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M M Chengappa

Publications and source records attributed to M M Chengappa.

At least 37 records · Page 2Linked to original sources
PubMed1998

Actin enhances the haemolytic activity of Escherichia coli.

Actin is a major cytoskeletal protein of mammalian muscle and non-muscle cells. Exposure of cells to soluble factors that damage cell membranes results in the release of actin into the extracellular spaces. The alpha-haemolysin (HlyA) of Escherichia coli is the prototype RTX (repeat in toxin) toxin and is thought to be important in virulence because of its ability to lyse cells by formation of pores in the cell membrane. These studies were conducted to determine if actin influences growth and haemolytic activity of E. coli. Growth of E. coli in the presence of actin resulted in culture supernatant haemolytic activity that was 2.4-, 2.7- and 3.3-fold greater than that of E. coli grown in medium containing BSA, non-supplemented medium, or medium containing heat-denatured actin, respectively. The enhanced haemolytic activity occurred only when actin was present during the growth phase and there was no effect when actin was added to culture supernatants containing haemolysin. The increased haemolytic activity by actin was concentration-dependent, detectable in early-exponential-phase growth, and associated with increased concentrations of secreted HlyA by Western blotting. Actin induced a 2.9-fold increase in alkaline phosphatase activity in E. coli CC118 with a TnphoA insertion in the hlyB determinant of the recombinant haemolysin plasmid pWAM04. These results indicate that extracellular actin enhances haemolysin production by E. coli and may have implications in the pathogenesis of E. coli infections.

Actins↗
PubMed1998

Use of ribotyping and hemolysin activity to identify highly virulent Streptococcus suis type 2 isolates.

Nineteen Streptococcus suis type 2 isolates were evaluated for their virulence in pigs and mice. Of these, seven were determined to be highly virulent in pigs on the basis of clinical sign scores and gross pathology and histopathology results. Clinical sign scores correlated with gross pathology and histopathology scores at P equal to 0.004 and P equal to 0.009, respectively. The virulence of highly virulent isolates in pigs compared somewhat with virulence in mice, but the correlation was not significant. No correlation of virulence was noted among the moderately virulent and avirulent isolates in pigs and mice. Chromosomal DNAs from all S. suis isolates were evaluated by PstI, PvuII, EcoRI, and HaeIII restriction enzyme digestion followed by hybridization with a digoxigenin-11-dUTP-labeled cDNA probe transcribed from 16S and 23S rRNAs from Escherichia coli. The hybridization patterns (ribotypes) varied depending upon the enzyme used, but a significant number of isolates determined to be highly virulent in pigs had unique hybridization patterns compared with those of the moderately virulent and avirulent isolates (P = 0.002). In addition, hemolysin activity showed a high correlation to virulence (P = 0.00008) and ribotype (P = 0.002).

Animals↗
PubMed1998

Liver abscesses in feedlot cattle: a review.

Liver abscesses in slaughtered beef cattle result from aggressive grain-feeding programs. The incidence, averaging from 12 to 32% in most feedlots, is influenced by a number of dietary and management factors. Liver abscesses represent a major economic liability to producers, packers, and ultimately consumers. Besides liver condemnation, economic impacts include reduced feed intake, reduced weight gain, decreased feed efficiency, and decreased carcass yield. Fusobacterium necrophorum, a member of the ruminal anaerobic bacterial flora, is the primary etiologic agent. Actinomyces pyogenes is the second most frequently isolated pathogen. Ruminal lesions resulting from acidosis generally are accepted as the predisposing factors for liver abscesses. F. necrophorum possesses or produces a number of virulence factors that participate in the penetration and colonization of the ruminal epithelium and subsequent entry and establishment of infection in the liver. However, only a few virulence factors have been characterized well. Control of liver abscesses in feedlot cattle generally has depended on the use of antimicrobial compounds. Five antibiotics (i.e., bacitracin methylene disalicylate, chlortetracycline, oxytetracycline, tylosin, and virginiamycin) are approved for prevention of liver abscesses in feedlot cattle. Tylosin is the most effective and the most commonly used feed additive. Tylosin feeding reduces abscess incidence by 40 to 70%. The mode of action of antibiotics in preventing liver abscesses is believed to be via inhibition of ruminal F. necrophorum. Protective immunity against F. necrophorum induced by a variety of antigenic components has ranged from ineffectual to significant protection.

Actinomyces↗
PubMed1998

Antimicrobial susceptibility of Fusobacterium necrophorum isolated from bovine hepatic abscesses.

OBJECTIVE: To determine the resistance and susceptibility to antimicrobial compounds of Fusobacterium necrophorum isolates from bovine hepatic abscesses. PROCEDURE: 37 isolates of F necrophorum (21 subsp necrophorum and 16 subsp funduliforme) isolated from bovine hepatic abscesses were obtained from cultures grown and maintained in anaerobic brain heart infusion broth. A broth dilution method was used as an initial screening to determine general susceptibility to 31 antimicrobial compounds. The minimal inhibitory concentrations (MIC) of 19 of the antimicrobial compounds that inhibited growth in the initial test were determined by use of the broth microdilution method. RESULTS: Fusobacterium necrophorum isolates were generally susceptible to penicillins, tetracyclines (chlortetracycline and oxytetracycline), lincosamides (clindamycin and lincomycin), and macrolides (tylosin and erythromycin), and were resistant to aminoglycosides (kanamycin, neomycin, gentamicin, and streptomycin), ionophores (except narasin), and peptides (avoparcin, polymyxin, and thiopeptin). The 5 antimicrobials (bacitracin, chlortetracycline, oxytetracycline, tylosin, and virginiamycin) that have FDA approval for prevention of liver abscesses in feedlot cattle were inhibitory to F necrophorum. Differences in antimicrobial susceptibility patterns were observed between the 2 subspecies only for clindamycin and lincomycin. The MIC of F necrophorum isolates from antibiotic-fed cattle were similar to those for isolates from nonantibiotic-fed cattle. CONCLUSIONS: The MIC of FDA-approved antibiotics were not reflective of the efficacy of antibiotics in preventing liver abscesses in feedlot cattle. Also, continuous feeding of tylosin did not appear to select resistant F necrophorum.

Animals↗
PubMed1998

Biochemical and ribotypic comparison of Actinomyces pyogenes and A pyogenes-like organisms from liver abscesses, ruminal wall, and ruminal contents of cattle.

OBJECTIVE: To isolate Actinomyces pyogenes and A pyogenes-like (APL) organisms from the ruminal wall and ruminal contents of cattle and compare them with isolates from liver abscesses from the same animals, using ribosomal DNA restriction fragment length polymorphism analysis or ribotyping. PROCEDURE: Specimens of liver abscesses, ruminal walls, and ruminal contents were collected from 59 cattle at slaughter. All beta-hemolytic, pinpoint colonies that were gram positive, pleomorphic rod-shaped, and catalase negative, and that hydrolyzed casein and gelatin were presumptively identified as A pyogenes and were characterized biochemically, using an identification kit. The isolates that resembled A pyogenes but fermented mannitol or raffinose, or both, were called APL organisms. Isolates from the ruminal wall and ruminal contents were compared with liver abscess isolates from the same animal by use of ribotyping. RESULTS: Actinomyces pyogenes and APL organisms were isolated more frequently from the ruminal wall than from ruminal contents. Ruminal isolates of A pyogenes and APL had biochemical characteristics similar to those of the isolates from liver abscesses. Among 6 sets of isolates (4 A pyogenes and 2 APL), 2 isolates from liver abscesses had ribopatterns identical to the corresponding ruminal wall isolates. Also, the APL organisms isolated from the ruminal content matched with the corresponding liver abscess isolates for both sets of specimens tested. CONCLUSIONS: The ruminal wall may be the niche for A pyogenes and APL organisms in the rumen. The genetic similarity, on the basis of ribotyping among isolates from liver abscesses, the ruminal wall, and ruminal contents of the same animal suggests that A pyogenes and APL organisms that cause liver abscesses originate from the rumen.

Abscess↗
PubMed1997

Application of recombinant bovine viral diarrhea virus proteins in the diagnosis of bovine viral diarrhea infection in cattle.

The National Animal Disease Laboratory (NADL) vaccine strain of bovine viral diarrhea virus (BVDV) genes for gp48 and p80 were expressed in Escherichia coli. The BVDV-NADL gene for gp62 was integrated into a baculovirus genome for expression in Spodoptera frugiperda (Sf-9) insect ovarian cells. The antigenicity of baculovirus expressed BVDV protein was detected by anti-BVDV specific antibodies in an enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescent assay (IFA) and radio-immunoprecipitation (RIP). The recombinant proteins isolated from bacteria showed antigenic properties when analyzed by ELISA and immunoblotting using BVDV antibodies. The recombinant proteins were then used in ELISA or IFA to detect BVDV infection by testing 54 independent bovine serum samples. The baculovirus-expressed BVDV protein was used as an ELISA and IFA antigen, and the bacteria-expressed proteins were used as ELISA antigens. BVDV-NADL-infected Madin-Darby bovine kidney (MDBK) cell monolayers served as a control antigen. Statistical analysis showed a high degree of correlation between the reactivity of recombinants and natural antigens in ELISA using bovine sera. The results of ELISA or IFA proved there is a high degree of correlation with the virus neutralization. In the comparative ELISA assays, the insect-cell-mediated expression revealed greater specificity and sensitivity than the bacterial expression or the natural BVDV antigens produced by cell cultures.

Animals↗
PubMed1997

Streptococcus suis: past and present.

Steptococcus suis is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. In swine, the disease has spread worldwide but is more prevalent in countries with intensive swine management practices. The disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicaemia, endocarditis, polyserositis, abortions and abscesses. S. suis has also been implicated in disease in humans, especially among abattoir workers and swine and pork handlers. In humans, S. suis type 2 can cause meningitis, which may result in permanent hearing loss, septicaemia, endocarditis and death. The pathogenic mechanism of S. suis is not well defined. Several virulence factors have been identified, but their roles in pathogenesis and disease have not been well elucidated. Much work is in progress on characterization of virulence factors and mechanisms, with emphasis on the control of the disease. Because of the non-availability of suitable immunoprophylaxis, control of S. suis infection has depended mainly on the use of antimicrobials.

Abortion, Veterinary↗
PubMed1997

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.

Animal Feed↗
PubMed1997

Effect of Fusobacterium necrophorum leukotoxoid vaccine on susceptibility to experimentally induced liver abscesses in cattle.

The efficacy and the optimum dose of Fusobacterium necrophorum crude leukotoxoid vaccine required to immunize and protect steers against experimentally induced liver abscesses were evaluated. The vaccine consisted of cell-free culture supernatant of a high leukotoxin-producing strain of F. necrophorum, inactivated with formalin and homogenized with an adjuvant. Twenty-five steers were assigned randomly to the following five treatment groups: control; three doses (1.0, 2.0, and 5.0 mL) of the culture supernatant; and 2.25 mL of the concentrated supernatant (equivalent to 5 mL of the original supernatant). Vaccine was injected subcutaneously on d 0 and 21. Blood samples were collected weekly to monitor antileukotoxin antibody titers. Three weeks after the second vaccination (d 42), all steers were injected intraportally with F. necrophorum culture to induce liver abscesses. Three weeks later (d 63), steers were euthanatized and necropsied; livers were examined and protection assessed. Antileukotoxin antibody titers in the control steers generally did not differ from the baseline (wk 0) titers. The titers in the vaccinated groups increased, more so after the second injection, and the increase was generally dose-dependent. Necropsy examination revealed that all steers in the control group had abscesses in the liver. In the vaccinated groups, two of five steers in the 1.0-mL group and one each in the 2.0-, 5.0-, and 2.25-mL (concentrated) groups had liver abscesses. Antileukotoxin antibody titers were higher (P < .05) in steers that did not develop abscesses than in steers that developed abscesses. The difference suggested a protective effect of antileukotoxin antibodies against experimentally induced liver abscesses.

Animals↗
PubMed1996

Growth and microbial flora of nonmedicated, segregated, early weaned pigs from a commercial swine operation.

OBJECTIVE: To determine whether segregated, early weaned pigs have better growth performance and different microbial flora than those pigs raised on-site. DESIGN: Prospective, observational study. ANIMALS: Pigs from a commercial operation that were known to be infected with several common swine pathogens. PROCEDURE: Pigs (7 to 10 days old) were weaned and segregated from the farm of origin and compared with littermate control pigs (14 to 17 days old) that were weaned and raised on-site. Pig weight was measured and microbial flora were isolated at 14-day intervals for 84 days, beginning when the pigs were 7 to 10 days old. RESULTS: At 50 days of age, the segregated, early weaned pigs had a mean weight of 23.7 kg, compared with a mean weight of 12.5 kg for control pigs. Pasteurella multocida was isolated from fewer segregated, early weaned pigs than from controls. Signs of Mycoplasma hyopneumoniae infection were detected in control pigs but not in segregated early weaned pigs. Clinical, serologic, or bacteriologic signs of early postnatal vertical transmission of Actinobacillus pleuropneumoniae were not detected in either group. CLINICAL IMPLICATION: Vertical transmission of M hyopneumoniae was prevented by weaning pigs at 7 to 10 days of age and segregating them off-site, without the use of medication. Although medicated controls were not compared, results from this herd revealed that use of antibiotics is not the most important factor for disease control in segregated, early weaning programs. Minimizing antibiotic use in disease-control protocols reduces costs as well as removes the need for extra-label drugs.

Actinobacillus pleuropneumoniae↗
PubMed1996

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.

Animals↗
PubMed1996

The serum neutralizing antibody response in cattle to Fusobacterium necrophorum leukotoxoid and possible protection against experimentally induced hepatic abscesses.

The serum antileukotoxin antibody response and protection against subsequent experimental challenge with Fusobacterium necrophorum were investigated in 30 steers vaccinated with crude F. necrophorum leukotoxoid. Culture supernatant of F. necrophorum, strain 25, containing leukotoxoid was concentrated. The steers were assigned randomly to six groups (n = 5): PBS control with Stimulon adjuvant; vaccinated with concentrated supernatant diluted to provide 2.5, 5.0, 10.0, or 20.0 ml with the water-soluble Stimulon adjuvant; and 5.0 ml with the Ribi oil-emulsion adjuvant. The steers were injected subcutaneously on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titres. On day 42, all the steers were challenged intraportally with F. necrophorum culture. Three weeks later (day 63), the steers were killed and necropsied for examination of their livers and assessment of protection. Steers vaccinated with crude leukotoxoid tended to have higher antileukotoxin titres than the controls, but the difference was not significant. Also, the antibody titre did not appear to be dose-dependent. In the control group, 3 out of 5 steers developed liver abscesses. The incidence of liver abscesses in steers vaccinated with Stimulon adjuvant was not dose related; however, only 8 of the 25 vaccinated steers developed abscesses. None of the steers vaccinated with the 5.0 ml dose with Ribi had any abscesses. Evidence for a relationship between antileukotoxin antibody and protection was shown by the lower titre in those steers that developed abscesses compared to those that did not. It was concluded that antileukotoxin antibody titres probably provided some degree of protection against experimentally induced liver abscesses, but further dose-titration studies using Ribi or possibly another more effective adjuvant will be needed to confirm this.

Adjuvants, Immunologic↗
PubMed1996

Identification and partial characterization of an Actinomyces pyogenes hemolysin.

Twenty-two Actinomyces pyogenes isolates were recovered from hepatic abscesses in cattle and evaluated for hemolysin production. Hemolysin was collected from supernatant of cultures grown in 6% CO2 in brain heart infusion (BHI) broth. The effect of oxidizing and reducing agents, enzymes, temperatures and pH on hemolytic activity were studied using sheep erythrocytes as the target cells. Our study showed that A. pyogenes hemolysin is oxygen stable; sensitive to treatment by protease, trypsin, and amylase; and destroyed by treatment at extreme temperatures (56 and 100 degrees C) and pH (pH 3 and 11). Production of hemolysin was studied in BHI, RPMI-1640, and a defined serum-free A. pyogenes medium under aerobic and anaerobic conditions. Maximum hemolysin was produced in BHI incubated aerobically in 6% CO2 and to a lesser degree anaerobically in RPMI-1640. No hemolysin was produced in the defined A. pyogenes medium. Differential filtration, isoelectric focusing and sodium dodecyl sulfate polyacrylamide gel electrophoresis identified two hemolysin proteins with pI values of 3.40 and 9.45 and estimated molecular masses of 62 and 58 kDa, respectively. Cell-free supernatant samples positive for hemolysin activity also were screened for leukotoxin activity. Significant levels of leukotoxin were detected in all samples screened.

Actinomyces↗
PubMed1996

Antibacterial activity of a synthetic peptide (PR-26) derived from PR-39, a proline-arginine-rich neutrophil antimicrobial peptide.

PR-39 is a proline-arginine-rich (PR) neutrophil antibacterial peptide originally identified and purified from the porcine small intestine. We report on the synthesis of a functional antibacterial domain of PR-39, the first 26 amino acid residues of the NH2 terminus. PR-26 was as potent as or more potent than PR-39 against enteric gram-negative bacteria. This truncated form of PR-39 potentiated neutrophil phagocytosis of Salmonella choleraesuis and decreased the level of S. typhimurium invasion into intestinal epithelial cells. Scanning electron microscopy confirmed that these peptides did not lyse cells by pore-forming mechanisms; however, they potentiated the antibacterial capabilities of a pore-forming peptide, magainin A. In addition, PR-26 was not toxic to epithelial cells at concentrations several times greater than its bactericidal concentration. These data suggest that PR-39 and its functional domain, PR-26, may potentiate the host's defense capabilities against gram-negative infections.

Amino Acid Sequence↗
PubMed1996

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.

Animals↗
PubMed1996

Influence of lipopolysaccharide-induced immune challenge and diet complexity on growth performance and acute-phase protein production in segregated early-weaned pigs.

Segregated early-weaned pigs (initially 4.0 kg and 14 +/- 1.5 d of age) were used to quantify the effects of lipopolysaccharide (LPS)-induced immune challenge and nursery diet complexity (complex, medium, and simple) on growth performance and haptoglobin production. Three treatments of immune challenge consisted of pigs given ad libitum access to feed (control), challenged with LPS and given ad libitum access to feed (LPS-challenged), or pair-fed to receive the same amount of feed as the LPS-challenged pigs (pair-fed). The absence of interactions (P > .10) between diet complexity and immune challenge with LPS indicated that the responses were independent. Control pigs were the heaviest (P < .01), LPS-challenged the lightest (P < .01), and pair-fed intermediate in weight on d 18 after weaning. Approximately two thirds of the decreased growth of LPS-challenged pigs was due to decreased ADFI and one third was due to decreased feed efficiency (G/F). Pigs fed the complex diet were heaviest (P < .05), and pigs fed the simple diet were lightest (P < .05) on d 18 after weaning. The increased growth of pigs fed the complex compared with those fed the medium diet was due to the increased ADFI of the former. The decreased growth of pigs fed the simple diet compared with those fed the medium or complex diets was due to both decreased ADFI and G/F. The LPS-challenged pigs had increased (P < .01) haptoglobin concentrations, suggesting that inflammatory cytokine production was higher in immune-challenged pigs. These data suggest that LPS immune challenge caused decreased growth by decreasing ADFI and altering nutrient partitioning and that growth responses to diet complexity are independent of immune challenge.

Acute-Phase Proteins↗
PubMed1996

Serum neutralizing antibody response and protection against experimentally induced liver abscesses in steers vaccinated with Fusobacterium necrophorum.

OBJECTIVE: To determine the efficacy of leukotoxin-based Fusobacterium necrophorum vaccines and dietary tylosin in providing protection against experimentally induced hepatic abscesses in steers. DESIGN: 30 steers assigned randomly to 6 treatment groups of 5 steers each: 1, phosphate-buffered saline solution (PBSS; control); 2, PBSS control, fed tylosin (100 mg/steer) daily; 3, inactivated whole-cell culture with oil emulsion adjuvant; 4, culture supernatant (crude toxoid) with oil emulsion adjuvant; 5, semipurified leukotoxoid with oil emulsion adjuvant; and 6, semipurified leukotoxoid with saponin adjuvant. PROCEDURE: Steers were inoculated SC with emulsified antigen or PBSS on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titer. On day 42, all steers were challenge exposed intraportally with F necrophorum culture. Three weeks later (day 63), steers were euthanatized and necropsied to examine liver and assess protection. RESULTS: Antileukotoxin antibody titers of all vaccinated groups markedly increased from baseline values, and mean titers of vaccinated groups were higher than those of the control and tylosin-treated groups. Steers vaccinated with culture supernatant with oil emulsion adjuvant or semipurified leukotoxoid with saponin adjuvant had the highest mean antibody titers. All 5 steers in the control group developed liver abscesses. Tylosin feeding did not protect steers challenge exposed with F necrophorum intraportally. CONCLUSIONS: Culture supernatant was more protective than whole-cell culture or semipurified leukotoxin against experimentally induced hepatic abscesses. Partial purification of leukotoxin appeared to reduce its protective immunity.

Abscess↗