Gram Postive Bacteria Flashcards
What is the difference between Gram Positive and Gram Negative cells?
Differences in cell wall structure/ composition
Positive- thick peptidoglycan layer
Negative- thinner peptidoglycan layer, lipopolysaccharide layer (endotoxin)
What is the process of a Gram Stain?
Fixation with heat, Crystal violet stain, iodine treatment, decolorization with acetone, counter stain safranin
What does a Gram positive stain show?
Stain blue-black
Some have spores
More sensitive to penicillin and vancomycin
What does a Gram negative stain show?
Stain pink
Mostly resistant to penicillin and vancomycin
How do shapes and sizes of bacteria differ?
1-2 micrometres wide
Cocci- round
Bacilli/Rods- elongated
Curved or spiral
What are the types of aerobic Gram positive bacteria?
Coccus- Staphylococcus (three planes, grape formation)
Streptococcus (one plane, straight)
Bacillus- Bacillus (Wide and thick)
Listeria (thinner)
Corynebacterial (palisade/ wigwam)
What are the types of Staphylococci bacteria?
S. aureus
Coagulase negative Staph
What are the virulence factors of S. aureus?
Golden= more yellow, more pathogenic
Coagulase- clotting
Hyaluronidase- hydrolyses hyaluronic acid in connective tissues
Haemolysins- breakdown of blood
What are the exotoxins of S. aureus?
Toxic shock syndrome toxin- 1
Panton- Valentine Leukocydin
Where are the sites of S. aureus colonisation?
Preceding step to infection, develop infection with the same strain
Anterior nares, axilla, perineum, throat, GI tract
What are the host factors involved in S. aureus colonisation?
Nasal phenotypic differences Competence of immune system- (haemodialysis, Diabetes Mellitus, end-stage liver disease, cancer, HIV infection) Caucasian Age Previous skin infection
What are the clinical manifestations of S. aureus?
Skin and soft tissue infections Pneumonia Bone and joint infections Endocarditis- Discitis Toxin mediated diseases- scalded skin syndrome, toxic shock syndrome, gastroenteritis
Describe Coagulase negative Staph
Normal commensal flora of skin/ low grade pathogen
S. epidermidis/ S. capitis
Infection in prosthetic material- arthroplasty, metallic heart valves, central lines
What are the types of Streptococcus?
Alpha Haemolytic
Beta Haemolytic- A/B/C/D/E/F/G
What does a-haemolysis mean?
Incomplete degradation of haemoglobin
Describe Streptococci Pneumoniae
Gram Positive diplococci
Produces pneumolysin causing a-haemolysis
Peptidoglycan and theicoic acid cell wall
Forms capsule to prevent phagocytosis
Colonisation of nasopharynx- 5/10% adults, 20/40% children
What are the clinical implications of Streptococci Pneumoniae?
Most common cause of Community Acquired Pneumonia
Meningitis, sinusitis, otitis media, infective endocarditis
What does b- haemolysis mean?
Complete lysis of red blood cells
Historically considered more pathogenic
Lancefield grouping- types of carbohydrate antigens in bacterial cell wall
Describe Streptococci pyogenes group A
Multiple virulence factors- Protein M
Activate multiple cells in immune system
Response immune system kills
Pharyngitis, Scarlet fever, Rheumatic, fever, post-streptococcal glomerulonephritis, bacteraemia, necrotising fasciitis
What is necrotising fasciitis?
Breakdown of tissue
Thrombosis, loss of skin integrity
What is Bacillus Anthracis?
Multiple toxins and virulence factors- high mortality
Site of inoculation, necroing of skin, oedema and inflammation
Humans incidental host- cutaneous inoculation, inhalation
What are the types of Gram positive anaerobic bacteria?
Coccus- anaerobic coccus
Bacillus (rod)- Clostridium
What are the types of Clostridium bacteria?
tetani, botulinum, difficile, perfringens
Gram Positive rods, large, pleomorphic, obligate anaerobes, highly toxigenic
Describe Clostridium tetani?
Transmission- spores ubiquitous in soil/ contaminates wounds
Neuro-toxin- excitation of motor neurones by blocking release of inhibitory GABA
Spastic paralysis (rigidity of voluntary muscles/lock jaw)
Hyper-sympathetic state as catecholamine release not inhibited
Fatal outcome, slow outcome
Not sterile equipment to cut umbilical cord
Describe C botulinum?
Food-bourne transmission/ spores germinate- soil wound botulism
Neuro-toxin- prevents release of acetylcholine
Symmetrical flaccid descending paralysis
Oculomotor motors affected, dysphagia, respiratory depression
Cranial nerves- cant open eyes, swallow, foaming in mouth
Botox
Describe Clostridium difficile?
Ingestion of spores in hospital environment
NB spores survive alcohol
Enterotoxin- diarrhoea and cell death of colonic epithelium
Severe watery diarrhoea, major cause of healthcare associated infection
Describe Clostridium perfringens
Spores ubiquitous to soil and human gut
a-toxin/ lecithinase- damages cell membranes including haemolysis
Gas gangrene and other soft tissue infections
Food poisoning
