Washington, John A.

During a 2.5-year study, streptococci were isolated from 280 patients (19% of those with bacteremia). Of this number, 54 had group D streptococci (45 were enterococci), 218 had α- or γ-hemolytic nongroup D streptococci, and 49 had β-hemolytic streptococci.

The Analytab system of 20 biochemical tests for identification of Enterobacteriaceae was evaluated in parallel with conventional tests on 128 Enterobacteriaceae , 5 Aeromonas , and 1 Yersinia enterocolitica. The results of tests for H 2 S and indole production, citrate utilization, lysine and ornithine decarboxylase, arginine dihydrolase, nitrate reduction, β-galactosidase, and fermentation of arabinose, rhamnose, mannitol, and glucose showed almost complete agreement between the two systems. Eighty-eight per cent of Enterobacteriaceae were correctly speciated with the Analytab system; on repeat testing with heavier inocula of organisms failing to ferment glucose initially, the proportion of Enterobacteriaceae correctly speciated became 93%.

A new coagulase-mannitol reagent-impregnated strip test has been evaluated with 322 Micrococcaceae. Mannitol fermentation was determined accurately by this test; however, the coagulase reaction was difficult to interpret and was subject to significant error.

McFarland barium sulfate standards prepared in 1952 were compared spectrophotometrically with freshly and identically prepared standards; the results were nearly identical.

An evaluation of the accuracy and convenience of the Auxotab Enteric 1 System for identification of Enterobacteriaceae was performed with 160 bacteria. Identification at the species level was correct in 134 (83.8%) instances and at the generic level in 144 (90%) instances. Sixty strains failed to achieve the minimal concentration of organisms required to complete the identification process within 7 hr. The system was judged to be laborious and to present a potential hazard to those working with it.

Seventeen strains of H 2 S-producing variants of Escherichia coli were isolated from specimens submitted for microbiological study (ten from stool, five from urine, and two from postmortem material). Production of H 2 S was unstable in several strains; however, other than their production of H 2 S, all strains closely resembled typical E. coli in their biochemical reactions. In vitro susceptibilities of the H 2 S-producing variants to antimicrobics closely resembled those of typical E. coli in this laboratory.

Media and techniques for in vitro testing with respect to screening for methicillin-resistant Staphylococcus aureus are discussed.

The characterization of 556 Micrococcaceae isolates from various clinical sources has been presented. The incidence of coagulase-negative mannitol-positive staphylococci was 3.2% and that of coagulase-positive mannitol-negative staphylococci was 1.6%. There appears to be insufficient justification for the routine reporting of staphylococcal variants from a general bacteriology laboratory, and biotyping should be reserved for special circumstances.

The use of a differential quantitative blood culture technique (Isolator) to diagnose intravascular-device-related bacteremia (IDRB) was studied prospectively. During septic episodes in 44 patients, blood was obtained simultaneously through the suspected infected device and from a peripheral venipuncture. The blood samples were processed by the Isolator technique, which enables easy quantification of microorganisms. The cannula was removed, and its tip was cultured semiquantitatively. Of the 52 cannulas studied, 15 were the cause of IDRB, but only 7 of these showed a significantly higher bacterial count in blood obtained through the device compared with peripheral blood. The bacterial count was higher in blood drawn through the device than in peripheral blood in four of six cases that did not fulfill the definition of IDRB. Some blood cultures obtained through the device were positive despite negative cultures of peripheral blood and cannula tips (six cannulas). Quantitative blood cultures were not useful in diagnosing IDRB in this study.