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Chapter 11: Bacteria Bacterial Groups

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Chapter 11: Bacteria Bacterial Groups Bacterial Groups u Most widely accepted taxonomic classification for bacteria is Bergey’s Manual of Systematic Bacteriology. u 5000 bacterial species identified, 3100 classified. Chapter 11: Bacteria u Bacteria are divided into four divisions (phyla) according to the characteristics of their cell walls. u Each division is divided into sections according to: u Gram stain reaction u Cell shape u Cell arrangements u Oxygen requirements u Motility u Nutritional and metabolic properties u Each section contains several genera. Four Divisions of Bacteria Classification of Bacteria Procaryotes Gram-Negative Division II Wall-Less Archaea Bacteria Bacteria Bacteria Bacteria (Gracilicutes) (Firmicutes) (Tenericutes) (Mendosicutes) Thin Cell Walls Thick cell Walls Lack cell walls Unusual cell walls Division I. Gram-Negative Bacteria Gram Negative Bacteria Spirochetes 1. Spirochetes u Helical shape. Flexible. u Contain two or more axial filaments (endoflagella). u Move in corkscrew pattern. u Medically important members: F Treponema pallidum: Syphilis F Borrelia spp.: Lyme disease, relapsing fever F Leptospira: Leptospirosis 1 Syphilis is Caused by a Spirochete Lyme Disease is Caused by a Spirochete Primary syphilitic chancre and secondary rash. Source: Tropical Medicine and Parasitology, 1997 Lyme Disease early lesion at tick bite site. Source: Medical Microbiology, 1998 2. Aerobic, Motile, Helical/Vibroid Gram- Negative Bacteria Gram Negative Bacteria u Rigid helical shape or curved rods. Aerobic, Motile, Helical/Vibroid u Lack axial filaments (endoflagella); have polar Gram-Negative Bacteria flagella instead. u Most are harmless aquatic organisms. u Genus Azospirillum fixes nitrogen in soil. u Genus Bdellovibrio attacks other bacteria. u Important pathogens include: F Campylobacter jejuni: Most common bacterial food- borne intestinal disease in the United States (2 million cases/year). Associated with undercooked chicken. F Helicobacter pylori: Causes most gastric ulcers in humans. F Campylobacter fetus: Abortions in domestic animals. Helicobacter pylori causes Gastric Ulcers 4. Gram-Negative Aerobic Rods and Cocci Contains many medically significant groups. F Genus Pseudomonas: Rods with polar flagella. Many secrete pigments in media. • Pseudomonas aeruginosa: Urinary tract infections (UTIs), septicemia, abcesses, burns, pulmonary infections in cystic fibrosis patients, and meningitis. F Genus Legionella: Rods that live in natural waters. Frequently found in air conditioning systems, humidifiers, showers, spas, and fountains. • Legionella pneumophila: Legionnaires’ disease (pneumonia, 1976) and Pontiac fever. F Genus Neisseria: Diplococci. Frequently found on human mucous membranes. Only grow well around body temperature. • Neisseria gonorrhea: Gonorrhea. • Neisseria meningitidis: Meningitis. 2 Neisseria gonorrhea Causes Salpingitis Neisseria gonorrhea Causes Neonatal Blindness Ophtalmia neonatorum caused by Neisseria gonorrheae Source: Microbiology Perspectives, 1999 5. Facultative Anaerobic Gram-Negative 4. Gram-Negative Aerobic Rods and Cocci Rods (Continued) Many cause diseases of gastrointestinal tract. F Genus Moraxella: Aerobic egg-shaped cocco-bacilli. • Moraxella lacunata: Conjunctivitis. Contains three medically significant families. F Genus Brucella: Small nonmotile coccobacilli. I. Family Enterobacteriaceae (Enterics) All species are obligate parasites of mammals. l Inhabit intestinal tracts of animals. Cause brucellosis. Can survive phagocytosis. l Motile bacteria with peritrichous flagella or nonmotile. F Genus Bordetella: Nonmotile rods. Virulent forms l Many have fimbriae for attachment to mucous membranes have capsules. and sex pili for exchange of DNA (antibiotic resistance • Bordetella pertussis: Whooping cough (P in DPT vaccine). genes) F Genus Francisella: Small pleomorphic bacteria. l Most ferment glucose and other sugars. • Francisella tularensis: Tularemia F Genus Escherichia: E. coli is common inhabitant of F Genera Rhizobiumand Bradyrhizobium: Form human intestinal tract. Most strains are not pathogenic, nodules on legume roots and fix nitrogen in soil. but others can cause UTIs (urinary tract infections), traveler’s diarrhea, and food-borne disease. I. Family Enterobacteriaceae (Continued) I. Family Enterobacteriaceae (Continued) F Genus Salmonella: Almost all members are potential F Genus Proteus: Actively motile. Cause UTIs, wound pathogens. Common inhabitants of animal GI tract. Can infections, and infant diarrhea (nosocomial). contaminate food (eggs, meat). F Genus Yersinia: • Salmonella typhi: Typhoid fever, severe illness. • Yersinia pestis: Causes bubonic plague (black death). • S. enteritidis: Causes salmonellosis, the second most common Transmitted by fleas, respiratory droplet, and contact with bacterial food-borne disease. animals. Over 1.3 million cases/year in the U.S. F Genus Erwinia: Important plant pathogens. F Genus Shigella: Only found in humans. Second most F Genus Enterobacter: Cause UTIs and nosocomial common cause of traveler’s diarrhea. infections. F Genus Klebsiella: Cause respiratory and UTIs. • Klebsiella pneumoniae: Antibiotic resistant strains cause pneumonia and nosocomial infections. F Genus Serratia: Opportunistic respiratory and urinary tract infections. • Serratia marcescens: Produces a red pigment. Important cause of nosocomialinfections. 3 5. Facultative Anaerobic Gram-Negative Cholera is Caused by Vibrio cholerae Rods II. Family Vibrionaceae l Found in aquatic habitats. l Straight or slightly curved rods F Genus Vibrio: Slightly curved rods. • Vibrio cholerae: Cholera, profuse & watery diarrhea. • Vibrio parahaemolyticus: Gastroenteritis. Shellfish. Rice-water stool of cholera. Source: Tropical Medicine andParasitology, 1995 5. Facultative Anaerobic Gram-Negative 6. Anaerobic Gram-Negative Rods Rods May be straight, helical, or curved. III. Family Pasterellaceae u Genus Bacteroides: Nonmotile. Live in human intestinal l Found in aquatic habitats. tract (1 billion/gram of feces) and gum crevices. Cause peritonitis, abscesses, and deep tissue infections. l Straight or slightly curved rods u Genus Fusobacterium: Long slender rods with pointed F Genus Pasteurella: Pathogens of domestic animals. tips. Found in gingival crevices, cause dental abscesses. F Genus Hemophilus: Important pathogens that inhabit mucous membranes of upper respiratory tract, mouth, vagina, and intestinal tract. Require blood in culture. 7. Sulfur-Reducing Bacteria • Hemophilus influenzae: Causes meningitis, ear infections, bronchitis, arthritis, and pneumonia in children. Obligate anaerobes that release H2S into the • H. ducreyi: Cause of sexually transmitted chancroid. atmosphere. F Genus Gardnerella: Not assigned to any family. Found in soil and intestinal tract of animals. • G. vaginalis causes common form of vaginitis. Ecologically important. 8. Anaerobic Gram-Negative Cocci Chlamydias: Cocci shaped bacteria. Transmitted to Nonmotile cocci typically found in pairs. humans by interpersonal contact or by airborne respiratory routes. u Genus Veillonella: Cause dental plaque. Unique life cycle: Form a reticulate and elementary bodies in infected cells. 9. Rickettsias and Chlamydias Three species: Gram negative bacteria. Obligate intracellular parasites. u Chlamydia trachomatis: Causes blindness in humans and nongonococcal urethritis (most common STD in U.S.). Rickettsias: Rod shaped bacteria or coccobacilli, u C. psittaci: Parrot fever. highly pleomorphic. Transmitted to humans by u C. pneumoniae: Mild pneumonia. insects and ticks (except for Coxiella burnetti which causes Q fever). u Genus Ehrlichiae: Live in white blood cells. u Genus Rickettsia: Cause spotted group fevers (Rocky mountain spotted fever, endemic typhus). 4 Division II. Gram-Positive Bacteria Diseases Caused by Staphylococcus 17. Gram-Positive Cocci aureus l Non-spore forming cocci. l Aerobic to strictly anaerobic. l Pyogenic (pus-forming) u Genus Staphylococcus: Tend to form grape-like clusters. Grow well under high osmotic pressure and low moisture. Very common infections, because almost always found on skin and in nasal mucous membranes. F Staphylococcus aureus: (aureus = golden) Yellow pigmented colonies. Produce several toxins. Cause pimples, sties, skin abscesses, toxic shock syndrome, food poisoning, and nosocomial infections. Antibiotic resistance is big problem. Scalded Sty Toxic Shock Vancomycin is last line of defense against antibiotic resistant Skin Syndrome Syndrome strains. 17. Gram-Positive Cocci Scarlet Fever is Caused by a Strain of u Genus Streptococcus: Most are pathogens. Tend to Streptococcus pyogenes appear in chains or pairs. Do not use oxygen, but most are aerotolerant. Classified based on their effect on red blood cells (hemolysis). Cause a wide range of diseases: Strep throat, respiratory infections, abscesses, puerperal fever, and opportunistic infections. A flesh eating Streptococcus strain emerged in 1994 and 1998. After initial infection, bacteria live on dead flesh, produce toxins, and are not treatable by antibiotics. F Streptococcus pneumoniae: Bacterial pneumonia, ear infections, meningitis, and sinus infections. F Streptococcus pyogenes: Strep throat, scarlet fever, rheumatic fever, impetigo, skin infections, erysipelas, puerperal fever, glomerulonephritis. Flesh-Eating Streptococcus pyogenes Erysipelas is Caused by Strep. pyogenes Necrotizing fasciitis with blood filled vesicles. Source: Perspectives in Microbiology, 1995 Erysipelas on face due to S. pyogenes infection Source: Color Guide to
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