Aging and memory for pictures of faces.

The hypothesis that pictorial aspects of face-recognition memory are lower in old age was tested in 2 studies. Young and elderly Ss viewed 48 face pictures, and then took a test containing identical copies of input faces, pictorially changed versions of input faces, and entirely new faces. Replicating prior findings, Experiment 1 showed that false recognitions of entirely new faces were higher among elderly Ss. However, there were no age differences in distinguishing identical from pictorially changed faces. Using a modified test, Experiment 2 showed that although the elderly Ss had good knowledge that changed faces were changed, they had relatively poor knowledge of how they were changed. There appears to be age differences in analytical matching of pictorial information against information in memory.

Precision Parameters for AOAC Bacillus stearothermophilus Disc Assay Based on FDA Milk Laboratory Quality Assurance 1982-1986 Samples.

Inhibitory substance (antibiotic) test results from State Split Milk Samples were used to estimate precision parameters and to compare antibiotic medium 4 (A4) and PM indicator (PM) agars. Five inhibitory substances (ampicillin, cephapirin, erythromycin, neomycin, and penicillin-G) were tested. Repeatability relative standard deviations (RSDr) ranged from 1.0 to 4.8%, and the reproducibility relative standard deviations (RSDR) ranged from 4.8 to 10.4%. Zone sizes of erythromycin, neomycin, and penicillin-G were significantly larger on PM agar (α = 0.05) than on A4 agar. The reverse was observed for cephapirin. No difference between agars was noted for ampicillin.

Detectability and Precision of the AOAC Bacillus stearothermophilus Disc Assay Demonstrated in the 1981 FDA Split Milk Sample Testing Program.

Four blind duplicate milk samples containing ß-lactam residues were analyzed by 149 analysts at 47 laboratories. Four official variations were used: (a) antibiotic 4 (A4) agar and 55°C incubation, (b) A4 agar and 64°C incubation, (c) PM indicator (PMI) agar and 55°C incubation, and (d) PMI agar and 64°C incubation. A ß-lactam concentration of 0.008 IU/ml was detectable 100% of the time by variations a, b, and c and 98% of the time by variation d, with average zone diameters of 18.7, 17.7, 16.4 and 17.6 mm, respectively. The 0.005 IU/ml concentration was detected 92% of the time by variation a, 99% by b, 57% by c and 89% by d, with average zone diameters of positive units of 16.3, 15.5, 14.9 and 15.2 mm, respectively.

Quantitative estimates of beta-lactam residues in raw milk around a reference standard: collaborative study.

A collaborative study was conducted to determine the reliability of a Bacillus stearothermophilus disc assay method for differentiating various concentrations of penicillin in raw milk. Participating laboratories tested 10 different samples (including one negative) in blind duplicate. Triplicate standards were alternated with triplicate unknowns around the periphery of each of 5 different plates. Zone diameters were measured and the difference in zone size of pairs of adjacent standard and unknown samples were analyzed by a paired t-test. Penicillin concentrations 0.003 IU/mL different from the reference concentrations were consistently distinguishable at a 95% confidence level. Such discriminatory power was determined to be possible with as few as 3 plates (9 replicates) per unknown. The method has been adopted official first action.

Bacillus stearothermophilus disc assay for detection of inhibitors in milk: collaborative study.

A 2-part (A and B) collaborative study was conducted on a Bacillus stearothermophilus paper disc (12.7 mm) method to detect residual inhibitors in milk. The 18 participating collaborators assayed raw milk samples spiked with a beta-lactam (penicillin G). Of the 18 collaborators, 14 participated in part A and 16 in part B. Part A demonstrated that either Antibiotic Medium No. 4 or PM Indicator Agar is suitable for use in the assay. The lowest concentration detectable, not significantly different from 100% at the alpha = 0.05 level, was 0.008 unit/mL with either medium. Part B demonstrated that the sensitivity of the method is equal to that of the current AOAC method (16.131-16.136). The concentration of beta-lactam detected by 50% of the analysts was 0.003-0.005 unit/mL in this study, compared with 0.005 unit/mL reported in an earlier collaborative study on the current AOAC method. No false positive results were reported in part A or part B. All samples found positive by the confirmatory test in part B were correctly identified as a beta-lactam with commercial Penase discs. The lowest concentration detectable by the method, not significantly different from 100% at the alpha = 0.05 level, was 0.008 unit/mL. The method was adopted official first action.

Replicate Counting Errors by Analysts and Bacterial Colony Counters.

Replicate counting errors were computed when a plate of a sample of pasteurized milk was counted twice by one analyst and twice by two analysts. The results were used to make recommendations for revising methods for the determination of bacterial counts of milk in Standard Methods for the Examination of Dairy Products and to evaluate the counting accuracy of four bacterial colony counters used to enumerate the aerobic plate count of 14 food products.

Variation in Food Microbiological Tests Used to Evaluate Analyst Performance.

Procedures for evaluating analyst performance in state and federal milk and food laboratory quality assurance programs depend on the estimates of variation for the methods used. The total components of variance for a method consist of replicate error, among-analysts variance, and analyst-sample interaction components. Eleven methods were evaluated in this study. Total variance estimates of milk analytical procedures for the Standard Plate Count, plate loop count, coliform plate count, direct microscopic somatic cell count, electronic somatic cell count and Wisconsin mastitis test were 0.01045, 0.01371, 0.01590, 0.01265, 0.00504 and 4.06, respectively. Estimates of the logarithmic total variance of food analytical procedures for the aerobic plate count, coliform most probable number (MPN), Escherichia coli MPN, fecal coliform MPN and Staphylococcus aureus MPN were 0.00853, 0.10205, 0.14705, 0.14780 and 0.24245, respectively. The study showed that current analyst performance levels used by state and federal laboratory quality assurance programs are satisfactory.

Direct plating method for enumeration of Staphylococcus aureus: collaborative study.

Considerable evidence has been published regarding the adverse effect of sodium chloride on physiologically impaired cells of Staphylococcus aureus, such as are to be expected in processed foods. A direct plating method for enumeration of S. aureus eliminating the use of sodium chloride was devised and subjected to collaborative study by 16 analysts. Results obtained by the direct plating method were compared to those obtained by the AOAC official first action method (46.036--46.040). Participating analysts examined duplicate samples at population levels of 91, 34, and 20 S. aureus/g. Coefficients of variation among analysts were considerably lower for the direct plating method (31, 81, and 48%, respectively) than for method 46.040 (59, 156, and 150%, respectively) at all 3 population levels. High coefficients of variation for the direct plating method at 2 of the 3 levels were due principally to low populations of S. aureus. The direct plating method has been adopted as official first action for general purpose use and use of method 46.036--46.040 has been restricted to raw food ingredients and nonprocessed foods.

Production of enterotoxin A in milk.

Enterotoxin A production in milk was studied by use of variables of milk quality, initial numbers of enterotoxigenic staphylococci, incubation temperature, and time. In both raw and pasteurized milks having a low total viable count, enterotoxin was detected in minimal incubation times of 6 to 9 hr at 35 C, 9 to 12 hr at 30 C, 18 hr at 25 C, and 36 hr at 20 C, after inoculation with 10(6)Staphylococcus aureus cells per ml. When similar milks were inoculated with 10(4)S. aureus cells per ml, enterotoxin was detected in 12 hr at 35 C, 18 hr at 30 C, 24 to 36 hr at 25 C, and 48 to 96 hr at 20 C. In high-count raw milk, enterotoxin was detected only in samples inoculated with 10(6)S. aureus cells per ml and incubated at 35 C. Generally, a concentration of 5 x 10(7)S. aureus cells per ml of milk was reached before enterotoxin A was detected.

Serological identification of enterotoxigenic staphylococci from cheese.

Single and double gel-diffusion techniques were employed to examine serologically coagulase-positive staphylococci from cheese for enterotoxigenicity. Supernatant fluid from sac cultures was examined for enterotoxins A and B. The results indicated that 9 of 155 cultures from market cheese and 7 of 77 cultures from food-poisoning cheese produced enterotoxin A, and that none of the cultures produced detectable levels of enterotoxin B. Results of serological tests were confirmed by intravenous injection of cats.