Screens Flashcards
Who undergoes screening and why these patients?
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
What are the most important organisms in pre-operative cardiac patients transplant patienets
In pre-operatives = BHSs -> think endocarditis etc
In transplants think BHS + Candida
What are the specimen requirements for screens
MRSA: Amies Transport Swab
VRE: Amies Transport Swab
CRE: Copon faecal swabs for molecular detection
What is the most common sample for VREs?
Rectal swabs
What agar is used for VREs?
ChromID VRE agar
What are the two most common VREs?
E. faecium and E. faecalis
What is the main reason we reject VRE requests?
Positive VRE within the last 4 months
When would a patient undergo a VRE screen?
Any new inpatients are required to undergo a VRE screen
Who commonly gets VREs?
VREs are found in the gut of those who have undergone prolonged antibiotic usage
When are VREs a problem?
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
How are VREs transmitted
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
What swabs do you require for an MRSA screen?
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
What does it mean for a pre-op patient to be MRSA positive?
This means they will be put at the end of the operating list to avoid spread to other patients
What is causing the increase in healthcare associated MRSA?
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
What is the principal mode of transmission of MRSA
Through colonised hands of hospital personnel
What are CPEs
Enterobacteriacea which have one or more specific families of genes that encode for the production of a carbapenemase
Give some examples of genes which produce carbapenemases
OXA-48
KPC
NDM
VIM
IMP
Who goes for CPE screening?
All new inpatients
How do we screen for CPE
Initially molecular testing for genes
Any positives are then cultured on blood agar for sensitivites
What plates are put up for transplant patients
Blood
Staph
MRSA
Candida
PDA
How do you put up a transplant screen
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
What plates do pre-operative (cardiac) patients get
Blood, staph, MRSA
How do you put up the plates for a pre-operative patient
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
What plates do dialysis patients get?
Staph and MRSA only
How do you put up the plates for a dialysis patient
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
What is the principle behind chromogenic media
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
How should chromogenic media be stored
Chromogenic media are affected by light; therefore plates should be stored in the dark and not left in the light before or after inoculation.
How does the ChromID VRE agar work
○ 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
What do we do with any VRE positives
Put up on blood agar
Need to be IDd first
What would you do if there were purple and green colonies on a VRE chromagar
ID both organisms
How long do we keep our cultures for prior to picking
1 week just in case
Is the VRE chromagar diagnostic
NO
VRE chromagar only acts as a PID -> Confirmatory testing e.g. MALDI required
e.g. colonies could be a GNB etc
What would you do if a purple colony grew on a VRE agar but it was IDd as a non enterococci organism
Repeat the ID
The colour produced by the colonies may be the agar itself reacting and not the bacteria -> false positive
What is CxMRSA agar
○ 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
What do you do if query staph
Staphaurex agglutination
What do we do with any MRSA agar positives
Put up on blood agar and send for sens
ID colony after sens
What do we do a non S. aureus organism on the MRSA plate e.g. CNS
We dont culture these or send for sens
If its not MRSA we dont care
What is the CxSA plates
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
For what patients do we put up a SA plate
Transplant
Pre-op
Dialysis
What is the PDA plate
Potato dextrose agar
Versatile growing medium for bacteria and fungi
All your fungi will grow on this -> good for query aspergillus
What is your Candida plate
Specific plat for Candida species
C. albicans = green
Non C. albicans = not green
What gene is responsible for methicillin resistance in S. aureus?
mecA gene
What infections does HCA MRSA tend to cause?
Pneumonia
Bacteremia
Invasive infections
What are the six known VRE genetic phenotypes
VanA
VanB
VanC
VanD
VanE
VanF
What VRE genes are found in E. faecalis and E. faecium
Van A and Van B
Describe the resistance of VanA versus VanB
VanA are resistant to Vancomycin And Teicoplanin
VanB are resistant to Vancomycin But are susceptible to teicoplanin
How do VREs gain their resistant
Either by mutation or by receipt of foreign genetic material
What VRE strains are more often seen in hospital outbreaks
VanA and VanB
