bsac rolling programme for devising acceptable limits for control strains jenny andrews the bsac...

BSAC rolling programme for devising acceptable limits for

control strainsJenny AndrewsJenny Andrews

The BSAC Standardized Method The BSAC Standardized Method Development CentreDevelopment Centre

Acceptable limits for control strains

Used by diagnostic laboratories to monitor the Used by diagnostic laboratories to monitor the performance of testing.performance of testing.

There are gaps in the tables that need filling.There are gaps in the tables that need filling. At present At present S. aureusS. aureus is used to control testing of is used to control testing of

fastidious organisms and this may not be ideal fastidious organisms and this may not be ideal because the growth requirements of fastidious because the growth requirements of fastidious organisms are different to that of staphylococci.organisms are different to that of staphylococci.

Findings from a previous BSAC study

Confirmed that agar poured `in-house’ to a depth Confirmed that agar poured `in-house’ to a depth between 3.5-4.5 mm, and pre-poured plates from between 3.5-4.5 mm, and pre-poured plates from Oxoid and bioMerieux gave acceptable results by Oxoid and bioMerieux gave acceptable results by BSAC methodology.BSAC methodology.

When combined data from these plates was used When combined data from these plates was used to calculate the acceptable limits for all of the to calculate the acceptable limits for all of the antibiotic/strain combinations tested, the ranges antibiotic/strain combinations tested, the ranges were similar to those found in previous `field were similar to those found in previous `field studies’. So it was proposed that this procedure studies’. So it was proposed that this procedure could be used to fill the gaps in the tables.could be used to fill the gaps in the tables.

Programme design

After discussion the Working Party decided After discussion the Working Party decided that it would be prudent if acceptable limits that it would be prudent if acceptable limits were calculated using data from several were calculated using data from several laboratories rather than one centre.laboratories rather than one centre.

However, SMDC acceptable ranges could However, SMDC acceptable ranges could be used as a guide for comparison.be used as a guide for comparison.

Request for help

Needed the help of laboratories using the BSAC Needed the help of laboratories using the BSAC method, but unsure if laboratories would take part. method, but unsure if laboratories would take part.

Letter sent to known users of the BSAC methodLetter sent to known users of the BSAC method Asking if they would take part and select from a Asking if they would take part and select from a

list of antibiotic/strain combinations those they list of antibiotic/strain combinations those they were prepared to testwere prepared to test

20 laboratories agreed to take part20 laboratories agreed to take part

QC Study

SMDC calculated acceptable limits by SMDC calculated acceptable limits by testing discs 40 times each on ISA poured testing discs 40 times each on ISA poured to a depth of 3.5, 4 & 4.5mm and pre-to a depth of 3.5, 4 & 4.5mm and pre-poured plates from Oxoid & bioMerieux. poured plates from Oxoid & bioMerieux. 200 observations200 observations

The participating laboratories were asked to The participating laboratories were asked to test discs (supplied by SMDC) 5 times on test discs (supplied by SMDC) 5 times on 10 separate occasions. 250 observations.10 separate occasions. 250 observations.

How are the acceptable limits for the control strains calculated?

Obtain at least 200 zone diameters for the Obtain at least 200 zone diameters for the strain/antibiotic disc combination.strain/antibiotic disc combination.

Determine the number of observations at each Determine the number of observations at each zone diameter.zone diameter.

Calculate the cumulative % at each zone diameter.Calculate the cumulative % at each zone diameter. Construct a graph of cumulative % versus zone Construct a graph of cumulative % versus zone

diameter.diameter. Read off the zones equivalent to 2.5% & 97.5% of Read off the zones equivalent to 2.5% & 97.5% of

observations to give the acceptable range.observations to give the acceptable range.

Plot of cumulative % v zone diameter

05

101520253035404550556065707580859095

100

25 26 27 28 29 30 31 32 33 34

Zone diameter (mm)

Cum

ulat

ive

%

E. coli ATCC 25922

CT2 (Chester MS)CT2 (Chester MS) CT6 (Oxoid)CT6 (Oxoid) CT1 (Oxoid)CT1 (Oxoid) CT25 (Oxoid)CT25 (Oxoid) CT24 (In-house)CT24 (In-house)

Pip/tazoPip/tazo PiperacillinPiperacillin Nalidixic acidNalidixic acid LevofloxacinLevofloxacin AmpicillinAmpicillin

E. coli NCTC 10418

CT4 (Taunton PHL)CT4 (Taunton PHL) CT8 (In-house)CT8 (In-house) CT14 (bioMerieux)CT14 (bioMerieux) CT12 (Chester PHL)CT12 (Chester PHL) CT 20 (Oxoid)CT 20 (Oxoid)

Pip/tazoPip/tazo PiperacillinPiperacillin ChloramphenicolChloramphenicol ColistinColistin

E. faecalis ATCC 29212

CT17 (Oxoid)CT17 (Oxoid) CT15 (E&O)CT15 (E&O) CT16 (Taunton MS)CT16 (Taunton MS) CT29 (bioMerieux)CT29 (bioMerieux) CT10 (Leeds PHL)CT10 (Leeds PHL)

Pip/tazoPip/tazo MeropenemMeropenem ImipenemImipenem LinezolidLinezolid AzithromycinAzithromycin

E. coli ATCC 25922: Ampicillin 25 ug Participant zones compared with

SMDC acceptable limits

19

20

21

22

23

24

25

26

27

28

29

30

31

Zone

dia

met

er (m

m)

CT25 (Oxoid) CT1 (Oxoid) CT24 (In-house) CT6 (Oxoid) CT2 (Chester MS)

Observations

E. coli NCTC 10418 : Chloramphenicol 10 ug Participant zones compared with


18192021222324252627282930313233343536

Zone

dia

met

er (m

m)

CT4 (Taunton PHL) CT8 (In-house) CT20 (Oxoid) CT14 (bioMerieux) CT12 (Chester PHL)

Observations

E. faecalis ATCC 29212: Azithromycin 15 ug Participant zones compared with


10

11

12

1314

15

16

17

18

1920

21

22

23

Zone

dia

met

er (m

m)

CT17 (Oxoid) CT15 (E&O) CT16 (Taunton MS) CT29 (bioMerieux) CT10 (Leeds PHL)

Observations

E. faecalis ATCC 29212: Linezolid 10 ug Participant zones compared with


19202122232425262728293031323334

Zone

dia

met

er (m

m)

CT17 (Oxoid) CT15 (E&O) CT16 (Taunton MS) CT29 (bioMerieux) CT10 (Leeds PHL)

Observations

E. faecalis ATCC 29212: Pip/tazo 85ug disc

Participant zones compared with SMDC acceptable limits

23

24

25

26

27

28

29

30

31

32

33

34

Zon

e d

iam

ete

r (m

m)

CT17 (Oxoid) CT15(E&O) CT16 (Taunton MS) CT29 (bioMerieux) CT10 (Leeds PHLS)

Observations

E. faecalis ATCC 29212: Pip/tazo 85ugAcceptable limits using data from 5 centres

(SMDC 27-32 mm)

23

24

25

26

27

28

29

30

31

32

33

34

Zone

dia

met

er (m

m)

CT17 (Oxoid) CT15(E&O) CT16 (Taunton ) CT29 (bioMerieux)

Observations

CT10 (Leeds PHL)

E. coli NCTC 10418: Centres where zone diameters outside the SMDC acceptable ranges

AntibioticAntibiotic CT4CT4

(Taunton (Taunton PHL)PHL)

CT8CT8

(Oxoid)(Oxoid)

CT20CT20

(bioMerieux(bioMerieux))

CT14CT14

(Oxoid)(Oxoid)

CT12CT12

(Chester (Chester PHL)PHL)

Pip/tazoPip/tazo

85ug85ug

XX

Too largeToo large

PiperacillinPiperacillin

75ug75ug

XX

Too largeToo large

ChloramphenicolChloramphenicol

10ug10ug

XX

Too largeToo large

ColistinColistin

25ug25ug

Summary of acceptable ranges (mm) for E. coli NCTC 10418

AntibioticAntibiotic SMDCSMDC

(mm)(mm)

5 centres5 centres

(mm)(mm)

4 centres*4 centres*

(mm)(mm)

SMDC &SMDC &

4 centres*4 centres*ChloramphenicolChloramphenicol

10ug10ug23-2723-27 20-2820-28 20-2620-26 21-2721-27


75ug75ug31-3531-35 30-3630-36 29-3529-35 30-3530-35

Pip/tazoPip/tazo

85ug85ug31-3431-34 30-3630-36 29-3429-34 30-3530-35

ColistinColistin

25ug25ug15-1915-19 16-2016-20 16-1916-19 15-1915-19

* Excluding CT12

E. coli ATCC 25922: Centres where zone diameters outside the SMDC acceptable ranges


(Oxoid)(Oxoid)

CT11CT11

(Oxoid)(Oxoid)

CT24CT24

(Chester)(Chester)

CT6CT6

(Oxoid)(Oxoid)

CT2CT2

(Oxoid)(Oxoid)

Pip/tazoPip/tazo

85ug85ug

XX

Too largeToo large

XX

Too largeToo large

XX

Too largeToo large

XX

Too largeToo large

XX

Too largeToo large


75ug75ug

XX

Too largeToo large

XX

Too largeToo large

XX

Too largeToo large

Nalidixic acidNalidixic acid

30ug30ug

XX

Too largeToo large

XX

Too largeToo large

XX

Too largeToo large

LevofloxacinLevofloxacin

1ug1ug

XX

Too largeToo large

XX

Too largeToo large

AmpicillinAmpicillin

25ug25ug

XX

Too largeToo large

NB. NCTC E. coli: CT12 (Chester MS) also large zones

Summary of acceptable ranges (mm) for E. coli ATCC 25922


(mm)(mm)

5 centres5 centres

(mm)(mm)


(mm)(mm)

SMDC &SMDC &



75ug75ug

26-3126-31 29-3429-34 28-3228-32 27-3227-32

Pip/tazoPip/tazo

85ug85ug

26-3026-30 28-3228-32 28-3228-32 26-3126-31

Nalidixic acidNalidixic acid

30ug30ug

26-3026-30 26-3226-32 26-3126-31 26-3226-32

LevofloxacinLevofloxacin

1ug1ug

29-3329-33 28-3628-36 28-3428-34 28-3428-34

AmpicillinAmpicillin

25ug25ug

20-2620-26 22-2822-28 22-2822-28 21-2821-28

* Excluding CT24 & CT6

E. Faecalis ATCC 29212: Centres where zone diameters outside the SMDC acceptable ranges


(Oxoid)(Oxoid)

CT15CT15

(E&O)(E&O)

CT16CT16

(Taunton)(Taunton)

CT28CT28(bioMerieux)(bioMerieux)

CT10CT10

(Leeds)(Leeds)

Pip/tazoPip/tazo

85ug85ug

XX

Too largeToo large

XX

Too smallToo small

MeropenemMeropenem

10ug10ug

XX

Too largeToo large

XX

Too smallToo small

XX

Too smallToo small

ImipenemImipenem

10ug10ug

XX

Too smallToo small

LinezolidLinezolid

10ug10ug

XX

Too largeToo large

XX

Too smallToo small

AzithromycinAzithromycin

15ug15ug

XX

Too largeToo large

XX

Too smallToo small

XX

Too largeToo large

Summary of acceptable ranges (mm) for E. faecalis ATCC 29212


(mm)(mm)

5 centres5 centres

(mm)(mm)


(mm)(mm)

SMDC &SMDC &


Pip/tazoPip/tazo

85ug85ug

27-3227-32 24-3224-32 26-3126-31 26-3226-32

MeropenemMeropenem

10ug10ug

24-2824-28 19-2819-28 21-2721-27 22-2822-28

LinezolidLinezolid

10ug10ug

25-3025-30 22-3122-31 24-2824-28 24-2924-29

ImipenemImipenem

10ug10ug

28-3328-33 25-3225-32 28-3228-32 28-3228-32

AzithromycinAzithromycin

15ug15ug

15-2015-20 11-2111-21 14-2114-21 15-2115-21

*Excluding CT15 & CT17

Conclusions

Reasonable to exclude data from the Reasonable to exclude data from the analysis that is outside the acceptable limits analysis that is outside the acceptable limits generated by SMDC or that is different to generated by SMDC or that is different to the other laboratoriesthe other laboratories

Conclusions

Very worthwhile exercise and the rolling Very worthwhile exercise and the rolling programme is to be continued including programme is to be continued including looking at fastidious controls.looking at fastidious controls.

In future studies control strains will be In future studies control strains will be provided.provided.

Laboratories asked to test `once daily’ as Laboratories asked to test `once daily’ as this reflects `real life’. this reflects `real life’.

Future meeting

Intend to have a meeting with the Intend to have a meeting with the participating laboratoriesparticipating laboratories

Need to look at data from centres where Need to look at data from centres where zones are generally different from SMDC & zones are generally different from SMDC & other participants other participants

Acknowledgments QE Hospital, Woolwich, LondonQE Hospital, Woolwich, London Department of Clinical Medicine, ManchesterDepartment of Clinical Medicine, Manchester Truro PHLSTruro PHLS Rotherham DGHRotherham DGH Craigavon Area HospitalCraigavon Area Hospital Addenbrookes Hospital, CambridgeAddenbrookes Hospital, Cambridge Singleton PHL, SwanseaSingleton PHL, Swansea University Hospital, BirminghamUniversity Hospital, Birmingham Bedford HospitalBedford Hospital Bristol Royal InfirmaryBristol Royal Infirmary QE2, HertfordshireQE2, Hertfordshire UCL Hospitals, LondonUCL Hospitals, London Russells Hall Hospital, West MidlandsRussells Hall Hospital, West Midlands Manchester Royal InfirmaryManchester Royal Infirmary New Cross Hospital, WolverhamptonNew Cross Hospital, Wolverhampton

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