MICR102B - MIDTERMS

Staphylococcus

Genus of Gram-positive cocci that are pathogens of humans and animals

Coagulase reaction

Laboratory basis for grouping staphylococci into coagulase-positive and coagulase-negative

Staphylococcus aureus

Coagulase-positive species and most pathogenic member of the genus

Coagulase-negative staphylococci (CNS)

Group of more than 30 species usually skin commensals but capable of opportunistic infection

Coagulase

Enzyme used as marker for S. aureus but not a proven virulence factor

Virulence factors

Bacterial components that enhance ability to cause disease including toxins, enzymes, surface proteins, and polysaccharides

Extracellular toxins

Secreted toxic substances that damage host cells and tissues

Enzymes

Bacterial proteins that facilitate invasion and spread in host tissues

Surface proteins

Cell-associated proteins that promote adhesion and immune evasion

Polysaccharides

Carbohydrate components that aid in protection and colonization

Antibiotics

Antimicrobial drugs used to treat staphylococcal infections

Surgical drainage

Physical removal of pus or abscess material as part of treatment

Gram-positive

Bacteria that retain crystal violet stain due to thick peptidoglycan cell wall

Cocci

Spherical bacterial cells

Clusters

Grape-like arrangement of cocci due to division in multiple planes

Streptococcus spp.

Gram-positive cocci that characteristically grow in chains

Specimen source

Pus collected from suppurative wounds of humans or animals for laboratory examination

Mannitol Salt Agar (MSA)

Selective and differential medium containing 7.5% NaCl for isolation of halotolerant staphylococci

7.5% NaCl

High salt concentration that inhibits most bacteria except halotolerant organisms

Phenol red

pH indicator that turns yellow in acidic conditions due to mannitol fermentation

Mannitol fermentation

Metabolic process producing acid that changes MSA color from red to yellow

Blood agar

Enriched medium used to observe hemolysis and support bacterial growth

Nutrient agar

General-purpose medium for non-fastidious organisms

Tryptic Soy Agar (TSA)

General-purpose enriched medium for bacterial cultivation

Heart infusion agar

Nutrient-rich medium supporting growth of fastidious organisms

Gram stain

Differential staining technique used to identify Gram-positive cocci in clusters

Catalase test

Biochemical test detecting catalase enzyme by bubble formation with hydrogen peroxide

Coagulase test

Test detecting clot formation indicating presence of coagulase enzyme

Thermostable DNase

Heat-resistant enzyme that degrades DNA and is commonly positive in S. aureus

Latex agglutination test

Rapid test detecting Protein A and clumping factor on bacterial surface

Protein A

Surface protein that binds Fc portion of IgG interfering with opsonization

Clumping factor

Surface-bound coagulase that causes bacterial cells to agglutinate

Isolation procedure

Streaking wound pus on MSA, incubating at 37°C for 24 hours, and observing colony characteristics

Incubation

Maintenance of inoculated media at 37°C for 24 hours to allow bacterial growth

Colony form

Circular shape of colonies on solid media

Colony elevation

Convex upward growth pattern of colonies

Colony size

Medium colonies measuring 1–3 mm after 24 hours incubation

Golden yellow pigment

Characteristic colony color commonly produced by S. aureus

White to cream pigment

Colony color typical of coagulase-negative staphylococci

Pus

Thick exudate formed during acute inflammation containing cells, bacteria, and tissue debris

Acute inflammation

Rapid host response to infection characterized by neutrophil infiltration

Neutrophils

White blood cells that phagocytose bacteria during acute infection

Tissue necrosis

Localized death of tissue resulting from infection and inflammation

Suppurative wound

Wound producing pus due to pyogenic bacterial infection

Dead neutrophils

Major cellular component of pus

Necrotic tissue debris

Dead tissue fragments present in purulent exudate

Serum or exudate

Fluid component of pus derived from inflamed blood vessels

Cellular enzymes

Enzymes released from neutrophils and bacteria contributing to tissue liquefaction

Fibrin

Protein involved in clot formation present within purulent material

Skin commensal

Microorganism normally residing on skin without causing disease

Hyaluronidase

Enzyme that breaks down connective tissue aiding bacterial spread

DNase

Enzyme that degrades DNA facilitating bacterial dissemination

Abscess

Localized collection of pus within tissue

Boil

Painful pus-filled infection of a hair follicle

Pyogenic ability

Capacity of bacteria to produce pus

Gram-negative rods

Rod-shaped bacteria with thin peptidoglycan layer that may also infect wounds

Coagulase test

Laboratory test that detects the enzyme coagulase

Catalase test

Laboratory test that detects the enzyme catalase

Staphylococcus aureus

Coagulase-positive and catalase-positive species of Staphylococcus

Staphylococcus epidermidis

Coagulase-negative but catalase-positive species of Staphylococcus

Streptococcus spp.

Catalase-negative Gram-positive cocci used for differentiation from Staphylococcus

Coagulase principle

Coagulase converts fibrinogen into fibrin resulting in clot formation

Fibrinogen

Plasma protein converted into fibrin during coagulation

Fibrin

Insoluble protein that forms a clot

Clot formation

Visible solidification of plasma indicating positive coagulase activity

Encapsulation of infection

Formation of fibrin barrier around bacteria helping localize infection

Resistance to phagocytosis

Ability of bacteria to avoid engulfment by immune cells

Bound coagulase

Surface-associated coagulase also called clumping factor detected by slide test

Clumping factor

Cell-bound protein that directly converts fibrinogen to fibrin causing agglutination

Free coagulase

Extracellular coagulase detected by tube test and considered definitive

Slide coagulase test

Rapid method detecting bound coagulase by visible clumping

Tube coagulase test

Confirmatory method detecting free coagulase by clot formation in plasma

Positive coagulase result

Visible clumping or clot formation

Negative coagulase result

No clumping and smooth suspension

Catalase principle

Catalase breaks down hydrogen peroxide into water and oxygen

Hydrogen peroxide (H2O2)

Reactive compound used to detect catalase activity

Catalase reaction

2H2O2 converted into 2H2O and O2

Oxygen bubbles

Visible effervescence indicating catalase activity

Positive catalase result

Immediate vigorous bubbling after adding hydrogen peroxide

Negative catalase result

Absence of bubbles after adding hydrogen peroxide

Agglutination

Visible clumping of bacterial cells

Smooth milky suspension

Uniform mixture without clumps indicating negative coagulase

Prothrombin

Plasma protein that reacts with coagulase to form staphylothrombin

Staphylothrombin

complex formed by coagulase and prothrombin that converts fibrinogen to fibrin

Immune evasion

Mechanism by which bacteria avoid host immune defenses

Positive isolate

Bacterial isolate showing clumping or clot formation identified as S. aureus

Negative isolate

Bacterial isolate without clumping identified as S. epidermidis

Open wound bubbling

Release of oxygen bubbles when hydrogen peroxide contacts catalase in tissues or bacteria

Tissue catalase

Catalase enzyme present in host tissues contributing to bubbling reaction

Blood cell catalase

Catalase in erythrocytes that decomposes hydrogen peroxide

Catalase-positive bacteria

Bacteria capable of producing catalase enzyme causing bubbling reaction

Piglet scouring

Neonatal diarrhea commonly affecting piglets 0–4 days old

Escherichia coli

Gram-negative bacillus commonly associated with piglet scouring

Gram-negative bacillus

Rod-shaped bacterium with thin peptidoglycan layer and outer membrane

Facultative anaerobe

Organism capable of growing in presence or absence of oxygen

Lactose fermenter

Bacterium that ferments lactose producing acid

Mixed acid fermentation

Glucose fermentation pathway producing multiple acids and gas

Normal intestinal flora

Microorganisms normally inhabiting the intestine without causing disease

Pathogenic strain

Variant capable of causing disease under specific conditions

Enterotoxin adherence

Attachment of enterotoxins to small intestinal mucosa