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Category: Clinical Microbiology
Francisella and Brucella * , Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap44-1.gif /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap44-2.gifAbstract:
The family Francisellaceae, a member of the gamma subclass of proteobacteria, consists of the single genus Francisella. Francisella tularensis, Francisella novicida, Francisella philomiragia, and Francisella noatunensis as well as unclassified Francisella spp. comprise the genus. Characterization data indicate that these Francisella spp. are distinct from F. tularensis, F. novicida, and F. philomiragia. The genus Francisella comprises tiny gram-negative coccobacilli that can be distinguished from similar genera by several features. A few key differences separate species of the Francisella genus. Under microscopic examination of Gram-stained specimens, Francisella cells (single and pleomorphic) appear tiny and counterstain so faintly with safranin that they can easily be missed. It is important to consider that many F. tularensis PCR assays cross-react with F. novicida. All Francisella isolates examined to date are β-lactamase positive, so penicillins and cephalosporins are not effective and should not be used to treat tularemia. Antimicrobial susceptibility testing of F. tularensis is not usually performed in clinical microbiology laboratories because of safety concerns in working with this organism. Currently, the most effective treatment regimen and optimal duration of treatment remain unclear. Interpretation of serologic test results in relation to exposure, diagnosis, and prognosis of the disease necessitates an accurate assessment of the clinical history and current status of patients and understanding the usefulness and pitfalls of the laboratory tests. Positive cutoff titers in the Brucella agglutination test for diagnosis have generally been considered to be greater than equal to 160 in symptomatic patients.
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F. tularensis on CA (A) and CHAB (B) after 48 hours of growth; B. melitensis on blood agar (C) and Mueller-Hinton broth (D) after 48 hours of growth.
F. tularensis on CA (A) and CHAB (B) after 48 hours of growth; B. melitensis on blood agar (C) and Mueller-Hinton broth (D) after 48 hours of growth.
Gram stain of F. tularensis (A) and B. melitensis (B). Magnification, ~ ×810.
Gram stain of F. tularensis (A) and B. melitensis (B). Magnification, ~ ×810.
DFA staining of a culture of F. tularensis. Magnification, ˜ ×490.
DFA staining of a culture of F. tularensis. Magnification, ˜ ×490.
Presumptive differentiation of Francisella and Brucella from similar gram-negative genera a
a +, greater than or equal to 90% positive; –, less than or equal to 10% positive; V, variable (11 to 89% positive); ccb, coccobacilli. Data are from reference 169.
b Does not include Bartonella bacilliformis, which is the only motile species.
c Formerly Moraxella phenylpyruvica.
d Haemophilus spp. requiring X and V factors or V factor only.
e While not required, X factor (hemin) enhances growth for many strains.
f May be difficult to demonstrate.
g The number before the colon indicates the number of carbons; the number after the colon is the number of double bonds, vindicates the location of the double bond counting from the hydrocarbon end of the carbon chain, OH indicates a hydroxy group at the 2 or 3 position from the carboxyl end, c indicates the cis isomer, and cyc indicates a cyclopropane ring structure. Hydroxy acids listed are at least 2% of the total cellular fatty acid (CFA) composition; all others are at least 10%.
h B. canis lacks 19:0cyc. Cellular fatty acid data for marine mammal strains are not available.
Presumptive differentiation of Francisella and Brucella from similar gram-negative genera a
a +, greater than or equal to 90% positive; –, less than or equal to 10% positive; V, variable (11 to 89% positive); ccb, coccobacilli. Data are from reference 169.
b Does not include Bartonella bacilliformis, which is the only motile species.
c Formerly Moraxella phenylpyruvica.
d Haemophilus spp. requiring X and V factors or V factor only.
e While not required, X factor (hemin) enhances growth for many strains.
f May be difficult to demonstrate.
g The number before the colon indicates the number of carbons; the number after the colon is the number of double bonds, vindicates the location of the double bond counting from the hydrocarbon end of the carbon chain, OH indicates a hydroxy group at the 2 or 3 position from the carboxyl end, c indicates the cis isomer, and cyc indicates a cyclopropane ring structure. Hydroxy acids listed are at least 2% of the total cellular fatty acid (CFA) composition; all others are at least 10%.
h B. canis lacks 19:0cyc. Cellular fatty acid data for marine mammal strains are not available.
Characteristics of Francisella spp.
a Standard bacteriological media: blood, Trypticase soy, and brain heart infusion.
b Delayed or variable reaction. F. tularensis subsp. mediasiatica does not ferment glucose ( 165 ).
c V, variable or slow reaction.
d NT, not tested.
Characteristics of Francisella spp.
a Standard bacteriological media: blood, Trypticase soy, and brain heart infusion.
b Delayed or variable reaction. F. tularensis subsp. mediasiatica does not ferment glucose ( 165 ).
c V, variable or slow reaction.
d NT, not tested.
Epidemiology of Francisella spp. affecting humans
Epidemiology of Francisella spp. affecting humans
Tests commonly used in laboratory diagnosis of brucellosis
Tests commonly used in laboratory diagnosis of brucellosis
Interpretation of commonly used serologic tests based on the immunoglobulin type detected and usefulness in the diagnosis of different disease categories/stages of human brucellosis
Interpretation of commonly used serologic tests based on the immunoglobulin type detected and usefulness in the diagnosis of different disease categories/stages of human brucellosis