1. What is the correct storage for Sensi-Disc™?

Sensi-Disc™ discs should be stored at -20 to +8ºC upon receipt. If the laboratory refrigerator is opened and closed frequently, then only an amount that can be used within one week should be stored there. Some discs such as Β-lactams should preferably be kept frozen at -20ºC. Discs should be warmed to room temperature prior to use and promptly returned to the refrigerator after application of the discs is complete. Discard any discs left out overnight or discs that have been frequently removed from refrigeration (otherwise they must be tested for acceptable performance prior to use). Use oldest discs first and discard any expired discs.

2. My Sensi-Disc™ dispenser is broken. Can I have a replacement?

6 and 8-place dispensers are warranted for 1 year after purchase. If the dispenser is damaged before warranty expires, it can be replaced through Technical Services. 12-place dispensers are warranted for 2 years after purchase. At this time, all damaged 12-place dispensers are replaced by Technical Services regardless of age or warranty status.

3. Can we still use discs that have been out of refrigeration for a period of time?

We cannot guarantee the integrity of any product that has not been stored according to package insert instructions.

4. My zone sizes for QC are not in range. What could I be doing wrong?

Many factors can cause incorrect zones with recommended control organisms.

• storage of the discs (refer to question #1)
• the inoculum (equivalent to a 0.5 McFarland or prepared using the BBL™ Prompt) and should be used within 15 minutes of preparation
• the depth of the medium (about 4 mm)
• incubation time (20-24 hrs for Neisseria gonorrhoeae, S. pneumoniae and other streptococci, a full 24 hrs for Staphylococcus spp. for methicillin resistance and Enterococcus spp for vancomycin / nafcillin / oxacillin resistance, and 16-18 hrs for all others)
• atmosphere of incubation (Neisseria gonorrhoeae, Haemophilus sp., and streptococci should be incubated in an atmosphere enriched with 5% CO₂)
• spacing of discs:
• N. gonorrhoeae, Haemophilus influenzae and S. pneumoniae- no more than 9 discs per 150 mm plate or more than 4 discs per 100 mm plate
• penicillin and cephalosporin-disc centers 30 mm apart and no less than 10 mm from edge of plate
• all others-disc centers at least 24 mm apart
• temperature (35ºC)
• reading of zones (only read zones of complete inhibition).
• Use only pure cultures derived from specimens, preferably prior to initiation of antimicrobic therapy in the patient

5. Are Cefuroxime discs Cefuroxime axetil or Cefuroxime sodium?

BD Sensidiscs contain Cefuroxime sodium, which is the parenteral drug. Cefuroxime axetil is an oral drug.

6. How do you regenerate the desiccant in the Designer Dispenser?

The desiccant should be regenerated when the silica gel, as viewed through the window on top of the canister, has turned pink. Heat the canister in a 300ºF oven for approximately three hours to regenerate. Once cooled, the canister can be reused. The desiccant is capable of re-absorbing moisture to its full capacity.

CEFINASE QUESTIONS

1. What strain of Haemophilus influenzae is beta-lactamase positive?

Haemophilus influenzae ATCC 35540 is beta-lactamase positive.

2. Do we offer Nitrocefin in a powder form?

Yes. The following catalog numbers are for Nitrocefin powder: 296289-1.0 g and 297065-0.25 g
Formula:

mg of antimicrobic =

(mL of stock solution) (stock conc. µg/mL) Assay of antimicrobic powder, µg/mg

3. What is the chromogenic cephalosporin used in Cefinase™?

Nitrocefin.

4. What enzyme does Cefinase™ detect?

Cephalosporinase (Beta-Lactamase).

5. Can Cefinase™ be used to detect -lactamase in Enterococci?

Yes. Cefinase™ discs can be used with isolated colonies of Neisseria gonorrhoeae, Staphylococcus species, Haemophilus influenzae, enterococci and anaerobic bacteria.

6. My Cefinase™ discs are slightly pink before use. Is there something wrong with them?

Cefinase™ discs are normally tan/yellow in color. A pink color indicates that the cartridges were not stored properly. Our package insert states that after opening, the discs should be stored in an air-tight glass container containing a desiccant. They should be kept at -20 to +8ºC while not in use, and discarded 60 days after opening. The pink color results from exposure to moisture and these discs should be discarded.

TAXO QUESTIONS

1. Which Taxo disc is used for the presumptive identification of Streptococcus pneumoniae?

Taxo P Disc (Optochin). Each disc contains approximately 5.0 µg of ethyl hydrocuprein hydrochloride. Taxo P tests are presumptive. Positive tests should be followed with confirmatory tests. (See product insert for more detail). Note: Customers should not confuse these discs with the Sensi-Discs for Penicillin, which also have a P on them (Penicillin discs also have a 2 or a 10, ex. P10, P2).

2. Is any zone size obtained with the Taxo P Disc indicative of S. pneumoniae?

No. Zones of inhibition of 14 mm or more are formed with pure cultures of S. pneumoniae. Other organisms may show zone sizes less than 14 mm in diameter. A diameter between 6 and 14 mm is questionable for pneumococci and the strain should be presumptively identified as a pneumococcus only if it is bile soluble.

3. What is Optochin?

Optochin is a drug, which was used for pneumonia therapy before sulfonamides became available.

4. Which Taxo disc is used for the presumptive identification of Group A Streptococcus?

Taxo A Disc. This disc contains .04 units of Bacitracin. Note: These are not to be interchanged with the Bacitracin Sensi-discs that contain 2 and 10 units of Bacitracin.

5. Is differentiation by Taxo A disc a confirmatory test for Group A Strep?

No. The Taxo A disc is approximately 65% accurate. Organisms other than Group A Strep may exhibit bacitracin sensitivity (6% of group B and 7.5% of groups C & G streptococci may produce zones of inhibition/false positive result). A confirmatory test for Group A Strep is required.

MEDIA

1. Can Vancomycin Screen Agar be used for the testing of Vancomycin resistant Staphylococcus aureus?

No. Vancomycin Screen Agar contains 6g/mL of vancomycin. This medium has not been approved for testing vancomycin resistance in S. aureus, which is considered resistant at a different level of vancomycin.

2. How long do I incubate Oxacillin Screen Agar?

For Staphylococcus aureus, the plates should be incubated for a full 24 hrs.

3. What medium should I use for the sensitivity testing of Neisseria gonorrhoeae?

A GC II Agar Base with 1% defined growth supplement is the required medium for the disc diffusion susceptibility testing of Neisseria gonorrhoeae incubated in 5% CO₂. (Catalog # 221240; GC II Agar w/ IsoVitaleX™ Enrichment). Chocolate II Agar cannot be used because it contains hemoglobin in addition to the IsoVitaleX.
Note: Use no more than nine discs on a 150mm plate or four discs on a 100mm plate.

4. What medium should I use for the sensitivity testing of Streptococcus pneumoniae and other streptococci?

Meuller Hinton agar supplemented with 5% defibrinated sheep blood should be used for testing S. pneumoniae and other streptococci.

5. What type of medium should I use for sensitivity testing of Haemophilus species?

The zone diameter standards and the quality control limits apply only to tests with Haemophilus species using Haemophilus Test Medium (HTM).

ENTEROTUBE/OXIFERM

1. What is the glucose concentration in the glucose well of the Enterotube?

The glucose concentration is 20.0 g/L.