Absence of siderophore activity in Legionella species grown in iron-deficient media.

Growth of Legionella species in a defined medium deficient in iron did not result in the production of phenolic or hydroxamate siderophores which could be detected by chemical or biological assay methods. Growth of a variety of other gram-negative organisms under the same conditions resulted in the production of both hydroxamate and phenolate siderophores. The iron-deficient medium limited growth of the Legionella species more severely than it did the growth of the other gram-negative organisms. We have concluded that Legionella species do not make the commonly recognized siderophores, probably because they are restricted in their growth to those environments in which inorganic iron is readily available or is supplied in a form bound to an unknown carrier.

Salmonella typhi: the laboratory as a reservoir of infection.

As a part of educational and proficiency exercises thousands of students and laboratory personnel have been exposed to Salmonella typhi. In a retrospective study 24 cases of laboratory-acquired typhoid fever in the United states during a 33-month period were identified; laboratory-acquired cases represented only 2.4% of all typhoid cases but 11.2% of the sporadic cases. Twenty-one of the 24 cases occurred when S. typhi was voluntarily introduced into the laboratory for educational proficiency testing or research purposes. Twelve patients were exposed to S. typhi when working with it as an unknown organism; another five were merely present in the laboratory. Obvious breaks in technique were found to be the cause of infection for only seven of the 24 patients, although infection of the others implies that breaks in technique occurred. Laboratory-acquired typhoid fever may severe as a marker for other less severe laboratory-acquired infections; these data suggest that such infections could be common.

Collaborative investigation of the AutoMicrobic System Enterobacteriaceae biochemical card.

The Enterobacteriaceae biochemical card used in six separate laboratories to identify 170 representatives of Enterobacteriaceae. The AutoMicrobic System (Vitek Systems, Inc.) performed with an accuracy of 97.8% as compared with 98.1% by the standard method selected and 97.6% by a commerically prepared manual system approach. During this time, 5,450 clinical isolates belonging to Enterobacteriaceae were analyzed. Compared with the routine methods used in the various laboratories, the AutoMicrobic System identified 96.4% correctly

Multi-laboratory evaluation of an automated microbial detection/identification system.

An automated and computerized system (Automicrobic System [AMS]) for the detection of frequently encountered bacteria in clinical urine specimens was tested in a collaborative study among six laboratories. The sensitivity, specificity, reliability, and reproducibility of the AMS were determined, and the system was compared with conventional detection and identification systems. In this study, pure cultures and mixtures of pure cultures were used to simulate clinical urine specimens. With pure cultures, the sensitivity of the AMS in identifying the nine groups of organisms most commonly found in urine averaged 92.8%. The specificity averaged 99.4%, and the reliability of a positive result averaged 92.1%. The latter value was strongly influenced by a relatively high occurrence of false positive Escherichia coli results. The AMS was capable of detecting growth of most organisms, including those which it was not designed to identify. However, it identified some of these incorrectly as common urinary tract flora. Reproducibility of results, both within laboratories and among different laboratories, was high. Fast-growing organisms, such as E. coli and Klebsiella/Enterobacter species, were detected often at cell populations well below the AMS enumeration threshold of 70,000/ml. In mixed culture studies, high levels of sensitivity and specificity were maintained but when Serratia species were present in mixtures with other organisms, there was often a false positive report of E. coli. The overall performance of the AMS was considered satisfactory under the test conditions used.

Training and certification of clinical microbiologists.

Microbiologists are being effectively absorbed into the labor market. As a group they have a considerably lower unemployment rate (1.2%) than the national average. This is also applicable to medical and clinical microbiologists. Certification of microbiologists by nationally recognized certifying organizations is standardized for those with bachelor's or master's degrees. For those with doctorate degrees there are inconsistencies of postdoctoral training requirements and of reciprocal recognition of the two major certifying organizations. Bilateral reciprocal recognition of board-certified doctoral-level microbiologists is vital for meeting manpower needs. Improved and equitable certification could be achieved by maintaining an adequate number of funded, approved training programs in medical and clinical microbiology and augmenting them with uniform continuing medical education programs designed to meet the requirements for periodic recertification.

Evaluation of the Enteric Analyzer, an instrument to aid in the identification of Enterobacteriaceae.

This study evaluated the Enteric Analyzer, an instrument designed to identify Enterobacteriaceae, with data obtained from the Modified r/b Enteric Differential System, other rapid identification systems, or conventional identification systems. It is programmed for 19 reactions with data obtained from Center for Disease Control publications. The instrument is very simple to use. Typical strains from 25 of 28 species were unequivocally identified. With the other three species, two choices were given. A switch allows the user to identify all species possibilities where a given biochemical pattern occurs in more than 1% of the strains or more than 10% of the strains. The instrument is useful both in the clinical laboratory and for teaching purposes.

Laboratory evaluation of a rapid, automatic susceptibility testing system: report of a collaborative study.

Seven laboratories participated in a collaborative study to evaluate the Autobac 1 system. Results obtained with this assay system were compared to those obtained by the standardized Bauer-Kirby disk diffusion test, and each of these two methods was compared to the agar dilution technique. Comparison of the Autobac 1 and the disk diffusion results from the seven laboratories showed an overall average of 91.5% interpretive agreement with the 17 antimicrobial agents tested. The distribution in the levels of Autobac 1/disk diffusion agreement was such that with 13 antimicrobial drugs agreement was 90% or higher; with three, between 85 and 90%; and with one, 77% (nitrofurantoin). Comparison of the Autobac 1 and disk diffusion tests with the International Collaborative Study agar dilution test showed that both methods gave levels of agreement with the International Collaborative Study agar dilution technique that were generally high and equivalent. The average overall agreement between the agar dilution test and each of the other two methods was approximately 90%. Disagreements that did occur tended to involve organisms that were drug susceptible by the Autobac 1 system but intermediate or resistant by the other two methods. This was in part due to the narrow intermediate interpretive zone of the Autobac 1 test. In reproducibility studies with the Autobac 1 and disk diffusion methods, no significant differences were observed between the interpretive reproducibility of the two methods.

Evaluation of the Bactrol Disks, a set of quality control cultures.

A set of commercially available quality control cultures was evaluated. These cultures were found to be an acceptable alternate to lyophilized or continuously subcultured cultures for a quality control program.

r-b Expanders: their use in identifying routinely and unusually reacting members of Enterobacteriaceae.

This cooperative study between a large clinical laboratory and a reference laboratory evaluated the performance of the expanded r/b system for identifying Enterobacteriaceae. The 2,200 cultures isolated in the normal hospital routine presented no problem of identification to the r/b system. About 250 "atypical" cultures which were exchanged between the collaborating laboratories were also identified accurately. The expanded r/b system was found to perform as well as most biochemical-physiological identification systems, and when used appropriately was highly satisfactory as a system for identification of Enterobacteriaceae.

Evaluation of the improved Auxotab 1 System for identifying Enterobacteriaceae.

The improved Auxotab Enteric 1 System is more accurate in identifying Enterobacteriaceae than is the original product, and results correlate better with those obtained with conventional tests.

Micromethod system for identification of anaerobic bacteria.

A micromethod multitest system prepared by Analytab Products, Inc. and conventional tests employed at the Center for Disease Control for identification of anaerobes were compared. All procedures were conducted in an anaerobic glove box. A total of 104 cultures, including 18 reference strains and 86 diagnostic cultures, were examined. Ninety-one percent of the total tests performed with the two systems were in agreement. Greater than 90% agreement between the two systems was obtained with 12 of the 17 differential tests compared. The tests for nitrate reduction and H(2)S production gave the poorest agreement, 77.8 and 80.8%, respectively. Only 66% of the 86 diagnostic cultures could be presumptively identified with the micromethod system supplemented only with microscopy and colonial characteristics. However, when appropriate supplementary tests and gas-liquid chromatography were used with the micromethod system, 85% of the 86 strains could be identified. When Ehrlich reagent, instead of Kovac reagent, was used with the micromethod to test for indole, the agreement in identification was raised to 93%.