Studies on the Variation of Bacterium Tularense

Abstract

Although the virulence of Bacterium tularense may be maintained for prolonged periods of cultivation on artificial media, a considerable reduction in v-irulence has been frequently observed. As early as 1922 Francis reported the loss of vTirulence of certain strains of B. tularense following serial transfer on seium glucose agar. Foshay (1932) described the loss of virulence of two strains isolated from fatal human cases following prolonged cultivation on coagulated egg yolk medium. Ransmeier (1943) reported a reduction of virulence after serial transfer of an originally highly virulent strain on glucose cystine blood agar. It is also well known that repeated passage of cultures through a given animal species may result in a marked increase in virulence for the particular host (Philip and Davis, 1935). Thus, changes in virulence have been amply demonstrated; however, it has not been possible to correlate these changes with any other easily detectable characteristics. All attempts to correlate cellular morphology with virulence (Hesselbrock and Foshay, 1945; Eigelsbach, Chambers, and Coriell, 1946) have met with failure. Because various bacterial species display a high degree of correlation between colonial morphology, pathogenicity, and immunogenic properties (Braun, 1947), an attempt was made to determine whether such correlations may also exist for B. tularense. As far as the authors are aware, studies on the colonial morphology of B. tularense have not been reported previously in the literature. MATERIALS AND METHODS The majority of experiments were initiated with either a highly virulent culture, Schu, originally isolated by Foshay in 1941 from a human ulcer, or with an avirulent culture, 38, which was originally isolated by Francis in 1920 from a human lymph node and subsequently became totally avirulent (Hesselbrock and Foshay, 1945). These cultures, as well as variant types subsequently isolated, were maintained on glucose cysteine blood agar (GCBA) at 5 to 10 C following a 24-hour growth period at 37 C. The solid transparent medium used for viable count and colony type observations consisted of 2 per cent Difco peptone, 1 per cent NaCl, 0.1 per cent glucose, 0.1 per cent cysteine hydrochloride, and 2 per cent agar with a final reaction of pH 6.8 (Snyder et al., 1946). The basal liquid medium used was identical in composition except for the absence of agar. Vliable counts were made by plating serial dilutions on GCBA; total growth was determined by packed cell volume in modified hematocrit tubes after centrifugation at 4,000 rpm for 1 hour. Colony types wvere inspected under a dissecting microscope with the help of obliquely transmitted light, achieved by placing the mirror, concave side up, 557

A dose and time response Markov model for the in-host dynamics of infection with intracellular bacteria following inhalation: with application toFrancisella tularensis

“…The most severe form of the disease is pneumonic (or respiratory) tularaemia, which is caused by inhalation of aerosolized particles [19]. Of interest to this study is the Schu S4 strain [20] of the highly virulent tularensis subspecies [17,21]. While this intracellular organism is considered facultative in vitro, it is thought to be obligate in vivo [21,22].…”

Phase variation in Francisella tularensis affecting intracellular growth, lipopolysaccharide antigenicity and nitric oxide production

“…Both biotypes of F. tularensis segregate avirulent colony-opacity variants at a frequency of 1 0 -~-1 0 -~ per generation (Eigelsbach et a/., 1951). In this work we show that the change in the colony phenotype correlates with an antigenic shift in the LPS 0-antigen and an enhanced ability of the LPS and lipid A to stimulate the production of NO.…”

Immunogenicity and toxicity of lipopolysaccharide from Francisella tularensis LVS

“…It is a small singly-occurring, bipolar rod. On solid media, F. tularensis shows a mucoid; smooth colony form [1][2][3][4][5]. The bacterium exhibits a three-laminar membrane structure [6], similar to other Gramnegative bacteria [7].…”