Gram film interpretation Flashcards
What colour will gram positive organisms stain?
Purple
What colour will gram negative organisms stain?
Red/pink
What are the bacterial morphologies (shapes of the bacteria)?
Cocci (singular: coccus) = circle shaped
Bacilli (singular: bacillus) = rod shaped
Vibrio = curved C shape
Coryneform = club-shaped
Spirochete = spiral
Coccobacillus = rod and circle shaped
How are bacteria named?
Based on how they grow in relation to each other:
- Growing in pairs = diplococci
- Growing in clusters = staphylococci
- Growing in a chain = streptococci
Features of gram positive cocci in clusters?
Examples
Staphylococcus
e.g.
Staph aureus
Disease presentation
-Cellulitis
-Endocarditis
-Osteomyelitis
-Iatrogenic (from cannula/central line insertion)
Other examples
*Staph epidermidis
- Can cause endocarditis in prosthetic heart valves
Features of gram positive diplococci?
Examples
Strep pneumoniae
Disease presentation
-Pneumonia
-Meningitis
-Otitis media
Other examples
*Enterocci
e.g. enterococcus faecium, enteroccocus
*faecalis
Can cause UTIs, intra-abdominal infections
Features of gram positive cocci in chains?
Examples
- Strep pyogenes (aka Group A strep)
Disease presentation
- Tonsilitis
- Scarlet fever
- Rheumatic fever
- Cellulitis
Other examples
- Strep agalactiae (aka Group B strep)
- Causes neonatal sepsis
How is streptococci grouped?
Grouped initially on whether they are able to haemolyse (breakdown blood) within the blood agar.
Beta haemolysis: complete haemolysis
Alpha haemolysis: incomplete haemolysis
Gamma haemolysis: no haemolysis
What is the lancefield grouping system?
The Lancefield grouping system primarily focuses on classifying different strains of streptococcal bacteria based on the presence of specific antigens in their cell walls.
These antigens are designated by letters such as A, B, C, D, etc.
For example, Streptococcus pyogenes, which causes strep throat and other infections, is classified as Group A streptococcus (GAS), while Streptococcus agalactiae, associated with infections in newborns and pregnant women, is classified as Group B streptococcus (GBS).
Why is the lancefield grouping system useful in microbiology?
The Lancefield grouping system is important in microbiology for identifying and characterizing different bacterial strains, which can be useful in diagnosing infections, understanding epidemiology, and developing vaccines and treatments.
Features of gram positive bacilli?
Examples
- Clostridium perfringens
Disease presentation
- Gas gangrene
- Cholecystitis
- Gastroenteritis
Other examples
- Clostridiodes difficile – gastroenteritis
- Clostridium tetani – tetanus
- Listeria monocytogenes – meningitis,
gastroenteritis, neonatal sepsis
Features of gram negative diplococci?
Examples
- Neisseria meningitidis
Disease presentation
- Meningitis
Other examples
- Moraxella catarrhalis
- Causes pneumonia, otitis media, sinusitis
Features of gram negative coccobacilli?
Examples
- Haemophilus influenzae
Disease presentation
- Pneumonia
- Meningitis
Other examples
- Bordetella pertussis which causes whooping cough
- Acinetobacter which causes hospital-acquired infections
Features of gram negative bacilli?
Examples
- E.Coli
- Proteus
- Klebsiella
Disease presentation
- UTI
- Pyelonephritis
- Cholecystitis
- Cholangitis
- Intra-abdominal infections
Features of vibrios?
Examples
- Vibrio cholerae
Disease presentation
- Cholera
Other examples
- Vibrio vulnificus
- Causes cellulitis, diarrhoea
Vibrio parahaemolyticus which causes gastroenteritis
Features of spirochetes?
Examples
- Treponema pallidum
Disease presentation
- Syphilis
Other examples
- Borrelia burgdorferi which causes Lyme disease
Examples of bacteria that do not gram stain?
Examples
- Mycobacteria e.g. mycobacteria tuberculosis
Mycobacteria tuberculosis causes TB
Other examples
Chlamydia
Mycoplasma
Structural and chemical differences between gram positive and gram negative bacteria?
Gram-positive bacteria have cell walls consisting of thick layers of peptidoglycan, while Gram-negative bacteria have cell walls with a thin layer of peptidoglycan.
During the gram staining procedure, a gram-positive cell retains the purple-coloured stain, while gram-negative bacteria stain pink.
Gram-positive bacteria produce exotoxins, whereas gram-negative bacteria produce endotoxins.
Gram-negative bacteria cause many infections in humans.
What bacteria is the most common gram negative within the body?
E.coli
How is infection diagnosed?
History (hypothesise differential diagnoses)
Examination (review differential diagnoses)
Investigations (radiology, biochemistry, immunology etc) refine differential diagnoses even further
Microbiology: Blood, stool, urine, wound, tissue cultures
- Microscopy: stool, urine, CSF, sputum.
- Serology
- Antigen detection
- PCR/ molecular studies
What are the 3 classification topics for bacteria?
Shape
- Bacilli
- Cocci
- Spirilla
Gram stain
- Gram +ve
- Gram -ve
Oxygen demand
- Aerobic
- Anaerobic
Gram negative bacteria examples?
E.coli
Vibrio.cholera
Salmonella
Pseudomonas
Periodontal disease bacteria
Acetic acid bacteria from vinegar
Xanthomonas from xanthan gum
Zymomonas from tequila
Gram positive bacteria examples?
Staph.aureus
Mycobacterium.tuberculosis
Enterococci
Strep.pneumoniae
Clostridium.botulinum
Haemolytic bacteria
Lactic acid bacteria from yogurt
What are some examples of bacteria that are spirochetes (spiral shaped)?
Borrelia burgdorferi (causative agent of Lyme disease) and Treponema pallidum (causative agent of syphilis)
What is the mean inhibitory concentration (MIC)?
Concentration of drug required for kill of 99.9% of organisms during 18 to 24 hours
The concentration of drug that allows a tube (or well) containing the pathogen to remain clear by visual examination after 18 to 24 hours.
What bacteria type is c.difficile?
Gram-positive, anaerobic, spore-forming, toxin-producing bacilli
How does c.difficile mainly spread?
Spores are spread by the faecal-oral route from person to person but also from the environment
Main clinical features of c.difficile infection?
Watery diarrhoea
Fever
Abdominal pain
Risk factors for c.difficile infection?
Antibiotic use
Hospitalisation
Gastric acid suppression
Age >65
Co-morbidities
What are the investigations and treatment components of sepsis 6?
Investigations:
- Lactate
- Urine output
- Blood cultures
Treatments:
- Oxygen
- IV fluids
- IV antibiotics
What is the first line antibiotic used for c.difficile in all cases?
Oral vancomycin
IV vancomycin is also useful for c.difficile infections. True/false?
False
IV vancomycin is not effective
Further management of c.difficile infection after administration of oral vancomycin?
NG or PR route if oral administration is not feasible
Isolate in single room with contact precautions
Soap and water for hand hygiene – spores resistant to alcohol gel
What are some non-infective causes of diarrhoea?
Common non-infective causes include medication, overflow, IBD.
What are the hallmarks of infections for shiga toxin producing E.coli?
painful, bloody diarrhoea with or without fever
What is haemolytic uraemic syndrome?
Haemolytic uremic syndrome (HUS) is a rare but serious medical condition characterized by the destruction of red blood cells, acute kidney failure, and a low platelet count.
It is most commonly caused by infection with certain strains of bacteria, particularly a strain of Escherichia coli (E. coli) known as O157:H7
What is the underlying pathology of haemolytic uraemic syndrome?
HUS occurs when toxins produced by certain bacteria, particularly E. coli, enter the bloodstream and cause damage to the lining of blood vessels, leading to the destruction of red blood cells, kidney damage, and a decrease in platelet count.
Management of haemolytic uraemic syndrome (HUS)?
Typically involves supportive care to manage symptoms and complications, such as maintaining hydration and electrolyte balance, managing blood pressure, and in some cases, dialysis may be necessary for kidney failure.
Are antibiotics used for treating HUS caused by E.coli infection?
No
Antibiotics are generally not recommended for treating HUS caused by E. coli infection, as they can potentially worsen the condition by releasing more toxins.
What is staph aureus bacteraemia?
Staph aureus bacteremia, or Staphylococcus aureus bacteremia, is a serious bloodstream infection caused by the bacterium Staphylococcus aureus.
How does staph aureus bacteraemia occur?
Staph aureus bacteremia occurs when these bacteria get into the bloodstream, usually through a wound, surgical site, or a catheter, and spread throughout the body.
Clinical features of staph aureus bacteraemia?
Fever, chills, rapid heartbeat, and low blood pressure.
Must be treated promptly to avoid complications i.e. infective endocarditis or sepsis.
Gold standard treatment for staph aureus bacteraemia?
IV flucloxacillin 2g QDS is the gold standard
What is the next best antibiotic for staph aureus bacteraemia after IV flucloxacillin if patient is penicillin allergic?
In true penicillin allergy, IV vancomycin is next best alternative
- Requires TDM (drug monitoring) to ensure levels 15-20
- Higher mortality compared to flucloxacillin
