The frequency of antimicrobial agent-resistant enterococci is increasing, making accurate identification and screening for susceptibility essential. We evaluated the ability of MicroScan Positive Breakpoint Combo Type 6 panels (Dade MicroScan Inc., West Sacramento, Calif.) to identify Enterococcus species and to detect ampicillin and vancomycin resistance. A total of 398 well-characterized Enterococcus isolates from two institutions were inoculated into MicroScan panels, into conventional biochemical assays, and into ampicillin and vancomycin agar dilution media. Resistance was verified by the broth macrodilution method. MicroScan panels accurately detected resistance to ampicillin in 132 of 132 enterococcal isolates, while three isolates for which the MICs were <16 g/ml were classified incorrectly by MicroScan panels as resistant. No beta-lactamaseproducing enterococci were detected. All 64 isolates showing resistance to vancomycin (MICs >32 g/ml) were correctly classified by MicroScan panels. Seven isolates for which the vancomycin MICs were 8 and 16 g/ml were incorrectly classified as susceptible by MicroScan panels, while eight isolates for which the MICs were 4 g/ml were incorrectly labeled as intermediate. Fourteen of these 15 isolates were subsequently identified as motile enterococci. Overall, there were three major errors in susceptibility testing for ampicillin and 15 minor errors for vancomycin. Conventional testing confirmed the identity of 181 Enterococcus faecalis isolates, 157 E. faecium isolates, and 60 isolates of other species; however, 56 of these 60 isolates were misidentified by the MicroScan panels. After recognition of this problem, a reviased approach which included tests for pigment, motility, and sucrose fermentation was devised. In combination with these additional assays, the conventional MicroScan panels accurately identified the 56 originally misidentified isolates. In summary, the ability of MicroScan panels to detect vancomycin and ampicillin resistance in enterococci was confirmed. Our study found that the inability of MicroScan panels to identify enterococci other than E. faecalis and E. faecium can be compensated for by the addition of standard assays.
The infectivity of Actinomyces israelii in a susceptible-weanling-mouse was increased by the presence of Eikenella corrodens in the inoculum. A minimal infecting dose of 1.7 X 10(7) CFU of A. israelii was required to establish chronic lesions after an intraperitoneal injection. When E. corrodens (3.8 X 10(7) CFU) was included in the inoculum, chronic lesions were established with a dose of 8.5 X 10(4) CFU of A. israelii. E. corrodens alone did not produce persistent lesions. Viable E. corrodens could be recovered from chronic mixed actinomycotic lesions in numbers that often equaled or exceeded the populations of A. israelii in the lesions. The duration of acute actinomycotic infections caused by A. viscosus was temporarily extended by the presence of E. corrodens. The cellular inflammatory response and overall morphology of mixed experimental lesions containing A. israelii and E. corrodens did not appear to be significantly different from those of pure-culture lesions containing A. israelii alone. E. corrodens cells could not be readily discerned in stained histological sections of mixed experimental lesions.
A nucleic acid-based test (Gen-Probe PACE 2C System) was evaluated for the ability to detect Chlamydia trachomatis and Neisseria gonorrhoeae from endocervical specimens in a single assay. Three swab samples, randomized for collection order, were obtained from each patient and tested by N. gonorrhoeae and C. trachomatis culture and by the PACE 2C probe assay. Fifty of 395 specimens were culture positive for N. gonorrhoeae (17 specimens), C. trachomatis (26 specimens), or both (7 specimens), of which PACE 2C testing detected 48 specimens. The PACE 2C assay was positive for 56 specimens, including 8 specimens not positive by culture. Of the total of 10 discrepancies between culture and PACE 2C results, resolution testing yielded four false-negative culture, four false-positive PACE 2C, and two false-negative PACE 2C results. The sensitivity, specificity, and positive and negative predictive values for PACE 2C after reevaluation were 96.3, 98.8, 92.9, and 99.4%, respectively. The overall sensitivities for C. trachomatis and N. gonorrhoeae culture were 89.2 and 88.9%, respectively. The prevalence rate for C. trachomatis was 9.4%, and that for N. gonorrhoeae was 6.8%. The Gen-Probe PACE 2C System is a reliable alternative for screening endocervical specimens for both C. trachomatis and N. gonorrhoeae in a single assay.
Mixed actinomycotic infections were established in a susceptible weanling mouse model by using combinations of Actinomyces israelii and Eikenella corrodens or A. israelii and Actinobacillus actinomycetemcomitans. Acute lesions caused by either of the gram-negative organisms alone were resolved within a few weeks; however, these organisms persisted up to 3 months in chronic lesions in combination with A. israelii.
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