Lecture 2 Bacterial Pathogens Part 1 Flashcards
Bacteria Gram Stains
Gram positive: Purple,Thick cell wall, one memebrane
Gram negative: Pink, Thin cell wall, double membrane
Grain Stain Procedure Steps
- Application of crystal violet
- Application of iodine
- Alcohol Wash
- Application of safranin
Which organisms will not be stained with a gram stain?
organisms without a cell wall - ex. mycoplasma/ureaplasma species, chlamydia species ⇒ use acridine orange (DNA stain)
acid fast bacteria - ex. mycobacterium species ⇒ acid fast stains
Viruses - far too small to be seen with light microscopy
Fungi stain unpredictably - may appear + or - (or none at all) ⇒ use chitin or capsule stains
How are most clinical sample or microorganisms cultured and identified?
growth patterns - hemolysis on blood agar, growth on different media, growth with or without O2
colonial morphology
gram stain
biochemicals
automated ID systems, MALDI-TOF MS, molecular testing (ex. PCR
What are examples of biochemical ID tests for microorganisms?
catalase, coagulase, PYR test (pyrrolidinyl arylamidase), oxidase, indole
What are examples of gram + cocci and bacilli?
Cocci: staphylococcus, streptococcus, enterococcus
Bacilli: listeria monocytogenes, corynebacterium diphtheriae, bacillus anthracis
Regarding S. aureus, what are the types, its natural habitat, and the associated infections with it?
Types: MSSA, MRSA, CA-MRSA, HA-MRSA, VISA, VRSA
Habitat: skin, mucous membranes, respiratory tract, air, environment, usually carried in anterior nares of pt and medical staff
Infections: skin and soft tissue (boils, abscesses, impetigo, wounds), osteomyelitis, joint, sepsis, endocarditis, prosthetic material infection, necrotizing pneumonia, toxin-mediated diseases
What are basic ID factors for S. aureus?
golden colonies when streaked on most agar, is catalase positive, gram + cocci in clusters on gram stain, coagulase positive as well
What are infections that are associated with S.aureus?
folliculitis, impetigo (superficial infection of epidermis, gold crusting), erysipelas (infection of upper dermis, raised and clear demarcation), cellulitis (infection of deeper dermis and SC fat)
scalded skin syndrome: occurs mostly in infants, blistering and loss of superficial layer of skin, fever, skin pain, irritability, due to exfoliative toxin
What are virulence factors associated with S. aureus?
has catalase: breaks down H2O2 (protective)
has coagulase: causes fibrin clot formation on cell surface (may protect against phagocytosis)
has hyaluronidase: breaks down tissue
has hemolysins: causes breakdown of RBCs
has Panton-valentine leukocidin: causes destruction of WBCs by pore formation
has exfoliative toxins: destroys connections between keratinocytes (responsible for SSS)
has TSST-1: toxic shock syndrome toxin
has enterotoxins: can cause TSS and food poisoning
What are different types of coagulase negative staphylococci (CNS), what is their habitat and associated infections?
Types: many, staphylococcus epidermidis ⇒ habitat in skin, mucous membranes, respiratory tract, air, environment ⇒ infections: prosthetic material, stitch abscesses, IV catheter, catheter associated UTIs, prosthetic joint, sepsis, endocarditis
also staphylococcus saprophyticus ⇒ habitat is in genitourinary mucous membranes in women of child bearing age ⇒ associated with UTIs
What are basic ID factors for S. epidermidis?
streaks white colonies on most agar,, is catalase positive and coagulase negative
What type of coccus are responsible for beta and alpha-hemolytic activity, that is causing hemolysis of RBCs when streaked on blood agar plates?
Group A streptococcus (S. pyogenes) and Group B streptococcus (S. agalactiae) cause full hemolysis
S. pneumoniae and viridans group streptococci are alpha-hemolytic (partial hemolysis)
some streptococci are also gamma-hemolytic (no hemolysis)
Regarding S. pyogenes, what are the types, natural habitat, and associated infections?
Types: this, also called Group A streptococcus (GAS) based on carb surface antigen, many M-types
Habitat: ubiquitous, skin, throats of asymptomatic carriers
Infections: skin and soft tissue infections (abscesses, erysipelas, cellulitis), pharyngitis, tonsillitis, immune-mediated diseases (rheumatic fever, acute glomerular nephritis), toxin-mediated diseases
What are basic ID factors for S. pyogenes?
small beta-hemolytic colonies on blood agar
gram + cocci in chains
PYR positive
reacts with anti-A antibodies
catalase negative
What are infections associated with S. pyogenes?
scarlet fever: associated with pharyngeal infection, due to pyrogenic exotoxins, red rash with sandpaper feel, small red spots on soft and hard palates (strawberry tongue)
necrotizing fasciitis: infection of deep tissues that results in destruction of muscle fascia and SC fat
Regarding S. agalactiae, what are types, habitat, and infections?
Types: this, also called Group B streptococcus (GBS) based on carb surface antigen, 10 capsular subtypes
Habitat: vagina, cervix, GI tract
Infections: postpartum sepsis, neonatal pneumonia, neonatal sepsis, neonatal meningitis
they are beta-hemolytic, catalase negative
Regarding S. pneumoniae, what are types, habitat, and infections?
Types: this, around 100 capsular types, capsule types basis of vaccines: 23-valent polysaccharide vaccine and 13-valent conjugate vaccine
Habitat: URT, asymptomatic carriage common
Infections: pneumonia, OM, sinusitis, sepsis, meningitis
they are gram + diplococci and are alpha-hemolytic
Regarding enterococcus, what are the types, habitat, and infections?
Types: two main ones ⇒ E. faecalis and E. faecium, formerly called Group D streptococci, also VRE
Habitat: skin, mouth, GI tract, urogenital tract, environment
Infections: post-surgical wound infections (especially GI or GU), intra-abdominal infections and abscesses, sepsis, endocarditis
What are basic ID factors for enterococci?
react with group D antiserum
grow in high salt (6.5% NaCl) at 10 C and 40 C, and at high pH
survive exposure to 60 C for 30 min
hydrolyze esculin in presence of bile
sometimes vancomycin resistant
Regarding listeria, what are the types, habitat, and infections?
Types: multiple species, only human pathogen is L. monocytogenes
Habitat: GI tract, environment
Infections: usually causes disease in pregnant women, infants, elderly, and those with certain underlying disease (immunocompromised, cancer, alcoholism), diarrhea, gastroenteritis, sepsis, endocarditis, meningitis, spontaneous abortion, stillbirth
usually infects humans by entering food production, able to grow at 4 C
What are basic ID factors for L. monocytogenes?
gram + rods
have small zone of beta-hemolysis
catalase positive
motile at 20 C
bile esculin positive
Regarding Corynebacterium diphtheriae, what are types, habitat, infections?
Types: most important human pathogen is this, has four biotypes: this mitis, intermedius, gravis, and belfanti
Habitat: nasopharynx, skin, environment
Infections: respiratory this, cutaneous this
has widespread availability of vaccine
What are basic ID factors for C. diphtheriae?
white opaque colonies on blood agar, gram + bacilli with club like appearance, black colonies on specialized media help in ID
Regarding bacillus anthracis, what is the habitat, and infections?
Habitat: infected animals, spores in soil, water, vegetation
bioterrorism
Infections: cutaneous this, inhalation this, GI this, this meningitis, injection this
What are basic ID factors for bacillus anthracis?
white-gray colonies with “comet trails”,, gram + bacilli with chains of cells with central spores
What is inhalation anthrax?
caused by bacillus anthracis
inhaled spores germinate in lungs and cause fever, declining respiratory status, pleural effusions, mediastinal widening
high mortality rate
