Bacterial Structures Flashcards
Peptidoglycan function and chemical composition
- provides rigid support, protects against osmotic pressure
- made of sugar backbone with peptide side chains cross-linked by transpeptidase
Cell wall function and chemical composition
- major surface antigen
- peptidoglycan for support
- Lipoteichoic acid induces TNF and IL-1
Outer membrane function and chemical composition
present in gram negatives
- site of endotoxin (lipopolysaccharide [LPS])
- major surface antigen
- Lipid A induces TNF adn IL-1
- O polysaccharide is the antigen
Plasma membrane function and chemical composition
- site of oxidative and transport enzymes
- made of phospholipid bilayer
Ribosome function and chemical composition
- Protein synthesis
- Made of 50S and 30S subunits
Periplasm function and chemical composition
- space between cytoplasmic membrane and outer membrane in gram negative bacteria
- Contains many hydrolytic enzymes, including beta-lactamases
Pilus/fimbria function and chemical composition
- mediate adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation
- made of glycoprotein
flagellum function and chemical composition
- motility
- made of protein
Spore function and chemical composition
- resistant to dehydration, heat, and chemicals
- made of keratin-like coat; dipicolinic acid; peptidoglycan
Plasmid function and chemical composition
- contains variety of genes for antibiotic resistance, enzymes, and toxins
- comprised of DNA
Capsule function and chemical composition
- protects against phagocytosis
- comprised of organized, discrete polysaccharide layer (except Bacillus anthracis, which contains D-glutamate)
Glycocalyx function and chemical composition
- mediates adherence to surface, esp foreign surfaces (e.g. indwelling catheters)
- comprised of loose network of polysaccharides
characteristics unique to gram positive bacterial structure
lipoteichoic acid
features common to both gram positive and gram negative bacterial
Flagellum Pilus Capsule cell wall peptidoglycan cytoplasmic membrane
features unique to gram negative bacterial structure
porin endotoxin/LPS (outer membrane) Periplasmic space (Beta lactamase location)
Bugs that don’t gram stain well
- Treponema- too thin to be visualized
- Mycobacteria (high lipid content; mycolic acids in cell wall detected by carbolfuschin in acid-fast stain)
- Mycoplasma (no cell wall)
- Legionella pneumophilia (primarily intracellular)
- Rickettsia (intracellular parasite)
- Chlamydia (intracellular parsite; lacks classic peptidoglycan because of low muramic acid)
“These Microbes May Lack Real Color”
How to visualize Tremponemes
Not Gram stain – too thin to be visualized
- Dark-field microscopy and fluorescent antibody staining
How to visualize Legionella
NOT Gram stain since primarily intracellular – Silver stain
For what bugs is Giemsa stain used
Chlamydia, Borrelia, Rickettsia, Trypanosomes, Plasmodium
“Certain Bugs Really TRY my Patience”
for what bugs is PAS stain used
- Periodic acid-Schiff
- Stains glycogen, mucopolysaccharides; used to diagnose Whipple disease (Tropheryma whipplei)
“PASs the sugar”
For what bugs is Ziehl-Neelsen stain used
- Carbol fuscin
- Acid fast bacteria (Nocardia, Mycobacteria), protozoa (Cryptosporidium oocysts)
alternative to Ziehl Neelsen stain
auramine-rhodamine stain for screening–inexpensive, more sensitive but less specific
for what bugs is India ink used
detect Cryptococcus neoformans (mucicarmine can also be used to stain thick polysaccharide capsule red)
for what bugs is Silver stain used
Fungi (e.g. Pneumocystis), Legionella, Helicobacter pylori
Obligate Intracellular bugs
Rickettsia, CHlamydia, COxiella
- rely on host ATP
“Stay inside (cells) when it is Really CHilly and COld”
Facultative Intracellular bugs
Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis
“Some Nasty Bugs May Live FacultativeLY”
Encapsulated Bacteria examples
Streptococcus pneumoniae, Haemophilus influenzae type B, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, Gropu B strep
“SHiNE SKis”
- capsules serve as antiphagocytic virulence factor
- Capsule + protein conjugate serves as antigen in vaccines
How does body deal with encapsulated bacteria
opsonized by spleen. Asplenics have decreased opsonizing ability and thus increased risk for severe infections
- give S. pneumo, H flu, N meningiditid vaccines
Encapsulated bacteria vaccines
some vaccines with polysaccharide capsule antigens are -conjugated to a carrier protein, enhancing immunogenicity by promoting T cell activation and subsequent class switching
- Polysaccharide antigen alone can’t be presented to T cells
Conjugate vaccine examples
Examples
- Pneumococcal vaccine: PCV (pneumococcal conjugate vaccine, ie. Prevnar); PPSV (pneumococcal polysaccharide vaccine with no conjugated protein– Pneumovax)
- H influenzae type B (conjugate vaccine)
- Meningococcal vaccine (conjugate)
Urease positive organisms
Cryptococcus H. pylori Proteus Ureaplasma Nocardia Klebsiella S. epidermidis S. saprophyticus
“CHuck Norriss hates PUNKSS”
Catalase positive organisms
Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E. coli, Staphylococci, Serratia
“Cats Need PLACESS to hide”
Catalase function
- degrades H2O2 into H2O and bubbles of O2 before it can be converted to microbicidal products by enzyme myeloperoxidase
- Ppl with chronic granulomatous disease (NADPH oxidase deficient) have recurrent infections with catalase + organisms
Pigment producing organisms
- Actinomyces israelii = yellow “sulfur” granules composed of filaments of bacteria
- S. aureus = yellow/Gold (AU- Gold)
- Pseudomonas aeruginosa= blue-green pigment
- Serratia marcescens = red pigment (think red maraschino cherries)
