Evaluation of two broth disk methods for antibiotic susceptibility testing of anaerobes.

We evaluated the aerobic thioglycolate broth disk and the vaspar overlay broth disk methods for antibiotic susceptibility testing of 144 strains of anaerobes. For penicillin, carbenicillin, chloramphenicol, and metrionidazale, both broth disk methods yielded at least 95% agreement with results obtained by the National Committee for Clinical Laboratory Standards reference agar dilution procedure. For cefoxitin and clindamycin, the agreement was ca. 90%. Overall, the aerobic thioglycolate broth disk and vaspar overlay broth disk methods yielded agreements of 93.3 and 93%, respectively, with the National Committee for Clinical Laboratory Standards method.

Isolation of Campylobacter fetus subsp. jejuni from human fecal specimens by incubation at 35 and 42 degrees C.

Campylobacter strains were isolated from human stool specimens that were cultured on modified Skirrow agar and incubated at 35 and 42 degrees C. Incubation at 42 degrees C resulted in more isolates, increased colony numbers, and earlier isolation than was found at 35 degrees C.

Rapid laboratory identification of Neisseria gonorrhoeae by coagglutination.

We compared the Phadebact Gonococcus Test with conventional methods in identifying 210 strains of Neisseria gonorrhoeae. Of these, 209 strains were correctly identified (99.5%).

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).

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.

Aerobically incubated thioglycolate broth disk method for antibiotic susceptibility testing of anaerobes.

The anaerobic broth disk (AnBD) method of Wilkins and Thiel and a new modification, designated the thioglycolate broth disk method, were compared with an agar dilution technique. The thioglycolate broth disk method was incubated aerobically (AeTBD) or anaerobically (AnTBD). One hundred anaerobic bacteria representing 15 species were tested with clindamycin, chloramphenicol, erythromycin, penicillin, and tetracycline. Agreement of results by the two methods with minimal inhibitory concentration determinations were: AnBD, 95.2%; AnTBD, 91.5%; AeTBD, 94.5%. With clindamycin, chloramphenicol, and penicillin, the agreement of the AeTBD and agar dilution results was 100%, 100%, and 95%, respectively. Using the AeTBD method, only 1.1% of all tests gave false susceptible readings, whereas 4.4% gave false resistant readings. All susceptibility testing errors occurred with tetracycline, erythromycin, and, to a lesser extent, penicillin. For each method, the changes in designation of bacteria as being susceptible or resistant to an antibiotic between trials primarily involved strains with minimal inhibitory concentrations which were +/- one dilution of the respective breakpoint value. The same situation was true for most bacteria that yielded false resistant readings within each trial. False resistant readings with tetracycline were determined to be unrelated to excess cation content of test media. These results reaffirm the reliability of the AnBD method and indicate that the AeTBD modification is equally reliable. The greater convenience and lower cost of the AeTBD method should make possible more widespread performance of susceptibility testing for anaerobic bacteria in hospital laboratories.