Lecture 11 Microbiology Chapter 10 PDF

CHAPTER 10 (Complement) Bacterial Diversity Copyright © 2021 W. W. Norton & Company, Inc. Bacterial Diversity Chapter Objectives ▪ Describe the diversity of microbes associated with the human body. ▪ Distinguish major kinds of Gram-positive bacteria from Gram- negative bacteria. ▪ Describe...

CHAPTER 10 (Complement) Bacterial Diversity Copyright © 2021 W. W. Norton & Company, Inc. Bacterial Diversity Chapter Objectives ▪ Describe the diversity of microbes associated with the human body. ▪ Distinguish major kinds of Gram-positive bacteria from Gram- negative bacteria. ▪ Describe the unique cell traits of pathogenic spirochetes. 2 You Should See the Other Guy! – 1 Scenerio ▪ Cody, a 32-year-old Fort Worth, Texas, rancher, drove to Malone’s Pub to shoot pool. After drinking several beers, he got into a brawl with Ty, who was also drunk. A quick right cross to the face made short work of Ty, but Cody received a deep bite wound to his fist in the process Signs and Symptoms ▪ The wound was red, swollen, warm to the touch, and so painful that Cody couldn’t move his fingers. He had a fever of 37.9°C (100.2°F), but his lymph nodes were not swollen. 3 You Should See the Other Guy! – 2 Testing ▪ An X-ray ruled out broken bones. Meanwhile, swabs of the wound material were sent to the lab for culture. Culture results after 48 hours yielded a polymicrobial infection that included mouth and skin bacteria identified as Eikenella corrodens, Streptococcus pyogenes, Fusobacterium nucleatum, and Porphyromonas gingivalis. 4  Overview In broad terms, medically interesting bacteria belong to one of two large categories: 1. The “typical” bacteria—the rods and cocci (spheres) that lack unusual morphological features. ▶ Gram+ and Gram-ve 2. The “atypical” bacteria – all that don’t fall in the first category. ▶ Acid-fast bacteria ▶ Chlamydiae ▶ Rickettisia ▶ Mycoplasma ▶ Spirochetes 5  “Typical” Bacteria The Gram stain property reflects fundamental differences among bacteria ▶ presence of an outer membrane in the Gram-ve bacteria ▶ Thick PG layer in the Gram+ bacteria Gram+ and Gram-ve can be divided into rods and cocci The Gram+ cocci and the Gram-ve rods are the most common agents of infection ▶ followed by Gram-ve cocci and Gram+ rods 6  “Typical” Bacteria Gram-Positive Cocci The two most medically relevant genera of Gram+ cocci: Streptococcus and Staphylococcus. Streptococci grow in chains of spherical cells constitute a large diverse group, subdivided according to properties shown when grown on agar-containing blood. ▶ Alpha and beta hemolytic 7  “Typical” Bacteria Gram-Positive Cocci Streptococci β-hemolytic streptococci (or “beta strep”), ▶ lyse red blood cells signified by a clear area around the colonies. ▶ cause most streptococcal infections The α-hemolytic streptococci ▶ turn blood-containing media around the colony green. 𝛾-hemolytic streptococci ▶ do not change the blood at all. Many streptococci strains are nonpathogenic ▶ found in the environment and normal human intestine. ▶ Some strains used for yogurt and cheese. 8  “Typical” Bacteria Gram-Positive Cocci Streptococci (Don’t need to memorize) The main pathogenic Streptococcus spp. are the β-hemolytic strains (β-strep) β-strep are further subclassified into groups (A,B,C,D,F and G) ▶ based on presence of different cell wall polysaccharides Most well-known strains in human disease are group A strep. ▶ referred to as “group A strep” or “GAS” ▶ cause “strep throat,” infections of soft tissues, and other serious infections. α-Hemolytic streptococci include one major pathogen: Streptococcus pneumoniae ▶ the principal agent of bacterial pneumonia 9  “Typical” Bacteria Gram-Positive Cocci Streptococci The main pathogenic Streptococcus spp. are the β-hemolytic strains (β-strep) β-strep are further subclassified into groups (A,B,C,D,F and G) ▶ based on presence of different cell wall polysaccharides Most well-known strains in human disease are group A strep. ▶ referred to as “group A strep” or “GAS” ▶ cause “strep throat,” infections of soft tissues, and other serious infections. α-Hemolytic streptococci include one major pathogen: Streptococcus pneumoniae ▶ the principal agent of bacterial pneumonia 10  “Typical” Bacteria Gram-Negative Cocci Gram-ve cocci include several medically important genera ▶ most significant: Neisseria. Neisseria spp are found in the mouth and pharynx of healthy people two important pathogens: ▶ gonococcus (Neisseria gonorrhoeae) → gonorrhea ▶ meningococcus (N. meningitidis) → meningitis and septicemia outer membranes contain endotoxin (LPS) N. meningitidis 11  “Typical” Bacteria Gram-Positive Rods Abundant in the environment Rare source of disease in developed world. Corynebacterium diphtheriae Corynebacterium diphtheriae ▶ The agent of diphtheria, a deadly disease in children o Eradicated via vaccination ▶ relatives called diphtheroids polar granules, o Found on mucosal tissues and skin Revealed by special o Can cause opportunistic infections stains 12  “Typical” Bacteria Gram-Positive Rods Gram stain the most common Gram+ rods B. cereus and E. coli associated with humans are spore forming. largest of the typical bacteria ▶ 5 to 10x size of average E. coli ▶ 3 - 5 μm in length. Three important genera: Bacillus, Clostridium, Listeria Bacillus spp. Aerobic spores one clinically important species: Bacillus anthracis (anthrax), 13  “Typical” Bacteria Gram-Positive Rods C. difficile Clostridium spp. strict anaerobes Commensal spp.→ Important contributors of SCFA Pathogenic species include: ▶ C. difficile (→ pseudomembranous colitis) ▶ C. botulinum (→ botulism) L. monocytogenes ▶ C. tetani (→ tetanus) ▶ C. perfringens (and others) (→ gas gangrene) ▶ Symptoms of clostridial diseases are caused by powerful exotoxins. Listeria L. monocytogenes → enteric pathogen ▶ serious infections in infants, immunocompromised adults, pregnant. 14  “Typical” Bacteria Gram-Negative Rods Gram-negative rods are major representatives of human pathogens Many within enterobacteracieae ▶ E. coli (infectious diarrhea) ▶ Salmonella (typhoid fever and food poisoning) S. Typhi Shigella ▶ Shigella (bacillary dysentery) ▶ Yersinia (plaugue, enteritis) divided into two main groups ▶ Lactose fermenters (E. coli and others) ▶ Non-lactose fermenters (Salmonella and Shigella). 15  “Typical” Bacteria Gram-Negative Rods Non-enterobacteraceae Yersinia → Plague and intestinal infections Vibrionaceae ▶ Vibrio spp. including V. cholorae (cholera) Pseudomonaceae V. cholorae (cholera) ▶ Psuedomonas spp. ▶ Pseudomonas genus members = “Psuedomonads” ▶ Found in aqueous environments and soils Campylobacteraceae ▶ Campylobacter jejuni, → infectious diarrhea Helicobacteraceae ▶ Helicobacter pylori → gastritis, gastric ulcers, and gastric cancer. 16  “Typical” Bacteria Gram-Negative Rods “Fastidious” and Small Gram-Negative Rods “fastidious” – have complex nutritional requirements tend to be smaller than E. coli. Legionella Included in this group are the following genera: ▶ Haemophilus (which causes pneumonia and meningitis), ▶ Bordetella (whooping cough), ▶ Brucella (brucellosis), ▶ Francisella (tularemia), ▶ Bartonella (catscratch fever), ▶ Legionella (Legionnaires disease, a form of pneumonia). 17  “Typical” Bacteria Gram-Negative Rods Strictly Anaerobic Gram-Negative Rods Bacteroides genus is among most clinically important common in the human body B. fragilis colonies Gram stain Major representative of gut microbiota, ▶ critical stimulus for proper gut development ▶ break down some polysaccharides in the human diet. also found in gingival pockets that surround the teeth. usually harmless may cause serious disease when deposited in deep SEM tissues (e.g. peritonitis) 18 Clicker Question How many species of Streptococcus are found in Group A Strep a. 4 b. 2 c. 1 d. 3 e. 5. 19 Clicker Question Gram-negative cocci do not exist a. True b. False 20  “Atypical” Bacteria The “atypical” bacteria include organisms that have special shapes, sizes, or staining properties. each group has its own unique features. mycoplasma M. tuberculosis Chlamydia 21  “Atypical” Bacteria Acid-Fast Bacteria Acid-Fast bacteria is almost synonymous with the notorious genus Mycobacterium, M. leprae ▶ tubercle bacillus, M. tuberculosis, ▶ leprosy bacillus, M. leprae. The name “Mycobacterium” has root word for fungus (myco) ▶ the organisms can form branches that look somewhat like fungi. Their “acid fastness” means these microbes can resist decolorization by acids used in diagnostic staining ▶ Due to waxy envelope resistant to dyes unless the bacteria are heated or treated with detergents. grow slowly, resistant to chemical agents but not to heat. 22  “Not So Typical” Bacteria Acid-Fast Bacteria the Ziehl-Neelsen technique for staining acid- fast bacteria treat “smears” with a solution of a red dye (fuchsin) + detergents. After washing, the smear is treated with a solution of 3% HCl to remove the dye from all bacteria except acid-fast organisms. A blue dye that counterstains all other A. Blue: non-acid fast B. Pink: acid fast bacteria, white blood cells, etc is used. Tubercle or leprosy bacilli, (stain red), are clearly visible against the blue background. 23  “Not So Typical” Bacteria Acid-Fast Bacteria Some mycobacterial species free living within the environment our sources of opportunistic infections ▶ Target immunocompromised patients. ▶ complex known as Mycobacterium avium-intracellulare. o Includes several species o M. avium, M. intracellulare, M avium paratuberculosis, others. Skin lesions on the lower limb Acid-fast bacillus Lower limb after abx before treatment stain of biopsy tissue treatment. A young boy with disseminated Mycobacterium avium complex infection 24  “Not So Typical” Bacteria Acid-Fast Bacteria Streptomyces Fungi Actinomycetes ▶ have fungal morphology o form branches and long filaments with Plate complex structures ▶ relatives of the mycobacteria ▶ Gram-positive, weakly acid-fast. two pathogenic genera that cause forms of pneumonia & soft tissue infections ▶ Nocardia (aerobic) ▶ Actinomyces (strict anaerobes) SEM Genus Streptomyces (nonpathogenic) makes important antibiotics ▶ (streptomycin, tetracycline, etc.). 25  “Not So Typical” Bacteria Chlamydiae Among smallest forms of cellular life Chlamydia pneumoniae strictly intracellular bacteria ▶ cannot be grown in artificial media. Morphology differs between intracellular and intercellular states. ▶ Elementary bodies (metabolically inert but infectious) ▶ Reticulate bodies (replicative) Chlamydia trachomatis ▶ most common cause of STD (chlamydial urethritis) and other more unusual infections. Chlamydia pneumoniae ▶ an agent of pneumonia in young adults 26  “Not So Typical” Bacteria Chlamydiae Among smallest forms of cellular life strictly intracellular bacteria ▶ cannot be grown in artificial media. Morphology differs between intracellular and intercellular states. ▶ Elementary bodies (metabolically inert but infectious) ▶ Reticulate bodies (replicative) Chlamydia trachomatis ▶ most common cause of STD (chlamydial urethritis) and other more unusual infections. Chlamydia pneumoniae ▶ an agent of pneumonia in young adults 27  “Not So Typical” Bacteria Rickettsiae the “rickettsiae” (“tribe” in between Rickettsia typhi Ehrlichia family and genus) are small, rod- shaped intracellular bacteria ▶ obligate parasites. ▶ complex life cycles ▶ cause of epidemic typhus and Rocky Mountain spotted fever. Includes related genus Ehrlichia ▶ bacteria that infect white blood cells https://www.hgsc.bcm.edu/rickettsia-typhi in humans and animals. Each species is transmitted via arthropod bites (lice, fleas, ticks, etc.), 28  “Not So Typical” Bacteria Mycoplasmas Mycoplasma pneumoniae Mycoplasmas lack a rigid cell wall. “plastic” in structure, grow slowly on laboratory media, have special nutritional requirements. ▶ need for sterols (unique for Mycoplasmas) Mycoplasmas lack murein (peptidoglycan) ▶ resistant to penicillin and other cell wall antibiotics. Mycoplasmas pathogenic to humans ▶ Mycoplasma pneumoniae (form of pneumonia). ▶ Ureaplasma urealyticum (implicated in various diseases. 29  “Not So Typical” Bacteria Mycoplasmas Mycoplasma pneumoniae Basis for survival without cell wall in Mycoplasma cell membrane is triple layered Must pump sodium ions out of cell to maintain equal pressure across membrane Contain sterols in membrane to give added strength 30 Clicker Question 3 Scientists have determined that Mycoplasma spp., bacteria that lack a cell wall, are most closely related to Firmicutes, a phyla defined by having a “thick skin” made up of many peptidoglycan layers. What lead scientists to conclude these species are closely related? a. Both Firmicutes and Mycoplasma spp. are coccoid in shape. b. Mycoplasma spp. utilize the same type of metabolism as Firmicutes. c. Sequencing of the 16s rRNA d. Firmicutes and Mycoplasma spp. are obligate parasites. 31  Phylum Spirochaetes: Twisted-Cell Pathogens and Symbionts ▪ Spirochetes are spiral-shaped bacteria. Technically Gram-negative (has outer membrane) Flagellum located in periplasmic space Treponema pallidum subspecies pallidum (Syphilis) Treponema pallidum subspecies pertenue (Yaws, a chronic skin infection characterized by noncancerous lumps (papillomas) and ulcers. 32