Gas-liquid chromatography of cellular fatty acids for identification of staphylococci.

A commercially available, computer-assisted microbial identification system (MIS) employs gas-liquid chromatographic analyses of bacterial fatty acids. The MIS was used to identify 470 isolates of Staphylococcus species. The accuracy of the MIS was compared with the accuracies of conventional methods. There was a complete agreement between the MIS and conventional methods in the identification of 413 (87.8%) strains. For 36 of 45 misidentified strains, the correct identification was listed by the MIS as a choice but not as the first choice. Twelve strains could not be matched. All strains of Staphylococcus cohnii, S. epidermidis, S. intermedius, S. lugdunensis, S. schleiferi, S. sciuri, S. simulans, and S. xylosus were correctly identified. Two species, S. hominis and S. saprophyticus, accounted for 52.6% (30 of 57) of the misidentifications. Seventy-eight organisms were retested. Identification of 73 organisms remained unchanged, and for five organisms, the second choice became first and vice versa. The overall performance of the MIS is acceptable, and the system can be used as an alternate identification method for staphylococci.

Comparison of culture, cytotoxin assay and two EIA tests with clinical diagnosis of Clostridium difficile-associated diarrhea.

OBJECTIVE: The most common etiology of infectious diarrhea in hospitalized patients is Clostridium difficile. No single laboratory test yields a definitive diagnosis. Four methods were evaluated for their sensitivity and specificity in patients who had clinically defined C difficile-associated diarrhea. METHODS: Clinical criteria for C difficile-associated diarrhea were defined. All adult in-hospital patients whose stools were tested for C difficile were prospectively followed. Stools were examined with culture on a selective medium, a commercial cytotoxicity assay (cta), and two commercially available enzyme immunoassays (eias) for toxin A (Meridian) and toxin AB (cbc). RESULTS: During the study period 235 stool specimens from 185 patients were tested. Fifty-one patients were positive for C difficile or its markers, cta was most sensitive (80%), whereas cbc-eia was most specific (98%). Differences in the sensitivities of cta and Meridian-eia were minor (80% versus 73.3%) and they were equally specific (95.5%). CONCLUSIONS: The sensitivity and specificity of eia for toxin A is similar to other tests. However, due to rapidity and ease of performance, it may be a more practical test for the diagnosis of C difficile-associated diarrhea, especially if the cytotoxin assay is not available.

Comparison of the E-test and reference agar dilution method for susceptibility of gram-negative anaerobic organisms.

Minimal inhibitory concentrations (MICs) of clindamycin, cefoxitin, imipenem, and metronidazole were determined by the E-Test and a reference agar dilution method for 92 gram-negative anaerobic organisms. For 335 MIC pairs, the agreement between the two systems was 80.1%; 60 (17.9%) differed by two or more twofold dilutions. The best agreement was observed with imipenem (91.7%) and the poorest with cefoxitin (67%). With the E-Test (PDM Epsilometer for antimicrobial susceptibility testing [AB Bodisk, Solna, Sweden]), MICs for individual organisms are simple to achieve, although for certain antibiotics discrepancies with the reference method are unacceptable.

Frequency of ocular chlamydial infection among young adults.

Young adults are at particular risk for Chlamydia trachomatis infection. To determine whether there is a high rate of asymptomatic ocular chlamydial infection in this population, 131 eyes from 72 patients aged 18 to 30 years with no symptoms of conjunctivitis were tested for C. trachomatis by means of McCoy cell culture and a direct enzyme immunoassay. In addition, 51 of the patients underwent serologic testing to detect systemic chlamydial disease. Ocular chlamydial infection was not found in any of the patients, including the 26 with a positive result of serologic testing. We conclude that routine screening of young adults for ocular chlamydial infection would be of no benefit in detecting systemic chlamydial infection and its sequelae.

Evaluation of MicroScan Rapid Pos Combo panels for identification of staphylococci.

MicroScan Rapid Pos Combo panels (Baxter Diagnostics, Inc., MicroScan, West Sacramento, Calif.) contain substrates conjugated with fluorophores and substrates with a fluorescent pH indicator. AutoSCAn W/A, an automated panel processor equipped with a fluorometer, reads the panels after 2 h of incubation and can identify staphylococci to the species level. We tested 239 strains belonging to 17 species of staphylococci. All the strains were identified by conventional methods (W.E. Kloos and K.H. Schleifer, J. Clin. Microbiol. 1:82-88, 1975) and by the MicroScan Rapid ID system. The system correctly identified 219 (91.6%) strains; nine (3.8%) identification results were probably correct, and six (2.5%) results were incorrect. The system designated five (2.1%) strains as rare biotypes. The automated MicroScan Rapid ID system is useful and reliable in identifying most human isolates of staphylococci encountered in the clinical laboratory.

Campylobacter jejuni infected bursitis.

Campylobacter jejuni is a common cause of enteritis, and has been isolated from patients with bacteremia, meningitis, and cholecystitis. We describe here an unusual case of a chronically inflamed bursitis infected with C. jejuni.

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.

Comparison of the MicroScan system with the API Staph-Ident system for species identification of coagulase-negative staphylococci.

To evaluate the accuracy of the MicroScan System (American Hospital Supply Corp., Sacramento, Calif.) for identification of coagulase-negative staphylococci, we tested 175 clinical isolates of coagulase-negative staphylococci. The results obtained by the MicroScan system were compared with those of the API Staph-Ident system (Analytab Products, Plainview, N.Y.). Forty-three discrepancies between the two systems were resolved by the conventional method of Kloos and Schleifer (W.E. Kloos and K.H. Schleifer, J. Clin. Microbiol. 1:82-88, 1975). The MicroScan and the Staph-Ident systems correctly identified 146 (86.4%) and 154 (88%) of 175 strains, respectively. The API system failed to identify phosphatase-negative Staphylococcus epidermidis. The MicroScan system demonstrated the greatest accuracy in the identification of S. epidermidis and S. saprophyticus, whereas lesser accuracy was achieved with S. hominis, S. warneri, and S. sciuri.

Comparison of American MicroScan dry and frozen microdilution trays.

This study compared the American MicroScan frozen microdilution tray and dehydrated microdilution tray. A total of 153 gram-negative and 106 gram-positive isolates were tested concurrently on both tray types and read visually. Very major and major antimicrobial susceptibility discrepancies amounted to 1.0% of all results, and minor discrepancies amounted to 0.4% of all results. The biochemical discrepancy rate for gram-negative organisms was 1.3%, resulting in no identification errors either at the genus or the species level. Gram-positive identification was not evaluated, as the formulation of biochemicals was changed after this evaluation was completed. Overall, the results with the dry tray were acceptable, providing a suitable alternative to the frozen tray.

Inhibition of Haemophilus vaginalis (Corynebacterium vaginale) by metronidazole, tetracycline, and ampicillin.

The minimal inhibitory concentrations (MICs) of ampicillin, tetracycline, and metronidazole for 71 strains of Haemophilus vaginalis (Corynebacterium vaginale) were compared by use of an agar-dilution method and an inoculum of 10(6) organisms/ml. All strains were sensitive to 1 microgram of ampicillin/ml, 70% to 4 micrograms of tetracycline/ml, and only 13% of the strains to 8 micrograms of metronidazole/ml. Under anaerobic conditions the susceptibility to metronidazole increased markedly, and 48% of the strains were inhibited by 8 micrograms/ml. In determinations of MICs in broth cultures, reduction of the inoculum size to 10(4) organisms/ml increased susceptibilities to metronidazole and tetracycline, whereas incubation of 48 hr instead of 24 hr decreased susceptibilities to these two drugs. Minimal bactericidal concentrations (MBCs) were generally two- to fourfold greater than the MICs for the three drugs. The results demonstrate that anaerobic conditions, inoculum size, and duration of incubation influence the susceptibility of H. vaginalis to antibiotics in vitro.