gram positive bacteria Flashcards
What are the key clinically significant Gram-positive bacteria?
Cocci: Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus spp.
Bacilli: Clostridium difficile, Bacillus anthracis, Listeria monocytogene
Where can Staphylococcus aureus colonize in the body?
Nose, skin, axilla, perineum
Where can Streptococcus pneumoniae colonize in the body?
Nasopharynx.
Where is Clostridium difficile commonly found?
Gastrointestinal tract, especially in asymptomatic carriers
What is the difference between colonization and infection?
Presence of bacteria without causing disease.
Example: S. aureus in the nasal passage.
Infection: Active invasion and damage to host tissues.
Example: S. aureus causing wound infection
What are the common infections caused by Staphylococcus aureus?
Boils, abscesses, wound infections, sepsis, osteomyelitis.
What are the common infections caused by Streptococcus pyogenes?
Pharyngitis, cellulitis, necrotizing fasciitis.
What are the common infections caused by Streptococcus pneumoniae?
Pneumonia, meningitis, septicemia
What are the common infections caused by Clostridium difficile?
Diarrhea, pseudomembranous colitis, toxin-mediated gut infections.
Why is Gram staining important in microbiology?
Quick, simple, and inexpensive way to classify bacteria.
Differentiates Gram-positive from Gram-negative based on cell wall.
Helps guide initial treatment with appropriate antibiotics.
What color do Gram-positive bacteria stain, and why?
Purple, due to the thick peptidoglycan layer in their cell walls retaining the crystal violet dye.
Name an example of a toxin-mediated disease caused by Gram-positive bacteria.
Tetanus (Clostridium tetani).
Pseudomembranous colitis (Clostridium difficile).
Anthrax (Bacillus anthracis).
What is the clinical significance of Staphylococcus aureus?
A major human pathogen.
Causes a wide range of diseases, from skin infections to life-threatening conditions like sepsis.
What is the role of Lancefield grouping in classifying Streptococcus species?
Classifies Streptococcus based on carbohydrate antigens in the cell wall.
Groups A-G are clinically significant (e.g., Group A: S. pyogenes, Group B: S. agalactiae).
examples of hospital acquired strains
MRSA Streptococcus
clostridium difficile
normal flora for clostridium perfingens
soil , faeces ,, contaminated food
action of clostridium tetanus
production of a superantigen which causes inhibition of the PNS and there is release of inhibitory neurotransmitters
type of bacteria that is common in children
group B streptococcus causes meningitis , sepsis and is transmitted from mother`s genital during birth.
behaviour of alpha haemolytic
agar jar is green
beta haemolytic
full haemolysis the agar jar is clear.
classification of streptococcus
haemolysis of the cell that is alpha beta and no haemolysis.
classification of beta haemolytic streptococcus
group A
group B
Group D
bacteria that is not stained by grams stain
mycobacteria , chlamydia , mycoplasma.
all gram negatives are resistant to vancomycin ( true or all false)
true
gut commensals
e coli
proteus sp
klebsiella sp
example of gram negative cocci
neisseria spp
moraxella catarrhalis
culture for neisseria spp
culture of the CSF and other sterile sites
meningitis
inflammation of the meninges and septicaemia
gram negative bacteria
have a red grams stains
example of gram negative bacilli
coliforms for example salmonella spp and e coli
commensals of gram negative bacteria
gut and large intestine
method of classifying gram negative bacilli
lactose fermentation
e coli virulence mechanisms
pili,
capsule,
endotoxin and
exotoxins.
ferments lactose
types of escherichia coli
- Enterotoxogenic E.coli
- commonest cause of traveller’s
diarrhoea
2.Enterohaemorrhagic E.coli
- bloody diarrhoea
- haemolytic uraemic syndrome (HUS)
associated with E.coli O157
Acid And Alcohol Fast Bacilli (AAFB)
Resistant to decolourisation by acid or alcohol after
staining with carbol fuchsin.
examples of AAFB
Mycobacterium species are visualised with special
stains e.g Ziehl-Neelsen (ZN) or Auramine.
identification of mycobacteria
ZN or Auramine phenol (screening).
* Does not identify species!!!
* Culture required for ID.
* New automated liquid culture.
* Growth in 2-4 weeks.
* Molecular detection and
identification of MTB possible.
tuberculosis challenges
Multi-Drug
Resistant (MDR-TB).
diseases caused by mycobacterium
leprosy
tuberculosis
examples of spirochaetes
treponema pallidum
Long, spiral-shaped bacteria.
* Not easily visualised by light microscopy.
* Very difficult to culture (never Treponema pallidum).
* Dark ground microscopy or immunofluorescence.
* Often diagnosed by serology
common spirochaetes disease
Organism Disease
Treponema pallidum Syphilis
Borrelia burgdorferi Lyme disease
Leptospira interrogans Leptospirosis
syphilis presentation
Primary syphilis: non-painful skin lesion (chancre) at the
site of infection (skin or mucous membranes)
* Secondary syphilis (6-8 weeks after primary symptoms):
generalised systemic illness and rash
* Latent phase: symptomatic episodes may occur
* Tertiary syphilis (years after primary symptoms): central
nervous system
* Congenital syphilis: stillbirth, neonatal death or disease
