No abstract

A total of 204 psychrotrophic isolates from raw ewes' milk (hand and machine milked) were identified by conventional methods. In addition, a numerical taxonomic study was conducted on 180 of these isolates and 19 reference strains. Three of the isolates were yeasts. Using identification schemes, 54 isolates were assigned to genera of Gram-negative aerobic rods (Pseudomonas, Acinetobacter, Flavobacterium, Moraxella and Psychrobacter), 48 were Enterobacteriaceae (Enter obacter, Hafnia, Klebsiella, Citrobacter and Serratia) and one was identified as Aeromonas hydrophila. The 98 Gram-positive isolates were identified as Enterococcus, Streptococcus, Leuconostoc, Lactococcus, Bacillus, Staphylococcus, Micrococcus, Aureobacterium, Kurthia and Microbacterium. At the 82% similarity level {S SM ), 18 clusters were formed. Cluster I included 34 strains of Lactococcus, Streptococcus and Leuconostoc. Most of the 35 strains in cluster II were Enterococcus. Clusters III and IV were identified as Kurthia and Microbacterium respectively. Cluster V was identified as Aureobacterium and cluster VI consisted of coagulase-negative staphylococci. Gram-negative isolates formed 12 clusters: Aeromonas (one cluster), Enterobacteriaceae (two clusters), Flavobacterium (two clusters), Pseudomonas and Psychrobacter immobilis (three clusters) and Acinetobacter (four clusters). Non-motile variants of Ps. fragi were found. Enterococcus and Enterobacteriaceae did not have significant spoilage properties. As expected, Gram-negative aerobic rods were proteolytic and/or lipolytic even at low temperature. Contamination with certain types of psychrotrophs (Gram-negative aerobic rods and enterococci) seemed to be associated with the milking method. The isolate of Aes. hydrophila had properties associated with virulence.

Listeria monocytogenes is a foodborne pathogen of special concern for ready-to-eat food producers. The control of its presence is a critical step in which food-grade sanitizers play an essential role. L. monocytogenes is believed to persist in food processing environments in biofilms, exhibiting less susceptibility to sanitizers than planktonic cells. This study aimed to test the susceptibility of L. monocytogenes in planktonic culture and biofilm to three commercial food-grade sanitizers and to benzalkonium chloride; together with the genetic subtyping of the isolates. L. monocytogenes isolates were collected from raw materials, final products and food-contact surfaces during a 6-year period from a ready-to-eat meat-producing food industry and genetically characterized. Serogrouping and pulsed-field gel electrophoresis (PFGE) revealed genetic variability and differentiated L. monocytogenes isolates in three clusters. The biofilm-forming ability assay revealed that the isolates were weak biofilm producers. L. monocytogenes strains were susceptible both in the planktonic and biofilm form to oxidizing and ethanol-based compounds and to benzalkonium chloride, but not to quaternary ammonium compound. A positive association of biofilm-forming ability and LD90 values for quaternary ammonium compound and benzalkonium chloride was found. This study highlights the need for preventive measures improvement and for a conscious selection and use of sanitizers in food-related environments to control Listeria monocytogenes.

A total of 268 strains of Pseudomonas isolated during storage life of lamb carcasses was identified to species level. One-hundred and thirteen strains obtained at 30 degrees C were Ps. fragi (51), Ps. lundensis (17), Ps. fluorescens biovars I (10), III (9) and VI (1), Ps. putida biovar A (8 strains) and unidentified (17 strains). Species and biovars isolated at 7 degrees C (155) were Ps. fragi (101), Ps. lundensis (32), Ps. fluorescens biovar I (6), Ps. putida biovar A (8) and unidentified (8). Numerical analysis (82% SSM, UPGMA) of 'psychrotrophic' and 'mesophilic' strains resulted in the formation of nine and eight clusters respectively. The dendrograms obtained exhibited similar structures. Most of the strains of Ps. lundensis and Ps. fragi clustered together. Strains of this latter species also joined the type strain of Ps. testosteroni and appeared included with phenons containing the Ps. putida strains. There were clusters made up exclusively of strains assigned to one biovar or group (Ps. fluorescens biovars I and II and unidentified). A high level of similarity was observed between clusters of Ps. fluorescens biovar I and those containing the Ps. fragi-Ps. lundensis complex (> 74% SSM) and Ps. lundensis (> 80%). The recovery of pseudomonads seemed to be affected by the sampling day.

for the technical support and Carla Carneiro for the discussion time. We acknowledge the logistic support of CIISA -