Luba Stoakes

Prospective Comparison of a New Chromogenic Medium, MRSASelect, to CHROMagar MRSA and Mannitol-Salt Medium Supplemented with Oxacillin or Cefoxitin for Detection of Methicillin-Resistant Staphylococcus aureus

ABSTRACT MRSASelect agar was compared to CHROMagar, mannitol-salt agar with oxacillin, and mannitol-salt agar with cefoxitin (MSA-CFOX) for the isolation of methicillin-resistant Staphylococcus aureus (MRSA). The sensitivities and specificities were 97.3% and 99.8%, 82.9% and 99.1%, 80.2% and 79%, and 99.1% and 84.8%, respectively. MSA-CFOX and MRSASelect had a high sensitivity. MRSASelect, however, was more specific and proved to be a more reliable and rapid medium for the detection of MRSA.

Detection of Methicillin Resistance in Primary Blood Culture Isolates of Coagulase-Negative Staphylococci by PCR, Slide Agglutination, Disk Diffusion, and a Commercial Method

ABSTRACT The methicillin resistance of 363 coagulase-negative staphylococci isolated from blood cultures was determined by a slide latex agglutination (LA) test for penicillin-binding protein 2a (PBP 2a), the presence of the mecA gene by PCR, disk diffusion, and Vitek. LA was performed on primary cultures, and PBP 2a expression was induced by placing an oxacillin disk in the primary inoculum. Compared to the PCR results, LA was the most sensitive and specific in the detection of methicillin resistance. Without induction, LA failed to detect 50% of mecA-positive strains grown on two different media.

A new approach for presumptive identification of clinically important streptococci.

Several tests, bacitracin, CAMP, pyroglutamic acid-B-naphthylamide test (PYR test), bile aesculin hydrolysis, salt tolerance and pigment production tests were evaluated for their reliability and speed in presumptive identification of streptococci. Bacitracin correctly identified all of the group A streptococci but 5% of other beta haemolytic streptococci were misidentified as group A. The PYR reaction was just as sensitive but more specific for group A streptococci and the results were available within 2-3 h. The PYR reaction also effectively differentiated between enterococcal and non-enterococcal group D streptococci. Both the salt tolerance test and the PYR reaction misidentified bile aesculin positive non-group D streptococci as non-enterococcal group D streptococci. Pigment production by group B streptococci was more reliable than the CAMP test for identifying group B streptococci. The combination of PYR, bile aesculin and pigment production allowed rapid differentiation of several medically important groups of streptococci.

Comparison of susceptibility results of anaerobic organisms determined by agar dilution method and Sceptor Anaerobe MIC/ID Micro Broth Dilution Panels.

A commercial broth microdilution system (Sceptor Anaerobe MIC/ID, BBL) for susceptibility testing of anaerobic bacteria was compared to a reference agar dilution system. Of the 172 organisms tested, only 7% failed to grow sufficiently for testing in the Sceptor system. In 1,590 antibiotic/organism combinations, 86.7% of the Sceptor results were identical or within one doubling dilution of the reference system. In 91.9% of the cases, interpretation of the results was same in both systems. Two hundred and twelve MIC values, however, differ by greater than or equal to 2 log2 dilution from the reference system. Due to this reduced correlation in the actual MIC values with the reference results, further studies are warranted before the Sceptor system can be recommended for routine use.

Comparison of RapID-ANA and minitek with a conventional method for biochemical identification of anaerobes

Two micromethods for the identification of anaerobes, one requiring growth (Minitek) and one nongrowth dependent (RapID-ANA), were compared with a conventional identification culture system. For 222 clinical isolates, RapID-ANA agreed with PRAS in 187 (84%) and Minitek agreed for only 170 strains (76%). Both systems identified common isolates well, but encountered some difficulty in identifying less common clostridia and Gram-negative bacilli. Although adequate for most strains, the results from both systems should be interpreted with caution, particularly for less frequently isolated species.

Supplement Peptone Agar — A Simple Carbohydrate Degradation Plate Medium for the Identification of Neisseria Species

A carbohydrate degradation medium was developed for the detection of acid production by Neisseria species and Branhamella catarrhalis. A total of 223 clinical isolates were identified by Supplemented Peptone Agar and the results were compared with those of Cystine Trypticase Agar. Supplemented Peptone Agar and Cystine Trypticase Agar correctly identified 99.1% and 93.7% of the total strains respectively within 24 h. With Cystine Trypticase Agar method another 4% of the isolates could be identified but required an additional 24 h of incubation.