Isolation of L-Forms in a Clinical Microbiology Laboratory

Previous studies have demonstrated that L-forms of bacteria may play a role in persistent, chronic, or recurrent urinary-tract infections. A 2-year program was initiated to determine the feasibility of culturing for L-forms on a routine basis, and to determine the effectiveness of such a program. In relation to the total number of specimens, few L-forms were actually isolated. In comparison with the amount of equipment and technician time required, the return was negligible; only 0.5% of all urine specimens were positive for L-forms. An increase to only 1.2% was noted when culturing for L-forms was limited to patients with a diagnosis of bacteriuria or pyelonephritis. It is recommended that this technique be reserved for those patients with a long history of recurrent urinary-tract infections, after other attempts to cure the patient have met with failure.     

Electronic Data Processing System for the Clinical Microbiology Laboratory

Owing to the increased volume of laboratory services and the shortage of skilled medical microbiologists who presently spend up to 30% of their time in clerical matters, pragmatic applications of electronic sorting techniques and computers should be considered to alleviate this problem. Moreover, surveillance of the hospital community, with particular reference to changing patterns of microbial resistance and the distribution of potentially infectious pathogens, requires detailed information which can be readily supplied by electronic sorting analysis. Mark-sense and prescored Port-A-Punch IBM cards were used to: (i) analyze antibiotic susceptibility data; (ii) tabulate total test loads according to conditions set down by the American Society for Clinical Pathologists; and (iii) to prepare a bacteriological report on the surveillance of hospital infections. After proper sorting and analysis, the cards also serve as a convenient reference file in the laboratory for pertinent information recorded by either blackening the appropriate areas (mark-sense style) or pushing out the preperforated rectangular holes with a simple inexpensive board and stylus (Port-A-Punch). No one scheme can fulfill the requirements of all laboratories or purposes, but ideas contained herein might serve as starting points for the design of similar systems in other laboratories.     

Rapid Identification of the Taxon Rhodochrous in the Clinical Laboratory

Degradation of ethylene glycol in Middlebrook 7H-10 agar medium by 26 out of 29 strains of the taxon rhodochrous seems to permit its separation from rapidly growing mycobacteria and certain actinomycetes which only exceptionally showed this property.     

微生物实验室管理模式初探

根据微生物学的实践教学特点, 从改革实验大纲和管理方式入手, 积极探索并初步构建了开放微生物实验室在空间场地、仪器设备、实验时间、实验内容等方面的运行与管理模式, 并在实践中收到了良好的成效。     

Identification of Enterobacteriaceae with the Minitek system

A total of 417 strains (361 Enterobacteriaceae, 56 Vibrionaceae) was examined in all the available Minitek system tests. The results were processed through four successive identification schemes devised by the manufacturer and the proportion of strains correctly identified, not identified or incorrectly identified determined for each scheme. From the results, a probability matrix was constructed incorporating all 35 Minitek tests. Test results for each strain were then processed through this matrix to determine its success in identification. From the matrix the order of separating value of the tests was determined. Forty-three of the strains were each tested three times to assess the level of test reproducibility; the corrected error rate was 0.85%.     

Identification of Enterobacteriaceae with the Minitek system

A total of 417 strains (361 Enterobacteriaceae, 56 Vibrionaceae) was examined in all the available Minitek system tests. The results were processed through four successive identification schemes devised by the manufacturer and the proportion of strains correctly identified, not identified or incorrectly identified determined for each scheme. From the results, a probability matrix was constructed incorporating all 35 Minitek tests. Test results for each strain were then processed through this matrix to determine its success in identification. From the matrix the order of separating value of the tests was determined. Forty-three of the strains were each tested three times to assess the level of test reproducibility; the corrected error rate was 0.85%.     

微生物学实验多样化教学之初探

实验教学是微生物教学的重要组成部分,是培养学生动手能力、分析和解决问题等能力的重要教学环节.通过适当修改实验方案、整体设计实验、解决实际问题和开设综合性实验等途径实现多样化的教学模式,实践表明可以显著提高学生的学习兴趣,充分调动学生的积极性、主动性和创造性.     

Numerical Diagnostic Key for the Identification of Enterobacteriaceae

A numerical diagnostic key for enteric organisms is described which permits the identification of typical strains and of biochemical variants with high accuracy. Unknown strains are inoculated into a basic set of five media which permit the testing of eight biochemical reactions. The positive reactions are assigned points, and the score of a strain is added up, after which the identification of the strain is obtained from a table. In many instances, the final identification is obtained with this set of biochemical tests; and, in other instances, a small number of additional tests are required to distinguish between organisms giving the same score in the basic set of biochemical tests. The key permits an accurate, rapid, and economical differentiation of the typical and the more common atypical biotypes of enteric organisms in the clinical laboratory.     

医学微生物实验课教学的思考

医学微生物学是高等医学院校课程体系的重要组成部分,实验课在本课程中占有重要的地位。为提高学生学习的主动性及积极性,进而提高教学质量,作者就几年来教学经验谈些体会。     

Incidence and Identification of Pseudomonas fluorescens and Pseudomonas putida in the Clinical Laboratory

Strains of Pseudomonas producing fluorescin but no pyocyanin or pyorubrin were studied by biochemical and antibiotic sensitivity testing. A rapid nitrate test was found to be useful in distinguishing P. aeruginosa (positive) from P. fluorescens and P. putida (both negative). A shortened gelatin test differentiated P. fluorescens (positive) from P. putida (negative). P. fluorescens and P. putida were very sensitive to low levels of kanamycin and resistant to carbenicillin, a pattern just the opposite of that obtained with P. aeruginosa.     

Intravenous Catheter-Associated Bacteremia: Role of the Diagnostic Microbiology Laboratory

A 2-year review of 316 routine intravenous catheter cultures revealed 57 positive cultures (18%), with 57% of the 74 organisms recovered interpreted as pathogens. There were five episodes of catheter-associated septicemia.     

Evaluation of the Minitek System for Identification of Enterobacteriaceae

Clinical isolates (869) and stock cultures (35) of Enterobacteriaceae were tested in parallel with the Minitek and conventional systems. The Minitek correctly identified 822 of 904 cultures. When a deoxyribonuclease plate was inoculated along with the Minitek, it was possible to speciate Enterobacteriaceae within 24 h. False-positive hydrogen sulfide reactions were the major fault with this system. Reactions were clear-cut and easy for technologists to read.     

Rapid Ornithine Decarboxylase Test for the Identification of Enterobacteriaceae

Conventional methods for detecting ornithine decarboxylase activity require an extended period of incubation. However, with a few simple modifications, accurate results were obtained within a few hours rather than several days. The broth medium was modified, primarily by omitting glucose and by decreasing the pH to 5.5. A 1-ml amount of this broth was inoculated with one colony and then overlaid with sterile mineral oil. Within 2 to 4 hr, the pH increased if ornithine was decarboxylated, thus changing the color of the internal pH indicator to a dark purple. If the amino acid was not decarboxylated, the pH decreased to pH 5.0 to 5.2, enough to give a definite yellow color. With 347 selected clinical isolates, the rapid test gave results identical to those obtained in 1 to 4 days with Moeller's decarboxylase medium. Less reliable results were obtained with Difco's decarboxylase medium with 0.3% agar which was stabinoculated and read after 18 to 24 hr without a mineral oil seal. The rapid ornithine decarboxylase test represents a simple, accurate technique which is well suited for the clinical microbiology laboratory.     

Laboratory Identification of Rothia dentocariosa and Its Occurrence in Human Clinical Materials

Fifty isolates of Rothia dentocariosa from diverse clinical sources were characterized by 28 separate tests. An attempt was made to select practical tests that could be completed in a minimal length of time. Rothia is also compared with Actinomyces and Nocardia with which it is often confused. Of the isolates 100% were positive in the following reactions: catalase production, nitrate and nitrite reduction, esculin hydrolysis, and acid production from glucose, sucrose, maltose, salicin, and glycerol. The importance of recognizing this organism is based on the fact that it is frequently isolated from human clinical materials and must be differentiated from morphologically similar organisms of the genera Actinomyces and Nocardia, which contain pathogenic members.     

Identification of Members of the Family Enterobacteriaceae by the R-B System

The R-B system was evaluated in parallel with conventional bacteriological procedures for the identification of members of the family Enterobacteriaceae by using bacterial strains from a variety of clinical specimens and from stock cultures. The R-B tests found to be reliable were, in decreasing order, the reactions for phenylalanine deaminase, hydrogen sulfide, and indole, the production of gas from glucose, and the decarboxylation of ornithine. The reactions in the R-B system found to be unreliable were motility, the decarboxylation of lysine, and the fermentation of both glucose and lactose. In addition, the reactions of the R-B system were more difficult to read and interpret than those of the conventional system. On the basis of this evaluation, it was concluded that the R-B system is not an acceptable alternative to the conventional methods in the identification of the Enterobacteriaceae.     

Catalase Test as an Aid to the Identification of Enterobacteriaceae

Although the catalase test has been used for many years for rapid differentiation of the genera of gram-positive organisms, little has been said about its use in the family Enterobacteriaceae. It was further noted that a wide variety of methods exist for the execution of the catalase test, that there is no universally accepted strength specified for the hydrogen peroxide, and that no gradations for the vigor and speed of the reaction have been mentioned. Under the conditions of the clinical laboratory, we have developed a simple, rapid, and accurate method for the catalase test that has been of great value as an aid in the identification of the Enterobacteriaceae. With 3% H(2)O(2), it was observed that Serratia, Proteus, and Providencia were vigorous catalase reactors. Only Salmonella and rare Escherichia, Enterobacter, and Klebsiella isolates were moderate catalase reactors. Escherichia and Shigella strains were mostly nonreactive, with less than one-third weekly (+) reactive, whereas most Enterobacter strains tended to be weakly reactive. Klebsiella strains were divided equally between nonreactive and weakly reactive. In practice, this test was also of great value in discerning nonpigmented Serratia cultured from the hospital environment and in detecting mixed flora containing nonspreading Proteus.