Inactivation of Spores of Bacillus cereus in Cheese by High Hydrostatic Pressure with the Addition of Nisin or Lysozyme

Abstract

The objective of this work was to study high hydrostatic pressure (HHP) inactivation of spores of Bacillus cereus ATCC 9139 inoculated in model cheeses made of raw milk, together with the effects of the addition of nisin or lysozyme. The concentration of spores in model cheeses was approximately 6-log10 cfu/g of cheese. Cheeses were vacuum packed and stored at 8 degrees C. All samples except controls were submitted to a germination cycle of 60 MPa at 30 degrees C for 210 min, to a vegetative cells destruction cycle of 300 or 400 MPa at 30 degrees C for 15 min, or to both treatments. Bacillus cereus counts were measured 24 h and 15 d after HHP treatment. The combination of both cycles improved the efficiency of the whole treatment. When the second pressure-cycle was of 400 MPa, the highest inactivation (2.4 +/- 0.1 log10 cfu/g) was obtained with the presence of nisin (1.56 mg/L of milk), whereas lysozyme (22.4 mg/L of milk) did not increase sensitivity of the spores to HHP. For nisin (0.05 and 1.56 mg/L of milk), no significant differences were found between counts at 24 h and 15 d after treatment. Considering that mesophilic spore counts usually range from 2.6 to 3.0 log10 cfu/ml in raw milk, HHP at mild temperatures with the addition of nisin may be useful for improving safety and preservation of soft curd cheeses made from raw milk.

Inhibition of Bacillus anthracis Spore Outgrowth by Nisin

“…Previous studies reported that nisin prevented the growth of Bacillus spores derived from several different species (4,14,32,35,43). To evaluate the action of nisin against spores responsible for this inhibitory activity, spores were prepared from B. anthracis Sterne 7702, which is a strain commonly employed as a model for investigation of the early stages of anthrax disease (24,47 Table 1).…”

“…In this study, B. anthracis was used as a model, but previous work indicated that nisin is also inhibitory against spores from other Bacillus species (3,7,30,32,35,43), as well as from Clostridium species (36), suggesting that the new information on the inhibitory activity of nisin obtained in this study will be applicable to determination of the mechanism of action of nisin against spores from these other organisms as well. Here, nisin was demonstrated to act upon and kill germinated spores of B. anthracis prior to development into elongated and dividing bacilli and before LT was generated.…”

“…To date, nisin inhibition of Bacillus spore outgrowth has been documented by various methods, including the spectrophotometric measurement of liquid culture turbidity (3), the enumeration of CFU (4,14,32,35,43), well diffusion assays on solid agar (14,39), and microscopic observations (41). Although these approaches are useful, they have provided few details about nisin's mode of action against Bacillus spores.…”

Cloning and functional expression of a human lysozyme gene (hly) from human leukocytes in Pichia pastoris

“…Of note, the anti-HIV activity of lysozyme is independent of its muramidase activity (5). In addition, findings of previous studies have shown that it is effective in inactivating spores of Bacillus cereus in cheese by causing high hydrostatic pressure following the addition of lysozyme (6).…”

Nisinin Sinerjistik Antimikrobiyel Etkisi

“…Hücre için önemli enzimlerin denatüre olması ve ribozomun zarar görmesi mikroorganizmanın inaktivasyonuna neden olmaktadır [101]. Nisinin HHP uygulaması ile birlikte gösterdiği sinerjistik antimikrobiyel etki ise söz konusu iki engelin hücre zarında meydana getirdikleri kümülatif hasardan ileri gelmektedir [102,106]. HHP uygulamasının antimikrobiyel etkinliği uygulanan bakteri popülasyonunun özelliklerine ve hücrelerin bulundukları gelişim evrelerine göre değişkenlik gösterir.…”