Avian Pasteurella multocida Vaccine, Inactivated (Strain C48-2) is a concentrated bacterial antigen intermediate, not a finished biological product. The master seed designation C48-2 is the primary regulatory identifier for the production strain; no separate trade model is attached to the veterinary grade API. The material is intended for downstream formulation into injectable emulsions, solutions, powders, granules, premixes, tablets, and capsules by licensed veterinary pharmaceutical manufacturers. The injectable route is the most widely supported presentation for inactivated Pasteurella multocida antigens in poultry, while solid oral forms require additional stabilization and controlled challenge validation. Liquid presentations are typically released as chilled suspensions standardized by pre-inactivation cell density equivalent between 1×10⁹ and 5×10⁹ CFU/mL; lyophilized presentations are standardized by antigenic mass or protein nitrogen content. Representative release parameters include pH 7.0–7.4, residual moisture ≤1.0% for lyophilized cake, identity by slide agglutination or polymerase chain reaction, and absence of viable Pasteurella after inactivation. The product is not terminally sterilized by heat because whole-cell bacterial antigens are thermolabile.

Because C48-2 is an inactivated whole-cell antigen, the API cannot be characterized by viable count after inactivation. Final dosage forms are therefore expressed as pre-inactivation cell equivalent per dose, antigenic mass units, or reference vaccine units against an approved reference standard. Manufacturers converting the API into a finished product must establish a formulation-specific conversion factor; dilution based on volume alone is insufficient because adsorption to aluminum gel or entrapment in oil emulsion alters the effective antigen presentation.

Production-scale manufacture of C48-2 antigen commonly uses stirred-tank bioreactors with animal-component-free media. Batch pH is maintained at 7.2–7.4 with concentrated sodium hydroxide or ammonium hydroxide, dissolved oxygen is held at ≥30% saturation, and temperature is controlled at 37±0.5 °C. Harvest is performed in late exponential phase because capsular polysaccharide expression can decline during prolonged stationary phase. Tangential-flow filtration with 100 kDa cassettes concentrates the bacterial biomass; downstream inactivation is usually validated with formalin or a regulatory-approved alternative, with contact time and concentration defined in the site-specific production dossier. Actual C48-2 productivity data are lot-specific and not provided in this document.

The C48-2 seed lot system is maintained at −70 °C or as lyophilized master seed; working seed expansion typically uses tryptic soy broth supplemented with 5% animal-component-free serum replacement. Production cultures are monitored for capsular antigen expression by acriflavine flocculation or, if the master seed is confirmed as capsular type A, by hyaluronidase sensitivity. Spontaneous capsule loss can occur at frequencies proportional to passage number. Low-capsule variants must be excluded from final antigen pools because they reduce vaccine potency and may be associated with reduced protection against homologous challenge.

What Distinguishes C48-2 Inactivated Antigen from Live Attenuated and Autogenous Pasteurella Preparations?

The primary distinction is the absence of replication-competent organisms in C48-2 inactivated antigen. Live attenuated Pasteurella vaccines retain limited in vivo replication, induce mucosal and systemic responses, and may require a single dose in some schedules; however, they present a defined reversion risk and are generally unsuitable during antibiotic treatment or in immunologically compromised flocks. Inactivated C48-2 antigen carries no reversion risk and is compatible with layer and breeder health programs, but efficacy depends on adjuvant-driven humoral stimulation and a two-dose primary series in most finished vaccines. Compared with an autogenous bacterin prepared from a farm-specific field isolate, C48-2 offers a defined master seed with reproducible antigenic composition, but cross-protection against antigenically distant field isolates must be confirmed by challenge because Pasteurella multocida capsular types A, B, D, and F and somatic antigens vary regionally. Recombinant subunit products targeting outer membrane proteins or iron-regulated proteins exhibit narrower antigenic breadth, whereas C48-2 whole-cell antigen retains the native array of outer membrane proteins, lipopolysaccharide, and capsular material.

Formulation of C48-2 antigen into tablets, capsules, powders, granules, or premixes requires lyophilization or spray-drying with protective saccharides such as trehalose or sucrose at 5–15% w/v. The dried antigen is hygroscopic and should be blended at relative humidity below 30% RH to maintain water activity below 0.35; otherwise antigenic activity decreases. Tableting with microcrystalline cellulose and croscarmellose sodium at 100–250 MPa compression pressure is feasible, but antigen recovery and friability must be monitored because shear forces during roller compaction can denature surface-exposed bacterial proteins. Published data for the C48-2 strain in oral solid-dose poultry applications is limited; any oral claim must be supported by controlled challenge because the inactivated antigen must survive passage through the acidic proventriculus at pH 2.0–3.5 and mechanical degradation in the gizzard. Without enteric coating or an acid-stable carrier matrix, significant antigen degradation is likely.

Downstream formulation of C48-2 antigen into solutions requires pH-compatible buffers that avoid phosphate precipitation with aluminum adjuvants. Phosphate-buffered saline can strip aluminum hydroxide gel if used at high phosphate concentration; isotonic saline or Tris-buffered systems are preferred for aluminum-adsorbed products. Oil-emulsion products should not be mixed with saline diluents in-line without compatibility testing because electrolyte concentration above 150 mM sodium chloride can disturb interfacial film stability.

Adjuvant Loading, Emulsion Viscosity, and Injectable Final Form Criteria

For injectable solutions and emulsions, C48-2 antigen is commonly combined with mineral oil adjuvants or aluminum hydroxide gel at 2.0–3.0 mg/mL final aluminum content. Emulsification through a Silverson L5T rotor-stator at 8,000–12,000 rpm for 5–10 min yields a water-in-oil emulsion with median droplet diameter D50 1–5 µm; droplet sizes exceeding 10 µm are associated with sedimentation and uneven antigen distribution. Final viscosity at 20 °C should be maintained between 25 and 100 mPa·s to permit injection through 20–22 G needles in automated poultry vaccination lines. Aseptic processing is required, and terminal heat sterilization is incompatible. Sterile filtration of whole-cell C48-2 suspensions is not feasible because the bacterial cell size exceeds 0.22 µm; downstream processing therefore depends on validated aseptic assembly and sterile raw material control.

High-pressure homogenization above 500 bar can reduce droplet size below 0.5 µm, but excessive shear may strip capsular polysaccharide and increase free lipopolysaccharide in the aqueous phase. Batch failures in oil-emulsion processing are typically observed as phase separation, color change from cream-white to gray-white, or viscosity drift greater than ±15% after 24 h at room temperature. These failures require discard or rework because antigen distribution cannot be recovered by simple remixing.

Aseptic processing of C48-2 injectable final products requires an ISO 14644-1 Class 5 fill zone with unidirectional airflow and validated sterilizing-grade filtration of heat-stable process fluids. The antigen fill cannot be terminal-filtered because whole bacterial cells exceed 0.22 µm membrane pore size. Combination of C48-2 API with live attenuated viral vaccines or live bacterial vaccines in the same syringe or administration line is not recommended without documented compatibility. Preservatives such as thimerosal above 0.01% w/v and cationic surfactants can reduce antigenic integrity.

When Freeze-Drying or Spray-Drying C48-2 Antigen for Powders and Premixes

Freeze-drying of C48-2 antigen for vial reconstitution or powder blending requires a lyophilization cycle with primary drying shelf temperature below the formulation collapse temperature, typically −25 °C to −35 °C, followed by secondary drying at 20–25 °C for 6–12 h to achieve residual moisture ≤1.0%. Cake collapse occurs when the product temperature exceeds the collapse temperature before the sublimation front completes; on production units with shelf areas of 20–40 m², fill depths above 1.5 cm and an excipient-to-antigen ratio below 2:1 w/w are common causes of batch-to-batch reconstitution time variation. Spray-drying, if used for feed premix granules, should maintain inlet temperature below 120 °C and outlet temperature below 60 °C; inlet temperatures above 140 °C are generally incompatible with gram-negative bacterial antigen stability. The resulting powder is blended with lactose monohydrate or dextrose carriers, and segregation can occur if particle size distributions differ by more than 250 µm D50. Final premix or granule formulations intended for oral delivery should be assayed by antigen-capture ELISA or Western blot for C48-2-specific antigen integrity after blending.

If the final product is formulated as a powder or premix, the antigen should not be blended with high-moisture ingredients or acidic mineral carriers because low pH can hydrolyze surface proteins and reduce antigen recovery. For injectable finished vaccines, the API is diluted to the final dose volume after potency adjustment. The target dose is usually expressed as pre-inactivation cell equivalent per 0.5 mL dose, but the exact dose volume, route, and age of administration are determined by the finished product license. The API is not intended for direct use in birds or for farm-level compounding.

Quality control of the C48-2 API should include identity by slide agglutination or polymerase chain reaction, inactivation completeness by passage in suitable bacterial growth media for 14 days, sterility for injectable grade per 9 CFR 113.26 or equivalent pharmacopoeial method, endotoxin below the manufacturer-validated limit, and antigenic potency by vaccination-challenge or validated in vitro antigen mass. Storage at 2–8 °C protected from light is required; freezing of liquid antigen is not recommended unless the formulation contains validated cryoprotectants. Liquid containers should be used within 24 h of opening, and nonsterile oral premix intermediates should meet a bioburden limit of ≤10³ CFU/g and absence of Salmonella in 25 g. These are typical release criteria; the current manufacturer’s certificate of analysis prevails for each lot.