Another useful preservative is potassium sorbate. Potassium acetate is used as a food additive as a preservative and acidity regulator. Salicylic acid is used as a food preservative, a bactericidal and an antiseptic. The most commonly used antimicrobial preservative is lactic acid. Sulfites are used as a food preservative or enhancer. It is used as a disinfectant, antioxidant, and preservative agent. The formaldehyde used as a preservative produces false negatives in both reactions. Copper is also commonly used as a wood preservative or fungicides. Zinc naphthenate is used as wood preservative. The most universal wine preservative is sulphur dioxide. Later poles were treated instead with creosote or copper sulphate for the preservative. Some LABs produce the antimicrobial nisin, which is a particularly effective preservative. It now finds increasing use as a preservative and antibacterial in livestock feed. Some commercial manufacturers add vinegar as a preservative. Tributyltin oxide is used as a wood preservative.