Log Mean Numbers Research Articles

The effects on product of a hot water pasteurizing treatment applied routinely in a commercial beef carcass dressing process

The effects of a pasteurizing treatment on the microbiological condition and the appearance of carcasses, routine in a commercial carcass dressing process, were examined. Beef carcass sides were pasteurized with water at 85°C. During 2-h periods, all sides from the dressing process were treated for 8, 9, 10, 11 or 12 s. During each period, microbiological samples were obtained by swabbing five randomly selected sides before and five others after the treatment, with a single sample being obtained from 25 treated and 25 untreated sides from each treatment time. All treatments similarly reduced the log mean numbers of total aerobic counts by about 1 log unit, but the reductions in the log total numbers of coliforms orEscherichia coli recovered from 25 samples increased with increasing treatment time, to >2 log units with treatment times of 11 or 12 s. Cooling of the sides did not obviously reduce the numbers of total aerobic bacteria on beef sides, but there were small reductions in the numbers of coliforms and E. coli on both treated and untreated sides. After cooling, sides treated routinely for 10 s yielded total aerobic counts at log mean numbers of about 2 log cfu cm−2, and coliforms and E. coli at log total numbers of <2 and <1 log cfu 2500 cm−2, respectively. After the carcass breaking process, loin primal cuts and manufacturing beef from such sides yielded total aerobic counts at log mean numbers of about 3 and about 4 log cfu cm−2, respectively; coliform counts at log total numbers of about 3 and about 4 log cfu 2500 cm−2, respectively; and E. coli counts at log total numbers >2 log cfu 2500 cm−2; which indicated that product was contaminated from improperly cleaned equipment during the carcass breaking process. When sides treated for 10 s with water that had previously been used to treat 120 or more sides were compared after cooling with untreated sides from the same carcasses, the appearances of treated sides were judged to be less desirable than those of the untreated sides because of the less desirable appearance of the fat tissue on the treated sides. However, the mean differences between untreated and treated sides for overall appearance and the appearance of fat tissue were only 0·45 and 0·46 assessment units, respectively, for assessments on a seven-point scale. The small adverse effect of the pasteurizing treatment on the appearance of beef carcass sides apparently did not affect the value of the meat. Thus, the data indicated that, in commercial practice, pasteurizing treatment times should be set by reference to reductions in numbers of E. coli rather than of total aerobic counts, to assure the maximum possible reduction in the number of enteric pathogens; that protein suspended in the circulating water of pasteurizing equipment will accumulate to levels that affect the appearance of carcass fat, unless the water is changed at appropriate intervals or actions are taken to remove the protein from the water or carcass surfaces; and that pasteurizing of carcasses alone is inadequate for assuring the safety of meat when recontamination of product with enteric organisms occurs during the carcass-breaking process.

Microbiological Conditions of Sheep Carcasses from Conventional or Inverted Dressing Processes

At a small abattoir, 25 sheep carcasses were dressed conventionally, with the carcass suspended by the rear legs, and 25 carcasses were dressed while inverted, with the carcasses suspended by the forelegs. Two swab samples were obtained from randomly selected sites on each carcass, and total aerobic, coliform, and Escherichia coli counts were enumerated for each sample. Each type of count was arranged in two sets of 25 counts for each type of dressing process, and a log mean number and/or log total number recovered was calculated for each set of counts. The log mean number of total aerobic counts for one set of counts from carcasses dressed while inverted was less than the corresponding log mean numbers for both sets from the conventionally dressed carcasses and the other set from the carcasses dressed while inverted, and differed from them by about 0.7 log units. The coliforms recovered from carcasses were largely E. coli. The log total numbers of coliform or E. coli counts recovered from carcasses dressed while inverted were about 1.5 log units less than the corresponding log total numbers recovered from conventionally dressed carcasses. Those data indicate that the substitution of inverted for conventional dressing might serve to reduce the numbers of E. coli on sheep carcasses by reducing the microbiological contamination of the hindquarters but that the general microbiological condition of the carcasses would be little improved unless some means of preventing or removing contamination of the forequarters was also used.

Evaluation of the hygienic performances of the processes for cleaning, dressing and cooling pig carcasses at eight packing plants

The hygienic performances of the processes for the production of cooled carcasses at eight pork packing plants were assessed from small sets of microbiological data. At each plant, a single sample was obtained from a randomly selected site on each of 25 randomly selected carcasses at each of three stages of processing, which were after polishing, after washing at the end of the dressing process, and after cooling. The aerobic bacteria, coliforms and Escherichia coli recovered from each sample were enumerated. When bacteria of one type were recovered from ≥20 of 25 samples, the log mean number of those bacteria on the population of carcasses undergoing processing was estimated on the assumption that the set of counts was normally distributed. The log of the total number recovered from 25 samples was calculated for each set of counts. The log mean numbers of total aerobic bacteria recovered from the polished carcasses at different plants ranged from about 1.9 to 3.8 log cfu cm −2. At six of the plants, the log mean numbers of total aerobes on the cooled carcasses did not differ substantially from the log mean numbers on the polished carcasses, but the log mean numbers on the cooled carcasses were substantially higher at one plant and substantially lower at another than on the polished carcasses. Coliforms and E. coli were recovered from too few samples in most sets from cooled carcasses for estimation of their log mean numbers. However, the log total numbers of coliforms and E. coli recovered indicated that substantial numbers of those organisms were added to carcasses during the dressing processes at four of the plants, and that the numbers on the carcasses were substantially reduced by the processes for cooling without spraying at two of the plants. At seven of the plants, the total numbers of coliforms and E. coli recovered from cooled carcasses were <3.1 and <2.2 log cfu 2500 cm −2, respectively. The findings indicate that production processes for pig carcasses can be operated to give cooled carcasses with log mean numbers of total aerobes <2 cm −2, and log total numbers of coliforms and E. coli each <1 2500 cm −2.

The microbiological conditions of the carcasses of six species after dressing at a small abattoir

At a small abattoir, samples were collected from carcasses of cattle, pigs, deer, bison, ostriches and emus at the ends of the dressing processes. A single sample was collected from each of 50 or 25 carcasses of each species, by swabbing a randomly selected area of 100 cm2. Total aerobes, coliforms and Escherichia coli were enumerated in each sample. The microbiological conditions of the carcasses were assessed by reference to the log mean numbers of total aerobes, coliforms and E. coli estimated from sets of counts recovered from 25 samples, or to the log total numbers of coliforms and E. coli recovered from each set of 25 samples. The log mean numbers of total aerobes on beef carcasses were about 2·5 log cfu cm−2. The log mean numbers of aerobes on deer carcasses were similar, but the log mean numbers on other types of carcass were 0·5–1 log unit more. The coliforms recovered from carcasses were largely E. coli, except for pig carcasses where E. coli were only about 10% of the coliforms recovered. Escherichia coli were recovered from the majority of samples from beef and pig carcasses, at log mean numbers about 1·5 and 2·5 log cfu 100 cm−2, respectively, and log total numbers recovered >3 log cfu 2500 cm−2. Escherichia coli were recovered from minorities of samples from deer, buffalo, ostrich and emu carcasses at log total numbers about 2 log cfu 2500 cm−2. The findings indicate that when carcasses of different species are dressed at an abattoir, similar microbiological contamination of the various types of carcass cannot be assumed.

Microbiological Sampling of Carcasses by Excision or Swabbing

Groups of 25 carcasses were obtained by random selection of carcasses at the end of each of eight commercial processes for the dressing or cooling of carcasses. Samples were collected from six groups of pig or beef carcasses by excision or swabbing with sponge, gauze, or cotton wool, with one sample obtained by each of the four methods from a separate, randomly selected site on each carcass. Total aerobic counts, coliforms, and Escherichia coli from each sample were enumerated. Values for the mean log10, log10 mean, and log10 total numbers recovered were calculated for each set of total aerobic counts. Those statistics indicated that the numbers of bacteria recovered by excision or swabbing with sponge or gauze were similar, while the numbers recovered by swabbing with cotton wool were at the lower end of or below the range of the numbers recovered by the other methods. The numbers of coliforms or E. coli recovered from carcasses by sampling areas up to 100 cm2 were too few for the estimation of log mean numbers. Sampling of two groups of carcasses by swabbing with gauze indicated that each 10-fold increase in the area sampled, from 10 to 1,000 cm2, approximately doubled the number of samples from which coliforms or E. coli were recovered. Sampling of six groups of carcasses from one process indicated that the sizes of swabs and volumes of diluent used for processing swabs did not have to be increased proportionally to the area of carcass surface sampled to recover numbers of E. coli proportional to the sampled area. It therefore appears that carcass sampling techniques can be varied widely without compromising the recovery of bacteria, and that the relative efficiencies with which bacteria are recovered by different techniques can be assessed by sampling each carcass in a group of 25 by each of the methods to be compared.

Serum immunoglobulin response and protection from homologous challenge by Proteus mirabilis in a mouse model of ascending urinary tract infection.

We tested the hypothesis that experimental Proteus mirabilis urinary tract infection in mice would protect against homologous bladder rechallenge. Despite production of serum immunoglobulin G (IgG) and IgM (median titers of 1:320 and 1:80, respectively), vaccinated (infected and antibiotic-cured) mice did not show a decrease in mortality upon rechallenge; the survivors experienced only modest protection from infection (mean log(10) number of CFU of P. mirabilis Nal(r) HI4320 per milliliter or gram in vaccinated mice versus sham-vaccinated mice: urine, 100-fold less [3.5 versus 5.5; P = 0.13]; bladder, 100-fold less [3.1 versus 5.1; P = 0.066]; kidneys, 40-fold less [2.7 versus 4.3; P = 0.016]). Western blots using protein from the wild-type strain and isogenic mutants demonstrated antibody responses to MR/P and PMF fimbriae and flagella. There was no correlation between serum IgG or IgM levels and protection from mortality or infection. There was a trend toward elevated serum IgA titers and protection from subsequent challenge (P >/= 0.09), although only a few mice developed significant serum IgA levels. We conclude that prior infection with P. mirabilis does not protect significantly against homologous challenge.

Assessment of the Microbiological Conditions of Tails, Tongues, and Head Meats at Two Beef-Packing Plants

Newly skinned tails of beef carcasses at two packing plants were similarly contaminated with total aerobes and with coliforms that were largely Escherichia coli at log mean numbers about 3.5/cm2 and 4.5/100 cm2, respectively. The log mean numbers of aerobes and coliforms on the skinned tails after washing at plant A were, respectively, 1 and 2 log units less than the numbers on the newly skinned tails. At plant B, the log mean numbers of aerobes on skinned and on washed tails were similar while the log mean numbers of E. coli on washed tails were only about 1 log unit less than the numbers on skinned tails. Cooling of tails on racks in a chiller at plant B reduced the log mean numbers of E. coli by about 1 log unit but did not reduce the numbers of total aerobes. Tongues in the heads of carcasses at both plants were similarly contaminated with total aerobes and with coliforms that were largely E. coli at log mean numbers of about 4.5/cm2 and 4.5/100 cm2, respectively. The log mean numbers of aerobes on and the log total number of E. coli recovered from washed tongues were, respectively, about 2 and 4 log units less than for unwashed tongues at plant A and about 1 and 3 log units less than for unwashed tongues at plant B. The log mean numbers of aerobes and E. coli on washed cheeks and lips were both about 2 log units less than the numbers on unwashed tongues at both plants. With appropriate collection and washing procedures, the microbiological conditions of beef tails, tongues, and head meats can apparently be comparable to those of primal cuts and manufacturing beef at the times that the products are packed.

Control of the contamination of pig carcasses by Escherichia coli from their mouths

Swab samples from the mouths of 40 pig carcasses all yielded Escherichia coli, at estimated log mean numbers of 2.3 per sample. Single colonies of E. coli 0157:H7 were isolated from two, and single colonies of other verotoxigenic strains of E. coli from a further two of those samples. E. coli from the mouth were deposited on the surfaces of carcasses during usual, commercial carcass dressing operations for cutting open the throat and the floor of the mouth, and freeing the tongue. After those operations had been performed, E. coli were recovered from a neck site on 45 of 50 carcasses which were sampled by swabbing that site. When 50 carcasses on which those operations had been performed were pasteurized, the log mean numbers of total aerobic counts recovered from the neck site on carcasses were reduced by two as compared with the unpasteurized carcasses, and only one E. coli was recovered from those carcasses. Pasteurization bleached the small areas of cut muscle exposed during the operations on the mouth and throat, but apparently had no other effect on the appearance of the carcasses. It is suggested that pasteurization of pig carcasses after operating on and regulatory inspection of the mouth and throat may be a commercially viable approach to reducing the contamination of pork with pathogens from the mouths of carcasses.

Evaluation of the hygienic performances of the processes for beef carcass dressing at 10 packing plants.

The hygienic performances of the carcass dressing processes at 10 beef packing plants were assessed from small sets of microbiological data. For each process, a single sample was obtained from a randomly selected site on each of 25 randomly selected beef sides leaving the process. In addition, during a period of about a year, a further nine such sets of samples were obtained from each of two of those processes. The aerobic bacteria, coliforms and Escherichia coli recovered from each sample were enumerated. For each set of 25 counts, values for the mean log and standard deviation were calculated on the assumption that the log values were normally distributed, and the log of the arithmetic mean was estimated for each set from the mean log and the standard deviation. The processes were ranked with respect to the log mean numbers of E. coli, coliforms and total counts estimated for the products. Log mean numbers of E. coli, coliforms and total counts ranged from about 2 to < 100 cm-2, from about 3 to < 100 cm-2, and from about 5 to about 2 cm-2, respectively. For one of the processes, 8, 7, and 8 of the log mean values for the replicated sets of aerobic, coliform and E. coli counts, respectively, differed by < 1 log unit. For the other process 5, 7, and 9 of the log mean values for the replicated sets of aerobic, coliform and E. coli counts, respectively, differed by < 1 log unit. These results indicate that the first process was generally consistent in the contamination of carcasses with aerobes, coliforms and E. coli. The contamination of carcasses in the second process with coliforms and E. coli was also generally consistent, but contamination of those carcasses with aerobes was inconsistent. The findings suggest that beef carcass dressing processes can be operated consistently with respect to the bacterial contamination of carcasses, and that log mean numbers of 1 +/- 0.5 to 100 cm-2, 1 +/- 0.5 to 100 cm-2 and 3 +/- 0.5 cm-2 for E. coli, coliform and total counts, respectively, may be appropriate, commercially attainable acceptance criteria for the hygienic performance of beef carcass dressing processes.

Decontamination of carcasses by vacuum-hot water cleaning and steam pasteurizing during routine operations at a beef packing plant

The microbiological effects of three operations for cleaning areas on dressed beef carcasses with vacuuming equipment which also applies hot water to the carcass, and of an operation for pasteurizing beef carcass sides with steam, were assessed. All four operations were routine in a commercial carcass dressing process. For each operation, swab samples were obtained from randomly selected carcasses, with a single sample being collected from each carcass, from a site selected at random from those affected by the operation. For the cleaning operations, 25 samples were obtained before and 25 after each operation. For the pasteurizing operation, 50 samples were obtained before and 50 after the operation. In addition, 50 samples were obtained from beef sides after the carcass cooling process which followed the pasteurizing operation. Total aerobic counts, coliforms and Escherichia coli from each sample were enumerated. The cleaning operations generally reduced the log mean numbers of bacteria on treated areas by ≤ 0.5 and had no discernible effect on the overall microbiological condition of the carcasses emerging from the process. The pasteurizing operation reduced the log mean numbers of total aerobic bacteria on carcasses by about 1, and the log mean numbers of coliforms and E. coli by > 2. The cooling process had no affect on the total counts, but further reduced the log mean numbers of coliforms and E. coli, apparently by about 1, to give beef sides from which E. coli were not recovered.

Assessment of the Hygienic Characteristics of a Beef Carcass Dressing Process

Swab samples were obtained from the surfaces of randomly selected beef carcasses passing through a high-speed dressing process. A single sample was obtained from each selected carcass from one of 10 sites. At each of 3 points in the process, 25 samples were obtained from each carcass site. The aerobic bacteria, coliforms, and Escherichia coli recovered from each sample were enumerated. Values for the means and standard deviations of each set of 25 values were calculated on the assumption that each set of values was log-normally distributed. The E. coli data indicated relatively heavy (mean log numbers > 2/100 cm2) contamination of carcasses with E. coli during the skinning of posterior sites; redistribution of E. coli, from relatively heavily to relatively lightly (mean log numbers about 0/100 cm2) contaminated sites during evisceration operations, and reduction of E. coli numbers at most sites as a result of trimming and washing operations. However, posterior sites remained the most heavily contaminated with E. coli. The findings for coliforms were similar to those for E. coli. In contrast, the total count data indicated heavy (mean log numbers > 3/cm2) contamination of anterior (brisket) sites as well as posterior sites and little redistribution of bacteria during evisceration operations. After trimming and washing operations, the mean log total numbers at most sites were about 2/cm2, but one brisket site remained heavily contaminated. It is suggested that E. coli or coliform data are appropriate for assessing carcass dressing processes for hazard analysis critical control point (HACCP) system purposes, while total count data are inappropriate for that purpose but may be appropriate, in relation to product storage stability, for quality management (QM) system purposes.

Clinical Trial in Adults of an Antimicrobial Varnish for Reducing Mutans Streptococci

An abbreviated treatment with a chlorhexidine-containing varnish was compared with a similar treatment with a placebo varnish and with a prophylaxis alone for its effects on the numbers of detectable salivary mutants streptococci in 51 adults. The varnishes, applied once weekly for four weeks, were held in place with a covering layer of either of two polyurethane sealants (FluorProtector or Adhesit). On the first appointment, the varnish-sealant combination was applied to all tooth surfaces, but on succeeding appointments only the occlusal and approximal surfaces were covered. The chlorhexidine varnish, covered with either sealant, reduced the salivary mutans streptococci by an average of 3 logs (99.9%) in all of the 20 subjects treated, and below detectable levels for at least four weeks in nine of them. In the groups receiving placebo varnish-sealant combinations, the mean log number of mutans streptococci of the subjects was reduced only by approximately 0.5 log (32%), and none of the subjects experienced loss of their detectable mutans streptococci for four weeks, although one subject did so for three weeks. No significant difference between the effects of the two polyurethane sealants was observed. Treatment with a single prophylaxis had no effect on mutans streptococcus levels. Subjects treated with chlorhexidine varnish also experienced an increase in S. sanguis and a small decrease in yeasts. Loss of detectable mutans streptococci did not cause changes in the numbers of other micro-organisms examined, beyond those observed with chlorhexidine varnish treatment alone.

Evaluation of a standard scrubbing method for the recovery of aerobic skin flora

The most reliable method for sampling skin flora is still a matter of debate, although the subject is of importance in many fields ranging from clinical to basic research. For the evaluation of normal skin flora, Williamson and Kligman's scrub method is the most commonly used. In order to determine the value of this method, standardized for the evaluation of topical antimicrobial agents on aerobic skin flora, we compared its results to those obtained both from bacterial counts and from microscopic studies on biopsies performed at the same site. After different experiments had established the optimal experimental conditions on human and pig skin, a comparative study on six healthy subjects was carried out in the peri-umbilical area. The mean log numbers of aerobic bacteria in the scrub samples and in the biopsies were respectively, 3.1 and 2.9, which were not statistically significant. These numerical results were similar to those obtained by electron microscopy. Hence, the standard scrub method may be considered satisfactory for the recovery of aerobic bacteria from healthy human skin.

Heat transmission in boilers

To obtain information about the microbiological quality of horse meat exported from North America, the microbiological conditions of hot or cold boned primal cuts and carcass quarters from horse carcasses processed at a North American packing plant were examined. In addition, temperature histories were obtained from boxes of hot boned meat during cooling, and from horse carcass quarters air freighted to Europe. The log mean numbers of aerobes recovered from horse carcasses after dressing were >2 log cfu/cm2. Log total numbers of coliforms and Escherichia coli recovered from 25 samples from such carcasses were >2 log and <2 log cfu/2500 cm2, respectively. Numbers of bacteria generally similar to those were recovered from cooled carcasses or hot or cold boned cuts. The cooling process for hot boned meat met with standards for hot boned beef cooling processes based on calculated growth of E. coli at box centres. The deep tissues of carcass quarters cooled and the temperatures of their surfaces rose during air freighting, but surface temperatures mostly remained below 7 °C. The microbiological condition of horse carcass quarters delivered to plants in Europe would likely be comparable with the microbiological conditions of hanging beef delivered from packing plants to distant customers within North America.