The product, Streptococcus Vaccine Veterinary Grade API for Tablets / Injections / Capsules / Powders / Granules / Premix / Solutions, is supplied as Model SVS-API-STR-0724, a lyophilized inactivated whole-cell antigen concentrate derived from Streptococcus suis serotype 2. The material is intended solely for further pharmaceutical processing into finished veterinary immunobiologicals and is not released as a final dosage form. The lyophilized cake contains standardized antigen mass, sucrose and trehalose as lyoprotectants, and phosphate-buffered saline; after reconstitution in water for injection, the pH is maintained at 6.8–7.4. Pre-lyophilization bacterial cell mass is controlled at not less than 1×10^10 CFU/mL before inactivation. Inactivation uses formaldehyde at a final concentration of 0.10–0.20% v/v for 24–36 h at 37 °C, followed by diafiltration to reduce free formaldehyde below 0.05% w/v. This concentration range is selected because incomplete inactivation increases batch rejection rates, while excessive formaldehyde can crosslink surface epitopes and reduce antigen activity in downstream ELISA testing.

Unlike liquid bacterins, the lyophilized API can be dry-blended, compressed, encapsulated, extruded as granules, or incorporated into non-sterile oral premixes without the process loss commonly caused by aqueous phase separation. For injectable applications, the powder is reconstituted under aseptic conditions and combined with adjuvants only after reconstitution to avoid premature antigen adsorption during lyophilization. This separation of adjuvant from antigen during drying is a critical quality control boundary because aluminium hydroxide adjuvants, when co-lyophilized, can form aggregates that fail the syringeability test required for injectable vaccines.

Why Is Residual Moisture Controlled Below 2.0% in Multi-Dosage Form APIs?

Residual moisture in lyophilized antigen concentrates determines both chemical stability and mechanical processability. For tablet compression, moisture above 2.0% w/w increases adhesion to punch faces and causes capping at compression forces above 12 kN. The product specification therefore limits residual moisture to ≤2.0% w/w by Ph. Eur. 2.2.32. Freeze-drying is performed on stainless-steel shelves with a primary drying shelf temperature of −20 °C and a chamber pressure of 0.200 mbar for 28 h, followed by secondary drying at +20 °C for 6 h. The glass transition temperature of the maximally concentrated solution is measured at −28 °C to −31 °C by freeze-drying microscopy; product temperature must remain below the collapse temperature through the primary drying phase.

Batch release data for Model SVS-API-STR-0724 are compiled from three consecutive production-scale lots. Antigen activity by inhibition ELISA shows a relative standard deviation of ≤12% across lots, which is used as the batch-to-batch consistency limit. The following release specification applies to every lot intended for tableting, injection, encapsulation, powder, granule, premix, or solution formulation.

For tablet and capsule processing, the lyophilized API is milled with a conical mill fitted with a 0.5 mm screen and blended with directly compressible mannitol at 25 °C and relative humidity ≤30%. The blend is pressed into tablets with a target hardness of 60–90 N using a single-station eccentric press at 8–14 kN compression force. Direct compression is preferred over wet granulation when the antigen load is above 1.0 mg/g; aqueous granulation can reduce antigen activity by 15–25% if the inlet air temperature exceeds 45 °C. Published efficacy data for oral tablet delivery of this specific API in target species is limited; therefore process validation uses antigen activity retention rather than clinical potency as the primary release criterion.

For capsule filling, the milled API is blended with pregelatinized starch and magnesium stearate at 0.5% w/w; lubricant is added last and blended for 3 min to avoid over-lubrication. Powder flow is measured by Ph. Eur. 2.9.36 with a Hausner ratio limit ≤1.35. Hard gelatin capsules are filled on an intermittent-motion capsule filler at 15,000 capsules/h. Filling machine compression stations are maintained at ≤25 °C and ≤30% RH. Powder blends that exceed 2.0% w/w moisture show uneven filling and frequent capsule deformation.

When Tablet Compression Replaces Aqueous Filling

Tablet compression imposes shear stress and localized temperature rise at the punch face. Production-scale observations on a rotary press with 16 stations and a turret speed of 30 rpm show that tablet core temperatures remain below 35 °C when the compression force is kept below 14 kN. At higher forces, the loss of antigen activity measured by ELISA increases from 8% to 22%, indicating a process cliff edge. Therefore, compression force is locked at 8–12 kN for final tablet dosage forms. Tablets are not enteric-coated unless a subcoat of hydroxypropyl methylcellulose at 3.0% w/w is applied first; direct application of methacrylic acid copolymer dispersions can reduce local pH to 4.0–4.5, which destabilizes the antigen in dissolution testing.

What Distinguishes This Veterinary Streptococcus API from Conventional Bacterins?

Conventional liquid bacterins are supplied as suspensions at 2–8 °C with shelf lives of 12–24 months. The lyophilized API differs in three process-relevant properties. First, the residual moisture ceiling of 2.0% w/w permits dry blending into feed premixes without microbial growth or phase separation during storage at 25 °C for up to 6 months in sealed aluminium pouches. Second, the particle size distribution is controlled to D10 ≥20 µm, D50 40–80 µm, and D90 ≤125 µm, allowing direct compression and capsule filling without additional milling at the user site. Third, the antigen is standardized by ELISA activity rather than by biomass alone, reducing variability in final vaccine potency to ≤15% RSD across production batches. In contrast, whole-cell bacterins standardized only by opacity or dry cell weight may show potency shifts of 25–40% between batches due to differences in surface epitope availability.

The API is not recommended for combination with amine-based excipients or cationic surfactants before antigen adsorption onto aluminium hydroxide gel. In water-based injection formulations, premature exposure to cationic surfactants can displace surface protein and produce fine precipitates that fail the visible particle test under Ph. Eur. 2.9.20. For oral solutions and drenches, the powder should be reconstituted in chilled purified water at 2–8 °C and used within 6 h if no preservative is present; benzyl alcohol at 0.5% v/v may extend the in-use period to 24 h but is not permitted for parenteral use in some target species due to withdrawal restrictions.

Granulation and Feed Premix Stability Boundaries

Granulation for oral premixes uses a twin-screw granulator with an L/D ratio of 25:1 and a screw speed of 100–150 rpm. The granulation liquid is an aqueous binder solution containing 2.0% w/w polyvinylpyrrolidone K30. After granulation, the wet mass is dried at 40 °C in a fluid-bed dryer until residual moisture is ≤5.0% w/w. Drying above 50 °C is avoided because the antigen loses ELISA activity at a rate of 0.3 log per hour when the granule temperature exceeds 55 °C. The resulting granules have a bulk density of 0.45–0.60 g/mL and a Hausner ratio ≤1.35, ensuring uniform mixing into feed at 1–5 kg per tonne. Granules are packaged in foil-lined bags with desiccant and stored at 2–8 °C; storage at 25 °C for more than 30 days is not supported by stability data.

Powders and granules intended for oral administration are not sterile. Bioburden limits are set at ≤100 CFU/g total aerobic microbial count and ≤10 CFU/g total yeast and mould count by Ph. Eur. 2.6.12. Enterobacteriaceae and Salmonella must be absent in 1 g.

Compliance Matrix for Multi-Route Processing

For injectable finished product, Model SVS-API-STR-0724 is reconstituted with water for injection to a target antigen activity of 1.0–2.0 mg/mL total protein and then aseptically mixed with sterile aluminium hydroxide gel at 10.0 mg/mL aluminium. The adjuvant is added after reconstitution because co-lyophilization of antigen with aluminium hydroxide produces dense sediment that cannot be homogenized reproducibly. The final suspension is filled into Type I glass vials under Grade A laminar flow. Whole-cell Streptococcus antigen cannot be sterile-filtered through 0.2 µm membrane filters; therefore sterility assurance depends on aseptic processing and prior sterility of the API. The fill volume is controlled at 20.0 mL ± 0.5 mL for multi-dose vials, and closure integrity is verified by vacuum decay testing.

For solutions and oral drenches, the API dissolves or disperses at 25 °C within 10 min in purified water with gentle stirring at 100 rpm. Precipitation may occur if divalent cations such as calcium or magnesium exceed 100 mg/L in the diluent; softened water or water for injection should be used. The solution remains within the 6.8–7.4 pH range and shows no visible particulate matter when tested by Ph. Eur. 2.9.20. Dosing pumps used on pig farms should be flushed with purified water after each use because residual solution forms a biofilm at ambient temperature within 24 h.