Comparison of four chromogenic media and Hektoen agar for detection and presumptive identification of Salmonella strains in human stools

Several chromogenic media have been developed to enhance the specificity of Salmonella detection. We compared the performance of four commercial chromogenic media-namely, ABC medium (Lab M. Ltd., Bury, United Kingdom), COMPASS Salmonella agar (Biokar Diagnostics, Beauvais, France), CHROMagar Salmonella agar (CHROMagar Company, Paris, France), and SM ID agar (bioMerieux, Marcy l'Etoile, France)-with conventional Hektoen medium. Nine hundred sixteen stool samples from inpatients at three hospitals were cultured, in parallel, on the five media, both by direct inoculation and after selective enrichment in selenite broth. Sixty-four Salmonella strains with 12 serotypes were isolated on at least one medium. After 48 h of incubation, sensitivity before and after enrichment was 62.5 and 89.1% with ABC medium, 77.1 and 93.8% with COMPASS agar, 66.7 and 89.1% with CHROMagar, 68.8 and 85.9% with SM ID agar, and 85.4 and 98.4% with Hektoen agar, respectively. Broth enrichment and prolonged incubation (48 versus 24 h) increased the sensitivity of all five media. Only one strain was not isolated on Hektoen agar. The number of false-positive isolates was higher with all five media after enrichment in selenite broth and after incubation for 48 h compared to 24 h. The specificity of the four chromogenic media was better than 91% after incubation for 24 h (77.7% with Hektoen agar) and better than 84% after incubation for 48 h (74.8% with Hektoen agar). This higher specificity reduces the need for confirmatory tests, thereby cutting technical time and reagent requirements. Both COMPASS agar and CHROMagar Salmonella, which after simple additional tests showed close efficiencies (96 and 97%, respectively), can be recommended as single-plate media of choice for the detection and presumptive identification of salmonellae in stools.

Comparison of three chromogenic agar plates for isolation and identification of urinary tract pathogens

OBJECTIVE

To comparatively assess the performance of three chromogenic agar plates, CPS ID2, Chromogenic UTI, and USA, for the detection and enumeration of all urinary tract pathogens and the direct identification of Escherichia coli, Proteus mirabilis and Enterococcus spp.

METHODS

Two hundred and forty-three urine specimens prospectively collected from hospitalized patients were randomly inoculated in parallel on the three media.

RESULTS

Of the 243 urine specimens, 235 yielded positive cultures, of which 151 were pure cultures and 84 were mixed cultures. CPS ID2, Chromogenic UTI and USA agar gave detection rates of 99.1%, 97.1% and 96.6%, respectively. The main difference in non-detection between CPS ID2 agar and the two new media concerned Staphylococcus spp. strains. Based on the total number of strains detected (n = 348), the total identification rates of E. coli, P. mirabilis and Enterococcus spp. on CPS ID2 agar, Chromogenic UTI agar and USA agar were 60.3%, 61.2% and 59.2%, respectively.

CONCLUSION

The detection rates and identification rates of the three media were very close and only minor differences were noted. The lower detection rates for Chromogenic UTI and USA were mainly due to their lesser ability to support growth of Staphylococcus spp.

Performance of the chromogenic medium CHROMagar Staph Aureus and the Staphychrom coagulase test in the detection and identification of Staphylococcus aureus in clinical specimens

CHROMagar Staph aureus (CSAM) (CHROMagar Microbiology, Paris, France) is a new chromogenic medium designed to enable detection of colonies of Staphylococcus aureus by their pink color. A total of 775 specimens were cultured in parallel on CHROMagar Staph aureus and conventional media. Among the 267 S. aureus strains recovered on at least one medium, 263 were isolated on CSAM medium (sensitivity, 98.5%), and 245 (sensitivity, 91.8%) were isolated on conventional media. The specificity of presumptive identification of S. aureus on the basis of pink colony color on CSAM medium was 97% (493 of 508). This specificity increased to 100% when coagulase detection with the Staphychrom coagulase test was added and to 98.8% when S. aureus surface components were detected by agglutination in the Pastorex Staph Plus test. Susceptibility testing of 67 S. aureus strains, performed in parallel on pink CSAM colonies and on colonies grown on blood agar, gave similar results. Thus, rapid and accurate recognition and identification of S. aureus isolates were achieved with CSAM as the primary isolation medium, followed by the staphylocoagulase Staphychrom test. Antimicrobial susceptibility testing (disk-diffusion method or ATB STAPH System) can be performed directly on pink CSAM colonies.

Comparative evaluation of five chromogenic media for detection, enumeration and identification of urinary tract pathogens

Five chromogenic agar plates--CPS ID2 medium (bioMérieux, France), CHROMagar Orientation medium (Becton Dickinson, France), UriSelect3 medium (Sanofi Diagnostics Pasteur, France), Rainbow Agar UTI medium (Biolog, USA) and Chromogenic UTI medium (Oxoid, Germany)--for the detection, enumeration and direct identification of urinary tract pathogens were compared using 443 urine specimens at two hospital laboratories. The enumeration of microorganisms was consistent on the five media for 403 of the 477 (84.5%) microorganisms. Chromogenic UTI, CPS ID2, UriSelect3, CHROMagar Orientation and Rainbow UTI gave detection rates of 98.3%, 97.9%, 97.3%, 96.9% and 94.1%, respectively, with some problems in yeast growth occurring on Rainbow UTI agar and problems in Staphylococcus spp. growth occurring on UriSelect3. For the direct identification of Escherichia coli, sensitivities were 93.8%, 88.5%, 86.1% and 82.2% for CHROMagar Orientation, CPS ID2, UriSelect3 and Rainbow UTI, respectively. Chromogenic UTI medium did not allow the accurate identification of Escherichia coli, since the indole reaction cannot be applied to this medium. Depending on the media, Enterococcus spp. could be identified at the genus or the species level. Slight differences were detected in the presumptive identification of the Proteus-Morganella-Providencia group and the Klebsiella-Enterobacter-Serratia group. Additionally, on Rainbow UTI agar, 12 of 20 Klebsiella pneumoniae strains and two of nine Pseudomonas aeruginosa strains were correctly identified. In conclusion, CPS ID2 medium and CHROMagar Orientation medium showed similar performance overall, while the UriSelect3, Rainbow UTI and Chromogenic UTI media require some improvement.

Evaluation of six commercial systems for identification of medically important yeasts

Six commercially available systems for the identification of yeasts were evaluated using 133 clinical isolates and four reference strains that had been previously identified by conventional methods and 19 recent clinical isolates that had been identified by the ID32C system (bioMérieux, France). The total identification rates (TIR) established for the total number of strains tested and the database identification rates (DBIR) established for the strains included in the respective manufacturer databases were both determined. After incubation for 4 h, the TIR and DBIR were 78% and 84%, respectively, for the RapID Yeast Plus system (Innovative Diagnostic Systems, USA). After incubation for 24 h, the TIR and DBIR were 32% and 32%, respectively, for the ID32C, 65% and 67% for the Auxacolor system (Sanofi Diagnostics Pasteur, France), 62% and 65% for the Fungichrom I system (International Microbio, France), 52% and 65% for the Fungifast I twin system (International Microbio), and 62% and 68% for the API Candida system (bioMérieux). The maximum TIR and DBIR (+/- 1%) obtained after incubation for 48 h were 86% and 88% for the Auxacolor, 85% and 89% for the Fungichrom I, 78% and 98% for the Fungifast I twin, and 82% and 91% for the API Candida. For the ID32C, the maximum TIR and DBIR were 98% and 98%, respectively, but these values were obtained only after 72 h of incubation. In addition, the six systems varied in their ease of use and readings. In conclusion, based on results obtained with 156 strains, the Auxacolor and Fungichrom systems seem the most appropriate for use in a clinical microbiology laboratory, due to their ease of use and reading, their rapidity, their cost per test, and their relatively high TIR results, which indicated acceptable performance with strains frequently isolated in our hospital. For a reference identification, the ID32C remains the sole system usable.

Comparison of three commercial media for direct identification and discrimination of Candida species in clinical specimens

One hundred and ninety-two clinical specimens were used to compare the three chromogenic media Albicans ID, Candiselect, and CHROMagar Candida to a standard method using a Sabouraud-chloramphenicol agar medium and standard methods for identification of yeasts. The detection rates were 83.79, 83.24, 86.59 and 84.91% respectively. For the chromogenic media, the rates of direct identification (growth plus specific pigmentation) for Candida albicans were 56.50, 37.68 and 11.59% after 24 hours' incubation and 92.75, 91.30 and 88.57% after 72 hours' incubation respectively, with 100% specificity. Furthermore, CHROMagar Candida identified the five Candida tropicalis and the two Candida krusei strains detected after 48 hours' incubation.

Evaluation of latex reagents for rapid identification of Candida albicans and C. krusei colonies

A total of 322 yeast strains and yeastlike organisms belonging to the genera Candida, Cryptococcus, Geotrichum, Saccharomyces, and Trichosporon were tested with the new monoclonal antibody-based Bichro-latex albicans and Krusei color latex tests. Comparison of results with those obtained by conventional identification methods showed 100% sensitivity for both latex tests and 100% and 95% specificity for the Bichro-latex albicans and Krusei color tests, respectively. Because the test is easy to read and quick to perform, the Bichro-latex albicans test may be useful for rapid identification of Candida albicans colonies in the clinical laboratory.

Direct identification and recognition of yeast species from clinical material by using albicans ID and CHROMagar Candida plates

Two chromogenic media, Albicans ID and CHROMagar Candida agar plates, were compared with a reference medium, Sabouraud-chloramphenicol agar, and standard methods for the identification of yeast species. This study involved 951 clinical specimens. The detection rates for the two chromogenic media for polymicrobial specimens were 20% higher than that for the Sabouraud-chloramphenicol agar plates. The rates of identification of Candida albicans for Albicans ID and CHROMagar Candida agar plates were, respectively, 37.0 and 6.0% after 24 h of incubation and 93.6 and 92.2% after 72 h of incubation, with specificities of 99.8 and 100%. Furthermore, CHROMagar Candida plates identified 13 of 14 Candida tropicalis and 9 of 12 Candida krusei strains after 48 h of incubation.

Spermoculture: improvement of the bacteriological quality of samples by direct verbal counseling before semen collection

OBJECTIVE

To compare the bacteriologic quality of samples after direct verbal or written counseling for semen collection.

DESIGN

Prospective randomized comparative study.

SETTING

Laboratories of biology of reproduction and microbiology in university hospitals.

PATIENTS

Male partners of infertile couples on their first attempt to collect semen were assigned randomly into two groups.

INTERVENTION

In one group (n = 52) the patients were given direct verbal instruction by one of the investigators on how to avoid bacterial contamination during semen collection. In the other group (n = 52) the patients were asked to follow the usual written instructions.

MAIN OUTCOME MEASURE

Bacterial count, number of species, classification of the samples in positive, negative, and noninformative cultures.

RESULTS

Direct verbal teaching significantly reduced the bacterial count (2.06 +/- 1.6 versus 3.29 +/- 1.6 log cfu/mL; mean +/- SD) and number of species (1.44 +/- 2.02 versus 3.25 +/- 2.25), increased the percentage of sterile cultures (59.6% versus 23.1%), and decreased the percentage of noninformative cultures (29.9% versus 50%).

CONCLUSION

Direct verbal counseling on how to avoid bacterial contamination during semen collection significantly improves the bacteriologic quality of the samples.

Rapid identification of Candida albicans by using Albicans ID and fluoroplate agar plates

Two commercially available agar media, Albicans ID and Fluoroplate, that use a chromogenic or a fluorogenic substrate for the detection and identification of Candida albicans were evaluated. From 1,006 clinical samples containing 723 yeast strains, 352 C. albicans strains were detected with either of the two media. The sensitivity of each of the two media was 93.8% and the specificity was 98.6%, with five false-positive reactions for Candida tropicalis and no false-negative reactions.

Evaluation of two new chromogenic media for detection of Salmonella in stools

A clinical collaborative study was conducted to compare two new chromogenic agar media, Rambach agar and the Salmonella Detection and Identification Medium (SMID) (bioMérieux, France), with two conventional media, Salmonella-Shigella agar and Hektoen agar. Thirty-nine Salmonella strains involving 14 serotypes were isolated from 1,454 stool specimens. After enrichment in a selective broth, 100% sensitivity was obtained with each medium. The SMID and Rambach agars are considerably more specific than the conventional media. Although SMID agar detects all Salmonella serotypes, it is not as specific as Rambach agar, which requires a complementary test (C8 esterase test) to detect all serotypes.

Evaluation of five commercial antifungal susceptibility testing systems

Five commercial antifungal susceptibility testing systems were studied for repeatability and reproducibility as well as concordance of results with the MICs for ten reference strains belonging to six different species. Repeatability was determined by testing each strain in triplicate on the same day, and reproducibility by repeating this triple determination on three different days. On the basis of 630 yeast-antifungal agent results for Mycototal and Mycostandard, 540 for Candifast, and 450 for ATB Fungus and Diff Test, repeatability was consistently equal to or greater than 95%. Reproducibility was 80.07% for Candifast and greater than 95% for the other systems. The concordance with the reference MICs was 51.65% for Candifast, 75.33% for ATB Fungus, 80.89% for Diff Test, 90.16% for Mycostandard and 90.32% for Mycototal. Although the performance of Diff Test and ATB Fungus was satisfactory, Mycototal and Mycostandard gave notably better results with imidazoles. Mycostandard, which is easier to use and includes tests for fluconazole and itraconazole, would seem to be potentially the most useful antifungal susceptibility test available at present.

Evaluation of four commercial systems for identification of medically important yeasts

Four commercially available systems for identification of yeasts were evaluated using 178 clinical isolates and seven reference strains previously identified by a conventional method. After 72 h of incubation, the rate of correct identification was 86.5% with API20C Aux, 86% with Auxacolor, 68% with Mycotube and 51.1% with Candifast. When considering only the reference strains included in the manufacturers' databases, the identification rate was 90%, 91%, 87% and 61.2% respectively. Although the results at 72 h obtained with API20C Aux and Auxacolor were similar, Auxacolor led to more rapid identification of the strains, 67.9% versus 14.6% being identified at 24 h and 80.9% versus 64% being identified at 48 h.

Detection of salmonellae by using Rambach agar and by a C8 esterase spot test

In food microbiology, Rambach agar facilitates the differentiation of non-typhi Salmonella through a specific red pigmentation of the colonies. The usefulness of Rambach agar was examined relative to its usefulness to the field of clinical microbiology. Of 170 non-typhi Salmonella strains, 92 and 97% gave bright red colonies after 24 and 48 h of incubation, respectively, while 100% of 112 other members of the family Enterobacteriaceae were of a different color (blue, green, beige, or colorless). Red colonies were also found with five of five Acinetobacter isolates and one of three Pseudomonas isolates. To further detect Salmonella typhi and the rare beige or colorless colonies atypical of Salmonella isolates, a C8 esterase detection spot test was carried out. With UV light, that test revealed fluorescent colonies for all Salmonella isolates tested.

[Determination of antibacterial activity of antiseptic biotextiles in vitro after standard washings]

A method in vitro is developed for evaluating antibacterial activity of antiseptic "biotextiles". The latter are particular in that they possess remanent antimicrobial properties, given their ability to carry antiseptic molecules. The method has to detect and measure a potential activity, but also point out it's stability. The biotextile and an appropriated control were repeatedly washed, put in contact with reference bacterial strains and subsequently incubated. The survival bacteria are then plated and counted by method of successive dilution. Compared with the controls, all the washed biotextiles presented a significant activity.

In vitro susceptibilities of 40 Campylobacter fetus subsp. jejuni strains to niridazole and metronidazole

The activities of niridazole and metronidazole were compared by an agar dilution method against 40 strains of Campylobacter fetus subsp. jejuni of human origin. Niridazole had a markedly higher activity than metronidazole.

Serological grouping of streptococci: a collective evaluation in six laboratories of three rapid methods

Three serological methods for streptococci grouping: latex agglutination after pronase extraction (LAP), latex agglutination after nitrous acid extraction (LAN) and counterimmunoelectrophoresis after nitrous acid extraction (CIEN) were evaluated in six laboratories with 310 strains of streptococci. To reduce the possible influence of a particular laboratory, each serological procedure was performed in two different laboratories with identical protocols and strains. Between the three procedures, a total agreement of 81.3% with six identical results was obtained. Since only one discordant result was obtained in 12.2% (CIEN 4.8%-LAN 5.8%-LAP 1.6%) and two discordant results with two different serological methods in 2.6%, it could be concluded that agreement between the three procedures was 96%. For B (99 strains tested) and D(100 strains tested) groups, total agreements of respectively 95% and 92% were achieved. In conclusion, LAP, LAN, and CIEN gave equivalent results for streptococci grouping, but LAN was the most simple needing no heating, centrifugation, or electrophoresis equipment and lacking cross-reactivity of group C antibody.

[Susceptibility of anaerobic bacteria to cefoxitin (author's transl)]

Nine strains of Clostridium perfringens type A and 10 strains of Bacteroïdes fragilis s. spec. fragilis, recently isolated from blood culture, were tested for their cefoxitin susceptibility. The MIC for Clostridium perfringens ranged from 0,6 to 5 mg/l and 1,2 to 10 mg/l for Bacteroïdes fragilis. In most cases, the MBC were identical with the MIC for Clostridium perfringens, but for Bact. frag. there was a difference of 2 dilutions in their MBC. Cefoxitin activity was not modified by a variation in inoculum density.

[Urinary tract infection in urology (author's transl)]

We studied the rate of infection in 144 pre- and post-operative patients. Before intervention the rate is 21,5% and in the post at the discharge of the patient from the hospital, the rate is 28%.

[Urinary infection in urology. A rapid technique for confirmation of the diagnosis and the orientation of medical treatment (author's transl)]

A rapid technique for confirmation of the diagnosis and the orientation of medical treatment of urinary infection. Performance of direct antibiotic sensitivities on urine is a rapid (14 to 18 hours) procedure for determining the presence of organisms in the urine and seeking the antibiotic most active against them. In order to assess the value of the procedure, it was compared with classical bacteriological techniques. The correlation was found to be satisfactory. This procedure of direct sensitivity studies on urine is not in to way in competition with classical bacteriological techniques but is of great value in rapidly confirming the diagnosis of urinary infection and in the orientation of therapy. It eliminates a number of the justifications of blind treatment.