[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated the adaptation of selected Pseudomonas spp. to QACs and monitored the changes in susceptibility to these compounds after serial exposure to QACs. Additional study was performed on the QACs efficacy on cells on different types of surfaces and the data were correlated to surface properties. Results showed that wild type Pseudomonas fluorescens and Pseudomonas fragi exhibited more susceptibility to QACs in comparison with Pseudomonas putida. In addition, the investigations carried out on the adhesion of both wild and adapted strains to different types of surface materials using thermodynamic approaches showed that hydrophilic Pseudomonas strains exhibited highest adhesion to the tile surface, while least adhesion was observed on the stainless steel surface material. A diverse relationship was detected between the thermodynamic affinity of cells to the surfaces (higher water contact angle and energy of adhesion) and cell inactivation. The results can be useful to the hygiene manufacture of food processing facilities or to choose appropriate sanitation strategies for the existing plants.
Full-text · Article · Dec 2015 · Food and Bioproducts Processing
[Show abstract][Hide abstract] ABSTRACT: Enterobacter gergoviae is a recurrent contaminant of cosmetic and hygiene products. To understand how this bacterium adapts to biocides, we studied E. gergoviae CIP 76.01 and its triclosan and MIT-CMIT tolerant isogenic mutants. They were compared with others also isolated from contaminated cosmetics. Phenotypic differences were noted and these included changes in the bacterial envelope and flagella along with differences in motility, and biofilm growth rates. Triclosan and MIT-CMIT derivatives expressed flagella and other MIT-CMIT derivatives exhibited some external appendages. Those bacteria expressing a high-level MIC to MIT-CMIT, expressed a strong biofilm formation. No differential phenotypes were noted for carbon source utilisation. E. gergoviae demonstrated a diverse response to both of these preservatives contained in cosmetic preparations, depending on their concentrations. Interestingly, this adaptive response is associated with modifications of filament structure-related proteins contributing to increase the organism motility and the production of biofilm. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
No preview · Article · Apr 2015 · Letters in Applied Microbiology
[Show abstract][Hide abstract] ABSTRACT: Chlorhexidine is one of the most widely used biocides in health and agricultural settings as well as in the modern food industry. It is a cationic biocide of the biguanide class. Details of its mechanism of action are largely unknown. The frequent use of chlorhexidine has been questioned recently, amidst concerns that an overuse of this compound may select for bacteria displaying an altered susceptibility to antimicrobials, including clinically important anti-bacterial agents. We generated a Salmonella enterica serovar Typhimurium isolate (ST24(CHX)) that exhibited a high-level tolerant phenotype to chlorhexidine, following several rounds of in vitro selection, using sub-lethal concentrations of the biocide. This mutant showed altered suceptibility to a panel of clinically important antimicrobial compounds. Here we describe a genomic, transcriptomic, proteomic, and phenotypic analysis of the chlorhexidine tolerant S. Typhimurium compared with its isogenic sensitive progenitor. Results from this study describe a chlorhexidine defense network that functions in both the reference chlorhexidine sensitive isolate and the tolerant mutant. The defense network involved multiple cell targets including those associated with the synthesis and modification of the cell wall, the SOS response, virulence, and a shift in cellular metabolism toward anoxic pathways, some of which were regulated by CreB and Fur. In addition, results indicated that chlorhexidine tolerance was associated with more extensive modifications of the same cellular processes involved in this proposed network, as well as a divergent defense response involving the up-regulation of additional targets such as the flagellar apparatus and an altered cellular phosphate metabolism. These data show that sub-lethal concentrations of chlorhexidine induce distinct changes in exposed Salmonella, and our findings provide insights into the mechanisms of action and tolerance to this biocidal agent.
Full-text · Article · Aug 2014 · Frontiers in Microbiology
[Show abstract][Hide abstract] ABSTRACT: Some Enterobacteriaceae possess the ability to survive in low-moisture environments for extended periods of time. Many of the reported food-borne outbreaks associated with low-moisture foods involve Salmonella contamination. The control of Salmonella in low-moisture foods and their production environments represents a significant challenge for all food manufacturers. This review summarizes the current state of knowledge with respect to Salmonella survival in intermediate- and low-moisture food matrices and their production environments. The mechanisms utilized by this bacterium to ensure their survival in these dry conditions remain to be fully elucidated, however, in depth transcriptomic data is now beginning to emerge regarding this observation. Earlier research work described the effect(s) that low-moisture can exert on the long-term persistence and heat tolerance of Salmonella, however, data are also now available highlighting the potential cross-tolerance to other stressors including commonly used microbicidal agents. Sources and potential control measures to reduce the risk of contamination will be explored. By extending our understanding of these geno- and phenotypes, we may be able to exploit them to improve food safety and protect public health.
Full-text · Article · Nov 2013 · Frontiers in Microbiology
[Show abstract][Hide abstract] ABSTRACT: Consumers trust commercial food production to be safe, and it is important to strive to improve food safety at every level.
Several outbreaks of food-borne disease have been caused by Salmonella strains associated with dried food. Currently we do not know the mechanisms used by Salmonella enterica serovar Typhimurium to survive in desiccated environments. The aim of this study was to discover the responses of S. Typhimurium ST4/74 at the transcriptional level to desiccation on a stainless steel surface and to subsequent rehydration.
Bacterial cells were dried onto the same steel surfaces used during the production of dry foods, and RNA was recovered for
transcriptomic analysis. Subsequently, dried cells were rehydrated and were again used for transcriptomic analysis. A total
of 266 genes were differentially expressed under desiccation stress compared with a static broth culture. The osmoprotectant
transporters proP, proU, and osmU (STM1491 to STM1494) were highly upregulated by drying. Deletion of any one of these transport systems resulted in a reduction
in the long-term viability of S. Typhimurium on a stainless steel food contact surface. The proP gene was critical for survival; proP deletion mutants could not survive desiccation for long periods and were undetectable after 4 weeks. Following rehydration,
138 genes were differentially expressed, with upregulation observed for genes such as proP, proU, and the phosphate transport genes (pstACS). In time, this knowledge should prove valuable for understanding the underlying mechanisms involved in pathogen survival
and should lead to improved methods for control to ensure the safety of intermediate- and low-moisture foods.
Full-text · Article · May 2013 · Applied and Environmental Microbiology
[Show abstract][Hide abstract] ABSTRACT: Triclosan is a biocidal active agent commonly used in domestic and industrial formulations. Currently, there is limited understanding of the mechanisms involved in triclosan tolerance in E. coli O157. The aim of this study was to identify the differences between a triclosan susceptible E. coli O157:H19 isolate (minimum inhibitory concentration; MIC 6.25 μg/ml) and its triclosan tolerant mutant (MIC >8000 μg/ml) at a proteomic and phenotypic level. Two dimensional DIGE was used to identify differences in protein expression between the reference strain and triclosan tolerant mutant in the presence and absence of triclosan. DIGE analysis indicates the proteome of the reference E. coli O157:H19 was significantly different to its triclosan tolerant mutant. Significant changes in protein expression levels in the triclosan tolerant mutant included the known triclosan target FabI which encodes enoyl reductase, outer membrane proteins and the filament structural protein of flagella, FliC. Phenotypic studies showed that the triclosan tolerant mutant MIC decreased in the presence of efflux inhibitor phenyl-arginine-β-naphthylamide and biofilm formation was increased in the mutant strain. The data generated indicates that enhanced triclosan tolerance is a result of multiple mechanisms which act together to achieve high-level resistance, rather than mutation of FabI alone.
No preview · Article · Jan 2013 · Journal of proteomics
[Show abstract][Hide abstract] ABSTRACT: Concern has been expressed about the overuse of biocides in farm animal production and food industries. Biocide application can create selective pressures that lead to increased tolerance to one or more of these compounds and are concomitant with the emergence of cross-resistance to antibiotics. A triclosan sensitive Salmonella enterica serovar Typhimurium and the isogenic triclosan tolerant mutant were studied at the proteomic level in order to elucidate cellular mechanisms that facilitate biocide tolerance. 2-D differential fluorescent gel electrophoresis (DIGE) compared protein profiles of parent and mutant Salmonella, in the presence and absence of triclosan. Differentially expressed proteins were identified by mass spectrometry and divided into two groups: Group A describes proteins differentially expressed between susceptible and triclosan tolerant Salmonella and includes the known triclosan target FabI which contained a mutation at the triclosan target binding site. Group B identified proteins differentially expressed in response to triclosan exposure and defines a general cell defence network. Only four proteins were common to both groups highlighting the diverse range of pathways employed by Salmonella to counteract biocides. These data suggest that sub-lethal concentrations of triclosan induce discernible changes in the proteome of exposed Salmonella and provide insights into mechanisms of response and tolerance.
No preview · Article · May 2012 · Journal of proteomics
[Show abstract][Hide abstract] ABSTRACT: Cronobacter species (formerly known as Enterobacter sakazakii) are opportunistic pathogens that can cause necrotizing enterocolitis, bacteraemia and meningitis, predominantly in neonates. Infection in these vulnerable infants has been linked to the consumption of contaminated powdered infant formula (PIF). Considerable research has been undertaken on this organism in the past number of years which has enhanced our understanding of this neonatal pathogen leading to improvements in its control within the PIF production environment. The taxonomy of the organism resulted in the recognition of a new genus, Cronobacter, which consists of seven species. This paper presents an up-to-date review of our current knowledge of Cronobacter species. Taxonomy, genome sequencing, current detection protocols and epidemiology are all discussed. In addition, consideration is given to the control of this organism in the manufacturing environment, as a first step towards reducing the occurrence of this pathogen in PIF.
Full-text · Article · Mar 2012 · Journal of Applied Microbiology
[Show abstract][Hide abstract] ABSTRACT: Biocides play an essential role in limiting the spread of infectious disease. The food industry is dependent on these agents, and their increasing use is a matter for concern. Specifically, the emergence of bacteria demonstrating increased tolerance to biocides, coupled with the potential for the development of a phenotype of cross-resistance to clinically important antimicrobial compounds, needs to be assessed. In this study, we investigated the tolerance of a collection of susceptible and multidrug-resistant (MDR) Salmonella enterica strains to a panel of seven commercially available food-grade biocide formulations. We explored their abilities to adapt to these formulations and their active biocidal agents, i.e., triclosan, chlorhexidine, hydrogen peroxide, and benzalkonium chloride, after sequential rounds of in vitro selection. Finally, cross-tolerance of different categories of biocidal formulations, their active agents, and the potential for coselection of resistance to clinically important antibiotics were investigated. Six of seven food-grade biocide formulations were bactericidal at their recommended working concentrations. All showed a reduced activity against both surface-dried and biofilm cultures. A stable phenotype of tolerance to biocide formulations could not be selected. Upon exposure of Salmonella strains to an active biocidal compound, a high-level of tolerance was selected for a number of Salmonella serotypes. No cross-tolerance to the different biocidal agents or food-grade biocide formulations was observed. Most tolerant isolates displayed changes in their patterns of susceptibility to antimicrobial compounds. Food industry biocides are effective against planktonic Salmonella. When exposed to sublethal concentrations of individual active biocidal agents, tolerant isolates may emerge. This emergence was associated with changes in antimicrobial susceptibilities.
Full-text · Article · Feb 2012 · Applied and Environmental Microbiology