THE ONPG TEST IN DIAGNOSTIC BACTERIOLOGY

Indigogenic substrates for detection and localization of enzymes

Indoxyl esters and glycosides are useful chromogenic substrates for detecting enzyme activities in histochemistry, biochemistry and bacteriology. The chemical reactions exploited in the laboratory are similar to those that generate indigoid dyes from indoxyl-beta-d-glucoside and isatans (in certain plants), indoxyl sulfate (in urine), and 6-bromo-2-S-methylindoxyl sulfate (in certain molluscs). Pairs of indoxyl molecules released from these precursors react rapidly with oxygen to yield insoluble blue indigo (or purple 6,6'-dibromoindigo) and smaller amounts of other indigoid dyes. Our understanding of indigogenic substrates was developed from studies of the hydrolysis of variously substituted indoxyl acetates for use in enzyme histochemistry. The smallest dye particles, with least diffusion from the sites of hydrolysis, are obtained from 5-bromo-, 5-bromo-6-chloro- and 5-bromo-4-chloroindoxyl acetates, especially the last of these three. Oxidation of the diffusible indoxyls to insoluble indigoid dyes must occur rapidly. This is achieved with atmospheric oxygen and an equimolar mixture of K(3)Fe(CN)(6) and K(4)Fe(CN)(6), which has a catalytic function. H(2)O(2) is a by-product of the oxidation of indoxyl by oxygen. In the absence of a catalyst, the indoxyl diffuses and is oxidized by H(2)O(2) (catalyzed by peroxidase-like proteins) in sites different from those of the esterase activity. The concentration of K(3)Fe(CN)(6)/K(4)Fe(CN)(6) in a histochemical medium should be as low as possible because this mixture inhibits some enzymes and also promotes parallel formation from the indoxyl of soluble yellow oxidation products. The identities and positions of halogen substituents in the indoxyl moiety of a substrate determine the color and the physical properties of the resulting indigoid dye. The principles of indigogenic histochemistry learned from the study of esterases are applicable to methods for localization of other enzymes, because all indoxyl substrates release the same type of chromogenic product. Substrates are commercially available for a wide range of carboxylic esterases, phosphatases, phosphodiesterases, aryl sulfatase and several glycosidases. Indigogenic methods for carboxylic esterases have low substrate specificity and are used in conjunction with specific inhibitors of different enzymes of the group. Indigogenic methods for acid and alkaline phosphatases, phosphodiesterases and aryl sulfatase generally have been unsatisfactory; other histochemical techniques are preferred for these enzymes. Indigogenic methods are widely used, however, for glycosidases. The technique for beta-galactosidase activity, using 5-bromo-4-chloroindoxyl-beta-galactoside (X-gal) is applied to microbial cultures, cell cultures and tissues that contain the reporter gene lac-z derived from E. coli. This bacterial enzyme has a higher pH optimum than the lysosomal beta-galactosidase of animal cells. In plants, the preferred reporter gene is gus, which encodes beta-glucuronidase activity and is also demonstrable by indigogenic histochemistry. Indoxyl substrates also are used to localize enzyme activities in non-indigogenic techniques. In indoxyl-azo methods, the released indoxyl couples with a diazonium salt to form an azo dye. In indoxyl-tetrazolium methods, the oxidizing agent is a tetrazolium salt, which is reduced by the indoxyl to an insoluble coloured formazan. Indoxyl-tetrazolium methods operate only at high pH; the method for alkaline phosphatase is used extensively to detect this enzyme as a label in immunohistochemistry and in Western blots. The insolubility of indigoid dyes in water limits the use of indigogenic substrates in biochemical assays for enzymes, but the intermediate indoxyl and leucoindigo compounds are strongly fluorescent, and this property is exploited in a variety of sensitive assays for hydrolases. The most commonly used substrates for this purpose are glycosides and carboxylic and phosphate esters of N-methylindoxyl. Indigogenic enzyme substrates are among many chromogenic reagents used to facilitate the identification of cultured bacteria. An indoxyl substrate must be transported into the organisms by a permease to detect intracellular enzymes, as in the blue/white test for recognizing E. coli colonies that do or do not express the lac-z gene. Secreted enzymes are detected by substrate-impregnated disks or strips applied to the surfaces of cultures. Such devices often include several reagents, including indigogenic substrates for esterases, glycosidases and DNAse.

Phenotypic characterization of Flavobacterium meningosepticum strains identified by DNA-DNA hybridization

Fifty-two strains found to belong to Flavobacterium meningosepticum on the basis of DNA-DNA hybridization analyses were characterized and found to be phenotypically homogeneous. All strains were oxidase, catalase, indole, gelatinase and beta-galactosidase positive, and produced acid from glucose, mannose, fructose, maltose and mannitol; nitrate was not reduced. F. meningosepticum could be differentiated from Flavobacterium group IIb by its ability to produce beta-galactosidase, and by the latter taxon's ability to produce a bright yellow pigment in contrast to the weak or non-existing pigmentation of F. meningosepticum. Phenotypic characteristics that could differentiate between the two main DNA relatedness groups of F. meningosepticum were not discovered, wherefore a subdivision of the present species into two species cannot be recommended. Strains from the DNA relatedness groups comprising 19 of 20 CSF isolates were found to be able to grow at 40 degrees C and to produce a weak yellow pigment; in contrast, strains from the three other DNA relatedness groups were unable to grow at 40 degrees C and produced no pigment.

Numerical taxonomy of proteolytic psychrotrophs from Queensland raw milks

Eighty-seven proteolytic psychrotrophic micro-organisms were isolated from 11 bulk milk supplies of two Queensland factories from different climatic regions, before and after storage at 4 degrees C for 7 d. These isolates together with 15 reference strains formed the basis of a numerical taxonomic study involving 81 attributes. All but six isolates were pseudomonads. The strains clustered into nine groups, of which one group consisted of four yeasts. One group, containing 39 isolates, was designated as Pseudomonas fluorescens biovar 1; three groups, containing 27 isolates, as Ps. fluorescens biovar 5; and one group, containing 10 isolates, as Ps. putida biovar A. This study showed that the proteolytic psychrotrophic microflora of the 11 milks supplying the two factories was substantially different and that the proteolytic flora of 7 d refrigerated milk could not be estimated by examining the flora before storage.

Antigenic and biochemical characteristics of Mobiluncus mulieris and Mobiluncus curtisii

Twenty-four strains of Mobiluncus mulieris and 27 strains of Mobiluncus curtisii were tested with respect to 6 different biochemical characteristics: arginin-decarboxylase activity, beta-galactosidase activity, synergistic hemolysis with Staphylococcus aureus, hydrolysis of hippurate, migration through soft agar and reduction of nitrate. Antigens of the same strains, prepared by ultrasonication, were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by immunoblotting using polyclonal rabbit antisera against two of the M. mulieris strains and five of the M. curtisii strains. Two different strongly reacting protein antigens could be detected in the M. mulieris strains. These strains could be separated into three groups based on the possession of either of the two antigens or both. In the M. curtisii strains, 10 strongly reacting protein antigens could be detected. Four strains possessed only one of these antigens, one did not possess any, while the remaining strains possessed different sets of 9 of them. Within each species common protein antigens were detected. No antigens were found which were shared by both species. The biochemical characteristics studied could not differentiate between the antigenic groups in any of the species. None of the antigenic subgroups of M. curtisii found in the present study was identical with any of the two subspecies (curtisii and holmesii) which have been proposed.

An investigation of a collection of yellow-pigmented Pseudomonas

Thirty-six strains of yellow-pigmented Pseudomonas from clinical as well as non-clinical material and 11 reference strains of Pseudomonas were investigated by means of conventional bacteriological methods (a total of 53 different tests). Eighteen of the 36 yellow-pigmented strains could be classified as P. paucimobilis. Apart from the presence of lipid inclusions on beta-hydroxybutyrate, hydrolysis of DNA, and Tween 80 our results showed a high degree of accordance with other investigations. Eight strains showed characteristics compatible with inclusion in the CDC VE group; one orange-yellow strain showed the characteristics of P. vesicularis, and one was a pyoverdin negative, yellow P. putida. Eight strains remained unidentified. Strains of P. paucimobilis were most often resistant to antibiotics used for P. aeruginosa infections (viz. piperacillin, cefsulodin, ceftazidime) while the strains of the CDC VE group were often susceptible. Most strains were susceptible to the aminoglycosides. The difficulties in distinguishing yellow-pigmented strains of Pseudomonas from Flavobacterium spp. or Xanthomonas spp. are discussed.

Rapid identification of Capnocytophaga isolated from septicemic patients

Four Capnocytophaga strains from blood cultures of immunocompromised patients with malignant disease and the type strains of three Capnocytophaga species were examined and compared to strains representing five other genera that are hard to differentiate from Capnocytophaga. With three rapid identification methods, negative catalase and oxidase reactions and positive ONPG assay, Capnocytophaga was easily separated from Eikenella corrodens, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, and CDC group DF-2. Haemophilus aphrophilus was excluded by leucine, valine and cystine arylamidase and alpha-glucosidase reactions (API ZYM). Further confirmatory reactions constituted gelatin hydrolysis, haemin requirement, and carbohydrate and esculin breakdown. Although rapid identification of Capnocytophaga to the genus level was feasible, differentiation on a species level proved impossible.

Phenotypic differentiation of Cardiobacterium hominis, Kingella indologenes and CDC group EF-4

Eleven strains of Cardiobacterium hominis, two strains of Kingella indologenes and six strains of CDC group EF-4 were characterized. Since all three taxa are oxidase-positive, fastidious gram-negative rods with relatively few positive reactions, they may be easily confused in the microbiological laboratory. Common characteristics are acid production from glucose, aerobic growth in semi-solid agar and very slow anaerobic growth. Group EF-4 is distinguished from the other two species by its capacity to produce catalase and its lack of indole production. Cardiobacterium hominis can be distinguished from Kingella indologenes by its ability to ferment mannitol and sorbitol and by differences in enzyme production. The three taxa also differ considerably with regard to morphological and cultural characteristics.

Identification and characterization of Kingella kingae

Kingella kingae is a rarely isolated opportunistic pathogen in the family Neisseriaceae. Thirteen strains of this organism, including six strains isolated in Denmark, were characterized. They formed a homogeneous group of small, non-motile, fastidious Gram-negative rods which were beta-haemolytic, oxidase positive, catalase negative and saccharolytic. Acid was produced for glucose and maltose. Growth was most pronounced aerobically but corroding colonies increased considerably in size during anaerobic incubation.

An epidemic of Salmonella typhimurium infection among aircraft passengers

In February 1976 an outbreak of gastroenteritis occurred among 819 aircraft passengers to and from Gran Canaria. 360 of them had gastroenteritis and 88 were hospitalized. Fecal specimens were collected from 710 of the passengers and 344 of them were positive for Salmonella typhimurium phage type 15. Food served on the flight was the source of infection. The repeated incidences of this kind support the necessity of laying down rules and recommendations for the control of air catering services.

Correlation of the characters fermentation of trehalose, non-transmissible resistance to tetracycline, and relatively long flagellar wavelength in Proteus morganii

An investigation of strains of Proteus morganii isolated from patients in Odense, Denmark, and of 21 serotype strains revealed a close correlation between the fermentation of trehalose and a non-transmissible resistance to tetracycline. The trehalose fermenting, tetracycline resistant strains had a longer flagellar wavelength than the non-fermenting, sensitive strains. Resistance to chloramphenicol occurred only in strains of the former group.

Endocarditis caused by Actinomyces viscosus

A case of severe endocarditis caused by Actinomyces viscosus is described in a previously healthy 70-year-old man. The isolated strain has been characterized by biochemical tests, gas-liquid chromatography and serology. The pathogenic significance of the organism is discussed and the difficulty in reaching a correct diagnosis due to the similarity to species of Corynebacterium is pointed out.

Rapid diagnosis of Enterobacteriaceae. I. Detection of bacterial glycosidases

The paper describes a number of tests for the rapid detection of glycosidases including alpha-glucosidase, beta-glucosidase, beta-glucuronidase, beta-xylosidase and alpha-fucosidase. The methods use heavy suspensions of viable but non-multiplying bacteria in a buffered solution of a chromogenic substrate. The results of the tests are readable within 4 h. The application of these tests to a collection of 633 strains of Enterobacteriaceae and Vibrionaceae demonstrates that some of the tests may be valuable additions to the present tests available for the identification of bacteria belonging to these families. beta-glucuronidase activity was observed only in strains of the Escherichia-Shigella group. 97 per cent of the Escherichia strains possessed beta-glucuronidase activity. beta-xylosidase activity was almost completely restricted to strains of the Klebsiella-Enterobacter group in addition to Yersinia strains. None of the strains possessed alpha-fucosidase activity.

Differentiation between Pseudomonas cepacia and Pseudomonas pseudomallei in clinical bacteriology

If only conventional laboratory tests are used, the widely occurring species Pseudomonas cepacia may, due to its variability, sometimes be difficult to differentiate from the dangerous pathogen Pseudomonas pseudomallei. In a comparative study using fresh isolates it is shown that animal inoculation seems to be a useful additional method in the differentiation. Also the determination of the ability to utilize selected carbon sources such as starch, hydroxybenzoate and uracil is helpful in reaching a correct identification.

Description of a bacterium associated with redmouth disease of rainbow trout (Salmo gairdneri)

A description was given of a gram-negative, peritrichously flagellated, fermentative bacterium that was isolated on numerous occasions from kidney tissues of rainbow trout (Salmo gairdneri) afflicted with redmouth disease. Although the bacteria apparently were members of the family Enterobacteriaceae, it was impossible to determine their taxonomic position within the family with certainty. Hence it was recommended that their taxonomic position remain sub judice for the present. As a temporary designation RM bacterium was used.Redmouth disease was transmitted from infected to normal fish through the medium of water.

Beta-galactosidase for distinguishing between Citrobacter and Salmonella

Detection of beta-galactosidase with the aid of o-nitrophenyl-beta-d-galactopyranoside (ONPG) was examined as a means for distinguishing between Citrobacter and Salmonella. Several factors which influence sensitivity and reliability of the test were studied. A bacteriostat, sodium azide, was included to permit prolonged incubation of weak and negative strains of enteric bacilli. By the procedure described, salmonellae gave negative ONPG tests; all of 171 strains of Citrobacter gave positive tests.