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A Bacteriological and chemical study of commercial eggs in the producing districts of the central West

About: The article was published on 1914-01-01 and is currently open access. It has received 4 citations till now.

Summary (7 min read)


  • The chemical and bacteriological characteristics of perfectly fresh eggs-that is, eggs which are not more than 24 hours old and which are kept in a cool place-have been given by the first author of this report in a previous communication, entitled "A Chemical and Bacteriological Study of Fresh Eggs.".
  • ^In this study 150 high-quality eggs, not more than 24 hours old, were examined for the bacterial content in white and yolk.
  • The varieties of organisms present will be considered ^elsewhere.
  • Numerous cliemical analyses of fresh eggs have been made in this laboratory in connection with the investigation of the handling of eggs.


  • The eggs from which the preceding information was obtained can not be accepted as either a standard or an index of the eggs supplied to the people for food, because modern conditions of living and sources of food supplies make it impossible to furnish the market with eggs of uniform quality and minimum age.
  • It is necessary, therefore, as already stated, to study the common market grades of shell eggs accepted by the housewife and compare these with the iLoc. cit.
  • Absolutely fresh eggs, as well as with, the eggs put up for bakers' use.
  • Accordingly, ten open-market purchases were made of eggs as they went to the consumer, and anatytical data and candling records obtained, using the same method as in the case of the fresh eggs.

Dirtv eggs

  • Bacterially these eggs did not differ from the strictly fresh eggs.
  • According to the content of ammoniacal nitrogen they varied from absolutely fresh to the usual stale, but not rotten, eggs.
  • The price usually, but not invariably, was in accord with the quality.
  • The carton-packed eggs were individually marked with the sign, of the producer, who had a reputation for quality to maintain.


  • Experiments have shown that evidences of bacterial decomposition can not be recognized b}^the sense of sight and smell until the organisms have increased enormously in the food substance.
  • The principles observed by the investigators cited are corroborated by the results of the study of bacterial content and chemical changes in eggs.
  • Eighty commercial samples which contained organisms capable of producing gas from lactose in the presence of bile salt were examined for B, coll., as described in the chapter on laboratory practice (p. 76).
  • Probably 15 per cent more contained organisms which would be classed as typical B. coll by a majority of observers because they differed very slightly from the definition just given.
  • Some of them differed from an}^at present described in the literature.


  • The classification of the eggs was made on these observed characteristics, and on others noticed when the shell was broken, rather than on the bacterial condition revealed by the laboratory work.
  • The history of these eggs was known only in a very few instances.
  • The technique used is described on page 74.
  • The samples were anah^zed for the amount of loosely bound nitrogen they contained, as well as for the number of organisms.


  • A very large proportion oi the eggs going to the breakers are simply stale; that is, the shell shows an enlarged air space, the yolk has gained in opacity and definiteness of outline, and it is com-BULLEXIX 51, r. S. DEP-1ET:'.IE^"T OF AGPJCrLirEE.
  • The white is CTeqtientlT thin, and manv times rotigh handling, combmed with other age -accentuating conditions, have so separated the membrane lining the shell from the membrane inclosing the egg j)roper that the form and ^^o^ition of the air space can change as the egg is turned.
  • But because these terms are loosely used and have several meanings in different sections of the coimtry.
  • Or among different candlers, such conditions are characterized in this report as "movable air cells." this term actually describing the change which has occurred.
  • Such eggs, whether fertile or infertile, are good in.


  • Total number of bacteria per gram on plain agar, also known as No".
  • Table 5 shows another type of deterioration, which is further advanced and more spec-ific than that meant by the general term " stale.".
  • Ill); where it turns sluggishly when rotated.
  • During warm weather, when incubation goes on almost continuously, though very slowly, these eggs with settled yolks frequently show a germinal area about one-fourth inch in diameter, having a visible white line through their center-the "primitive streak" of the embryologists.
  • Their odor is generally good and their taste not objectionable, except for soft boiling or poaching.


  • The bacterial content of these eggs is generally slightly higher than in the earlier stage of staleness unless aging has occurred at the low temperatures of the egg storage warehouse, when the count is as low as or lower ^than in new-laid eggs.
  • Table 6 shows typical bacterial findings in eggs where deterioration had progressed along clilierent lines than those described under stale eggs and eggs with settled yolks.
  • The contents may be fresh and the Qgg itself may be large, but the dirt on the shell consigns it at once to the seconds, and it brings a lowered price all through the market.
  • Two eggs out of the 51 contain millions of organisms per gram in both white and yolk ; 4 show a count running into the thousands; 9 have more than a hundred organisms per gram ; and of the 36 remaining, 15, or 41.6 per cent, are sterile.
  • If one may draw any conclusion from the findings set forth in Table 7 it must be that the dirty shell,* per se, is not a sufficient ground on which to condemn an ^gg^t hough the odor of the ^gg when opened should be carefully observed, especially if the shell shows stains or other evidences of having been wet.


  • The inexpert or careless candler fails to notice these white rots; hence they are too often fotmd in the breaking room; when opened yolk and white are seen to be completely, or almost completely, mixed.
  • Very frequently the mixture is much thinner than the mixed yolk and white of a fresh egg and may or may not have an offensive odor.
  • Sometimes scraps of mem^brane are seen, suggesting a disintegrated embryo; again, the contents are thin, homogeneous, and pale yellow (see PL ^T^I).
  • Two of the eggs were sterile and two of them showed a low count.
  • The high bacterial content of these white rots is quite in accord with their apjjearance.


  • The ' spot rots " of commerce are eggs in which the yolk has become adherent to one or both of the shell membranes and, perhaps, to the shell itself by means of the mem^branes.
  • ^Ylien held before the candle, therefore, the yolk is seen as a distorted, deeply colored mass pressed against some j)art of the shell (see PL TV).
  • As the egg ages in temperatures which are lower than those causing incubation phenomena, the yolk of either the fertile or the infertile egg settles.
  • Others show distinct evidences of incubation, general deterioration, cracked shells, etc. BULLETIX 51, r. S. DEPAETMEXT OE AGEICULTURE.
  • Fourteen samples --or 33 per cent-were sterile in both yolk and white.


  • Damp cellars, wet nests, stolen nests, etc., are responsible for the condition of eggs which show, on candling, dense black areas of varying sizes inside the shell.
  • Both the white and the yolk of moldy eggs are apt to be discolored, usually becoming brownish.
  • Respectively, was in the air cell and apparently had not penetrated the egg membrane, though undoubtedly it would have done so in time.
  • So varied are the visible results upon the egg of the growth of mold inside the shell that much space might be consumed describing individual eggs.


  • They are recorded for comparative purposes only.
  • Black londer candle; egg had a bad odor before being opened, and a" still worse one afterwards; some shrinkage; fixed air cell.


  • For this investigation a large nnniber of samples were taken of the various types of eggs encotintered throtighont the egg-breaking season of 1912.
  • After every infected egg which could be detected by the senses, the operator replaced the knife and cup with sterile ecpaipment and washed and dried her hands.
  • They were graded from the daily re-ceiT>ts and held in chilled rooms until needed to fill out the regular quota of eggs for the breaking room.
  • The laboratory data oiven in Table 14 shoAV that three of five samples contained less than 1,000 bacteria per gram at 20°C .
  • Since the bacteriological findings given in Table 4 indicate that this grade of eggs, when opened aseptically, is practically sterile and contains no B. coli^it might be concluded that the organisms found in the samples opened in the packing house were referable, for the most part, to outside contamination and not to the eggs themselves.


  • Seconds constitute a large proportion of the eggs used in the frozen and desiccated egg industry.
  • In the spring, before the candling season begins, this grade consists of small, dirty, and oversized eggs sorted from receipts by inspection.
  • During the interval between May 4 and August 30, 1912, 9 samples of whites, 9 of yolks, and 25 of whole eggs were taken from the product obtained from seconds, the different lots varying in size from 6 to 30 dozen eggs.
  • During the process of breaking care was taken to discard all eg'^gs which, from appearance or odor, were abnormal.
  • The chemical results show, therefore, that the contents of the spring seconds were fresher than the summer firsts.

Yolks of 41011.

  • The lowest number of bacteria found at i^O^C. was SlX"^per gram in a sample taken during the early part of May. and the highest.
  • The quantity of ammoniacal nitrogen was practically the same in the two specimens, and was no higher than that found in some samples of summer firsts, seconds, and dirties.
  • These results show that either the bacteria had not been present long enough or had not multiplied to a sufficient extent to materially change the composition of the egg substance.
  • The eggs were recandled and 8 J-dozen eggs with broken 3'olks or with 3^olks stuck to the shell were discarded.
  • The counts of similar samples of eggs with blood rings which had not been kept for any extended period in a chill room varied from less than 1,000 to 950,000 for small blood rings and from under 1,000 to 4,300,000 for large blood rings.


  • It is observed that when eggs which have been in storage for some time are broken, many of them have a turbidity which is localized in the thick portion of the albumen, but this cloudiness disappears when the eggs are warm.
  • Breaking-Stock eggs are occasionally found "with contents which present the appearance of soft-boilecl eggs.
  • They probably had been dipped in hot water to prevent their use for hatching when they had been purchased, ostensibly for food purposes.
  • An egg laid on a haystack exposed to the direct rays of the sun becomes partially cooked and has the appearance of an egg which has been in boiling water about a minute.


  • Bacterial growth in an egg may cause cloudiness in the albumen analogous to that caused b}^the growth of bacteria in laboratory media.
  • One is caused by the action of high atmospheric temperatures and the other by exposure to damp surroundings.
  • If this sample had included " moldy spots " with offensive odors the laboratory results would show much more decomposition.


  • Black rots receive their name from the black appearance which they present before the candle.
  • A number of eggs have distinctive odors when out of the shell, though there may be no visible signs of deterioration.
  • Certain eggs show a distinctly greenish tinge in the white (see PL VIII).
  • Others, having an odor but not sufficient to preclude use according to old methods of grading, are given in Part lY.
  • It might be inferred from these facts that even though the number of bacteria in the egg be very high, as, for example, in Sample 4504, where 210,000,000 per gram were found, the infection is too recent to have produced chemical changes in the nitrogenous constituents.


  • The term " sour eggs,'' or " sour rot," is used by the egg breaker to describe an egg that has when opened a peculiar pungent odor.
  • In the later stages they may ]jave an odor suggesting sourness in the usual acceptance of the term.
  • All were obtained from the current egg suj^ply in the several packing houses, were broken by cracking on a sterilized knife edge, and were emptied into a sterilized glass cup.
  • The bacterial content of the eggs with a faintly sour odor and those with a distinctly sour odor is about the same, with the exception of Sample 4256, in which the bacterial count agrees with the eggs in Part III in having a decidedly sour odor.


  • The eggs called musty by the bakers have a strong odor, very j)enetrating and persistent, becoming more pronounced Tvhen heat is applied.
  • All such eggs are sharply watched for by egg breakers and discarded.
  • Fortunately they are not very plentiful, even in the early spring and late summer, when they are most conmion.
  • The sense of smell alone must be depended upon to detect them.
  • It is highly desirable that further and detailed studies be made of this type of egg, which is interesting from practical and scientific viewpoints.


  • Stmimarizing the total bacterial contents of individual eggs ox^ened aseptically in the laboratory, shows that the greatest percentage of second-grade food eggs examined, the mediiun stale eggs, hatch-spot eggs, heavy rollers, dirty eggs, cracked eggs, and eggs with yolk jDartially mixed with albumen, contained less than 1,000 bacteria per gram.
  • Most of the specimens contained less than 10 B. coli per gram.
  • A small opening was made in the ajDex with sterile, fine-pointed forceps, about 2 square centimeters of the shell removed, and the membrane punctured.
  • B. Flaming method.--The Qgg was washed in running water, rinsed in sterile water, dried with a sterile towel, and placed, large end upjDermost, in a suitable holder.


  • The details of the collection and handling of the samples are described on page 39.
  • Plates of agar were also exposed to the air for three minutes during each plating to show the relative freedom from air contamination.
  • After a large num]5er of gelatin plates had been made and it was found that irregular counts were very frequent, it was decided to abandon the method except in special instances where special information was required.
  • As far as time permitted, one of the higher dilutions from each sample showing gas production was plated qualitatively either on litmus lactose agar or Endo's medium.
  • For this purpose they were subjected to the following tests, morphology.


  • The nutrient agar, gelatin, and broth were made from fresh beef practically in accordance with the directions given in Standard Methods of Water Analj^sis, American Public Health Association, except that they were made in larger quantities than there specified and were cleared with ^gg white and filtered through paper.
  • For liquid egg, 50 grams were weighed into a liter suction flask, 200 cc of water were added, and the flask violently shaken until a uniform suspension was secured.
  • There was then added in turn 100 cc of 95 per cent alcohol, to prevent foaming, 2 grams of sodium carbonate, to render the solution alkaline, and 1 gram of sodium fiuorid as a preserA'ative, the mixture being shaken after the addition of each reagent.
  • After the air current had passed for five hoiu's the apparatus was disconnected, the second trap and connecting tubes were rinsed off into the absorption flask, and the excess of acid titrated with twentieth-normal ammonia solution, using congo red as an indicator.
  • The sample was then reheated in vacuo imtil constant or increased weight was noted, weighing at intervals of two hours.

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