A crude suspension of Staphylococcus aureus cell walls (strain Cowan III) in buffer solution was shown by electron microscopy to lyse slightly after 16 hr, probably owing to the action of autolysin. The lysis was considerably faster and more intense after the addition of lysozyme. A remarkable reduction in thickness and rigidity of the cell walls, together with the appearance of many irregular protrusions in their outlines, was observed after 2 hr; after 16 hr, there remained only a few recognizable cell wall fragments but many residual particulate remnants. When autolysin was previously inactivated by trypsin, there was a complete inhibition of the lytic action of lysozyme; on the other hand, when autolysin was inactivated by heat and lysozyme was added, a distinct decrease in the thickness of the cell walls was observed, but there was no destruction of the walls. The lytic action of lysozyme, after treatment with hot 5 % trichloroacetic acid, gave rise to a marked dissolution of the structure of the cell walls, which became lost against the background, without, however, showing ostensible alteration of wall outlines. From a morphological point of view, the lytic action of autolysin plus lysozyme was quite different from that of trichloroacetic acid plus lysozyme, as shown by electron micrographs, but in both cases it was very intense. This would suggest different mechanisms of action for these agents.

SUMMARY– 392 samples of precooked frozen shrimp from two Chilean manufacturers, A and B, were quantitatively examined for the presence of Staphylococcus aureus by direct plating on Difco mannitol salt agar (MSA, 10% NaCI). 140 samples (35.7%) were found to contain Staphylococci but only half of these had counts of over 100,82.4% remaining within the acceptable limit. Frozen shrimps are prone to contamination by Staphylococcus during processing, especially if hand‐processed, but these results show that it is possible to obtain a good‐quality product when stringent sanitary measures are observed. MSA was compared with Baird Parker's egg yolk medium (BPM) by plating simultaneously on it 141 samples from manufacturer B; BPM detected S. aureus in a smaller number of samples (7.8%), and gave rise to fewer colonies than MSA. BPM seemed to be inhibitory even to some Staphylococcus strains, i.e., it is unsuitable for use in these frozen foods. From 2 other manufacturers, C and D, 80 samples of frozen shrimp, together with 60 nasal swab samples from food handlers were plated to investigate some cultural characteristics of S. aureus. 57 strains of this organism were obtained, 41 belonging to shrimp samples and 16 to nasal carriers from both manufacturers. The strains were isolated and, when tested by anaerobic fermentation of mannitol, deep growth in cysteine agar, catalase and coagulase reactions, all gave positive tests. Phosphatase and DNase reactions were less constant. All the strains with 1 exception were sensitive to 8 antibiotics tested. Thus, the general properties ascribed to S. aureus species appear unaltered in frozen shrimps. 28 strains (49.1%) could be typified with the set of 21 international phages, most of them belonging to group III; only in manufacturer D strains coming from food and food handlers were phage type related. In manufacturer C most strains were untypable.

SUMMARY– 392 samples of precooked frozen shrimps from 2 Chilean industries (A and B) were analyzed for total bacterial count, conforms and enterococci throughout a period of 8 months. 1‐lb samples of breaded shrimp were received directly from the manufacturers after a freezing period of 10 days at —18δC. Total bacterial count ranged from 104 to 105 organisms perg. Conforms were absent in 65% of the samples from A, and in 40% of those from 8; 89.6% of the samples from A and 50.1% of those from B were bacteriologically acceptable considering a limit of not more than 50 coliforms per g. 98% of the frozen shrimp samples belonging to A contained enterococci, as did 66% of the samples from B. Smaller percentages (17% for A and 54% for B) of acceptable samples are obtained from both industries when 100 enterococci per g is considered as the limit. During the period of observation some sanitary measures were adopted and subsequent coliform counts improved. In plant A working conditions are better and the understanding of bacteriological grounds for the proper handling of food materials has led to the elaboration of a product of consistently better quality. Enterococci counts are in contradiction with coliform counts, since the low‐level coliform samples are rejected on the basis of their enterococcal content. In plant B there is a better correlation between coliform and enterococcal counts. Though not investigated, this may be related to the precooking system employed: steaming in an enclosed conveyor in A versus immersion in boiling sea‐water in B.

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