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MRCOG Part one > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is the difference I cell biology of gram +ve be gram -ve bacteria.

A

Gram +ve bacteria have thicker peptidoglycan layer and lack outer lipopolysaccharide layer.

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2
Q

How does gram staining differentiate between gram +ve and gram -ve bateria

A

After staining with Crystal violet and fixation with iodine, a third decolouriser is added, this remove the stain from gram -ve bacteria but not gram +ve (remains purple).

A final stain is added (pink safranin) which is taken up by gram -ve

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3
Q

What other characteristic are used to classify bacteria?

A

Shape:
Cocci vs bacilli

Oxygen requirement:
Aerobes:
- oblique arobes
- faculatative aerobes

Anaerobes

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4
Q

List differences between exotoxins and endotoxins

A 
Exotoxins:
Gram +ve organisms
Proteins 
Heat labile and denatures by formaldehyde 
Neutralised by specific antibodies

Endotoxins
Gram -ve organisms
Lipopolysaccaride
Heat stable and not denatured by formaldehyde
Poorly antigenic (partially denaturalised by antibodies)

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5
Q

What group of bacteria is streptococcaeae?

What is the 2 main pathogens in this genera?

A

Gram +ve, facultative anaerobes that grow in pairs or chains, negative catalase test.

Streptococcus
Enterococcus

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6
Q

If diagnosed with skin infection cause by streptococcus pyogenes what should happen?

A

Highly infectious and virulent.

Isolated until 48 hours of IV Abx

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7
Q

Explains the causative agents of the types of necrotising fasciitis

A

NF type 1: poly microbial: anaerobes, gram negative, strep, staph

NF type 2: group A strep (+/- concomitant staph)

NB: group A: streptococcus pyogenes (Lancefield group A)

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8
Q

What complication can arise by invasive streptococcal disease if exotoxins are release?

A

Streptococcal pyogenic exotoxins A and C can result in toxic shock syndrome - systemic inflammation response + shock - few superficial signs

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9
Q

Group B strep is what bacteria!

Where is it’s normal habitat?

A

Streptococcus agalactiae (lancefield group B)

Normal flora of lower GI, throat and female genital tract.

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10
Q

What % of woman have GBS in pregnancy

What % of babies born to mothers colonised with GBS will become colonised through the passage of the vagina?

A

30% but may be intermittent

60%

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11
Q

What are the risk factors for the baby accruing GBS

A 
Preterm <37/40
PROM (more than 18 hours)
Intrapartun fever >38
Precious infant GBS
Heavy maternal carriage of GBS
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12
Q

How can GBS present in the infant?

A

Early (hours to days): bacteraemia, meningitis, pneumonia
Significant morbidity neurological sequela (blindness, mental retardation)

Late (not a quite during del): meningitis with bacreraemia

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13
Q

Incidence of neonatal GBS disease in UK

A

0.5/1000

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14
Q

Which mother receive prophylactic Abx intrapartun?

A

Previous GBS disease in baby or pregnancy
GBS found in vagina or urine during pregnancy
PROM (18 hours)
Preterm rupture of membrane in labour (<37/40)
Preterm rupture of membrane with known GBS (whether in labour or not)
Intrapartun temp

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15
Q

What is the Abx regime to prevent GBS in labour + if pen allergic

A

IV benpen 3g at onset of labour, 1.5G every 4 hours until delivary

IV clinda 900mg every 8 hours

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16
Q

Despite the gram stain and morphology of staphylococceae .

Result of catalase test

A

Gram +ve, facultative anaerobes in clusters (like grapes)

Catalase test +ve (note streptococci is negative)

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17
Q

How is the presence of extra cellular enzyme coagulate used to classify staph

A

The prsescence of coagulase allows the ability to clot plasma

S.aureus: coagulse +ve
Coag negative: S.epidermidis, s.haemolyticus

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18
Q

How to decolonisw those identified with MRSA

A

Chlorexidine gluconate: shampoo, body wash and mouthwash

Nasal mupirocin

19
Q

Do coagulase negative staphylococci cause serious infections

A

Mostly low pathogenicity,

Often contaminants of microbiological specimens

20
Q

What gram stain and morphology is listeria monocytogenes (most significant form of listeria)

A

Gram +ve, rod, facultative anaerobes

Beta haemolytic on blood agar

21
Q

Where is Listeria monocytogenes often found in the environment, how can it be contracted by humans?

A

Soil, water, faeces of many animals,
Can multiply in foods that have been refrigerated for long periods of time,

Food borne outbreaks: contaminated milk, soft cheese, undercooked meat, unwashed or uncooked vegetables

22
Q

What is the effect of listeria monocytogenes in pregnancy on the mother + baby

A

Mother: asymptotic or mild febrile illness with conjunctive, headache sore throat

Fetal infection can occur at any gestation
Early: spont abortion
Late: Preterm, stillbirth
Infant: neonatal listeriosis (less than 2 days), mortality 60%

23
Q

How if it Dx in mothers?

A

HVS, MSU, stool sample

AF may be discoloured or contain meconium

24
Q

If late neonatal listeriosis - where has the baby likely contracted the infection

A

Either during labour/passage through the birth canal or hospital cross infection

Mortality 10%

25
Q

Tx listeriosis

A

High dose IV Amox +/- gent - which dose not cross BBB

Resistant to ceph

26
Q

Gram stain and morphology of enterobacteriaceae

A

Gram -ve rods that ferment glucose

27
Q

2 main groups of enterobacteriaceae

A

Commensalism bacteria (e coil, klebsiella, enterobacter)

Overt pathogens produce virulence factors (Salmonella typhi (typhoid), shigella, campylobacter)

28
Q

What is the incidence of asymptotic bacteriuria in pregnancy? What is it associated with?

A

2-5%

May progress to pyelonephritis, increases risk of preterm birth

29
Q

E. Coli is common in which infections

A 
UTI
Biliary tract infection 
Neonatal sepsis and meningitis 
Wound infection 
Septicaemia - Abx should always cover gram -ves eg co amox or 3rd gen cephalosporin like ceftriaxone

If gram negative resistance suspected - gent or carbapenems

30
Q

What is the gram stain and morphology of neisseria.

Name 2 significant pathogens

A

Gram -ve, diplococus
Positive catalase and oxidase test

Neisseria meningitis and neisseria gonorrhoea

31
Q

CSF for nesiera meningitis

A

High protein
Low gluclose
High WBC predominant neutrophil

32
Q

Tx of Meningococcal infection

A

In community: IM benpen
Hospital: IV benpen or ceftriaxone
Contacts: ciprofloxaxine or rifampicin

33
Q

What bacteria cause syphilis and what it gram stain and morphology

A

Treponema pallium
No gram stain
Spiral rod shape

34
Q

Incidence of TB in UK and London

A

15/100,000 UK
50/100,000 London

3 x higher not born in UK

35
Q

Lab Dx of TB

Histology findings

A

Fluorochrome stain and confirmed Ziehl-Belsen stain (pink)

Caseating granulomas with multinucleate giant cells

36
Q

Tx of Tb and associates side effects of the drugs

A

Rifampicin: orange body secretion + hepatoxicity
Isoniazid: peripheral neuropathy, hepatoxicity
Pyrazinamide: arthralgia, raised Utica acid/gout
Ethambutol hydrochloride: renal inpairment

37
Q

What is a common predisposing factor for abdominal actinomyocosis

A 
Perforated appendicitis (65%)
Intrauterine device (30%)
38
Q

What are the 4 species of Protozoa which cause malaria.

Which causes the majority of deaths

A

P. Falciparum, P vivax, P ovale, P malariae

p falciparum

39
Q

What complications can be seen in severe malaria

A 
Severe anaemia 
Acute pulmonary oedema 
hypogylcaemia  
cerebral malaria 
consciousness and seizure 
DIC 
acute renal failure
40
Q

which Tx for malaria are CI in pregnancy?

A

Primaquine
Tetracycline
Doxycycline

41
Q

How long should women of childbearing age been advise to wait before seeking to conceive

A

mefloquine 3 months
doxycycline 1 week
atovaquone/proguanil hydrochloride 2 weel

42
Q

advise to pregnant women traveling to malra zones

A

Avoid
if unavidoabl clothing precautions, DEET >50%
Chloroquine and proguanil hydrochloride (need high dose folic acid) safe but not good at prevent p falciparum
If high p falciparumarea consider mefloquine in 2nd/3rd trimester

43
Q

In wound infection if patient is colonised with MRSA what Abx should be used?

A

Teicoplanin or doxycycline

44
Q

When should intraopertive prophylactic abx be given

A

At time of aeanaethetic age, no more than 30 mins prior to skin incision

MRCOG Part one (28 decks)

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