MICROBIOLOGICAL ASPECTS OF A VACUUM CONTACT-PLATE DEHYDRATION PROCESS

SUMMARY: A process for dehydrating fish under vacuum and in contact with heated plates is described. Although the conditions, in respect of time and temperature, appeared suitable for microbial development, a reduction in the number of bacteria usually occurred. A survey of the data accumulated over twenty months, including a series of experimental production periods, showed that the bacterial population estimated at 22° was reduced in the process as a whole to about 1% of its initial value and that estimated at 37° to about 10%. Species of the genus Micrococcus tended to predominate on the finished product. Contrary to earlier expectations, there should be no serious microbiological hazards if high standards of personal and factory hygiene are maintained.     

Bacterial canker of stone-fruits: Infection experiments with Pseudomonas mors-prunorum and P. syringae

The effect was compared of inoculating Pseudomonas mors-prunorum and P. syringae at high inoculum concentration through wounds in plum stems and cherry branches, and through cherry-leaf scars. In the wound inoculations a North American cherry strain of P. syringae was considerably more virulent than any of three indigenous cherry strains of P. mors-prunorum, but two pear strains of P. syringae were less virulent. P. mors-prunorum showed a much greater capacity to invade through leaf scars, particularly towards the end of the leaf-fall period, when all three P. syringae strains were largely ineffective. Evidence is discussed which suggests that the greater infectivity of the P. mors-prunorum strains through leaf scars was related to their capacity to colonize the host tissues from small inocula. The P. syringae strains died out in cherry cankers earlier than P. mors-prunorum strains and they were less stable during host passage. The results of the experiments indicate that virulence in these organisms is a complex phenomenon and determined by several factors.     

Enzyme Variation of Eimeria arizonensis from Peromyscus truei and P. boylii

ABSTRACT. Cricetid rodents, Peromyscus truei and P. boylii , were inoculated with sporulated oocysts of Eimeria arizonensis collected from wild P. truei maintained in the lab. In P. truei the prepatent period was 4–5 days, the patent period was 9–11 days, and sporulated oocysts were 21.5 × 25.0 (20–23 × 24–26) μm with sporocysts 7.7 × 12.0 (6–8 × 10–13) pm. In P. boylii the prepatent period was 6–7 days, the patent period was 8–9 days, and sporulated oocysts were 20.1 × 23.2 (18–22 × 21–24) pm with sporocysts 6.8 × 10.0 (5–8 × 9–12) pm. Sporulated oocysts from both host species were used in direct side-by-side comparison of isozyme banding patterns using protein electrophoresis. The parasite has polytypic loci for leucine aminopeptidase (LAP), lactate dehydrogenase (LDH), and 6-phosphogluconate dehydrogenase (6-PGD). In oocysts from P. truei , LAP showed one band with fast migration and LDH and 6-PGD each showed two bands, one with fast and one with slow migration. In oocysts from P. boylii , LAP and LDH each had one band with slow migration and 6-PGD had one band with moderate migration. Oocysts of E. arizonensis collected from P. boylii were used to inoculate P. truei. The prepatent and patent periods, structural measurements, and isozyrne banding patterns of the resultant oocysts were the same as those from P. truei when inoculated with oocysts from P. truei.     

Changes in the microbial population of apple leaves associated with the inhibition of the perfect stage of Venturia inequalis after urea treatment

Treatment of detached apple leaves in October with urea induced a rapid and prolonged increase in the microbial populations present in the leaves during the winter. These effects were accompanied by a major shift in the population balance from a predominantly Gram-positive, chromogenic type of microflora to one dominated by Gram-negative and non-chromogenic organisms. Fluorescent pseudomonads became particularly numerous in the urea-treated leaves and many were found to suppress the development in vitro of Venturia inaequalis. An organism forming yellow colonies, possessing exceptional activity against the scab fungus, which was also found in urea-treated leaves, was shown to be a Gram-negative, peritrichous bacterium. No antagonistic organisms were isolated from untreated control leaves, but many were found–usually chromogenic forms–which appeared to stimulate the scab fungus in vitro. Treatment with urea accelerated the decomposition of the leaves and suppressed the development of V. inaequalis in the portions of the laminae which remained structurally intact until the following spring. Many of the effects of urea were enhanced by the addition of glucose, streptomycin, or a suspension of a Pseudomonas sp. isolated from leaves during the winter. Streptomycin alone reduced the total numbers of microorganisms in the leaves but increased the proportion of Gram-negative organisms: this was associated with diminished ascospore production in the spring. There was no direct evidence that the antagonistic flora stimulated by urea was responsible for the inhibition of V. inaequalis, and alternative explanations are suggested.     

The Effects of Conditions of Growth, Extraction and Reaction on a Nucleotide Phosphatase Activity Obtained from the Shoot-Root Axes of Pisum sativum var. Alaska Seedlings

Nucleotide phosphatase activity in extracts from etiolated peaseedlings (Pisum sativum var, Alaska) was studied. A markedincrease followed rupture of the seed coat by the elongatingradicle, indicating a dependence on aerobic respiration fordevelopment of the activity. Activity from the shoot-root axiswas directly correlated with axis size, inhibition of growthresulting in a reduced activity. Growth in continuous illuminationalso reduced activity, as did imbibition of phenylalanine, tyrosine,glutathione, and sodium phosphate. The activity was greaterin the shaft regions of the axis than in the tip regions. About30 percent of the activity was associated with the nuclear—mitochondral—cellwall pellet, while the reminder was more or less evenly distributedbetween a membranee fraction of high specific activity and asoluble fraction. The effects of substractes, ions, and inhibitorson the activities of membrane and soluble fractions was quitedifferent.