Microbiology Flashcards
Osteomyelitis
Inflammation of the bone or bone marrow usually due to infection
Caused most commonly by staphylococcus aureus or TB
Risk factors for osteomyelitis
Diabetes
Kidney failure
Smoking and/or IV drug use
Traumatic wounds
Joint replacement/fixation devices
TB specific osteomyelitis is also known as what?
Pott Disease
Osteomyelitis that Moves to the spine specifically.
Possible pathogens that cause osteomyelitis outside of TB or S. Aureus
Salmonella: Sickle cell patients
S. Epidermidis: prosthetics patients
P. Multocida: cat and dog bite patients
Gonorrhea: STI
Osteomyelitis treatment
Antibiotic beads that surround the bone and/or joint.
Staphylococcus aureus osteomyelitis specific risk factors
Prosthetic joints
Sickle cell
IV drug use
Trauma of the spine
Quick characteristics of S. Aureus
Gram positive cocci that tends to cluster
Aerobic pathogen
B-hemolytic: complete hemolysis
Coagulase and catalase positive
Has protein A
Protein A
Binds to host antibodies to prevent antibody-mediated clearance of bacteria
Why is Staph Aureus such a good pathogen?
Produces its own unique virulence factors all the time and controls up and down regulation of them.
Examples of S. Aureus structural virulence factors
Capsule: inhibits proliferation of mononuclear cells
Slime layer: facilitates adherence to foreign bodies
Peptidoglycan wall: increases osmotic stability, enables release of endogenous endotoxins and inhibits phagocytosis
Teichoic acid: binds to fibronectin
Protein A: inhibits antibody-mediated clearance by binding to antibodies.
Examples of S. Aureus enzymatic virulence factors
Coagulate: converts fibroids to fibrin and promotes clots
Hyalurnidase: hydrolysis hyaluronic acids promoting spread deep in connective tissue
Fibrinolysin: dissolves fibrin clots
Lipase: Hydrolysis lipids
Nuclease: hydrolysis DNA
Biofilms
Colonies of bacteria that enable bacteria to survive better and make it much harder to kill the bacteria.
Slime layers are present in order to form biofilms
Examples of S. Aureus toxin virulence factors
Cytotoxins
Exfoliating toxins: scalded skin syndrome
Enterotoxins: food poisoning
Toxic Shock Syndrome Toxin: TSS
Superantigens
MRSA commonly affected areas
Out in Community: 50%
Health care-acquired places outside of hospitals: 42%
Hospital acquired: 8%
Most common symptoms of MRSA infection =
- cellulitis and skin ulcers
- Pneumonia
- Septicemia
Endocarditis, myocarditis and pericarditis
Infections in the heart muscle most commonly caused by S. Aureus
- most common in the endocardium
- often cause valve replacement or worse
Infective myositis
Pretty rare infection of deep skeletal muscle around the spine
- almost always caused by S. Aureus
- usually asymptomatic until actually having it
Septic arthritis
Infection moves to joint caused by trauma to the joints
Common causative agents
- S. Aureus (most common overall)
- Strep A and B: (most common in children)
- haemophillus influenza: (not common)
- N. Gonorrhoeae: (often causative agent if multiple joints affected)
Borrelia burgdorferi: (often causative agent in conjunction with Lyme disease patients
- sporothrix schencii: (fungal infection via rose thorns. Increased likelihood with HIV positive patients)
Viral arthritis
Same as septic arthritis but viral instead of bacterial
Common causative agents:
- Hep B: (often caused in prodromal period)
- rubella: (common in young women and via live viral vaccination)
- mumps: ( rare and only in men)
- paravovirus: (follows adult infection)
Ross river (follows mosquito infections)
Prodromal period
Period before diagnosis
Myonecrosis gangrene
C. Perfringens causes deep muscle infections
Often caused by fecal contamination
Pathogenesis of myonecrosis Gangrene
C. Perfringens pathogen reaches anaerobic environment and begins anaerobic multiplication
- causes anaerobic cellulitis
- invades muscle and produces gas and necrosis of muscle cells
- may or may not get into blood. If enters blood often fatal via hemolysis and renal failure*
C. Perfringens characteristics
Game positive rod
Spore forming anaerobe
Toxins can hemolysis if in blood and food poisoning in GI
Treated via hyperbaric chambers (flood with oxygen and suffocates C. Perfringens
Types of toxins produced by C. Perfringens
Perfringolysin O: Forms pores in cells
Alpha toxin (AKA lecithinase or PPC): destroys cell membranes via phospholipase C activity - antitoxin not affective since alpha toxin destroys pathways for it to get there.
ALL toxins cause clumping of leukocytes in blood vessels and prevents immune system from getting to primary site of infection
