Chemical and biological properties of lipopolysaccharides from Fusobacterium necrophorum biovar A and biovar B strains

Development of an experimental model for liver abscess induction in Holstein steers using an acidotic diet challenge and bacterial inoculation

Holstein steers (n = 40; initial BW = 84.9 ± 7.1 kg) were used to study the genesis of liver abscesses (LA) using an acidotic diet challenge with or without intraruminal bacterial inoculation. Steers were housed in individual pens inside a barn and randomly assigned to one of three treatments: (1) low-starch control diet comprised primarily of dry-rolled corn and wet corn gluten feed (CON); (2) high-starch acidotic diet with steam-flaked corn (AD); or (3) acidotic diet plus intraruminal inoculation with Fusobacterium necrophorum subsp. necrophorum (9.8 × 108 colony forming units [CFU]/mL), Trueperella pyogenes (3.91 × 109 CFU/mL), and Salmonella enterica serovar Lubbock (3.07 × 108 CFU/mL), previously isolated from LA (ADB). Steers in AD and ADB were fed the acidotic diet for 3 d followed by 2 d of the CON diet, and this cycle was repeated four times. On day 23, ADB steers were intraruminally inoculated with the bacteria. At necropsy, gross pathology of livers, lungs, rumens, and colons was noted. Continuous data were analyzed via mixed models as repeated measures over time with individual steer as the experimental unit. Mixed models were also used to determine the difference in prevalence of necropsy scores among treatments. Ruminal pH decreased in AD and ADB steers during each acidotic diet cycle (P ≤ 0.05). LA prevalence was 42.9% (6 of 14) in ADB vs. 0% in AD or CON treatments (P < 0.01). Ruminal damage was 51.1% greater in ADB than in AD (P ≤ 0.04). Culture of LA determined that 100% of the abscesses contained F. necrophorum subsp. necrophorum, 0% contained T. pyogenes, 50% contained Salmonella, and 50% contained a combination of F. necrophorum subsp. necrophorum and Salmonella. The F. necrophorum subsp. necrophorum was clonally identical to the strain used for the bacterial inoculation based on phylogenetic analysis of the whole genome. This experimental model successfully induced rumenitis and LA in Holstein steers and confirms the central dogma of LA pathogenesis that acidosis and rumenitis lead to the entry of F. necrophorum into the liver to cause abscesses. Our findings suggest that an acidotic diet, in conjunction with intraruminal bacterial inoculation, is a viable model to induce LA. Further research is needed to determine the repeatability of this model, and a major application of the model will be in evaluations of novel interventions to prevent LA.

Human infection with Fusobacterium necrophorum (Necrobacillosis), with a focus on Lemierre's syndrome

Human infection with Fusobacterium necrophorum usually involves F. necrophorum subsp. funduliforme rather than F. necrophorum subsp. necrophorum, which is a common pathogen in animals. Lemierre's syndrome, or postanginal sepsis, is the most common life-threatening manifestation. Tonsillitis is followed by septic thrombophlebitis of the internal jugular vein and then a septicemia with septic emboli in lungs and other sites. Recent evidence suggests that F. necrophorum can be limited to the throat and cause persistent or recurrent tonsillitis. F. necrophorum is unique among non-spore-forming anaerobes, first for its virulence and association with Lemierre's syndrome as a monomicrobial infection and second because it seems probable that it is an exogenously acquired infection. The source of infection is unclear; suggestions include acquisition from animals or human-to-human transmission. Approximately 10% of published cases are associated with infectious mononucleosis, which may facilitate invasion. Recent work suggests that underlying thrombophilia may predispose to internal jugular vein thrombophlebitis. Lemierre's syndrome was relatively common in the preantibiotic era but seemed to virtually disappear with widespread use of antibiotics for upper respiratory tract infection. In the last 15 years there has been a rise in incidence, possibly related to restriction in antibiotic use for sore throat.

Fusobacterium necrophorum infections in animals: Pathogenesis and pathogenic mechanisms

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two subspecies of F. necrophorum, subsp. necrophorum (biotype A) and subsp. funduliforme (biotype B), have been recognized, that differ morphologically, biochemically, and biologically. The subsp. necrophorum is more virulent and is isolated more frequently from infections than the subsp. funduliforme. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis), either specific or non-specific infections, in a variety of animals. Of these, bovine liver abscesses and foot rot are of significant concern to the cattle industry. Liver abscesses arise with the organisms that inhabit the rumen gaining entry into the portal circulation, and are often secondary to ruminal acidosis and rumenitis complex in grain-fed cattle. Foot rot is the major cause of lameness in dairy and beef cattle. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins or secreted products, such as leukotoxin, endotoxin, hemolysin, hemagglutinin, proteases, and adhesin, etc., have been implicated as virulence factors. The major virulence factor appears to be leukotoxin, a secreted protein of high molecular weight, active specifically against leukocytes from ruminants. The complete nucleotide sequence of the leukotoxin operon of F. necrophorum has been determined. The operon consists of three genes (lktBAC) of which the second gene (lktA) is the leukotoxin structural gene. The leukotoxin appears to be a novel protein and does not share sequence similarity with any other leukotoxin. F. necrophorum is also a human pathogen and the human strains appear to be different from the strains involved in animal infections.

Stability and stabilization of Fusobacterium necrophorum hemolysin

The stability and stabilization of the hemolytic activity of Fusobacterium necrophorum subsp. necrophorum and Fusobacterium necrophorum subsp. funduliforme were monitored over a period of four weeks using culture supernatants. The hemolytic activity was completely lost after one week at room temperature and 37 degrees C. After a two-week storage at 4 degrees C and -80 degrees C only trace activity was detected with -80 degrees C being the better of the two conditions. The addition of cysteine monohydrochloride, bovine serum albumin or Tween 80 as stabilizers, however, led to the detection of a considerable amount of the hemolytic activity in the sample stored at 4 degrees C and - 80 degrees C throughout the period investigated. The hemolytic activity appeared to be more stable in the presence of Tween 80 at -80 degrees C. Cysteine monohydrochloride was found to crystallize at - 80 degrees C and was therefore ineffective as a stabilizer at this temperature. Hemoglobin was also ineffective as a stabilizer.

Fusobacterium necrophorum infections: virulence factors, pathogenic mechanism and control measures

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morphologically, biochemically, and biologically. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis) such as bovine hepatic abscesses, ruminant foot abscesses and human oral infections. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins, such as leukotoxin, endotoxin, haemolysin, haemagglutinin and adhesin, have been implicated as virulence factors. Among these, leukotoxin and endotoxin are believed to be more important than other toxins in overcoming the host's defence mechanisms to establish the infection. F. necrophorum is encountered frequently in mixed infections and, therefore, synergisms between F. necrophorum and other pathogens may play an important role in infection. Several investigators have attempted to induce protective immunity against F. necrophorum using bacterins, toxoids, and other cytoplasmic components. Generally, none of the immunogens has afforded satisfactory protection against Fusobacterium infections. Because of the unavailability of suitable immunoprophylaxis, the control of F. necrophorum infection has depended mainly on the use of antimicrobial compounds.

Studies on the factors affecting the hemolytic activity of Fusobacterium necrophorum

The in vitro activity of the hemolysin of Fusobacterium necrophorum was determined using the hemolysis of horse erythrocytes as an assay. The effects of medium composition and pH on hemolysin production were investigated. Calf serum and casitone stimulated a comparatively higher hemolytic activity in F. necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme, respectively. However, sugars, such as glucose, galactose and fructose were inhibitors of hemolytic activity. The spectrum of erythrocyte sensitivity to the hemolysin indicated that horse and quail erythrocytes were more sensitive to the hemolysin of both F. necrophorum subsp. necrophorum and subsp. funduliforme, than were cat, dog, rabbit, pigeon and human erythrocytes. Cat erythrocytes were however insensitive to the hemolysin of subsp. funduliforme. Cattle, sheep and chicken erythrocytes were insensitive to the hemolysin of the two subspecies. Medium pH near neutral were more effective in enhancing hemolytic activity, and hemolytic activity was positively correlated with growth. In general, F. necrophorum subsp. necrophorum was more hemolytic than subsp. funduliforme.

Biochemical and biological characterization of ruminal Fusobacterium necrophorum

Biochemical characteristics, biological activities, and antimicrobial susceptibilities of ruminal Fusobacterium necrophorum (eight subsp. necrophorum and eight subsp. funduliforme) and of isolates (three of each subsp.) obtained from bovine hepatic abscesses were determined. F. necrophorum subsp. necrophorum strains had higher phosphatase and DNase activities, produced more leukotoxin, and were more pathogenic to mice than subsp. funduliforme strains. The leukotoxin titer for culture supernatants of ruminal subsp. necrophorum strains was approximately 15 times lower than that of hepatic subsp. necrophorum strains. Hemagglutination activity was present in all hepatic, but only in some ruminal, strains of subsp. necrophorum. The antimicrobial sensitivity profile of the ruminal isolates was similar to that of hepatic isolates.

Structural studies of the O-antigenic polysaccharide of Fusobacterium necrophorum

The O-specific polysaccharide component of the lipopolysaccharide produced by Fusobacterium necrophorum is of the teichoic acid type, with repeating units connected by phosphoric diester linkages. Dephosphorylation of the polysaccharide by treatment with aqueous hydrogen fluoride yielded a carbohydrate composed of a trisaccharide linked to an acidic component. This product, and the polysaccharide, were investigated by chemical methods and 1H-, 13C-, 31P- and 15N-NMR spectroscopy and the former also by fast-atom-bombardment mass spectrometry. It is proposed that the polysaccharide is composed of repeating units having the following structure, in which Fuc represents fucose (6-deoxy-galactose), Am represents an acetamidino group and Sug 2,4-diamino-2,4,6-trideoxy-D-glucose ('bacillosamine') acetylated at the 2-position and acylated with a (S)-3-hydroxybutanoic acid at the 4-position. The acid was identified as a 2-amino-2-deoxy-2-C-methyl-pentonic acid (2-amino-2-methyl-3,4,5-trihydroxypentanoic acid). The configuration of this acid remains to be determined. [formula: see text]

Aggregation of bovine platelets by Fusobacterium necrophorum

Washed cell suspensions of biovar A strains of Fusobacterium necrophorum aggregated cattle platelets, but similar suspensions of biovar B strains did not. Platelets were also aggregated by heat-treated bacterial cells or the lipopolysaccharide of biovar A. No platelet aggregation occurred in the presence of the cell-free culture supernatant of biovar A and of all samples prepared from biovar B. Scanning electron microscopy revealed that aggregated platelets were not damaged. Platelet aggregation was inhibited by EDTA, aspirin and quinacrine, and lag time was retarded by these inhibitors, indicating the reaction was a Ca(2+)-dependent, cyclo-oxygenase sensitive event. Platelet aggregation may be a virulence marker, probably mediated by the lipopolysaccharide of F. necrophorum biovar A strains.

The effects of Escherichia coli endotoxin as a trigger for hepatic infection of rabbits with Fusobacterium necrophorum

To evaluate the effects of endotoxin in hepatic infection with Fusobacterium necrophorum, rabbits were given several combinations of F. necrophorum and Escherichia coli endotoxin. Severe hepatic necrosis with multiplication of F. necrophorum was induced by inoculation of endotoxin via the bile duct and following inoculation of both endotoxin and F. necrophorum. Inoculation with F. necrophorum alone, preceded by inoculation of endotoxin via the bile duct, also induced hepatic necrosis, whereas rabbits which received a single inoculation of endotoxin or F. necrophorum had only slight necrotic lesions. The pathogenetic mechanism of experimental hepatic infection with F. necrophorum is discussed.