Yu, Pauline K. W.

Regression lines were calculated for cephalothin, cephalexin, and cephaloridine by relating zone diameters of inhibition to minimal inhibitory concentrations (MIC) obtained in Mueller-Hinton agar and in Trypticase Soy Agar. A regression line was calculated for cephaloglycin by obtaining MIC values in Trypticase Soy Agar at p H 6.6. Regression lines calculated from MIC values in Mueller-Hinton agar were practically superimposable on those based on MIC values in Trypticase Soy Agar. Organisms susceptible by disc testing to cephalothin were usually susceptible to cephalexin and cephaloridine.

The characteristics of 25 hydrogen sulfide-negative strains of Citrobacter were studied. The majority of isolates were from the respiratory tract and usually were of indeterminate clinical significance. All strains were highly susceptible to polymyxin B, gentamicin, kanamycin, nalidixic acid, and nitrofurantoin.

The in vitro activity of minocycline against 1,028 bacterial strains was determined in parallel in Mueller Hinton Agar and Trypticase Soy Agar. The broad antibacterial effect of minocycline against gram-positive cocci and gram-negative bacilli is confirmed. Minimal inhibitory concentrations for gram-positive bacteria in Mueller Hinton Agar were at least twofold less than in Trypticase Soy Agar. Minimal inhibitory concentrations for gram-negative bacilli in Mueller Hinton Agar were usually fourfold less than in Trypticase Soy Agar.

The characteristics of an atypical group of the family Enterobacteriaceae resembling Enterobacter cloacae were studied. The urinary tract was the most common source of these organisms, and most strains represented infections of secondary clinical significance. In contrast to typical Enterobacter strains, the atypical strains were highly susceptible to the cephalosporins; otherwise, there was a high degree of susceptibility to five other antibiotics and resistance to ampicillin except in very high concentration.

In a paired, double-blind study, the modified (“Beckford tube”) R-B system was compared with conventional bacteriological procedures for the identification of members of the family Enterobacteriaceae from clinical isolates and stock cultures. The tests in the R-B system yielding positive reactions comparable to those predicted by Ewing's taxonomic classification of Enterobacteriaceae were production of hydrogen sulfide and presence of lysine and ornithine decarboxylasè activities. The test reactions in the R-B system found to be comparable to those in the conventional method were fermentation of glucose, hydrogen sulfide production, and lysine and ornithine decarboxylase activities. The production of gas from glucose was positive in the R-B system more often than in the conventional method; however, the motility test and the production of indole were positive less often in the R-B system. Adequate preliminary identification of the Enterobacteriaceae with the R-B system is enhanced if Simmons' citrate and Christensen's urea tests are used concomitantly. These findings emphasize the manufacturer's instructions that, in interpretation of results, colonial morphology and biochemical reactions must be used concurrently to make an accurate identification.

A study was performed with simulated blood cultures to evaluate the production of 14 CO 2 as an index of bacterial growth. With a range of inoculum sizes from 4 to 4,250 colony-forming units, it was not possible to detect 14 CO 2 within 6 hr after inoculation in 59 separate experiments. In a limited trial with patients' blood cultures, the radiometric method failed to provide any earlier evidence of bacteremia than did routine broth cultures.

The Enterotube 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. Excellent agreement between the two test systems was obtained with the following reactions: hydrogen sulfide, indole, Simmons' citrate, glucose, and lactose. Agreement was not as good (<85%) with the urea, phenylalanine deaminase, and dulcitol reactions. The Enterotube lysine decarboxylase test was unsatisfactory. The Enterotube method will correctly identify strains of the family Enterobacteriaceae approximately 50% of the time; if identification only as Klebsiella-Enterobacter-Serratia group is needed, the method will be correct 85% of the time. On the basis of this evaluation, the Enterotube system appears to be both simple and rapid for the presumptive identification of these bacteria. Because of the limited usefulness of the lysine decarboxylase test, the results obtained by this test system are less reliable than those obtained by conventional methods.

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 .

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.