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MRSA theory > Clinical Microbiology > Flashcards

Clinical Microbiology Flashcards

1
Q

What are the main actions of antibiotics?

A
  1. Inhibit cell wall formation
  2. Inhibit protein synthesis
  3. Inhibit DNA synthesis
  4. Inhibit RNA synthesis
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2
Q

Give some examples of antibiotics that inhibit cell wall formation?

A

penicillin
cephalosporins

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3
Q

Give some examples of antibiotics that inhibit protein synthesis?

A

aminoglycosides (cause misreading of mRNA)
chloramphenicol
macrolides (e.g. erythromycin)
tetracyclines
fusidic acid

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4
Q

Give some examples of antibiotics that inhibit DNA synthesis?

A

quinolones (e.g. ciprofloxacin)
metronidazole
sulphonamides
trimethoprim

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5
Q

Give some examples of antibiotics that inhibit RNA synthesis?

A

rifampicin

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6
Q

Features of campylobacter jejuni?

A

-Most common cause of acute infective diarrhoea
-Spiral, gram negative rods
-Usually infects caecum and terminal ileum.
-Local lymphadenopathy is common
-May mimic appendicitis as it has marked right iliac fossa pain
-Reactive arthritis is seen in 1-2% of cases

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7
Q

Features of shigella spp.?

A

-Members of the enterobacteriaceae
-Gram negative bacillii
-Clinically causes dysentery
-Shigella soneii is the commonest infective organism (mild illness)
-Usually self limiting, ciprofloxacin may be required if individual is in a high risk group

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8
Q

Features of salmonella?

A

-Facultatively anaerobic, gram negative, enterobacteriaceae
-Infective dose varies according to subtype

Salmonellosis: usually transmitted by infected meat (especially poultry) and eggs

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9
Q

Features of E.coli?

A

MAIN TYPES:

-Enteropathogenic
-Enteroinvasive: dysentery, large bowel necrosis/ulcers
-Enterotoxigenic: small intestine, travelers diarrhoea
-Enterohaemorrhagic: 0157, cause a haemorrhagic colitis, haemolytic uraemic syndrome and thrombotic thrombocytopaenic purpura

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10
Q

Features of yersinia enterocolitica?

A

-Gram negative, coccobacilli
-Typically produces a protracted terminal ileitis that may mimic Crohns disease
-Differential diagnosis acute appendicitis
-May progress to septicaemia in susceptible individuals
-Usually sensitive to quinolone or tetracycline

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11
Q

What are the features of vibrio cholera?

A

-Short, gram negative rods
-Transmitted by contaminated water, seafood
-Symptoms include sudden onset of effortless vomiting and profuse watery diarrhoea
-Correction of fluid and electrolyte losses are the mainstay of treatment
-Most cases will resolve, antibiotics are not generally indicated

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12
Q

what are typhoid and paratyphoid caused by?

A

Salmonella typhi and Salmonella paratyphi (types A, B & C) respectively

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13
Q

Symptoms of typhoid/paratyphoid?

A
  • initially systemic upset
  • relative bradycardia
  • abdominal pain, distension
    constipation: although
    Salmonella is a recognised cause of diarrhoea, constipation is more common in typhoid
  • rose spots: present on the trunk in 40% of patients, and are more common in paratyphoid
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14
Q

Complications of typhoid/paratyphoid?

A
  • osteomyelitis (especially in sickle cell disease where Salmonella is one of the most common pathogens)
  • GI bleed/perforation
  • meningitis
  • cholecystitis
  • chronic carriage (1%, more likely if adult females)
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15
Q

What is Streptococcus bovis septicaemia associated with?

A

carcinoma of the colon
(also endocarditis)

gram +VE

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16
Q

Features of S.Aureus?

A

Facultative anaerobe
Gram positive coccus
Haemolysis on blood agar plates
Catalase positive

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17
Q

What can S.Aureus cause?

A

cutaneous infections
abscesses
Exo and entero toxin may result in toxic shock syndrome and gastroenteritis respectively

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18
Q

Ideal treatment of S.Aureus?

A

penicillins although many strains now resistant

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19
Q

Features of S.pyogenes?

A

Gram positive, forms chain like colonies, Lancefield Group A Streptococcus
Produces beta haemolysis on blood agar plates
Rarely part of normal skin microflora
Catalase negative

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20
Q

Treatment of S.Pyogenes?

A

penicillin, macrolides may be used as an alternative

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21
Q

What does S.pyogenes release?

A

proteins/ virulence factors: hyaluronidase, streptokinase which allow rapid tissue destruction

Superantigens such as pyogenic exotoxin A which results in scarlet fever

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22
Q

What does H.pylori release?

A

urease that breaks down gastric urea> Carbon dioxide and ammonia> ammonium>bicarbonate

Produces hydrogenase that can derive energy from hydrogen released by intestinal bacteria

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23
Q

what does Hlpylori colonise?

A

usually gastric antrum

Irritates resulting in increased gastrin release and higher levels of gastric acid

24
Q

Is Hpylori gram positive or negative?

A

Gram negative, helix shaped rod, microaerophillic

25
Q

Risks of H.Pylori?

A

10-20% risk of peptic ulcer, 1-2% risk gastric cancer, <1% risk MALT lymphoma.

26
Q

Diagnosis of H.pylori?

A

serology (approx. 75% sensitive). Biopsy urease test during endoscopy probably the most sensitive

27
Q

Features of staphylococcus epidermis?

A

tends to colonise plastic devices and forms a biofilm

(difficult to eradicate without removal of device e.g. breast implant)

28
Q

what is malignant otitis external cause by?

A

Pseudomonas aeruginosa

29
Q

Key features of malignant otitis external?

A

Diabetes (90%) or immunosuppression (illness or treatment related)
Severe, unrelenting, deep-seated otalgia
Temporal headaches
Purulent otorrhea
Possibly dysphagia, hoarseness, and/or facial nerve dysfunction

30
Q

What can malignant otitis external progress to?

A

Progresses to temporal bone osteomyelitis

31
Q

Treatment of malignant otitis externa?

A

Anti pseudomonal antimicrobial agents
Topical agents
Hyperbaric oxygen is sometimes used in refractory cases

32
Q

Main causes fo lactational mastitis?

A

S.Aureus

33
Q

Which pathogen is associated with gangrene?

A

C.perfringes

34
Q

WHO definitions of diarrhoea?

A

Diarrhoea: > 3 loose or watery stool per day
Acute diarrhoea < 14 days
Chronic diarrhoea > 14 days

35
Q

Common causes of osteomyelitis (pathogens)?

A

S aureus and occasionally Enterobacter or Streptococcus species
In sickle cell: Salmonella species

36
Q

what sort of virus is hepatitis B?

A

double-stranded DNA virus

37
Q

Complications of hepatitis B infection?

A

Chronic hepatitis (5-10%)
Fulminant liver failure (1%)
Hepatocellular carcinoma
Glomerulonephritis
Polyarteritis nodosa
Cryoglobulinaemia

38
Q

Treatment of hepatitis B infection?

A

Pegylated interferon-alpha
lamivudine, tenofovir and entecavir

39
Q

How are patients screened for MRSA?

A

nasal swab and skin lesions or wounds
the swab should be wiped around the inside rim of a patient’s nose for 5 seconds
the microbiology form must be labelled ‘MRSA screen’

40
Q

Suppression of MRSA once carrier identified?

A

nose: mupirocin 2% in white soft paraffin, tds for 5 days
skin: chlorhexidine gluconate, od for 5 days. Apply all over but particularly to the axilla, groin and perineum

41
Q

Common cause of bladder calcification?

A

Schistosoma haematobium causes haematuria

Schistosomiasis is the most common cause of bladder calcification worldwide.

42
Q

Management of schistosomiasis?

A

Single oral dose of praziquantel

43
Q

what is the most common pathogen implicated in cholangitis?

A

E.coli
[Klebsiella species
Enterococcus species
Streptococcus species ]

44
Q

Clinical features of cholangiitis?

A

Charcot’s triad:
Fever (90% cases)
Right upper quadrant pain
Jaundice

Reynolds pentad: Above plus confusion and hypotension

45
Q

Management of cholangitis:?

A

ERCP -usually after 72 hours of antibiotics
Percutaneous transhepatic cholangiogram and biliary drain

46
Q

Features of enterobiasis?

A

Due to organism Enterobius vermicularis
Common cause of pruritus ani
Diagnosis usually made by placing scotch tape at the anus, this will trap eggs that can then be viewed microscopically
Treatment is with mebendazole

47
Q

What is Ancylostoma duodenale?

A
  • Hookworms that anchor in proximal small bowel
  • Most infections are asymptomatic although may cause iron deficiency anaemia
  • Larvae may be found in stools left at ambient temperature, otherwise infection is difficult to diagnose
  • Infection occurs as a result of cutaneous penetration, migrates to lungs, coughed up and then swallowed
    -Treatment is with mebendazole
48
Q

What is Ascariasis?

A
  • Due to infection with roundworm Ascaris lumbricoides
  • Infections begin in gut following ingestion, then penetrate duodenal wall to migrate to lungs, coughed up and swallowed, cycle begins again
  • Diagnosis is made by identification of worm or eggs within faeces
  • Treatment is with mebendazole
49
Q

When is bacteroides fragilis found?

A

severe peritoneal infections and as it is facultatively anaerobic may be present in pus. It has a pungent aroma.

50
Q

Risk factors for c.diff?

A

Broad spectrum antibiotics
Use of proton pump inhibitors
Contacted with persons infected with c.difficile

51
Q

Management of c.diff?

A

Consider stopping proton pump inhibitor treatment
First-line therapy is now oral vancomycin 125mg orally 4 times daily for 10 days
Patients who do not respond to vancomycin may respond to oral fidaxomicin
Patients with severe and unremitting colitis should be considered for combination therapy of oral vancomycin and metronidazole. Some cases may require emergency colectomy

52
Q

What is Fasciola hepatica?

A

common liver fluke (parasitic trematode)
Infects humans as part of a plant/ food trematode infection

53
Q

Symptoms of fasciola hepatica?

A

Acute: fever, nausea, swollen liver, skin rashes, and extreme abdominal pain
Chronic: intermittent pain, jaundice, and anemia.

54
Q

Treatment of fasciola hepatica?

A

triclabendazole. Some patients may need ERCP

55
Q

Classic diphtheria symptoms?

A

systemic illness that lasts several days. The tonsils or pharynx can be covered in a thick grey membrane which bleeds on attempted removal.
Cervical adenopathy
Bulls neck appearance

56
Q

What are melanosis coli?

A

occur as a result of laxative abuse and consists of lipofuschin laden macrophages that appear brown.

MRSA theory (20 decks)

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