Isolation and characterization by conventional methods and genetic transformation of Psychrobacter and Acinetobacter from fresh and spoiled meat, milk and cheese

Microbial dynamics of South Korean beef and surroundings along the supply chain based on high-throughput sequencing

Microbiological safety and quality of beef is crucial as beef can serve as a reservoir for a variety of bacteria, including spoilage-related and foodborne pathogens. Controlling microbial contamination is a critical aspect of food quality and safety, but it is difficult to prevent as there are several potential sources of contamination from production to distribution. In this study, the microbiological ecology of cattle/beef and associated environmental samples (n = 69) were trace-investigated to reveal microbiome shifts in cattle/beef and possible cross-contaminants throughout the entire supply chain using 16S rRNA gene sequencing. Pseudomonas, Psychrobacter, and Acinetobacter, known as spoilage bacteria, opportunistic pathogens, or antibiotic-resistant bacteria, were the main microorganisms present in cattle/beef, and Staphylococcus became abundant in the final products. The dominance of Acinetobacter and Pseudomonas was noticeable in the slaughtered carcasses and slaughterhouse environment, indicating that the slaughterhouse is a critical site where hygienic practices are required to prevent further contamination. Taxonomic similarities between cattle/beef and several environmental samples, as well as diversity analysis, presented a high potential for microbial transmission. Source tracking identified environmental samples that primarily contributed to the microbiota of cattle/beef. Farm floor (48%), workers' gloves (73%), and carcass splitters (20%) in the slaughterhouse were found to be major sources influencing the microbiome of cattle/beef at the farm, slaughterhouse, and processing plant, respectively. These findings demonstrated the dynamics of bacterial communities in cattle/beef according to stage and detected potential contamination sources, which may aid in a better understanding and control of microbial transmission in beef production.

Changes in the Physicochemical Properties and Microbial Communities of Air-Fried Hairtail Fillets during Storage

This study assessed the physicochemical properties of air-fried hairtail fillets (190 °C, 24 min) under different storage temperatures (4, 25, and 35 °C). The findings revealed a gradual decline in sensory scores across all samples during storage, accompanied by a corresponding decrease in thiobarbituric acid reactive substances (TBARS) and total viable count over time. Lower storage temperatures exhibited an effective capacity to delay lipid oxidation and microbiological growth in air-fried hairtail fillets. Subsequently, alterations in the microbiota composition of air-fried hairtail fillets during cold storage were examined. Throughout the storage duration, Achromobacter, Escherichia-Shigella, and Pseudomonas emerged as the three dominant genera in the air-fried hairtail samples. Additionally, Pearson correlation analysis demonstrated that among the most prevalent microbial genera in air-fried hairtail samples, Achromobacter and Psychrobacter exhibited positive correlations with the L* value, a* value, and sensory scores. Conversely, they displayed negative correlations with pH, b* value, and TBARS. Notably, air-fried samples stored at 4 °C exhibited prolonged freshness compared with those stored at 25 °C and 35 °C, suggesting that 4 °C is an optimal storage temperature. This study offers valuable insights into alterations in the physicochemical properties and microbial distribution in air-fried hairtail fillets during storage, facilitating the improvement of meat quality by adjusting microbial communities in air-fried hairtail fillets.

Phenotypic and genomic characterizations of Klebsiella pneumoniae ssp. pneumoniae and Rahnella inusitata strains reveal no clear association between genetic content and ropy phenotype

Ropy defect of pasteurized fluid milk is a type of spoilage which manifests itself by an increased viscosity, slimy body, and string-like flow during pouring. This defect has, among other causes, been attributed to the growth, proliferation and exopolysaccharide production by coliform bacteria, which are most commonly introduced in milk as post-pasteurization contaminants. As we identified both Klebsiella pneumoniae ssp. pneumoniae and Rahnella inusitata that were linked to a ropy defect, the goal of this study was to characterize 3 K. pneumoniae ssp. pneumoniae strains and 2 R. inusitata for (1) their ability to grow and cause ropy defect in milk at 6°C and 21°C and to (2) probe the genetic basis for observed ropy phenotype. Although all K. pneumoniae ssp. pneumoniae and R. inusitata strains showed net growth of >4 log10 over 48 h in UHT milk at 21°C, only R. inusitata strains displayed growth during 28-d incubation period at 6°C (>6 log10). Two out of 3 K. pneumoniae ssp. pneumoniae strains were capable of causing the ropy defect in milk at 21°C, as supported by an increase in the viscosity of milk and string-like flow during pouring; these 2 strains were originally isolated from raw milk. Only one R. inusitata strains was able to cause the ropy defect in milk; this strain was able to cause the defect at both 6°C and 21°C, and was originally isolated from a pasteurized milk. These findings suggest that the potential of K. pneumoniae ssp. pneumoniae and R. inusitata to cause ropy defect in milk is a strain-dependent characteristic. Comparative genomics provided no definitive answer on genetic basis for the ropy phenotype. However, for K. pneumoniae ssp. pneumoniae, genes rffG, rffH, rfbD, and rfbC involved in biosynthesis and secretion of enterobacterial common antigen (ECA) could only be found in the 2 strains that produced ropy defect, and for R. inusitata a set of 2 glycosyltransferase- and flippase genes involved in nucleotide sugar biosynthesis and export could only be identified in the ropy strain. Although these results provide some initial information for potential markers for strains that can cause ropy milk, the relationship between genetic content and ropiness in milk remains poorly understood and merits further investigation.

Bacterial microbiota in different types of processed meat products: diversity, adaptation, and co-occurrence

As a double-edged sword, some bacterial microbes can improve the quality and shelf life of meat products, but others mainly responsible for deterioration of the safety and quality of meat products. This review aims to present a landscape of the bacterial microbiota in different types of processed meat products. After demonstrating a panoramic view of the bacterial genera in meat products, the diversity of bacterial microbiota was evaluated in two dimensions, namely different types of processed meat products and different meats. Then, the influence of environmental factors on bacterial communities was evaluated according to the storage temperature, packaging conditions, and sterilization methods. Furthermore, microbes are not independent. To explore interactions among those genera, co-occurrence patterns were examined. In these respects, this review highlighted the recent advances in fundamental principles that underlie the environmental adaption tricks and why some species tend to occur together frequently, such as metabolic cross-feeding, co-aggregate at microscale, and the intercellular signaling system. Further investigations are required to unveil the underlying molecular mechanisms that govern microbial community systems, ultimately contributing to developing new strategies to harness beneficial microorganisms and control harmful microorganisms.

Bacterial Changes in Boiled Crayfish between Different Storage Periods and Characterizations of the Specific Spoilage Bacteria

This study investigated changes in the microbial compositions of crayfish tails during storage at 4 °C (for 0-12 days) as measured using high-throughput sequencing (HTS). The specific spoilage organisms (SSOs) in the crayfish tails were isolated using culture-dependent cultivation methods, and they were identified by 16S rRNA and characterized for their enzymatic spoilage potentials (e.g., protease, lipase, phospholipase, and amylase). The spoilage abilities of the selected strains in the crayfish tails were assessed by inoculating them into real food. Moreover, the microbial growth and the volatile basic nitrogen (TVB-N) changes were monitored during the storage period. The results from the HTS showed that the dominant genus of shrimp tails evolved from Streptococcus (D0) to Pseudomonas (D4) and, finally, to Paenisporosarcina (D12) during storage. Seven bacterial species (Acinetobacter lwoffii, Aeromonas veronii, Kurthia gibsonii, Pseudomonas sp., Exiguobacterium aurantiacum, Lelliottia amnigena, and Citrobacter freundii) were screened from the spoiled shrimp tails by the culture-dependent method, among which Aeromonas veronii had the strongest spoilage ability.

Linking microbial contamination to food spoilage and food waste: the role of smart packaging, spoilage risk assessments, and date labeling

Ensuring a safe and adequate food supply is a cornerstone of human health and food security. However, a significant portion of the food produced for human consumption is wasted annually on a global scale. Reducing harvest and postharvest food waste, waste during food processing, as well as food waste at the consumer level, have been key objectives of improving and maintaining sustainability. These issues can range from damage during processing, handling, and transport, to the use of inappropriate or outdated systems, and storage and packaging-related issues. Microbial growth and (cross)contamination during harvest, processing, and packaging, which causes spoilage and safety issues in both fresh and packaged foods, is an overarching issue contributing to food waste. Microbial causes of food spoilage are typically bacterial or fungal in nature and can impact fresh, processed, and packaged foods. Moreover, spoilage can be influenced by the intrinsic factors of the food (water activity, pH), initial load of the microorganism and its interaction with the surrounding microflora, and external factors such as temperature abuse and food acidity, among others. Considering this multifaceted nature of the food system and the factors driving microbial spoilage, there is an immediate need for the use of novel approaches to predict and potentially prevent the occurrence of such spoilage to minimize food waste at the harvest, post-harvest, processing, and consumer levels. Quantitative microbial spoilage risk assessment (QMSRA) is a predictive framework that analyzes information on microbial behavior under the various conditions encountered within the food ecosystem, while employing a probabilistic approach to account for uncertainty and variability. Widespread adoption of the QMSRA approach could help in predicting and preventing the occurrence of spoilage along the food chain. Alternatively, the use of advanced packaging technologies would serve as a direct prevention strategy, potentially minimizing (cross)contamination and assuring the safe handling of foods, in order to reduce food waste at the post-harvest and retail stages. Finally, increasing transparency and consumer knowledge regarding food date labels, which typically are indicators of food quality rather than food safety, could also contribute to reduced food waste at the consumer level. The objective of this review is to highlight the impact of microbial spoilage and (cross)contamination events on food loss and waste. The review also discusses some novel methods to mitigate food spoilage and food loss and waste, and ensure the quality and safety of our food supply.

Dynamic Changes of Bacterial Communities and Microbial Association Networks in Ready-to-Eat Chicken Meat during Storage

Ready-to-eat (RTE) chicken is a popular food in China, but its lack of food safety due to bacterial contamination remains a concern, and the dynamic changes of microbial association networks during storage are not fully understood. This study investigated the impact of storage time and temperature on bacterial compositions and microbial association networks in RTE chicken using 16S rDNA high-throughput sequencing. The results show that the predominant phyla present in all samples were Proteobacteria and Firmicutes, and the most abundant genera were Weissella, Pseudomonas and Proteus. Increased storage time and temperature decreased the richness and diversity of the microorganisms of the bacterial communities. Higher storage temperatures impacted the bacterial community composition more significantly. Microbial interaction analyses showed 22 positive and 6 negative interactions at 4 °C, 30 positive and 12 negative interactions at 8 °C and 44 positive and 45 negative interactions at 22 °C, indicating an increase in the complexity of interaction networks with an increase in the storage temperature. Enterobacter dominated the interactions during storage at 4 and 22 °C, and Pseudomonas did so at 22 °C. Moreover, interactions between pathogenic and/or spoilage bacteria, such as those between Pseudomonas fragi and Weissella viridescens, Enterobacter unclassified and Proteus unclassified, or those between Enterobacteriaceae unclassified and W.viridescens, were observed. This study provides insight into the process involved in RTE meat spoilage and can aid in improving the quality and safety of RTE meat products to reduce outbreaks of foodborne illness.

Influence of Tissue Type on the Bacterial Diversity and Community in Pork Bacon

In current study, bacterial diversity and community in different tissues of pork bacon were determined using high-throughput sequencing. In total, six phyla and 111 bacterial genera were identified. Among them, three dominant genera (Staphylococcus, Acinetobacter, and Macrococcus) were shared by all bacon samples. The linear discriminant analysis showed that 24 bacterial taxa significantly differentiated between the tissues. Results of non-metric Multidimensional Scaling and redundancy analysis showed that physicochemical characteristics of the tissue prominently structured the bacterial communities. Network analysis also illustrated that tissue type was an important factor impacting the bacterial interactions in different types of tissue. The results of current study can add valuable insights to the traditional homemade pork bacon.

The Maternal Milk Microbiome in Mammals of Different Types and Its Potential Role in the Neonatal Gut Microbiota Composition

Maternal milk, a main source of nutrition for neonates in early life, has attracted attention. An increasing number of studies have found that maternal milk has a high microbial diversity, as well as factors that might influence this diversity. However, there is a lack of knowledge regarding the effects of host diet and phylogeny on maternal milk microbes and the contribution of the maternal milk microbiota to the neonatal gut microbiota. Here, we analyzed the maternal milk and fecal microbiota of nine species (lion, dog, panda, human, mouse, rhesus macaque, cow, goat, and rabbit) of mammals of three type groups (herbivore, omnivore, and carnivore) using 16S rRNA amplicon sequencing. Our study provided evidence of host diet and phylogeny on the maternal milk microbiota. Moreover, functional prediction revealed that the carnivores had a significantly higher percentage of base excision repair, glycerolipid metabolism, taurine and hypotaurine metabolism, inorganic ion transport and metabolism, and nucleotide metabolism; while arginine and proline metabolism showed enrichment in the herbivore group. Source-tracking analysis showed that the contributions of bacteria from maternal milk to the microbiota of neonates of different mammals were different at day 3 after neonatal birth. Overall, our findings provided a theoretical basis for the maternal milk microbiota to affect neonatal fecal microbiota at day 3 after neonatal birth.

Microbiota of Chicken Breast and Thigh Fillets Stored under Different Refrigeration Temperatures Assessed by Next-Generation Sequencing

Chicken is one of the most widely consumed meats worldwide. The exploration of the bacterial diversity of chicken meat may provide new insights into the chicken-associated microbiome that will lead to moderation of food spoilage or safety. This study was undertaken to explore the bacterial communities of chicken breast and thigh fillets stored at refrigeration (0 °C and 5 °C) and slightly abuse (10 °C) temperatures for 5 days through conventional cultural methods along with next-generation sequencing (NGS) analysis. Total viable counts (TVC), Brochothrix thermosphacta, Pseudomonas spp., and lactic acid bacteria (LAB) were enumerated, while the bacterial communities were mapped through 16S rRNA gene amplicon sequencing. Chicken breast and thigh fillets possessed a complex bacterial structure that incorporated a total of >200 Operational Taxonomic Units (OTUs) at the genus level. The core microbiota of fresh samples consisted of Acinetobacter, Brochothrix, Flavobacterium, Pseudomonas, Psychrobacter, and Vibrionaceae (family). These genera persisted until the end of storage in >80% of samples, except Psychrobacter and Flavobacterium, while Photobacterium was also identified. Hierarchical clustering showed a distinction of samples based on storage time and chicken part. Conventional plate counting with growth media commonly used in spoilage studies did not always correspond to the microbial community profiles derived from NGS analysis, especially in Pseudomonas, Acinetobacter, Photobacterium, and Vibrionaceae. Results of the present study highlight Photobacterium and Vibrionaceae, in general, as potent chicken meat spoilers and suggest the necessity to combine classical microbiological methods along with NGS technologies to characterize chicken meat spoilage microbiota.

Diversity and succession of the microbial community and its correlation with lipid oxidation in dry-cured black carp (Mylopharyngodon piceus) during storage

This study aimed to achieve deeper insights into the microbiota composition and dynamic succession of the dry-cured black carp during storage using a high-throughput sequencing technique (HTS). The effect of lipid oxidation on microorganisms was also evaluated. Over 651 bacterial genera belonging to 37 phyla were identified. Firmicutes, Proteobacteria and Actinobacteria were the main bacterial phylum, some are highly associated with meat spoilage. Staphylococcus, Macrococcus and Acinetobacter were the most three microbial genera throughout the entire storage period (30 days). Between two different storage temperature, refrigeration at 4 °C could facilitate maintaining the microbial diversity, while 25 °C storage led to the formation of dominant microflora and the reduction of community diversity. Canonical correspondence analysis (CCA) showed that acid value (AV), malondialdehyde (MDA) and 4-hydroxy-2-hexenal (HHE) contents were three key environmental factors (oxidation products) affecting the profile of the microbiota. Staphylococcus presented a positive correlation with HHE content, while Macrococcus and Acinetobacter were negatively correlated with HHE content. These results could expand our knowledge on the effect of lipid oxidation on change of microbial distribution, it could also present an guideline to develop advanced storage methods for the vacuum packed dry-cured fish products.

Acinetobacter spp. in food and drinking water - A review

Acinetobacter spp. has emerged as a pathogen of major public health concern due to their increased resistance to antibiotics and their association with a wide range of nosocomial infections, community-acquired infections and war and natural disaster-related infections. It is recognized as a ubiquitous organism however, information about the prevalence of different pathogenic species of this genus in food sources and drinking water is scarce. Since the implementation of molecular techniques, the role of foods as a source of several species, including the Acinetobacter baumannii group, has been elucidated. Multidrug resistance was also detected among Acinetobacter spp. isolated from food products. This highlights the importance of foods as potential sources of dissemination of Acinetobacter spp. between the community and clinical environments and reinforces the need for further investigations on the potential health risks of Acinetobacter spp. as foodborne pathogens. The aim of this review was to summarize the published data on the occurrence of Acinetobacter spp. in different food sources and drinking water. This information should be taken into consideration by those responsible for infection control in hospitals and other healthcare facilities.

Polyarthritis Caused by Acinetobacter kookii in a Rothschild's Giraffe Calf (Giraffa camelopardalis rothschildi)

We report the first isolation of Acinetobacter kookii from a Rothschild's giraffe calf (Giraffa camelopardalis rothschildi) that had severe polyarthritis. The isolate was resistant to more than one representative of each of four classes of antibiotics (penicillins, macrolides, lincosamides and tetracyclines). As A. kookii has not been previously associated with disease in humans or animals, it may be an emerging opportunistic pathogen posing a threat to immunocompromised patients. Furthermore, as transmission of Acinetobacter spp. with similar patterns of antimicrobial resistance has been previously reported in human and animal populations, special care should be taken when handling infected animals.

Characterization of the Spoilage Microbiota of Hake Fillets Packaged Under a Modified Atmosphere (MAP) Rich in CO2 (50% CO2/50% N2) and Stored at Different Temperatures

The aim of this study was to characterize the spoilage microbiota of hake fillets stored under modified atmospheres (MAP) (50% CO₂/50% N₂) at different temperatures using high-throughput 16S rRNA gene sequencing and to compare the results with those obtained using traditional microbiology techniques. The results obtained indicate that, as expected, higher storage temperatures lead to shorter shelf-lives (the time of sensory rejection by panelists). Thus, the shelf-life decreased from six days to two days for Batch A when the storage temperature increased from 1 to 7 °C, and from five to two days—when the same increase in storage temperature was compared—for Batch B. In all cases, the trimethylamine (TMA) levels measured at the time of sensory rejection of hake fillets exceeded the recommended threshold of 5 mg/100 g. Photobacterium and Psychrobacter were the most abundant genera at the time of spoilage in all but one of the samples analyzed: Thus, Photobacterium represented between 19% and 46%, and Psychrobacter between 27% and 38% of the total microbiota. They were followed by Moritella, Carnobacterium,Shewanella, and Vibrio, whose relative order varied depending on the sample/batch analyzed. These results highlight the relevance of Photobacterium as a spoiler of hake stored in atmospheres rich in CO₂. Further research will be required to elucidate if other microorganisms, such as Psychrobacter, Moritella, or Carnobacterium, also contribute to spoilage of hake when stored under MAP.

Bacterial Diversity in Chinese Rushan Cheese From Different Geographical Origins

Rushan cheese, an essential part of the Bai culture, has been produced and consumed for centuries by the Bai people living mostly in Yunnan province of China, however, studies on the naturally occurring microbial communities of Rushan cheese are lacking. In this study, we applied high throughput sequencing technique to analyze the microbial compositions of Rushan cheese samples from three different geographical origins (i.e., Weishan, Eryuan, and Jianchuan). The microbiota in Weishan, Eryuan and Jianchuan Rushan cheese samples were distinct in terms of taxonomic composition and abundance. Linear discriminant analysis (LDA) of effect size (LEfSe) analysis found the characteristic taxonomic species in Weishan Rushan cheese samples were Lactobacillus pentosus, Lactobacillus crustorum, Lactobacillus brevis, Leuconostoc mesenteroides, and Pediococcus pentosaceus; the representing taxonomic species in Eryuan Rushan cheese samples were Lactobacillus kefiranofaciens, Lactococcus lactis, Acetobacter pasteurianus and Moraxella osloensis; by comparison, Acinetobacter was enriched in Jianchuan Rushan cheese samples. Characterization of the microbial diversity in Rushan cheese samples from different geographical origins will contribute to the understanding of microorganisms responsible for the Rushan cheese fermentation, and enable us to develop bioresources derived from Rushan cheese in the future.

Seafood spoilage microbiota and associated volatile organic compounds at different storage temperatures and packaging conditions

Seafood comprising of both vertebrate and invertebrate aquatic organisms are nutritious, rich in omega-3 fatty acids, essential vitamins, proteins, minerals and form part of healthy diet. However, despite the health and nutritional benefits, seafood is highly perishable. Spoilage of seafood could be as a result of microbial activity, autolysis or chemical oxidation. Microbial activity constitutes more spoilage than others. Spoilage bacteria are commonly Gram negative and produce off odours and flavours in seafood as a result of their metabolic activities. Storage temperature, handling and packaging conditions affect microbial growth and thus the shelf-life of seafood. Due to the complexity of the microbial communities in seafood, culture dependent methods of detection may not be useful, hence the need for culture independent methods are necessary to understand the diversity of microbiota and spoilage process. Similarly, the volatile organic compounds released by spoilage bacteria are not fully understood in some seafood. This review therefore highlights current knowledge and understanding of seafood spoilage microbiota, volatile organic compounds, effects of storage temperature and packaging conditions on quality of seafood.

Consequences of packaging on bacterial growth. Meat is an ecological niche

Meat is a good support for bacterial growth and particularly for bacteria which are specific of meat and meat products. Little is known about the physiological and biochemical factors which could explain why some bacterial species are only isolated from meat. This review tentatively points out, from an ecological point of view, some of these factors in Gram negative and Gram positive micro-organisms influencing storage life.

Changes in bacterial composition of zucchini flowers exposed to refrigeration temperatures

Microbial spoilage is one of the main factors affecting the quality of fresh fruits and vegetables, leading to off-flavor, fermented aroma, and tissue decay. The knowledge of microbial growth kinetics is essential for estimating a correct risk assessment associated with consuming raw vegetables and better managing the development of spoilage microorganisms. This study shows, for the first time, that only a part of total microbial community, originally present on fresh harvested female zucchini flowers, was able to adapt itself to refrigerated conditions. Through the study of microbial growth kinetics it was possible to isolate forty-four strains belonging to twenty-two species of the genera Acinetobacter, Arthrobacter, Bacillus, Enterobacter, Erwinia, Klebsiella, Pantoea, Pseudoclavibacter, Pseudomonas, Serratia, Staphylococcus, and Weissella, suggesting Enterobacteriaceae as potentially responsible for pistil spoilage.

Enhanced surface colonization by Escherichia coli O157:H7 in biofilms formed by an Acinetobacter calcoaceticus isolate from meat-processing environments

A meat factory commensal bacterium, Acinetobacter calcoaceticus, affected the spatial distribution of Escherichia coli O157:H7 surface colonization. The biovolume of E. coli O157:H7 was 400-fold higher (1.2 x 10(6) microm(3)) in a dynamic cocultured biofilm than in a monoculture (3.0 x 10(3) microm(3)), and E. coli O157:H7 colonized spaces between A. calcoaceticus cell clusters.

Incidence, radioresistance, and behavior of Psychrobacter spp. in rabbit meat

The relative incidence of Psychrobacter spp. in rabbit meat, the radioresistance of these bacteria, and the growth of nonirradiated and irradiated psychrobacter isolates, alone and in coculture, during chilled storage of inoculated sterile rabbit meat was investigated. Psychrobacter spp. accounted for 4.2% of the storage psychrotrophic flora of 30 rabbit carcasses. The radiation D10-values of 10 Psychrobacter isolates, irradiated at 4 degrees C in minced rabbit meat, ranged from 0.8 to 2.0 kGy, with significant (P < 0.05) differences among strains. Over 12 days of storage at 4 degrees C, pure cultures of two nonirradiated psychrobacter strains (D10 = 2 kGy) were capable of substantial increases (up to 3 log CFU/g) in sterile rabbit meat, but when the fastest growing strain was cocultured with Pseudomonas fluorescens and Brochothrix thermosphacta isolates, maximum cell densities and growth rates were significantly (P < 0.01) lower. After irradiation (2.5 kGy) of pure cultures in sterile rabbit meat, surviving cells of both Psychrobacter strains decreased for a period of 5 to 7 days and then resumed multiplication that, at day 12, resulted in a similar increase (1.6 to 1.7 log CFU/g) over initial survivor numbers. When irradiated in combination with the spoilage bacteria, one of the strains required 12 days to reach initial numbers. In conclusion, Psychrobacter spp. are radioresistant nonsporeforming bacteria with a low relative incidence among the storage flora of rabbit meat, unable to compete with food spoilage bacteria in this ecosystem and apparently not a major contributor to the spoilage of rabbit meat after irradiation.

The bacterial flora of fresh and chill-stored pork: analysis by cloning and sequencing of 16S rRNA genes

The composition of the initial bacterial flora of pork and the development of the flora after storage at +4 degrees C for 4 days were analysed by amplification, cloning and sequencing of 16S rDNA. A total of 122 clones were obtained, with lengths of > or =400 nucleotides and > or =95% similarity to database sequences. Nineteen clones were similar to sequences in database not assigned to any genera. Fourteen different genera were represented in clones from fresh meat, with 36.5% of the clones most resembling Acinetobacter and 17.3% resembling Staphylococcus and Macrococcus. After storage, the clones were composed of six different genera, with 44.3% resembling Pseudomonas, 17.1% resembling Aeromonas and only 14.3% resembling Acinetobacter. This study shows that the overall pattern of the initial and chill-stored pork flora, as shown by a molecular approach, was in agreement with results obtained in previous studies using traditional cultivation methods.

Antimicrobial properties of commercial annatto extracts against selected pathogenic, lactic acid, and spoilage microorganisms

Annatto preparations are used to impart distinctive flavor and color to foods and are a primary colorant in dairy foods such as cheese and butter. There are several reports indicating that certain fractions of the annatto plant have biological activities against microorganisms of significance in food fermentation, food preservation, and human health. However, little is reported describing the nature of the antimicrobial compound(s) or their potential presence in commercial annatto colorant preparations. This study was conducted to determine whether commonly available annatto extracts are capable of influencing the outgrowth of selected lactic acid, spoilage, and pathogenic microorganisms. Disk diffusion and tube macrodilution techniques were used to determine the MICs and MBCs of double-strength water-soluble annatto extracts. Standard antibiotic disks were used as controls for the disk diffusion assay. The results demonstrate that annatto has an inhibitory effect on Bacillus cereus, Clostridium perfringens, and Staphylococcus aureus, with MICs of 0.08, 0.31, and 0.16% (vol/vol) and diameters of inhibition of 9 to 10, 12 to 13, and 15 to 16 mm, respectively. A concentration of 0.63% (vol/vol) inhibited the growth of Streptococcus thermophilus, Lactobacillus casei subsp. casei, Lactococcus lactis, and Paenibacillus polymyxa. The MICs for Listeria monocytogenes and Enterococcus durans were 1.25 and 2.5% (vol/vol), respectively. No activity was detected against Lactobacillus plantarum, Bifidobacterium bifidum, yeasts, or selected gram-negative bacteria.

Comparison of differential plating media and two chromatography techniques for the detection of histamine production in bacteria

The bacterial enzyme histidine decarboxylase (Hdc) catalyses the conversion of histidine into histamine. This amine is essential for the biosynthesis of iron chelators (siderophores) and is an important cause of food poisoning after consumption of fish contaminated with histamine-producing bacteria. In this work we compared different methods for detecting histamine secreted by different bacterial strains. The presence of histamine in the culture supernatant of Vibrio anguillarum, which produces Hdc and secretes the histamine-containing siderophore anguibactin, was detected by thin-layer chromatography. Similar results were obtained using the culture supernatant of the Acinetobacter baumannii 19606 prototype strain that secretes the histamine-containing siderophore acinetobactin. Conversely, histamine was not detected in the culture supernatant of an isogenic V. anguillarum Hdc mutant and the A. baumannii 8399 strain that secretes a catechol siderophore different from anguibactin and acinetobactin. These results were confirmed by capillary gas chromatography/mass spectrometry. However, all these strains tested positive for histamine secretion when cultured on differential plating media containing histidine and a pH indicator, which were specifically designed for the detection of histamine-producing bacteria. The pH increase of the medium surrounding the bacterial colonies was however drastically reduced when the histidine-containing medium was supplemented with peptone, beef extract, and glucose. The histidine-containing culture supernatants of the A. baumannii and V. anguillarum strains showed an increase of about two units of pH, turned purple upon the addition of cresol red, and contained high amounts of ammonia. Escherichia coli strains, which are Hdc negative and do not use histidine as a carbon, nitrogen, and energy source, gave negative results with the differential solid medium and produced only moderate amounts of ammonia when cultured in the presence of excess histidine. This study demonstrates that, although more laborious and requiring some expensive equipment, thin-layer and gas chromatography/mass spectrometry are more accurate than differential media for detecting bacterial histamine secretion. The results obtained with these analytical methods are not affected by byproducts such as ammonia, which are generated during the degradation of histidine and produce false positive results with the differential plating media.

Comparative characterization of Acinetobacter strains isolated from different foods and clinical sources

Eighty-three Acinetobacter strains from clinical sources, and 170 from various foods (including fresh and spoiled meat and fish, vegetables, raw milk and cheese) were identified according to recently improved taxonomy, using a computer-assisted probabilistic method based on phenotyping tests. Apart from some atypical characters, most of the strains (94%) were identified to belong to the genospecies or groups of genospecies described in the literature. Among our strains from hospitals, the A. calcoaceticus- A. baumannii complex predominated, whereas the strains isolated from food were predominated by genospecies 7 (A. johnsonii), followed by genospecies 8/9 (A. lwoffii). The isolates from clinical environments showed a major incidence of antibiotic resistance, haemolytic strains and strains producing polysaccharidic material.