1
|
Wang W, Cao Y, Li J, Lu S, Ge H, Pan S, Pan X, Wang L. The impact of osmotic stresses on the biofilm formation, immunodetection, and morphology of Aeromonas hydrophila. Microbiol Res 2023; 269:127301. [PMID: 36689842 DOI: 10.1016/j.micres.2023.127301] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 12/29/2022] [Accepted: 01/09/2023] [Indexed: 01/15/2023]
Abstract
Aeromonas hydrophila (Ah) is a zoonotic pathogen of great importance to aquaculture and human health. This study systematically evaluated the impact of salinity, sugar, ammonia nitrogen, and nitric nitrogen levels on the fitness of Ah by using Luria-Bertani (LB) broth supplemented with different concentrations of NaCl, sucrose, NH4Cl, urea, NaNO2 or NaNO3. Results showed that the static biofilm formation of Ah was higher at 28 °C compared to 37 °C (P < 0.05). At 28 °C, as the NaCl (>1 %) and sucrose levels increased, the Ah biofilm formation and the binding between Ah cells and monoclonal antibodies (mAbs, for immunodetection) decreased. Elevated ammonia nitrogen and nitric nitrogen levels generated no significant impact on Ah biofilm formation or immunodetection (P > 0.05). The expression of mAbs-targeted Omp remained unchanged under high NaCl or sucrose conditions. Further analysis showed that high sucrose conditions led to the over-expression of the extracellular polysaccharides (PS) and promoted the formation of capsule-like structures. These over-expressed PS and capsule structures might be one reason explaining the inhibited immunodetection efficacy. Results generated from this study provide crucial insights for the design of recovery and detection protocols for Ah present in food or environmental samples.
Collapse
Affiliation(s)
- Wenbin Wang
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Key Laboratory of Healthy Freshwater Aquaculture, Ministry of Agriculture and Rural Affairs; Key Laboratory of Fish Health and Nutrition of Zhejiang Province; Zhejiang Institute of Freshwater Fisheries, Huzhou, China; Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Ye Cao
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Jing Li
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Shuaichen Lu
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Hongxing Ge
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Saikun Pan
- Jiangsu Key Laboratory of Marine Bioresources and Environment, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Key Laboratory of Healthy Freshwater Aquaculture, Ministry of Agriculture and Rural Affairs; Key Laboratory of Fish Health and Nutrition of Zhejiang Province; Zhejiang Institute of Freshwater Fisheries, Huzhou, China; Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Jiangsu Ocean University, Lianyungang, Jiangsu, China; Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang, Jiangsu, China
| | - Xiaoyi Pan
- Key Laboratory of Healthy Freshwater Aquaculture, Ministry of Agriculture and Rural Affairs; Key Laboratory of Fish Health and Nutrition of Zhejiang Province; Zhejiang Institute of Freshwater Fisheries, Huzhou, China.
| | - Luxin Wang
- Department of Food Science and Technology, University of California Davis, Davis, CA 95616, USA.
| |
Collapse
|
2
|
Lee HJ, Tokle IF, Lunestad BT, Lerfall J, Hoel S, Jakobsen AN. The effect of food processing factors on the growth kinetics of Aeromonas strains isolated from ready-to-eat seafood. Int J Food Microbiol 2023; 384:109985. [DOI: 10.1016/j.ijfoodmicro.2022.109985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 10/17/2022] [Accepted: 10/18/2022] [Indexed: 11/06/2022]
|
3
|
Dong J, Yan T, Yang Q, Song Y, Cheng B, Zhou S, Liu Y, Ai X. Palmatine Inhibits the Pathogenicity of Aeromonas hydrophila by Reducing Aerolysin Expression. Foods 2022. [PMCID: PMC9601346 DOI: 10.3390/foods11203250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Aeromonas hydrophila, an opportunistic aquatic pathogen widely spread in aquatic environments, is responsible for a number of infectious diseases in freshwater aquaculture. In addition, A. hydrophila can transmit from diseased fish to humans and results in health problems. The occurrence of antibiotic-resistant bacterial strains restricts the application of antibiotics and is responsible for failure of the treatment. Moreover, residues of antibiotics in aquatic products often threaten the quality and safety. Therefore, alternative strategies are called to deal with infections caused by antibiotic-resistant bacteria. Aerolysin, one of the most important virulence factors of A. hydrophila, is adopted as a unique anti-virulence target on the basis of the anti-virulence strategy to battling infections caused by A. hydrophila. Palmatine, an isoquinoline alkaloid from a variety of herbal medicines that showed no anti-A. hydrophila activity, could reduce hemolysis of the bacterium by decreasing aerolysin production. The results of the qPCR assay demonstrated that the transcription of the aerA gene was suppressed. Moreover, cell viability and in vivo study showed that palmatine treatment could decrease the pathogenicity of A. hydrophila both in vitro and in vivo. In summary, palmatine is a leading compound against A. hydrophila-associated infection in aquaculture by inhibiting the expression of aerolysin.
Collapse
Affiliation(s)
- Jing Dong
- Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
| | - Tianhui Yan
- College of Food Science and Engineering, Bohai University, Jinzhou 121013, China
| | - Qiuhong Yang
- Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
| | - Yi Song
- Chinese Academy of Fishery Sciences, Beijing 100039, China
| | - Bo Cheng
- Chinese Academy of Fishery Sciences, Beijing 100039, China
| | - Shun Zhou
- Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
| | - Yongtao Liu
- Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
| | - Xiaohui Ai
- Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223, China
- Correspondence: ; Tel.: +86-027-81780298
| |
Collapse
|
4
|
Grilo ML, Pereira A, Sousa-Santos C, Robalo JI, Oliveira M. Climatic Alterations Influence Bacterial Growth, Biofilm Production and Antimicrobial Resistance Profiles in Aeromonas spp. Antibiotics (Basel) 2021; 10:1008. [PMID: 34439058 PMCID: PMC8389027 DOI: 10.3390/antibiotics10081008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 07/27/2021] [Accepted: 08/17/2021] [Indexed: 11/26/2022] Open
Abstract
Climate change is expected to create environmental disruptions that will impact a wide array of biota. Projections for freshwater ecosystems include severe alterations with gradients across geographical areas. Life traits in bacteria are modulated by environmental parameters, but there is still uncertainty regarding bacterial responses to changes caused by climatic alterations. In this study, we used a river water microcosm model to evaluate how Aeromonas spp., an important pathogenic and zoonotic genus ubiquitary in aquatic ecosystems, responds to environmental variations of temperature and pH as expected by future projections. Namely, we evaluated bacterial growth, biofilm production and antimicrobial resistance profiles of Aeromonas species in pure and mixed cultures. Biofilm production was significantly influenced by temperature and culture, while temperature and pH affected bacterial growth. Reversion of antimicrobial susceptibility status occurred in the majority of strains and tested antimicrobial compounds, with several combinations of temperature and pH contributing to this effect. Current results highlight the consequences that bacterial genus such as Aeromonas will experience with climatic alterations, specifically how their proliferation and virulence and phenotypic resistance expression will be modulated. Such information is fundamental to predict and prevent future outbreaks and deleterious effects that these bacterial species might have in human and animal populations.
Collapse
Affiliation(s)
- Miguel L. Grilo
- Centro de Investigação Interdisciplinar em Sanidade Animal (CIISA), Faculdade de Medicina Veterinária, Universidade de Lisboa, 1300-477 Lisbon, Portugal
- Marine and Environmental Sciences Centre (MARE), Instituto Universitário de Ciências Psicológicas, Sociais e da Vida (ISPA), 1100-304 Lisbon, Portugal; (A.P.); (C.S.-S.); (J.I.R.)
| | - Ana Pereira
- Marine and Environmental Sciences Centre (MARE), Instituto Universitário de Ciências Psicológicas, Sociais e da Vida (ISPA), 1100-304 Lisbon, Portugal; (A.P.); (C.S.-S.); (J.I.R.)
| | - Carla Sousa-Santos
- Marine and Environmental Sciences Centre (MARE), Instituto Universitário de Ciências Psicológicas, Sociais e da Vida (ISPA), 1100-304 Lisbon, Portugal; (A.P.); (C.S.-S.); (J.I.R.)
| | - Joana I. Robalo
- Marine and Environmental Sciences Centre (MARE), Instituto Universitário de Ciências Psicológicas, Sociais e da Vida (ISPA), 1100-304 Lisbon, Portugal; (A.P.); (C.S.-S.); (J.I.R.)
| | - Manuela Oliveira
- Centro de Investigação Interdisciplinar em Sanidade Animal (CIISA), Faculdade de Medicina Veterinária, Universidade de Lisboa, 1300-477 Lisbon, Portugal
| |
Collapse
|
5
|
Ahmad A, Tahir Ul Qamar M, Shoukat A, Aslam MM, Tariq M, Hakiman M, Joyia FA. The effects of genotypes and media composition on callogenesis, regeneration and cell suspension culture of chamomile ( Matricaria chamomilla L.). PeerJ 2021; 9:e11464. [PMID: 34113490 PMCID: PMC8158175 DOI: 10.7717/peerj.11464] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Accepted: 04/26/2021] [Indexed: 11/20/2022] Open
Abstract
Background Chamomile is an important herb being used widely for medicinal purposes. Its multitherapeutic, cosmetic, and nutritional values have been established through years of traditional and scientific use and research. Increased use of medicinal plants necessitates rational use as well as sustainable production of such genetic resources. Plant in vitro micro-propagation poses unique opportunities for sustainable production of medicinal herbs, their regrowth and conservation. The present study aimed to investigate the effects of different explants, plant growth regulators (PGRs) combinations and media type on callogenesis, in vitro regeneration and cell suspension of six chamomile genotypes to enhance its sustainable production. Methods The shoot, lateral sprout, and leaf derived explants of six chamomile genotypes including Isfahan, Shiraz, Kazeron, Goral, Sharokashari and Presso were used for direct and indirect regeneration. For indirect regeneration various doses of NAA and kinetin were used to induce calli which were cultured on MS media containing PGRs for direct and indirect regeneration. Later, cell suspension was established and morphological characterization of CrO3 stained cells was carried out using microscopy. Results and Discussion Our findings revealed that the highest callus percentage and callus volume were observed from lateral sprouts and shoots of genotype Isfahan on MS medium containing 1 mg/L NAA and 1 mg/L kinetin. The in vitro regeneration was found to be genotype dependent while 77% and 77.5% was the highest percentage for indirect and direct regeneration, respectively. Additionally, the maximum shoot number (two shoots/explant) and shoot length (2.22 cm) were also observed in Isfahan genotype. Cell suspension culture showed the highest fresh weight (18.59 g) and dry weight (1.707 g) with 0.75 g inoculum of the callus derived from lateral sprouts cultured on MS medium. Microscopy of CrO3 stained cells was carried on each 3rd day for 27 days that revealed larger and spongier cells in the early days as compared to final days when the cell number was greater but cell size was smaller. Conclusion The callogenesis, organogenesis, and cell suspension culture of chamomile may be genotype dependent. Hence, optimization of media ingredients and culture conditions is of utmost importance for devising tissue culture based conservation strategy of any chamomile genotype and secondary metabolite production.
Collapse
Affiliation(s)
- Aqeel Ahmad
- Faculty of Life Sciences, Department of Biotechnology, University of Central Punjab, Lahore, Pakistan
| | - Muhammad Tahir Ul Qamar
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bio resources, College of Life Sciences and Technology, Guangxi University, Nanning, China
| | - Almeera Shoukat
- Faculty of Life Sciences, Department of Biotechnology, University of Central Punjab, Lahore, Pakistan
| | - Mehtab Muhammad Aslam
- Center for Plant Water-Use and Nutrition Regulation, College of Life Sciences, Joint International Research Laboratory of Water and Nutrient in Cops, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Mohsin Tariq
- Department of Bioinformatics and Biotechnology, Government College University, Faisalabad, Faisalabad, Pakistan
| | - Mansor Hakiman
- Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, Serdang, Malaysia.,Laboratory of Sustainable Resources Management, Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, Serdang, Malaysia
| | - Faiz Ahmad Joyia
- Centre of Agricultural Biochemistry and Biotechnology (CABB), University of Agriculture Faisalabad, Faisalabad, Pakistan
| |
Collapse
|
6
|
In vitro disinfection efficacy and clinical protective effects of common disinfectants against acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio isolates in Pacific white shrimp Penaeus vannamei. J Microbiol 2020; 58:675-686. [PMID: 32720097 DOI: 10.1007/s12275-020-9537-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Revised: 06/04/2020] [Accepted: 06/16/2020] [Indexed: 10/23/2022]
Abstract
Acute hepatopancreatic necrosis disease (AHPND) is one of the most significant bacterial diseases in global shrimp culture, causing severe economic losses. In the present study, we carried out in vitro antimicrobial tests to investigate the disinfection efficacy of 14 common disinfectants toward different AHPND-causing Vibrio spp., including eight isolates of V. parahaemolyticus, four isolates of V. campbellii, and one isolate of V. owensii. Polyhexamethylene biguanidine hydrochloride (PHMB) was revealed to possess the strongest inhibitory activity. Through analyzing and evaluating the results of antimicrobial tests and acute toxicity test, we selected PHMB and hydrogen peroxide (H2O2) for further clinical protection test. Clinical manifestations indicated that both PHMB (2 mg/L and 4 mg/L) and H2O2 (12 mg/L) could effectively protect juvenile Penaeus vannamei from the infection of V. parahaemolyticus isolate Vp362 at 106 CFU/ml, and the survival rate was over 80%. When the bacterial concentration was reduced to 105 CFU/ml, 104 CFU/ml, and 103 CFU/ml, the survival rate after treated by 1 mg/L PHMB was 64.44%, 93.33%, and 100%, respectively. According to the results, PHMB and H2O2 showed a lower toxicity while a better protection activity, particularly against a lower concentration of the pathogens. Therefore, these two disinfectants are proved to be promising disinfectants that can be applied to prevent and control AHPND in shrimp culture. Moreover, the methods of this study also provided valuable information for the prevention of other important bacterial diseases and suggested a reliable means for screening potential drugs in aquaculture.
Collapse
|
7
|
Asakura H, Makino SI, Watanabe K, Tuchida Y, Kawabe M, Sakurai D. Kuma Bamboo Grass (Sasa veitchii) Extracts Exhibit Protective Effects Against Atypical Aeromonas salmonicida Infection in Goldfish (Carassius auratus). Biocontrol Sci 2020; 24:145-154. [PMID: 31527345 DOI: 10.4265/bio.24.145] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
Atypical Aeromonas salmonicida ( i.e. subsp. achromogenes and subsp. masoucida) are one of the major opportunistic pathogens that cause ulcer diseases in a variety of fishes, in which this pathogen has become a worldwide economic threat in sectors that handle of particular high-priced ornamental fishes like varicolored carp and goldfish due to appearance damages. Here we reported that the kuma bamboo grass (Sasa veitchii) extracts (KBGE) that contained a variety of fatty acids, exhibited antibacterial activity against nine Aeromonas strains including 5 atypical A. salmonicida strains. Experimental challenges with four atypical A. salmonicida strains revealed that supplementation with 375 to 750 μg/ml of the KBGE restored the survival of goldfish in coincidence of inhibition of both bacterial replication and superoxide dismutase (SOD) activity upon infection, compared with those of untreated control. Together, our data demonstrating the antibacterial effects of the plant extracts proposes its possible implication for prevention of Aeromonas infection in the ornamental fish.
Collapse
Affiliation(s)
- Hiroshi Asakura
- Division of Biomedical Food Research, National Institute of Health Sciences
| | | | | | | | | | | |
Collapse
|
8
|
John N, Vidyalakshmi VB, Hatha AAM. Effect of pH and Salinity on the Production of Extracellular Virulence Factors by Aeromonas from Food Sources. J Food Sci 2019; 84:2250-2255. [PMID: 31313323 DOI: 10.1111/1750-3841.14729] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 06/08/2019] [Accepted: 06/10/2019] [Indexed: 11/29/2022]
Abstract
The ability to produce various extracellular enzymes is considered as an important virulence feature in Aeromonas spp., in addition to producing specific virulence factors such as aerolysin and hemolysin. In this study, the effect of salinity and pH on the production of extracellular virulence factors by Aeromonas was investigated. Aeromonas was obtained from different food sources. A comparative study of the activities of extracellular enzymes secreted by these bacteria at different environmental conditions can widen our understanding on their pathogenicity. The activities of various extracellular enzymes such as amylase, gelatinase, and caseinase, which are implicated as virulence factors, were measured in vitro by calculating the enzymatic activity index (EAI) of each enzyme using standard laboratory protocols. For all enzymes, a significant change (P < 0.05) in the EAI was observed when the concentration of NaCl in the media increased from 0.5% to 3%. Among three enzymes tested, caseinase was found to be affected the most by salinity, with a significant difference in EAI when NaCl concentration in the media increased from 0.5% to 2%. Similarly, amylase was found to be affected the most by acidity. The pH values ranging from 6 to 9 did not exert any significant change in EAI of amylase; however, a pH value of 5 had a significant effect. Overall, compared to salinity, the change in pH was found to be less effective in controlling the extracellular virulence factor production in Aeromonas. PRACTICAL APPLICATIONS: The practical application is to minimize the extracellular virulence factor production by Aeromonas in food commodities by altering the salt content and pH. The results demonstrate that an increase in salinity and a decrease in pH can minimize the extracellular virulence factor production by Aeromonas spp.
Collapse
Affiliation(s)
- Nifty John
- Dept. of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Lakeside Campus, Cochin Univ. of Science and Technology, Cochin, 682 016, Kerala, India
| | - V B Vidyalakshmi
- Dept. of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Lakeside Campus, Cochin Univ. of Science and Technology, Cochin, 682 016, Kerala, India
| | - A A Mohamed Hatha
- Dept. of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Lakeside Campus, Cochin Univ. of Science and Technology, Cochin, 682 016, Kerala, India
| |
Collapse
|
9
|
Nagar V, Pansare Godambe L, Bandekar JR, Shashidhar R. Biofilm formation by Aeromonas
strains under food-related environmental stress conditions. J FOOD PROCESS PRES 2017. [DOI: 10.1111/jfpp.13182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Vandan Nagar
- Food Technology Division; Bhabha Atomic Research Centre; Mumbai 400 085 India
| | | | - Jayant R. Bandekar
- Food Technology Division; Bhabha Atomic Research Centre; Mumbai 400 085 India
| | | |
Collapse
|
10
|
Effect of starvation on survival and virulence expression of Aeromonas hydrophila from different sources. Arch Microbiol 2014; 197:431-8. [PMID: 25533849 DOI: 10.1007/s00203-014-1074-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/09/2014] [Accepted: 12/12/2014] [Indexed: 01/05/2023]
Abstract
Aeromonas hydrophila is an aquatic bacterium responsible for several human illnesses. The aim of this work was to investigate the survival ability and virulence expression of two strains from different sources (fish, strain 87 and surface water, strain LS) maintained in a seawater microcosm. The strains were analyzed for the total and viable bacterial counts, adhesion ability to Hep-2 cells and aerA gene expression by qPCR throughout the experiment (35 days). Both strains reached a putative VBNC state and lost adhesive properties but exhibited a different behavior in the expression of aerA. This could be due to the different origin of the two strains; the former adapted to a habitat rich of nutrient and the latter already used to survive in a more hostile environment. Moreover, our results indicate that the quantitative determination of aerA mRNA can be a useful indicator of virulence expression under stress conditions.
Collapse
|
11
|
Chen M, Wang W, Feng Y, Zhu X, Zhou H, Tan Z, Li X. Impact resistance of different factors on ammonia removal by heterotrophic nitrification-aerobic denitrification bacterium Aeromonas sp. HN-02. BIORESOURCE TECHNOLOGY 2014; 167:456-461. [PMID: 25006021 DOI: 10.1016/j.biortech.2014.06.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2014] [Revised: 05/31/2014] [Accepted: 06/02/2014] [Indexed: 06/03/2023]
Abstract
To give reference for the application of heterotrophic nitrification-aerobic denitrification bacteria in actual wastewater treatment, the impact resistance of extreme pH, low temperature, heavy metals and high salinity on ammonia removal by a typical heterotrophic nitrifying-aerobic denitrifying bacterium Aeromonas sp. HN-02 was investigated. The results showed that HN-02 demonstrated strong acid- and alkali-resistance. In addition, it remained active at 5°C, and the removal rates of ammonia and COD were 0.90 mg L(-1)h(-1) and 22.34 mg L(-1)h(-1), respectively. Under the same extent of immediate temperature drop, the temperature correction coefficients of ammonia, COD removal rates and cell growth rate were close. Moreover, HN-02 could survive in the solution containing 0.5 mg L(-1) Cu(2+) or 8 mg L(-1) Zn(2+), or 0.5 mg L(-1) of equivalent Cu(2+)-Zn(2+). Furthermore, efficient ammonia removal was retained at salinity below 20 g L(-1), thus it could be identified as a halotolerant bacterium. At last, stronger stress resulted in higher ΔCOD/ΔTN ratio.
Collapse
Affiliation(s)
- Maoxia Chen
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| | - Wenchao Wang
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| | - Ye Feng
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| | - Xiaohua Zhu
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| | - Houzhen Zhou
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| | - Zhouliang Tan
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China.
| | - Xudong Li
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China; Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China
| |
Collapse
|
12
|
Saejung C, Hatai K, Sanoamuang L. The in-vitro antibacterial effects of organic salts, chemical disinfectants and antibiotics against pathogens of black disease in fairy shrimp of Thailand. JOURNAL OF FISH DISEASES 2014; 37:33-41. [PMID: 24131294 DOI: 10.1111/j.1365-2761.2012.01452.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Revised: 02/09/2012] [Accepted: 02/18/2012] [Indexed: 06/02/2023]
Abstract
The antibacterial effects of organic salts, chemical disinfectants and antibiotics were evaluated on cultures of Aeromonas hydrophila C03, Aeromonas sobria C26, A. sobria C29, Aeromonas caviae C24 and Acinetobacter sp. SH-94B, the pathogens that cause black disease found in fairy shrimps (Streptocephalus sirindhornae Sanoamuang et al. (2000) and Branchinella thailandensis Sanoamuang, Saengphan & Murugan) of Thailand. The minimal inhibitory concentrations (MICs) of organic salts (sodium chloride and potassium chloride) and antibiotics (oxytetracycline dihydrate, streptomycin sulphate, kanamycin monosulphate, chloramphenicol and ampicillin) were determined using the agar-dilution method. The effect of chemical disinfectants (sodium hypochlorite and chlorine dioxide) was evaluated by exposing bacteria to different concentrations of these chemicals for different periods of time. Interestingly, all strains were intrinsically resistant to 0.25-3% sodium chloride and potassium chloride. The effect of sodium hypochlorite was greater than that of chlorine dioxide, and 5-20 μg mL(-1) of sodium hypochlorite was sufficient to inhibit the growth of these bacteria, but the exposure time varied, depending on the bacterial species. Of the antibiotics tested, chloramphenicol and oxytetracycline dihydrate completely inhibited the selected strains. Chloramphenicol showed the highest antibacterial effect against all pathogenic species--the MIC and minimal bactericidal concentration (MBC) ranged from 0.8 to 3.1 μg mL(-1) from 3.1 to 6.25 μg mL(-1), respectively. To achieve control of black disease during cultivation of fairy shrimp, data derived from this study can be used as a basis for further toxicity tests in vivo.
Collapse
Affiliation(s)
- C Saejung
- Applied Taxonomic Research Center, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand
| | | | | |
Collapse
|
13
|
Pianetti A, Battistelli M, Barbieri F, Bruscolini F, Falcieri E, Manti A, Sabatini L, Citterio B. Changes in adhesion ability of Aeromonas hydrophila during long exposure to salt stress conditions. J Appl Microbiol 2012; 113:974-82. [PMID: 22805151 DOI: 10.1111/j.1365-2672.2012.05399.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 06/29/2012] [Accepted: 07/06/2012] [Indexed: 11/27/2022]
Abstract
AIMS Stressful environmental conditions influence both bacterial growth and expression of virulence factors. In the present study, we evaluated the influence of NaCl on Aeromonas hydrophila adhesiveness at two temperatures. This agent is often involved in clinical cases; however, its pathogenic potential is still not fully understood. METHODS AND RESULTS Bacteria were grown in presence of 1·7%, 3·4%, 6·0% NaCl over a 188 day period and then reinoculated in fresh Nutrient Broth with incubation at 4 and 24°C. Bacterial adhesiveness was tested on Hep-2 cells, and specimens were processed for light, scanning and transmission electron microscopy. Adhesive capacity decreased over time with an increase in reduction percentages depending on NaCl concentrations. At 1·7% NaCl, the reduction was apparently temporary and adhesiveness rapidly recovered in revitalized bacteria, while 3·4%, 6·0% NaCl seemed to be detrimental. Normal, elongated and filamentous bacteria retained adhesiveness capability, although with reduced expression, while in spherical cells, this property seemed to be lost or dramatically reduced. CONCLUSIONS Our study shows that high osmolarity plays a significant role in adhesion inhibition, therefore having possible implications in the pathogenesis of the infections by Aer. hydrophila. SIGNIFICANCE AND IMPACT OF THE STUDY This study intends to give a contribution to a better understanding of the pathogenic role of this bacterium whose pathogenicity is still under debate.
Collapse
Affiliation(s)
- A Pianetti
- Biomolecular Sciences Department, University of Urbino Carlo Bo, Urbino, Italy.
| | | | | | | | | | | | | | | |
Collapse
|
14
|
Takahashi E, Ito H, Kobayashi H, Yamanaka H, Takeda Y, Balakrish Nair G, Arimoto S, Negishi T, Okamoto K. Production and properties of lipase of Aeromonas sobria. Microbiol Immunol 2012; 56:295-307. [PMID: 22376235 DOI: 10.1111/j.1348-0421.2012.00445.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Aeromonas have been isolated from a wide variety of aquatic environments. However the number of Aeromonas in sea water is extremely small compared to that in fresh water. In in vitro culture, Aeromonas can grow in mediums containing NaCl at a concentration of 3.0%, this concentration corresponding to that of sea water. It is unclear why the number of Aeromonas is low in sea water. Exoproteins of bacteria are thought to be important for bacterial growth and survival in the environment. Previously, the present authors have shown that mediums containing 3.0% NaCl suppress production of two proteases, serine protease and metalloprotease. In this experiment, other exoproteins whose production is influenced by the amount of NaCl in the medium were analyzed. A protein whose production is repressed in medium containing 3.0% NaCl was found and purified. Biological assay of the purified protein showed that it degrades tributyrin and hydrolyzes para-nitrophenyl-fatty acylesters. These results show that the protein is a lipase. Subsequently, the nucleotide sequence of the gene encoding the lipase was determined and the amount of mRNA of the lipase gene in the cells measured. It was found that transcription of the gene is not inhibited by NaCl in the medium. This result indicates that the lipase might be synthesized, but the folding process to become an active structure does not progress smoothly in a medium containing 3.0% NaCl.
Collapse
Affiliation(s)
- Eizo Takahashi
- Laboratory of Protein Function, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Kitaku, Okayama, Japan.
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Kakizaki E, Kozawa S, Matsuda H, Muraoka E, Uchiyama T, Sakai M, Yukawa N. In vitro study of possible microbial indicators for drowning: Salinity and types of bacterioplankton proliferating in blood. Forensic Sci Int 2011; 204:80-7. [DOI: 10.1016/j.forsciint.2010.05.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2009] [Revised: 04/20/2010] [Accepted: 05/16/2010] [Indexed: 11/24/2022]
|
16
|
Takahashi E, Kobayashi H, Yamanaka H, Nair GB, Takeda Y, Arimoto S, Negishi T, Okamoto K. Inhibition of biosynthesis of metalloprotease of Aeromonas sobria by sodium chloride in the medium. Microbiol Immunol 2010; 55:60-5. [DOI: 10.1111/j.1348-0421.2010.00282.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
17
|
Glycine betaine enhances growth of nitrogen-fixing bacteria Gluconacetobacter diazotrophicus PAL5 under saline stress conditions. Curr Microbiol 2010; 59:593-9. [PMID: 19688374 DOI: 10.1007/s00284-009-9479-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Accepted: 07/30/2009] [Indexed: 10/20/2022]
Abstract
In this study, the effect of glycine betaine as osmoprotectant compound for Gluconacetobacter diazotrophicus PAL5 was evaluated by kinetic growth parameters. Batch fermentation assays were performed employing media supplemented with different sodium chloride concentrations to simulate saline stress conditions. Salt concentrations of 50-300 mM led to decreased cell concentrations, while the maximum specific growth rates and cell productivities were reduced at concentrations above 100-mM NaCl. Salt inhibition was mainly observed in media with 200- and 300-mM NaCl, in which drastic changes in cell morphology were also noted. The addition of glycine betaine to the media showed to be efficient to counteract the salt inhibitory effect by increasing some fermentation parameters. However, the osmoprotectant was not able to revert the polymorphism promoted by higher salt concentrations.
Collapse
|
18
|
Fermentation and growth kinetic study of Aeromonas caviae under anaerobic conditions. Appl Microbiol Biotechnol 2009; 83:767-73. [DOI: 10.1007/s00253-009-1983-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2009] [Revised: 03/19/2009] [Accepted: 03/19/2009] [Indexed: 11/25/2022]
|
19
|
Pianetti A, Battistelli M, Citterio B, Parlani C, Falcieri E, Bruscolini F. Morphological changes of Aeromonas hydrophila in response to osmotic stress. Micron 2009; 40:426-33. [PMID: 19264494 DOI: 10.1016/j.micron.2009.01.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Revised: 01/27/2009] [Accepted: 01/28/2009] [Indexed: 11/17/2022]
Abstract
The adaptive response of bacteria to stressful environmental situations may lead to a modification of physiological and phenotypical characteristics, including morphology. The aim of this study was the analysis of the ultrastructural changes in Aeromonas hydrophila exposed to different NaCl concentrations (1.7%, 3.4%, 6%) at 4 and 24 degrees C for 188 days. Bacterial cultures were processed for scanning and transmission electron microscopy, and specimens were analysed at different times during osmotic stress. SEM reveals the presence of three predominant morphotypes: rod, filamentous and spherical forms, depending on the time and culture conditions. Normal rod cells prevail in 1.7% NaCl growth conditions, maintaining high rates until the end of the trial at 4 degrees C. The most favourable conditions for the elongated morphotype are 3.4% NaCl at 4 degrees C. Spherical forms appear later, increase with time and are the prevalent population at the end of the trial at 24 degrees C, in all culture conditions. TEM reveals the presence of normal, necrotic-like and apoptotic-like forms; these latter forms increase with time according to salt concentration and temperature. Initially, a detachment of the external membrane appears, with cytoplasmic clumping into small, dense masses; as the process continues, both these features become more evident with increasing salt concentrations. This behaviour has been compared to that of eukaryotic cells undergoing growth factor deprivation-induced apoptosis. Occasionally, surface blebs are observed. In conclusion, the study suggests that the exposure of A. hydrophila to stressful conditions (osmolarity, temperature and nutrients) leads to the generation of varying morphotypes, which promote cell survival in adverse conditions and a rapid repopulation in post-stress environments.
Collapse
Affiliation(s)
- A Pianetti
- Dip. di Scienze Biomolecolari, Università degli Studi di Urbino Carlo Bo, Italy.
| | | | | | | | | | | |
Collapse
|
20
|
Pianetti A, Manti A, Boi P, Citterio B, Sabatini L, Papa S, Rocchi MBL, Bruscolini F. Determination of viability of Aeromonas hydrophila in increasing concentrations of sodium chloride at different temperatures by flow cytometry and plate count technique. Int J Food Microbiol 2008; 127:252-60. [DOI: 10.1016/j.ijfoodmicro.2008.07.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2008] [Revised: 07/05/2008] [Accepted: 07/16/2008] [Indexed: 10/21/2022]
|
21
|
Khan R, Takahashi E, Ramamurthy T, Takeda Y, Okamoto K. Salt in surroundings influences the production of serine protease into milieu by Aeromonas sobria. Microbiol Immunol 2008; 51:963-76. [PMID: 17951986 DOI: 10.1111/j.1348-0421.2007.tb03993.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Previously we have shown that the open reading frame 2 protein (ORF2 protein), which is encoded at the 3 ' end of serine protease of Aeromonas sobria (ASP), functions as a chaperone protein in periplasm in the production of ASP. Both proteins, ASP and ORF2 protein, associate in periplasm and ORF2 protein helps ASP to take an active form. ASP which is dissociated from ORF2 protein emerges in milieu . In this study, we examined the effect of sodium chloride (NaCl) in medium on ASP production by A. sobria. The ASP activity of culture supernatant was extremely decreased when A. sobria was cultured in medium containing 3.0% NaCl (concentration almost equivalent to sea water salinity). Our analysis showed that the transcription of asp by A. sobria is not inhibited by NaCl in medium and that A. sobria synthesizes and releases ASP in milieu even under the condition of 3.0% NaCl. However, these ASPs in milieu formed complex as with ORF2 proteins. This indicates that the maturation pathway of ASP is disturbed in A. sobria cultured in medium containing 3.0% NaCl. It is likely that ASP does not associate with ORF2 protein in the correct form in periplasam when A. sobria is cultured in medium containing 3.0% NaCl, though both proteins, ASP and ORF2 protein, make complexes and emerge outside of the cell. This idea suggests that the chaperone system of ASP possesses the ability to sense NaCl in surroundings and regulates the production of active ASP.
Collapse
Affiliation(s)
- Rasel Khan
- Laboratory of Protein Function, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan
| | | | | | | | | |
Collapse
|
22
|
Lambert RJW, Bidlas E. An investigation of the Gamma hypothesis: A predictive modelling study of the effect of combined inhibitors (salt, pH and weak acids) on the growth of Aeromonas hydrophila. Int J Food Microbiol 2007; 115:12-28. [PMID: 17140685 DOI: 10.1016/j.ijfoodmicro.2006.10.011] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2006] [Revised: 05/29/2006] [Accepted: 10/03/2006] [Indexed: 10/23/2022]
Abstract
The Gamma hypothesis, that multiple inhibitory factors combine independently, is the underlying hypothesis for the quantification of the Hurdle concept used in food manufacture. The literature, however, is confused as to whether interactive effects exist and under which circumstances they occur, if at all. Using the method of time to detection (TTD), the inhibitory effect of pH, salt and specific weak acids (acetic, propionic, sorbic and benzoic) and combinations of these with respect to the growth of Aeromonas hydrophila (ATCC 7966) were analysed. A model based on the relative rate to detection described all combinations analysed as having independent effects on the TTD. No synergistic interactions were found between pH and salt, between pH and individual weak acids or between combinations of weak acids and pH for any of the systems under study. This study supports the validity of the Gamma concept -- that individual environmental effects act independently and should, in turn, facilitate attempts to model the growth of other microorganisms under a variety of conditions.
Collapse
Affiliation(s)
- Ronald J W Lambert
- Quality and Safety Department, Nestlé Research Centre, Vers-chez-les-Blanc, Lausanne 1000, Switzerland.
| | | |
Collapse
|
23
|
Chihib NE, Tierny Y, Mary P, Hornez JP. Adaptational changes in cellular fatty acid branching and unsaturation of Aeromonas species as a response to growth temperature and salinity. Int J Food Microbiol 2005; 102:113-9. [PMID: 15925007 DOI: 10.1016/j.ijfoodmicro.2004.12.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2003] [Revised: 07/23/2004] [Accepted: 12/30/2004] [Indexed: 11/25/2022]
Abstract
The effects of growth temperature and salinity on the cellular fatty acids were investigated on Aeromonas caviae, Aeromonas hydrophila and Aeromonas sobria. Under optimal growth conditions, fatty acids patterns were dominated by even-numbered chains C(16:0), C(16:1cis9), C(18:1cis11), C(12:0) and C(14:0). Growth temperature modifications induced, in the three Aeromonas species, important changes in fatty acid (i) unsaturation, (ii) branching and (iii) chain length. An important decrease in the C(18:1cis11) fatty acid content was observed for the three species below 15 degrees C and above 25 degrees C. The evolution of C(18:1cis11) and C(16:0) showed a mirror image for the three Aeromonas species. Low NaCl concentrations did not elicit significant changes in the fatty acids content of the three Aeromonas species. However, for high NaCl concentration in the medium, the growth ability was related to an important decrease of the unsaturated to saturated fatty acids ratio indicating a membrane rigidification. Thermal and salinity adaptations were branched fatty acid-dependent for A. caviae, whereas this phenomenon was less significant for A. hydrophila and A. sobria.
Collapse
Affiliation(s)
- Nour Eddine Chihib
- Université des Sciences et Technologies de Lille, Laboratoire de Microbiologie, Bâtiment SN2, Cité Scientifique, F-59655 Villeneuve d'Ascq Cedex, France.
| | | | | | | |
Collapse
|
24
|
Mary P, Sautour M, Chihib NE, Tierny Y, Hornez JP. Tolerance and starvation induced cross-protection against different stresses in Aeromonas hydrophila. Int J Food Microbiol 2003; 87:121-30. [PMID: 12927714 DOI: 10.1016/s0168-1605(03)00061-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Aeromonas hydrophila is sometimes considered as a controversial human pathogen and reported to be susceptible to food processing procedures and environmental stresses. In this study, we have shown that early stationary phase cells of A. hydrophila were readily killed during up shifts in temperature (in the range 50-70 degrees C), the course of drying (at relative humidity, temperature and brightness of the laboratory) and after 5 min exposure to 20%, 30% and 40% v/v ethanol. However, this bacterium was found moderately susceptible to down shift to 4 degrees C in nutrient poor water, sodium chloride stresses (1.5 and 2 M) and to 12% and 15% v/v ethanol stresses. Tolerance against 1 M NaCl and 10% v/v ethanol was observed. At ambient temperature (24.5 degrees C), this microorganism exhibited a starvation survival state, which was largely independent of the initial cell concentrations (8.82, 7.71 and 6.76 log units). The cross-protection experiments showed that cells starved for short (1 day) or prolonged (50 days) periods developed increased resistance to down shift at 4 degrees C and ethanol stress. This may be of concern to the food-processing industry from the public health perspective.
Collapse
Affiliation(s)
- Patrice Mary
- Laboratoire de Microbiologie, Université des Sciences et Technologies de Lille, Bâtiment SN2, F-59655 Villeneuve d'Ascq Cedex, France.
| | | | | | | | | |
Collapse
|
25
|
Mellefont LA, McMeekin TA, Ross T. The effect of abrupt osmotic shifts on the lag phase duration of foodborne bacteria. Int J Food Microbiol 2003; 83:281-93. [PMID: 12745233 DOI: 10.1016/s0168-1605(02)00377-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The effects of osmotic environment and inoculum history on lag times were examined. Abrupt osmotic shifts of cultures were found to induce lag phases in a variety of foodborne bacteria. Relative lag times (RLT; the ratio of lag time to generation time) were used to differentiate the effects of the shift from those of the outgrowth environment. In general, osmotic downshifts induced larger RLTs than equivalent upshifts. An observed reduction in RLT at very low a(w), however, was unexpected. For an osmotic downshift, differences were observed in the RLT response of the Gram-negative and -positive strains tested. RLTs were usually extended for Gram-negative organisms as conditions became less favourable for growth. In comparison, RLT remained relatively unaffected for Gram-positive organisms. The observations reported in this study demonstrate that lag time can be understood in terms of the amount of work to be done to adjust to new environmental conditions and the rate at which that work is done, and are consistent with known strategies for osmoregulation employed by the various organisms studied.
Collapse
Affiliation(s)
- L A Mellefont
- Centre for Food Safety and Quality, School of Agricultural Science, University of Tasmania, GPO Box 252-54, Hobart 7001, Tasmania, Australia.
| | | | | |
Collapse
|