Lecture 2 - Bacterial Pathogens Part 1

what are the 4 clinical laboratory identification methods

direct examination

gram stain

other stains

biochemicals

what is direct examination of a specimen

fixed to slide, usually stained, and examined under microscope

allows presumptive identification - gram neg vs pos, yeast vs mould

provides evidence of infection even if culture is negative - why???

sensitivity is usually lower than culture, so does not rule out infection????

what is the Gram stain procedure

1. application of crystal violet (purple)

2. application of iodine (mordant)

3. alcohol wash (decolorization)

4. application of safranin (counterstain)

what organisms do not stain well with Gram stain

no cell wall (e.g. mycoplasma/ureaplasma species, chlamydia)

acid fast bacteria (very thick, waxy cells walls e.g. mycobacterium species)

viruses (too small to be seen)

fungi - unpredictable (may appear Gram pos or neg or not stain at all)

what are individual bacteria identified in a culture

growth patterns (hemolysis on blood agar plates, selective media, presence/absence of oxygen)

colonial morphology

Gram stain

biochemicals

automated identification systems (MALDI-TOF MS, molecular testing e.g. PCR)

what are examples of biochemical identification tests

catalase

coagulase

PYR test (pyrrolidonyl arylamidase)

oxidase

indole

what are types of gram positive cocci

staphylococcus

streptococcus

enterococcus

what are types of gram positive bacilli

listeria monocytogenes

corynebacterium diphtheriae

bacillus anthracis

what type of gram positive cocci shows a positive catalase test

staphylococcus

what type of gram positive cocci shows a negative catalase test

streptococcus and enterococcus

what staphylococcus species show a positive coagulase test

S. aureus

what staphylococcus species show a negative coagulase test

S. epidermidis

S. saprophyticus

S. lugdunensis

S. hominis

what is the natural habitat os S aureus

skin, mucous membranes, respiratory tract, air/environment

usually carried in the anterior nares of patients and medical staff

many health people are colonized with infection

what are some associated infections with S aureus

skin/soft tissue infections

osteomylitis

joint infections

sepsis

endocarditis

prosthetic material infection (e.g. IV catheters)

necrotizing pneumonia

toxin-medicated diseases

what is the basic identification of S aureus

gold colonies (blood agar plates)

gram positive cocci in clusters

catalase positive

coagulase positive

what are some examples of skin related infections with S aureus

folliculitis - infection of hair follicles

impetigo - superficial infection of the epidermis (gold crusting)

erysipelas - infection of the upper dermis (raised, clear demarcation)

cellulitis - infection of deeper dermis and subcutaneous fat

scalded skin syndrome - infants, blistering, loss of superficial layer of skin, fever, pain, irritability, due to exfoliative toxin

what are the virulence factors of S aureus

catalase

coagulase

hyaluronidase

hemolysins

panton-valentine leukocidin

exfoliative toxins

TSST-1

enterotoxins

what is catalase

breaks down hydrogen peroxidase

protective virulence factor

what is coagulase

causes fibrin clot formation on cell surface

may protect against phagocytosis

what is hyaluronidase

breaks down tissue

what are hemolysins

causes the breakdown of RBCs

what is panton-valentine leukocidin

causes destruction of WBCs by pore formation

what are exfoliative toxins

destroy connections between keratinocytes

responsible for scalded skin syndrome

what is TSST-1

toxic shock syndrome toxin

what are enterotoxins

can cause TSS and food poisoning

what is the natural habitat of S epidermidis

skin

mucous membranes

respiratory tract

air/environment

what are associated infections of S epidermidis

usually cause prosthetic material infections

stick abscesses, IV catheter infection, cather-associated UTIs, prosthetic joint infections, sepsis, endocarditis (prosthetic valves)

what is the natural habitat of S saprophyticus

genitourinary mucous membranes in women of childbearing age

what are the associated infections of S. saprophyticus

UTIs

what is the basic identification of S epidermidis

white colonies (blood agar)

catalase positive

coagulase negative

what are some types of beta hemolytic streptococcus species

strep pyogenes (group A)

strep agalactinae (group B)

group C and G streptococci

what are some types of alpha hemolytic streptococcus species

viridans group streptococci

strep pneumoniae

what are some types of gamma hemolytic streptococcus species

some viridans group streptococci

what does beta hemolysis look like on a blood agar plate

full hemolysis

what does alpha hemolysis look like on a blood agar plate

partial hemolysis

what does gamma hemolysis look like on a blood agar plate

no hemolysis

what is the natural environment of strp pyogenes

ubiquitous

skin

throats of asymptomatic carriers

what infections are associated with strep pyogenes

skin/soft tissue infections

pharyngitis, tonsillitis

immune mediated diseases

toxin mediated diseases

what is scarlet fever

type of strep pyogenes infection

associated with pharyngeal infection, due to pyrogenic endotoxins

sx: red rash with sandpaper texture, red spots on soft/hard palates of mouth, strawberry tongue

what is necrotizing fasciitis

type of strep pyogenes infection

infection of deep tissues that results in destruction of muscle fascia and subcutaneous fat

what is the natural environment of strep agalactinae

vagina

cervix

GI tract

what infections are associated with strep agalactinae

postpartum sepsis

neonatal pneumonia

neonatal sepsis

neonatal meningitis

what is the natural habitat of strep pneumoniae

upper respiratory tract

asymptomatic carriage common

what infections are associated with strep pneumoniae

pneumonia

otitis media

sinusitis

sepsis

meningitis

what 5 groups make up streptococci viridians groups

S. mitis

S. anginosus

S. mutans

S. salivarius

S. bovis

what is the natural habitat of viridans group strep

mouth

GI tract

respiratory tract

urogenital tract

environment

what infections are associated with viridans group strep

dental carries

brain, oropharynx, GI tract abscesses

sepsis

endocarditis

what are the 2 main species of enterococci bacteria

E faecalis

E faecium

what is the natural habitat of enterococcus bacteria

skin

mouth

GI tract

urogenital tract

environment

what infections are associated with enterococcus bacteria

post surgical wound infections

intra-abdominal infections and abscesses

sepsis

endocarditis