Gram Positive Bacterial Infection

What is characteristic of staphylococcus spp

Part of human flora; difficult to treat; can become abx resistant easily; cause disease by toxin production or penetration; food poisoning

What are extracellular toxins example

TSST, haemolysin etc

What is TSST

Superantigen

What are enterotoxin

heat stable toxin that cause food poisoning

Catalase function

HO → H2O + O2

What is catalase test used for

Diff staphylococci (POSITIVE) from streptococci (NEGATIVE)

What is staphylococci pathology

Adhere to damaged skin, cell wall proteins attach to tissue, protein A teichoic acid peptidoglycan etc interfere with opsonization

What are the clinical findings of staphylococcal infections

Local = pimple, hair follicle infection, abscess; food poisoning has short incubation period and NO FEVER; TSST has high fever, rash, vomiting and diarrhea

What are tests used to diag staph infections

Specimen, catalase test (positive), coagulase test (negative except for staph. aureus), novobiocin testing

What is characteristic of staph. aureus

Facultative anaerobe, grape like; beta-hemolytic; cause of pimples, sinusitis, food poisoning; opportunistic; drug resistant

Staph aureus uses what type of agar and what is the result

Mannitol salt agar which turns yellow

What is association of staph. aureus and TSST

Some staph strains can cause septic shock and release TSST into blood

What is staph. epidermidis

Commensal bacterium in skin and mucous membrane; non-hemolytic; nosocomial pathogen in biomaterials; form biofilms

Which staph form biofilm

staph. epidermidis

What agar is used for staph. epidermidis and what is the result

White blood agar; novobiocin sensitive

What are skin signs of staph. epidermidis

Impetigo (honey colored crust), cellulitis

What is staph. saprophyticus

Negative coagulase; novobiocin resistant; part of human flora; cause uncomplicated UTI; colonize bladder and ureter epithelium

What agar is used for staph. saprophyticus and what is the result

Bright white to creamy blood agar; novobiocin resistant

What is streptococcus spp

Chains or pairs, facultative anaerobes, catalase NEGATIVE; major normal flora in mouth

What is lancefield grouping

Test to classify streptococci spp based on polysaccharide and teichoic acid antigen in cell wall

Beta hemolysis

Alpha hemolysis

Gamma hemolysis

What is strep. pyogenes

Associated with local/systemic invasion; produce capsules of hyaluronic acid that delays phagocytosis; Group A streptococcus (GAS) that cause strep throat

Strep pyogenes is the causative agents of what

Necrotizing fasciitis, pharyngitis, impetigo, erysipelas, bacteremia/sepsis

What is a group A streptococcus

Strep. pyogenes

What is a group B streptococcus

Strep. agalactiae

What toxins are in strep. pyogenes

Streptokinase (fibrinolysin), deoxyribonuclease, hyaluronidase, pyrogenic exotoxin, hemolysin

What is process of streptococcal toxic shock

S. pyogenes grow in wound → GABHS enter bloodstream and produce superantigen → Fever, rash and shock

What causes scarlet fever

Pyrogenic exotoxin A-C associated with s. pyogenes pharyngitis, sore throat and swollen neck glands, sandpaper rash

What are pyogenes secreted factors

TSST-1 and SPEA

What is the difference between staph toxic shock and strep toxic shock

Staph: Fever > 38.9, rash, hypotension; strep: isolation of SPEA, hypotension

Strep. pyogenes can cause what disease

Strep throat; strep pyoderma (impetigo)

Post streptococcal diseases examples

Nephritis (glomerlonephritis), rheumatic fever

Mechanism of disease in strep. pyogenes

SPEA → STSS; Enzyme release → Local inflammation invasion of tissue → skin infection/pharyngitis/otitis media; bacteremia → meningitis/arthritis/osteomyelitis; antigen → immune complex formation → glomerulonephritis; antibody formation by B lymphocyte → rheumatic fever

What agar cultures streptococci pyogenes

Blood agar

What is strep. agalactiae

non-motile, no spores, facultative anaerobe, catalase negative, bacitracin resistant, beta hemolysis; Group B strep that cause neonatal sepsis and meningitis; colonize GI tract and vagina

What is strept. pneumoniae

gram positive, diplococci, facultative anaerobe, non-motile, no spores, alpha hemolytic, catalase negative; cause bacterial pneumonia, septicemia and meningitis

What is the pathogenesis of strep. pneumoniae

High temperature, aches and pains, headache; multiply in tissue; has capsule

What is non-invasive pneumococcal infections

Outside major organs in blood and less serious (bronchitis, otitis, sinusitis)

What is invasive pneumococcal infection

Inside major organs and more serious (bacteremia, septicemia, osteomyelitis, septic arthritis, pneumonia, meningitis)

Clinical findings of strep. pneumoniae

Fever, chills and sharp pleural pain; sputum is bloody/rusty; can spread to mastoid in meninges

Lab diag for strep. pneumoniae

Blood, CSF and sputum samples; stained smears, capsule swelling tests, culture (blood agar), immunity

What is treatment for strep. pneumoniae

Penicillin G

What is corynebacterium diphtheriae

In respiratory tract, wounds and skin of infected people; spread by droplet/concent and grow on mucous membranes where it starts to produce toxin; heat labile; forms pseudomembrane

Clinical findings of corynebacterium dipherieae

Incuation period of 2-5 days; sore throat + low grade fever; pseudomembrane in posterior pharynx (sometimes obstruct airway); toxin can cause neuropathy

Diagnostic lab test of corynbacterium diphtheriae

Blood agar and selective medium; must warn lab beforehand

Treatment for corynbacterium diphtheriae

Antimicrobial drugs and antitoxin