Comparison of extracellular enzymes of Fusobacterium necrophorum subsp. necrophorum and Fusobacterium necrophorum subsp. funduliforme

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.

Standardization of loop-mediated isothermal amplification for detection of D. nodosus and F. necrophorum causing footrot in sheep and goats

The loop-mediated isothermal amplification (LAMP) was standardized for rapid detection of Dichelobacter nodosus and Fusobacterium necrophorum. A total of 250 foot swabs were screened from sheep (200) and goats (50) from different districts of Rayalaseema, viz., Chittoor, Nellore, Kadapa, and Anantapur. Out of 250 samples 75 (30.0%) and 85 (34.0%) were positive for D. nodosus and F. necrophorum, respectively. All the 250 samples were screened individually for both the organisms by LAMP. Among them, 104 (41.6%) were found to be positive for D. nodosus and 120 (48.0%) were positive for F. necrophorum. The efficacy of LAMP in terms of sample DNA detection limit was compared with the PCR by using standard dilutions of DNA extracted from D. nodosus and F. necrophorum cultures. The detection limit was found to be higher than PCR for both the organisms. The sensitivity of LAMP is compared with PCR by targeting 16S rRNA gene of D. nodosus and lktA gene of F. necrophorum. In case of D. nodosus, out of 250 samples, 75 (30.0%) were positive by PCR and 104 (41.6%) were positive by LAMP. Among 250 samples, 85 (34.0%) were positive by PCR and 120 (48.0%) were positive by LAMP in case of F. necrophorum. The LAMP was found to be more sensitive than PCR in detecting the organisms with high statistical significance.

Leukotoxin production by Fusobacterium necrophorum strains in relation to severity of liver abscesses in cattle

Fusobacterium necrophorum, a Gram-negative anaerobe, is the primary etiologic agent of liver abscesses of beef cattle. The bacterium, a member of the microbial community of the rumen, travels to the liver via portal circulation to cause abscesses. The severity of liver abscesses vary from mild with one or two small abscesses to severe with medium to large multiple abscesses. Leukotoxin, a secreted protein, is the critical virulence factor involved in the infection. Our objective was to compare leukotoxin production between strains of F. necrophorum isolated from mild and severe liver abscesses collected from slaughtered cattle. The quantification of leukotoxin was based on assays to measure cytotoxicity and protein antigen concentration. One-hundred strains, 50 from mild and 50 from severe abscesses, were utilized in the study. Cell-free supernatants were prepared from cultures grown in anaerobic broth at 9 and 24 h incubations. The leukotoxic activity was quantified by measuring cytotoxicity based on the release of lactic dehydrogenase from bovine lymphocyte cells, BL3, treated with the culture supernatant. Leukotoxin protein concentration was quantified by a sandwich ELISA assay with a leukotoxin-specific monoclonal antibody as the capture antibody. The leukotoxin activity and concentration were highly variable among the strains within each severity of liver abscesses. Although the leukotoxic activity was unaffected by incubation time, leukotoxin protein concentration was consistently higher at 24 h compared to 9 h incubation. Strains from severe liver abscesses had significantly higher leukotoxic activity and higher protein concentration compared to strains from mild liver abscesses (P < 0.0001) at both 9 and 24 h culture supernatants. Across all strains, the correlation coefficients between leukotoxic activity and leukotoxin concentration at 9 and 24 h were 0.14 (P = 0.17) and 0.47 (P < 0.0001), respectively. In conclusion, strains isolated from severe liver abscesses had significantly higher leukotoxic activities and leukotoxin protein concentrations compared to strains isolated from mild liver abscesses.

Extracellular DNA: the tip of root defenses?

This review discusses how extracellular DNA (exDNA) might function in plant defense, and at what level(s) of innate immunity this process might operate. A new role for extracellular factors in mammalian defense has been described in a series of studies. These studies reveal that cells including neutrophils, eosinophils, and mast cells produce 'extracellular traps' (ETs) consisting of histone-linked exDNA. When pathogens are attracted to such ETs, they are trapped and killed. When the exDNA component of ETs is degraded, trapping is impaired and resistance against invasion is reduced. Conversely, mutation of microbial genes encoding exDNases that degrade exDNA results in loss of virulence. This discovery that exDNases are virulence factors opens new avenues for disease control. In plants, exDNA is required for defense of the root tip. Innate immunity-related proteins are among a group of >100 proteins secreted from the root cap and root border cell populations. Direct tests revealed that exDNA also is rapidly synthesized and exported from the root tip. When this exDNA is degraded by the endonuclease DNase 1, root tip resistance to fungal infection is lost; when the polymeric structure is degraded more slowly, by the exonuclease BAL31, loss of resistance to fungal infection is delayed accordingly. The results suggest that root border cells may function in a manner analogous to that which occurs in mammalian cells.

Lemierre syndrome: a pediatric case series and review of literature

BACKGROUND

Lemierre syndrome is a rare disease of the head and neck often affecting adolescents and young adults. Classically, infection begins in the oropharynx with thrombosis of the tonsillar veins followed by involvement of the parapharyngeal space and the internal jugular vein. Septicemia and pulmonary lesions develop as infection spreads via septic emboli. Although a rare entity in modern times, Lemierre syndrome remains a disease of considerable morbidity and potential mortality.

METHODS

This was a retrospective review of 3 cases and associated literature.

RESULTS

A common 1- to 2-week history of fever, sore throat, neck pain, and fatigue was observed in all patients. Patient 1 developed right facial swelling, neck tenderness, trismus, and tonsillar exudate. Patient 2 displayed right tonsillar erythema and enlargement with right neck tenderness. Patient 3 revealed bilateral tonsillar enlargement with exudate and left neck tenderness. Subsequent studies included blood cultures and computed tomography, after which empiric antibiotic therapy was started. Patient 1 underwent drainage of a right peritonsillar abscess, right pressure equalization tube placement, and ligation of the right external jugular vein. He subsequently developed subdural empyemas, cavernous sinus thrombosis, and carotid artery narrowing and required 9 weeks of antibiotic therapy. Patients 2 and 3 developed pulmonary lesions and received 6 weeks of antibiotic therapy. Timing was crucial in all cases.

CONCLUSIONS

Lemierre syndrome is a rare but severe opportunistic infection with poor prognostic outcomes if left untreated. Early diagnosis and treatment is essential. Aggressive antibiotic therapy coupled with surgical intervention, when necessary, provides excellent outcomes.

Human Fusobacterium necrophorum strains have a leukotoxin gene and exhibit leukotoxic activity

Fusobacterium necrophorum, a Gram-negative anaerobe, causes a variety of necrotic infections in humans and animals. There are two subspecies: subsp. necrophorum and subsp. funduliforme. In cattle, subsp. necrophorum is more prevalent and production of leukotoxin is a major virulence factor. The leukotoxin operon (lktBAC) consists of three genes, lktB, lktA and lktC, of which lktA is the structural toxin gene. The subspecies identity of human F. necrophorum is less certain and it is not known whether human strains possess the leukotoxin gene or leukotoxin activity. Therefore, the objective of this study was to identify the subspecies status of four human clinical strains of F. necrophorum and determine whether they have the leukotoxin gene or leukotoxin activity. Phenotypic and genotypic characteristics suggested that the four strains belonged to subsp. funduliforme, which was confirmed by sequencing the 16S rRNA gene. Analysis of the four strains by PCR revealed the presence of the leukotoxin operon. Partial DNA sequencing identified one human strain with full-length lktA, whereas the others exhibited considerable heterogeneity in size. All strains had a leukotoxin operon promoter-containing intergenic region similar to that of bovine subsp. funduliforme strains, which was confirmed by DNA sequencing and Southern blotting. Despite variations in the lktA gene, all strains secreted leukotoxin as demonstrated by Western blotting. Flow cytometry assays revealed that the leukotoxin was toxic to human white blood cells. In conclusion, the human strains examined contained a leukotoxin gene whose gene product was biologically active. The importance of leukotoxin as a virulence factor in human fusobacterial infections needs further evaluation.

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.

Lemierre's syndrome: Porphyromonas asaccharolytica as a putative pathogen

A case of Lemierre's syndrome is reported in which metastatic abscesses resulted from septic thrombophlebitis of the internal jugular vein secondary to bacterial pharyngitis. A 32-year-old male suffering from a painful left-sided neck mass, sore throat, and fever was admitted to our hospital. Computed tomography revealed thrombosis of the left internal jugular vein, septic pulmonary emboli, and a liver abscess. Blood culture showed Porphyromonas asaccharolytica. Although empyema occurred transiently during the treatment, the patient recovered following prolonged antimicrobial therapy. Although Fusobacterium species are a well-known cause of Lemierre's syndrome, cases in whom Porphyromonas species was isolated have scarcely been reported. Moreover, case reports from Japan have been few.

Phylogenetic analysis of Fusobacterium necrophorum, Fusobacterium varium and Fusobacterium nucleatum based on gyrB gene sequences

The nucleotide sequences of the DNA gyrase B subunit gene (gyrB) of Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme and F. varium were determined and analyzed together with those of F. nucleatum subsp. nucleatum and F. nucleatum subsp. vincentii. On the phylogenetic tree constructed, the strains of each fusobacterial species formed distinct clusters with deep sublines. The degree of sequence similarity within each cluster was 93.2% or more, whereas similarities between clusters ranged from 70.1 to 72.7%. These clusters were recovered with 100% bootstrap probabilities and are in very good agreement with the species of Fusobacterium. These data suggest that gyrB is an accurate genealogical marker for the classification of the fusobacterial taxa considered in this study.

Specific detection and differentiation of two subspecies of Fusobacterium necrophorum by PCR

The phylogenic relationships of two subspecies of Fusobacterium necrophorum were investigated by randomly amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR). With each of the 12 random primers, the DNA fingerprints generated were subjected to cluster analysis for dendrograms. The analysis indicated that twelve strains were organized into two major clusters, and that all strains of each subspecies were confined to one cluster. Furthermore, two of the random primers examined each generated a unique band in F. n. necrophorum strains. We cloned these specific bands and determined the nucleotide sequences. A search for amino acid sequence homologies revealed that the two specific fragments had significant homology to the rpoB gene of Lactococcus lactis subsp. lactis and the hemagglutinin-related protein gene of Ralstonia solanacearum, respectively. New specific primers designed for the rpoB gene were able to amplify 900bp fragments from both subspecies. However, the specific primers designed for the hemagglutinin-related protein gene amplified only a 250bp fragment of the genome of the F. n. necrophorum strains, suggesting that this gene is unique to F. n. necrophorum. These results were further confirmed by dot blot hybridization. Finally, a one-step duplex PCR technique in a single tube for the rapid detection and differentiation of the F. necrophorum subspecies was developed.

Immunohistochemical and ultrastructural identification of Fusobacterium necrophorum subsp. necrophorum in bovine fatal necrotizing glossitis

A 37-day-old male Japanese black calf showing marked salivation and leucocytosis died and was examined the tissues histologically. Histological lesions were characterized by severe focal necrotic glossitis on the ventral side of the root of the tongue. Immunohistochemically, Fusobacterium necrophorum subsp. necrophorum antigen was detected in the necrotic tissues and its distribution corresponded to that of the gram-negative, nonsporeforming, long filamentous organisms. Ultrastructural similarities between the organism and F. necrophorum subsp. necrophorum, but not subsp. funduliforme were observed. These findings clearly demonstrated that the fatal necrotic glossitis was caused by F. necrophorum subsp. necrophorum. This is the first report of bovine fatal necrotizing glossitis with leucocytosis caused by F. necrophorum subsp. necrophorum infection, and this organism may be an important fatal pathogen in calves with glossal lesions.

Characterization of the 16S-23S rRNA intergenic spacer regions among strains of the Fusobacterium necrophorum cluster

The 16S-23S rRNA intergenic spacer regions (ISRs) of Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme were characterized. Products of two sizes, about 360 bp (small) and 530 bp (large), were generated by PCR amplification from the 16S-23S rRNA ISR of all the strains tested. The large and small 16S-23S rRNA ISRs of F. necrophorum exhibited a level of sequence similarity of 93.9% to 99.7% and 94.2% to 98.6% homologies within the species, respectively. Only the large spacer regions in these bacteria contained one or two tRNA genes. F. necrophorum subsp. necrophorum contains the isoleucine and alanine tRNA gene, whereas F. necrophorum subsp. funduliforme contains the isoleucine tRNA gene.

Comparison of the 16S-23S rRNA intergenic spacer regions between Fusobacterium varium and "Fusobacterium pseudonecrophorum" strains

The 16S-23S rRNA intergenic spacer regions (ISRs) of five strains of "Fusobacterium pseudonecrophorum" which had been proposed as a new species, were compared with those of F. varium ATCC 8501T. All the strains of "F. pseudonecrophorum" exhibited of sequence similarities of 97.7% to 100% to the strain of F. varium in their 16S-23S rRNA ISR sequences. This indicates that the strains of "F. pseudonecrophorum" and the type strain of F. varium are identical at the species level.

Differentiation of Fusobacterium necrophorum subspecies from bovine pathological lesions by RAPD-PCR

Nineteen strains from bovine abscesses identified as Fusobacterium necrophorum by the VPI method were examined by other methods. The API 20A test kit characterized all 19 strains as F. necrophorum. Seven of the strains had haemagglutinating activity and were classified as F. necrophorum subspecies necrophorum, and the remaining, 12 nonhaemagglutinating strains, were classified as F. necrophorum subspecies funduliforme. We used RAPD-PCR with a 10-mer oligonucleotide primer, W1L-2, to confirm this differentiation of the two subspecies. These results suggest that random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) with a suitable primer can be used as a new tool for the differentiation of F. necrophorum subspecies isolated from bovine pathological lesions.

Human necrobacillosis, with emphasis on Lemierre's syndrome

Lemierre's syndrome is the classical presentation of human necrobacillosis. It is characterized by a primary infection in the head in a young, previously healthy person who subsequently develops persistent high fever and disseminated metastatic abscesses, frequently including a septic thrombophlebitis of the internal jugular vein. The main pathogen is Fusobacterium necrophorum, an obligate anaerobic, pleomorphic, gram-negative rod. Clinical microbiologists have a key role in alerting clinicians and advising proper antibiotic treatment when the characteristic microscopic morphology of the pleomorphic F. necrophorum is seen in Gram stains from positive anaerobic cultures of blood and pus. Early diagnosis and prolonged appropriate antibiotic treatment with good anaerobic coverage are crucial to reduce morbidity and mortality. F. necrophorum also causes human necrobacillosis with foci caudal to the head, mainly in elderly patients with high mortality related to age and predisposing diseases, such as cancers of the primary focus.

The erythrocyte receptor for Fusobacterium necrophorum hemolysin: phosphatidylcholine as a possible candidate

An attempt was made to determine the receptor for the hemolysin of Fusobacterium necrophorum using horse erythrocyte or its membranes as target. The spectrum of erythrocyte sensitivity has indicated that horse, dog and mouse erythrocytes are highly sensitive whereas cattle, sheep, goat and chicken red blood cells are insensitive to this hemolysin. A high correlation between sensitivity and phosphatidylcholine content of the erythrocyte membranes was noted. Binding of hemolysin to horse erythrocyte membranes was reduced significantly by prior treatment of membranes with phospholipase A2 but not with phospholipase C. Pretreatment of erythrocyte membranes with pronase, proteinase K, trypsin or neuraminidase did not alter binding of hemolysin to the membranes, suggesting that protein or sialyl residues are not involved as receptors. Gas liquid chromatography analysis showed that the fatty acid profile from hydrolysis of bovine liver phosphatidylcholine by hemolysin and phospholipase A2 were similar. In conclusion, this report presents evidence that phosphatidylcholine may be acting as a possible receptor for the hemolysin of F. necrophorum.

Ribotyping ofFusobacterium necrophorumStrains Isolated from Bovine and Ovine Hepatic Abscesses

A microbiological study was made of 100 strains of Fusobacterium necrophorum isolated from hepatic abscesses in bovine and ovine herds. Differences between the biological activity and ribotypes within the two F. necrophorum subspecies were studied. Conventional methods identified 89 isolates as F. necrophorum subsp. necrophorum and 11 as F. necrophorum subsp. funduliforme. For ribotyping, 50 strains (35 F.n. subsp. necrophorum, 11 F.n. subsp. funduliforme and 4 reference strains) were digested with restriction endonucleases (HindIII, EcoRI and BamHI) and examined after hybridization with digoxigenin-labelled cDNA probe transcribed from a 16 and 23S rRNAs from Escherichia coli. The most discriminating restriction endonuclease enzymes for ribotyping were EcoRI and BamHI. The presence or absence of two distinct band of 5 kb (EcoRI) and 10.5 kb (BamHI) differentiated the two subspecies. This technique also revealed genetic differences between isolates which could be used in the epidemiological study of clinical processes caused by F. necrophorum.

Ribotyping to compare Fusobacterium necrophorum isolates from bovine liver abscesses, ruminal walls, and ruminal contents

Restriction fragment length polymorphism analysis of rRNA genes was employed to genetically compare Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolates from multiple abscesses of the same liver and isolates from liver abscesses, the ruminal wall, and ruminal contents from the same animal. Four livers with multiple abscesses and samples of ruminal contents, ruminal walls, and liver abscesses were collected from 11 cattle at slaughter. F. necrophorum was isolated from all liver abscesses, nine ruminal walls, and six ruminal content samples. Chromosomal DNA of the isolates was extracted and single or double digested with restriction endonucleases (EcoRI, EcoRV, SalI, and HaeIII); then restriction fragments were hybridized with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16S and 23S rRNAs from Escherichia coli. EcoRI alone or in combination with EcoRV yielded the most discriminating ribopatterns for comparison. Within the subspecies multiple isolates from the same liver were indistinguishable based on the ribopattern obtained with EcoRI. The hybridization patterns of liver abscess isolates were concordant with those of the corresponding isolates from ruminal walls in eight of nine sets of samples. None of the six ruminal content isolates matched either the liver abscess isolates or the ruminal wall isolates. The genetic similarity between the isolates from liver abscesses and ruminal walls supports the hypothesis that F. necrophorum isolates of liver abscesses originate from the rumen.

Interactions between Fusobacterium necrophorum hemolysin, erythrocytes and erythrocyte membranes

The interactions between the hemolysin of Fusobacterium necrophorum subsp. necrophorum, erythrocytes and erythrocyte membranes were studied as an attempt to determine the initial characteristics leading to hemolysis. The spectrum of erythrocyte sensitivity indicated that horse, dog and mouse erythrocytes were highly sensitive whereas those of cattle, sheep, goat and chicken were insensitive to the hemolysin. Binding of hemolysin to horse and dog erythrocytes or their ghosts was more pronounced than to those of cattle and sheep as detected by a decrease of hemolytic activity from hemolysin preparations. The kinetics of hemolysis revealed that lysis is preceded by a prelytic phase characterized by binding of hemolysin to erythrocytes. Treatment of horse erythrocytes with hemolysin at various temperatures prior to incubation at 37 degrees C also revealed that this binding prelytic phase is temperature independent. This was followed by a temperature dependent lytic stage since erythrocytes pretreated with hemolysin and incubated at 4 degrees C showed no hemolysis. An inverse relation was found between erythrocyte concentration and hemolytic activity suggesting a multiple-hit mechanism of hemolysis.

The effects of physical and chemical agents on the secretion and stability of a Fusobacterium necrophorum hemolysin

The effect of various agents as enhancers or inhibitors of hemolysin secretion by Fusobacterium necrophorum was investigated. The hemolysin secreted in phosphate buffered saline (PBS) alone was inactivated shortly after secretion. Tween-80 or albumin preserved the hemolytic activity in PBS in which cultures of F. necrophorum had been suspended. Hemoglobin was found to enhance hemolysin secretion. However, higher concentrations diminished secretion. Chloramphenicol, an inhibitor of protein synthesis, exhibited no effect on the hemolytic activity. However, the addition of sodium azide, an energy metabolic inhibitor, significantly reduced the hemolytic activity. Lower temperatures and pH above 9 and below 6 all yielded a low hemolytic activity. Cells suspended in Tween-80 prior to sonication yielded a substantial amount of extracellular hemolytic activity with low intracellular activity detected. However, cells suspended in PBS alone yielded a low extracellular activity but rather a high intracellular activity. The same spectrum of red blood cells of different species were found to be sensitive to both the extracellular and intracellular hemolysins.

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.

Evidence for phospholipase B activity in Fusobacterium necrophorum cultures and its association with hemolysin/leucocidin activities

Phospholipase B (PLB) activity was present in Fusobacterium necrophorum cultures and it correlated closely with virulence and co-purified with the hemolysin/leucocidin activities. All three activities were associated with a large molecule or molecular complex (6 x 10(2)-2 x 10(3) kDa) exhibiting varying degrees of aggregation. These were present mainly in the culture medium and to a lesser extent in cell sonicates. The PLB and toxin activities were sensitive to heat, dissociating agents, proteolytic enzymes, prolonged purification regimes, freeze-drying and repeated freeze-thawing. The toxin(s) were stable over a broad range of pH, did not require divalent ions or reducing agents and could be kept for several months as an ammonium sulfate precipitate at 4 degrees C, or stored as a concentrated liquid in the presence of proteolytic inhibitors at - 20 degrees C.

Ribotyping to differentiate Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolated from bovine ruminal contents and liver abscesses

Differences in biological activities (hemagglutination, hemolytic, leukotoxic, and virulence) and ribotypes between the two subspecies of Fusobacterium necrophorum of bovine ruminal and liver abscess origins were investigated. Hemagglutination activity was present in all hepatic, but only some ruminal, strains of Fusobacterium necrophorum subsp. necrophorum. Ruminal F. necrophorum subsp. necrophorum had low leukotoxin titers yet was virulent in mice. Fusobacterium necrophorum subsp. funduliforme of hepatic or ruminal origin had no hemagglutination activity, had low hemolytic and leukotoxic activities, and was less virulent to mice. For ribotyping, chromosomal DNAs of 10 F. necrophorum subsp. necrophorum and 11 F. necrophorum subsp. funduliforme isolates were digested with restriction endonucleases (EcoRI, EcoRV, SalI, PstI, and HaeIII) and examined by restriction fragment length polymorphisms after hybridizing with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16 and 23S rRNAs from Escherichia coli. The most discriminating restriction endonuclease enzyme for ribotyping was EcoRI. The presence or absence of two distinct bands of 2.6 and 4.3 kb differentiated the two subspecies. Regardless of the origin, only F. necrophorum subsp. necrophorum, a virulent subspecies, had a ca. 2.6-kb band, whereas F. necrophorum subsp. funduliforme, a less virulent subspecies, had a ca. 4.3-kb band. Ribotyping appears to be a useful technique to genetically differentiate the two subspecies of F. necrophorum.

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.