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Infection > Bacterial Infections > Flashcards

Bacterial Infections Flashcards

1
Q

What signs suggest pharyngitis has a bacterial cause?

A
  • Fever in past 24 hrs
  • rapid attendance (within 3 days or less of 1st symptoms)
  • muscle aches
  • absence of cough
  • severely inflamed tonsils (with visible pus, not just red)
  • Enlarged anterior cervical glands
    (more than 4 of these means probably bacterial
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2
Q

What viruses can cause pharyngitis and how is it managed?

A
  • adenovirus, influenza virus, EBV, Rhinovirus (common cold)

- usually let limiting so manage supportivly

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3
Q

What bacteria most commonly cause pharyngitis ?

A

Streptococcus pyogenes

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4
Q

What organisms commonly cause meningitis?

A

strep pneumonia
neisseria meningitidis
haemophilus influenzae type b
some viruses- less severe

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5
Q

What are the features of neisseria meningitidis on a gram stain?

A
  • gram negative (red)

- diplococcus

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6
Q

How is neisseria meningitidis spread?

A

by respiratory secretions- coughing ect

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7
Q

Is neisseria meningitidis encapsulated?

A

yes

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8
Q

What are the key virulence factors of neisseria meningitidis?

A
  • pilus- enhances attachment
  • polysaccharide capsule- promotes adherence and evades phagocytes
  • lipopolysaccharide endotoxin- triggers inflammation
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9
Q

What antibiotic is used to treat meninigitis and why?

A

ceftriaxone

  • active against pathogens that usually causes menigitis in late teens
  • penetrates into CSF well
  • can be administered IV
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10
Q

What tests would be conducted when meningitis is suspected ?

A
  • lumbar puncture and PCR to find causative organism (if appropriate)
  • FBCs- are WBC higher
  • U&E- check renal function
  • CRP- marker of severity of inflammation
  • coagulation studies- checks liver function
  • blood gases - lactic acidosis?
  • liver function- AST, ALT ect
  • blood sugar- ensure its high enough
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11
Q

Which strain of neisseria meningitidis is most common in UK?

A
  • group B
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12
Q

What are the key features of a septic strep. pneumoniae infection?

A
  • yellow sputum
  • short of breath
  • cough
  • chest crackles
  • fluid on chest x ray
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13
Q

What are the key features of a septic E. coli infection?

A
  • peritonitis
  • abdo pain
  • bowl gas seen on xray under diaphragm
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14
Q

In what population are UTIs most common?

A

sexually active females

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15
Q

What are the common causative organisms of UTIs?

A
  • 70- 95% caused by e. coli

- rest usually staph. Saprophyticus (gram +)

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16
Q

How are UTIs treated?

A
  • trimethoprim
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17
Q

What organism commmonly causes infective endocarditis, what are its key features on a gram stain and how does it enter the blood?

A
  • viridans steptococcus (also staph aureus)
  • gram + coccus in chains
  • usually through cuts in gums
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18
Q

How does infective endocarditis occur?

A
  • bacteria get into blood
  • heart valve faulty causing stagnant blood
  • bacteria stay there longer so able to infect valve and endocardium
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19
Q

What is the common presentation of someone with infective endocarditis?

A
  • high fever
  • weight loss
  • generally unwell
  • cardiac symptoms (murmer ect)
  • history of heart valve problems
  • high WBC, low Hb (haemolytic anaemia), high CRP
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20
Q

What are the key features of all streptococci on a gram stain?

A

gram + cocci in chains

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21
Q

What are the 3 main groups of streptococci? Describe each group and give an example

A

alpha haemolysis
- partially break down RBCs and produce a green colour on red agar
- known as viridans streptococcus
- most common example is strep. pneumoniae
beta haemolysis
- fully breakdown RBCs and clear a zone around them on red agar
- strep pyogenes
Non- haemolytic
- enterococcus faecalis

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22
Q

How can beta haemolytic streptococci be classified?

A
  • by cell wall antigens (lancefield)- A,B,C ect

- by sherman group (pyogenic, viridans, enterococcal, lactic)

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23
Q

what is another name for strep. pyogenes?

A
  • group A, beta hamolytic streptococci
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24
Q

What disease is the most common result of a strep. pyogenes infection?

A
  • strep throat (streptococcal pharyngitis)
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25
Q

How do strep. pyogenes spread and what are the different possible outcomes of infection?

A
  • spread by droplets (short range) or break through skin
  • colonisation with no harm
  • just secrete toxins (pharyngitis)
  • invade blood stream (septicaemia)
  • spread to subcutaneous tissue (cellulitis), fasica (fascaeitis) and muscle (myonecrosis)
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26
Q

Describe 3 endotoxins that act as virulence factors for strep. pyogenes?

A
  • hyaluronic capsule: inhibits phagocytosis
  • M protein: resists phagocytosis, complement and aids adhesion
  • Adhesins: helps colonise
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27
Q

describe 2 key exotoxins and state 2 others that are released by strep. pyogenes

A
  • DNAases
  • hyaluronidase
  • streptakinas (dissolves clots)
  • streptacoccal pyrogenic exotoxin-causes toxic shock syndrome
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28
Q

In what age group is strep throat most common?

A

5-15 yrs old

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29
Q

Describe the key features of strep throat

A
  • abrupt onset of mild sore throat (severe sore throats more likely to be viral)
  • fever
  • headache
  • enlarged lymphoid tissue with tonsil exudate and pus
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30
Q

How is strep throat treated?

A

supportively

no antibiotics because its self limiting - could use flucoxacillin

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31
Q

Why are overcrowded living conditions associated with spread of strep throat?

A

as it is spread by droplets

32
Q

How does scarlet fever develop from strep throat?

A

if ppl dont have an antibody to the exotoxin and the strain must release a pyogenic exotoxin

33
Q

What is scarlet fever?

A

When strep throat is accompanied by a characteristic rash on the neck and trunk and a ‘strawberry’ tongue
- often leads to high fever, sepsis, arthiritis and jaundice

34
Q

Name some suppurative complications of strep throat?

A
  • peritonsillar cellulitis/ abcesses
  • retropharyngeal abcess
  • mastoiditis, sinusitis, otis media
  • meningitis, brain abcesses
35
Q

What is acute rheumatic fever?

A
  • inflammation of heart, joints and CNS 10-14 days after step throat
  • due to rheumatic M proteins causing antibody production against own tissues
  • rarely seen in UK
36
Q

What is acute post- strep glomerulnophritis?

A
  • inflammation of glomerulus leading to renal failure as a result of specific M proteins
37
Q

What is impetigo? What causes it and what is it the most common cause of?

A

A superficial infection of the skin by strep pyogenes that causes blisters and sores. It occurs when the skin is innoculated and then breaks.
It is highly contageous and generally occurs in 2-5 yr olds.
It is the most common cause of glomerulonephritis

38
Q

What is erysipelas?

A

Deep strep. pyogenes infection of skin involving dermis and lymphatics. Commonly in face after strep. throat and lower limbs after trauma, skin disease or fungal infection

39
Q

What is cellulitis? what are risk factors for it?

A

skin and subcutaneous tissue infected by strep. pyogenes or staph (or other) following break in skin.
risk factors inc impaired lymphatic drainage, IV drug use ect

40
Q

What is necrotising fascitis and presentation

A
  • infection to deep cutaneous tissue and fascia.
  • very rapid deterioration and extensive necorsis
  • secondary to skin break
  • severe pain at first w/ high fever
  • high mortality rate, need to remove necrotic tissue
41
Q

what is streptococcal toxic shock syndrome? How does it occur?

A
  • entry of s. pyogenes into blood and deeper tissue

- leads to vascular collapse and organ failure, death within hrs of onset

42
Q

How does streptococcal toxic shock syndrome occur?

A
  • M proteins being released and binding with fibrinogen
  • This complex stimulated some WBCs to release hydrolytic enzymes, respiratory burst ect into endothelium and damage it
  • this leads to hypercoaglation (leads to DIS), organ damage and vascular leakage- hypotension
43
Q

What does strep pneumoniae look like on gram stain?

A

gram + diplococcus

44
Q

Where can strep. pneumonia be carried harmlessly?

A

nasopharynx

45
Q

When can infection of strep. pneumonia occur?

A
  • when a carries has less ressistance

- when a non infected individual looses inhales infected droplets

46
Q

What disease is most commonly caused by strep. pneumoniae infection?

A

pneumonia

meningitis also

47
Q

What are the virulence factors for strep. pneumoniae?

A
  • capsule

- cell associated enzymes

48
Q

How does pneumonia present?

A
  • often preceeded by upper/ mid respiratory tract infection (coughing, fever, purelent red/ yellow sputum, breathlessness, malaise anorexia)
  • fluid accumulated in lungs can be heard and seen on CXR
  • high breathing and heart rate
  • low blood pressure and O2
49
Q

What does staph. aureus look like on a gram stain?

A

gram + cocci in clusters

50
Q

Where does staph. areus normally reside?

A

skin, mucous membranes

51
Q

What diseases does staph areus most commonly cause?

A
  • most common is skin and soft tissue infections in breaks of skin (cuts, needle stick ect)
  • also endocarditis, septicemia, food poisioning, toxic shock, necrotising pneumonia, osteomyelitis
52
Q

Name some virulence factors for staph areus

A
  • protein A in cell wall inactivated IgG
  • capsule
  • many exotoxins
  • enterotoxins (cause sickness when ingested on food)
  • toxic shock sydrome toxin ( activates T cells to produce massive release to cytokines like TNF, IL-2 ect
53
Q

How does staph. areus infections lead to abcesses?

A
  • infects skin break
  • bacteria clump together
  • causes inflammation, necrosis of nearby tissue and pus
  • fibroblasts from fibrous wall around bacteria due to clotting induced by coagulase release from the bacteria
  • this means abcess present
54
Q

What is the difference between coagulase negative and positive bacteria? out of staph epididermis and staph areus which is coagulase positive?

A
  • coagulase positive bacteria produce coagulase and so induce more clotting and create abcesses
  • epididermis is coagulase negative, areus is coagulase positive
55
Q

Where do staph epididermis normally reside?

A

skin and eyes

56
Q

What infections does staph epididermis often cause?

A
  • infections of prosthetics and catheters (it produces adhesion molecules to help it stick to prosthetics)
  • infections of wounds
  • infections of heart valves
57
Q

What are the gram stain features of clostridium difficile?

A

gram + rods

58
Q

How do c. diff infections usually occur? name 2 virulence factors and how they cause diarrhoea and bowel ulcers

A
  • normal in small numbers
  • some antibiotics change normal flora of gut
  • c. diff able to reproduce as less competition
  • produces toxin A which causes excessive fluid secretion (diarhoea) and inflammation
  • and toxin B which disrupts protein synthesis and disorganises cytoskeletons (necrosis of epithilium leads to ulcers)
59
Q

What antibiotics carry high risk of c. diff infection?

A
  • clindamycin
  • ampicillin
  • cephalosporins
  • amoxicillin
60
Q

How can c. diff infections be detected?

A
  • in stool sample
61
Q

What symptoms come with c. diff infections

A
  • diarrhoea
  • exudate in bowel
  • ulcers of bowel (blood in stool)
  • vomiting
  • fever
62
Q

How does c. diff infection be managed?

A
  • fluids, antibitoics (metronidazole or might have to be IV vancomysin if severe)
  • isolate Pt and PPE to prevent spread
63
Q

What are the gram stain features of escherichia coli?

A
  • gram - rods
64
Q

Is E. coli found naturally in body?

A

yes in colon

65
Q

What infections does E. coli commonly cause?

A
  • UTIs
  • Meningitis in infants
  • travellers diarrhoea (if its a strain producing enterotoxin)
66
Q

What is route of transmission of e coli?

A
  • faecal- oral (contaminated food/ water)

- spread for anus to urethra via peritoneum

67
Q

What are key virulence factors to e. coli?

A
  • pilli facilitate adhesion
  • exotoxins to enable attachment and invasion of host cells
  • enterotoxins
68
Q

Are haemophilus influenzae normally found in the body?

A

yes in upper resp tract

69
Q

What are gram stain features of haemophilus influenzae?

A

gram - rods

70
Q

How is H. influenzae transmitted?

A
  • resp droplets from coughing, sneezing ect
71
Q

What is common presentation of H. influenzae infection?

A
  • upper resp tract infections in children
  • pneumonia in elderly and immunosurpressed
  • also meningitis (rare cause)
72
Q

How can H. influenzae be treated and prevented?

A
  • vaccine can be given

- amoxycillin

73
Q

What are general signs and symptoms of sepsis?

A
  • look unwell
  • fever
  • headache
  • unresponsive
  • weakness
  • chills and rigour
  • photophobia
  • high HR
  • low BP
  • nausia
  • abdopain and muscle aches
74
Q

What type of bacteria is legionella pneumonia?

A

a gram neg rod with a capsule

75
Q

how does legionella spread?

A

swimming in contaminated water, resp droplets person to person

76
Q

What infection does legionella cause?

A

respiratory tract infections (pneumonia)

- lobar pneumonia

Infection (9 decks)

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