Screens

Question 1

Who undergoes screening and why these patients?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What are the specimen requirements for screens

Answer 3

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

Question 4

What is the most common sample for VREs?

Answer 4

Rectal swabs

Question 5

What agar is used for VREs?

Answer 5

ChromID VRE agar

Question 6

What are the two most common VREs?

Answer 6

E. faecium and E. faecalis

Question 7

What is the main reason we reject VRE requests?

Answer 7

Positive VRE within the last 4 months

Question 8

When would a patient undergo a VRE screen?

Answer 8

Any new inpatients are required to undergo a VRE screen

Question 9

Who commonly gets VREs?

Answer 9

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

Question 10

When are VREs a problem?

Answer 10

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

Question 11

How are VREs transmitted

Answer 11

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

Question 12

What swabs do you require for an MRSA screen?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What is causing the increase in healthcare associated MRSA?

Answer 14

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

Question 15

What is the principal mode of transmission of MRSA

Answer 15

Through colonised hands of hospital personnel

Question 16

What are CPEs

Answer 16

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

Question 17

Give some examples of genes which produce carbapenemases

Answer 17

OXA-48
KPC
NDM
VIM
IMP

Question 18

Who goes for CPE screening?

Answer 18

All new inpatients

Question 19

How do we screen for CPE

Answer 19

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

Question 20

What plates are put up for transplant patients

Answer 20

Blood
Staph
MRSA
Candida
PDA

Question 21

How do you put up a transplant screen

Answer 21

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

Question 22

What plates do pre-operative (cardiac) patients get

Answer 22

Blood, staph, MRSA

Question 23

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

Answer 23

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

Question 24

What plates do dialysis patients get?

Answer 24

Staph and MRSA only

Question 25

How do you put up the plates for a dialysis patient

Answer 25

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

Question 26

What is the principle behind chromogenic media

Answer 26

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

Question 27

How should chromogenic media be stored

Answer 27

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

Question 28

How does the ChromID VRE agar work

Answer 28

○ 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

Question 29

What do we do with any VRE positives

Answer 29

Put up on blood agar Need to be IDd first

Question 30

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

Answer 30

ID both organisms

Question 31

How long do we keep our cultures for prior to picking

Answer 31

1 week just in case

Question 32

Is the VRE chromagar diagnostic

Answer 32

NO VRE chromagar only acts as a PID -> Confirmatory testing e.g. MALDI required e.g. colonies could be a GNB etc

Question 33

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

Answer 33

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

Question 34

What is CxMRSA agar

Answer 34

○ 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

Question 35

What do you do if query staph

Answer 35

Staphaurex agglutination

Question 36

What do we do with any MRSA agar positives

Answer 36

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

Question 37

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

Answer 37

We dont culture these or send for sens If its not MRSA we dont care

Question 38

What is the CxSA plates

Answer 38

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

Question 39

For what patients do we put up a SA plate

Answer 39

Transplant Pre-op Dialysis

Question 40

What is the PDA plate

Answer 40

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

Question 41

What is your Candida plate

Answer 41

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

Question 42

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

Answer 42

mecA gene

Question 43

What infections does HCA MRSA tend to cause?

Answer 43

Pneumonia Bacteremia Invasive infections

Question 44

What are the six known VRE genetic phenotypes

Answer 44

VanA VanB VanC VanD VanE VanF

Question 45

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

Answer 45

Van A and Van B

Question 46

Describe the resistance of VanA versus VanB

Answer 46

VanA are resistant to Vancomycin And Teicoplanin VanB are resistant to Vancomycin But are susceptible to teicoplanin

Question 47

How do VREs gain their resistant

Answer 47

Either by mutation or by receipt of foreign genetic material

Question 48

What VRE strains are more often seen in hospital outbreaks

Answer 48

VanA and VanB