Occurrence and antibiotic resistance of Escherichia coli,Staphylococcus aureus and Bacillus cereus in raw milk and dairy products in Turkey

In this survey, 150 samples of raw milk, white cheese and ice cream from three different dairy‐processing plants in Ankara were analysed to find out if they were contaminated with Escherichia coli, Staphylococcus aureus or Bacillus cereus. The highest contamination percentages were found in raw milk samples as follows: B. cereus (90%), E. coli (74%) and S. aureus (56%) followed by cheese (70% B. cereus, 60% E. coli, and 48% S. aureus) and ice cream (56% E. coli, 36% S. aureus and 20% B. cereus). The survey showed that 2% of cheese samples were contaminated with E. coli O157. It was also found that the numbers of S. aureus and E. coli in raw milk, cheese and ice cream samples exceeded the numbers permitted under the Turkish Food Codex (TFC). The number of B. cereus in raw milk, cheese and ice cream samples was lower than the limit given in the TFC standards. The study also showed that E. coli and S. aureus exhibit resistance to ampicillin, penicillin, tetracycline, erythromycin, gentamicin and trimethoprim/sulfamethoxazole. Escherichia coli isolates also showed resistance to chloramphenicol and ciprofloxacin but none of them exhibited resistance to cefotaxime. All S. aureus isolates were found to be susceptible to cefotaxime, chloramphenicol, and ciprofloxacin. Bacillus cereus isolates were found to be resistant to ampicillin, penicillin and trimethoprim/sulfamethoxazole and sensitive to cefotaxime, chloramphenicol, ciprofloxacin erythromycin, gentamicin and tetracycline.     

Effect of nisin‐producing Lactococcus lactis starter cultures on the inhibition of two pathogens in ripened cheeses

The effect of Lactococcus lactis nisin‐producing strains, isolated from Italian fermented foods, on the survival of two foodborne pathogens namely Listeria monocytogenes and Staphylococcus aureus was investigated in experimental cheese production. One of the three Lactobacillus lactis nisin innoculated as starters, Lactobacillus lactis 41FL1 lowered S. aureus count by 1.73 log colony‐forming units (cfu)/g within the first 3 days, reaching the highest reduction, 3.54 log cfu/g, by the end of ripening period of 60 days. There was no effect on L. monocytogenes. The application of L. lactis 41FL1 as bioprotective culture in controlling S. aureus shows considerable promise.     

Biofilm formation by Staphylococcus aureus strains and their control by selected phytochemicals

Biofilm formation by 30 Staphylococcus aureus dairy isolates and their control by phytochemicals were investigated. The majority of strains were biofilm positive by phenotypic analysis. The nuc and icaA genes were present in 30 and 27 strains, respectively. In addition, 13 strains were positive for all nuc, clfA, fnbA and icaA genes. The antimicrobial and antibiofilm activities of citral, cinnamaldehyde, eugenol, farnesol, limonene and terpinen‐4‐ol were also evaluated for seven strains. It was shown that the use of farnesol, cinnamaldehyde or terpinen‐4‐ol at a concentration of 2 mg/mL could be at least 80% effective on S. aureus strains and their biofilms.     

Effects of Mentha longifolia L. essential oil and Lactobacillus casei on the organoleptic properties and on the growth of Staphylococcus aureus and Listeria monocytogenes during manufacturing,ripening and storage of Iranian white‐brined cheese

This research evaluated the effects of Mentha longifolia L. essential oil (EO) in concentrations 0, 50, 150 and 300 ppm and Lactobacillus casei (10⁸–10⁹ CFU/mL) on the growth of Staphylococcus aureus and Listeria monocytogenes during the manufacturing, ripening and storage of Iranian white‐brined cheese. The growth of the two pathogens was significantly reduced (P < 0.01) by both EO concentrations ≥50 ppm and probiotic and their combination in the standard manufacturing and storage process conditions of the cheese. Furthermore, the treatment containing 150 ppm of this EO combined with probiotic had a favourable inhibitory effect on the growth of two pathogenic micro‐organisms and also was the most appropriate treatment in sensory assessment. The synergistic effects of the above‐mentioned concentration level between the essential oil and probiotic were significant compared to other treatments, including essential oil and probiotic only. Thus, a lower concentration of this EO can be used when it is combined with this probiotic.     

Formation of dairy fouling deposits on food contact surfaces

This study aimed to compare microbiological, biochemical and physical methods to quantify dairy fouling deposits. The influence of factors affecting dairy fouling formation is investigated by selected methods with respect to material type (polytetrafluoroethylene and stainless steel) and temperature (4 and 20 °C) for a defined time. The factors were investigated using nonmicrobiologically caused and microbiologically caused dairy deposits formed by UHT and pasteurised milk inoculated with Pseudomonas fragi. Both deposit types exhibited different adhesion behaviours. The highest positive correlation coefficient was found between biochemical and microbiological methods (0.932) obtained at both incubation temperatures after 24 and 48 h.     

Prevalence and risk factors for Bacillus cereus in raw milk in Inner Mongolia,Northern China

The prevalence of Bacillus cereus in raw milk from dairy herds in Inner Mongolia and associated risk factors were determined. In total, 160 raw milk samples collected from 2014 to 2015 and examined by culture methods to isolate B. cereus. Fifty‐five samples (34.38%) were positive. The prevalence of B. cereus in raw milk was significantly (P < 0.01) lower in winter (15%) than in summer (50%). The highest prevalence of B. cereus in raw milk was seen in samples collected from small‐ to medium‐sized dairy herds in summer. The results of this study indicated that B. cereus could be a common pathogen in Inner Mongolia because of its high prevalence. It is essential for dairy farmers and producers to strengthen hygienic practices in summer to control B. cereus contamination in raw milk. These results will be useful in establishing proper management procedures to reduce the prevalence of B. cereus in raw milk.     

Effects of Zataria multiflora boiss essential oil,ultraviolet radiation and their combination on Listeria monocytogenes biofilm in a simulated industrial model

The objective of this study was to investigate the inhibitory effect of Zataria multiflora boiss essential oils (ZEOs), ultraviolet (UV) radiation and their combination against Listeria monocytogenes biofilm in a simulated industrial model (SIM). The effect of minimal inhibitory concentration (MIC) and sub‐MIC concentration of ZEOs, different contact time of UV and their combination was evaluated in a SIM on 6‐ and 12‐day‐old L. monocytogenes biofilm. In a SIM, 0.3% ZEOs were adequate to completely eliminate 6‐ and 12‐day‐old biofilm grown on stainless steel coupons. The population of viable L. monocytogenes biofilm cells under a 15‐ to 45‐min contact time of UV treatment declined significantly at 6‐ and 12‐day‐old biofilm. The combined effect of ZEO and UV showed antagonist effects. These findings indicated that in the single use, ZEO and UV revealed a suitable antilisteria biofilm activity, while combining them is not a promising method to remove listeria biofilms from stainless steel surfaces.     

Occurrence,heat and antibiotic resistance profile of Bacillus cereus isolated from raw cow and processed milk in Mezam Division,Cameroon

Bacillus cereus is the aetiologic agent of two distinct forms of food poisoning: the diarrhoeal and emetic syndromes. Little data exist on the prevalence of B. cereus in raw milk and milk products sold in Cameroonian towns. This study was aimed at investigating the occurrence, heat and antibiotic resistance of B. cereus isolated from raw milk and selected milk products in Mezam division, Cameroon. Bacillus cereus was isolated by inoculating samples onto mannitol‐egg yolk‐polymyxin B agar. Isolates were characterised morphologically and biochemically. The occurrence of B. cereus in raw milk (8.22%) was less than that in milk powder (13.33%). Bacillus cereus was not isolated from fermented milk. There was no significant difference (P < 0.05) between the B. cereus load in raw milk (2.6 × 10³ cfu/mL) and milk powder (3.0 × 10² cfu/mL). All the isolates showed haemolysin activity and were sensitive to tetracycline, gentamicin, chloramphenicol and nalidixic acid, but resistant to penicillin, ampicillin and trimethoprim/sulphamethoxazole. The detection of drug‐resistant, haemolysin‐positive isolates should serve as a warning for an impending health hazard following consumption of untreated milk. Heat resistance of isolates was assessed by determining the decimal reduction time; D‐value (time to inactivate 90% of the B. cereus spores); and the heat sensitivity, z (temperature increase leads to a tenfold reduction in the D‐value). The values for D₁₀₀ ranged from 0.5 to 3.5 min, and z‐values ranged from 10.0 to 32.6 °C. These results could be used in the dairy industry to evaluate the importance of heat treatment on B. cereus inactivation and calculation of process efficiency.     

Synergistic effect between Helichrysum italicum essential oil and cold nitrogen plasma against Staphylococcus aureus biofilms on different food‐contact surfaces

Staphylococcus aureus is the most common pathogen in human, and the most diseases produced by S. aureus are associated with biofilms. Helichrysum italicum essential oil (EO), as a natural and safe spice, was employed to disperse S. aureus biofilm by cold nitrogen plasma (CNP) assist. After S. aureus biofilm formation on food container surfaces, they were exposed to CNP and then treated with Helichrysum italicumEO for biofilm dispersion. The population of S. aureus biofilm was approximately reduced by 2 logs after individual treatment of 0.5 mg mL^?1 Helichrysum italicumEO or 400 W CNP. Interestingly, the combined treatment of Helichrysum italicumEO (0.5 mg mL^?1, 40 min) and CNP (400 W, 1 min) reduced the S. aureus viable count in biofilm below 2 logs CFU per cm² after 1‐day storage. Therefore, the synergetic treatment holds great promise to improve the current treatment systems of bacterial contamination on different food‐contact surfaces.     

In vitro characterisation of probiotic properties of Enterococcus faecium and Enterococcus durans strains isolated from raw milk and traditional dairy products

In this study, some probiotic characteristics such as antimicrobial activity, vancomycin resistance, growth ability at pH, resistance to bile salts, bile salt deconjugation and hydrophobicity of 30 Enterococcus faecium and Enterococcus durans strains isolated and identified from raw milk and various dairy products were investigated. According to the study results, antimicrobial activity profiling, pH and bile salt resistance and bile salt deconjugation ability of Enterococcus strains varied depending on the species and strains and all the strains showed resistance to the tested bile salt concentrations. It was concluded that the E. faecium and E. durans strains tested showed probiotic characteristics and have the potential to be used in food production.     

Antilisterial effect of two bioprotective cultures in a model system of Iberian chorizo fermentation

This study reports the different effects of two bioprotective cultures on the growth of different Listeria monocytogenes strains by a rapid assay simulating the first stage of Iberian chorizo fermentation. Ground pork with or without protective cultures was inoculated with L. monocytogenes and incubated under two different conditions simulating the traditional, slow fermentation temperature (7 °C, 1 day) and a high, fast fermentation temperature (20 °C, 1 day), followed in both cases by storage at 7 °C for 13 days. Both bioprotective cultures reduced the growth of L. monocytogenes by at least 2 log CFU g^?1 at the end of both incubation periods compared with a noninoculated culture control lot. The best results were obtained with the strain Lactobacillus sakei CTC494, which exerted a bactericidal effect on L. monocytogenes under both conditions assayed, achieving a 5.4‐log reduction after 14 days compared with the control when the initial temperature was 20 °C.     

Modelling the cross‐contamination of Listeria monocytogenes in pork during bowl chopping

This study has developed a predictive model for the cross‐contamination of pork by Listeria monocytogenes during bowl chopping. The transfer rates of L. monocytogenes were measured in sixteen chopping scenarios based on practical work. Meanwhile, contaminated bowl chopper was cleaned with either a dry rag (DR), warm water (WW) or 70% ethanol + water (EW), respectively. It was showed that significant differences (P < 0.05) were observed among the three cleaning methods on the reduction of L. monocytogenes, the greatest log reduction being achieved by EW. Moreover, the model introduced by a previous study, predicting cross‐contamination of L. monocytogenes during meat slicing, was improved and validated in this study. Verification results showed that the improved model was acceptable for predicting L. monocytogenes cross‐contamination during pork chopping with coefficients of determination (R² > 0.82), accuracy factors (A_f < 1.44), bias factors (B_f < 1.42), and root mean square error (RMSE < 0.99). Furthermore, the modified model might provide an effective tool for assessing the risk of the cross‐contamination of meat products.     

Influence of temperature variations on growth,injury survival and inactivation of Listeria monocytogenes in goat milk samples at laboratory scale

Transmission of the thermo‐tolerant pathogen Listeria monocytogenes via contaminated milk and its products, can lead to serious food‐borne illness. In this study, the effects of selected temperatures on survival, percentage injury and inactivation of L. monocytogenes in goat milk samples collected from two different farms were evaluated. Low temperature ranges (0, 5, 10 °C) had a bacteriostatic effect; while at temperatures of 25 and 45 °C, this pathogen grew luxuriantly. However, growth was comparatively slow at 15 °C throughout a 12‐h stress period. Furthermore, a high temperature range (50, 55, 60 and 65 °C) resulted in the elimination of this pathogen within 4 h of stress. Results of Scanning Electron Microscopy showed morphological changes in the cells upon induction of stress temperatures.     

Technologically important characteristics of Enterococcus isolates from milk and dairy products

Enterococcus faecium (54 strains), E. faecalis (40 strains), and E. durans (14) were isolated from various dairy products (raw milk, cream, butter and fermented milk products) during a previous study (Wessels et al., 1988). In this article various characteristics of these isolates, which may have a bearing on their significance in dairy products, have been studied. A large percentage of the identified strains of all three species were able to grow at 7°C. Seventy-six percent of the E. faecium strains, 62% E. faecalis and 50% E. durans strains also showed proteolytic activity at psychrotrophic temperatures. The fact that proteolytic activity could be detected within 2 days at 7°C is significant, since bulk cooled milk is normally held for 3 to 4 days at temperatures between 4 and 7°C at farms or factories prior to processing. This examination confirmed that enterococci are proteolytic rather than lipolytic.     

Antibacterial effects of chitosan coating containing Mentha aquatica L. essence against Escherichia coli,Staphylococcus aureus and Listeria monocytogenes in Iranian white cheese

The effect of a chitosan coating and Mentha aquatica L. essence on Iranian white cheese was investigated. Results showed 100% inhibition of Escherichia coli growth using 1.5% essence after 10 days. After 15 days of incubation, the Staphylococcus aureus population was reduced by 44.2%, 70.0%, and 88.5% using 0.5, 1.0 and 1.5% essence, respectively. After 15 days, Listeria monocytogenes growth was inhibited by 63.84%, 70.12%, and 85.9% using 0.5, 1.0, and 1.5% essence, respectively. Inhibition zone diameter studies also confirmed the antibacterial effects of applied coating against all the above‐mentioned bacteria in Iranian white cheese.     

Utilisation possibility of Enterococcus faecalis isolates from neonate's faeces for production of fermented sausages as starter cultures

This study aimed at assessing the utilisation possibility of Enterococcus faecalis as starter cultures for production of fermented sausages. The E. faecalis isolates isolated from faeces samples of 5‐day‐old healthy newborn babies, identified by 16SrDNA sequencing and free from virulence determinants as proven by genomic sequencing, were used for fermented sausages production as starter culture. Six treatments (four inoculated with four different E. faecalis isolates, one with commercial starter culture and one control) were prepared. The inoculation with E. faecalis showed a stronger acidification compared with the control. The treatments with E. faecalis showed significantly higher flavour and acceptability scores in comparison with the control or commercial starter culture. Both of commercial starter culture and E. faecalis were positive with tyramine. Apart from the amine production, the inoculation with E. faecalis generally improved the acidifying activity and flavour of the products, suggesting their application potentials in fermented sausages production as starter cultures.     

Listeria monocytogenes survival during production and storage of water buffalo Mozzarella cheese

The ability of Listeria monocytogenes to survive during the manufacture of water buffalo Mozzarella and to grow during its shelf life was evaluated. A wild‐type and a reference strain were used to contaminate raw milk. The viable count of the reference strain ATCC 9525 dropped after the stretching process, and in the cheese, it fell to below 100 cfu/g. When the wild‐type strain was used, however, stretching did not appear to have any effect on the pathogen. The artificially contaminated cheeses were stored, for eleven days, at 4, 20 and 30 °C. Pathogen populations increased at 20 (≈2.60 log cfu/g) and 30 °C (≈1.95 log cfu/g).