Novel quality assurance procedure for the Gram strain

To read the full-text of this research, you can request a copy directly from the authors.


The Gram staining procedure is one of the most basic and important tests performed in the clinical microbiology laboratory. Currently, the only control method for determining the validity of this test is by the use of known bacterial cultures. Consequently, a novel method using the KOH technique for confirming the Gram staining reaction is described. This chemical procedure has been found to be a simple, effective and accurate quality control method for the Gram stain.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Coloration à la fuchsine 10 % pendant l à 2 minutes, puis lavage à l'eau et séchage.Les bactéries Gram + positif apparaissent violettes ; les bactéries Gramnégatif sont roses.Une méthode de contrôle de la validité d'une coloration de Gram réalisée sur une bactérie à déterminer est d'utiliser des cultures témoins de bactéries connues. Une autre technique récente, simple et rapide, dite technique à la potasseKOHN et HENNEMAN, 1977) permet de vérifier le caractère Gram + ou Gram -d'une bactérie : A une goutte de potasse à 3 % déposée sur une lame de verre, on mélange une colonie de la bactérie à tester prélevée sur une culture de 24 heures en milieu gélosé. Si après 1 minute environ le mélange devient visqueux et filant, la bactérie est dite KOH+. ...
The physico-chemical and microbiological process of round baled wet hay was studied under storage conditions. It appeared that the microbial population dynamics resulting in the replacement of the field flora by a mainly thermophilic and xerophilic storage flora did not depend on the initial temperature peak. The determinism of heating phenomena was then studied under laboratory conditions, taking as a basis both the measurements of the respiratory intensity of cut plants and the experiments on sterilized and contaminated hay conservation. The role of the plant respiration in the initial thermogenesis and that of microorganisms in persisting heating and partial loss of organic matter were respectively defined. The experiment conducted on liquid and solid preservatives did not prove satisfactory because the field treatment was insufficiently homogeneous (such was the case of propionic acid). The negative effect of heterogeneity increased with marketed products and sodium chloride because of inappropriate required doses and limited inhibitory action. Ammonia introduced by fumigation in covered stacks allows a far better conservation but requires specific care when dispensing the treated hay to the livestock.
A century ago,HansChristian Gramdevel- opeda staining procedure whichenabled the separation ofmostcommonly encountered bac- teria into twogroups: grampositive andgram negative. Today,Gramstaining remains the mostimportant differential technique applied to bacteria (2); infact, for8 ofthe19major groupings ofbacteria (1), staining isrequired as aprimary aidtoidentification. Although many biochemical features ofdiagnostic bacteriology havebeenadapted forincreased time-cost effi- ciency, theGramstain technique isessentially thesamenowasitwasin1884. Premixed stains canbepurchased, buttheprocedure isstill relatively timeconsuming, costly, andoften
A rapid nonstaining (KOH) method for the determination of the Gram reactions of bacteria is described, and its application to marine isolates is discussed. To perform the test, place a drop of 3% aqueous KOH on a slide. If one prefers, 10 μl from an automatic pipette is adequate. In practice, as many as 8 to 10 tests per slide can be done conveniently. Using a sterile loop, transfer a visible amount of bacterial growth from an agar culture to the drop of KOH. Mix the cells and KOH thoroughly on the slide, constantly stirring over an area about 1.5 cm in diameter. If the bacterium-KOH suspension becomes markedly viscid or gels within 5 to 60 sec, the isolate is gram negative. If no gelling is observed, the isolate is gram positive. The best way to determine viscosity is to raise the loop about 1 cm from the slide. If an obvious stringiness is present, then the culture is gram negative. All gram-positive and gram-negative results obtained by gram staining were confirmed by the KOH method. Gram-variable bacteria produced equivocal results.
A simple and rapid (< 60 s) nonstaining technique with 3% potassium hydroxide to determine Gram reactions was tested with 495 food-borne and waterborne bacteria and yeasts. In KOH, suspensions of gram-negative bacteria become viscous and string out. Gram-positive bacteria are not affected. There was 100% correlation between the KOH string test results and gram-positive and gram-negative strains.
ResearchGate has not been able to resolve any references for this publication.