Test Answers on Determinative Bacteriology – Flashcards
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| Micrococcus |
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•Gram positive cocci •Tetrads, clusters •Aerobic •Nonmotile •Catalase+ •Oxidase+ •Genetic relatedness to Arthrobacter and Actinomyces. •Found in the environment and transient flora skin of humans and other animals. •M. luteus, M. lylae
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| Planococcus |
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•Gram positive cocci •Pairs, tetrads •Aerobic •“motile coccus”, all strains have 1 to 3 flagella •Catalase + •Oxidase + •Strains capable of growth in 15% NaCl •P. citreus, P. kocuri
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| Stomatococcus (Rothia) |
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•Encapsulated Gram positive coccus that is part of the normal human respiratory tract •Associated with endocarditis •S. mucilaginosus, non motile, weakly catalase +. Currently known as R. mucilaginosa.
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| Staphylococcus |
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•Gram positive cocci •Grape like clusters •Facultatively anaerobic •Nonmotile •Catalase + •Oxidase – •Salt tolerant to 10 % •Hemolytic with variation •Genetically related to Enterococci, Streptococci, Lactobacilli and Bacillus. •35 species/ 17 associated with mucous membranes humans, animals. •S. capitis, S. auricularis, and S. intermedius.
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| S. aureus |
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•Most important human pathogen. •Found in the external environment and anterior nares of 20-40% of adults. •Usually part of human normal flora, however it can be “opportunistic” •Opportunistic if: –Defects in immunological system, complement deficiencies, leukocyte chemotaxis. –Skin injuries, burns –Presence of foreign bodies, (sutures, IV lines) –Viral infection, influenza. –Other underlying diseases, malignancy, alcoholism, heart disease. –Antimicrobial agents in use
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| Differentiate Micrococcus from Staphylococcus |
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•Furazolidone Disk •Oxidase Disk •Bacitracin Disk •Lysostaphin •Acid from glucose under anaerobic conditions
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| Staphylococcal pathogenesis |
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•Genes for pathogenesis have 2 sources in S. aureus. •Lysogenic conversion: certain staphylcoccal virulence genes are encoded by prophages. staphylokinase, PVL, enterotoxin and exofoliatin. •Chromosomal encoded virulence genes: hemolysins, proteases, Protein A, clumping factor, capsule production, nucleases
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| Determinants of Pathogenicity Staphylococcus aureus |
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•Cellular Antigens –Capsules –Polysaccharide A –Protein A –Clumping Factor –Adhesions
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| Capsule |
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•Helps prevent ingestion by polymorphonuclear cells. •11 types of different polysaccharides, type 5 and 8 most common. Both of these capsules are antiphagocytic.
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| Polysaccharide A |
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•Linear ribitol teichoic acids. Function in adherence to mucosal surfaces. •Function for adherence of Gram + bacteria to mucosal surfaces. •Provide rigidity to the cell •Several functions to inactivate the immunological system of the host.
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| Protein A |
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•S. aureus cell walls have a unique protein that will bind the Fc region of host IgG molecule. This protein is on the cell wall of the bacterium. •This interference is with the host’s immune system, specifically by interfering with opsonization and ingestion of bacteria by PMN’s. •The presence of this Protein A forms the basis for the coagglutination test, in the lab. •42,000 dalton protein, and is immunogenic.
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| Clumping Factor |
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•Bound or surface material, is able to bind fibrinogen and fibrin. Thus allows S.aureus to attach to surfaces.
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| Adhesions |
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•Surface proteins that enable the bacterium to bind to proteins such as collagen. These are covalently incorporated into the structure of the peptidoglycan.
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Determinants of Pathogenicity
•Extracellular Proteins
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–Catalase –Coagulase “free”, not bound. –Hydrolyases –Staphylokinase (fibrinolysin) –β lactamase enzyme –Hemolysins –Pyrogenic Exotoxins –Other Exotoxins »Panton-Valentine Leukocidin »Epidermolytic toxin
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| Catalase |
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•The function of this enzyme in S. aureus is to inactivate hydrogen peroxide and free radicals formed by the myeloperoxidase system in phagocytic cells after ingestion of microbes.
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| “Free” Coagulase |
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•Cultural filtrates, act to coat the bacteria with fibrin, rendering them resistant to phagocytosis. Converts fibrinogen to fibrin, during abscess formation, walls of the abscess.
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| Hydrololases |
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•Lipases, help the spread of the organisms in cutaneous and subcutaneous tissues. •Phospholipase C, tissues impacted by this enzyme are more susceptible to damage from the components of Complement. •Hyaluronidase, hydrolyzes the intercellular matrix of mucopolysaccharides, thus allowing the organism to spread. •Thermonuclease, cleaves host DNA and RNA.
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| Staphylokinase |
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•Fibrinolysin, extracellular, produced by several strains of S. aureus, it dissolves fibrin clots and thus contributes to the spread of the organism from local sites.
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| β Lactamase Enzyme |
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•Inducible enzymes formed in the presence of certain β lactam antimicrobial agents. Genes for these enzymes usually reside on plasmids. Resistance genes may be transferred by transduction or transformation. Over 80% of all S. aureus produce one form of this enzyme.
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| Pyrogenic Exotoxins |
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•Now called “toxic shock syndrome toxin 1”, TSST-1, seen in 1981 in patients, 22,000 daltons, it is a superantigen broad effects, stimulates the proliferation of T cells. •Many effects in the body during the course of the illness. Direct effects on the myocardium, skeletal muscle, liver and kidney. Produces chills, fever, shock, hypotension and rash.
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| Enterotoxins |
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•Are heat stable molecules responsible for the clinical picture of food poisoning. •Enterotoxins A-E,H and I, responsible for the clinical features of Staph food poisoning. Most common form of food poisoning in the US. Mode of action is unknown, but increase intestinal peristalsis. •Usually via the ingestion of pre formed molecules, baked goods, potato salads, processed meats, •Vomiting and + or - diarrhea in 2 to 8 hours. Inflammatory changes are seen in the entire GI tract.
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| Hemolysins |
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•S. aureus, can produce several: –β hemolysin, a sphingomyelinase, active on a variety of cells. Has a MW of 35,000 daltons, requires Mg ++ for activity. Attacks the sphingomyelin content in cell membranes. –δ hemolysin, MW 3,000 daltons, acts as a surfactant and disrupts the cell membrane to cause channels, result in leakage of cellular components.
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| Other Exotoxins |
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•Leucocidin, Panton-Valentine, direct effect on human PMN cell membranes, causes cell swelling and lysis. •Exofoliations or epidermolytic toxins, 2 proteins, each has a MW of 24,000 daltons, ET-A heat stable, and ET-B not heat stable, one chromosomal encoding, other plasmid encoded. Proteolytic and dissolve the mucopolysaccharide matrix of the epidermis, “staphylococcal scalded skin syndrome”.
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| Identification Tests Staphylococcus |
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•Coagulase •Acid from mannitol •DNase •Novobiocin •Anaerobic growth •Hemolysis
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Diseases of the staphylococci
•S. aureus, abscesses (suppurative-pus forming), endocarditis, osteomylitis, food poisoning and toxic shock syndrome. Cogulase +. •S. epidermidis, endocarditis. Coagulase -. •S. saprophyticus, infrequent cause of UTI, coagulase - •Female genital tract, Toxic shock syndrome (TSS). •Primary disease of the respiratory tract, bronchopneumonia with multiple abscesses.
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•S. S. saprophyticussaprophyticus, , infrequent cause of UTIinfrequent cause of UTI, , coagulase-. •Female genital tract, Toxic shock syndrome (TSS).Female genital tract, Toxic shock syndrome (TSS). •Primary disease of the respiratory tract, bronchopneumonia with multiple abscesses.Primary disease of the respiratory tract, bronchopneumonia with multiple abscesses. •Primary disease of the GI tract, staphylococcal colitis, or necrotizing Primary disease of the GI tract, staphylococcal colitis, or necrotizing enterocolitisenterocolitis.. Food poisoning.Food poisoning. •Septicemia, Septicemia, osteomyelitisosteomyelitis, arthritis. , arthritis. •Primary diseases of the skin and subcutaneous tissue. Primary diseases of the skin and subcutaneous tissue.Primary diseases of the skin and subcutaneous tissue.
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| Treatment of S. aureus |
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•In the U.S. 80% or greater of S. aureus were resistant to penicillin G in 1987, via β lactamase production plasmid encoded. Therefore use vancomycin.
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| Epidemiology of MRSA and VISA |
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•MRSA Methicillin resistant Staphylococcus aureus, hospitals are pre screening patients for MRSA SA. Initially a nosocomial infection, today a community infection. Risk factors include IV drug use, outpatient antimicrobial care, previous hospitalization, other diseases. •VISA Vancomycin intermediate resistant, a glycopeptide agent, Staphylococcus aureus. First seen in 1996, report to the CDC, isolate patients to prevent spread to other patients.
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| Current Strategies MRSA |
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•New York: Pre screen certain patients for MRSA. Nose swab, 2 hr DNA test. •Illinois: first state bill requiring pre screening test for admission to the hospital. •Britain: MD’s using green-fly maggots to treat infected foot ulcers in diabetic patients. Patients were infected with MRSA.
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| Practical Examination for Staphylococcus aureus |
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•Finding the strain in the real world
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| S. epidermidis |
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•Coagulase – •Represents 50-80% of all coagulase – isolates recovered in the clinical lab. •Almost all infections are nosocomially acquired. •Causes endocarditis, wound infections, UTI’s. Forms a biofilm on the plastic medical devices.
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| Virulence Factors S. epidermidis |
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•PS/A, capsular polysaccharide adhesin. High MW, succinylated, β 1,6 linked polyglucosamine molecule. Can block plastic catheters in vitro. •PIA, polysaccharide intercellular adhesin, binds cells together. This is a linear polysaccharide composed of β 1,6 linked 2 deoxy 2 amino glucopyranosyl residues. It also functions as a hemagglutnin. •Another 140 kdal extracellular protein has been identified.
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| S. saprophyticus |
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•Coagulase – •Causes UTI in young healthy females. •Most common after E. coli. •Adheres to uroepithelial, and urethral cells more than other species of staph. •Patients experience, dysuria, pyuria and hematuria.
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| Virulence factors S. saprophyticus |
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•Urease production, contributes to bladder invasion. •Slime producer. •Adherence to uroepithelial cells. •Ssp, surface associated protein, adherence to uroepithelial cells. •Hemagglutnin on the surface of these bacteria, aids in binding to uroepithelial cells.
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| Family Micrococcaceae |
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•Clusters,tetrads •catalase + H2O2 _> H2O + O2 •Growth in presence of 5% NaCl •Most are strict aerobes –Four Genera –Micrococcus –Planococcus –Staphylococcus –Stomatococcus
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| Current Classification |
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•Based on 16s rRNA studies. •Planococci and staphylococci, belong to the Bacillus/Lactobacillus/Streptococcus phyletic line. The micrococci and stomatococci belong to the amycelial actinomycetes. •Staphylococci are in the phylum Firmicutes. •Planococci are a marine cocci that grow in 15% NaCl containing media. •Micrococcus consists of 2 species, M. luteus and M. lylae. Stomatococcus, part of the human respiratory tract normal flora, is now a member of the genus, Rothia. S. mucilaginosus is now R. mucilaginsa
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| Family Micrococcaceae |
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•Genus: Staphylococcus, Micrococcus, Planococcus, Stomatococcus •Mol%G+C 30-35 70-75 40-51 56-60 •Cytochrome c - + ND + •LysostaphinS + - - - •FurazolidoneS + - ND ND
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•Primary diseases of the skin and subcutaneous tissue. Primary diseases of the skin and subcutaneous tissue. (Staphylococcus)
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––Furuncle,Furuncle, painful, painful, induratedindurated, , erythematouserythematousabscess, central area of necrosis walled off from subcutaneous tissue. abscess, central area of necrosis walled off from subcutaneous tissue. ––CarbunclesCarbuncles, the above pathogenic process goes deeper into the fibrous tissue, multiple openings with pus discharge. Healing leads to scarring., the above pathogenic process goes deeper into the fibrous tissue, multiple openings with pus discharge. Healing leads to scarring. ––ImpetigoImpetigo, seen in newborns, usually on the face, eyes, lips, nose and sometimes limbs. More severe than a furuncle., seen in newborns, usually on the face, eyes, lips, nose and sometimes limbs. More severe than a furuncle. ––Scalded skin syndromeScalded skin syndrome, in children, like a furuncle, bacteria release , in children, like a furuncle, bacteria release exfoliatveexfoliatve toxin.toxin.
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