Inhibitory activity of natural antimicrobial compounds alone or in combination with nisin againstEnterobacter sakazakii

Bacteriocins from lactic acid bacteria: purification strategies and applications in food and medical industries: a review

Background

Bacteriocins are generally defined as ribosomally synthesized peptides, which are produced by lactic acid bacteria (LAB) that affect the growth of related or unrelated microorganisms. Conventionally, the extracted bacteriocins are purified by precipitation, where ammonium sulphate is added to precipitate out the protein from the solution.

Main text

To achieve the high purity of bacteriocins, a combination with chromatography is used where the hydrophobicity and cationic properties of bacteriocins are employed. The complexity column inside the chromatography can afford to resolve the loss of bacteriocins during the ammonium sulphate precipitation. Recently, an aqueous two-phase system (ATPS) has been widely used in bacteriocins purification due to the several advantages of its operational simplicity, mild process conditions and versatility. It reduces the operation steps and processing time yet provides high recovery products which provide alternative ways to conventional methods in downstream processing. Bacteriocins are widely approached in the food and medical industry. In food application, nisin, which is produced by Lactococcus lactis subsp. has been introduced as food preservative due to its natural, toxicology safe and effective against the gram-positive bacteria. Besides, bacteriocins provide a board range in medical industries where they are used as antibiotics and probiotics.

Short conclusion

In summary, this review focuses on the downstream separation of bacteriocins from various sources using both conventional and recent ATPS techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.

Natural Compounds With Antibacterial Activity Against Cronobacter spp. in Powdered Infant Formula: A Review

Bacteria from the genus Cronobacter are opportunistic foodborne pathogens capable of causing severe infections in neonates, the elderly and immunocompromised adults. The majority of neonatal infections have been linked epidemiologically to dehydrated powdered infant formulas (PIFs), the majority of which are manufactured using processes that do not ensure commercial sterility. Unfortunately, the osmotolerance, desiccation resistance, mild thermotolerance and wide-ranging minimum, optimum and maximum growth temperatures of Cronobacter spp. are conducive to survival and/or growth during the processing, reconstitution and storage of reconstituted PIFs. Consequently, considerable research has been directed at the development of alternative strategies for the control of Cronobacter spp. in PIFs, including approaches that employ antimicrobial compounds derived from natural sources. The latter include a range of phytochemicals ranging from crude extracts or essential oils derived from various plants (e.g., thyme, cinnamon, clove, marjoram, cumin, mint, fennel), to complex polyphenolic extracts (e.g., muscadine seed, pomegranate peel, olive oil, and cocoa powder extracts), purified simple phenolic compounds (e.g., carvacrol, citral, thymol, eugenol, diacetyl, vanillin, cinnamic acid, trans-cinnamaldehyde, ferulic acid), and medium chain fatty acids (monocaprylin, caprylic acid). Antimicrobials derived from microbial sources (e.g., nisin, other antibacterial peptides, organic acids, coenzyme Q0) and animal sources (e.g., chitosan, lactoferrin, antibacterial peptides from milk) have also been shown to exhibit antibacterial activity against the species. The selection of antimicrobials for the control of Cronobacter spp. requires an understanding of activity at different temperatures, knowledge about their mode of action, and careful consideration for toxicological and nutritional effects on neonates. Consequently, the purpose of the present review is to provide a comprehensive summary of currently available data pertaining to the antibacterial effects of natural antimicrobial compounds against Cronobacter spp. with a view to provide information needed to inform the selection of compounds suitable for control of the pathogen during the manufacture or preparation of PIFs by end users.

Evaluation of Antimicrobial Activity of Buforin I and Nisin and Synergistic Effect of the Combination of them as a Novel Antimicrobial Preservative

One of the most effective methods for increasing the antimicrobial activity of a substance is to combine it with one or more other antimicrobial agents. The aim of the present study was to evaluate the antimicrobial effect of buforin I and nisin alone and investigate the synergistic action of these compounds against the most important food spoilage microorganisms in clouding B. subtilis, S. epidermidis, L. innocua, E. coli, S. Enteritidis, A. oryzae, R. glutinis and G. candidum. The results of MIC and MBC/MFC examinations showed that buforin I had higher antimicrobial activity than nisin on all the microbial strains used in this study (p≤0.5). E.coli was the most resistant to both antimicrobial agents, while Listeria innocua and Staphylococcus epidermidis were the most sensitive to nisin and buforin I, respectively. The results of synergistic interaction between buforin I and nisin indicated that the combination of buforin I and nisin on B. subtilis, S. epidermidis and A. oryzae showed synergistic effect, while it had no effect on S. Enteritidis and Geotrichum candidum. The combination of buforin I and nisin showed partial synergistic effect on Listeria innocua, Escherichia coli, Rhodotorula glutinis. Assessment of viability of the microorganisms under the antimicrobial agents alone and in combination with each other at MICs and FICs indicated that use of these antimicrobial agents in combination enhances antimicrobial activity at lower concentrations of both agents. The present study investigated the antimicrobial properties of buforin I against food spoilage microorganisms for the first time and suggests that its use alone or in combination with nisin may provide a clear horizon for the application of antimicrobial peptides as natural preservatives. Thus, the combination of antimicrobial peptides and traditional antimicrobial food preservative could be a promising option for the prevention of contamination, spoilage, and infestation of food and beverage products.

Antibacterial Activity of Biocellulose with Oregano Essential Oil against Cronobacter Strains

Biocellulose, named "the biomaterial of the future", is a natural and ecologically friendly polymer, produced by selected acetic acid bacteria strains. Biocellulose impregnated with antimicrobial agents can be used as a novel, safe, and biodegradable food packaging material, helping extend the shelf life of some products and may also have the chance to replace typical plastic packaging, which is a big environmental problem these days. This study aimed to evaluate if cellulose impregned with natural oregano essential oil could show antibacterial activity against Cronobacter strains, which can occur in food, causing diseases and food poisoning. Bacterial cellulose was obtained from two acetic bacteria strains, Gluconacetobacter hansenii ATCC 23769 and Komagataeibacter sp. GH1. Antibacterial activity was studied by the disc-diffusion method against chosen Cronobacter strains, isolated from the plant matrix. Oregano essential oil has been shown to penetrate into the structure of bacterial cellulose, and after applying cellulose to the solid medium, it showed the ability to migrate. Biopolymer from the strain K. sp. GH1 was able to better absorb and retain essential oregano oil (OEO) compared to bacterial cellulose (BC) produced by the G. hansenii ATCC 23769. Bacterial cellulose with oregano essential oil from strain Komagataeibacter GH1 showed generally greater inhibitory properties for the growth of tested strains than its equivalent obtained from G. hansenii. This was probably due to the arrangement of the polymer fibers and its final thickness. The largest zone of inhibition of strain growth was observed in relation to C. condimenti s37 (32.75 mm ± 2.8). At the same time, the control sample using filter paper showed an inhibition zone of 36.0 mm ± 0.7. A similar inhibition zone (28.33 mm ± 2.6) was observed for the C. malonaticus lv31 strain, while the zone in the control sample was 27.1 mm ± 0.7. Based on this study, it was concluded that bacterial cellulose impregnated with oregano essential oil has strong and moderate antimicrobial activity against all presented strains of the genus Cronobacter isolated from plant matrix. Obtained results give a strong impulse to use this biopolymer as ecological food packaging in the near future.

Comparison of ultrastructural changes and the anticarcinogenic effects of thymol and carvacrol on ovarian cancer cells: which is more effective?

Ovarian cancer is the seventh most common cancer worldwide in women. Many anticancer drugs are currently used clinically have been isolated from plant species or are based on such substances. Thymol (5-methyl-2-isopropylphenol) and carvacrol are oxygenated aromatic compounds from the monoterpene group. They are the main constituents of thyme essential oil and show antiproliferative, antioxidant, and antiseptic properties. The aim of this study is to compare the antiproliferative and apoptotic effects of thymol and carvacrol on SKOV-3 ovarian cancer cell line. The cancer cells were treated with different concentrations of thymol and carvacrol (100, 200, 400, 600 µM) at 24 h and 48 h durations. The cell viability was investigated by MTT assay and analysis of apoptosis with annexin V assay was determined. The study show that thymol and carvacrol significantly induced apoptosis in all groups as dose and time-dependent (p < .05). The data in the present study demonstrated that thymol and carvacrol have apoptotic and antiproliferative properties in a concentration-dependent manner toward ovarian cancer cells. SKOV-3 cancer cell line was much more sensitive to the toxic effect of thymol than carvacrol.

Antimicrobial activity of trans-cinnamic acid and commonly used antibiotics against important fish pathogens and nonpathogenic isolates

AIMS

Antibiotics and several other chemicals have been used to prevent fish diseases. However, this situation results in economic loss for the companies in the aquaculture industry and most importantly it pollutes the environment. Cinnamic acid is a naturally occurring aromatic acid and is considered to be safe for human consumption. Therefore, in this study, the antibacterial activity of trans-cinnamic acid and commonly used antibiotics, namely chloramphenicol, vancomycin, streptomycin and erythromycin, were tested against 32 bacteria, including fish pathogens, nonpathogenic isolates and collection strains.

METHODS AND RESULTS

Trans-cinnamic acid was applied against the bacteria using the disc diffusion and microdilution method under in vitro conditions. Antibiotics were also tested under similar conditions against all tested bacteria using the disc diffusion method. The results show that among 32 bacterial strains trans-cinnamic acid exhibited potent inhibitory effect on the Gram-negative fish pathogen Aeromonas sobria. In addition, a moderate inhibition of trans-cinnamic acid of fish pathogens Aeromonas salmonicida, Vibrio (Listonella) anguillarum, Vibrio crassostreae and Yersinia ruckeri was also observed for trans-cinnamic acid in our study. On the contrary, the majority of nonpathogenic intestinal isolates were resistant to trans-cinnamic acid.

CONCLUSIONS

To the best of our knowledge, this is the first report on the antimicrobial activity of trans-cinnamic acid on 24 of the studied bacteria isolated from fish. In conclusion, trans-cinnamic acid can be used as an environmentally friendly alternative additive to prevent and control primarily A. sobria, as well as other pathogenic bacteria such as A. salmonicida, V. anguillarum, V. crassostreae and Y. ruckeri.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicated that trans-cinnamic acid may present an environmentally friendly alternative therapeutic agent against A. sobria infections in the aquaculture industry.

Antimicrobial Activity and Possible Mechanism of Action of Citral against Cronobacter sakazakii

Citral is a flavor component that is commonly used in food, beverage and fragrance industries. Cronobacter sakazakii is a food-borne pathogen associated with severe illness and high mortality in neonates and infants. The objective of the present study was to evaluate antimicrobial effect of citral against C. sakazakii strains. The minimum inhibitory concentration (MIC) of citral against C. sakazakii was determined via agar dilution method, then Gompertz models were used to quantitate the effect of citral on microbial growth kinetics. Changes in intracellular pH (pH_in), membrane potential, intracellular ATP concentration, and membrane integrity were measured to elucidate the possible antimicrobial mechanism. Cell morphology changes were also examined using a field emission scanning electron microscope. The MICs of citral against C. sakazakii strains ranged from 0.27 to 0.54 mg/mL, and citral resulted in a longer lag phase and lower growth rate of C. sakazakii compared to the control. Citral affected the cell membrane of C. sakazakii, as evidenced by decreased intracellular ATP concentration, reduced pH_in, and cell membrane hyperpolarization. Scanning electron microscopy analysis further confirmed that C. sakazakii cell membranes were damaged by citral. These findings suggest that citral exhibits antimicrobial effect against C. sakazakii strains and could be potentially used to control C. sakazakii in foods. However, how it works in food systems where many other components may interfere with its efficacy should be tested in future research before its real application.

Antimicrobial Activity of Ferulic Acid Against Cronobacter sakazakii and Possible Mechanism of Action

Cronobacter sakazakii is an opportunistic pathogen transmitted by food that affects mainly newborns, infants, and immune-compromised adults. In this study, the antibacterial activity of ferulic acid was tested against C. sakazakii strains. Minimum inhibitory concentration of ferulic acid against C. sakazakii strains was determined using the agar dilution method. Changes in intracellular pH, membrane potential and intracellular ATP concentration were measured to elucidate the possible antibacterial mechanism. Moreover, SYTO 9 nucleic acid staining was used to assess the effect of ferulic acid on bacterial membrane integrity. Cell morphology changes were observed under a field emission scanning electron microscope. The minimum inhibitory concentrations of ferulic acid against C. sakazakii strains ranged from 2.5 to 5.0 mg/mL. Addition of ferulic acid exerted an immediate and sustained inhibition of C. sakazakii proliferation. Ferulic acid affected the membrane integrity of C. sakazakii, as evidenced by intracellular ATP concentration decrease. Moreover, reduction of intracellular pH and cell membrane hyperpolarization were detected in C. sakazakii after exposure to ferulic acid. Reduction of green fluorescence indicated the injury of cell membrane. Electronic microscopy confirmed that cell membrane of C. sakazakii was damaged by ferulic acid. Our results demonstrate that ferulic acid has moderate antimicrobial activity against C. sakazakii. It exerts its antimicrobial action partly through causing cell membrane dysfunction and changes in cellular morphology. Considering its antimicrobial properties, together with its well-known nutritional functions, ferulic acid has potential to be developed as a supplement in infant formula or other foods to control C. sakazakii.

Essential oil encapsulations: uses, procedures, and trends

Recently there has been an increased interest towards the biological activities of essential oils (EOs).

Antifungal effect of Mexican oregano (Lippia berlandieri Schauer) essential oil on a wheat flour-based medium

The antimicrobial activity of oregano has been attributed mainly to the presence of volatile compounds found in its essential oil (EO), mainly carvacrol and thymol. The search for antimicrobial activity of oregano EO with different concentrations of thymol and carvacrol, can lead to products with a wider range of applications. The aim of this work was to describe the in vitro antifungal effect of Mexican oregano (Lippia berlandieri Schauer) EO fractions on the growth of Aspergillus, Penicillium, and Rhizopus sp. The Mexican oregano EO fractions studied had different concentrations of carvacrol, which decreased from fraction 1 to 5 (81% to 23%), while thymol content increased from 3% to 64%. Fungal inhibition was evaluated on a wheat flour-based medium with EO fractions concentrations ranging from 50 to 200 mg/kg. Radial growth curves were fitted using the modified Gompertz model (R(2)(adj) = 0.989 ± 0.01). No significant differences (P > 0.05) were found with the different composition of the Mexican oregano EO fractions; nevertheless, fraction concentration presented significant (P < 0.05) mold inhibition as concentration increased. Rhizopus sp. (Rh18) showed a linear reduction on specific growth rate, on the maximum mold growth at the stationary phase, and an increase in the lag time as the concentration of the oregano EO increased; mold growth inhibition were achieved at 150 mg/kg in fractions 1 to 4, and at 100 mg/kg for fraction 5. Aspergillus sp. (As6) and Penicillium sp. (Pe36) were inhibited at 150 and 200 mg/kg, respectively. Results obtained suggest that Mexican oregano EO (Lippia berlandieri Schauer) compounds could be used as antimicrobial agents to prevent fungal growth in bakery products.

Carvacrol decreases neuronal excitability by inhibition of voltage-gated sodium channels

The monoterpenoid carvacrol (1) is present in many essential oils of plants and has attracted attention because of its beneficial biological activities, especially analgesic activity. However, the mechanism of action of 1 remains unknown. The present study aimed to explore the mechanisms whereby 1 produces its effects on the peripheral nervous system. Carvacrol reversibly blocked the excitability of the rat sciatic nerve in a concentration-dependent manner with an IC(50) value of 0.50 ± 0.04 mM. At 0.6 mM, 1 increased the rheobase from 3.30 ± 0.06 V to 4.16 ± 0.14 V and the chronaxy from 59.6 ± 1.22 μs to 75.0 ± 1.82 μs. Also, 1 blocked the generation of action potentials (IC(50) 0.36 ± 0.14 mM) of the intact dorsal root ganglion (DRG) neurons without altering the resting potential and input resistance. Carvacrol reduced the voltage-gated sodium current of dissociated DRG neurons (IC(50) 0.37 ± 0.05 mM). In this study it has been demonstrated that 1 blocks neuronal excitability by a direct inhibition of the voltage-gated sodium current, which suggests that this compound acts as a local anesthetic. The present findings add valuable information to help understand the mechanisms implicated in the analgesic activity of carvacrol.

Extensive manipulation of caseicins A and B highlights the tolerance of these antimicrobial peptides to change

Caseicins A and B are low-molecular-weight antimicrobial peptides which are released by proteolytic digestion of sodium caseinate. Caseicin A (IKHQGLPQE) is a nine-amino-acid cationic peptide, and caseicin B (VLNENLLR) is a neutral eight-amino-acid peptide; both have previously been shown to exhibit antibacterial activity against a number of pathogens, including Cronobacter sakazakii. Previously, four variants of each caseicin which differed subtly from their natural counterparts were generated by peptide synthesis. Antimicrobial activity assays revealed that the importance of a number of the residues within the peptides was dependent on the strain being targeted. In this study, this engineering-based approach was expanded through the creation of a larger collection of 26 peptides which are altered in a variety of ways. The investigation highlights the generally greater tolerance of caseicin B to change, the fact that changes have a more detrimental impact on anti-Gram-negative activity, and the surprising number of variants which exhibit enhanced activity against Staphylococcus aureus.

Effect of vanillin, ethyl vanillin, and vanillic acid on the growth and heat resistance of Cronobacter species

Preservatives could be part of an effective intervention strategy for the control of Cronobacter species in foods, but few compounds with the desired antimicrobial properties have been identified to date. We examined the antibacterial activity of vanillin, ethyl vanillin, and vanillic acid against seven Cronobacter spp. in quarter-strength tryptic soy broth with 5 g/liter yeast extract (TSBYE) adjusted to pH 5.0, 6.0, and 7.0 at 10, 21, and 37°C. All compounds exhibited pH- and temperature-dependant bacteriostatic and bactericidal activity. MICs of vanillin and ethyl vanillin consistently increased with decreasing pH and temperature, but vanillic acid had little activity at pH values of 6.0 and 7.0. The MICs for all temperatures, pH values, and bacterial strains tested were 2 mg/ml ethyl vanillin, 3 mg/ml vanillin, and >8 mg/ml vanillic acid. MBCs also were influenced by pH, although significantly higher concentrations were needed to inactivate the bacteria at 21°C than at 10 or 37°C. Survivor curves for Cronobacter sakazakii strains at the MBCs of each compound revealed that all treatments resulted in immediate loss of cell viability at 37°C. Measurements of propidium iodide uptake indicated that the cell membranes were damaged by exposure to all three compounds. The thermal resistance of C. sakazakii was examined at 58°C in TSBYE supplemented with MBCs of each compound at pH 5.0 and 6.0. D-values at pH 5.0 were reduced from 14.56 ± 0.60 min to 0.93 ± 0.01, 0.63 ± 0.01, and 0.98 ± 0.02 min for vanillin, ethyl vanillin, and vanillic acid, respectively. These results suggest that vanillin, ethyl vanillin, and vanillic acid may be useful for the control of Cronobacter spp. in food during preparation and storage.

Genomic analysis of bacteriophage ESP2949-1, which is virulent for Cronobacter sakazakii

Virulent phage ESP2949-1, which was isolated from sewage, has an icosahedral head, a contractile tail, and a double-stranded DNA genome with a length of 49,116 bp with 50.09% G+C content. Phage ESP2949-1 showed 3% similarity to enterobacteria phage TLS. Bioinformatics analysis of the phage genome revealed 43 putative open reading frames (ORFs). Predicted protein products of the ORFs were determined and described. Based on its morphology, phage ESP2949-1 can be classified as a member of the family Myoviridae. To our knowledge, this is the first report of the genomic sequence and characterization of phage ESP2949-1 isolated from sewage.

Genomic sequence analysis of virulent Cronobacter sakazakii bacteriophage ES2

Virulent Cronobacter sakazakii bacteriophage ES2 was isolated from swine fecal samples, and the genome sequence by was determined GS-Flx. Bacteriophage ES2 had a double-stranded DNA genome with a length of 22,162 bp and a G+C content of 50.08%. The morphological characteristics under a transmission electron microscope indicated that bacteriophage ES2 belongs to the family Myoviridae. The structural proteins, including the phage coat protein, were separated by SDS-PAGE and identified by Q-TOF. Bioinformatics analysis of the bacteriophage genome revealed 30 putative open reading frames (ORFs). The predicted protein products of the ORFs were determined and described. To our knowledge, the genome of the newly isolated bacteriophage ES2 was not significantly similar to that of any previously reported bacteriophages of members of the family Enterobacteriaceae.

Real-time monitoring of luciferase-tagged Cronobacter sakazakii in reconstituted infant milk formula

The aim of this study was to examine the potential of using a lux-tagged Cronobacter sakazakii strain to monitor growth of the bacterium in various liquids. C. sakazakii was transformed with plasmid p16S lux, and integration of the plasmid at the desired site on the chromosome was confirmed by PCR. The growth of the lux-tagged strain was similar to that of the non-lux-tagged strain, and the integrated plasmid was stable when cells were cultured in the absence of antibiotic. Growth of the lux-tagged strain was monitored in real time in Luria-Bertani broth, skim milk, and infant milk formula by using both the Luminoskan luminometer and the Xenogen IVIS imager. Bioluminescence could be detected when the lux-tagged strain was cocultured with other bacteria. The effect of monocaprylin and nisin on the growth of C. sakazakii in milk was monitored by measuring bioluminescence. In conclusion, growth of a lux-tagged C. sakazakii can be monitored in real time in both clear and opaque liquids by measuring bioluminescence. lux-tagged C. sakazakii strains could be potentially used in high-throughput assays to monitor the effects of various infant milk formula compositions on growth of the bacterium.

Cronobacter (Enterobacter sakazakii): an opportunistic foodborne pathogen

Cronobacter spp. (Enterobacter sakazakii) are a recently described genus that is comprised of six genomospecies. The classification of these organisms was revised based on a detailed polyphasic taxonomic study. Cronobacter spp. are regarded as ubiquitous organisms having been isolated from a wide variety of foods. These bacteria are opportunistic pathogens and are linked with life-threatening infections in neonates. Clinical symptoms of Cronobacter infection include necrotizing enterocolitis, bacteremia, and meningitis, with case fatality rates of 50-80% being reported. Contaminated powdered infant formula has been epidemiologically linked with infections. Recently, infections among immunocompromised adults, mainly the elderly, have also been reported. A high tolerance to osmotic stress and elevated temperatures contribute to the survival of Cronobacter spp. in dried foods such as powdered infant formula. Controlling the organism in the production environment, thereby reducing dissemination, necessitates the provision of suitable diagnostic tools. Studies demonstrated that a high degree of variability exists amongst the phenotypic-based methods used to identify Cronobacter spp. However, advances in molecular detection and subtyping techniques have significantly improved the identification and characterization of Cronobacter spp. The dose required to induce infection has yet to be determined. In vitro virulence studies have shown that Cronobacter spp. may survive in macrophage cells and efficiently attach to and invade epithelial cell lines. The production of exopolysaccharide may contribute to the formation of biofilm and active efflux pumps promote resistance to antimicrobial agents such as bile salts and disinfectants. A holistic approach combining techniques such as comparative genome analysis, proteomics, and in vivo challenges could help unravel the complex interactions between this pathogen and its host. These data would help identify those properties in Cronobacter spp. which enable the bacterium to survive in the production environment and infect vulnerable neonates via the food chain.

Microbial antagonists to food-borne pathogens and biocontrol

Application of natural antimicrobial substances (such as bacteriocins) combined with novel technologies provides new opportunities for the control of pathogenic bacteria, improving food safety and quality. Bacteriocin-activated films and/or in combination with food processing technologies (high-hydrostatic pressure, high-pressure homogenization, in-package pasteurization, food irradiation, pulsed electric fields, or pulsed light) may increase microbial inactivation and avoid food cross-contamination. Bacteriocin variants developed by genetic engineering and novel bacteriocins with broader inhibitory spectra offer new biotechnological opportunities. In-farm application of bacteriocins, bacterial protective cultures, or bacteriophages, can decrease the incidence of food-borne pathogens in livestock, animal products and fresh produce items, reducing the risks for transmission through the food chain. Biocontrol of fungi, parasitic protozoa and viruses is still a pending issue.

Influence of desiccation on the sensitivity of Cronobacter spp. to lactoferrin or nisin in broth and powdered infant formula

Although outbreaks caused by Cronobacter spp. (Enterobacter sakazakii) are rare, infections by this organism have a case-fatality rate which may reach 80%. Powdered infant milk formula (PIMF) is considered a major source for human infection with Cronobacter spp. The organism has the capability to survive in dry environments for long periods (approximately 2 years). Current interest in the use of natural antimicrobials including lactoferrin (LF) and nisin has developed because of the desire for preservative-free food products. The objective of the present study was to evaluate the antimicrobial activity of bovine LF or nisin against undesiccated and desiccated Cronobacter spp. cells in 0.2% peptone water (PW) and reconstituted PIMF at different temperatures. In 0.2% PW, 2.5 mg/ml LF was able to inactivate 4 log(10) CFU/ml of undesiccated cells of Cronobacter spp. in 4 h at 37 degrees C but at lower temperatures, higher concentrations of LF as well as longer exposure were needed to achieve the same effect as at 37 degrees C. Similarly, the effect of nisin against undesiccated cells of Cronobacter spp. was concentration and temperature dependent in 0.2% PW. It was found that 1500 IU/ml caused a 4 log(10) CFU/ml reduction of undesiccated cells of Cronobacter spp. at 21 degrees C and 37 degrees C. Desiccated Cronobacter spp. cells in 0.2% PW were more sensitive to LF action than were undesiccated cells. A 4 log(10) CFU/ml reduction was obtained with 2.5 mg/ml LF after 1 h at 21 and 37 degrees C or 8 h at 10 degrees C. In contrast, desiccated cells of Cronobacter spp. were more resistant to nisin. Furthermore, neither LF nor nisin had detectable antimicrobial activity against desiccated or undesiccated Cronobacter spp. in reconstituted PIFM. Heating at 55 degrees C for 5 min with nisin in reconstituted PIFM did not enhance the antimicrobial activity of nisin. Unexpectedly, nisin appeared to protect Cronobacter spp. from the damaging effects of heat treatment. The reduced antimicrobial activity of LF and nisin in reconstituted PIMF was potentially explained by the higher concentration of Ca(2+), Mg(2+) and Fe(3+) in the latter.