Differentiation of Bacteroides nodosus biotypes and colony variants in relation to their virulence and immunoprotective properties in sheep

Protection of sheep against experimental footrot by vaccination with pili purified fromBacteroidesnodosus

Merino sheep vaccinated with either whole Bacteroides nodosus organisms, a crude surface antigen preparation or highly purified pili (>99% homogeneity) in oil adjuvant, developed significant resistance to artificial footrot infection when compared with unvaccinated control sheep inoculated with saline-in-oil emulsion (Freund;s incomplete adjuvant) alone. The pili-vaccinated sheep generally had higher K-agglutinating antibody titres than sheep vaccinated with whole B. nodosus. These results confirmed the role of B. nodosus pilus protein both as a protective antigen and the K-agglutinogen. Vaccines prepared with Freund;s incomplete adjuvant containing either purified pili, crude pili or B. nodosus whole cells did not produce significantly different injection-site reactions.

A method to differentiate between virulent and benign isolates ofBacteroides nodosusbased on the thermal stability of their extracellular proteinases

A rapid modification of the hide powder azure proteinase degrading test was devised to distinguish between benign and virulent strains of Bucteroides nodosus grown as cultures on either liquid or solid media. The assay was based on the difference in stability, at 60 degrees C, of the enzymes released in the growth medium. The assay can be completed in four hours. Results for ovine virulent strains and their culture variants were similar and were clearly distinguishable from those of the ovine benign, bovine, deer and goat isolates which were similar to each other. The proteinase isozymes from cultures of the deer and goat isolates were separated by polyacrylamide gel electrophoresis and their molecular weights determined.

Duration of resistance to experimental footrot infection in Romney and Merino sheep vaccinated withBacteroides nodosusoil adjuvant vaccine

Groups of 10-12 Romney and Merino wethers were challenged simultaneously with homologous experimental footrot infection after having received the second of 2 doses of Bacteroides nodosus (strain 198) vaccine 0, 4, 8, 12, 16 and 20 weeks previously. Inoculations were carried out 28 days apart and unvaccinated sheep of both breeds were challenged as controls. Most Romneys that had been vaccinated up to 16 weeks prior to challenge were resistant to footrot whereas 8 of 10 controls were susceptible. This resistance was lost by about 20 weeks after vaccination. By contrast, protection against challenge in vaccinated Merinos lasted only about 4-5 weeks, although residual benefits of vaccination were apparent after longer intervals from the reduced number and severity of foot lesions among vaccinates compared with controls. Agglutinin titres, which did not differ markedly after similar intervals between Romneys and Merinos, reached maximum levels between 4 and 8 weeks after the second vaccine dose and subsequently declined. Although peak titres were generally recorded at the time of maximum protection in Merinos, the relationship between agglutinin levels and resistance in the Romneys was ill-defined.

The detection and characterisation of Dichelobacter nodosus from cases of ovine footrot in England and Wales

Footrot, caused by the strictly anaerobic bacterium Dichelobacter nodosus, is the most common cause of lameness in sheep in Great Britain but problems exist in association with its diagnosis and control. The fastidious nature of D. nodosus means that complex media and several weeks are required for characterisation. An alternative method to simplify and enhance the detection of D. nodosus in clinical samples is therefore highly desirable. In terms of control, anecdotal evidence from the farming community suggests that the commercially available vaccine, based on Australian isolates of D. nodosus, is not widely employed in this country due to its perceived inefficacy. Seven hundred and six isolates, collected from outbreaks in England and Wales, were therefore used to investigate these issues. A 16S rRNA PCR was adapted to detect D. nodosus in clinical material within 1 day of sampling; a 15% increase in detection compared with culture and less than 1% false negatives were achieved. This represents a major advance in the rapid diagnosis of footrot and will be of great value to practitioners and diagnostic laboratories. Bacterial virulence was tested using protease thermostability and zymogram assays, whilst serogrouping was performed by slide agglutination. All isolates demonstrated virulence patterns previously recorded in Australia and all nine serogroups of D. nodosus (A-I) were represented. Serogroup H was predominant. There was, therefore, no evidence for the presence of novel strains of D. nodosus compared with Australia suggesting the need for further investigation into farmers' views on the use of the commercial vaccine in Great Britain.

Identification and characterisation of serogroup M among Nepalese isolates of Dichelobacter nodosus, the transmitting agent of footrot in small ruminants

One thousand and sixty three isolates of Dichelobacter nodosus cultured between 1992 and 1996 from cases of footrot in sheep and goats of migratory flocks of Nepal were characterised by agglutination test using prototype antisera of the Australian classification system. Of those, sixty six isolates could not be classified into any of the nine serogroups (A-I). This study was therefore undertaken to characterise these isolates. It was established that they were agglutinated by antiserum against serotype M of an alternative classification system. The distinct antigenic character of these isolates was further confirmed by DNA sequence analysis of the gene for the fimbrial subunit protein of two of them. At a molecular level, these isolates were closer to the prototype of serogroup F, VCS 1017. However, when compared with VCS 1017, the number of amino acid substitutions (28) in the fimbrial protein of these isolates was similar to that expected between isolates of different serogroups. Because these isolates are antigenically similar to 'serotype' M, but meet all the criteria to be classified into an independent serogroup, it is proposed that these isolates together with isolates previously classified as serotype M be classified as 'serogroup M'.

Improved laboratory diagnosis of ovine footrot: an update

Ovine footrot is a complex clinical disease syndrome primarily resulting from infection by the anaerobic bacterium Dichelobacter nodosus. In order to aid clinical diagnosis, various laboratory tests based on the detection and measurements of phenotypic properties of D. nodosus have been developed for genus-specific detection as well as virulence determination. However, these tests are generally time-consuming, and tend to be variable with external factors that affect the growth and metabolism of the bacterium. A new generation of diagnostic reagents, such as monoclonal antibodies, gene probes and polymerase chain reaction, has been developed recently. Preliminary assessment of these reagents has shown potential to vastly improve the laboratory identification and determination of the virulence of D. nodosus. It is important that these new reagents are vigorously assessed against existing laboratory tests, such as the elastase test and gelatin gel test, prior to their adoption for the routine diagnosis of footrot.

Assessment of gelatin gel and elastase tests for detection of protease activity of Dichelobacter nodosus isolates from ovine footrot

Protease tests (the gelatin gel protease thermostability test, the elastase test or both) were performed on 4296 isolates of Dichelobacter nodosus derived from 452 outbreaks of ovine footrot occurring in New South Wales. Both tests showed a high level of repeatability. In the gelatin gel test, culture broths were heated for 16 min at 66.8 degrees C. Heated broths containing thermostable protease digested gelatin (positive gelatin gel test) while those broths containing thermolabile protease failed to digest gelatin (negative gelatin gel test). Gelatin gel positive isolates were unable to be graded into subcategories on the basis of the percentage stability of their protease. In the elastase test, the ability of isolates to digest (positive elastase test) or not digest elastin particles (negative test) was measured up to 28 days incubation. Individual elastase positive isolates yielded a graded result based on the number of days to reach a positive result. There was a very high level of agreement between the gelatin gel and the elastase tests consistent with their separating isolates into two groups based on protease activity (either gelatin gel positive and elastase positive or gelatin gel negative and elastase negative). Either test is suitable for use in footrol control and eradication schemes. The gelatin gel test provides clearcut separation of isolates into positive and negative categories and has the major advantage of yielding a more rapid result than the elastase test. The elastase test should be utilised where a graded assessment of protease activity is desired.

Grading the lesions of ovine footrot

Sixteen methods of grading the lesions of ovine footrot were assessed on the basis of the effect of the lesions on the humoral immune response of the host to a causative bacterium, Dichelobacter nodosus. Methods that allowed for qualitative and quantitative differences in lesion scores between sheep were the best predictors of host response, and methods that assessed the lesions in each of the eight digits were more efficient than methods that did not grade the digits within feet. Weighting the scores for lesions that involved underrunning of the keratin of the hoof provided the most powerful means of predicting host response. The correlations between host response and the more elaborate weighted scores were close to the highest possible among additive linear estimators. Total weighted footscore, which is the sum of the footscores of the four feet weighted for underrun lesions, is proposed as a simple and effective grading system for sheep with lesions of footrot. There was a significant association within sheep between the number of underrun feet and the severity of lesions in individual feet.

Experimental evaluation of a commercial footrot vaccine against native Canadian strains of Dichelobacter nodosus

Two serotypes of the anaerobic bacterium Dichelobacter nodosus were used to experimentally infect young sheep resulting in infectious pododermatitis or footrot characteristic of the natural disease in sheep. The specific serotypes of D. nodosus were reisolated from the feet and identified using immunofluorescent microscopy of hoof scrapings. Prior immunization of sheep with a commercially available bacterin containing whole cell preparations of ten strains of D. nodosus resulted in serum IgG reactive to a serotype of D. nodosus common to the vaccine. Immunization also produced serum IgG reactive to a serotype of D. nodosus not incorporated in the vaccine. A less severe infection occurred in the immunized sheep than in the controls regardless of the serotype of bacteria used to infect them. Clinical lameness and lesion severity were milder in sheep infected with the serotype of D. nodosus common to the vaccine. Western blot analysis of sera from convalescent sheep showed cross-reactive antibodies to nonfimbrial cell surface proteins, as well as bacterial lipopolysaccharide. Such cross-reactivity may explain the partial protection seen in animals infected with a serotype distinctive from the ones in the vaccine. Despite the historical emphasis of fimbrial immunogens in ovine footrot this study using a new model of experimental ovine footrot suggests other surface antigens may also be important in protective immunity.

Cloning, sequence and expression of the gene (aprV5) encoding extracellular serine acidic protease V5 from Dichelobacter nodosus

The acidic protease V5-encoding gene (aprV5) from Gram- Dichelobacter nodosus virulent strain 198 was isolated from a cosmid bank by activity screening and sequenced. The 2371-bp nucleotide (nt) sequence contained an open reading frame coding for a protein precursor of 595 amino acid (aa) residues composed of a signal peptide, a pro-region, a mature active protease of 347 aa and a C-terminal extension region of 120 aa. The deduced aa sequence of the pre-pro-mature protease regions showed about 65% similarity to that of D. nodosus basic protease while the C-terminal extension region showed only about 26% similarity. The aprV5 gene, without its C-terminal extension region, was cloned and expressed in Escherichia coli. The acidic protease B5-encoding gene (aprB5) from non-virulent strain 305 was also cloned and sequenced. The aprB5 nt sequence showed 99% homology to that of aprV5 with two single-aa changes occurring in the precursor.

Characterisation of virulent and benign strains of Bacteroides nodosus

The extracellular proteases of 395 isolates of B. nodosus from ovine, bovine and caprine foot lesions were classified as either thermostable or thermolabile. Stable protease was associated with one and unstable protease with four distinctive isoenzyme patterns, each pattern differentiated by the relative mobility of paired isoenzymes. Pathogenicity tests on 64 isolates showed a correlation between the production of stable protease and the production of virulent ovine footrot lesions. The mean values for total protease activity, twitching motility and colony diameter were significantly higher for virulent compared to benign isolates, but the range of values overlapped. SDS-PAGE whole-cell electrophoretic profiles of virulent isolates were similar to the profiles of some benign isolates.

Advances in the control of foot rot in sheep

All cases of foot rot, whether acute, chronic, benign, or inapparent, must be identified. If the outbreak is severe and production losses warrant, each foot of each animal must be examined thoroughly. Proper handling facilities and equipment, adequate light, and dry working conditions are needed to properly examine each foot. Infected sheep must be separated from the clean flock. Following extensive treatment, these animals must be diagnosed as free from the disease before returning to the clean flock. Animals that do not respond must be culled from the flock. Although copper sulfate and formalin are effective materials for footbathing, zinc sulfate is equally effective and does not irritate the skin, eyes, or lungs as does formalin, or stain the wool as does copper sulfate. A 10% zinc sulfate solution with a nonionic surfactant is an effective footbathing or foot soaking solution. The cure rate is improved by a thorough foot paring and a foot soak of at least 30 minutes. A number of treatment options along with formulations are outlined in the 1988 edition of the Sheep Production Handbook of the Sheep Industries Development Program, Inc, 6911 Yosemite, Englewood, CO 80112.

Measurement of protease thermostability, twitching motility and colony size of Bacteroides nodosus

Total extracellular protease activity of Bacteroides nodosus in TAS liquid culture varied directly with cell mass and buffer concentration between 20 and 50 mM HEPES, MOPS and TES buffers, but not with Tris which gave anomalous high cell counts, nor with Na2Co3 which showed a decline of protease activity and cell mass. The stability of HEPES-buffered crude protease preparations were estimated on the basis of temperature or Ca2+ activity. Variation of the estimates for cellular twitching was greater than that for colony diameter in benign and virulent strains of B. nodosus. Surface translocation, quantified on the basis of colony diameter, reached a limit after 72 h incubation on modified TAS agar, ranging from 0.04 to 0.14 mm per h for six isolates tested.

A role for DNA characterisation in ovine footrot

Bacteroides nodosus involved in several outbreaks of ovine footrot over a number of years were subjected to DNA restriction endonuclease analysis. Individual isolates were found to have characteristic Bam HI profiles which permitted their accurate identification and differentiation from other isolates. Bam HI profiles of B. nodosus isolates were used in epidemiological investigations involving consecutive outbreaks of footrot on individual and neighbouring farms. The relationship of given isolates to a common source could be established by this means. Restriction endonuclease analysis provides an additional epidemiological tool in ovine footrot investigations as it accurately identifies interstrain differences in a manner not possible by conventional bacteriological and serological means.

Intracellular crystal formation in Bacteroides nodosus

An intracellular crystalline structure was found in at least two strains of Bacteroides nodosus. The inclusion appeared to be associated with good growth of the organism under optimum conditions following selective passage of rough colonies containing highly fimbriate cells. Several morphological forms of the inclusion were noted. Indiscriminate subculture of crystal-forming cultures led to the loss of this particular property indicating a genetically controlled system of either bacterial or bacteriophage origin.

Pilins of Bacteroides nodosus: molecular basis of serotypic variation and relationships to other bacterial pilins

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Characterization of Pseudomonas aeruginosa mutants with altered piliation

The pilus-specific Pseudomonas aeruginosa bacteriophage P04 was used to select spontaneous mutants of strain PAK which have altered piliation. The largest class of phage-resistant mutants synthesized the pilin polypeptide, but did not assemble pili. These mutants are likely to contain mutations in genes required for pilus assembly and not mutations in the pilin structural gene, as they could not be complemented by a normal copy of the pilin gene. In addition, two alterations in pilin gene transcription were found among the mutants--hyperpiliated mutants which overproduce pilin mRNA, and a mutant with temperature-sensitive pilin gene transcription. We also present a model for the regulation of pilin gene transcription by a feedback mechanism sensitive to the relative rates of pilus assembly and disassembly.

Protection of sheep against footrot with a recombinant DNA-based fimbrial vaccine

Recombinant Pseudomonas aeruginosa cells containing the Bacteroides nodosus fimbrial subunit gene under the transcriptional control of a strong promoter produce large amounts of B. nodosus-type fimbriae. We have carried out vaccination trials which show that these fimbriae are just as effective as either natural fimbriae or whole cell preparations of B. nodosus in inducing protective immunity against homologous footrot challenge. The recombinant-produced fimbriae are also effective therapeutically in accelerating the rate of healing of pre-existing footrot lesions. These results confirm that the structural subunit of the fimbrial strand is a primary protective antigen against footrot, and demonstrate the practicality and potential of recombinant DNA approaches to the development of new vaccines against B. nodosus and other Type 4 fimbriate pathogens.

The pathogenicity and cultural characteristics of virulent, intermediate and benign strains of Bacteroides nodosus causing ovine foot-rot

The relationship between the cultural and biochemical characteristics of 22 strains of Bacteroides nodosus and their virulence for sheep was examined. Virulent, intermediate and benign strains were recognised. Although there was some relationship between virulence and colony morphology on hoof medium with 4% agar, colonies of one virulent and 4 intermediate strains resembled those of benign strains. However, on hoof medium with 2% agar and on blood Euonagar, colonies of this virulent and one intermediate strain differed from each other and the other 3 intermediate strains, which in turn differed from the benign. The degree of piliation, as assessed by electron microscopy, was not a reliable indicator of virulence in strains not possessing a beaded colony type. Together, the results of colony morphology and proteolytic tests such as zymogram, degrading proteinase and elastin-agar tests allowed better discrimination of virulent and benign strains. Intermediate strains generally possessed virulent protease activity. In strains with benign zymogram patterns, activity bands 2 and 3 were more labile than in strains with virulent patterns. The addition of CaCl2 to the culture medium resulted in greater stability of proteolytic activity, particularly with benign strains, and prevented the disappearance of protease activity in the band 5 position in virulent, intermediate and benign strains during prolonged incubation. There were slight differences in the sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) patterns of outer membrane proteins of some benign strains but those of intermediate category resembled virulent strains. There was some relationship between the apparent Mr of the pilin monomer on SDS-PAGE gels and serogroup specificity.

Comparative antigenic analysis of extracellular proteins of Bacteroides nodosus isolated from virulent and benign ovine footrot

Antigens in the extracellular protein (ECP) complexes of Bacteroides nodosus, isolated from sheep with either benign or virulent footrot, were studied by immunoelectrophoresis (IEP). Rabbit antisera against ECP from virulent and benign strains, were used in homologous and heterologous crossed IEP. Four precipitin peaks unique to the virulent strain, and five peaks unique to the benign strain were identified. In an attempt to characterize the different antigens in ECP, rabbit antisera were raised against an outer membrane protein (OMP, mol. wt. 35 000 daltons), pili and various proteases of virulent and benign strains of B. nodosus. No precipitin band was observed when ECP from both B. nodosus strains were reacted against anti-OMP and anti-pilus antisera. However, single precipitin bands unique to one protease from the benign strain and one protease from the virulent strain were identified. The results suggest that specific antigens other than proteases or pili are important in determining whether a B. nodosus isolate is virulent or benign.

Current and Future Applications of Monoclonal Antibodies against Bacteria in Veterinary Medicine

This chapter discusses the current and future applications of monoclonal antibodies against bacteria in veterinary medicine. It discusses the existing applications of monoclonal antibodies, including the use of pilus-specific monoclonal antibodies for passive immunization of calves and piglets against enteropathogenic E. coli (EPEC) infections as well as the development of rapid diagnostic test kits for field diagnosis of EPEC infections. The potential applications of monoclonal antibodies for passive immunization against a variety of veterinary pathogens are passive immunization against Moraxella bovis (pinkeye), Bacteroides nodosus (foot rot), EPEC enterotoxin (enteric colibacillosis), Pasteurella haemolytica (pneumonic pasteurellosis), and Streptococcus equi (strangles). Three main areas of application for monoclonal antibodies against bacterial antigens in veterinary medicine are passive immunization, improved immunodiagnostics, and immunotherapy. Monoclonal antibodies, because of their specificity, unlimited availability, and high titer, represent excellent passive immunizing agents. However, their potential usefulness in preventing infection must be evaluated on a case-by-case basis.

The protection given by pilus and whole cell vaccines of Bacteroides nodosus strain 198 against ovine foot-rot induced by strains of different serogroups

A highly purified pilus vaccine prepared from cells of Bacteroides nodosus strain 198 provided a high level of protection against homologous challenge and small, not statistically significant, levels of protection against challenge with 4 other strains each from different serogroups. In a second experiment, a partially purified pilus vaccine from strain 198 induced significant immunity to 1 of 4 heterologous strains which were different from those used in the first experiment. In a third experiment a strain 198 whole cell vaccine produced significant immunity against 3 of 6 heterologous strains used in the first 2 experiments. There was no obvious relationship between the colony type, degree of piliation and level of cross-protection obtained against a particular strain. The results provide further evidence that immunogens associated with, but distinct from, the pilus are involved in cross-protection and that cross-protective antigens are common to some, but not all, strains.

Isolation and characterization of Bacteroides nodosus fimbriae: structural subunit and basal protein antigens

We examined the isolation of fimbriae from Bacteroides nodosus. It was found that the best preparations were obtained from the supernatant of washed cells cultured on solid medium, from which fimbriae could be recovered in high yield and purity by a simple one-step procedure. Analysis of such preparations by sodium dodecyl sulfate gel electrophoresis showed that greater than 98% of the protein consisted of fimbrial structural subunits whose molecular weight was ca. 17,000. These preparations also usually exhibited minor contamination with a polypeptide of ca. 80,000 molecular weight, as well as trace amounts of lipopolysaccharide. Attempts to release additional fimbriae by the traditional means of subjecting the bacterial cells to physical stress, such as shearing or heating, resulted primarily in an increase in the level of contamination, without significant gain in the yield of fimbriae. Removal of the 80,000-dalton component could not be achieved by any of a variety of techniques normally used in fimbriae purification, including isoelectric precipitation, MgCl2 precipitation, and CsCl gradient ultracentrifugation, implying a direct physical association with the fimbrial strand. Electron micrographs of fractions containing this protein show cap-shaped structures attached to the ends of what appeared to be fimbrial stubs. These observations suggest that the 80,000-dalton polypeptide may actually constitute the basal attachment site which anchors the fimbria to the outer membrane, analogous to a similar protein recently described in enterotoxigenic strains of Escherichia coli. In B. nodosus, this 80,000-dalton protein is a major surface antigen, and like the fimbrial subunit, exhibited variation in electrophoretic mobility between serotypically different isolates.

Cloning and expression in Escherichia coli of the gene encoding the structural subunit of Bacteroides nodosus fimbriae

Bacteroides nodosus is the primary causative agent of ovine foot rot. Virulent isolates of this bacterium contain fimbriae which appear to play a major role in both infectivity and protective immunity. This paper presents the cloning and expression in Escherichia coli of the gene encoding the structural subunit of the fimbriae of B. nodosus. Total DNA was isolated from B. nodosus VCS 1001 (serogroup A), digested with HindIII, and inserted into the positive-selection vector pTR262. Recombinant E. coli clones were screened directly with anti-fimbrial antiserum by using a colony immunoassay. Several positive colonies were identified, each of which contained the same 5.5-kilobase HindIII insert. The prototype has been designated pBA101. Some clones also contained additional flanking sequences from the B. nodosus genome. Western transfer analyses verified that the positive clones were producing the B. nodosus fimbrial structural subunit, molecular weight ca. 17,500. The level of expression of the antigen in E. coli was comparable to that in B. nodosus itself and was unaffected by the insertion site or orientation of the cloned fragment, indicating that synthesis was being directed from an internal promoter. Restriction mapping and deletion analyses localized the fimbrial subunit gene to the vicinity of a PvuII site near the central region of the original HindIII insert. The expressed antigen was located in the membrane-cell wall fraction and may be exposed on the surface of the recombinant E. coli cells.

The thermostability of proteases from virulent and benign strains of Bacteroides nodosus

Protease enzymes, produced by Bacteroides nodosus strains isolated from animals with virulent and benign forms of ovine footrot, were partially purified by ultra-filtration, ion exchange chromatography and gel permeation chromatography. Each enzyme had a similar pH optimum, was inhibited by phenylmethylsulfonyl fluoride (PMSF), ethylene diamine tetraacetic acid (EDTA) and ethyleneglycot-bis-aminoethylether-N,N-tetraacetic acid (EGTA), but was not inhibited by 1,10-phenanthroline. The results suggest that these enzymes are serine proteases that require divalent cations for activity. The enzymes could be distinguished by their differential temperature stability and differing susceptibility to irreversible inactivation by EDTA. Both enzymes were stabilised by incubation in the presence of Ca2+, but the enzyme purified from the virulent isolate required less Ca2+ for maximum stability. These results suggest that the differential thermostability of the protease activity detected in virulence tests is an intrinsic property of the protease enzymes.

Classification of Bacteroides nodosus by agglutination tests

One thousand two hundred and sixty seven isolates of Bacteroides nodosus from 292 sheep in 58 flocks were examined. Of these, 1260 could be classified by slide agglutination into 8 serogroups designated A to H. Up to 6 serogroups were detected in individual flocks, with up to 4 serogroups being detected in a single foot. Of the 292 sheep examined, 38 (13%) carried mixed serogroup infections. Determination of the range of serological types infecting a flock frequently required the examination of a number of isolates from each of a number of sheep. Cross-tube agglutination tests carried out on 44 isolates and their antiserums indicated that members of some serogroups could be divisible into subgroups or serotypes. These results suggested that 16 or more serotypes of B. nodosus might exist. The nature of the antigens responsible for both slide and tube agglutination reactions needs to be determined.

Quantitative test for Bacteroides nodosus pilus protein by an agglutination-absorption test

A pili agglutination-absorption test (PAAT) was developed for the quantitative measurement of pilus protein in cultures of Bacteroides nodosus and to quantify pili yields during purifications. The test was calibrated by recording the amount of pilus protein required to absorb a measurable amount of anti-pili antibody from antiserum. The amount of anti-pilus antibody in absorbed and unabsorbed serum was specifically measured by a Bact. nodosus K-agglutination test. The PAAT could be calibrated using any combination of crude or pure pili preparations and specific anti-pili serum or non-specific anti-Bact. nodosus serum. This had advantages over the use of radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) techniques for measurement of pili because they require the use of highly purified reagents for calibration. The minimum quantity of pilus protein measurable by PAAT was 0.1 microgram per test which was similar in sensitivity to that reported for RIA and ELISA. The reagents used in PAAT were stable for at least six months. The amount of pilus protein per bacterium as measured by PAAT was directly proportional to the average number of pili per bacterium as measured by electron microscopy. The test was Bact. nodosus serotype specific.