Nihal Yucel

Prevalence of Listeria, Aeromonas, and Vibrio Species in Fish Used for Human Consumption in Turkey

A total of 78 raw retail fish samples from 30 freshwater and 48 marine fish were examined for the presence of Listeria, Aeromonas, and Vibrio species. The overall incidence of Listeria spp. was 30% in freshwater samples and 10.4% in marine fish samples. Listeria monocytogenes (44.5%) was the most commonly isolated species in freshwater fish, and Listeria murrayi (83.5%) was the most commonly isolated species in marine fish samples. Motile aeromonads were more common in marine fish samples (93.7%) than in freshwater fish samples (10%). Vibrio alginolyticus, Vibrio fluvialis, and Vibrio damsela were isolated only in marine fish samples, representing 40.9, 38.6, and 36.3% of Vibrio isolates, respectively. In freshwater and marine fish, the highest incidences of Listeria and Aeromonas were found in skin samples; the highest incidence of Vibrio in marine fish was found in gill samples. The location of Listeria spp. and L. monocytogenes in a fish was significantly different among freshwater fish. A high incidence of these bacterial pathogens was found in the brown trout (Salmo trutta) and horse mackerel (Trachurus trachurus). Handling of contaminated fish, cross-contamination, or eating raw fish might pose a health hazard, especially in immunosuppressed individuals, elderly people, and children. This study highlights the importance of bacterial pathogens in fish intended for human consumption, but more study is needed.

Virulence properties and characterization of aeromonads isolated from foods of animal origin and environmental sources.

Aeromonas species are increasingly recognized as enteric pathogens, and they possess several virulence factors that may contribute to illness. In this work, the biochemical, enzymatic, and some virulence properties of 73 potentially pathogenic strains of Aeromonas spp. isolated from food and environmental sources were investigated to compare strains from different sources and establish the possible relationships between some phenotypic characters and pathogenicity. Virulence factors (hemolysin and siderophores), biochemical properties (Voges-Proskauer and lysine decarboxylase reactions), and enzymatic properties (lipase, phospholipase, protease, and DNase activities) were examined in these strains. Results indicated that 57% of the strains from environmental sources produced siderophores and hemolysin, whereas 39.0% of strains from food produced siderophores and 60.5% produced hemolysin. Protease, lipase, DNase, and phospholipase activities in strains isolated from food and environmental sources were 69.5 to 94.3, 73.6 to 68.5, 52.6 to 68.6, and 71.0 to 68.4%, respectively. A higher percentage of strains of environmental origin (94.3%) had protease activity, and higher lipase activity (73.6%) was observed in food isolates. For all antimicrobials tested, all strains had the least resistance to meropenem, and high levels of resistance were found to amoxicillin-clavulanic acid and cephalothin. These findings demonstrate the presence of potentially pathogenic and multidrug-resistant Aeromonas spp. in environmental and food sources, thereby indicating a significant risk to public health.

Antimicrobial resistance profile of Staphylococcus aureus isolated from clinical samples and foods of animal origin.

Staphylococcus aureus has been well established as a clinical and epidemiological pathogen and can cause infections at many anatomical sites. Increasing insusceptibility to β-lactams and the glycopeptides complicates the treatment of these infections. We isolated 584 strains of S. aureus from various clinical and animal origin food samples during (from January 2006 to December 2007) the survey. Resistance to 15 antibiotics frequently used in human medicine and veterinary practice was also determined. A remarkable level of penicillin resistance was detected in both clinical (98.3%) and food (92.0%) S. aureus isolates. But, there were no S. aureus strains that were resistant to vancomycin, teicoplanin, linezolid, and quinupristin/dalfobristin. The rate of resistance to tetracycline, ciprofloxacin, levofloxacin, methicillin, gentamicin, tobramycin, norfloxacin, and moxifloxacin among the human and foods S. aureus isolates ranged from 50.3% to 56.3% and 1.4% to 9.5%, respectively. In our survey, in vitro susceptibility data suggested that the incidence of resistance among the S. aureus strains isolated from food were not remarkably high, excluding penicillin. Although the transfer of antibiotic resistance of S. aureus from foods to humans probably occurs less frequently than is generally assumed, the increasing prevalence of resistance in the strains of human origin may have important therapeutic implications.

Antibacterial Activity of the Essential Oil of Satureja wiedemanniana Against Bacillus Species Isolated from Chicken Meat

The antimicrobial activity of the essential oil (EO) of Satureja wiedemanniana against Bacillus spp. isolated from chicken meat was investigated. Thirty-seven Bacillus strains were isolated from 15 chicken meat samples and examined for proteolytic and lipolytic activities by agar well diffusion assay. Of 37 Bacillus isolated from raw chicken samples, which based on a clear zone diameter of ≥ 6 mm in agar well diffusion assays for proteolytic activity, 19 Bacillus strains were selected for this study. Bacillus licheniformis T11(1) and Bacillus lentus T10(14) have high proteolytic activity (14.0 mm zone diameter), whereas B. licheniformis T4(2) and Bacillus mycoides T 5(5) have high lipolytic activity (12.0 mm zone diameter). Thirty-two components representing 98.10% of the composition of the S. wiedemanniana EO were identified using gas chromatography/mass spectrometry. Both S. wiedemanniana EO and its main component p-cymene exhibited strong antimicrobial activity against some Bacillus strains. The results of this study confirmed the possibility of using S. wiedemanniana EO as a protective agent to chicken meat. But, detail studies are still needed to elucidate the effects of S. wiedemanniana EO against other spoilage microorganisms.

In Vitro Antimicrobial Effect of Satureja wiedemanniana Against Bacillus Species Isolated from Raw Meat Samples

In this study a total of 30 raw meat samples obtained from Ankara, Turkey were screened for the presence of Bacillus species. Among the meat samples analyzed, the predominant species isolated was Bacillus circulans; other Bacillus species were identified as Bacillus firmus, Bacillus lentus, Bacillus megaterium, Bacillus licheniformis, Bacillus mycoides, Bacillus sphaericus, and Bacillus cereus. Minced meat samples were more contaminated with Bacillus species than sliced beef sample. From these samples, 242 Bacillus species isolates were obtained, which were investigated for proteolytic and lipolytic activity, associated with meat spoilage. Interestingly, some Bacillus strains produced the highest values of proteolytic/lipolytic activities. Nineteen Bacillus strains were selected among the 242 isolates according to their proteolytic/lipolytic activity with a clear zone diameter of > or =6 mm. The essential oil of Satureja wiedemanniana (Lalem) Velen was also tested against these 19 Bacillus species that had proteolytic and lipolytic activity. The essential oil yield obtained from the aerial parts of the plant was 0.35% (vol/wt). The inhibition zones of the essential oil obtained against all the Bacillus species were in the range of 5.0-12.0 mm. The oil showed high antimicrobial activities against B. licheniformis M 6(26), M 11(16), and M 12(1) strains. B. licheniformis 12(1) showed high lipolytic activity (18.0 mm). Also, B. licheniformis M 6(26) and M 11(16) showed high proteolytic activity (16.0 and 14.0 mm). These results may suggest that an essential oil of S. wiedemanniana can be used as a natural preservative in meat against spoilage bacteria.