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Infectious Diseases > Gram Positive and Negative > Flashcards

Gram Positive and Negative Flashcards

1
Q

Describe the prokaryotic cell structure

A

 Non-compartmentalised

 DNA in cytoplasm rather than within membrane-bound nucleus

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2
Q

How do bacteria reproduce?

A
  • Binary fission

- Spore formation

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3
Q

What are the components of the cell membrane?

A

 Cytoplasm
 Cell membrane
 Peptidoglycan
 Lipopolysaccharide

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4
Q

What is the process of a gram stain?

A
  • Fixation with heat
  • Crystal violet (peptidoglycan layer)
  • Iodine treatment
  • Decolourisation (acetone)
  • Counter stain safranin
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5
Q

Describe a gram-positive gram stain result

A
  • Stain blue-black
  • Thick peptidoglycan
  • Some have spores
  • Mostly sensitive to penicillin, vancomycin
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6
Q

Describe a gram-negative gram stain result

A
  • Stain pink
  • Thin peptidoglycan
  • Lipopolysaccharide (=endotoxin)
  • Mostly resistant to penicillin, vancomycin
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7
Q

What are the types of aerobic gram positive bacteria?

A

-Coccus
=Staphylococcus (grape-like, divide in 3D)
=Streptococcus (chains, horizontal division)
-Bacillus
=Bacillus (thick and large)
=Listeria (small and single-celled)
=Corynebacteria (Chinese lanterns)

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8
Q

Examples of Staphylococcus

A
  • S. aureus

- Coagulase negative staph

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9
Q

Describe S. aureus infections

A
  • Includes MRSA
  • Is coagulase (virulent factor) positive
  • Pus-forming infections
  • Blood-stream infections, often device-related- 20-30% mortality
  • Toxin illness (scaled skin syndrome)
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10
Q

Describe coagulase-negative staphylococci infections

A
  • Lots of different species (staph epidermis, S, capitis)
  • Normal commensal flora of skin and mucosal surfaces, help skin integrity and compete with pathogenic bacteria
  • Normally only pathogenic with foreign body (prosthetic joint)
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11
Q

Examples of Streptococcus

A

-beta haemolytic (complete destruction of haemoglobin, highly virulent)
=(Lancefield groups A,B,C,F,G= antigens in cell walls and membranes, agglutinates with reciprocal serum)
-alpha haemolytic (incomplete)
=Strep pneumoniae
=Viridans streptococci

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12
Q

Describe streptococcus pneumoniae

A
  • Alias “pneumococcus”
  • CAP (community acquired pneumonia)
  • Meningitis
  • Bronchitis in COPD
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13
Q

Describe S. viridans

A
  • Mucosal (often mouth) flora
  • S. oralis, s. salivarius, s. sanguinis
  • Stick to gums, teeth etc, stick to heart valves so cause endocarditis (+primary heart problem)
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14
Q

Examples of group A b-haemolytic strep

A
  • S. pyogenes
  • Tonsillitis
  • Cellulitis
  • Severe necrotising soft tissue infections (necrotising fasciitis)
  • Puerperal sepsis (perinatal)

-Group C and G strep- similar to A but less aggressive

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15
Q

Examples of group B b-haemolytic strep

A
  • S. agalactiae
  • Normal rectal and vaginal flora
  • Neonatal meningitis and sepsis, bacteraemia, pneumonia
  • Common cause of infection during perinatal period- ascending through birth canal
  • Occasionally a pathogen in adults especially if immunocompromised
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16
Q

Describe Enterococcus

A
  • Gram positive cocci in chains (like strep)
  • Normal commensal gut flora
  • More resistant to antibiotics (vancomycin resistant enterococci)
  • Involved in intra-abdominal sepsis, urinary tract infection, bacteraemia
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17
Q

What are the two main types of Bacillus species?

A
  • bacillus anthracis

- bacillus cereus

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18
Q

Describe bacillus anthracis

A
  • Disease of herbivores, human is incidental host
  • Reservoir= soil
  • Multiple toxins and virulence factors- oedema toxin most pathogenic
  • Humans infected by cutaneous inoculation (IVDU) or inhalation (severe necrotising pneumonia)
  • Scottish outbreak 2012 IVDU, notifiable to public health
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19
Q

Describe bacillus cereus

A
  • Food poisoning- vomiting
  • Occasional pathogen if infected into sterile sites (endophthalmitis in eye)
  • Notifiable to public health
20
Q

Describe listeria monocytogenes

A
  • Intrauterine/ neonatal septicaemia/ meningitis
  • Can multiple at 4C
  • Risk in pregnancy from foods like soft cheese and coleslaw
  • Notifiable to public health
21
Q

Describe Corynebacterium diphtheriae

A
  • Transmission: respiratory droplets
  • Bacteria in pseudomembrane in throat (potential suffocation)- bull neck presentation due to inflammation of neck fascia
  • Diphtheria toxin produced in throat, via bloodstream and then inhibits protein synthesis in heart (so cardiac failure- presents septic but bradycardia) and peripheral nerve
  • Vaccine prevention, antitoxin and antibiotics
  • Notifiable to public health
22
Q

What are the gram positive anaerobes?

A
  • Coccus= anaerobic coccus
  • Bacillus= clostridia
  • Majority sensitive to metronidazole
23
Q

Examples of medically important Clostridia

A
  • Clostridium tetani
  • Botulinum
  • Difficile
  • Perfringens
24
Q

Describe C.tetani

A
  • Transmission: spores ubiquitous in soil, then contaminate wounds especially if devitalised tissue
  • Umbilicus cut with not sterile eqiupment
  • Toxin-mediated disease: Tetanus neuro-toxin causes excitation of motor neurones by blocking release of inhibitory GABA
25
Q

What are the symptoms and treatment of tetanus?

A

-Symptoms
=Spasms/ rigidity of voluntary muscle (lock jaw)
=Opisthotonus
=Autonomic system dysfunction, convulsions, hyperextension of neck
-Vaccine against toxin
-Assessment of tetanus prone wounds -use of immunoglobulin
-Slow-growing toxin (2-3 weeks)
-Public health

26
Q

Describe botulism

A
  • Usually food-borne: spores germinate anaerobically
  • Toxin-mediated: neuro-toxin prevents release of acetylcholine
  • Symptoms: symmetrical flaccid paralysis- descending (death through respiratory failure)
  • Therapeutically BoTox
  • Standards of food preparation
  • Public health
27
Q

Describe C. difficile

A
  • Major cause of healthcare associated infection

- Transmission: ingestion of spores (hospital)- survive alcohol

28
Q

Describe C. perfringens

A
  • Necrotising fasciitis
  • Transmission: spores ubiquitous in soil and human gut
  • Toxin-mediated disease: main toxin is a toxin, lecithinase (damages cell membranes inc haemolysis)
  • Public health
29
Q

Examples of gram negative cocci

A
  • Neisseria gonorrhoeae
  • Neisseria meningitidis
  • Moraxella cattheralis (COPD exacerbations)
  • Commensal Neisseria in mouth
30
Q

Describe Neisseria

A 
-Pus in gonorrhoeae
=Most common STI
=Resistant to antibiotics
=Neutrophils
-Rash in meningococcal disease
=Significant sepsis and shock
=Purpuric and non blanching
=Public health
31
Q

Groups of aerobic gram negative bacilli

A

-Non-fastidious
=sugar fermenters (Enterobacteriaceae)
=Non sugar fermenters (oxidase positive curved and non-curved)
-Fastidious (fussy slow growers)

32
Q

Examples of Enterobacteriaceae

A
  • E-coli
  • Klebsiella
  • Salmonella
  • Shigella
33
Q

Describe E. Coli

A
  • Normal human gut flora (most common)
  • Most common cause of UTI (ascending)
  • Some strain cause diarrhoea (0157)= haemolytic uraemic syndrome
  • Common cause of blood-stream infection (bacteraemia) secondary to UTI and intra-abdominal sepsis
34
Q

Describe Klebsiella

A
  • Second commonest coliform causing UTI and bacteraemia
  • Often antibiotic resistant amoxicillin, carbapenemase (acquiring enzymes involved in resistant)
  • Spreads easily between patients
  • Cousins= enterobacter, proteus, serratia
35
Q

Describe shigella

A
  • Important cause of gastroenteritis
  • Shigella= human reservoir only (colitis)
  • Ver infectious, public health
36
Q

Describe salmonella

A
  • Many hosts
  • typhi=typhoid, highly invasive, low and middle income countries
  • typhimurium and enteritidis= gastroenteritis
37
Q

Describe Pseudomonas aeruginosa

A
  • Non-fastidious, non-sugar fermenter oxidase positive non-curved
  • Most important non-fermenter
  • Reservoir: environment (especially water)
  • Human respiratory pathogen where biofilms important (CF, ventilator associated pneumonia in ITU)
  • Bacteraemia in immunocompromised (leukaemia)
  • Common coloniser in leg ulcers (biofilm)
  • Resistant to antibiotics
38
Q

Describe Vibrio cholerae

A

-Curved non-fastidious
-Reservoir warm salt water
-Toxin-mediated disease: increased cAMP within cells, decreased Na uptake and increase Cl secretion so massive water loss (rice water stool)
-Death from dehydration and electrolyte imbalance
-Treat with oral re-hydration
Public health

39
Q

Describe Campylobacter

A
  • Curved non-fastidious
  • Commonest bacterial cause of gastroenteritis in UK
  • Natural host= birds (80% chickens)
  • Self-limiting illness
  • Can become invasive during immunosuppression (mortality 40%)
40
Q

Describe fastidious gram negative bacilli testing

A

-Difficult to grow in culture
-Need enriched agar plates to grow
=Chocolate (lysed blood)/ specially prepared legionella agar
-May require molecular testing (PCR) to ascertain diagnosis

41
Q

Examples of fastidious GNB

A
  • Haemophilus influenzae
  • Legionella
  • Helicobacter
42
Q

Describe haemophilus influenzae

A
  • Unencapsulated strains are common (respiratory tract COPD, pneumonia in smokers)- chocolate agar plates
  • Capsulated serotype b causes meningitis in young children (rare UK as vaccine)
43
Q

Describe Legionella

A
  • 1976 outbreak of pneumonia US
  • Causes severe pneumonia (multi-lobar, hyponatremia, progresses quickly)
  • Difficult to grow in lab as slow-growth on enriched agar, urinary antigen or PCR
  • Lives in natural and engineered water systems inside amoebae
44
Q

Describe Helicobacter

A
  • Discovered 1984
  • Produces urase= breaks down urea to ammonia, buffers stomach acid to allow survival in anthrum of stomach
  • Causes inflammation leading to ulceration
  • Oral antibiotics, beta lactam and amoxicillin
45
Q

Examples and description of GN anaerobes

A

-Bacteroides
=Associated with intraabdominal and skin and soft tissue infections below waist
=Resistant to penicillin so metronazidole
-Fusobacterium
=Long filamentous rods
=Head and neck infections including brain abscesses
=Mixed intraabdominal infections
=Perirectal abscesses

Infectious Diseases (25 decks)

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