Petrifilm™ Rapid S. aureus Count Plate Method for Rapid Enumeration of Staphylococcus aureus in Selected Foods: Collaborative Study

A rehydratable dry-film plating method for Staphylococcus aureusin foods, the 3M™ Petrifilm™ Rapid S. aureus Count Plate method, was compared with AOAC® Official MethodSM 975.55 (Staphylococcus aureus in Foods). Nine foods—instant nonfat dried milk, dry seasoned vegetable coating, frozen hash browns, frozen cooked chicken patty, frozen ground raw pork, shredded cheddar cheese, fresh green beans, pasta filled with beef and cheese, and egg custard—were analyzed for S. aureus by 13 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample and 3 levels of inoculated test sample, each in duplicate. The mean log counts for the methods were comparable for pasta filled with beef and cheese; frozen hash browns; cooked chicken patty; egg custard; frozen ground raw pork; and instant nonfat dried milk. The repeatability and reproducibility variances of the Petrifilm Rapid S. aureus Count Plate method were similar to those of the standard method.

Residues of spinosad in the tissues of sheep after aerosol treatment of blowfly myiasis

OBJECTIVE

To measure the residues of spinosad and chlorhexidine in the tissues of sheep after treatment of blowfly strike.

PROCEDURE

Fourteen sheep with natural myiasis and 12 with artificial infestations of Lucilia cuprina larvae had the wool removed over their infestations and were treated with an aerosol wound dressing containing spinosad and chlorhexidine. Sheep were killed up to 14 days after treatment and residues of the chemicals measured in tissues.

RESULTS

Chlorhexidine was not detected in any tissue. Residues of spinosad were highest in fat, lowest in muscle and intermediate in liver and kidney. The highest residue detected was 0.2 mg/kg spinosad in perirenal fat 7 days after generous treatment of a sheep with a large fly strike. Residues of spinosad in fat peaked 3 to 7 days after treatment and 1 to 3 days after treatment in liver and kidney.

CONCLUSION

These studies present a realistic worst-case in struck sheep and at the highest dose studied, equivalent to 5.8 mg spinosad per kg body weight, the maximum residue detected of 0.2 mg/kg in peri-renal fat was 20% of the Australian maximum residue limit. Muscle, liver and kidney residues of spinosad were also below the Australian maximum residue limits at all times.

The role of nitric oxide in neoplastic transformation of C3H 10T1/2 embryonic fibroblasts

Nitric oxide synthase inhibitors block the neoplastic transformation of C3H 10T1/2 cells in vitro. Evidence presented herein suggests that they mediate their effects early in the carcinogenic process as brief treatment with the NOS inhibitor aminoguanidine (AG) during log phase cell growth (initiation phase) is sufficient to block foci formation. In contrast, treatment initiated after formation of a confluent monolayer was associated with diminished protection, while treatment commencing late in the promotional phase had no protective effect and appeared to enhance the number and stage of foci observed. These findings suggest that while AG treatment can inhibit transformation during the early promotional phase, it most effectively inhibits transformation during the initiation phase. In general AG enhanced growth of both normal and tumor cells, suggesting that effects on growth were unrelated to its anti-transformation properties, however, these effects could be related to the effect on tumor cell stage noted above. Although induction of inducible nitric oxide synthase (iNOS) by treatment with LI during the last 2 weeks of the assay was associated with enhanced transformation, the efficacy of AG in protecting against transformation was not clearly associated with substantial reductions in NO synthesis. The data suggest that AG inhibits transformation early in the transformation process independently of iNOS inhibition and that AG may have deleterious effects late in the process, possibly through stimulation of tumor cell growth.

Biological models of two acarine predators of the grain mite, Acarus siro L

A biological model of predation was developed using granular food held in closely packed screen trays to propagate the grain mite, Acarus Siro L., and two of its predators, Blattisocius dentriticus (Berl.) and Cheyletus eruditus (Schrank). Both predators limited prey abundance. Cannibalism among predators, particularly C. eruditus, was an important factor in ensuring the survival of the prey and predator populations. Cheyletus eruditus eliminated B. dentriticus when the two species were propagated in the same experimental universe. Cyclicity and dispersion of the interacting species appeared to result more from the initial age structure and from dispersion of the prey than from predator attack. A population model was used to assess the relative importance of the population components of A. siro and C. eruditus in the simplified predator–prey interactions.

Prey consumption in acarine predator-prey populations reared in the greenhouse

Two factors, in addition to temperature, could affect the assessment of Amblyseius fallacis as a natural enemy of Tetranychus urticae infesting alfalfa. These are initial prey density and sampling of the predator–prey populations during daylight hours. The influence of these factors was determined by propagating predator–prey populations having different initial prey densities on alfalfa in the greenhouse, recording the subsequent variation in the numbers of the two species during daylight hours, and comparing estimates of the rates at which prey entered and were removed from the populations. A. fallacis was able to reduce prey density before webbing of the alfalfa plants occurred. Prey consumption by the predator populations was judged capable of inducing the observed decline in prey numbers.

Effect of temperature on a greenhouse acarine predator–prey population

Populations of the two-spotted mite, Tetranychus urticae, and its acarine predator, Amblyseius fallacis, were propagated on alfalfa in the greenhouse at constant temperatures in the range 65 to 85 °F (18.3–29.4 °C). The predator limited the initial increase in prey abundance only at temperatures above about 70 °F (21.1 °C). At 80 and 85 °F (26.7 and 29.4 °C) fluctuations in prey and predator numbers increased in amplitude as propagation continued. The age structure of the predator population reared at 75 °F (23.9 °C) differed from that of populations propagated at the other temperatures.

ASPECTS OF THE INTERACTION BETWEEN A CHALCID PARASITE AND ITS ALEURODID HOST

Three populations of the greenhouse whitefly, Trialeurodes vaporariorum, and its chalcid parasite Encarsia formosa were propagated each year for three consecutive years on tomato plants in the greenhouse. The abundance of the host and parasite species fluctuated either with peaks of increasing amplitude, with peaks of decreasing amplitude, or with irregular peaks. The dominant process in the interaction was the occurrence of two qualitatively different types of host larval mortality: (a) parasitization, and (b) almost immediate killing after attack by adult parasites. Fluctuations in host and parasite abundance resulted from the almost immediate killing of small host larvae and the death of the short-lived adult parasites. The parasite population tended to destroy similar percentages of host populations of different densities but host mortality was also related to the age structure of the host population. Variation in host reproduction, caused by differences in rearing temperature and by seasonal variation in the physical environment, influenced host and parasite densities.

HOST LARVAL MORTALITY IN AN EXPERIMENTAL HOST–PARASITE POPULATION

Two populations of Trialeurodes vaporariorum (Westw.) and its chalcid parasite Encarsia formosa Gahan were reared on tomato plants in the greenhouse at 72–76 °F for 26 weeks. Although the abundance of both species fluctuated with peaks of increasing amplitude, the population that was initially larger remained so throughout the period of sampling because the parasite inflicted similar rates of mortality in both cases. The fluctuations of the two separate populations were synchronized throughout the period of propagation. Host mortality, which resulted either from almost immediate killing of host scales following attack by adult parasites or from death of host larvae following parasitization and development of parasite progeny, was determined by parasite density, host size, and possibly by a number of other factors such as the age structure of host larval populations, age of adult parasites, and succulence of leaves on which the host larvae developed. The interaction of host and parasite produced cycles in the age structures of host and parasite populations that, in turn, influenced the interaction of the two species. The death of host larvae following attack by adult parasites was a form of host protection, as it ensured the rapid decline in the abundance of the parasite population and was, therefore, the primary factor in the maintenance of the host–parasite system.

AN ACARINE PREDATOR–PREY POPULATION INFESTING STORED PRODUCTS

Populations of the stored product mite Tyrophagus putrescentiae (Schrank) and its predator Blattisocius dentriticus (Berl.) were propagated in two experimental universes. Although the predator determined the size of the prey populations, the densities of both species fluctuated with peaks of abundance occurring every 6 to 8 weeks. A number of factors modified, to some extent, the role of "predator searching" as a mechanism controlling both the average densities and fluctuations in abundance of the two species. With large fluctuations in the abundance of the prey there was a pronounced cycle in the age structure of the predator and prey populations. The larger stages of the prey were largely immune to attack by the predator. Individuals of the predator developed to about one-half their normal size when the prey were scarce. The combination of immune stages of the prey and adjustment of predators to scarcity of prey ensured the coexistence of the predator–prey system. Contamination of experimental populations by psocids was one of the major hazards in rearing the populations for extended periods.

EFFECTS OF INITIAL DENSITIES AND PERIODS OF INFESTATION ON THE GROWTH-FORMS OF A HOST AND PARASITE POPULATION

Initial densities and periods of infestation of adults of Trialeurodes vaporariorum and its chalcid parasite Encarsia formosa influence subsequent fluctuations in numbers of adults of both host and parasite.