Penicillin susceptibility of Streptococcus pneumoniae in 1978. Screening for resistance by disk testing.

Recently, strains of Streptococcus pneumoniae with greatly increased resistance to penicillin (minimal inhibitory concentrations or MICs, 1--8 microgram/ml) were recovered in cultures of blood from patients in South Africa and from one in Minnesota who had serious pneumococcal infections. The authors undertook a study to determine whether these resistant strains have become prevalent in their locale. Between January and July 1978, the laboratories of hospitals serving the greater Madison, Wisconsin, area (population 200,000) contributed 243 pneumococcal isolates for susceptibility testing by an agar dilution technic. Strains with greatly increased resistance (MICs greater than or equal to 1.0 microgram/ml) were not found; only six strains (2.4%) had relative resistance to penicillin (MICs .125--.50 microgram/ml), a range of susceptibility that has been associated with inconsistent clinical responses to treatment with penicillin. Overall, the susceptibility patterns of these 243 isolates are similar to those reported from other centers in North America over the past 30 years. Routine susceptibility testing of pneumococci by hospital laboratories in our area does not appear to be necessary now, but laboratories are advised to screen blood and spinal fluid isolates by a disk-diffusion method. Studies of these 243 isolates and seven South African multiply-resistant strains using a modified Kirby-Bauer technic, showed that a zone of inhibition less than 35 mm around a 10-unit penicillin disk, or better, less than 17 mm around a 1-microgram oxacillin disk, correlates strongly (P less than .001) with resistance to penicillin (MIC greater than or equal to .1 microgram/ml).

The use of CIE for the detection of Clostridium difficile toxin in stool filtrates: laboratory and clinical correlation.

Two CIE procedures (CIE-1, CIE-2) for the detection of Clostridium difficile in diarrheal stools were evaluated by comparison to cytotoxin assay and culture results and by comparison to a clinical likelihood of C. difficile-induced diarrhea. Using a combination of toxin assay and culture results for reference, the CIE-1 and CIE-2 procedures had sensitivities of 33% and 47%, specificities of 89% and 91%, and positive predictive values of 42% and 54%, respectively. Using clinical likelihood for reference, the best results were obtained by the CIE-2 method, which yielded a positive predictive value of 77%. Neither CIE procedure provided an acceptable sensitivity for the detection of C. difficile in stools.

Evaluation of C. diff.-CUBE test for detection of Clostridium difficile-associated diarrhea.

The toxin B assay was used to evaluate C. diff.-CUBE, a new dot-immunobinding assay (DIA) for the laboratory diagnosis of Clostridium difficile-associated diarrhea. The widely used latex agglutination test was also included for comparison. Stools from 100 patients suspected of having C. difficile-associated diarrhea were tested. The toxin B assay, latex agglutination, and DIA tests were positive for 12%, 9%, and 22% of the specimens, respectively. The sensitivity, specificity, and positive and negative predictive values of the DIA test were 67%, 84%, 36%, and 95%, respectively, compared with the toxin B assay. The specificity (98%) and positive predictive value (78%) for the latex agglutination test were significantly higher than those of the DIA test. Of 13 specimens solely positive by the DIA test, 11 were cultured and none were positive. Clinical assessment supported only two of the 13 positive DIA results. When clinical assessment was included in the analysis, the DIA positive predictive value rose to 45%. Although the sensitivity and negative predictive values of the DIA test are comparable to the latex agglutination test, the low specificity and positive predictive values of the DIA test make it an inappropriate method to use for screening in a population with a low prevalence of true positives.

Recovery of anaerobic, facultative, and aerobic bacteria from clinical specimens in three anaerobic transport systems.

With aspirated specimens from clinical infections, we evaluated the recovery of anaerobic, aerobic, and facultative bacteria in three widely used transport systems: (i) aspirated fluid in a gassed-out tube (FGT), (ii) swab in modified Cary and Blair transport medium (SCB), and (iii) swab in a gassed-out tube (SGT). Transport tubes were held at 25 degrees C and semiquantitatively sampled at 0, 2, 24, and 48 h. Twenty-five clinical specimens yielded 75 anaerobic strains and 43 isolates of facultative and 3 of aerobic bacteria. Only one anaerobic isolate was not recovered in the first 24 h, and then, only in the SGT. At 48 h, 73 anaerobic strains (97%) were recovered in the FGT, 69 (92%) in the SCB, and 64 (85%) in the SGT. Two problems hindered the recovery of anaerobes in the SCB and SGT systems: first die-off of organisms, as evidenced by a decrease in colony-forming units of 20 strains (27%) in the SCB and 25 strains (33%) in the SGT, as compared with 7 strains (9%) in the FGT, over 48 h; and second, overgrowth of facultative bacteria, more frequent with SCB and SGT. The FGT method was clearly superior at 48 h to the SCB and SGT systems in this study and is recommended as the preferred method for transporting specimens for anaerobic culture.

Evaluation of the phadebact and bactigen reagents for detection of Neisseria meningitidis in cerebrospinal fluid.

The Phadebact and Bactigen reagents were evaluated for detection of Neisseria meningitidis in cerebrospinal fluids. The Bactigen test yielded stronger agglutination reactions from clinical specimens and was significantly more sensitive when used with whole-cell suspensions and purified antigens.