Incidence of Salmonellae in Meat and Meat Products

Standard enrichment, plating, and biochemical techniques were used to assess the incidence of Salmonella species on beef and pork carcasses and processed meat products. The incidence of Salmonella in pork carcasses was 56% and in beef carcasses, 74%. These figures are about the same as previously reported for pork but much higher than previously reported for beef carcasses; however, they represent only three to five abattoirs in Georgia and do not necessarily represent contamination levels throughout the country. Examination of carcasses by area did not indicate greater incidence of Salmonella in any one area. Two areas suggested for representative sampling are the cervical and anal areas of the carcass. Of the sausage samples examined, 38% of the fresh pork sausage, 9% of the smoked pork sausage, and 1 sample (souse) of 16 samples of miscellaneous sausage products were contaminated. Examination of subsamples indicated that Salmonella, when present in sausage products, could be found in any section of the entire sample.     

Incidence of Salmonellae in Animal Feed and the Effect of Pelleting on Content of Enterobacteriaceae

During a survey of meat and bone meals, fish meals and poultry feeds salmonellae were found only in samples of meat and bone meal, for which 19% were Salmonella -positive. MPN estimations on 2 meat and bone meal samples gave figures of 6 and 39 salmonellae/ 100 g, respectively. Sampling of poultry feed before and after pelleting showed that this process gave up to 1000-fold reduction in numbers of Enterobacteriaceae depending on the type of processing involved.     

The Isolation of Salmonellae from the Bursa of Fabricius of Chickens Latently Infected with these Organisms

A nalidixic acid resistant mutant of Salmonella typhimurium was isolated more frequently from the Bursa of Fabricius than from the caecal contents, caecal tonsil, liver or spleen of chickens that had been given a culture of this mutant by mouth. Salmonellae were also isolated more frequently from the Bursa than from the caecal contents of naturally infected chickens.     

Salmonellae in health foods

Various health food products of different brands were purchased from stores in the metropolitan Atlanta area. These foods were examined for the presence of salmonellae by fluorescent-antibody and cultural methods. Included in the study were tablets of alfalfa, parsley, kelp, wheat bran, enzyme, bone meal, and vitamins. Beef liver powder and tablets and granola cereal were also studied. Salmonella minnesota, Salmonella anatum, and Salmonella derby were isolated from two of three lots of beef liver powder from one manufacturer. All other products were negative.     

Salmonellae in health foods.

Various health food products of different brands were purchased from stores in the metropolitan Atlanta area. These foods were examined for the presence of salmonellae by fluorescent-antibody and cultural methods. Included in the study were tablets of alfalfa, parsley, kelp, wheat bran, enzyme, bone meal, and vitamins. Beef liver powder and tablets and granola cereal were also studied. Salmonella minnesota, Salmonella anatum, and Salmonella derby were isolated from two of three lots of beef liver powder from one manufacturer. All other products were negative.     

Detection of Salmonellae in the Environment

The incidence of salmonellae in contrasting environments was compared in this study. Samples collected from or near surface waters in a lush hardwood forest yielded four salmonellae serotypes from six culturally positive samples. A total of 76 samples collected from the top of a granite outcropping over a 3-month period yielded 10 positive samples. Only two salmonellae serotypes were isolated, and one of these was isolated only once. The nature of the sample material had no significant effect on the detection of salmonellae from the two sampling sites. However, the presence or absence of visible moisture in the sample significantly affected the recovery of salmonellae. The results showed that even a harsh environment such as that found on top of Stone Mountain may serve as an ecological niche for the survival and transmission of salmonellae.     

Heat Resistance of Salmonellae in Concentrated Milk

The heat resistance of Escherichia coli, Salmonella typhimurium, and Salmonella alachua in milk solutions containing 10, 30, 42, and 51% (w/w) skim milk for total solids was determined. Increased milk-solids level effected a significant increase in the heat resistance of each organism. Although E. coli was more heat-resistant than both strains of Salmonella in 10% milk, the situation was reversed in 42 and 51% milk. Prior growth temperature was found to exert a profound effect on the heat resistance of S. typhimurium. Growth of S. typhimurium in 42% milk solids for 24 hr did not greatly enhance the thermal resistance of the organism when heated in a fresh 42% solids concentrate. Application of a partial vaccum during heating greatly diminished the decimal reduction times of S. typhimurium and E. coli and, in addition, virtually eliminated the protective effect of increased solids level.     

Dressed neurons: modeling neural-glial interactions

Based on recent experimental data, we design a model for neuronal membrane potentials that incorporates the influence of the surrounding glia (dressed neurons). A neurotransmitter released into the synaptic cleft triggers a Ca(2+) response in nearby glial cells that spreads as a Ca(2+) wave and interacts with other synapses via the release of glutamate from astrocytes. We consider the simple case of a neuron-glia circuit that consists of a single neuron that triggers a Ca(2+) response in the glial cell which in turn feeds back into synapses of the same neuron. It is shown that persistent spiking can occur if the glutamate receptors on the astrocytes are overexpressed--a condition that has been reported from patients suffering from mesial-lobe epilepsy.     

Behavior of Salmonellae in Sliced Luncheon Meats

Salmonellae inoculated onto the surface of bologna and liver cheese survived protracted storage at 5 C. Salmonellae grew when the meats were incubated at room temperature.     

Distribution of virulence plasmids within Salmonellae

The virulence region of the Salmonella dublin 50 MDa plasmid shared homology with 678 of 1021 salmonellae tested in colony hybridization experiments. The majority of S. dublin, S. typhimurium and S. enteritidis isolates tested hybridized with the region whereas, with the exception of S. hessarek, S. pullorum and S. gallinarum, other serotypes did not. Homologous virulence regions were plasmid encoded. In S. typhimurium a common 60 MDa plasmid was present in all phage types tested but not in DT4, DT37 and DT170. Smaller plasmids showing partial homology were found in DT12, DT18, DT193 and DT204C. In S. enteritidis a distinct plasmid profile for each of eight phage types was observed. Hybridizing plasmids were found in DT3, DT4, DT8, DT9 and DT11 whereas DT7, which was plasmid free, and DT10 and DT14, which harboured plasmids, did not hybridize. The extent of homology shared between S. dublin, S. typhimurium and S. enteritidis virulence plasmids was about 10 MDa and appeared conserved. Virulence plasmids from S. typhimurium and S. enteritidis did not show homology with a region of the S. dublin 50 MDa plasmid which was not associated with virulence functions whereas plasmids of about 24 MDa and 38 MDa in some S. typhimurium phage types did. The association of conserved virulence regions upon differing plasmids within salmonellae is discussed with reference to possible mechanisms of distribution and evolution of virulence genes.     

Isolation of Salmonellae from Pork Carcasses

Four hundred and twenty pork carcasses from four abattoirs were examined for the presence of salmonellae by use of swabbing-enrichment techniques and contact plate methods. Carcasses from only one abattoir were found to be contaminated by swabbing-enrichment (23.3%) and contact plate (17.9%) methods. The area of the skin side of the ham, near the anal opening, was determined to be the area to examine for isolating salmonellae from pork carcasses with the greatest frequency. The most frequently isolated species of salmonellae in this study were Salmonella derby, S. anatum, S. typhimurium, and S. indiana.     

Salmonellae interplay with host cells

Salmonellae are important causes of enteric diseases in all vertebrates. Characterization of the molecular mechanisms that underpin the interactions of salmonellae with their animal hosts has advanced greatly over the past decade, mainly through the study of Salmonella enterica serovar Typhimurium in tissue culture and animal models of infection. Knowledge of these bacterial processes and host responses has painted a dynamic and complex picture of the interaction between salmonellae and animal cells. This Review focuses on the molecular mechanisms of these host-pathogen interactions, in terms of their context, significance and future perspectives.     

Resistance of Salmonellae Isolated in 1962 to Chlortetracycline

Among 652 salmonellae examined, Salmonella typhimurium displayed a much higher incidence of resistance to chlortetracycline than did other serotypes. Among S. typhimurium cultures from man, the incidence of resistance (38%) increased markedly over that of cultures isolated 3 years previously (13.9%), whereas a similar increase was not noted among cultures from fowls. Resistance among cultures from animals other than fowls (72.5%) was due largely to the high incidence of resistance among cultures from bovine sources (93.7%).