bacteriology basics Flashcards
facultative anaerobe
can grow in presence of O2 and it’s absence
Virulence
the degree of pathogenicity as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host
Antigenic Switching
The altering of a microorganism’s surface antigens through genetic rearrangement, to elude detection by the host’s immune system
Virulence factors
- capsule
- protein A
- enzymes (catalase, coagulase)
- hemolysins
- toxins
spore forming bacteria
gram + rods ONLY!
-cell undergoes structural and metabolic changes to increase change of survival by forming then releasing endospores (parent cell lyses)
spore (endospore)
contains copy of DNA, reduced metabolic activity, impermeable envelope (does not divide)
2 types of endospore forming bacteria
- bacillis antracis (anthrax)
- clodstridium tetani (tetanus)
Clinical signs of anaerobic infection
Abscess, necrosis of tissue, inflammation, cellulitis, fasciitis, colitis, diarrhea,
Common aerobic infections
All Clostridiums
How to diagnose anaerobic infection
Anaerobic culture on blood culture, clinical presentation, Stool sample
clinical usefulness of bacteria subtyping
- Critical for understanding and tracking outbreaks.
- Allows for quicker treatment
- Example of subtyping: E. coli 0157 is a subtype E. coli
Normal Flora
- bacteria typically found at various anatomical sites in the body, generally do not cause infection, varies by site, age, sex, diet, nutrition, site, weaning, eruption of teeth, onset/cessation of ovarian functions, etc.
- Synthesize vitamines, outcompete pathogens, aid in immunity
normal flora in skin
- staph. epidermidis
- staph. aureus
- strep. pneumoniae
- strep. pyogenes
- corynebacteria
- mycobacteria
normal flora in mouth/UR tract
-mouth: Streptococci, lactobacilli, staphylococci, corynebacteria, with great number of
anaerobic bacteria
-upper respiratory tract: sinuses sterile, nares heavily colonized with coagulase-negative
staphylococci & corynebacteria (carrier site of staph. aureus),
normal flora in GI tract and rectum
- stomach: lactobacilli, helicobacter
- small intestine: enterococci, lactobacilli
-large intestine: enterobacteria, enterococcus faecalis, bacteroides, bifidobacterium,
eubacterium, peptococcus, peptostreptococcus, ruminococcus, clostridia, lactobacilli
normal flora in genitelia
- anterior urethra: coagulase-negative staphylococci, enterococcus, viridans
- GI bacteria & corynebacteria
-vagina: corynebacteria, staphylococci, streptococci, E. coli, and lactobacilli (lactobacilli
produce lactic acid, low pH inhibits infection by pathogenic bacteria & yeast)
normal flora in eye
-conj: staph epidermidis, staph A, Aerobic cornybacteria, Strep penumoniae, tears have lysozymes that keep populations in check
normal flora in urinary bladder
-sterile normally (but can be contaminated -> staph, enterococcus, viridians strep, GI bacteria and corynebacteria)
endotoxins
- lipopolysaccharides toxin produced by Gram Negative bacteria
- these toxins are generally cell bound and released only when the cell lyses.
- weakly toxic
- cause “septic shock”
- common bacteria: E. coli, Shigella, Salmonella, Neisserias, Yersinia Pestis
exotoxins
- (protein) Toxins that are released extracellularly as the organism grows
- may travel from a focus of infection to distant part of the body and cause damage
- from gram + or -
- highly toxic
virulence
- similar to pathogenicity (but quantifiable)
- these factors are characteristic of a bacterium that enhance its pathogenicity (properties that enable a microorg to establish self and replicate within host cell)
- how many organisms are required to cause disease in 50% of those exposed to pathogen
pathogenicity
bacterium’s ability to establish itself and replicate on or within a specific host, causing disease
infectious dose
Number of microorganisms required to cause infection in the hosts
lethal dose
Number of microorganisms required to kill the host
transmissibility
Droplets/airborne, direct physical contact, indirect physical contact, fecal-oral (common in peds)
adherence to host cells
- Ligands on the bacteria bind with receptors on the host cell, there are two types of adherence:
- Non-specific adherence: attractive forces between cells allow interaction (hydrophilic/hydrophobic, electrostatic)
- Specific adherence: interaction between complementary surface molecules
invasion of host cells and tissues
-invasins (proteins released by bact cells) can damage host cells and/or assist in growth and transmission of the bacteria; similar to exotoxins but generally don’t spread as far or produce cytotoxic effects
ability to evade the host immune system
Bacteria can evade the host immune system by coating/covering itself with host proteins such as fibrin and Ig, mimicking host cells–thus not triggering the immune response.
toxigenicity (endo/exotoxins)
Endotoxins: endotoxins are part of the outer membrane of the cell wall of Gram-negative bacteria; are released when the cell disintegrates. Also known as lipopolysaccharide (LPS).
-Exotoxins: toxin released by a living bacterial cell into the environment/area. Can impact/effect areas beyond where bacterial growth is located/where toxin was released.
