MLT 140 Unit 2

Chapters 8, 14, and 15

Gram negative bacillus

No growth on BAP, growth on chocolate = suspected Hemophilus

Gram negative diplococci

No growth on BAP, growth on choclate = suspected Neisseria

Alpha hemolysis

Partial hemolysis of RBC in blood agar

Greenish discoloration of agar

Ex: S. pneumoniae, V. streptococci

Beta hemolysis

Complete hemolysis of RBC in agar

Clear around colonies

Ex; S. aureus, S. pyogenes, S. agalactiae

Large zone of hemolysis with pin-point colonies

S. pyogenes

Small zone hemolysis with medium colonies

S. agalactiae

“Medusa head” filamentous appearance

Bacillus anthracis

Swarming on BAP and CHOC

Proteus mirabilis

Density of B-hemolytic streptococci

Translucent (except group B)

Color of enterococcus species

Gray

Color of CoNS species

White

Dry appearance

Diptheroids

Creamy appearance

Yeast

S. aureus elevation

Raised/convex

Flat elevation

E. coli, BHSB

Umbilicate (depressed) appearance

S. pneumoniae

Umbonate (raised) appearance

K. pneumoniae

Growth occurs only towards the top of the media

Obligate aerobe growth in liquid media

Growth only at the bottom of the media

Obligate anaerobes

Majority of growth near the top, sprinkles of growth in the media

Faculative anaerobes

Growth sporadically thoughout the media

Aerotolerant anaerobes

Growth a little further down from the top of the media

Microaerophilic

Stapylococci morphology

Gram positive cocci in clusters

Coagulase

An enzyme that converts fibrinogen to fibrin. S. aureus has coagulase

Coagulase test

Determines if the organism is S. aureus or Coagulase Negative Stapylococci

Can cause various cutaneous infections, which can involve other organ species, leading to bacteremia and septicemia

S. aureus

S. aureus virulence factors

Protein A (blocks phagocytosis), enzymes (can destroy tissue), and toxins (TSS toxin-1, exfoliative toxin, cytolytic toxin)

S. aureus infections (8)

Carbuncles (lesions)

boils

impetigo (pustules)

scalded skin syndrome

toxic shock syndrome

Food poisoning (primarily due to Endotoxins A, B, and D)

Osteomyelitis (bacteria in diaphysis that can cause infection)

S. pneumoniae (often secondary to flu)

Normal skin flora, cause of hospital-acquired infection (esp UTI)

S. epidermis

UTI in young women, 2nd most common cause of cystitis (bladder inflammation)

S. saprophyticus

A more virulent hospital-acquired infection

S. lugdunesis

Can cause wounds, bacteremia, endocarditis, UTI’s

S. haemolyticus

Best media for staph

Swabs (aspirate ok, swabs preferred)

Characteristics of stapylococcus (4)

Catalase positive

Non-motile

Non spore-forming

Aerobic/faculative anaerobes

Growth mediums for staphylococcus (5)

BAP, Mannitol Salt Agar (MSA), CNA, PEA, Chromagar (S. aureus and MRSA)

Can be B-hemolytic, yellow pigment

S. aureus

Smedium colonies, non-hemolytic, gray-white

S. epidermidis

Larger colonies, 50% yellow pigment, Novobiocin resistant

S. saprophyticus

Medium colonies, moderate/weak hemolysis, variable pigment production

S. haemolyticus

Medium colonies, typically B-hemolytic

S. lugdunesis

Catalase Test

Differentiates b/w stapylococcus and streptococcus

Positive = bubbles

Coagulase

Detects S. aureus

Slide test or tube test

clumps = positive

Mannitol Salt Agar (3)

Used for recovery and identification of staph from mixed microbiota

Yellow colonies = ferment mannitol

Helps look for S. aureus among other species

DNase test

Detects production of an active DNase exoenzyme by staph

Chromogenic Agar

S. aureus = deep pink/fuschia colonies

S. epidermidis = partially/totally inhibited

Novobiocin susceptibility

Detects S. saprophyticus

>16 mm = susceptible

S. saprophyticus is resistant

Micrococcus (2)

Found in environment and on skin

Catalase positive, coagulase negative

Modified oxidase (3)

Tests for cytochrome C

Positve = dark-blue (micrococcus)

Differentiates micrococus from stapylococcus

Bacitracin susceptibility (3)

Differentiate b/w micro and staph

Staph is resistant

Zone of inhibition >10mm = susceptible (micrococcus)

What is oxacillin resistance in MRSA the result of?

The mecA gene

Form pus through intense local inflammatory response dominated by neutrophils

S. aureus supprative infections

Streptococci/Enterococci characteristics (4)

Gram positive cocci in pairs and chains

Catalase negative

Non-spore forming

Aerotolerant anaerobes (some species capnophilic)

Major fermentation end product for streptococci/enterococci

Lactic acid

Lancefield grouping

Groups based of the species carbohydrate in their cell wall

Group A (3)

S. pyogenes

Beta hemolysis

Large hemolysis zone, small colonies

Group B (4)

S. agalactiae

Beta hemolysis

Narrow hemolysis

Common with neonatal infections

S. pyogenes infections (6)

Bacterial pharyngitis (GAS grouping)

Pyodermal infections

Necrotizing fascilitis

Streptococcal TSS (entire organ system collapse leading to death)

Rheumatic fever (poststrep sequelae) (after pharyngitis)

Acute Glomerulonephritis (AGN)

What is S. pyogenes susceptible to?

Penicillin

Poststrep sequelae (2)

Rheumatic Fever

Acute Glomerulonephritis (AGN)

S. pyogenes virulence factors (4)

M protein

Streptolycin O (anerobic, hemolysis on BAP)

Streptolycin S (aerobic, hemolysis on BAP)

Erythrogenic exotoxin (scarlet fever from strep throat)

S. pyogenes diagnosis (3)

Throat swab

Aerobic on BAP

No gram stain (part of normal flora)

S. pyogenes morphology (5)

Small, transparent, smooth

Large B-hemolysis zone

Bacitracin susceptible

Sulfamethoxazole-trimethoprim - resistant

PYR - hydrolyzes (pink)

Lancefield grouping

Groups strep species by the carbohydrate antigens in their cell wall

S. agalctiae characteristics

Group B

Normal flora in gastrointestinal and vaginal tract