Pathogenic Bacteria & Diagnostic M ?· Vibrio cholerae • Three major groups: • V. cholerae O1 •…

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  • Microbiology Review

    Clinical and Diagnostic Sciences Tera Webb, MS, MLS(ASCP)CM

  • Antibiotic Targets and Mechanism of Action

    TARGET

    Cell Wall

    DNA and RNA

    Synthesis

    Metabolic Pathways

    Protein Synthesis

    Cell Membrane

  • Staphylococcus

    Most common pathogen

    Media

    Microscopic

    Staphylococcus

    aureus

    Staphylococcus

    epidermidis

    Staphylococcus

    saprophyticus

    Staphylococcus

    lugdunersis

    3

  • Staphylococcus aureus

    Gram Stain GPC in clusters

    Colony Morphology Round, smooth, creamy, yellow to white colonies with beta- hemolysis

    Biochemical tests Catalase positive Coagulase positive

    Pathology Wound & skin infections, toxic shock syndrome, food poisoning, pneumonia,

    osteomyelitis, bacteremia, etc. Virulence Factors

    Enterotoxins Cytolytic toxins Extracellular Enzymes Protein A

  • Staphylococcus epidermidis

    Gram Stain

    GPC in clusters

    Colony Morphology

    Round, smooth, creamy, yellow to white colonies with no hemolysis

    Biochemical Tests

    Catalase positive

    Coagulase negative

    Pathology

    Normal skin flora, nosocomial infections, prosthetic valve endocarditis, catheters, septicemia

  • Other Coag-Negative Staphylococci

    Staphylococcus saprophyticus

    Addl Biochemical: Novobiocin resistant

    Pathology: UTIs in young, sexually active females

    Staphylococcus lugdunensis

    Addl Biochemical: PYR positive

    Pathology: endocarditis

  • Staphylococcus - Antimicrobial Susceptibility

    Abnormal susceptibility patterns

    Beta-lactam resistance

    MRSA Screening

    Treatment with vancomycin

    VISA and VRSA Limitations to disk diffusion & automated methods

    Macrolide resistance Resistance to clindamycin may not be obvious

    D test - Use erythromycin and clindamycin disks

    Inducible resistance is growth between disks but not on side of clindamycin disk

    7

  • Hemolysis

    Streptococci and Enterococci are speciated based on hemolysin production and biochemical properties.

    -Hemolysis

    RBCs are partially lysed, resulting in a greening of the area around the colony

    -Hemolysis

    RBCs are completely lysed, resulting in a clear area around the colony

    -Hemolysis (nonhemolytic)

    RBCs are not lysed, so there is no change in agar color

  • Streptococcus

    Streptococcus pyogenes

    Streptococcus agalactiae

    Streptococcus pneumoniae

    Streptococcus bovis

    Viridians Streptococcus

    Lancefield groupings

    Browns classification

    Media

    Microscopic

    9

  • Streptococcus pyogenes

    Gram Stain GPC in chains

    Colony Morphology Small, white, transparent, smooth colony with

    well-defined zone beta-hemolysis

    Biochemical Tests Catalase negative Strep Grouping A

    Pathology Pharyngitis, scarlet fever, skin infections, toxic

    shock syndrome, post-streptococcal sequelae Virulence Factors

  • Streptococcus agalactiae Gram Stain

    GPC in chains

    Colony Morphology Small, greyish-white, transparent, smooth colony with small zone beta- hemolysis

    Biochemical Tests Catalase negative Strep Grouping B Hippurate positive CAMP positive

    Pathology Neonatal sepsis Neonatal meningitis

  • Streptococcus pneumoniae

    Gram Stain GPC in pairs (lancet- shaped)

    Colony Morphology Small, round, glistening, mucoid, dome -shaped colony with alpha - hemolysis

    Biochemical Tests Catalase negative Optochin (P) Sensitive Bile soluble

    Pathology Pneumonia, sinusitis, otitis media, bacteremia, meningitis

  • Viridians Streptococcus

    Gram Stain

    GPC in chains

    Colony Morphology

    Small, round, colony with alpha -hemolysis

    Biochemical Tests

    Catalase negative

    Optochin (P) R

    Pathology

    Normal flora, opportunistic, subacute bacterial endocarditis

  • Streptococcus bovis

    Gram Stain GPC in chains

    Colony Morphology Small, greyish, smooth colony with gamma-hemolysis

    Biochemical Tests Catalase negative PYR negative Bile Esculin positive NaCl negative

    Pathology Opportunistic

  • Enterococcus spp.

    Gram Stain GPC in chains

    Colony Morphology Small, greyish, smooth colony with gamma-hemolysis

    Biochemical Tests Catalase negative PYR positive Bile Esculin positive NaCl positive

    Pathology UTIs, Wounds, endocarditis, etc

  • Streptococcus -Antibiotic Susceptibility

    E. faecalis

    Usually susceptible to ampicillin and penicillin.

    Can acquire resistance to vancomycin.

    Occasionally produce beta- lactamase.

    E. faecium

    Often resistant to ampicillin and penicillin.

    Can acquire resistance to vancomycin.

    E. gallinarum and E. casseliflavus

    Have intrinsic low level vancomycin resistance

    16

  • Corynebacterium spp. aka Diphtheroids

    Gram Stain Pleomorphic Gram positive rods Often palisading Can be club-shaped

    Colony Morphology White, non-hemolytic, opaque colonies

    Biochemical Tests Catalase positive Nitrate variable Glucose variable Maltose variable Sucrose variable Urease variable

    Pathology Considered normal skin flora or contaminant

  • Corynebacterium diphtheriae

    Gram Stain Pleomorphic Gram positive rods Often palisading Can be club-shaped

    Colony Morphology White, non-hemolytic, opaque colonies

    Biochemical Tests Catalase positive Nitrate positive Glucose positive Maltose positive Sucrose negative Urease variable

    Pathology Produces diptheria toxin

  • Listeria monocytogenes

    Gram Stain Small Gram positive rods (can be coccobacilli)

    Colony Morphology Grayish white colony, small zone beta-hemolysis

    Biochemical tests Catalase positive Esculin hydrolysis positive Hippurate hydrolysis positive Motility Wet prep = tumbling motility 25C semisolid media = inverted umbrella

    Pathology Pregnant women: premature labor, spontaneous abortion Neonates: sepsis, meningitis Immunocompromised

  • Bacillus species

    Gram Stain Large gram positive rods Can see spores (if organism is stressed)

    Colony Morphology Ground glass appearance, Large colonies,

    rough edges, beta- hemolytic

    Biochemical tests Catalase positive Motile

    Pathology Considered a contaminant, endophthalmitis,

    food poisoning (B. cereus)

  • Bacillus anthracis

    Gram Stain Large gram positive rods Can see spores (if organism is stressed)

    Colony Morphology Ground glass appearance, Large colonies, rough edges, NON- hemolytic

    Biochemical tests Catalase positive Non- motile

    Pathology Causes anthrax

  • Lactobacillus sp.

    Gram Stain Gram positive rods in chains

    Colony Morphology Alpha hemolytic colonies

    Biochemical tests Catalase negative

    Pathology Normal female urogenital flora

  • Gardnerella vaginalis

    Gram Stain Gram negative rod Direct smear: Clue cells

    Colony Morphology Tiny transparent colonies

    Biochemical tests Catalase negative

    Pathology Bacterial vaginitis

  • Differentiation of Major GNR Genera

    Utilization of Glucose

    Ferment F, oxidize O or inactive

    Oxidase

    Positive or negative

    Ability to grow on MacConkey agar

    Some GNRs that grow on BAP are unable to grow on MacConkey agar

    Microbiology

  • Family: Enterobacteriaceae General Characteristics

    All ferment glucose All reduce nitrate to nitrites All grow on MAC All are oxidase negative

    Except Plesiomonas

    Majority motile Gram-negative coccobacilli or rods

    Not very useful in identification other than ruling out other organisms

    Facultatively anaerobic Culture morphology

    Large moist, gray colonies Some mucoid

  • Lactose-Fermenters Escherichia coli

    Colony Morphology Most beta-hemolytic

    Biochemical tests Oxidase negative Indole positive Motile

    Pathology Normal colon flora Cause UTIs, septicemia, neonatal septicemia and meningitis and several GI tract diseases

    Travellers diarrhea (ETEC) Dysentary (EIEC) Diarrhea and Vomiting (EPEC) Hemolytic colitis (EHEC)

  • Lactose-Fermenters Klebsiella

    Biochemical tests Oxidase negative Indole

    K. pneumoniae = negative K. oxytoca = positive

    Urea positive Citrate positive Non-motile

    Polysaccharide capsule Pathology

    UTIs, pneumonia

  • Lactose-Fermenters Enterobacter

    Biochemical tests

    Oxidase negative

    Indole negative

    Urea positive

    Citrate positive

    Motile

  • Slow-Lactose Fermenters Citrobacter

    Biochemical tests Oxidase negative Indole negative H2S positive

    Motile Pathology

    Opportunistic

  • Slow-Lactose Fermenters Serratia

    Colony Morphology Colonies have a salmon red pigment

    Biochemical tests Oxidase negative Indole negative

    Motile Pathology

    Opportunistic

  • Proteeae Phenylalanine deaminase & Urea positive

    Proteus species Colony Morphology

    Swarming motility

    Biochemical tests Oxidase negative Indole

    Pr