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The study was aimed at the assessment whether foodstuffs contaminated with Bacillus cereus (B. cereus) may concurrently be vectors of spreading resistance. The contamination of foodstuffs with B. cereus strains was found in 31% of dairy and in 28% of meat products tested. Only one product from skimmed milk was contaminated. High-fat milk products that were heat-treated during the technological process (87 samples), as well as heat-treated meat products (65 samples), were contaminated significantly frequently (63% and 48% of the samples respectively) (P < 0.01). Almost all B. cereus isolates displayed low susceptibility to ampicillin, cephalothin, and to oxacillin. Except for streptomycin (STR) resistance, resistance to other 8 antimicrobial agents occurred sporadically. The STR resistant isolates came particularly from spreading buffer (8 samples) (P < 0.05). It was established that the same samples were contaminated with two subpopulations of B. cereus with different STR resistances. The frequent occurrence of B. cereus in foodstuffs with either fat content and/or subject to heat treatment in processing makes these products risky, however, our study did not confirm that foodstuffs contaminated with B. cereus are concurrently vectors of transmissible resistance genes.

In 2000–2002 samples of raw materials (milk and beef, 518 samples), ready-to-cook foods and final products from milk (30 and 200 samples) and from meat (105 and 110 samples) and swabs from surfaces in two meat-processing plants (41 samples) were examined for the presence of Listeria monocytogenes (L. monocytogenes). 70 isolates were tested using the standard microdilution method for the susceptibility to 12 antimicrobial drugs, minimum inhibitory concentration (MIC) characteristics (MIC_m, MIC₅₀, MIC₉₀) were determined. L. monocytogenes was isolated from raw milk samples (15 samples). It was not isolated from any of the semi-finished and final milk products except for one sample of pasteurized milk. Furthermore L. monocytogenes was isolated from samples of raw beef, meat emulsion, fermented dry meat products and from swabs from production equipment. In vitro testing of susceptibility showed the considerable effectiveness of examined antimicrobial substances with streptomycin and norfloxacin being least effective (MIC_m = 4 μg/ml). Apart from the intermediate resistance (MIC = 1–2 μg/ml) and resistance (MIC = 4 μg/ml) to clindamycin (37 and 5 strains, respectively), all strains were susceptible to the tested substances. While the presence of L. monocytogenes in foodstuffs, in particular, are serious, current tests of susceptibility of L. monocytogenes isolates indicate low probability untreatable infections as a result of resistant strains from foods or transfer of resistance to other microorganisms in the CzechRepublic.

Nápravníková E., L. Vorlová, L. Malota: Changes in Hygienic Quality of Vacuumpacked Pork During Storage. Acta Vet. Brno 2002, 71: 255-262. Hygienic quality of boned vacuum-packed pork was monitored during storage by sensory, chemical, and microbiological methods. Pork was vacuum-packed into polyamide/polyethylene (PA/PE) foil 72 h after slaughter. Initial temperature did not exceed 9°C. The meat was stored at 2.5 ± 0.5°C in the dark for 35 days and samples for laboratory examinations were collected at days 14, 21, 28, and 35 to assess appearance, colour, odour, and characteristics of released meat juice, to determine pH and concentrations of ammonia and D-and L-forms of lactic acid, and to enumerate lactacidogenic bacteria. Lactobacillus curvatus and Lactobacillus xylosus were identified as the causative agents of meat spoilage using the API system. The results were subjected to correlation analyses. The shelf life of boned vacuum-packed pork varied between 21 and 28 days, depending on initial pH. The results of correlation analyses indicated that only ripe pork with the optimum pH = 5.8 to 5.95 is suitable for vacuum-packing. In addition to the lactacidogenic bacteria count (LAC), the shelf life can be estimated also from ammonia concentration (LAC/ammonia r = 0.9584, P < 0.05), pH (LAC/pH r = -0.9317, P < 0.05) and the concentration of D-lactate (LAC/D-lactate r = 0.9867, P < 0.01). Pork, vacuum packing, lactobacilli, ammonia, pH, lactic acidMeat spoilage is a complex process in which microorganisms present in the muscular tissue due to secondary contamination during processing are involved, and which depends on ambient temperature. The storage of meat is associated with changes in quality resulting from microbial activity, shift of pH, production of toxic substances, and aberrant odour (Huis 1996). Most prone to spoilage are foods with a high protein content, such as meat, poultry, fish, and milk, which have a high dietetic value, neutral, or lightly acid pH, and a high water content providing favourable conditions for bacterial growth (Huis 1996). Bauer (1995) demonstrated that enzymes of the muscular tissue and bacterial enzymes are involved in chemical changes (production of biogenic amines, changes in colour and fat) occurring during storage. The most important factors influencing the development and growth of spoilage microorganisms on raw meat in cold storage include the initial relative number of psychrotrophic flora and its growth dynamics at low temperatures. Qualitative and quantitative composition of the microbial population responsible for meat spoilage depend on pH, water activity, storage atmosphere, and among-species relations (Gould 1995). Dominant in the microbial population of vacuum-packed meat are lactacidogenic bacteria which participate in the development of an unpleasant odour. Dainty (1996) detected indol and hydrogen sulphide by gas chromatography and identified them as the cause of this sensory defect. The microbial activity results in the production of typical metabolit...

E. faecalis (67%) and E. faecium (13.7%) were most frequently isolated among enterococci that contaminate cooled and frozen processed meat, follow-up heat-treated meat products and unheated fermented dry salami. Most isolates of both species were resistant to cephalothin (95 and 83 %) and clindamycin (77 and 67%, respectively). Furthermore, E. faecalis and E. faecium isolates were resistant to erythromycin (44 and 72%), tetracycline (34.5 and 17.4%), and streptomycin (13.3 and 4.3%, respectively). Only a few of the isolates were resistant to ampicillin, ampicillin-sulbactam, chloramphenicol, and vancomycin while all isolates were susceptible to gentamicin, penicillin, and teicoplanin. During the production of heat-treated meat products, numbers of resistant isolates increased in spite of the decreasing enterococcal contamination of the samples. An opposite situation was found in the production of fermented dry salami.