Evaluation of the MS-2 system for rapid identification of Enterobacteriaceae.

The precision, accuracy, and other performance characteristics of the MS-2 (Abbott Laboratories, Diagnostic Division, Dallas, Tex.) system for the identification of Enterobacteriaceae were evaluated in a collaborative study involving three clinical laboratories. When identifying 150 unknown, coded organisms, the MS-2 system was 97%, 98%, and 93% accurate, respectively, in three laboratories. The system showed an overall accuracy of 94% when compared with conventional manual tube methods in identifying 1,154 clinical isolates of 26 species of Enterobacteriaceae. Discrepancies between automated and conventional methods were chiefly caused by biochemical variants, especially among Enterobacter species. The MS-2 system was rapid and simple to operate and produced printed results of bacterial identification in 5 h. The cost of disposable components compared favorably with commercial, visually read systems for identifying Enterobacteriaceae.

Automated detection of microbial growth in blood cultures by using stainless-steel electrodes.

Sterile stainless-steel electrodes implanted in blood culture bottles and monitored electronically were used to detect growth of microorganisms. Each blood culture bottle contained 100 ml of medium and was inoculated with 10 ml of blood seeded with either 300 or 50 colony-forming units of one of several bacterial or yeast species that are commonly isolated from clinical blood cultures. Growth was indicated by a voltage change of at least 0.1 mV/min with an increasing slope over at least three consecutive 15-min intervals. This method was compared to the conventional visual method for detecting microbial growth in broth. Growth detection by both techniques was confirmed by subculture to solid media. Of the 163 cultures seeded with the high inoculum (300 colony-forming units) and confirmed as being positive, 148 (90.8%) were positive by the electronic detection system (EDS). At the lower inoculum (50 colony-forming units), 47 of 53 (88.7%) positive cultures were detected by EDS. Twelve of the 21 false-negatives by the EDS were cultures seeded with Cryptococcus neoformans. Excluding C. neoformans, the rate of detection of growth was 96.0%. Microbial growth was detected an average of 18 h earlier by EDS than by the conventional system in 176 (90.2%) of the cultures. Also examined were 156 patient blood cultures: 13 were positive both by EDS and by conventional methods.

Isolation of Aeromonas species from clinical sources.

In a period of one year, in a general hospital, Aeromonas hydrophila was isolated from 13 patients and Aeromonas shigelloides from one patient. Eight of the patients had superficial infections, two had urinary tract infections, and four had bacteriaemia. The association of Aeromonas bacteriaemia with cirrhosis of the liver and malignant disease, which has been previously reported, was observed in three of the four bacteriaemic patients. The key to laboratory diagnosis of this genus is the routine performance of the oxidase test in bacteriological procedures for the identification of Gram-negative bacilli.

Effect of hemodialysis and renal failure on serum and urine concentrations of cephapirin sodium.

Six patients undergoing chronic hemodialysis and 10 patients with chronic renal insufficiency hospitalized for nondialytic therapy received 1.0 g of cephapirin sodium by the intravenous route. The concentrations of cephapirin in arterial and venous plasma, dialysate, venous blood, and urine were measured during the ensuing 6 hr. The serum half-life of cephapirin was 105 to 108 min for the dialyzed patients and 95.9 min for the nondialyzed patients. Dialysis removed 22.8% of the administered dose. Nondialyzed patients excreted 19.5% of the administered dose in the urine. The concentration of cephapirin in the urine of all nondialyzed patients exceeded 50 mug/ml. The recovery of cephapirin in the urine collected for 6 hr after injection was from 34 to 770 mg (mean 195 mg). To maintain a concentration of cephapirin in the blood and urine which exceeds the minimal inhibitory concentration for most gram-positive and gram-negative microorganisms, nondialyzed patients should receive 15 to 18 mg of cephapirin per kg every 12 hr. Dialyzed patients should receive the same dose just prior to dialysis and every 12 hr thereafter.

Identification of Corynebacterium diphtheriae by immunofluorescence during a diphtheria epidemic.

During a large epidemic of diphtheria, the technique of immunofluorescence was applied to specimens obtained from 310 patients, 77 of whom were diagnosed clinically as having the disease. The technique made use of commerical fluorescent antisera prepared against the somatic antigens of Corynebacterium diphtheriae. The results obtained by immunofluorescence of slides prepared directly from swabs were found to be unsatisfactory but when the swabs were subjected to prior incubation in a growth medium the results of immunofluorescence and bacterial culture agreed in 95% of specimens. Immunofluorescence applied to bacterial colonies obtained on primary isolation agreed completely with definitive bacterial identification. These two methods for the rapid identification of C. diphtheriae appeared to be as reliable as formal cultural and biochemical methods and could be usefully and economically applied to the examination of large numbers of clinical specimens during an epidemic.

Complete suppression of haemoglobin A synthesis in haemoglobin D Los Angeles--beta thalassaemia.

A family study is reported in which all three siblings were shown to be doubly heterozygous for haemoglobin D Los Angeles and beta thalassaemia, which resulted in a complete suppression of haemoglobin A synthesis. This demonstrates the effects of genetic interaction which occur when the genes for haemoglobin D Los Angeles and beta thalassaemia are both transmitted to the offspring. The importance of family studies in the investigation of haemoglobin abnormalities is stressed.