Colony-forming Units Per Gram Research Articles

Effects of Probiotic Bacteria as Dietary Supplements on Growth and Disease Resistance in Young Channel Catfish, Ictalurus punctatus (Rafinesque)

ABSTRACT Three separate experiments were conducted to determine the beneficial effects of probiotic bacteria added commercial catfish diets. These commercial probiotics, singly and in combination, were incorporated into a commercial diet fed to juvenile channel catfish, Ictalurus punctatus (Rafinesque), in aquaria. Microbial analyses were conducted to confirm viability of the bacteria under storage conditions. Fish were fed twice daily to apparent satiation and weighed biweekly for a period of 5 to 8 weeks. After that time, representative fish were bled for serological analysis of protein, immunoglobulin, complement, and lysozyme. Disease resistance was additionally determined in the remaining fish by observing mortality after immersion challenge with pathogenic Edwardsiella ictaluri, the causative agent of enteric septicemia (ESC). Specific anti-ESC antibody was measured by ELISA after 15 days in the fish which survived challenge. The viability of the bacteria did not decline in storage at 5°C and could be recovered between 106 and 107 colony forming units per gram (CFU/g) of diet after storage for 4 weeks. No significant differences in levels of protein, immunoglobulin, complement, or lysozyme were noted between fish consuming probiotic diets or the control diet. In one feeding trial, weight gain per fish was significantly less in the fish receiving a combination of Pediococcus and Enterococcus probiotic bacteria when compared to those consuming either bacterial supplement diet alone or the control diet. We conclude that these particular commercial dietary supplements lack specific growth promoting or immune stimulating effects in juvenile channel catfish.

Microbiological quality of tomatoes and peppers produced under the good agricultural practices protocol AGRO 2-1 & 2-2 in Crete, Greece

The efficiency of the good agricultural practices (GAP) protocol AGRO 2-1 & 2-2, in advancing microbiological-quality of tomatoes and peppers, was studied in greenhouses at Ierapetra, Crete, Greece. The 240 tested vegetables-samples, produced under AGRO 2-1 & 2-2, showed satisfactory quality: Listeria monocytogenes absent per 25 g; Escherichia coli < 20 Colony Forming Units per gram (CFU/g); total coliforms 4.37–4.68 log CFU/g; aerobic plate counts 5.78–5.92 log CFU/g. Based on actual results and practices evaluation, we conclude that AGRO 2-1 & 2-2 can reduce microbial hazards for consumers and furthermore can establish practices in compliance to basic Euro-Retailer-Produce GAP (EUREPGAP) requirements.

Temperature Effect on Inactivation Kinetics of Escherichia coli O157:H7 by Electron Beam in Ground Beef, Chicken Breast Meat, and Trout Fillets

ABSTRACT: Ground beef, boneless skinless chicken breast meat, and boneless skinless trout fillets were inoculated with Escherichia coli O157:H7 and incubated to approximately 109 colony forming units per gram (CFU/g). Following incubation, temperature of the meat samples was equilibrated to −20, 4, and 22 °C. The meat samples at different temperatures were subjected to one‐sided electron beam (e‐beam) with fixed energy at 10 million electron volts (MeV) and doses at 0 (control), 0.5, 1.0, 2.0, 2.5, and 3.0 kGy. The survivors were enumerated using a standard spread‐plating method. The survivor curves were plotted on logarithmic scale as a function of e‐beam dose for each meat sample subjected to e‐beam at different temperatures. The D‐values were calculated as a negative reciprocal of the slope of the survivor curves. The D‐values for E. coli ranged from 0.22 to 0.35 kGy in trout at 4 °C and chicken at −20 °C, respectively. The D‐values were different between meat types. Regardless of temperature, E. coli in chicken had highest D‐value followed by beef and trout. The D‐values for E. coli in frozen samples were higher than D‐values in samples irradiated at 4 and 22 °C regardless of species. Although there were numerical differences between D‐values for samples subjected to e‐beam while chilled (4 °C) or frozen (−20 °C), they were statistically insignificant. Water radiolysis is considered as an indirect mechanism for microbial inactivation. Therefore, while the physical state of water (frozen or unfrozen) in foods seems the major contributor to microbial inactivation by e‐beam due to water radiolysis, product temperature most likely plays a minor role.

Mycoflora Distribution in Dry‐Milled Fractions of Corn in Argentina

ABSTRACTCorn samples and different commercial dry‐milled fractions collected from an industrial mill in Argentina were surveyed for fungal contamination. The percentage of Fusarium isolates in whole corn kernels among all fungi recovered was 2.0–97.0%; in corn grits, it was 2.6–50.0%. Maximum levels in the other fractions were 5.2 × 105 colony forming units per gram (CFU/g) in germ and bran, 5.0 × 103 CFU/g in C flour, and 2.7 × 103 CFU/g in corn meal. The high initial contamination from whole corn is reflected in germ and bran, which is destined for animal consumption, but not in corn meal. F. verticillioides and Aspergillus flavus were the most frequent species in the whole corn kernel, but F. verticillioides was prevalent in all the other industrial fractions. Other potentially toxigenic fungi that were isolated included Aspergillus parasiticus, Alternaria alternata, Penicillium citrinum, and P. funiculosum. In this first report about mold contamination in corn industrial dry‐milled fractions in Argentina, the high fungal contamination level observed in the stored corn could indicate the necessity to improve the hybrid quality and the storage conditions to diminish the risk of mycotoxin occurrence.

Effect of Water Activity and Temperature on Staphylococcus aureus Growth and Thermonuclease Production in Smoked Snoek

Smoked snoek at different water activity (aw) values (0.966, 0.956 and 0.944) were inoculated with Staphylococcus aureus at a concentration of approximately log 4.7 colony forming units per gram (CFU/g) and incubated at different temperatures (4, 12, 24 and 37 C) for various periods. Samples of inoculated and control snoek were taken at different intervals to determine the microbial populations (S. aureus, total organisms and enterococci), pH and presence of thermonuclease. No growth of S. aureus nor thermonuclease production occurred at 4 C. At 12 C, notwithstanding high S. aureus log counts of 6.75/g, 9.74/g and 9.69/g in the inoculated 0.966, 0.956 and 0.944 aw samples, respectively, thermonuclease was absent after 21 days of incubation. At 24 and 37 C at all three aw levels, very high S. aureus counts were recorded and were accompanied by thermonuclease production before the end of the relative incubation periods (5 and 3 days, respectively). A reduction of the aw of the snoek resulted in a slightly slower S. aureus growth rate at 37 C and also delayed thermonuclease production at 24 and 37 C. The thermonuclease test was an effective means of detecting S. aureus growth except in samples incubated at 12 C. Enterococcus numbers increased in all control samples during storage, but none were found to produce thermonuclease.