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3.0 Microbiology > Screens > Flashcards

Screens Flashcards

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1
Q

Who undergoes screening and why these patients?

A

Dialysis patients, transplant patients, pre-operative patients

At a high risk of developing blood stream infections or are due to have an invasive surgical procedure and are therefore at risk of surgical site infections

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2
Q

What are the most important organisms in pre-operative cardiac patients transplant patienets

A

In pre-operatives = BHSs -> think endocarditis etc
In transplants think BHS + Candida

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3
Q

What are the specimen requirements for screens

A

MRSA: Amies Transport Swab
VRE: Amies Transport Swab
CRE: Copon faecal swabs for molecular detection

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4
Q

What is the most common sample for VREs?

A

Rectal swabs

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5
Q

What agar is used for VREs?

A

ChromID VRE agar

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6
Q

What are the two most common VREs?

A

E. faecium and E. faecalis

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7
Q

What is the main reason we reject VRE requests?

A

Positive VRE within the last 4 months

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8
Q

When would a patient undergo a VRE screen?

A

Any new inpatients are required to undergo a VRE screen

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9
Q

Who commonly gets VREs?

A

VREs are found in the gut of those who have undergone prolonged antibiotic usage

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10
Q

When are VREs a problem?

A

VREs usually colonise the gut of their host but only cause a problem if there is a gastric tear and the bacteria then spreads to the blood stream

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11
Q

How are VREs transmitted

A

Most transmission is through health care workers, contaminated hands from working with carriers
Spread also through contaminated medical equipment
Surfaces and equipment act as reservoirs in hospitals
VREs are viable on surfaces for days to weeks as bacteria are resistant to desiccation(drying) and extreme temperatures

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12
Q

What swabs do you require for an MRSA screen?

A

Multiple swabs are usually required but sometimes only 2 or 1 are sent up
Throat, nasal, groin swabs -> inoculated on the one MRSA agar plate

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13
Q

What does it mean for a pre-op patient to be MRSA positive?

A

This means they will be put at the end of the operating list to avoid spread to other patients

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14
Q

What is causing the increase in healthcare associated MRSA?

A

Increased number of immunocompromised patients mostly due to an increase in invasive procedures through advanced surgical operations and life support treatments

Failures in infection control measures such as hand washing prior to patient contact and removal of catheters

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15
Q

What is the principal mode of transmission of MRSA

A

Through colonised hands of hospital personnel

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16
Q

What are CPEs

A

Enterobacteriacea which have one or more specific families of genes that encode for the production of a carbapenemase

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17
Q

Give some examples of genes which produce carbapenemases

A

OXA-48
KPC
NDM
VIM
IMP

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18
Q

Who goes for CPE screening?

A

All new inpatients

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19
Q

How do we screen for CPE

A

Initially molecular testing for genes
Any positives are then cultured on blood agar for sensitivites

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20
Q

What plates are put up for transplant patients

A

Blood
Staph
MRSA
Candida
PDA

21
Q

How do you put up a transplant screen

A

Three swabs: throat, nasal, groin

Blood agar gets throat (looking for BHSs)
Staph plate gets nasal and groin (looking for S. aureus colonisation)
MRSA, Candida and PDA plates get all three swabs -> if the patient has any fungi or MRSA we want to find it hence why you use all three swabs

22
Q

What plates do pre-operative (cardiac) patients get

A

Blood, staph, MRSA

23
Q

How do you put up the plates for a pre-operative patient

A

Three swabs
Blood gets throat swab -> looking for BHS
Staph plate gets groin and nasal -> looking for S, aureus colonisation
MRSA gets all three swabs -> if patient has MRSA we want to catch it hence why we use all three

24
Q

What plates do dialysis patients get?

A

Staph and MRSA only

25
Q

How do you put up the plates for a dialysis patient

A

Nasal, groin and umbilicus swabs
Staph plate swabbed with all three
MRSA plate swabbed with all three

Want to catch any Staph or MRSA as it can quickly cause an infection to a dialysis patient

26
Q

What is the principle behind chromogenic media

A

The principle behind chromogenic media is that the target organisms are characterized by enzyme systems that metabolise the substrates to release the chromogen. The chromogen can then be visually detected by direct observation of a distinct colour change in the medium

27
Q

How should chromogenic media be stored

A

Chromogenic media are affected by light; therefore plates should be stored in the dark and not left in the light before or after inoculation.

28
Q

How does the ChromID VRE agar work

A

○ VRE brilliance chromagar
○ A chromogenic screening plate for the detection of Vancomycin Resistant Enterococci (VREs)
○ The medium provides presumptive identification of Enterococcus faecium and Enterococcus faecalis, direct from clinical samples in 24 hours
○ Plates are incubated for 18-24 hours at 37 degrees
○ Selective for VREs, differential for E. faecium and E. faecalis
○ We incubate the plates for 2 days before reading
○ Colonies are either purple, green or colourless
▪ Purple = E. faecium -> indigo-purple
▪ Green = E. faecalis -> greeny blue
Nothing else should grow but sometimes organism such as Staph might grow, these will be yelllow coloured

29
Q

What do we do with any VRE positives

A

Put up on blood agar
Need to be IDd first

30
Q

What would you do if there were purple and green colonies on a VRE chromagar

A

ID both organisms

31
Q

How long do we keep our cultures for prior to picking

A

1 week just in case

32
Q

Is the VRE chromagar diagnostic

A

NO
VRE chromagar only acts as a PID -> Confirmatory testing e.g. MALDI required

e.g. colonies could be a GNB etc

33
Q

What would you do if a purple colony grew on a VRE agar but it was IDd as a non enterococci organism

A

Repeat the ID
The colour produced by the colonies may be the agar itself reacting and not the bacteria -> false positive

34
Q

What is CxMRSA agar

A

○ A selective and differential chromogenic medium for the qualitative detection of a colonisation by methicillin resistant Staphylococcus
○ 18-24 hours of aerobic incubation at 35-37 degrees needed
○ Rose/Mauve = MRSA
○ Colourless or blue = Non Staph Methicillin resistant bacteria
○ No growth = Methicillin Susceptible Staph
○ We incubate for 1 day
○ MRSA grows as large pink colonies
Small pink colonies usually aren’t MRSA

35
Q

What do you do if query staph

A

Staphaurex agglutination

36
Q

What do we do with any MRSA agar positives

A

Put up on blood agar and send for sens
ID colony after sens

37
Q

What do we do a non S. aureus organism on the MRSA plate e.g. CNS

A

We dont culture these or send for sens

If its not MRSA we dont care

38
Q

What is the CxSA plates

A

Staph aureus plates
- A selective chromogenic culture medium for the qualitative direct detection, differentiation and presumptive identification of S. aureus
○ Pink/mauve = S. aureus
Colourless/blue/inhibited = Other bacteria

39
Q

For what patients do we put up a SA plate

A

Transplant
Pre-op
Dialysis

40
Q

What is the PDA plate

A

Potato dextrose agar

Versatile growing medium for bacteria and fungi
All your fungi will grow on this -> good for query aspergillus

41
Q

What is your Candida plate

A

Specific plat for Candida species
C. albicans = green
Non C. albicans = not green

42
Q

What gene is responsible for methicillin resistance in S. aureus?

A

mecA gene

43
Q

What infections does HCA MRSA tend to cause?

A

Pneumonia
Bacteremia
Invasive infections

44
Q

What are the six known VRE genetic phenotypes

A

VanA
VanB
VanC
VanD
VanE
VanF

45
Q

What VRE genes are found in E. faecalis and E. faecium

A

Van A and Van B

46
Q

Describe the resistance of VanA versus VanB

A

VanA are resistant to Vancomycin And Teicoplanin

VanB are resistant to Vancomycin But are susceptible to teicoplanin

47
Q

How do VREs gain their resistant

A

Either by mutation or by receipt of foreign genetic material

48
Q

What VRE strains are more often seen in hospital outbreaks

A

VanA and VanB

3.0 Microbiology (21 decks)

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