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Evaluation of the DMS Rapid E system for identification of clinical isolates of the family Enterobacteriaceae.

A total of 387 unique clinical isolates of the family Enterobacteriaceae were examined with the new DMS Rapid E gram-negative identification system (DMS Laboratories, Inc., Flemington, N.J.) and the API 20E procedure (Analytab Products, Plainview, N.Y.). Altogether, 376 strains (97.2%) were correctly identified to species level within 4 h with the DMS Rapid E system; 366 strains (94.6%) were correctly identified with the API 20E after overnight incubation.

Bacteriological Techniques↗

Detection of beta-glucuronidase in lactose-fermenting members of the family Enterobacteriaceae and its presence in bacterial urine cultures.

Four hundred strains of lactose-fermenting Enterobacteriaceae were tested for hydrolysis of p-nitrophenyl-beta-D-glucopyranosiduronic acid, the chromogenic enzyme substrate of beta-glucuronidase. Escherichia coli was found to be homogeneous with respect to beta-glucuronidase: more than 94% of the examined E. coli strains were positive, whereas none of the other lactose-fermenting strains possessed beta-glucuronidase activity. The qualitative beta-glucuronidase test, as rapid and simple as the o-nitrophenyl-beta-D-galactopyranosidase test, proved to be of diagnostic value, especially in the identification of E. coli in primary urine cultures. No significant differences were observed in the results of experiments in which either substrate-impregnated disks prepared in the laboratory or commercially available tablets were used.

Bacteriuria↗

Escherichia fergusonii and Enterobacter taylorae, two new species of Enterobacteriaceae isolated from clinical specimens.

Escherichia fergusonii (formerly known as Enteric Group 10) and Enterobacter taylorae (formerly known as Enteric Group 19) are proposed as new species in the family Enterobacteriaceae. By DNA hybridization (32P, 60 degrees C, hydroxyapatite), strains of E. fergusonii were 90 to 97% related to the type strain (holotype) ATCC 35469. They were most closely related to Escherichia coli and more distantly related to species in other genera. E. fergusonii strains are positive for indole production, methyl red, lysine decarboxylase, ornithine decarboxylase, and motility. They ferment D-glucose with gas production and also ferment adonitol, L-arabinose, L-rhamnose, maltose, D-xylose, trehalose, cellobiose, and D-arabitol. They are negative for Voges-Proskauer, citrate utilization (17% positive), urea hydrolysis, phenylalanine deamination, arginine dihydrolase, growth in KCN, and fermentation of lactose, sucrose, myo-inositol, D-sorbitol, raffinose, and alpha-methyl-D-glucoside. By DNA hybridization (32P, 60 degrees C, hydroxyapatite), strains of E. taylorae were 84 to 95% related to the type strain (holotype) ATCC 35317. Their nearest relative was E. cloacae, to which they were 61% related. Other named species were more distantly related. Strains of E. taylorae are positive for Voges-Proskauer, citrate utilization, arginine dihydrolase, ornithine decarboxylase, motility, growth in KCN medium, and malonate utilization. They ferment D-glucose with gas production and also ferment D-mannitol, L-arabinose, L-rhamnose, maltose, D-xylose, trehalose, and cellobiose. They are negative for indole production, methyl red, H2S production on triple sugar-iron agar, urea hydrolysis, phenylalanine deamination, lysine decarboxylase, gelatin hydrolysis, and fermentation of adonitol, i-inositol, D-sorbitol, and raffinose. Both new species occur in human clinical specimens. Two strains of E. fergusonii were isolated from blood. Five stains of E. taylorae were isolated from blood, and one was from spinal fluid. These blood and spinal fluid isolates suggest possible clinical significance, but this point requires further study.

Aged↗

Comparative evaluation of the new Titertek Enterobac Rapid Automated System (TTE-RAS) for identification of members of the family Enterobacteriaceae.

The Titertek Enterobac Rapid Automated System (TTE-RAS; Flow Laboratories, SpA, Milan, Italy), a new semiautomated system for the identification of members of the family Enterobacteriaceae, was compared with the API 20E system (API System P.A., Montalieu Vercieu, France) by using 284 clinically isolated strains that were previously identified by conventional methods. Six strains from the American Type Culture Collection (Rockville, Md.) were included to evaluate the reproducibility of identification by both systems. Correct identifications at the species level were 93.7% with TTE-RAS and 96.1% with API 20E. Although some of the features of the TTE-RAS data base were not satisfactory, we consider this new miniaturized system to be a very valuable tool for the rapid identification of the most frequently isolated opportunistic bacteria.

Enterobacteriaceae↗

Rapid catalase supplemental test for identification of members of the family Enterobacteriaceae.

A simple, rapid, semiquantitative slide catalase test useful for differentiating members of the family Enterobacteriaceae is described. Judging by the time required for appearance of oxygen bubbles in 3% hydrogen peroxide, the immediate catalase reactors were Yersinia, Serratia, Proteus, Morganella, Providencia, Cedecea, and Hafnia spp. The delayed catalase reactors were Escherichia, Shigella, Klebsiella, Enterobacter, Salmonella, Citrobacter, Edwardsiella, Kluyvera, and Tatumella spp. This information is especially useful for differentiating Serratia from Enterobacter spp. and Yersinia from Escherichia and Shigella spp.

Catalase↗

Evaluation of the Mini-ID Enterobacteriaceae screen system.

A total of 932 typical and atypical enteric fermenters were used to evaluate the Mini-ID Enterobacteriaceae Screen/Identification System. At 4 h, final identifications were available for only 13.3%, but an additional 71% were screened into the correct group, according to the product's database. At 24 h, 58.8% were correctly identified to the species level, often with the use of an additional tube. When 118 of the cultures were arranged into a weighted assortment, as might be found in a clinical laboratory, 35 were definitively identified at 4 h, and another 72 were screened into the correct group. Of these 72, 31 were correctly identified to the species level at 24 h, for a total of 56.0%. False-negative ornithine and incorrect L-pyrrolidonyl-beta-naphthylamide and glucuronide xylopyranoside reactions accounted for 54% of the identification errors, while database problems accounted for 10.2% of the errors. Of the eight Salmonella paratyphi A cultures, seven were missed because of a false-positive lysine reaction. At best, the system serves only as a rough screen.

Bacteriological Techniques↗

Evaluation of Spectrum-10 system for identification of members of the family Enterobacteriaceae.

A total of 378 isolates of the family Enterobacteriaceae were tested with conventional biochemical tests and with the Spectrum-10 identification system. Of these, 97.4% were correctly identified to the species level by using the seven-digit profile of Spectrum-10. The preliminary four-digit profile provided the correct species for 61.1% and the correct genus for 79.4% of the strains. Most misidentifications were observed with aberrant biotypes of Citrobacter freundii.

Bacteriological Techniques↗

Comparative evaluation of the Roche Cobas IDA and Enterotube II systems for identifying members of the family Enterobacteriaceae.

Two Hoffmann-La Roche products were evaluated in parallel for their ability to identify 321 strains of the family Enterobacteriaceae. The first product was the well-established Enterotube II, which correctly identified 90% of the isolates after 24 h of incubation. The second was the ID-E rotor, originally designed for use in the Cobas Bact but here used in the new Cobas IDA system. The Cobas IDA, used with the full data base held in a microcomputer supplied with the product, identified 87% of strains after 4 h of incubation.

Bacteriological Techniques↗

Trabulsiella guamensis, a new genus and species of the family Enterobacteriaceae that resembles Salmonella subgroups 4 and 5.

In 1985 the vernacular name Enteric Group 90 was coined for a small group of strains that had been referred to our laboratory as probable strains of Salmonella but did not agglutinate in Salmonella typing antisera. By DNA-DNA hybridization (hydroxyapatite method, 32P), seven strains of Enteric Group 90 were found to be closely related (98 to 100% at 60 degrees C and 94 to 100% at 75 degrees C) to the first strain received (0370-85). The relatedness of Enteric Group 90 to 62 strains of other species of the family Enterobacteriaceae was only 6 to 41%, with the highest values obtained with strains of Salmonella, Kluyvera, Shigella, Klebsiella, Enterobacter, and Citrobacter. We propose a new genus, Trabulsiella, with a single new species, Trabulsiella guamensis, for the highly related group of eight strains formerly known as Enteric Group 90. The type strain is designated ATCC 49490 (CDC 0370-85). T. guamensis strains grew well at 36 degrees C and had positive reactions in the following tests: methyl red, citrate utilization (Simmons) (38% positive at day 1, 88% positive at 2 days), H2S production, lysine decarboxylase, arginine dihydrolase (50% positive at 2 days, 100% positive at 7 days), ornithine decarboxylase, motility, growth in KCN medium, mucate fermentation, acetate utilization, nitrate reduction to nitrite, weak tyrosine hydrolysis (88% positive at 2 days, 100% positive at 7 days), and ONPG (o-nitrophenyl-beta-D-galactopyranoside) test. The strains fermented D-glucose with gas production and fermented L-arabinose, cellobiose, D-galactose, D-galacturonate, maltose, D-mannitol, D-mannose, L-rhamnose, D-sorbitol, trehalose, and D-xylose. T. guamensis strains had negative reactions in the following tests: indole production (13% positive), Voges-Proskauer, urea hydrolysis, phenylalanine deaminase, malonate utilization, lipase (corn oil), DNase, oxidase, pigment production, and acid production from adonitol, D-arabitol, dulcitol, erythritol, myo-inositol, melibiose, alpha-methyl-D-glucoside, raffinose, and sucrose. There were delayed positive reactions for gelatin liquefaction (22 degrees C), which was positive at 12 to 23 days, esculin hydrolysis (13% positive at day 1, 50% positive at 7 days), lactose fermentation (13% positive at 3 to 7 days, 100% positive at 8 to 10 days), glycerol fermentation (88% positive at 7 days), and salicin fermentation (13% positive at day 1, 88% positive at 7 days). All strains were susceptible by the disk diffusion method to colistin, nalidixic acid, gentamicin, streptomycin, kanamycin, chloramphenicol, and trimethoprim-sulfamethoxazole, and most strains were susceptible to sulfadiazine (75% susceptible), tetracycline (88%), and carbenicillin (75%). The strains were resistant to penicillin, cephalothin, and ampicillin. The strains were isolated from vacuum cleaner dust (five strains), soil (one strain), and human feces (two strains). Although T. guamensis can occur in human diarrheal stools, there is no evidence that it actually causes diarrhea. Its main interest to clinical microbiologists may be its possible misidentification as a strain Salmonella.

DNA, Bacterial↗

Evaluation of new computer-enhanced identification program for microorganisms: adaptation of BioBASE for identification of members of the family Enterobacteriaceae.

We report the use of BioBASE, a computer-enhanced numerical identification software package, as a valuable aid for the rapid identification of unknown enteric bacilli when using conventional biochemicals. We compared BioBASE identification results with those of the Centers for Disease Control and Prevention's mainframe computer to determine the former's accuracy in identifying both common and rare unknown isolates of the family Enterobacteriaceae by using the same compiled data matrix. Of 293 enteric strains tested by BioBASE, 278 (94.9%) were correctly identified to the species level; 13 (4.4%) were assigned unacceptable or low discrimination profiles, but 8 of these (2.7%) were listed as the first choice; and 2 (0.7%) were not identified correctly because of their highly unusual biochemical profiles. The software is user friendly, rapid, and accurate and would be of value to any laboratory that uses conventional biochemicals.

Bacteriological Techniques↗

Outbreak of TEM-24-producing Enterobacter aerogenes in an intensive care unit and dissemination of the extended-spectrum beta-lactamase to other members of the family enterobacteriaceae.

We report an outbreak of Enterobacter aerogenes in an intensive care unit (ICU) and two medicine departments that produced the extended-spectrum beta-lactamase TEM-24, which was difficult to detect by disk agar diffusion. The strains were compared by DNA restriction fragment length polymorphism after pulsed-field gel electrophoresis following cleavage with XbaI. This typing method indicated that a single strain, first isolated in the ICU, spread throughout the other medical departments as a result of patient transfer. We also observed the transfer in vivo of the plasmid encoding TEM-24 from the strain of Enterobacter aerogenes to different strains of Escherichia coli and Citrobacter freundii in the ICU. It therefore appears that the epidemic involved results from two events: dissemination of one strain of Enterobacter aerogenes and dissemination of the plasmid encoding TEM-24 among various members of the family Enterobacteriaceae.

Anti-Bacterial Agents↗

Detection of extended-spectrum-beta-lactamase-producing members of the family Enterobacteriaceae with Vitek ESBL test.

A three-phase analysis of the Vitek ESBL test and a double-disk (2 disk) test was performed to assess their ability to detect extended-spectrum beta-lactamases (ESBLs) in members of the family Enterobacteriaceae. In the first two phases involving detection of ESBLs in 157 stains processing well-characterized beta-lactamases, sensitivity and specificity were found to be 99.5 and 100%, respectively, for the Vitek ESBl test and 98.1 and 99.4%, respectively, for the 2-disk test. In the third phase, in which the ability of each test to detect ESBLs in 295 clinical isolates was assessed, there was only one false positive (Vitek ESBL test). Across all three phases, the Vitek ESBL test was found to be much easier to perform than the 2-disk test. The latter also involved subjective interpretation of results. There were a total of 176 Escherichia coli and 157 Klebsiella pneumoniae isolates and less than 40 isolates of each of 14 other species evaluated. In a supplemental study of Klebsiella oxytoca, an organism possessing a chromosomal beta-lactamase similar to an ESBL, the Vitek ESBL test was found to be capable of detecting hyperproduction of this enzyme in strains of this species as well. These data indicate that the Vitek ESBL test is reliable for the detection of ESBLs in E. coli and K. pneumoniae, the two species in which ESBLs are most common, and of hyperproduction of the K. oxytoca beta-lactamase, a situation which engenders a level of resistance to this species similar to that seen with ESBLs.

Cephalosporins↗

Evaluation of L-pyrrolidonyl peptidase paper strip test for differentiation of members of the family Enterobacteriaceae, particularly Salmonella spp.

The L-pyrrolidonyl peptidase activities of 1,033 strains of the family Enterobacteriaceae were investigated by the paper strip method to evaluate their usefulness for screening those organisms, especially Salmonella cultures. We also evaluated the usefulness of indole and tryptophan deaminase paper strip tests as supplements to the L-pyrrolidonyl peptidase test for the rapid identification of Salmonella cultures. The paper strip tests are simple, and the results are obtainable within 10 min.

Amino Acid Oxidoreductases↗

Evaluation of the MicroScan rapid neg ID3 panel for identification of Enterobacteriaceae and some common gram-negative nonfermenters.

The MicroScan Rapid Neg ID3 panel (Dade Behring, Inc., West Sacramento, Calif.) is designed for the identification of gram-negative bacilli. We evaluated its ability to accurately identify Enterobacteriaceae that are routinely encountered in a clinical laboratory and glucose nonfermenting gram-negative bacilli. Using 511 stock cultures that were maintained at -70 degrees C and passaged three times before use, we inoculated panels according to the manufacturer's instructions and processed them in a Walk/Away instrument using version 22.01 software. The time to identification was 2 h and 30 min. All panel identifications were compared to reference identifications previously determined by conventional tube biochemicals. At the end of the initial 2.5-h incubation period, 405 (79.3%) identifications were correct. An additional 49 (9.6%) isolates were correctly identified after required additional off-line biochemical tests were performed. Thus, at 24 h, 88.8% of the 511 strains tested were correctly identified. Twenty-two (4.3%) were identified to the genus level only. Twenty-six (5.1%) strains were misidentified. Because the system is based on fluorogenics, there are no conventional tests readily available with which to compare possibly incorrect reactions. Of the 28 Salmonella strains that were tested, 5 were incorrectly reported. The 21 remaining errors were scattered among the genera tested. Testing on nine strains gave a result of "no identification" (very rare biotype). The Rapid Neg ID3 panel in this study approached 89% accuracy for the identification of gram-negative organisms encountered in the hospital laboratory.

Bacterial Typing Techniques↗

Comparison of the Rodac imprint method to selective enrichment broth for recovery of vancomycin-resistant enterococci and drug-resistant Enterobacteriaceae from environmental surfaces.

We compared the Rodac imprint technique to selective enrichment broth for detecting vancomycin-resistant enterococci (VRE) and multidrug-resistant Enterobacteriaceae (MDRE) on surfaces. Rodac plates contained tryptic soy agar with 5% sheep blood, vancomycin (6 microg/ml), ceftazidime (2 microg/ml), amphotericin B (2 microg/ml), and clindamycin (1 microg/ml). Two types of broth were used: brain heart infusion (BHI) and BHI plus vancomycin (6 microg/ml) and ceftazidime (2 microg/ml) (BHIVC). Of the 46 surfaces cultured for VRE, 12 (26%) were positive. Of the 12 VRE-positive surfaces, 11 (92%) grew from Rodac, 8 (67%) grew from BHIVC, and 7 (58%) grew from BHI. A larger study is needed for MDRE, as only 4 of 43 surfaces were MDRE positive. The Rodac imprint technique successfully recovered VRE from environmental surfaces.

Culture Media↗

Ability of the VITEK 2 advanced expert system To identify beta-lactam phenotypes in isolates of Enterobacteriaceae and Pseudomonas aeruginosa.

The Advanced Expert System (AES) was used in conjunction with the VITEK 2 automated antimicrobial susceptibility test system to ascertain the beta-lactam phenotypes of 196 isolates of the family Enterobacteriaceae and the species Pseudomonas aeruginosa. These isolates represented a panel of strains that had been collected from laboratories worldwide and whose beta-lactam phenotypes had been characterized by biochemical and molecular techniques. The antimicrobial susceptibility of each isolate was determined with the VITEK 2 instrument, and the results were analyzed with the AES to ascertain the beta-lactam phenotype. The results were then compared to the beta-lactam resistance mechanism determined by biochemical and molecular techniques. Overall, the AES was able to ascertain a beta-lactam phenotype for 183 of the 196 (93.4%) isolates tested. For 111 of these 183 (60.7%) isolates, the correct beta-lactam phenotype was identified definitively in a single choice by the AES, while for an additional 46 isolates (25.1%), the AES identified the correct beta-lactam phenotype provisionally within two or more choices. For the remaining 26 isolates (14.2%), the beta-lactam phenotype identified by the AES was incorrect. However, for a number of these isolates, the error was due to remediable problems. These results suggest that the AES is capable of accurate identification of the beta-lactam phenotypes of gram-negative isolates and that certain modifications can improve its performance even further.

Enterobacteriaceae↗

Contamination of the clinical microbiology laboratory with vancomycin-resistant enterococci and multidrug- resistant Enterobacteriaceae: implications for hospital and laboratory workers.

We surveyed environmental surfaces in our clinical microbiology laboratory to determine the prevalence of vancomycin-resistant enterococci (VRE) and multidrug-resistant Enterobacteriaceae (MDRE) during a routine working day. From a total of 193 surfaces, VRE were present on 20 (10%) and MDRE were present on 4 (2%) of the surfaces tested. In a subsequent survey after routine cleaning, all of the 24 prior positive surfaces were found to be negative. Thus, those in the laboratory should recognize that many surfaces may be contaminated by resistant organisms during routine processing of patient specimens.

Colony Count, Microbial↗

MORLUC numeric system for the identification of Enterobacteriaceae.

Foul hundred eighty-six members of the Enterobacteriaceae representing nine genera were identified by conventional methods, and the results were compared with MORLUC (Biotrol Company Inc., Jamaica, N.Y.). MORLUC, an acronym for melibiose, ONPG (o-nitrophenyl-beta-galactopyranoside), rhamnose, lysine decarboxylase, urease, and citrate, are six prepackaged reagent-impregnated paper loops which are sealed within a plastic packet. The hydrogen sulfide reaction obtained from a triple sugar iron slant is coupled with MORLUC results and is readily converted into a three-digit numerical code, which is referenced on a preprinted single page listing. Additionally, the triple sugar iron is used to confirm the glucose fermentation by an unknown isolate. Comparisons of individual MORLUC tests and standard methods results in a better than 92% agreement, except for unrease. Four hundred sixty-six of the 486 bacterial isolates, or 96% of the strains which were numerically identified by MORLUC, agreed with conventional diagnoses.

Carboxy-Lyases↗