COMPARISON OF COLIFORN AND ENTEROCOCCUS ORGANISMS AS INDICES OF POLLUTION IN FROZEN FOODS

Physiological and molecular aspects of bile salt response in Enterococcus faecalis

Analysis of the susceptibility and the acquisition of tolerance in Enterococus faecalis towards bile salts showed a nearly instantaneous killing effect and yielded evidence for homologous tolerance as well as for cross-protections. Two-dimensional (2-D) electrophoresis revealed 45 proteins which are amplified in response to the bile salt treatment. These include a set of seven proteins, the synthesis of which is increased not only with the bile salts but also with multiple sublethal stresses of various nature. Characterisation of the latter (called general stress proteins) showed that at least five of them are related to resistance to bile salts, heat, ethanol, oxidative and alkaline pH stresses and are probably involved in cross-protection development. On the other hand, random mutagenesis of E. faecalis allowed the isolation of 10 bile salt-sensitive mutants. Their characterisation revealed that the mutation loci corresponded to genes related to DNA repair, oxidative response, transcriptional regulation, dGTP hydrolysis, membrane composition or cell wall synthesis. Further characterisation of one mutant revealed that the insertion within the E. faecalis sagA gene led to morphology changes, to perturbations of cell division and to a decrease of the resistance towards several independent physicochemical stresses.

Identification and characterization of gsp65, an organic hydroperoxide resistance (ohr) gene encoding a general stress protein in Enterococcus faecalis

The Enterococcus faecalis general stress protein Gsp65 has been purified from two-dimensional gel electrophoresis. Determination of its N-terminal sequence and characterization of the corresponding gene revealed that the gsp65 product is a 133-amino-acid protein sharing homologies with organic hydroperoxide resistance (Ohr) proteins. Transcriptional analysis of gsp65 gave evidence for a monocistronic mRNA initiated 52 nucleotides upstream of the ATG start codon and for an induction in response to hydrogen peroxide, heat shock, acid pH, detergents, ethanol, sodium chloride, and tert-butylhydroperoxide (tBOOH). A gsp65 mutant showed increased sensitivity to the organic hydroperoxide tBOOH and to ethanol.

Identification of general stress genes in Enterococcus faecalis

The susceptibility and the acquisition of tolerance of E. faecalis ATCC 19433 to heat, ethanol, bile salts, NaCl, H2O2 and pH shifts were determined. During exposure to these environmental stresses, protein synthesis analysed by 2-D electrophoresis revealed 167 stress proteins. Six stress protein were found to be induced by at least six of the eight treatments and considered to be general stress proteins (Gsp). Western blotting identified two of these Gsp as DnaK and GroEL. Analysis of the four other Gsp revealed that at least two of them were not previously described.

Comparison of enterococci and coliform microorganisms in commercially produced pecan nut meats

Pecan nut meats in the unbroken shell are sterile for enteric microorganisms. Recovery of coliform microorganisms or enterococci from finished pecan nut meats indicated contact contamination, assuming the tempering procedures to be satisfactory. Results of specific studies, designed toward developing background data on the sanitary significance of enterococci and coliform microorganisms in the production of pecan meats are reported. Unbroken pecan nuts or nut meats from various stages of shelling operations were diluted with a phosphate-buffered diluent. Serial dilutions were inoculated into Lactose Broth and Azide Dextrose Broth. The lactose fermentors were carried through indole, methyl red, Voges-Proskauer, and citrate reactions; the positive Azide Dextrose cultures were confirmed in Ethyl Violet Azide Broth and microscopically. Viable plate counts were obtained. Enterococci were found resistant to many deterrent factors affecting coliforms. Recoveries of enterococci were detected long after pollution had occurred. Little correlation was found between enterococcal recovery and observed insanitary practices in commercial shelling operations. Using the coliaerogenes group and, specifically, Escherichia coli as a sanitation index, microorganisms allowed accurate appraisal of tempering, personnel practices, and contact surface contaminating factors. It is felt this was due, in part, to the more delicate growth characteristics of E. coli. The fact that other pathogenic microorganisms, capable of causing gastrointestinal upsets, are associated with the presence of E. coli introduces a health factor which is important to regulatory agencies concerned with consumer protection.

Bacteriological examination of unbottled soft drinks

A study of 300 samples, representing 14 different unbottled drinks, indicated that there are three vitally important criteria pertaining to their bacteriological examination. First, the total viable counts may be better accomplished by the pour-plate method, using enriched media, with incubation at either 30 or 37 C. Second, a comparative study of the coliaerogenes group and the enterococci as indices of pollution unquestionably favors the latter as the reliable indicator, owing to false interpretations of the presumptive test and to lack of accurate definition of fecal and nonfecal coliforms recovered from positive cases. The use of enterococci, however, did not provide as reliable an indicator as the pour-plate method. Third, the results with enterococci, in defining the probable source of pollution, are more precise. Experiments judiciously selected and simultaneously conducted revealed that the heat and heat-tellurite resistance tests, and the tetrazolium-reduction test, matched in relating 98.9% of available enterococci to an animal source. Negligible but vital discrepancies were obtained with the two odd strains which qualified as human-derived according to the heat and heat-tellurite resistance tests. The differential criterion of Skadhauge and Barnes, based on the failure of animal-derived enterococci to grow in the presence of a low concentration of potassium tellurite, did not apply to the other two methods, since 99.5% of the recovered strains were found tolerant to the specified tellurite concentration.

Microbiological standards and handling codes for chilled and frozen foods. A review

The usefulness of microbiological standards for frozen foods is now a controversy in the trade and scientific literature. Most reviewers have given arguments both for and against, and have concluded that they should be applied with great caution. Such standards have the advantage of putting questions of safety on a convenient numerical basis. Canadian workers have reported that promulgation of standards has invariably raised the hygienic level of the products controlled. Bacteriological standards have often been associated with the question of safety to the consumer. Everyone recognizes that food poisoning bacteria are a potential danger in any food. But many have argued that the history of food poisoning outbreaks from frozen foods is excellent and that there is no need for standards; on the other hand, proponents of standards have pointed to the incomplete investigation and reporting of outbreaks, and have argued that there may be more outbreaks than we realize. They have pointed to laboratory studies that have shown grossly mishandled precooked frozen foods to be truly dangerous. Some have proposed that pathogens should be absent from foods; but others have questioned that a microbiological standard can accomplish this end. Some pathogens, such as Salmonella or Staphylococcus have been shown to be so ubiquitous that their presence in some commercial foods is unavoidable. Also, sampling and analytical methods have been described as inadequate to guarantee that pathogens present will be detected. Some have argued that control at the source is a better way-through inspections of the plant operation, by enforcement of handling codes, or by processing procedures such as pasteurization, which would be more certain to result in a pathogen-free food.A most important part of any of the proposed standards is a "total count" of viable aerobic bacteria. English workers have found that foods causing poisoning outbreaks usually had total viable counts above 10 million per gram. On the other hand, these same workers found Salmonella on meats with very low total viable count. The assumption by many that low total count indicates safety has been shown to be not always true. Furthermore, high counts of nonpathogenic organisms, such as psychrophilic saprophytes would have no public health significance. The relation between bacterial level and quality is open to less controversy. Some authorities have pointed to bacterial level as a measure of sanitation, adequacy of refrigeration, or speed of handling. Others have indicated that to determine which of these factors caused a high count would be impossible with only a total count on the product as a guide. Some investigators have said a high count affects flavor adversely before actual spoilage is evident, and this may be a factor in competition on today's market. It is well established that initial bacterial level will affect the shelf-life of a chilled product. Methods of analysis are more nearly adequate for counts than for pathogens, but they need improvement, and should be clearly specified as part of any bacteriological standard. Foods with high count could sometimes be brought into compliance merely by storing them for a sufficient period frozen, or by heating them slightly. This has been cited by some authors as a disadvantage of bacteriological standards. The enterococci and the coliform group (except Escherichia coli) have been shown to be ubiquitous and therefore should not be used alone to indicate fecal contamination. Although E. coli has greater significance, its source should be determined each time it is found. Various reviewers have expressed the need for caution in the application of standards. The principal precautionary arguments we have found are as follows:1) A single set of microbiological standards should not be applied to foods as a miscellaneous group, such as "frozen foods" or "precooked foods."2) Microbiological standards should be applied first to the more hazardous types of foods on an individual basis, after sufficient data are accumulated on expected bacterial levels, with consideration of variations in composition, processing procedures, and time of frozen storage.3) When standards are chosen, there should be a definite relation between the standard and the hazard against which it is meant to protect the public.4) Methods of sampling and analysis should be carefully studied for reliability and reproducibility among laboratories, and chosen methods should be specified in detail as part of the standard.5) Tolerances should be included in the standard to account for inaccuracies of sampling and analysis.6) At first, the standard should be applied on a tentative basis to allow for voluntary compliance before becoming a strictly enforced regulation.7) Microbiological standards will be expensive to enforce.8) If standards are unwisely chosen they will not stand in courts of law.

Enterococci in milk and milk products

Enterococci are widely distributed in nature. They gain entry into milk and milk products through the water supply, equipment, and insanitary and unhygienic conditions of production and handling. They have been incriminated as direct or indirect agents of disease. The evidence concerning their involvement is only circumstantial. These reports are also disputed as the disease symptoms have not been experimentally induced in animal models. However, there is sufficient evidence to indicate that prolific growth of enterococci in foods may lead to formation of clinically significant levels of pressor amines. These amines are very thermostable and therefore remain active even after heat processing, which eliminates all viable streptococci. These pressor amines may be involved in the onset of migraine attacks and produce hypersensitive crises in psychiatric patients who are being treated with monoamine oxidase inhibitors for depression.

The ecology of the streptococci

All species of streptococci are divided into several groups according to the ecological niches they occupy. Members of the lactic acid group are found only in the plant environment and the dairy. Members of the pyogenic group and the buccal and intestinal residents of the subthermophilic group are found in intimate association only with homeothermic hosts. Members of the virulent pyogenic group, such asStreptococcus pyogenes, S. equi, andS. infrequens, are restricted to single hosts-the human, the horse, and the pig-whereas others, such asS. agalactiae can be found in several hosts. The intestinal dwellers of the subthermophilic group,S. bovis andS. equinus, occur in several animal species and are not isolated from other sources. The superficially homogeneousS. faecalis of the "enteric" group may actually consist of a group specifically restricted to the human host, and of a second group distributed among wild animals, insects, and plants. The latter group differs from the human type by the ability to hydrolyze starch and to produce a rennin-proteolytic type of curd in milk.Streptococcus faecium is widely distributed in both the homeothermic and poikilothermic environments, but no properties which differentiate the sources are known.Streptococcus faecium biot.casseliflavus has been isolated only from insects and plants.Streptococcus uberis occurs on the bovine lips and skin. Unidentified streptococci from all environments vary widely in properties. Many resembleS. lactis, S. faecalis, andS. faecium.