Evaluation of ATP bioluminescence-based methods for hygienic assessment in fish industry

AIMS

To evaluate ATP bioluminescence-based hygiene monitoring systems under conditions relevant to fish processing environments.

METHODS AND RESULTS

The ATP bioluminescence of fish fractions that are potentially present after insufficient cleaning of fish processing environments was determined. Different fractions and interfering substances representing the stages from slaughtering to smoking were prepared and measured using two different commercial systems (SystemSURE Plus and Clean-Trace). ATP bioluminescence was quenched by acidic liquid smoke and by sodium chloride even at concentrations as low as 0·9% NaCl. Large variations were observed between different types of trout homogenates: the ATP bioluminescence from raw belly fat homogenate was 100-1000 times lower than for trout blood. There were about a 1000-fold lower ATP bioluminescence in raw compared to heat-treated fractions from trout, with the exception of blood. The bioluminescence from Listeria monocytogenes was very low. Results from fish processing plants supported the laboratory findings.

CONCLUSIONS

The output from ATP-monitoring instruments depends on the nature of fish soil present, as well as the presence of sodium chloride and low pH. This may lead to considerable under- or overestimation of the level of organic soil.

SIGNIFICANCE AND IMPACT OF THE STUDY

ATP bioluminescence instruments are widely used by the fish industry for monitoring hygiene. The monitoring method will only give valuable information about the hygiene if critical limits are set after a validation period, distinguishing between areas with different types of soil and between different hygiene zones.

Microbial dynamics in mixed culture biofilms of bacteria surviving sanitation of conveyor belts in salmon-processing plants

AIMS

The microbiota surviving sanitation of salmon-processing conveyor belts was identified and its growth dynamics further investigated in a model mimicking processing surfaces in such plants.

METHODS AND RESULTS

A diverse microbiota dominated by Gram-negative bacteria was isolated after regular sanitation in three salmon processing plants. A cocktail of 14 bacterial isolates representing all genera isolated from conveyor belts (Listeria, Pseudomonas, Stenotrophomonas, Brochothrix, Serratia, Acinetobacter, Rhodococcus and Chryseobacterium) formed stable biofilms on steel coupons (12°C, salmon broth) of about 10(9) CFU cm(-2) after 2 days. High-throughput sequencing showed that Listeria monocytogenes represented 0·1-0·01% of the biofilm population and that Pseudomonas spp dominated. Interestingly, both Brochothrix sp. and a Pseudomonas sp. dominated in the surrounding suspension.

CONCLUSIONS

The microbiota surviving sanitation is dominated by Pseudomonas spp. The background microbiota in biofilms inhibit, but do not eliminate L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results highlights that sanitation procedures have to been improved in the salmon-processing industry, as high numbers of a diverse microbiota survived practical sanitation. High-throughput sequencing enables strain level studies of population dynamics in biofilm.

Physiological and Structural Differences Between Enterococcus faecalis JH2-2 and Mutant Strains Resistant to (P)-Divercin RV41

The aim of this study was to show the differences that could exist at the physiological and structural levels between Enterococcus faecalis JH2-2 (wild type) and three mutant strains resistant to divercin RV41. These mutant strains were recently isolated and characterized for their intermediate resistance to recombinant DvnRV41; a subclass IIa bacteriocin produced by Escherichia coli. These mutant strains were named 35A1 (altered in gene coding phosphoesterase activity), 35H1 (altered in gene coding σ(54) factor) and 36H4 (altered in gene coding glycerophosphodiesterase). The growth and resistance of each strain were tested against lysozyme. The inhibitory substance did not show any cross-resistance but exhibited an additive effect ascribed to the combined action of lysozyme and (P)-DvnRV41. The use of Fourier transform infrared spectroscopy (FT-IR) allowed to unravelling differences at the structural levels between the aforementioned strains. Thus, mutants 35H1 and 36H4 showed clear differences from mutant 35A1 and wild-type strain. These differences were located, mainly in the fatty acid region and in the polysaccharide composition. This study contributes to understanding more the resistance/sensitivity of Ent. faecalis to (P)-DvnRV41, a subclass IIa bacteriocin.

Microbial background flora in small-scale cheese production facilities does not inhibit growth and surface attachment of Listeria monocytogenes

The background microbiota of 5 Norwegian small-scale cheese production sites was examined and the effect of the isolated strains on the growth and survival of Listeria monocytogenes was investigated. Samples were taken from the air, food contact surfaces (storage surfaces, cheese molds, and brine) and noncontact surfaces (floor, drains, and doors) and all isolates were identified by sequencing and morphology (mold). A total of 1,314 isolates were identified and found to belong to 55 bacterial genera, 1 species of yeast, and 6 species of mold. Lactococcus spp. (all of which were Lactococcus lactis), Staphylococcus spp., Microbacterium spp., and Psychrobacter sp. were isolated from all 5 sites and Rhodococcus spp. and Chryseobacterium spp. from 4 sites. Thirty-two genera were only found in 1 out of 5 facilities each. Great variations were observed in the microbial background flora both between the 5 producers, and also within the various production sites. The greatest diversity of bacteria was found in drains and on rubber seals of doors. The flora on cheese storage shelves and in salt brines was less varied. A total of 62 bacterial isolates and 1 yeast isolate were tested for antilisterial activity in an overlay assay and a spot-on-lawn assay, but none showed significant inhibitory effects. Listeria monocytogenes was also co-cultured on ceramic tiles with bacteria dominating in the cheese production plants: Lactococcus lactis, Pseudomonas putida, Staphylococcus equorum, Rhodococcus spp., or Psychrobacter spp. None of the tested isolates altered the survival of L. monocytogenes on ceramic tiles. The conclusion of the study was that no common background flora exists in cheese production environments. None of the tested isolates inhibited the growth of L. monocytogenes. Hence, this study does not support the hypothesis that the natural background flora in cheese production environments inhibits the growth or survival of L. monocytogenes.

A synthetic furanone potentiates the effect of disinfectants on Salmonella in biofilm

AIMS

To study a possible effect of a synthetic brominated furanone on biofilm formation and biofilm resistance to disinfectants in Salmonella enterica.

METHODS AND RESULTS

The effect of a synthetic furanone on biofilm formation of Salm. enterica serovar Agona and Salm. enterica serovar Typhimurium (11 strains of different origins) was evaluated in a microtiterplate assay. A significant reduction in biofilm build-up in microtiterplates by the furanone was observed for seven of the strains tested. Biofilms by two Salm. Agona feed factory strains and the effects on survival after exposures to disinfectants (hypochlorite and benzalkonium chloride) were assessed for both strains. Pretreatment with furanone significantly potentiated the effect of the two disinfectants for both strains.

CONCLUSIONS

The effect of disinfectants on Salmonella in biofilm was significantly enhanced when the biofilm was grown in the presence of furanone. This was probably because of an effect on biofilm architecture, composition and in some cases also biofilm build-up.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study gives valuable new knowledge in the fight against Salmonella biofilm in the environment because of the potentiated effect of conventional disinfectants.

Characterization of Serratia marcescens surviving in disinfecting footbaths

AIM

To determine if disinfecting footbaths in the food industry were contaminated with bacteria and to characterize some of the bacteria present.

METHODS AND RESULTS

Bacterial strains were isolated from disinfecting footbaths containing TEGO 103G (amphoteric disinfectant) or TP-99 (alkyl amino acetate-based disinfectant) in five of six dairy factories. Fourteen strains identified as Cedecea spp. by their fatty acid composition were further characterized. Results from Rapid ID 32 E API analysis and 16S-rDNA-sequencing showed that all strains were Serratia marcescens. Unlike S. marcescens ATCC 13880, the isolates from disinfecting footbaths were not killed (<5 log10 reduction) by the recommended in-use concentration of TEGO 103G, TEGO 51 or benzalkonium chloride. Survival and multiplication in tap water with an in-use concentration of TEGO 103G was demonstrated for one of the strains. All strains were killed by the in-use concentrations of commercial disinfectants based on peracetic acid, hypochlorite, quaternary ammonium compounds and alkyl amino acetate (TP-99). There were no indications of cross-resistance between disinfectants and antibiotics.

CONCLUSION

Serratia marcescens may survive and multiply in disinfecting footbaths containing TEGO 103G or alkyl amino acetate because of disinfectant resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

Disinfecting footbaths may act as contamination sources in food factories and should not be used without regular hygienic monitoring.

Inhibition of Listeria monocytogenes in chicken cold cuts by addition of sakacin P and sakacin P-producing Lactobacillus sakei

AIMS

To evaluate the potential of sakacin P and sakacin P-producing Lactobacillus sakei for the inhibition of growth of Listeria monocytogenes in chicken cold cuts, by answering the following questions. (i) Is sakacin P actually produced in food? (ii) Is sakacin P produced in situ responsible for the inhibiting effect? (iii) How stable is sakacin P in food?

METHODS AND RESULTS

Listeria monocytogenes, a Lact. sakei strain and/or the bacteriocin sakacin P were added to chicken cold cuts, vacuum packed and incubated at 4 or 10 degrees C for 4 weeks. Each of two isogenic Lact. sakei strains, one producing sakacin P and the other not, had an inhibiting effect on the growth of L. monocytogenes. The effect of these two isogenic strains on the growth of L. monocytogenes was indistinguishable, even though sakacin P was produced in the product by one of the two Lact. sakei strains. The addition of purified sakacin P had an inhibiting effect on the growth of L. monocytogenes. A high dosage of sakacin P (3.5 microg x g(-1)) had a bacteriostatic effect throughout the storage period of 4 weeks, while a low dosage (12 ng x g(-1)) permitted initial growth, but at a slow rate. After 4 weeks of storage, the number of L. monocytogenes in the samples with a low dosage of sakacin P was 2 logs below that in the untreated control. When using a high dosage of sakacin P, the bacteriocin was detected in samples stored for up to 6 weeks.

CONCLUSIONS

(i) Sakacin P is produced by a Lact. sakei strain when growing on vacuum-packed chicken cold cuts. (ii) Inhibiting effects of Lact. sakei, other than sakacin P, are active in inhibiting the growth of L. monocytogenes growing on chicken cold cuts. (iii) Sakacin P is stable on chicken cold cuts over a period of 4 weeks.

SIGNIFICANCE AND IMPACT OF THE STUDY

Both sakacin P and Lact. sakei were found to have potential for use in the control of L. monocytogenes in chicken cold cuts.

Influence of complex nutrients, temperature and pH on bacteriocin production by Lactobacillus sakei CCUG 42687

The effects of process conditions and growth kinetics on the production of the bacteriocin sakacin P by Lactobacillus sakei CCUG 42687 have been studied in pH-controlled fermentations. The fermentations could be divided into phases based on the growth kinetics, phase one being a short period of exponential growth, and three subsequent ones being phases of with decreasing specific growth rate. Sakacin P production was maximal at 20 degrees C. At higher temperatures (25-30 degrees C) the production ceased at lower cell masses, when less glucose was consumed, resulting in much lower sakacin P concentrations. With similar media and pH, the maximum sakacin P concentration at 20 degrees C was seven times higher than that at 30 degrees C. The growth rate increased with increasing concentrations of yeast extract, and the maximum concentration and specific production rate of sakacin P increased concomitantly. Increasing tryptone concentrations also had a positive influence upon sakacin P production, though the effect was significantly lower than that of yeast extract. The maximum sakacin P concentration obtained in this study was 20.5 mg l(-1). On the basis of the growth and production kinetics, possible metabolic regulation of bacteriocin synthesis is discussed, e.g. the effects of availability of essential amino acids, other nutrients, and energy.