01 Basic Bacteriology Flashcards
What is Peptidoglycan?
Single covalently linked macromolecule (peptides, sugars). Provides rigid support for the cell. Maintains shape of cell and allows cell to withstand media of low osmotic pressure, such as water
What is the cell wall like for Gram (+) bacteria?
Thick peptidoglycan layer
What is the cell wall like for Gram (-) bacteria?
Complex outer layer consists of lipopolysaccharide (endotoxin), lipoprotein, and phospholipid. Periplasmic space b/w outer membrane layer and the cytoplasmic membrane. Thin peptidoglycan layer
What is unique about Mycobacteria?
“acid-fast” - inability to be gram-stained due to high concentration of mycolic acids. Classified as Gram (+)
What is a bacterial Capsule?
Gelatinous layer covering the entire bacterium. Composed of polysaccharide, sugar components vary among bacteria species
What are the functions of bacterial Capsules?
Determines virulence: limits ability of phagocytes to engulf the bacteria. Adherence of bacteria to human tissues
What do bacterial Capsules allow us to do?
Lab identification (use of antiserum against the capsular polysaccharide). Capsular polysaccharides used as antigen in vaccines (capable of eliciting protective antibodies)
How can Flagella help E.coli, Proteus sp.?
Propell the bacteria up the urethra into the bladder –> UTIs
What is an example of Flagella being used for lab identification?
Salmonella sp. - identified by use of specific antibodies against flagellar proteins
What are Pili?
Hairlike filaments that extend from the cell surface. Found mainly on Gram (-)
What are the Functions of Pili?
Mediate the ATTACHMENT of bacteria to specific receptors on the human cell surface –> initiates infection. Forms attachment between donor and recipient bacteria during CONJUGATION and allow genetic exchange
What is Glycocalyx?
Polysaccharide coating that is secreted by many bacteria. Covers surfaces like a film allowing bacteria to ADHERE firmly to various structures (skin, heart valves, catheters). Mediates adherence Strep mutans to surface of teeth –> forms plaque, precursor of dental carries
Which gram stain correlates with positive/negative?
Positive (Blue). Negative (Red)
What are the steps in gram staining?
Crystal violet dye stains cells blue. Iodine solution forms complex with violet. Solvent (acetone or EtOH) extracts blue (easier from lipid-rich, thin walled Gram (-)). Red dye safranin stains decolorized Gram (-) red; Gram (+) remains blue
Why are Mycobacteria NOT seen on Gram-Stain?
Acid-fast. Too much lipids in cell wall
Why are Treponema pallidum NOT seen on Gram-Stain?
Too thin to see
WHy are Mycoplasma pneumoniae NOT seen on Gram-Stain?
No cell wall; very small. This causes “walking pneumonia”
Why are Legionella pneumophila NOT seen on Gram-Stain?
Poor uptake of red counterstain
Why are Chlamydiae, Rickettsiae NOT seen on Gram-Stain?
Intracellular; very small
What is the common morphology of Gram-Positive Cocci?
Clusters. Chains
What are some common Gram-Positive Cocci found in CLUSTERS?
Usually characteristic of Staphylococcus spp., such as S. aureus
What are some common Gram-Positive Cocci found in CHAINS?
Usually characteristic of Streptococcus spp., such as S. pneumoniae, Group B streptococci (GBS)
What are some common Gram-Positive Bacilli that are THICK?
Usually characteristic of Clostridium spp., (i.e. C. perfringens, C. tetani)
What are some common Gram-Positive Bacilli that are THIN?
Usually characteristic of Listeria spp.
What are some common Gram-Positive Bacilli that are BRANCHED?
Usually characteristic of Actinomycetes and Nocardia, such as A. israelii
What are common morphologies of Gram-Negative Cocci?
Diplococci (usually characteristic of Neiseria spp., Moraxella spp., and Acinetobacter spp.). Coccobacilli
What are the common morphologies of Gram-Negative Bacilli?
Thin rods. Coccobacilli. Curved
What are some common Gram-Negative Bacilli THIN RODS?
Usually characteristic of enterobacteriaceae, such as E.coli
What are some common Gram-Negative Bacilli COCCOBACILLI?
Usually characteristic of Haemophilus spp., such as H. influenza
What are some common Gram-Negative Bacilli CURVED?
Usually characteristic of Vibrio spp.
What are the two most common Spirochete bacteria?
Borrelia burgdorferi (lime disease). Syphilis
What are Obligate Aerobes?
Require oxygen to grow
What are Facultative Anaerobes?
Utilize oxygen to generate energy if present, but can also use fermentation pathway in the absence of O2
What are Obligate Anaerobes?
Cannot grow in the presence of O2; some can survive but cannot grow while others are killed rapidly
How is Virulence measured?
By the number of organisms required to cause disease
What are the “Virulence Factors”?
Pili, exotoxins or endotoxins, capsule. Infectious dose of bacteria depends primarily on virulence factors
What are the determinants of bacterial pathogenesis?
Transmission. Adherence to cell surfaces. Invasiveness. Toxin production
What are the major mechanisms in which bacteria cause disease?
Adherence to host cell surface. Invasion of tissue followed by inflammation. Toxin production: exotoxins and endotoxins
What are the characteristics for bacteria adhering to cell surfaces?
Specialized macromolecular structures or production of adhesion molecules (capsules, glycocalcyes). Essential for organisms that attach to mucous membranes. Mammalian cell surface compounds (protein, glycolipids, carbohydrates) can serve as receptors for bacterial adhesins. Activates host cell receptors by co-opting with hose cell signaling pathway (i.e. cytoskeleton rearrangement, receptor modification)
What is Collagenase, Hyaluronidase?
Degrade collagen and hyaluronic acid allowing bacteria to spread through subcutaneous tissue –> cellulitis
Which bacteria commonly uses Collagenase, Hyaluronidase?
Strep pyogenes
What is Coagulase?
Accelerates formation of a fibrin clot from fibrinogen which protect the bacteria from phagocytosis by walling off the infected area and by coating the organisms with a layer of fibrin
Which bacteria commonly uses Coagulase?
Staph aureus
What is IgA protease?
Degrades IgA allowing organisms to adhere to mucous membranes
Which bacteria commonly use IgA Protease?
N. gonorrhea, S. pneumoniae, H. influenza
What do bacteria use for invasiveness?
Antiphagocytic factors: Capsule (S. pneumoniae, N. meningitidis), Cell wall proteins of Gram (+) cocci
How do some bacteria induce their own uptake into host cells?
Initiated by ligand-receptor interactions that activate host signaling with the actin cytoskeleton providing the necessary force to internalize the particle into a membrane-bound vacuole. Allows bacterial entry into protected niche and enabling pathogens to pass thru cellular barriers such as the intestinal epithelium or the blood-brain barrier
What is Type III Secretion System (T3SS)?
Exclusively in Gram Negative pathogenic bacteria. Delivers proteins into the cytosol of eukaryotic cells to interfere with host cellular processes. Secretion of effector proteins requires host target cell-bacteria contact
For T3SS, what are the 3 separate but coordinately functional protein complexes?
Secretion apparatus. Translocation or targeting apparatus (PcrV, PopB, PopD, Pcrl). Secreted toxins (ExoS, ExoT, ExoU, ExoY)
What are Exotoxins?
Secreted polypeptides consisting of 2 domains: one for binding to the cell membrane and entry into cell, the other possessing toxic activity
What are some Exotoxins from Gram Positive bacteria?
Neurotoxins (tatanus, botulinum). C. difficile - Exotoxin A - watery diarrhea, Exotoxix B - damages to colonic mucosa. Toxic Shock Syndrome (S. aureus). Gram Positive exotoxins are highly potent
What are some Exotoxins from Gram Negative bacteria?
E. coli - heat labile enterotoxin –> watery, nonbloody diarrhea. E. coli - heat stable enterotoxin (not inactivated by boiling for 30 minutes) –> bloody diarrhea assocaited with eating undercooked hamburger
What are Endotoxins?
Integral parts of the cells walls of Gram Negative cocci and bacilli. Lipopolysaccharides that are low in toxicity. Cause some generalized effects of fever and shock (septic shock) mediated by release of cytokines such as IL-1 and TNF
What types of problems can be found in blood?
Sepsis, endocarditis, osteomyelitis, meningitis, pneumonia
What types of problems can be found in the throat?
Pharyngitis, thrush
What types of problems can be the cause of sputum?
Pneumonia, TB, lung abscess
What types of problems can be found in spinal fluid?
Meningitis; presence of capsular antigens
What types of problems can be found in stool cultures?
Enterocolitis - Shigella, Salmonella, Campylobacter; fecal leukocytes
What types of problems can be found in the urine?
Cystitis, pyelonephritis
What types of problems can be found in the genital tract?
Gonorrhea, syphilis
What types of problems can be found be wounds and abscesses?
Anaerobes, S. aureus, Strep pyogenes
