Contamination of broiler carcass skin during commercial processing procedures: an electron microscopic study

Microbiological status of selected chicken carcases from a non-automated poultry processing plant

The microbiological status of chicken carcases sampled at three different processing points in a South African Grade B poultry abattoir slaughtering ca. 750 birds per hour, was determined. Six skin samples and two meat samples were aseptically collected from different sites on each carcase. Total bacterial counts were performed at 25 degrees C, 37 degrees C and 43 degrees C and all colonies from plates showing between 30 and 300 cfu were characterised. Bacterial counts of the skin samples at 37 degrees C were consistently the highest, followed by those at 25 degrees C and then 43 degrees, but for the two meat samples the highest bacterial counts were found at 37 degrees C and the lowest at 25 degrees C. Neck skin counts were marginally higher than bacterial counts of the other skin samples. The Gram negative genera Escherichia and Acinetobacter were isolated most frequently at all three incubation temperatures and from all sampling sites, while the dominant Gram positive genera were Staphylococcus and Enterococcus. Escherichia isolates predominated on the skin sampling site cranio-dorsal to the pygostyle, whilst Staphylococcus isolates predominated on the skin sampling site caudal to the breastbone. Microbiological contamination is a major problem in the abattoir studied and further studies should therefore aim to determine points of maximum contamination in the processing line.

Microbiological survey of five poultry processing plants in the UK

1. Neck skin samples were taken from chickens and turkeys at all the main stages of processing to monitor changes in total viable count (TVC) and counts of coliforms and pseudomonads. 2. Processing reduced TVC by up to 100-fold. Geometric mean counts after packaging were log10 4.4 to 5.3 CFU/g whilst corresponding counts of coliforms were 2.7 to 3.8 CFU/g. 3. Increases in mean TVC or coliforms as a result of either defeathering or evisceration did not exceed 0.6 log. 4. Pseudomonads represented only a minor fraction of the initial microflora of the bird and were often reduced by scalding to a figure which could not be detected by direct plating of samples; however, subsequent contamination resulted in means between log10 2.9 and 4.0 CFU/g for packaged carcases. 5. Although Staphylococcus aureus was readily isolated from defeathering equipment, mean counts from defeathered carcases were always below log10 3.0 CFU/g.

A model study of factors involved in adhesion of Pseudomonas fluorescens to meat

A study was undertaken to investigate the factors involved in the adhesion of Pseudomonas fluorescens to model meat surfaces (tendon slices). Adhesion was fast (less than 2.5 min) and was not suppressed by killing the cells with UV, gamma rays, or heat, indicating that physiological activity was not required. In various salt solutions (NaCl, KCl, CaCl2, MgCl2), adhesion increased with increasing ionic strength up to 10 to 100 mM, suggesting that, at low ionic strengths, electrostatic interactions were involved in the adhesion process. At higher ionic strengths (greater than 10 to 100 mM) or in the presence of Al3+ ions, adhesion was sharply reduced. Selectively blocking of carboxyl or amino groups at the cell surface by chemical means did not affect adhesion. These groups are therefore not directly involved in an adhesive bond with tendon. Given a sufficient cell concentration (10(10) CFU.ml-1) in the adhesion medium, the surface of tendon was almost entirely covered with adherent bacteria. This suggests that if the adhesion is specific, the attachment sites on the tendon surface must be located within collagen or proteoglycan molecules.

New method to study bacterial adhesion to meat

A new method was developed for the study of bacterial adhesion to meat surfaces. Thin slices of meat (40 microns thick) were inserted into a specially designed observation chamber. The meat slices were then exposed to a bacterial suspension (ca. 10(6) CFU.ml-1) to initiate adhesion (20 min of contact time) and subsequently rinsed to eliminate nonadherent bacteria. Because of the special chamber design, the disruptive force exerted on the bacteria during rinsing (shear stress) was uniform over the whole surface of the meat slices, was constant, and could be varied from 0 to 0.08 N.m-2. After being rinsed, the meat slices were stained with basic fuschin and observed under light microscopy to determine the number and distribution of adherent bacteria. This new method was used to study the adhesion of Acinetobacter strain LD2, a Lactobacillus sp., and Pseudomonas fluorescens to slices of beef fat and tendon. At 25 degrees C, most (greater than or equal to 99.9%) of the cells of the Lactobacillus sp. deposited on the meat were washed off the surface during rinsing (0.05 N.m-2), whereas a large number (ca. 10(5) CFU.cm-2) of Acinetobacter strain LD2 and P. fluorescens cells remained adherent. The extent of adhesion was similar on fat and tendon, and adherent bacteria were distributed evenly over the whole surface of the slices. This preliminary study indicates that the combined use of thin slices of meat and of the observation chamber provides us with the means to more accurately study bacterial adhesion to meat surfaces.

Bacteriological quality of broiler carcasses as affected by in-plant lactic acid decontamination

In an attempt to improve the bacteriological quality of broiler carcasses the bactericidal effect of treatments with 1% and 2% lactic acid was investigated. Bacterial colonisation was determined immediately after treatment, after the carcasses had been chilled and during storage at 0 degrees C. Examination included numbers of mesophilic aerobic and psychrotrophic aerobic colony-forming units (CFU), CFU of Enterobacteriaceae at 37 degrees C and CFU of Staphylococcus aureus. Immediately after treatment colonisation per gram skin was generally reduced by about 1 log. Initially 2% lactic acid was not found significantly more effective in reducing colony counts than 1%. However, treatment with 2% lactic acid suppressed post-decontamination colonisation with Enterobacteriaceae more effectively than 1% lactic acid, as determined after 15-18 days storage at about 0 degrees C. Lactic acid treatment was most effective when applied shortly before chilling. Successive treatment at three different stages during slaughtering did not increase reduction of colony counts. It is concluded that decontamination with 1-2% lactic acid at pH 2, when applied shortly before chilling, will markedly improve the bacterial safety and increase the refrigerated shelf life of broiler carcasses.

Contamination and bacterial retention capacity of beef carcasses at the abattoir

The contamination of beef carcasses was studied together with the capacity of meat surfaces to retain bacteria along the processing line in the slaughter hall. The results showed that the contamination varied along the processing line, but that this pattern was essentially dependent on the contamination at the dressing station. It decreased or remained unchanged during the first 12 min and then increased, even without additional contamination. The contamination varied according to carcasses and micro-organisms studied and was not greatly affected by spray cleaning. The number of bacteria retained changed at a rate similar to that of the contaminants. The attachment was instantaneous. The results are discussed and compared with the various hypotheses about contamination and bacterial attachment processes.

The influence of scald water pH on the death rates of Salmonella typhimurium and other bacteria attached to chicken skin

Factory trials where scald tank water was maintained at pH 9.0 +/- 0.2 showed that compared with the usual system of scalding when the water is at pH 6.0 for much of the working day the bacterial counts on carcases post scalding and plucking were significantly lower. In laboratory experiments, attached Salmonella typhimurium and the naturally occurring skin flora were found to be killed significantly more quickly in water at pH 9.0 +/- 0.2.

The preservation of mucus and surface-associated microorganisms using acrolein vapour fixation

Three fixation schedules were devised and compared in terms of their influence on the preservation of mucus and surface-associated microorganisms contained within it. Different mucus-secreting epithelial tissues from normal and spoiled oysters and normal rats were examined by scanning and transmission electron microscopy and light microscopy. On all tissues, mucus was best preserved in specimens fixed by 10% acrolein vapour for 1 h then immersed in 3% glutaraldehyde--3% formaldehyde fixative containing 0.05% ruthenium red, cacodylate buffer pH 7.4, for at least 3 h. This fixation schedule also greatly increased the preservation of microorganisms in mucus in specimens from spoiled oysters and normal rats. In contrast, the retention of mucus and surface-associated microorganisms was poor in tissues fixed either by 1% OsO4 vapour for 1 h followed by immersion in combined aldehyde fixative, or by direct immersion. The quality of preservation of the mucus layer, epithelium and sub-epithelium was also noted by transmission electron microscopy in tissues prepared by the different fixation schedules. Cellular preservation was satisfactory in directly immersed tissues but poor in vapour fixed specimens.

Most probable number cultures for assessing Salmonella contamination of eviscerated broiler carcasses

Rinse fluids collected from eight different lots of commercially processed broiler carcasses were cultured for salmonellae by a meat probable number method. Most probable number values of 80 or less were obtained from all carcasses in three of the eight lots, but two lots contained carcasses which yielded more than 1000 salmonellae. Similar numbers of salmonellae were recovered in repeated rinses of the same carcasses, suggesting that only a small proportion of the total population was recovered in each rinse. Five lots originated from flocks of known Salmonella status. More salmonella were recovered from carcasses which originated from flocks infected in the first week of life than from flocks infected at a later date. Carcasses from a flock which was processed immediately after a contaminated flock yielded more salmonellae than carcasses processed at the beginning of the day in a clean plant.

Attachment of Salmonella spp. to chicken muscle surfaces

Immersion of chicken muscle fascia in water or physiological saline caused collagen associated with the connective tissue to expand and form a dense network of fibers on the surface. Similar changes were noted for muscle perimysium. Two test strains of Salmonella spp. attached to the collagen fibers only when muscle was immersed for extended times in water. Bacteria did not attach to the fascia or perimysium of muscle that was transiently immersed in suspensions. The presence of sodium chloride in the suspension media prevented firm attachment, whereas saline rinses removed many attached cells.

Spoilage of chicken skin at 2 degrees C: electron microscopic study

Microscopic techniques were used in conjunction with normal microbiological procedures to examine the development of the spoilage microflora on the skin of chicken carcasses held at 2 degrees C. Pigmented and nonpigmented psychrotrophic pseudomonads were the major spoilage bacteria isolated at all stages of storage examined. The spoilage microflora grow within a liquid film covering the skin surface, as well as in feather follicle shafts. Penetration and disruption of skin tissue were not observed even after onset of organoleptic spoilage. Bacteria were not attached to the skin by extracellular bridging substances. These data suggest a nonspecific histological-microbiological relationship between he spoilage association and the skin substrate.