Staphylococcus

Protein A:

a surface protein that binds to the Fc region of IgG antibodies. Protein A: Inhibits opsonization Binds to Fc region (opposite side) of antibodies Stops antibodies from doing its function Should bind at Fab so that Fc can interact with other immune cells --> antibodies can't opsonize S. aureus Also can secrete Protein A and bind free antibodies

staphylococcal enterotoxin: characteristics

a type of exotoxin o Heat stable @ 100C for 30 minutes

Hemolysis on Blood Agar

b-hemolysis : complete hemolysis a - hemolysis : incomplete hemolysis --> green pigment γ-hemolysis: no hemolysis Yellow glow. Bacteria secreting enzymes that kill RBC in agar. Clearing of RBC, yellow is color of agar w/o blood Greenish halo: partial breakdown Gamma: no change to agar

how do superantigens work?

Bacterial or viral virulence factors that *nonspecifically activate many T cells* resulting in excessive pro-inflammatory cytokine production. • Subvert the normal process of antigen presentation to T cells

Coagulase in S. Aureus

1. pathogens produce coagulase 2. blood clot forms around pathogens. Fibrin is made by the host, so it acts as a cover for the bacteria. Bacteria can hide from phagocytes Bacteria can replicate inside the clot and then also produce enzyme to break down clot and escape

How do Coagulase and Protein A contribute to S. aureus' virulence? A. Destroy human host cells B. Allow the bacterium to invade mucosal tissues C. Prevent phagocytosis D. Act as endotoxin, inducing septic shock E. Make the bacteria resistant to antibiotic treatment

C

Staphylococcus - What do the terms "staphyl" and "cocci" refer to? A. staphyl- arranged as clusters; cocci- shaped as rods B. staphyl- arranged as pairs; cocci- S shaped C. staphyl- arranged as clusters; cocci- shaped as spheres D. staphyl- arranged as chains; cocci- shaped as spheres E. staphyl- arranged as chains; cocci- shaped as rods

C

how to determine Staphylococci vs streptococci

Catalase reaction. Mix bacteria with liquid hydrogen peroxide, bubbles if catalase is produced by bacteria. • Catalase breaks down H202 produced during oxidative metabolism Staphylocci do produce catalase, Streptococci don't produce catalase

symptoms of superantigens

Cause symptoms of high fever, malaise, nausea, vomiting, diarrhea, hypotension that sometimes leads to fatal shock

abscess

Collection of pus surrounded by fibrin • Pus contains debris consisting of dead PMNs and epithelial cells, dead and live bacteria and edema fluid • Pyogenic = pus producing

Management of Staphylococcal Infections

Control / prevention of nosocomial infections: • Careful hand hygiene • Adequate antisepsis and disinfection • Isolation of patients with open skin wounds • Boils, carbuncles may require minor surgery to drain pus • Antibiotic treatment often follows debridement (removed of dead/damaged tissue)

Why do you think the blood cultures failed to isolate any pathogens? A. Staph aureus is to difficult to grow up in the lab B. Staph aureus is too small to detect on a light microscope C. The cell wall of Staph aureus does not react with the Gram stain and therefore went undetected D. There were no bacteria in the blood samples because replicating bacteria were not causing the systemic disease E. Fever is not a typical sign of a bacterial infection so it is probably caused by a virus

D

Transmission of S. aureus

Direct skin to skin contact Indirect contact via Fomites Ingestion of contaminated food *High tolerance to salt and desiccation (drying conditions)*

What type of media is mannitol-salt agar? A.Selective B. Differential C. General purpose D.Enriched E. Selective and differential

E Selective for staph (only halotolerant bacteria) Differential based on pH

Clinically Relevant Bacteria: gram negative

Escherichia Coli • Salmonella • Shigella • Vibrio cholera • Campylobacter • Helicobacter • Klebsiella • Proteus • Pseudomonas • Haemophilus • Bordetella • Neisseria • Chlamydia

3 Causes of S. aureus Disease

Infection: --> colonization Intoxication: --> toxin production --> exotoxin (e.g. food poisoning) infection and intoxication: --> colonization --> produce exotoxin

what is the most common cause of pyogenic skin infections

S. aureus

fermentation: S. aureus vs S. epi

S. aureus can ferment, S. epi cannot

Distinguishing S. aureus from other staphylococci: what type of hemolysis?

S. aureus is beta hemolytic S. epi is gamma hemolytic

Pigment Production of S. aureus vs S. epi

Staph aureus - gold pigment (Au) Staph epi - white when cultured on enriched media

3 Toxin Mediated Diseases

Staphylococcal food poisoning Staphylococcal Scalded Skin Syndrome (SSSS) Toxic Shock Syndrome

what is SSSS

Staphylococcal scalded skin syndrome • Localized infection, Systemic intoxication • Caused by exfoliative toxin • an exotoxin that causes desquamation of the skin: Disrupts the desmosomes, there is separation, epidermis peels off • Also acts as superantigen, albeit weaker than TSST-1

Staphylococcus vs staphylococci

Staphylococcus = genus of bacteria (italisized) Staphylococci = informal name for this bacterium (species comes after, a strain comes after)

Clinically important species of Staphylococcus

Staphylococcus aureus • The most virulent staphylococcal species • Produces a variety of diseases Staphylococcus epidermidis • Low virulence • Normal microbiota of the skin • Causes opportunistic infections Common contaminent of clinical samples

Furuncle:

aka boil; large painful lesion that extends from hair follicle to surrounding tissues • Abscesses in the skin involving subcutaneous tissue • Resolves or progresses to carbuncle Plug of pus

Pyogenic infections are characterized by the formation of

an abscess

Staph aureus vs S. epidermidis

coag positive vs coag negative

What are some characteristics of staphylococci used in clinical diagnosis?

coagulase production, hemolysis on blood agar, Fermentation of Mannitol and Halotolerance

cause of gastroenteritis

commonly caused by bacteria, viruses or toxins ex. food poisoning

catalase in S. aureus

counteracts phagocytes' ability to kill bacteria by production of reactive oxygen species. Neutralize ROS

nosocomial infection

hospital acquired infection

Most common type of pyoderma?

impetigo skin infection characterized by pus production

Folliculitis:

infection of hair follicle • Superficial abscess • Usually mild, resolves or progresses to furuncle Forms a pustule (red pus filled bump) Accumulation of WBCs

Polysaccharide Capsule: in S. aureus

inhibits phagocytosis

Carbuncle:

multiple interconnected abscesses forming from the aggregation of furuncles • Extends deeper into the tissue • Requires debridement and antibiotics

What causes food poisoning?

o When it is caused by a toxin and not an infection, it is called food poisoning (NOT an infection)

what does Staphylococci produce as a defense mechanism

penicillinase (a type of beta lactamase) methicillin was then prescribed

TSST-1 acts as a....

potent superantigen

Coagulase Production

produced by staph aureus Mix bacteria with serum. If coagulase, it will turn the liquid serum into a solid Coagulase + Serum Factor --> fibrinogen in serum --> fibrin (clot)

Major virulence factors of S. aureus

protein A, Coagulase, catalase, polysaccharide capsule, other exotoxins

Foods most commonly contaminated : Ham and potato salad made with mayonnaise that have been left unrefrigerated: contaminated by what??

staphyloccoccal enterotoxin

Impetigo: cause, characteristics

• Abraded skin/insect bite/ burn gets infected • Small flattened red patches --> pus filled vesicles --> rupture and crust over • Usually little fever or pain; nearby lymph nodes often enlarge • Common among infants and young children • Itchy, Highly contagious (live and dead bacteria) • Also caused by Streptococcus pyogenes!

Staphylococcus aureus Diseases

• Causes more frequent and varied types of disease than any other human pathogen • Skin diseases (including abscesses) • Toxin-mediated: • Staphylococcal food poisoning • Scalded Skin syndrome • Toxic Shock syndrome

4 examples of localized skin diseases

• Folliculitis • Furuncle • Carbuncle • Impetigo

Virulence Factors that are Exotoxins produced by Staph

• Hemolysin- lyses red blood cells • Enterotoxin- potent gastrointestinal toxin as well as superantigen activity • Toxic Shock Syndrome Toxin 1 (TSST-1)acts as a superantigen • Exfoliative toxin - an exotoxin that causes desquamation of the skin

Epidemiology of S. aureus

• Humans are the main reservoir • About 30% of healthy adults are nasal carriers • May also colonize skin and mucous membranes • Serve as a source of infection to themselves and others

Staphylococcus epidermidis Disease

• Informal name= "staph epi" • Frequent contaminant in clinical samples • Relatively avirulent although production of a *slime layer helps it adhere to devices forming biofilms* (catheters, shunts, prosthetic joints, etc) • When introduced into deeper tissues or a normally sterile site, it causes opportunistic infections • Opportunistic infections usually acquired during a hospital stay • Infections include subacute endocarditis, infections of foreign bodies (ie catheters, shunts, prosthetic joints, etc) and urinary tract infections

Staphylococcal food poisoning: signs and symptoms

• Intoxication not an infection Rapid onset, usually within 4 hours Rapid recovery usually within 24 hours (no infection, and toxin degrades) • Symptoms: nausea and vomiting o No fever

what is Toxic shock syndrome caused by?

• Localized infection, systemic intoxication • Caused by Toxic Shock Syndrome Toxin 1 (TSST-1) • An exotoxin that induces fever, vomiting, rash and shock Systemic vasodilation, BP down --> shock, vital organs not perfused • TSST-1 causes 75% of all cases (TSS can also be caused by Streptococci)

Fermentation of Mannitol and Halotolerance

• Mannitol Salt agar contains 7.5% NaCl, which inhibits the growth of many organisms except staphylococci which is halotolerant (ie facultative halophile) because it is used to being on our salty skin • Organisms that ferment mannitol --> detected by a change in the pH indicator from red to yellow Fermentation --> lactic acid. Lower pH

Clinically Relevant Bacteria: atypical

• Mycoplasma (no cell wall) • Mycobacteria (acid-fast cell wall) • Spirochetes (thin cell wall) includes Treponema and Borrelia

Clinically Relevant Bacteria: gram positive

• Staphylococci • Streptococci • Bacilli • Clostridia • Corynebacteria

TSS symptoms, who it affects

• Symptoms: abrupt onset of high fever, red sunburn-like rash, desquamation, hypotension, multi system organ failure • Classically it affected menstruating women using high absorbency tampons but can also occur in men and children with wound infections

symptoms of SSSS, who it affects, complications

• Symptoms: red rash followed by desquamation • No scarring • Typically affects neonates and infants • Potential complication: a secondary infection of areas where the skin has peeled away Disease doesn't have long term complications, but they are more vulnerable when this is happening. No protective barrier, must be isolated

Virulence factors

• The genetic, biochemical or structural features that enable an organism to produce disease • Clinical outcome of an infection depends on the virulence of the pathogen and on the effectiveness of the host defenses. • Pathogenesis may depend on a single or multiple virulence factors. • For most disease caused by S. aureus, pathogenesis depends on the combined actions of several virulence factors

Methicillin Resistant S. aureus (MRSA)

• now, ~70% of clinical isolates are MRSA • Associated with worse outcomes such as longer hospital and ICU stays and higher mortality rates • Many hospitals now screen patients to limit spread • Many MRSA strains resistant to many other antibiotics, some being sensitive only to vancomycin • In 2002, VRSA was isolated