Modeling the Growth Boundary of Staphylococcus aureus for Risk Assessment Purposes

2001 ◽  
Vol 64 (1) ◽  
pp. 51-57 ◽  
Author(s):  
CYNTHIA M. STEWART ◽  
MARTIN B. COLE ◽  
J. DAVID LEGAN ◽  
LOUISE SLADE ◽  
MARK H. VANDEVEN ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Staphylococcus Aureus ◽  
Brain Heart Infusion ◽  
Toxin Production ◽  
Potassium Sorbate ◽  
Growth Responses ◽  
Microtiter Plates ◽  
Initial Ph ◽  
Data Points ◽  
Boundary Model

Knowing the precise boundary for growth of Staphylococcus aureus is critical for food safety risk assessment, especially in the formulation of safe, shelf-stable foods with intermediate relative humidity (RH) values. To date, most studies and resulting models have led to the presumption that S. aureus is osmotolerant. However, most studies and resulting models have focused on growth kinetics using NaCl as the humectant. In this study, glycerol was used to investigate the effects of a glass-forming nonionic humectant to avoid specific metabolic aspects of membrane ion transport. The experiments were designed to produce a growth boundary model as a tool for risk assessment. The statistical effects and interactions of RH (84 to 95% adjusted by glycerol), initial pH (4.5 to 7.0 adjusted by HCl), and potassium sorbate (0, 500, or 1,000 ppm) or calcium propionate (0, 500, or 1,000 ppm) on the aerobic growth of a five-strain S. aureus cocktail in brain heart infusion broth were explored. Inoculated broths were distributed into microtiter plates and incubated at 37°C over appropriate saturated salt slurries to maintain RH. Growth was monitored by turbidity during a 24-week period. Toxin production was explored by enterotoxin assay. The 1,280 generated data points were analyzed by SAS LIFEREG procedures, which showed all studied parameters significantly affected the growth responses of S. aureus with interactions between RH and pH. The resulting growth/no growth boundary is presented.

scholarly journals Staphylococcus aureus Growth Boundaries: Moving towards Mechanistic Predictive Models Based on Solute-Specific Effects

2002 ◽  
Vol 68 (4) ◽  
pp. 1864-1871 ◽  
Author(s):  
Cynthia M. Stewart ◽  
Martin B. Cole ◽  
J. David Legan ◽  
Louise Slade ◽  
Mark H. Vandeven ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Staphylococcus Aureus ◽  
Food Safety ◽  
Safety Issue ◽  
Toxin Production ◽  
Survival Models ◽  
Potassium Sorbate ◽  
Growth Responses ◽  
Growth Interface ◽  
Ph Values

ABSTRACT The formulation of shelf-stable intermediate-moisture products is a critical food safety issue. Therefore, knowing the precise boundary for the growth-no-growth interface of Staphylococcus aureus is necessary for food safety risk assessment. This study was designed to examine the effects of various humectants and to produce growth boundary models as tools for risk assessment. The molecular mobility and the effects of various physical properties of humectants, such as their glass transition temperatures, their membrane permeability, and their ionic and nonionic properties, on S. aureus growth were investigated. The effects of relative humidity (RH; 84 to 95%, adjusted by sucrose plus fructose, glycerol, or NaCl), initial pH (4.5 to 7.0, adjusted by HCl), and potassium sorbate concentration (0 or 1,000 ppm) on the growth of S. aureus were determined. Growth was monitored by turbidity over a 24-week period. Toxin production was determined by enterotoxin assay. The 1,792 data points generated were analyzed by LIFEREG procedures (SAS Institute, Inc., Cary, N.C.), which showed that all parameters studied significantly affected the growth responses of S. aureus. Differences were observed in the growth-no-growth boundary when different humectants were used to achieve the desired RH values in both the absence and the presence of potassium sorbate. Sucrose plus fructose was most inhibitory at neutral pH values, while NaCl was most inhibitory at low pH values. The addition of potassium sorbate greatly increased the no-growth regions, particularly when pH was <6.0. Published kinetic growth and survival models were compared with boundary models developed in this work. The effects of solutes and differences in modeling approaches are discussed.

scholarly journals Optimum cultural conditions to achieve the best biofilm formation and high level icaA transcription by Staphylococcus aureus

2021 ◽  
Author(s):  
Aram Sharifi ◽  
Abdolmajid Mohammadzadeh ◽  
Pezhman Mahmoodi ◽  
Taghi Zahraei Salehi
Keyword(s):  
Staphylococcus Aureus ◽  
Biofilm Formation ◽  
Culture Media ◽  
Brain Heart Infusion ◽  
Microtiter Plate ◽  
Broth Culture ◽  
Microtiter Plates ◽  
Cultural Conditions ◽  
Slime Layer ◽  
High Level

Abstract Background The aim of this study was to investigate the influences of different broth culture media supplemented with glucose, on the biofilm formation and ica expression of Staphylococcus aureus. The phenotypic ability to adhere to a polystyrene surface and to produce slime layer were evaluated using microtiter plate test (MtP) and Congo red tube test, respectively. Using PCR, the presence of ica locus in S. aureus strains was confirmed and subsequently, quantitative real-time RT-PCR was performed to investigate transcription of icaA in various media including Tryptic soy broth (TSB), Brain-heart infusion broth (BHIB), (Nutrient broth) NB and (Muller-Hinton broth) MHB contained 0, 0.25, 0.5, 1 and 2% glucose. Results Our results showed that although all of the studied strains adhered to the wells of polystyrene microtiter plates, the optimum rate of biofilm formation was observed for TSB medium contained 1% glucose, but biofilm formation was not significantly different in NB, MHB and BHIB media. Supplementation of all media with 1% glucose led to the highest production of biofilm formation and in all of media transcription of icaA was increased with glucose addition to one present. Conclusions The results of the present study indicated that TSB medium supplemented with 1% glucose was the most appropriate medium for evaluation of biofilm formation by S. aureus isolates.

Modeling the Aerobic Growth and Decline of Staphylococcus aureus as Affected by pH and Potassium Sorbate Concentration

1999 ◽  
Vol 62 (4) ◽  
pp. 356-362 ◽  
Author(s):  
LEDA GIANNUZZI ◽  
EDGARDO CONTRERAS ◽  
NOEMI ZARITZKY
Keyword(s):  
Staphylococcus Aureus ◽  
Incubation Temperature ◽  
Growth Parameters ◽  
Brain Heart Infusion ◽  
Gompertz Model ◽  
Potassium Sorbate ◽  
Aerobic Growth ◽  
Treatment Conditions ◽  
Effects Of Ph ◽  
Sorbate Concentration

The effects of pH (5.0, 5.2, 5.4, 5.6, and 5,8) and concentration of potassium sorbate (10.0 and 16.6 mM) at two water activity values (0.90 and 0.92) on the aerobic growth and decline of Staphylococcus aureus ATCC 6538P, 196-E, and FDA-C243 were studied using brain-heart infusion broth. The inoculum was approximately 4 to 5 log CFU/ml, and the incubation temperature was 30°C. Samples were periodically enumerated on tryptic soy agar. The Gompertz model was used to obtain microbial growth parameters, specific growth rate was obtained as a derived parameter, and the inhibition index was calculated. A linear model was fitted in cases of bacteriostatic or bactericidal action of the treatment. The ATCC 6538P strain showed the highest resistance in the range of tested conditions. Microbial behavior was modeled considering the main controlling factors, and a response surface methodology was used to determine the effects of undissociated acid concentration and pH. These results can be used to establish treatment conditions for microorganism growth or inhibition.

Staphylococcus aureus Growth and Enterotoxin A Production in an Anaerobic Environment

2002 ◽  
Vol 65 (1) ◽  
pp. 199-204 ◽  
Author(s):  
NEGASH BELAY ◽  
AVRAHAM RASOOLY
Keyword(s):  
Staphylococcus Aureus ◽  
Cell Density ◽  
Incubation Temperature ◽  
Food Poisoning ◽  
Brain Heart Infusion ◽  
Toxin Production ◽  
Anaerobic Growth ◽  
Anaerobic Conditions ◽  
Effects Of Temperature ◽  
Anaerobic Environment

The effects of strict anaerobic conditions on the growth of Staphylococcus aureus and the production of staphylococcal enterotoxin A (SEA) were studied. The growth of S. aureus, a facultative anaerobic bacterium, is slower anaerobically than aerobically. When grown on brain heart infusion broth at 37°C, the anaerobic generation time at mid-log phase was 80 min, compared with 35 min for the aerobic control. In contrast to previous studies demonstrating that staphylococcal cell density was 9- to 17-fold greater in aerobic than in anaerobic cultures, data for a staphylococcal strain implicated in food poisoning showed that the cell density was only two to three times as great in aerobic cultures. Production of SEA was monitored by Western immunoblotting and shown to be growth dependent. With slower anaerobic growth, relatively less toxin was produced than under aerobic conditions, but in both cases SEA was detected after 120 min of incubation. The combined effects of temperature and aeration on S. aureus were also studied. Growth and toxin production of aerobic and anaerobic cultures at temperatures ranging from 14 to 37°C were analyzed. Growth was still observed at low temperatures in both environments. A linear model for S. aureus aerobic or anaerobic growth as a function of incubation temperature was developed from these studies. The model was tested from 17 to 35.5°C, and the results suggest that the model can accurately predict the S. aureus growth rate in this temperature range. The data suggest that anaerobic conditions are not an effective barrier against S. aureus growth.

scholarly journals Screening for Intermediately Vancomycin-Susceptible and Vancomycin-Heteroresistant Staphylococcus aureus by Use of Vancomycin-Supplemented Brain Heart Infusion Agar Biplates: Defining Growth Interpretation Criteria Based on Gold Standard Confirmation

2015 ◽  
Vol 53 (11) ◽  
pp. 3543-3546 ◽  
Author(s):  
Riad Khatib ◽  
Kathleen Riederer ◽  
Mamta Sharma ◽  
Stephen Shemes ◽  
Sugantha P. Iyer ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Gold Standard ◽  
Population Analysis ◽  
Area Under The Curve ◽  
Brain Heart Infusion ◽  
Roc Curves ◽  
Clinical Samples ◽  
Content Type ◽  
Interpretation Criteria ◽  
Profile Area

BHI agars supplemented with vancomycin 4 (BHI-V4) and 3 (BHI-V3) mg/liter have been proposed for screening vancomycin intermediately susceptibleStaphylococcus aureus(VISA) and heteroresistant (hVISA) phenotypes, respectively, but growth interpretation criteria have not been established. We reviewed the growth results (CFU) during population analysis profile-area under the curve (PAP-AUC) of consecutive methicillin-resistantStaphylococcus aureus(MRSA) blood isolates, which were saved intermittently between 1996 and 2012. CFU counts on BHI-V4 and BHI-V3 plates were stratified according to PAP-AUC interpretive criteria: <0.90 (susceptible [S-MRSA]), 0.90 to 1.3 (hVISA), and >1.3 (VISA). CFU cutoffs that best predict VISA and hVISA were determined with the use of receiver operating characteristic (ROC) curves. Mu3, Mu50, and methicillin-susceptibleS. aureus(MSSA) controls were included. We also prospectively evaluated manufacturer-made BHI-V3/BHI-V4 biplates for screening of 2010-2012 isolates. The PAP-AUC of 616 clinical samples was consistent with S-MRSA, hVISA, and VISA in 550 (89.3%), 48 (7.8%), and 18 (2.9%) instances, respectively. For VISA screening on BHI-V4, a cutoff of 2 CFU/droplet provided 100% sensitivity and 97.7% specificity. To distinguish VISA from hVISA, a cutoff of 16 CFU provided 83.3% sensitivity and 94.7% specificity; the specificity was lowered to 89.5% with a 12-CFU cutoff. For detecting hVISA/VISA on BHI-V3, a 2-CFU/droplet cutoff provided 98.5% sensitivity and 93.8% specificity. These results suggest that 2-CFU/droplet cutoffs on BHI-V4 and BHI-V3 best approximate VISA and hVISA gold standard confirmation, respectively, with minimal overlap in samples with borderline PAP-AUC. Simultaneous screening for VISA/hVISA on manufacturer-made BHI-V4/BHI-V3 biplates is easy to standardize and may reduce the requirement for PAP-AUC confirmation.

Statistical Analysis of Avian Reproduction Studies

2021 ◽  
Author(s):  
John W Green ◽  
Manousos Foudoulakis ◽  
Timothy Fredricks ◽  
Tiffany Carro ◽  
Jonathan Maul ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Study Design ◽  
Model Averaging ◽  
Study Data ◽  
Design Elements ◽  
Avian Reproduction ◽  
Reproduction Study ◽  
Data Points ◽  
Set Up ◽  
Regulatory Risk Assessment

Abstract Avian reproduction studies for regulatory risk assessment are undergoing review by regulatory authorities, often leading to requests for statistical re-analysis of older studies using newer methods, sometimes with older study data that do not support these newer methods. We propose detailed statistical protocols with updated statistical methodology for use with both new and older studies and recommend improvements in experimental study design to set-up future studies for robust statistical analyses. There is increased regulatory and industry attention to the potential use of benchmark dose (BMD) methodology to derive the point of departure in avian reproduction studies, to be used as the endpoint in regulatory risk assessment. We present benefits and limitations of this BMD approach for older studies being re-evaluated and for new studies designed for with BMD analysis anticipated. Model averaging is recommended as preferable to model selection for BMD analysis. Even for a new study following the modified experimental design analyses with BMD methodology will only be possible for a restricted set of response variables. The judicious use of historical control data, identification of outlier data points, increased use of distributions more consistent with the nature of the data collected as opposed to forcing normality-based methods, and trend-based hypothesis tests are shown to be effective for many studies, but limitations on their applicability are also recognized and explained. Updated statistical methodologies are illustrated with case studies conducted under existing regulatory guidelines that have been submitted for product registrations. Through the adoption of improved avian reproduction study design elements combined with the suggested revised statistical methodologies the conduct, analyses, and utility of avian reproduction studies for avian risk assessments can be improved.

Toxin Production by Psychrotrophic Bacillus spp. Present in Milk

1990 ◽  
Vol 53 (9) ◽  
pp. 790-792 ◽  
Author(s):  
M. W. GRIFFITHS
Keyword(s):  
Bacillus Cereus ◽  
Brain Heart Infusion ◽  
Bacterial Count ◽  
Toxin Production ◽  
Latex Agglutination ◽  
Brain Heart Infusion Broth ◽  
Agglutination Assay ◽  
Bacillus Spp ◽  
Latex Agglutination Assay

Using a reversed passive latex agglutination assay, about 85% of psychrotrophic Bacillus spp. tested were shown to produce diarrhoegenic toxin during growth on brain heart infusion broth at 25°C. The majority of these strains were identified as Bacillus cereus or cereus-related strains. However, a number of other species was capable of synthesizing the toxin. Further investigation of four psychrotrophic Bacilli showed that the toxin was produced during growth in milk at temperatures ranging from 6 to 21°C. Toxin production increased with increasing temperatures and was not synthesized in appreciable quantities until the bacterial count exceeded 1 × 107 cfu/ml.

scholarly journals Prevalence of Methicillin-Resistant Staphylococcus aureus on Paper Currency Notes

2021 ◽  
pp. 25-32
Author(s):  
Rikhi Ram Marasini ◽  
Pratikshya Shrestha ◽  
Prabhat Dhakal ◽  
Sukra Raj Shrestha ◽  
Sirjana Adhikari ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Brain Heart Infusion ◽  
Biochemical Tests ◽  
Mannitol Salt Agar ◽  
Methicillin Resistant ◽  
Total Prevalence ◽  
Paper Currency ◽  
Antibiotic Susceptibility Test ◽  
Hygiene Measures

The main objective of this study was to determine the prevalence of Methicillin Resistant Staphylococcus aureus (MRSA) in paper currency. The paper currencies in circulation in Pokhara Metropolitan City were inspected. Bills of various denominations (Rs 5, 10, 20, 50, 100, 500 and 1000) were collected from five different locations; namely Food and Vegetable Shop, Bus conductor, Hospital Pharmacy, Butcher Shop and Grocery Shop. Collected sample were cultured and incubated for 24 hours at 37 oC in Brain Heart Infusion (BHI) Broth. The inoculums were further cultured on Mannitol Salt Agar (MSA) and Blood Agar (BA) media to obtain colonies, which were examined and evaluated for various parameters like gram staining and biochemical tests for identification. Then, antibiotic susceptibility test of the isolates was performed using standard procedures. A total of 35 sample of paper currency were processed, all of which showed positive growth. Out of 86 total isolates, 21 (24.42%) were Staphylococcus aureus followed by Coagulase Negative Staphylococci 19 (22.09%), Diptheroids 14 (16.3%), Bacillus spp 13 (15.11%), Micrococci 9 (10.46%), Streptococcus pneumonia 4 (4.65%), Viridans Streptococcus 4 (4.65%) and Streptococcus pyogenes 2 (2.32%). The total prevalence of MRSA in this study was 7 (33.33%). Paper currency contaminated with MRSA poses a high threat to those handling the bills as well as the community. Thus, this study suggests proper hygiene measures to be adopted after handling of paper currency to minimize the risk of contamination and emergence of diseases.

scholarly journals Quantitative Health Risk Assessment of Wastewater Treatment Plant Worker Exposed to Staphylococcus Aureus Bioaerosol During Warm and Cold Periods: Disease Burden and Sensitivity Analysis

2021 ◽  
Author(s):  
Jia-xin Ma ◽  
Bei-bei Cui ◽  
Man-li Liu ◽  
Jie Yuan ◽  
Cheng Yan
Keyword(s):  
Risk Assessment ◽  
Staphylococcus Aureus ◽  
Sensitivity Analysis ◽  
Wastewater Treatment ◽  
Health Risk ◽  
Disease Burden ◽  
Quantitative Estimation ◽  
Ingestion Rate ◽  
Treatment Plant ◽  
Quantitative Microbial Risk Assessment

Abstract Biological treatment in wastewater treatment plants (WWTPs) releases high amounts of bioaerosols carrying a variety of pathogens. Quantitative microbial risk assessment (QMRA) is a framework prevalently intended for the quantitative estimation of health risks for occupational exposure scenarios (e.g. in WWTPs). However, the quantitative contributions of health-risk-estimate inputted variable parameters remain ambiguous. Therefore, this research aimed to study the disease burden of workers exposed to Staphylococcus aureus bioaerosol during warm and cold periods and to strictly quantify the contributions of the inputted parameters of disease burden by sensitivity analysis based on Monte Carlo simulation. The results showed that the disease health risk burden in the warm period was higher than in the cold period, disease health risk burden in the rotating-disc aeration mode was regularly higher than in the microporous aeration mode. The disease health risk burden of the workers with personal protective equipment (PPE) almost all satisfied the WHO benchmark (≤10E-6 DALYs pppy), and was consistently lower by one or two orders of magnitude than the workers without PPE in both warm and cold periods. Referring to the sensitivity analysis, exposure concentration and aerosol ingestion rate were the most and second predominant factor for the estimated risk in all exposure scenarios, respectively. The sensitivity of the removal fraction by employing PPE ranked third in the contribution to disease health risk burden. In addition, no remarkable differences were revealed in the sensitivity percentage ratio between warm and cold periods. This research can deepen the understanding of the QMRA framework and promote the development of sensitivity analysis, especially under various meteorological conditions (warm and cold periods).

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