3, and 4) PROKARYOTES - FACTS Prokaryotes can be found everywhere on our planet, even in the most extreme environments. Prokaryotes are very flexible metabolically, so they are able to adjust their feeding to the...

THE PROKARYOTIC CELL AND MICROORGANISMS (Chapters 2.4, 3.3, and 4) PROKARYOTES - FACTS Prokaryotes can be found everywhere on our planet, even in the most extreme environments. Prokaryotes are very flexible metabolically, so they are able to adjust their feeding to the available natural resources. Prokaryotes live in communities that interact among themselves and with large organisms that they use as hosts (including humans). The totality of forms of prokaryotes (particularly bacteria) living on the human body is called the human microbiome, which varies between regions of the body and individuals, and changes over time. The totality of forms of prokaryotes (particularly bacteria) living in a certain region of the human body (e.g., mouth, throat, gut, eye, vagina) is called the microbiota of this region. Prokaryotes are classified into domains Archaea and Bacteria. In recent years, the traditional approaches to classification of prokaryotes have been supplemented by approaches based on molecular genetics. UNIQUE CHARACTERISTICS OF PROKARYOTES Prokaryotic cells differ from eukaryotic cells in that their genetic material is contained in a nucleoid rather than a membrane-bound nucleus. In addition, prokaryotic cells generally lack membrane-bound organelles. Prokaryotic cells of the same species typically share a similar cell morphology and cellular arrangement. A TYPICAL PROKARYOTIC CELL GENETIC MATERIAL The nucleoid region (the area enclosed by the green dashed line) is a condensed area of DNA found within prokaryotic cells. Because of the density of the area, it does not readily stain and appears lighter in color when viewed with a transmission electron microscope. Outside of the nucleoid, prokaryotic cells may contain extrachromosomal DNA in plasmids. BACTERIA HAVE EXTRA CHROMOSOMAL PIECES OF DNA IN THE CYTOPLASM CALLED a) plasmids. b) inclusion bodies. c) carboxysomes. d) nucleoids. © John Wiley & Sons, Inc. or the author, All rights reserved. RIBOSOMES Prokaryotic ribosomes (70S) are composed of two subunits: the 30S (small subunit) and the 50S (large subunit), each of which are composed of protein and rRNA components. Target for antibiotics ENDOSPORES Some prokaryotic cells are able to form endospores through sporulation to survive in a dormant state when conditions are unfavorable. Endospores can germinate, transforming back into vegetative cells when conditions improve. (a) Sporulation begins following asymmetric cell division. The forespore becomes surrounded by a double layer of membrane, a cortex, and a protein spore coat, before being released as a mature endospore upon disintegration of the mother cell. (b) An electron micrograph of a Carboxydothermus hydrogenoformans endospore. (c) These Bacillus spp. cells are undergoing sporulation. The endospores have been visualized using Malachite Green spore stain. (credit b: modification of work by Jonathan Eisen) CELL MEMBRANE The bacterial plasma membrane is a phospholipid bilayer with a variety of embedded proteins that perform various functions for the cell. Note the presence of glycoproteins and glycolipids, whose carbohydrate components extend out from the surface of the cell. The abundance and arrangement of these proteins and lipids can vary greatly between species. TRANSPORT ACROSS THE CELL MEMBRANE (credit: modification of work by Mariana Ruiz Villareal) CELL WALL Peptidoglycan is composed of polymers of alternating NAM and NAG subunits, which are cross-linked by peptide bridges linking NAM subunits from various glycan chains. This provides the cell wall with tensile strength in two dimensions. Some Archaea – pseudopeptidoglycan (NAM is replaced by N-acetyltalosaminuronic acid (NAT). THE BACTERIAL CELL WALL a) provides resistance to osmotic pressure and mechanical forces. b) is very similar in Gram-positive and Gram- negative bacteria. c) is composed of peptidoglycan in Gram- positive cells and pseudomurein in Gram- negative cells. d) is resistant to lysozyme in Gram-positive cells. © John Wiley & Sons, Inc. or the author, All rights reserved. CELL WALL Most prokaryotic cells have a cell wall that helps the organism maintain cellular morphology and protects it against changes in osmotic pressure. In cells that lack a cell wall, changes in osmotic pressure can lead to crenation in hypertonic environments or cell lysis in hypotonic environments. CAPSULE (a) Some prokaryotic cells produce glycocalyx coatings (made of polysaccharides), such as capsules and slime layers, that aid in attachment to surfaces and/or evasion of the host immune system. (b) A capsule stain of Pseudomonas aeruginosa, a bacterial pathogen capable of causing many different types of infections in humans. (credit b: modification of work by American Society for Microbiology) PILI Some prokaryotic cells have fimbriae or pili, filamentous appendages that aid in attachment to surfaces. Pili are also used in the transfer of genetic material between cells. Bacteria may produce two different types of protein appendages that aid in surface attachment. Fimbriae typically are more numerous and shorter, whereas pili (shown here) are longer and less numerous per cell. (credit: modification of work by American Society for Microbiology) FIMBRIAE ARE BASICALLY SHORT PILI. a) True b) False © John Wiley & Sons, Inc. or the author, All rights reserved. FLAGELLA Flagellated bacteria may exhibit multiple arrangements of their flagella. Common arrangements include monotrichous, amphitrichous, lophotrichous, or peritrichous. WHEN COMPARED TO THE CYTOPLASM OF EUKARYAL CELLS, THE CYTOPLASM OF BACTERIA IS a) exactly the same. b) completely different. c) similar in many respects, but still different. d) similar in a few respects, but still very different. © John Wiley & Sons, Inc. or the author, All rights reserved. BACTERIA USE A VARIETY OF MEANS TO ATTACH TO SOLID SUBSTRATES INCLUDING a) nematocysts b) fimbriae c) capsules d) b and c © John Wiley & Sons, Inc. or the author, All rights reserved. STAINING MICROSCOPIC SPECIMENS Samples must be properly prepared for microscopy. This may involve staining, fixation, and/or cutting thin sections. A variety of staining techniques can be used with light microscopy, including Gram staining, acid-fast staining, capsule staining, endospore staining, and flagella staining. FIXATION It is the process of attaching cells to the slide. Fixation is often achieved either by heating (heat fixing) or chemically treating the specimen. In addition to attaching the specimen to the slide, fixation also kills microorganisms in the specimen, stopping their movement and metabolism while preserving the integrity of their cellular components for observation. (a) A specimen can be heat-fixed by using a slide warmer like this one. (b) Another method for heat-fixing a specimen is to hold a slide with a smear over a microincinerator. (c) This tissue sample is being fixed in a solution of formalin (also known as formaldehyde). Chemical fixation kills microorganisms in the specimen, stopping degradation of the tissues and preserving their structure so that they can be examined later under the microscope. (credit a: modification of work by Nina Parker; credit b: modification of “Microbiology Laboratory Manual” by Gary E. Kaiser, PhD; credit c: modification of work by “University of Bristol”/YouTube)  GRAM STAINING: PROCEDURE Gram-staining is a differential staining technique that uses a primary stain and a secondary counterstain to distinguish between gram-positive and gram-negative bacteria. GRAM STAINING: RESULT In this specimen, the gram-positive bacterium Staphylococcus aureus retains crystal violet dye even after the decolorizing agent is added. Gram-negative Escherichia coli, the most common Gram stain quality-control bacterium, is decolorized, and is only visible after the addition of the pink counterstain safranin. (credit: modification of work by Nina Parker) GRAM STAINING: IMPORTANCE Besides their differing interactions with dyes and decolorizing agents, the chemical differences between gram-positive and gram- negative cells have other implications with clinical relevance. For example, Gram staining can help clinicians classify bacterial pathogens in a sample into categories associated with specific properties. Gram- (credit: modification of work by American Society for Microbiology) negative bacteria tend to be more resistant to certain antibiotics than gram- positive bacteria. CELL WALL AND GRAM STAIN Bacteria contain two common cell wall structural types. Gram-positive cell walls are structurally simple, containing a thick layer of peptidoglycan with embedded teichoic acid external to the plasma membrane. Gram-negative cell walls are structurally more complex, containing three layers: the inner membrane, a thin layer of peptidoglycan, and an outer membrane containing lipopolysaccharide (LPS). (credit: modification of work by “Franciscosp2”/Wikimedia Commons) AUDIENCE QUESTION Gram staining of acid fast bacteria shows: a) Purple color b) Pink Color c) Weakly purple d) Colorless  CELL WALL AND GRAM STAIN The outer membrane of a gram-negative bacterial cell contains lipopolysaccharide (LPS), a toxin composed of Lipid A embedded in the outer membrane, a core polysaccharide, and the O side chain. A MAJOR DIFFERENCE BETWEEN GRAM-POSITIVE AND GRAM-NEGATIVE CELL WALLS IS THE PRESENCE OF a) peptidoglycan in Gram-positive walls. b) lipopolysachharides in Gram-negative walls. c) periplasm in Gram-positive walls. d) teichoic acids in Gram-negative walls. © John Wiley & Sons, Inc. or the author, All rights reserved. ACID-FAST STAINS An acid-fast stain is able to differentiate two types of gram-positive cells: those that have waxy mycolic acids in their cell walls, and those that do not. The waxy, acid-fast cells retain the carbolfuchsin even after a decolorizing agent (an Ziehl-Neelsen staining has rendered these Mycobacterium tuberculosis cells red and the surrounding growth indicator medium blue. (credit: acid-alcohol solution) is modification of work by American Society for Microbiology) applied. A secondary counterstain, methylene blue, is then applied, which renders non–acid-fast cells blue. If AFB are present in a tissue sample, their red or pink color can be seen clearly against the blue background of the surrounding tissue cells. CELL WALL AND GRAM STAIN (a) Some gram-positive bacteria, including members of the Mycobacteriaceae, produce waxy mycolic acids found exterior to their structurally-distinct peptidoglycan. (b) The acid-fast staining protocol detects the presence of cell walls that are rich in mycolic acid. Acid-fast cells are stained red by carbolfuschin. (credit a: modification of work by “Franciscosp2”/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention)  CAPSULE STAINING Certain bacteria and yeasts have a protective outer structure called a capsule. Since the presence of a capsule is directly related to a microbe’s virulence. Capsules do not absorb most basic dyes; therefore, a negative staining technique (staining around the cells) is typically used for capsule staining. The dye stains the background but does not penetrate the capsules, which appear like halos around the borders of the cell. (a) India-ink was used to stain the background around these cells of the yeast Cryptococcus neoformans. The halos surrounding the cells are the polysaccharide capsules. (b) Crystal violet and copper sulfate dyes cannot penetrate the encapsulated Bacillus cells in this negatively stained sample. Encapsulated cells appear to have a light-blue halo. (credit a: modification of work by American Society for Microbiology; credit b: modification of work by American Society for Microbiology) ENDOSPORE STAINING Endospores are structures produced within certain bacterial cells that allow them to survive harsh conditions. Gram staining alone cannot be used to visualize A stained preparation of Bacillus subtilis showing endospores, which appear clear endospores as green and the vegetative cells as when Gram-stained cells are pink. (credit: modification of work by American Society for Microbiology) viewed. Endospore-staining techniques are important for identifying Bacillus and Clostridium, two genera of endospore- producing bacteria that contain clinically significant species. Among others, B. anthracis (which causes anthrax) has been of particular interest because of concern that its spores could be used as a bioterrorism agent. C. difficile is a particularly important species responsible for the typically hospital-acquired infection known as “C. diff.” FLAGELLA STAINING (UNCOMMON IN CLINICAL SETTING) A flagella stain of Bacillus cereus, a common cause of foodborne illness, reveals that the cells have numerous flagella, used for locomotion. (credit: modification of work by Centers for Disease Control and Prevention) BASIC STAINS (credit “basic stains”: modification of work by Centers for Disease Control and Prevention; credit “Acidic stains”: modification of work by Roberto Danovaro, Antonio Dell’Anno, Antonio Pusceddu, Cristina Gambi, Iben Heiner, Reinhardt Mobjerg Kristensen; credit “Negative stains”: modification of work by Anh-Hue Tu)  FIGURE 2.41 (credit “Gram stain”: modification of work by Nina Parker; credit “Acid-fast stain”: modification of work by American Society for Microbiology; credit “Endospore stain”: modification of work by American Society for Microbiology; credit “Capsule stain” : modification of work by American Society for Microbiology; credit “Flagella stain”: modification of work by Centers for Disease Control and Prevention) (credit “Gram stain”: modification of work by Nina Parker; credit “Acid-fast stain”: modification of work by American Society for Microbiology; credit “Endospore stain”: modification of work by American Society for Microbiology; credit “Capsule stain” : modification of work by American Society for Microbiology; credit “Flagella stain”: modification of work by Centers for Disease Control and Prevention) (credit “Coccus” micrograph: modification of work by Janice Haney Carr, Centers for Disease Control and Prevention; credit “Coccobacillus” micrograph: modification of work by Janice Carr, Centers for Disease Control and Prevention; credit “Spirochete” micrograph: modification of work by Centers for Disease Control and Prevention) FIGURE 3.14 AUDIENCE QUESTION You are observing a bacterial sample under the microscopes, after gram staining. The bacteria look purple rods. The sample most probably contains: a) Bacillus subtilis b) Streptococcus pneumoniae c) Vibrio cholera d) Staphylococcus aureus WHICH OF THE FOLLOWING IS CORRECTLY MATCHED? a) Streptococcus = rods in chains b) Staphylococcus = spheres in clumps c) Diplococcus = rods in clumps d) Streptobacillus = spheres in chains © John Wiley & Sons, Inc. or the author, All rights reserved. THE MOST COMMON SHAPES OF BACTERIA ARE a) rods (bacillus) b) spheres (coccus) c) curved rods (vibrio) d) all of these choices. © John Wiley & Sons, Inc. or the author, All rights reserved. AUDIENCE QUESTION You are observing a bacterial sample under the microscopes, after endospore staining. Which bacteria you will most probably see: a) Bacillus subtilis b) Clostridium botulinum c) Vibrio cholera d) Both a and b  GRAM NEGATIVE BACTERIA Genus Microscopic Unique Characteristics Morphology Bartonella Gram-negative, Facultative intracellular bacteria, transmitted by pleomorphic, flagellated lice and fleas, cause trench fever and cat scratch coccobacillus disease in humans Brucella Gram-negative, small, Facultative intracellular bacteria, transmitted by flagellated contaminated milk from infected cows, cause coccobacillus brucellosis in cattle and humans Coxiella Small, gram-negative Obligatory intracellular bacteria; cause Q fever; bacillus potential for use as biological weapon Ehrlichia Very small, gram- Obligatory intracellular bacteria; can be negative, coccoid or transported from cell to cell; transmitted by ticks; ovoid bacteria cause ehrlichiosis (destruction of white blood cells and inflammation) in humans and dogs Rickettsia Gram-negative, highly Obligate intracellular bacteria; transmitted by pleomorphic bacteria ticks; may cause Rocky Mountain spotted fever (may be cocci, rods, or and typhus threads) RICKETTSIAS Rickettsias require special staining methods to see them under a microscope. Here, R. rickettsii, which causes Rocky Mountain spotted fever, is shown infecting the cells of a tick. (credit: modification of work by Centers for Disease Control and Prevention)  GRAM NEGATIVE BACTERIA Genus Microscopic Unique Characteristics Morphology Bordetella A small, gram- Aerobic, very fastidious; B. pertussis causes pertussis negative (whooping cough) coccobacillus Burkholderia Gram-negative Aerobic, aquatic, cause diseases in horses and humans bacillus (especially patients with cystic fibrosis); agents of nosocomial infections Neisseria Gram-negative, Require moisture and high concentration of carbon dioxide; coffee bean- oxidase positive, grow on chocolate agar; pathogenic shaped coccus species cause gonorrhea and meningitis (dw about this forming pairs hoe) NEISSERIA MENINGITIDIS Neisseria meningitidis growing in colonies on a chocolate agar plate. (credit: Centers for Disease Control and Prevention) GRAM NEGATIVE BACTERIA Example Genus Microscopic Morphology Unique Characteristics Enterobacter Gram-negative bacillus Facultative anaerobe; cause urinary and respiratory Entero(affects gi tract infections in hospitalized patients; implicated in tract) the pathogenesis of obesity Escherichia (e Gram-negative bacillus Facultative anaerobe; inhabit the gastrointestinal coli) tract of warm-blooded animals; some strains are mutualists, producing vitamin K; others, like serotype E. coli O157:H7, are pathogens; E. coli has been a model organism for many studies in genetics and molecular biology Hemophilus Gram-negative bacillus Pleomorphic, may appear as coccobacillus, aerobe, or facultative anaerobe; grow on blood agar; pathogenic species can cause respiratory infections, chancroid, and other diseases Klebsiella Gram-negative bacillus; Facultative anaerobe, encapsulated, nonmotile; appears rounder and pathogenic species may cause pneumonia, thicker than other especially in people with alcoholism members of Enterobacteriaceae Legionella Gram-negative bacillus Fastidious, grow on charcoal-buffered yeast extract; L. pneumophila causes Legionnaires disease LEGIONNAIRES DISEASE (a) Legionella pneumophila, the causative agent of Legionnaires disease, thrives in warm water. (b) Outbreaks of Legionnaires disease often originate in the air conditioning units of large buildings when water in or near the system becomes contaminated with L. pneumophila. (credit a: modification of work by Centers for Disease Control and Prevention) GRAM NEGATIVE BACTERIA Proteus Gram-negative Common inhabitants of the human gastrointestinal tract; motile; bacillus produce urease; opportunistic pathogens; may cause urinary tract (pleomorphic) infections and sepsis Pseudomona Gram-negative Aerobic; versatile; produce yellow and blue pigments, making them s bacillus appear green in culture; opportunistic, antibiotic-resistant pathogens may cause wound infections, hospital-acquired infections, and secondary infections in patients with cystic fibrosis Serratia Gram-negative Motile; may produce red pigment; opportunistic pathogens bacillus responsible for a large number of hospital-acquired infections Shigella Gram-negative Nonmotile; dangerously pathogenic; produce Shiga toxin, which can bacillus destroy cells of the gastrointestinal tract; can cause dysentery Vibrio Gram-negative, Inhabit seawater; flagellated, motile; may produce toxin that causes comma- or curved hypersecretion of water and electrolytes in the gastrointestinal rod-shaped bacteria tract; some species may cause serious wound infections Yersinia Gram-negative Carried by rodents; human pathogens; Y. pestis causes bubonic bacillus plague and pneumonic plague; Y. enterocolitica can be a pathogen causing diarrhea in humans Salmonella Gram-negative A number of serotypes of Salmonella can cause salmonellosis, flagellated bacillus characterized by inflammation of the small and the large intestine, accompanied by fever, vomiting, and diarrhea. TYPHOID FEVER Salmonella typhi is the causative agent of typhoid fever. (credit: Centers for Disease Control and Prevention) GRAM NEGATIVE BACTERIA Example Genus Microscopic Unique Characteristics Morphology Campylobacter Gram- Aerobic (microaerophilic); often infects chickens; negative, may infect humans via undercooked meat, spiral-shaped causing severe enteritis rod Helicobacter Gram- Aerobic (microaerophilic) bacterium; can damage negative, the inner lining of the stomach, causing chronic spiral-shaped gastritis, peptic ulcers, and stomach cancer rod GASTRITIS Helicobacter pylori can cause chronic gastritis, which can lead to ulcers and stomach cancer. GRAM NEGATIVE BACTERIA Example Microscopic Unique Characteristics Genus Morphology Chlamydia Gram-negative, Obligatory intracellular bacteria; some cause coccoid or ovoid chlamydia, trachoma, and pneumonia bacterium Bacteroides Gram-negative Obligate anaerobic bacteria; abundant in the bacillus human gastrointestinal tract; usually mutualistic, although some species are opportunistic pathogens Cytophaga Gram-negative Motile by gliding; live in soil or water; bacillus decompose cellulose; may cause disease in fish  GRAM NEGATIVE BACTERIA Example Genus Microscopic Unique Characteristics Morphology Fusobacterium Gram-negative bacillus Anaerobic; form; biofilms; some species cause with pointed ends disease in humans (periodontitis, ulcers) Leptospira Spiral-shaped bacterium Aerobic, abundant in shallow water reservoirs; (spirochetes); gram infect rodents and domestic animals; can be negative-like (better transmitted to humans by infected animals’ viewed by darkfield urine; may cause severe disease microscopy); very thin Borrelia Gram-negative-like B. burgdorferi causes Lyme disease and B. spirochete; very thin; recurrens causes relapsing fever better viewed by darkfield microscopy Treponema Gram-negative-like Motile; do not grow in culture; T. spirochete; very thin; pallidum (subspecies T. pallidum pallidum) better viewed by darkfield causes syphilis microscopy AUDIENCE QUESTION Which of the following is true for both Treponema and Chalmydia? (Select all that apply) a) They both cause sexually transmitted diseases (STIs) b) They are both Gram negative c) They are both bacilli d) They both require antibiotics for treatment e) They both resolve on their own NORMAL FLORA Bacteroides comprise up to 30% of the normal microbiota in the human gut. (credit: NOAA) TUBERCULOSIS M. tuberculosis grows on Löwenstein-Jensen (LJ) agar in distinct colonies. (credit: Centers for Disease Control and Prevention)  58 TUBERCULOSIS - TB Caused by Mycobacterium tuberculosis Aerobic bacillus Tubercle bacilli is a common synonym for M. tuberculosis. Passed from infected humans and (much less commonly) cows (bovine) and birds (avian) TB is most commonly characterized by granulomas in the lungs: nodular accumulations of inflammatory cells (e.g., macrophages, lymphocytes) that are delimited (“walled off” with clear boundaries) and have a centre that has a cheesy or caseated consistency. Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  59 MYCOBACTERIUM INFECTIONS (CONT.) Tubercle bacilli are conveyed by droplets. Droplets are expelled by coughing or sneezing, and they then gain entry into the body by inhalation. Tubercle bacilli then spread to other body organs via blood and lymphatic systems. Tubercle bacilli may become dormant or walled off by calcified or fibrous tissue. Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  60 MYCOBACTERIUM INFECTIONS Common infection sites: Lung (primary site) Brain (cerebral cortex) Bone (growing end) Liver Kidney Genitourinary tract Virtually every other tissue and organ in the body Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  61 MYCOBACTERIUM INFECTIONS (CONT.) Mycobacterium tuberculosis a very slow-growing organism More difficult to treat than most other bacterial infections First infectious episode: primary TB infection Re-infection: chronic form of the disease Dormancy: may test positive for exposure but are not necessarily infectious Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  62 TUBERCULOSIS-RELATED INJECTIONS Purified protein derivative (PPD) (Mantoux®) A diagnostic injection given intradermally in doses of 5 tuberculin units (0.1 mL) to detect exposure to the TB organism Positive indicated by induration (not erythema) at the site of injection Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  63 DIAGNOSIS Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  64 INCIDENCE Canada has one of the lowest rates of active TB internationally. Decline is attributed to intensified public health efforts aimed at preventing, diagnosing, and treating TB as well as human immunodeficiency virus (HIV) infection. Incidence rate: 4.7 per 100 000 Higher incidence among Aboriginal people Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  65 INCIDENCE (CONT.) TB infects one third of the world’s population. TB is second to HIV in the number of deaths caused by a single infectious organism. A present concern is the increasing number of multidrug-resistant tuberculosis (MDR-TB) cases. Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  66 MULTIDRUG-RESISTANT TUBERCULOSIS Multidrug-resistant tuberculosis (MDR-TB) is TB that is resistant to both isoniazid (isonicotine hydrazine [INH]) and rifampin. Close contacts of patients with MDR-TB need to be treated for 6 to 9 months. Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  67 TUBERCULOSIS-RELATED INJECTIONS (CONT.) Bacille Calmette-Guérin (BCG) A vaccine injection derived from an inactivated strain of Mycobacterium bovis Used mainly in First Nations communities in the Northwest Territories and used in much of the world to vaccinate young children against TB Does not prevent infection but reduces active TB by 60 to 80% Effective at preventing more-severe cases involving dissemination of infection throughout the body Can cause false-positive results on the tuberculin skin test Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd.  68 ANTITUBERCULAR DRUG THERAPY CONSIDERATIONS Major effects of drug therapy: reduction of cough and thus reduction of the infectiousness of the patient Normally occurs within 2 weeks of the initiation of drug therapy if TB strain is drug sensitive Most cases of TB can be cured. Successful treatment: several antibiotic drugs for at least 6 months and sometimes for as long as 12 months Copyright © 2017 Elsevier Canada, a division of Reed Elsevier Canada, Ltd. GRAM POSITIVE BACTERIA Microbiologists currently recognize two distinct groups of gram- positive, or weakly staining gram-positive, prokaryotes. (a) Actinomyces israelii (false-color scanning electron micrograph [SEM]) has a branched structure. (b) Corynebacterium diphtheria causes the deadly disease diphtheria. Note the distinctive palisades. (c) The gramvariable bacterium Gardnerella vaginalis causes bacterial vaginosis in women. This micrograph shows a Pap smear from a woman with vaginosis. (credit a: modification of work by “GrahamColm”/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention; credit c: modification of work by Mwakigonja AR, Torres LM, Mwakyoma HA, Kaaya EE)  GRAM POSITIVE BACTERIA Actinobacteria: High G+C Gram-Positive Genus Microscopic Unique Morphology Characteristics Actinomyces Gram-positive bacillus; Facultative anaerobes; in soil, decompose organic in colonies, shows matter; in the human mouth, may cause gum disease fungus-like threads (hyphae) Bifidobacterium Gram-positive, Anaerobes commonly found in human gut microbiota filamentous actinobacterium Corynebacterium Gram-positive bacillus Aerobes or facultative anaerobes; form palisades; grow slowly; require enriched media in culture; C. diphtheriae causes diphtheria Gardnerella Gram-variable Colonize the human vagina, may alter the microbial coccobacillus ecology, thus leading to vaginosis Micrococcus Gram-positive coccus, Ubiquitous in the environment and on the human skin; form microscopic oxidase-positive (as opposed to morphologically clusters similar S. aureus); some are opportunistic pathogens GRAM POSITIVE BACTERIA Mycobacterium Gram-positive, acid- Slow growing, aerobic, resistant to drying and fast bacillus phagocytosis; covered with a waxy coat made of mycolic acid; M. tuberculosis causes tuberculosis; M. leprae causes leprosy Nocardia Weakly gram-positive May colonize the human gingiva; may cause severe bacillus; forms acid- pneumonia and inflammation of the skin fast branches Propionibacterium Gram-positive bacillus Aerotolerant anaerobe; slow-growing; P. acnes reproduces in the human sebaceous glands and may cause or contribute to acne Streptomyces Gram-positive, fungus- Very diverse genus (>500 species); aerobic, spore- like (filamentous) forming bacteria; scavengers, decomposers found in bacillus soil (give the soil its “earthy” odor); used in pharmaceutical industry as antibiotic producers (more than two-thirds of clinically useful antibiotics) C DIFF Clostridium difficile, a gram-positive, rod-shaped bacterium, causes severe colitis and diarrhea, often after the normal gut microbiota is eradicated by antibiotics. (credit: modification of work by Centers for Disease Control and Prevention) STREP PYOGENES (a) A gram-stained specimen of Streptococcus pyogenes shows the chains of cocci characteristic of this organism’s morphology. (b) S. pyogenes on blood agar shows characteristic lysis of red blood cells, indicated by the halo of clearing around colonies. (credit a, b: modification of work by American Society for Microbiology) G+ SPP (a) In this gram-stained specimen, the violet rod-shaped cells forming chains are the gram-positive bacteria Bacillus cereus. The small, pink cells are the gram-negative bacteria Escherichia coli. (b) In this culture, white colonies of B. cereus have been grown on sheep blood agar. (credit a: modification of work by “Bibliomaniac 15”/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention) STAPH AUREUS This SEM of Staphylococcus aureus illustrates the typical “grape-like” clustering of cells. (credit: modification of work by Centers for Disease Control and Prevention) GRAM POSITIVE BACTERIA Bacilli: Low G+C Gram-Positive Bacteria Genus Microscopic Unique Morphology Characteristics Bacillus Large, gram-positive bacillus Aerobes or facultative anaerobes; form endospores; B. anthracis causes anthrax in cattle and humans, B. cereus may cause food poisoning Clostridium Gram-positive bacillus Strict anaerobes; form endospores; all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis Enterococcus Gram-positive coccus; forms Anaerobic aerotolerant bacteria, abundant in microscopic pairs in culture the human gut, may cause urinary tract and (resembling Streptococcus other infections in the nosocomial environment pneumoniae) Lactobacillus Gram-positive bacillus Facultative anaerobes; ferment sugars into lactic acid; part of the vaginal microbiota; used as probiotics Leuconostoc Gram-positive coccus; may Fermenter, used in food industry to produce form microscopic chains in sauerkraut and kefir culture GRAM POSITIVE BACTERIA Bacilli: Low G+C Gram-Positive Bacteria Genus Microscopic Unique Morphology Characteristics Mycoplasma The smallest bacteria; appear Have no cell wall; classified as low G+C Gram- pleomorphic under electron positive bacteria because of their genome; M. microscope pneumoniae causes “walking” pneumonia Staphylococcus Gram-positive coccus; forms Tolerate high salt concentration; facultative microscopic clusters in culture that anaerobes; produce catalase; S. aureus can also resemble bunches of grapes produce coagulase and toxins responsible for local (skin) and generalized infections Streptococcus Gram-positive coccus; forms Diverse genus; classified into groups based on chains or pairs in culture sharing certain antigens; some species cause hemolysis and may produce toxins responsible for human local (throat) and generalized disease Ureaplasma Similar to Mycoplasma Part of the human vaginal and lower urinary tract microbiota; may cause inflammation, sometimes leading to internal scarring and infertility WHICH OF THE FOLLOWING CHARACTERISTICS ARE USED TO CLASSIFY BACTERIA? a) Cell morphology b) Growth characteristics c) DNA analysis d) All of these choices © John Wiley & Sons, Inc. or the author, All rights reserved. ARCHAEA Archaea are unicellular, prokaryotic microorganisms that differ from bacteria in their genetics, biochemistry, and ecology. Some archaea are extremophiles, living in environments with extremely high or low temperatures, or extreme salinity. Only archaea are known to produce methane. Methane-producing archaea are called methanogens. Halophilic archaea prefer a concentration of salt close to saturation and perform photosynthesis using bacteriorhodopsin. Some archaea, based on fossil evidence, are among the oldest organisms on earth. Archaea do not live in great numbers in human microbiomes and are not known to cause disease, however, diseases with some unknown causes might be associated with archaea such us Crohn’s, arthritis, lupus  FIGURE 4.26 Sulfolobus, an archaeon of the class Crenarchaeota, oxidizes sulfur and stores sulfuric acid in its granules.