Initial Bacterial Numbers Research Articles

Hyperarid soil microbial community response to simulated rainfall.

The exceptionally long and protracted aridity in the Atacama Desert (AD), Chile, provides an extreme, terrestrial ecosystem that is ideal for studying microbial community dynamics under hyperarid conditions. Our aim was to characterize the temporal response of hyperarid soil AD microbial communities to ex situ simulated rainfall (5% g water/g dry soil for 4 weeks) without nutrient amendment. We conducted replicated microcosm experiments with surface soils from two previously well-characterized AD hyperarid locations near Yungay at 1242 and 1609 masl (YUN1242 and YUN1609) with distinct microbial community compositions and average soil relative humidity levels of 21 and 17%, respectively. The bacterial and archaeal response to soil wetting was evaluated by 16S rRNA gene qPCR, and amplicon sequencing. Initial YUN1242 bacterial and archaeal 16S rRNA gene copy numbers were significantly higher than for YUN1609. Over the next 4 weeks, qPCR results showed significant increases in viable bacterial abundance, whereas archaeal abundance decreased. Both communities were dominated by 10 prokaryotic phyla (Actinobacteriota, Proteobacteria, Chloroflexota, Gemmatimonadota, Firmicutes, Bacteroidota, Planctomycetota, Nitrospirota, Cyanobacteriota, and Crenarchaeota) but there were significant site differences in the relative abundances of Gemmatimonadota and Chloroflexota, and specific actinobacterial orders. The response to simulated rainfall was distinct for the two communities. The actinobacterial taxa in the YUN1242 community showed rapid changes while the same taxa in the YUN1609 community remained relatively stable until day 30. Analysis of inferred function of the YUN1242 microbiome response implied an increase in the relative abundance of known spore-forming taxa with the capacity for mixotrophy at the expense of more oligotrophic taxa, whereas the YUN1609 community retained a stable profile of oligotrophic, facultative chemolithoautotrophic and mixotrophic taxa. These results indicate that bacterial communities in extreme hyperarid soils have the capacity for growth in response to simulated rainfall; however, historic variations in long-term hyperaridity exposure produce communities with distinct putative metabolic capacities.

Characterization of the Bacteriophage vB_VorS-PVo5 Infection on Vibrio ordalii: A Model for Phage-Bacteria Adsorption in Aquatic Environments.

A mathematical first-order difference equation was designed to predict the dynamics of the phage-bacterium adsorption process in aquatic environments, under laboratory conditions. Our model requires knowledge of bacteria and bacteriophage concentrations and the measurements of bacterial size and velocity to predict both the number of bacteriophages adsorbed onto their bacterial host and the number of infected bacteria in a given specific time. It does not require data from previously performed adhesion experiments. The predictions generated by our model were validated in laboratory. Our model was initially conceived as an estimator for the effectiveness of the inoculation of phages as antibacterial therapy for aquaculture, is also suitable for a wide range of potential applications.

Female immunity in response to sexually transmitted opportunistic bacteria in the common bedbug Cimex lectularius

Besides typical sexually transmitted microbes, even environmental, opportunistic microbes have been found in copulatory organs of insects and even humans. To date, only one study has experimentally investigated the sexual transmission of opportunistic microbes from male to female insects, whereas nothing is known about the transmission from females to males. Even if opportunistic microbes do not cause infection upon transmission, they might eventually become harmful if they multiply inside the female. While the immune system of females is often assumed to target sexually transmitted microbes, most studies ignore the role of mating-associated opportunistic microbes. Variation in immunity between populations has been linked to parasite or bacteria prevalence but no study has ever addressed between-population differences in immune responses to sexually transmitted opportunistic microbes. We here show that bacteria applied to the copulatory organs of common bedbugs, Cimex lectularius, are sexually transmitted to the opposite sex at a high rate, including the transmission from female to male. Bacterial growth in the female sperm-receiving organ was inhibited over the first hours after introduction, but after this initial inhibition bacterial numbers increased, suggesting a shift of investment from immune defence towards reproduction. However, 24 h after the injection of bacteria, male components, or saline as a control, the sperm-receiving organ showed lysozyme-like activity and inhibited the growth of Gram-negative and Gram-positive bacteria in vitro, potentially to mop up the remaining bacteria. Contrasting our prediction, neither bacterial growth nor immune responses differed between populations. Future studies should link transmission dynamics, immune responses and fitness effects in both sexes. Experimental manipulation of environmental bacteria could be used to investigate how transmission frequency and toxicity of sexually transmitted opportunistic microbes shapes bacteria clearance and immune responses across populations.

Hygienic properties exhibited by single-use wood and plastic packaging on the microbial stability for fish

In the present study, wooden (pine and poplar) and plastic (high-density polyethylene -HDPE- and expanded polystyrene -EPS-) materials were evaluated to assess hygienic properties. Three types of studies were carried out: evaluation of the natural microorganisms present in the materials, antibacterial efficacy tests against Staphylococcus aureus and cross-contamination tests using boxes of different materials in contact with two distinct fish species. Results showed that different materials presented natural microbial load. HDPE and EPS did not present antibacterial properties, showing an increase in S. aureus counts of 0.7 Log CFU cm−2 and 1.2 Log CFU cm−2, respectively. In contrast, poplar wood reduced the initial bacterial numbers by 0.1 Log CFU cm−2, and pine wood was able to significantly reduce S. aureus initial bacterial load by 2.84 Log CFU cm−2 (P < 0.05), presenting the higher antibacterial activity. Through studying the cross-contamination between wooden and plastic boxes and the fish product, it was indicated that wood does not affect fish quality or safety, as microbial counts decreased after they were in contact with the fish products for seven days. Based on the results obtained, single-use wood packaging is a hygienic option and highly recommended for fish product transportation.

Deterministic models of inhalational anthrax in New Zealand white rabbits.

Computational models describing bacterial kinetics were developed for inhalational anthrax in New Zealand white (NZW) rabbits following inhalation of Ames strain B. anthracis. The data used to parameterize the models included bacterial numbers in the airways, lung tissue, draining lymph nodes, and blood. Initial bacterial numbers were deposited spore dose. The first model was a single exponential ordinary differential equation (ODE) with 3 rate parameters that described mucociliated (physical) clearance, immune clearance (bacterial killing), and bacterial growth. At 36 hours postexposure, the ODE model predicted 1.7×10⁷ bacteria in the rabbit, which agreed well with data from actual experiments (4.0×10⁷ bacteria at 36 hours). Next, building on the single ODE model, a physiological-based biokinetic (PBBK) compartmentalized model was developed in which 1 physiological compartment was the lumen of the airways and the other was the rabbit body (lung tissue, lymph nodes, blood). The 2 compartments were connected with a parameter describing transport of bacteria from the airways into the body. The PBBK model predicted 4.9×10⁷ bacteria in the body at 36 hours, and by 45 hours the model showed all clearance mechanisms were saturated, suggesting the rabbit would quickly succumb to the infection. As with the ODE model, the PBBK model results agreed well with laboratory observations. These data are discussed along with the need for and potential application of the models in risk assessment, drug development, and as a general aid to the experimentalist studying inhalational anthrax.

Responses of feeding prebiotics on nutrient digestibility, faecal microbiota composition and short-chain fatty acid concentrations in dogs: a meta-analysis

The effects of prebiotics on digestibility, short-chain fatty acid (SCFA) concentrations and bacterial populations in the faeces and immunity in dogs were evaluated by meta-analyses. Overall, data from 15 published studies containing 65 different treatment means of 418 observations from different breeds of dogs were included in the data set. Feeding of prebiotics to dogs did not affect the nutrient intake (P > 0.10), nor did prebiotics change (P > 0.10) the digestibility of dry matter (DM) and fat. However, crude protein (CP) digestibility tended to decrease quadratically (P = 0.06) with increasing dosages of prebiotics, although the degree of prediction was low (R2 = 0.33). The concentration of total SCFA (P = 0.08; R2 = 0.90) tended to increase linearly, whereas concentration of acetate (R2 = 0.25), propionate (R2 = 0.88) and butyrate (R2 = 0.85) increased quadratically with increasing dosage of prebiotics in the faeces of dogs. The numbers of beneficial bifidobacteria (P < 0.01; R2 = 0.62) increased quadratically, but lactobacilli (P < 0.01; R2 = 0.66) increased linearly with increasing supplementation of prebiotics. The changes in healthy bacterial numbers were affected by the interaction of initial bacterial numbers and dose of prebiotics; bacterial numbers increased relatively more when initial bacterial numbers were low. Dietary composition did not influence the response of prebiotics on lactobacilli and bifidobacterial numbers in this study. The numbers of pathogenic Clostridium perfringens and Escherichia coli were not affected by prebiotics. Prebiotics did not affect the serum immunoglobulin (Ig) concentrations such as IgG, IgA and IgM in dogs. Although prebiotics may tend to have an adverse effect on CP digestibility, prebiotics at doses up to 1.40% food intake (DM basis) might increase the beneficial bacterial populations and SCFA concentrations in the faeces of dogs. Thus, the feeding of prebiotics has a great prospective to improve the intestinal health of dogs.

Parenteral lipids impair pneumococcal elimination by human neutrophils

Lipid-induced modulation of phagocyte function seems to contribute to increased susceptibility to infections in patients on parenteral nutrition, and an increased risk for development of pneumonia has been observed in this group. The role of various structurally different lipid emulsions, however, remains unclear. In this study, we therefore assessed phagocyte function, as the capacity of neutrophils to eliminate Streptococcus pneumoniae (i.e. combined result of phagocytosis and killing), in the presence of these lipids. Neutrophils from six healthy volunteers were incubated for 1 h in emulsions (5 mmol L(-1)) derived from soybean- (LCT), fish- (VLCT), olive- (LCT-MUFA), mixed soybean/coconut oils (LCT/MCTs) or structured lipids (SL). After opsonization of the pneumococci (strain OREP-4) by human immunoglobulins, bacteria and neutrophils were incubated in the presence of complement. Next, pneumococcal elimination was evaluated and expressed as the percentage of bacteria eliminated relative to the initial bacterial numbers in neutrophil-free samples. Neutrophils that were not exposed to lipids showed a pneumococcal elimination capacity of 75 +/- 3% (mean +/- SD). This significantly decreased after exposure to LCT-MUFA (70 +/- 6%), VLCT (67 +/- 2%), SL (63 +/- 9%), LCT (66 +/- 10%) and LCT/MCT (47 +/- 15%). These data demonstrate that parenteral lipids impair the microbial elimination capacity of neutrophils in a structure-dependent manner. In accordance with our previously reported in vitro effect on a range of phagocyte functions, LCT/MCT is by far the most potent in this respect.

Monitoring bacterial indicators and pathogens in cattle feedlot waste by real-time PCR

Quantitative microbial health risk assessment requires accurate enumeration of pathogens in hazard-containing matrices as part of the risk characterization process. As part of a risk management-oriented study of cattle feedlot waste contaminants, we investigated the utility of quantitative real-time PCR (qPCR) for surveying the microbial constituents of different faecal wastes. The abundance of Escherichia coli and enterococci were first estimated in five cattle feedlot waste types from five localities. Bacteria were quantified using two culture methods and compared to the number of genome copies detected by qPCR targeted at E. coli and Enterococcus faecalis. Bacterial numbers detected in the different wastes (fresh faeces, pen manure, aged manure, composted manure, carcass manure compost) ranged from 10− 7 to 10 2 g −1 (dry weight). Both indicator groups were detected by qPCR with a comparable sensitivity to culture methods across this range. qPCR measurements of E. coli and E. faecalis correlated well with MPN and spread plate data. As a second comparison, we inoculated green fluorescent protein (GFP) labeled reference bacteria into manure samples. GFP labeled E. coli and Listeria monocytogenes were detected by qPCR in concentrations corresponding to between 18% and 71% of the initial bacterial numbers, compared to only 2.5–16% by plating. Our results supported our selection of qPCR as a fast, accurate and reliable system for surveying the presence and abundance of pathogens in cattle waste.

Involvement of Cell Surface Structures in Size-Independent Grazing Resistance of Freshwater Actinobacteria

We compared the influences of grazing by the bacterivorous nanoflagellate Poterioochromonas sp. strain DS on ultramicrobacterial Actinobacteria affiliated with the Luna-2 cluster and ultramicrobacterial Betaproteobacteria of the species Polynucleobacter cosmopolitanus. These bacteria were almost identical in size (<0.1 microm(3)) and shape. Predation on a Polynucleobacter strain resulted in a reduction of >86% relative to the initial bacterial cell numbers within 20 days, while in comparable predation experiments with nine actinobacterial strains, no significant decrease of cell numbers by predation was observed over the period of >or=39 days. The differences in predation mortality between the actinobacterial strains and the Polynucleobacter strain clearly demonstrated size-independent grazing resistance for the investigated Actinobacteria. Importantly, this size-independent grazing resistance is shared by all nine investigated Luna-2 strains and thus represents a group-specific trait. We investigated if an S-layer, previously observed in an ultrastructure study, was responsible for the grazing resistance of these strains. Experiments aiming for removal of the S-layer or modification of cell surface proteins of one of the grazing-resistant strains by treatment with lithium chloride, EDTA, or formaldehyde resulted in 4.2- to 5.2-fold higher grazing rates in comparison to the levels for untreated cells. These results indicate the protective role of a proteinaceous cell surface structure in the size-independent grazing resistance of the actinobacterial Luna-2 strains, which can be regarded as a group-specific trait.

Monitoring of microbial souring in chemically treated, produced-water biofilm systems using molecular techniques

The identification of bacteria in oil production facilities has previously been based on culture techniques. However, cultivation of bacteria from these often-extreme environments can lead to errors in identifying the microbial community members. In this study, molecular techniques including fluorescence in situ hybridization, PCR, denaturing gradient gel electrophoresis, and sequencing were used to track changes in bacterial biofilm populations treated with nitrate, nitrite, or nitrate+molybdate as agents for the control of sulfide production. Results indicated that nitrite and nitrate+molybdate reduced sulfide production, while nitrate alone had no effect on sulfide generation. No long-term effect on sulfide production was observed. Initial sulfate-reducing bacterial numbers were not influenced by the chemical treatments, although a significant increase in sulfate-reducing bacteria was observed after termination of the treatments. Molecular analysis showed a diverse bacterial population, but no major shifts in the population due to treatment effects were observed.

Efficacy of Egg Cleaning Compounds on Eggshells Contaminated with Salmonella enterica Serovar Enteritidis

Salmonella Enteritidis infections of egg contents can be related to external contamination of the shell. In this study, the efficacy of three commercial cleaning and/or sanitizing compounds (sodium carbonate, sodium hypochlorite, and potassium hydroxide) was evaluated for bactericidal activity at pH values of 10, 11, and 12 against various concentrations (102, 104, or 106 CFU/ml) of Salmonella Enteritidis inoculated onto the eggshell surface. Efficacy of these chemical agents was also assessed against Salmonella Enteritidis in aqueous suspension. Our results indicated that none of the chemicals applied at the recommended manufacturer's concentrations (sodium carbonate, 36 ppm; other treatments, 200 ppm) could eliminate Salmonella Enteritidis from eggshells artificially contaminated with the highest bacterial concentrations (104 or 106 CFU/ml). Higher concentrations of each product, at least 5 to 20 times greater than recommended doses, were needed to destroy the bacteria on egg surfaces. However, at or slightly above the manufacturer's recommended use concentrations, all three formulations were effective against Salmonella Enteritidis in aqueous suspension (108 CFU/ml) or on eggshells contaminated with 102 CFU/ml. For both shell and suspension assays, inactivation of Salmonella Enteritidis occurred at lower concentrations at pH 12 than at pH 11 and pH 10. Contact time between chemicals and Salmonella apparently influenced bacterial inactivation. Extended contact times (2 to 10 min) reduced minimum chemical concentrations necessary to inactivate the bacteria. However, neither pH nor contact time influenced Salmonella Enteritidis inactivation when the initial bacterial numbers on eggshells were high.

Microbiological oxidation of hydrogen sulphide in a biofilter

The microbial oxidation of hydrogen sulphide present in an air stream was performed using a laboratory-scale biofilter packed with dry wastewater sludge (BSE, boues de station d'épuration) from an urban wastewater treatment plant. This granular and heterogeneous material contains organic and mineral components which favour colonization by bacteria. Adsorption and absorption of hydrogen sulphide taking place on such a packing (moisture content 30–40%) were determined. Results obtained with abiotic pilot units, fed with air (superficial air flow rate, 16 m/h) containing a sulphide level as high as 3260 mg/m3, showed that chemical oxidation can occur. The presence of numerous bacteria such as Thiobacillus spp. (i.e., 108–109 CFU/g dry weight) in biotic pilot units favoured complete oxidation to sulphate. High initial bacterial numbers and a neutral pH improved the removal efficiency of the biofilter. A high sulphide concentration (&gt;3000 mg/m3) had a negative effect on the removal efficiency. The leaching of the metals contained in the sludges was studied. Peat and BSE biofilters were compared.Key words: Thiobacillus spp., hydrogen sulphide, biofilter, deodorization, bioleaching.

Hot water decontamination of beef carcasses for reduction of initial bacterial numbers

Areas on freshly slaughtered beef carcasses were sprayed with hot (95°C), sterilized, distilled water in order to elevate carcass surface temperature to 82°C. A significant (P < 0·05) reduction in bacterial numbers was observed between control (prespray) and hot water treated carcass surfaces. These results indicate that microbial decontamination of beef carcasses with hot water will be effective if an approprite spraying apparatus is used.

Effects of Lactic Acid and Vacuum Packaging on Beef Processed in a Research Abattoir

Experiments were conducted in a research abattoir to assess the effects of lactic acid treatment of beef on carcass quality characteristics, bacterial growth on vacuum packaged longissimus dorsi (LD) muscle and the case life of rib-eye steaks. Ten paired carcass sides were alternately assigned to a 1% lactic acid-spray or water-spray treatment (1L/side) at 45min post-stunning. After chilling for 24h at 1°C, LD muscles were removed from each side, vacuum packaged and stored for up to 70d at 1°C. Although 1% lactic acid produced a transient reduction in carcass surface pH to 3.6 and a significant (p<0.05) 0.7 log reduction in surface contamination, lactic acid had no effect upon the survival of beef spoilage pseudomonads on artificially-inoculated muscle.Neither spray treatment had significant effects (p>0.05) upon deep muscle pH and temperature, fat or muscle color, grade fat thickness, loin eye area, marbling score or cooler shrinkage of carcass sides. Initial bacterial numbers on LD muscles from acid-treated or water-treated carcasses were no different, nor were there any significant differences (p>0.05) in the rates of bacterial growth for up to 70d of vacuum storage. The objective color and case life of rib-eye steaks from vacuum packaged LD muscle were unaffected by lactic acid. It was concluded that, with sanitary dressing and processing, the marginal reduction in carcass contamination affected by 1% lactic acid does not improve the bacteriological condition of vacuum packaged subprimals or the retail case life of steaks.

Survival of Pseudomonas fluorescens inocula of different physiological stages in soil

The influence of different soil conditioning and incubation temperatures and the effect of variability between different batches of inocula of Pseudomonas fluorescens on its survival in the soil were investigated. Bacterial numbers decreased exponentially as described by the function Y = A + B × (1 − R) t, based on the Gompertz equation, where Y is the logarithm of bacterial numbers at time t; A represents the logarithm of the final population; B is the difference between the logarithm of the initial bacterial numbers and A; R is the daily reduction factor and t the time in days. At both 5 and 15°C numbers of P. fluorescens changed similarly and stabilized between 2.2 × 10 3 and 1.8 × 10 3 cfu g −1 oven-dry soil. The daily reduction factors (R) were 0.075 at 5°C and 0.034 at 15°C. At 25°C, the competition between P. fluorescens and the endogenous microbial population reduced the numbers of P. fluorescens more abruptly, resulting in stable numbers of 1.3 × 10 2 bacteria g −1 oven-dry soil and a higher daily reduction factor of 0.132. A higher soil conditioning temperature (15°C) resulted in slightly better survival. At 15°C, P. fluorescens stabilized at 9.53 × 10 3 cells g −1 dry soil with a lower daily reduction factor (0.110); at 5°C, the final population size was 4.45 × 10 3 cells g −1 and the R value 0.169. Microcalorimetric measurements were made to characterize and standardize bacterial cultures of P. fluorescens. A significant correlation between heat output (time integral of the power-time curve) and bacterial numbers (correlation coefficient r 2 adjof 0.98) was obtained in a batch-culture experiment. The inoculum size affected the duration of the lag before heat production (a 10-fold increase in inoculum size reduced the lag by 3.5–4 h) but not the apparent growth rate. The growth stage of the inoculum (derived from the microcalorimetric output) affected both the duration of the lag and the specific growth rate upon reinoculation into the same medium. In a second experiment, it was established that introducing an inoculum from the late exponential phase (when the power output of the culture reached its maximum) into soil resulted in a higher stabilization level and a lower death rate than when early exponential or stationary phase inocula were used.

Chlorhexidine Wound Lavage and Suture Soaking for Prevention of Suture-Related Infections

The effectiveness of chlorhexidine in preventing suture-related infections in two groups of dogs at high and low levels of bacterial contamination was examined. Prior to placing the sutures, the lateral stifle incisions were inoculated with Staphylococcus aureus and lavaged with either a 1 % chlorhexidine solution (treated groups) or sterile normal saline (control groups). Chlorhexidine significantly reduced the initial bacterial numbers and clinical inflammatory response in wounds contaminated with high or low numbers of bacteria. Chlorhexidine significantly decreased the tissue inflammation associated with the polyester sutures when contaminated with high concentrations of bacteria.

COMBINED EFFECTS OF ELECTRICAL STIMULATION AND METHODS OF MEAT PRESERVATION UPON THE SURVIVAL OF BACTERIA

The synergistic effect caused by electrical stimulation and methods of meat processing on microbial numbers in meat was investigated. Electrical stimulation in all experiments reduced initial bacterial numbers and lowered tissue pH. Under the conditions of this research, no synergistic effect could be proven for electrical stimulation and 3% salt or 3% salt and 200 ppm of nitrite or for storage at -21°C. However, a synergistic effect was observed for electrical stimulation and heating at 60°C. This reduction in thermoresistance caused by electrical stimulation did not appear to be caused by the lowering of pH of the heating media.

The effect of temperature, pressure and chlorine concentration of spray washing water on numbers of bacteria on lamb carcases.

Combined analysis of three experiments showed that when lamb carcases with initial bacterial numbers of between logi103.29 and 4.22/cm2 were spray washed, statistically significant reductions in bacterial numbers of log10O.5 were obtained when the spray wash water temperature was &gt; 57°C, and reductions of log101.0 were obtained when the temperature was ≥ 80°C. Reductions at all temperatures were enhanced by log100.66 when the water contained 30 µg/ml chlorine, but increasing the concentration to 450 µg/ml reduced bacterial numbers only by a further log100–29. At highly contaminated sites increasing the duration of spraying from 30 to 120 s significantly increased the reductions obtained when water containing added chlorine was used. Reductions in bacterial numbers after spray washing with pressures of 3.5, 5.6. 7.7 kg/cm2 were not significantly different.

A Comparison of Consumer Methods of Storing Chicken Broilers at Home

Thirty-two broiler carcasses were purchased from a retail source and were then placed at 4 C for short term storage under household storage conditions. Carcasses were evaluated for bacterial growth initially and after one, five, and eight days of storage. Measurements included enumeration of psychrotrophic and mesophilic bacteria, coliform, and fungal concentrations on the breast surface of the broiler carcasses. Results from this experiment indicate that there was little benefit derived from opening the retail package prior to storage. Removing the carcasses from the retail package and repacking them in new packages resulted in a small increase in bacterial numbers which was probably due to the handling associated with repackaging. There was no improvement in product shelf-life that could be associated with the repackaging process. However, washing the carcasses in cold tap water prior to repackaging and subsequent storage resulted in a decrease in initial bacterial numbers and a subsequent increase in product shelf-life.

Survival of bacteria in carcasses

Bacteria injected into the bloodstream of guinea pigs shortly before death decreased in number in carcass tissues for about 1 h after death. If initial bacterial numbers were sufficiently low, all bacteria were eliminated, and carcass tissues were sterile 24 h after death. Carcass tissue sterility was maintained with an initial density of Clostridium perfringens or Salmonella typhimurium of 20 cells per g or with an initial density of the other species examined of several hundred cells per gram. With larger numbers of strict and facultative anaerobes, growth commenced after 3 h in carcasses incubated at 30 degrees C. Spores of C. perfringens were killed over the same period as vegetative cells, but growth did not commence until 8 h after death. Bactericidal activity in carcass tissues must therefore be taken into account in evaluating the significance of reports of deep-tissue contamination of carcasses from meat animals.