Lecture 2 - Bacterial Pathogens P1

How are specimens directly examined?

• via fixing on a slide, staining and examined under microscope

Why is direct examination of specimens useful? (3)

• allows presumptive identification of organism

  • gram negative vs gram positive bacteria

  • yeast vs molds

• provides evidence of infection even if culture is negative

• sensitivity is usually lower than culture so it does not rule out infection

After cultures, bacteria are identified based on… (5)

• growth patterns

• colonial morphology

• gram stain

• biochemicals

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

What growth patterns are observed after culturing? (3)

• hemolysis pattern on blood agar plates

• growth on selective media

• growth in the presence/absence of oxygen

Which organs do not stain with gram stain techniques? (4)

• organisms w/o a cell wall → mycoplasma/ureaplasma, chlamydia

• acid fast bacteria → mycobacterium

• viruses → too small

• fungi stain unpredictably → may stain but also may not

What are examples of gram + cocci (3)

staphylococcus

streptococcus

enterococcus

What are examples of gram + bacilli

• listeria monocytogenes

• corynebacterium diphtheriae

  • bacillus anthracis Wh

What are gram + cocci organisms?

• aerobic bacteria

  • spheres under microorganisms

What are gram + bacilli?

• aerobic bacteria

• rod shaped

What types Staph aureus are there? (6)

• MSSA = methicillin susceptible

• MRSA = methicillin resistant

• CA-MRSA = community associated

• HA-MRSA = healthcare associated

• VISA = vanco intermediate (not fully susceptible)

• VRSA = vanco resistant (but very RARE in Canada)

Where does Staph aureus reside on the body? (4)

• skin → armpits, groin

• mucous membranes

• respiratory tract

• air/environment

What are the associated infections of s. aureus? (8)

• skin/soft tissue → boils, abscesses, impetigo, wound

• osteomyelitis

• joint

• spesis

• endocarditis

• prostethic material infection → catheters, artificial joints

• toxin mediated diseases → food poisoning, TSS

• necrotizing pneumonia

Characteristics of S. Aureus (4)

• Blood agar plate → forms gold colonies

• Catalase → +

• Gram positive → cocci in clusiters

  • Coagulase → +

Folliculitis

• infection of hair follicles by s. aureus

  • presents as itchy bumps but not severe

Impetigo

A superficial infection of the epidermis (gold crusting) caused by s. aureus

Erysipelas

Infection of the upper dermis → raised, clear demaracaion

• caused by s. aureus

• deeper infection than impetigo

Cellulitis

Infection of deeper dermis and subq fat caused by s.aureus

• severe, pt can be quite ill developing fever/chills

• can enter bloodstream

Scalded skin syndrome

• occurs mostly in infants/newborns

• blistering, loss of superficial layer of skin → severe

• fever, skin pain, irritability

• due to exfoliative toxin

What are the virulence factors of s. aureus? (8)

• catalase: breaks down H2O2, protective for bacteria

• coagulase: causes fibrin clot formation on the cell surface → may protect against phagocytosis of the host

• hyluronidase → breaks down tissue

• hemolysins → causes the breakdown of RBC

• panton valentine leukocidin → causes destruction of WBCs by pore formation on membranes

• Exfliative toxins → destroy connections between keratinocytes; responsible for SSSS

• TSST-1 → toxic shock syndrome toxin

• entereotoxins → can cause TSS and food poisoning

What are some types of coagulase negative staph?

• s. epidermidis

• s. saprophyticus

• but this is a big family → lots of species

Where do S. epidermidis like to reside?

• skin

• mucous membranes

• respiratory tract

• air, environment

Where do S. saprophyticus reside?

• genitourinary mucous membranes in women of child bearing age → teens to about 40 y.o

What are associated infections with S. epidermidis?

• usually causes prosthetic material infections

• stich abscesses

• IV catheter associated urinary tract

• prosthetic joint infection

• sepsis

• endocarditis

How do we idenfity S. epidermidis?

• grey/silver/white colonies on blood agar plate aka no hemolysis

• catalase = +

• coagulase = -

Which streptococci organisms are beta-hemolytic aka full hemolysis?

• Group A -→ s. pyogenes

• Group B → S. agalactiae

Which streptococci organisms are alpha hemolytic aka partial hemolysis?

• s. pneumoniae

• viridans group

What is gamma hemolytic streptococci?

• no hemolysis observed

What are the types of streptococcci pygonees?

• s. pygoenes aka Group A strep (GAS)

• M- type

Where do S. pyogenes reside?

• ubiquitous

• skin

• throats of asymptomatic carriers

What are associated infections of s. pyogenes? (4)

• skin/soft tissue

• pharyngitis, tonsillitis

• immune mediated diseases

• toxic mediated diseases

Pharyngitis (6)

• aka strep throat

• white patches at the lining of the throat

• small, beta-hemolytic colonies

• gram + cocci in chains

• PYR positive

• reacts with anti A antibodies

Scarlet fever

• associated with pharyngeal infection

• caused by strep. pyogenes

• due to pyrogenic exotoxins

• presents as red rash with sandpaper texture

• small red spots on soft and hard palates

  • “strawberry tongue”

Necrotizing fasciitis (3)

• caused by strep. pyogenes

• infection of deep tissues that results in destruction of muscle fascia and subcut. fat

• will need antibiotics immediately and surgery -→ very severe

What are the types of s. agalactiae?

• s. agalactiae aka Group B strep (GBS) based on carb surface antigen

• 10 capsular subtypes

Where do S. agalactiae like to reside? (3)

• vagina

• cervix

• GI tract

What are the associated infections with s.agalactiae?

• Postpartum sepsis

• neonatal pneumonia

• neonatal sepsi

• neonatal meningitis

What are the types of S.pneumoniae

• ~100 different capsular types

Where do S. pneumoniae reside?

• upper resp. tract

Is asymptomatic carriage common for S. pneumoniae?

Yes

What are the associated infections of S. penumoniae

• pneumonia

• OM

• sinusitis

• sepsis

• meningitis

What characteristics do S. penumoniae have when stained?

• Gram +

• diplococci

What are the viridans group streptococci (VGS)? (5)

• s. mitis

• s. anginousus

• s. mutans

• s. salivarius

• s. bovis

5 groups total

Where to VGS organisms reside?

• mouth

• GI tract

• respiratory tract

• urogenital tract

• environment

What are associated infections with VGS? (4)

• dental caries

• brain, oropharynx, GI tract abscesses

• sepsis

• endocarditis but usually in those with already abnormal heart valves

What are the 2 main species of enterococci?

• e. faecalis

• e faecium

What is VRE

Vancomycin resistant enterococci → part of the enterococci family

Where do enterococci organisms reside?

• skin

• mouth

• GI tract

• urogenital tract

  • environment

What are the associated infections of Enterococci?

• post surgical wound infections → esp. GI or GU surgeries

• intra-abdominal infections and abscesses

• sepsis

• endocarditis

Identification of enterococcus organisms

• reacts with group D antiserum

• grow in high salt (6.5%) at 10C and 40C and at high pH

• survives exposure to 60C for 30 mins

• hydrolyze esculin in the presence of bile

• sometimes vancomycin resistant

• silver colonies on blood agar plate

What are the Listeria?

• has multiple species in this genus

  • BUT the only human pathogen is L. monocytogenes

Where do L.monocytogenes reside?

• GI tract

• environment

What are the associated infections of L. monocytogenes

• usually causes disease in pregnant women, infants, the elderly, and those with certain underlying diseases (immunocomp., cancer, alcoholism)

How does L.monocytogenes infection humans?

by entering food production

What temperature can L. monocytogenes grow in?

4C

Identifying L.monocytognees?

• bacilli structure when stained

• small zone of beta hemolysis on blood agar

• gram + rod

• catalase +

• motile at 20C

• bile esculin +