Occurrence of Listeria and listeriosis in Hungary.

Listeriosis is a rare human disease in Hungary. The number of cases is slowly increasing. Only sporadic events have been observed but the occurrence of epidemic listeriosis may be supposed. The Listeria monocytogenes (in abbreviation: L. m.) transmitter role of food in human infections has not yet been verified. The epidemiological character of animal listeriosis is different. Healthy carriers can be found among both humans and animals. Foodstuffs of animal as well as plant origin may be contaminated with Listeria. When the processing technology and/or hygienic conditions are not satisfactory, these microorganisms can be detected in food factories and in final products of the food industry.

[Problems of listeriosis]. / A listeriosis problémáiról.

The first human listeriosis case was diagnosed in 1965 in Hungary. Since that time about 90 bacteriologically verified cases have been recognized. The half of the cases occurred in pregnant women and newborns. 45% of the patients died. The author reports the newest information about characteristics and ecology of Listeria strains and epidemiology of listeriosis. So, importance of hygienic animal husbandry and food production, transmitter role of foods, possibilities of prevention, treatment and diagnostic methods are mentioned in this paper.

Meditation of the taxonomy of Listeria.

Listeria monocytogenes was exactly identified and named in 1924. Since then the name and taxonomic position of listeriae have been changed several times. The last classification was performed on the basis of genetic studies and of some biological properties (haemolytic character, virulence and acid production from sugars). On the basis of the taxonomic validity of these characters, the Listeria genus is proposed to be classified into three species: L. monocytogenes (four subspecies), L. ivanovii and L. grayi (two subspecies).

Data for the properties of Listeria strains (a review).

It seems that taxonomy of listeriae is in a fluid stage. Between beta-haemolytic property and virulence of these bacteria a strong relationship has been demonstrated. These characters are coded by hlyA gene which seems to belong to a monocistronic unit. Virulent Listeria strains possess specific surface antigens and can enter as well as multiply in host cells. Their exact human virulence is not known. Listeriae can grow from around 0 to 42 degrees C and can survive either the effect of frost or of temperature of 48 degrees C. They may form biofilm on different surfaces. Their growth kinetics, persistance and heat resistance can be influenced by many factors (type of growth environment, pH, acidulants, salts, chemicals, antibiotics, plant substances, enzymes, humidity, atmosphere, temperature, prior temperature-effects, microbial competition and the length of influences). Radiation sensitivity of Listeria is usual. Plasmid mediated antibiotic resistant mutant of Listeria monocytogenes is verified.

Problems of microbial zoonoses in Hungary. (A review).

Hungarian data of 36 zoonotic diseases are summarized. These illnesses cause problems not only for health, public health and veterinary health services but for the society and their importance has increased. Changing character of an old pathogen (Salmonella enteritidis PT4) resulted in new epidemiological situation. The number of cases of food-borne zoonotic diseases has rapidly grown. The number of pets has elevated and in consequence the possibility of an infection of owners, breaders, sellers and other persons has also grown. Growing number of HIV positive patients as well as ill persons treated with immunosuppressive drugs increases the importance of opportunistic zoonotic pathogens (Cryptosporidium, Toxoplasma). The most effective and less expensive way to prevent an exposed population is the active immunization (BCG, tetanus, tick-borne encephalitis). Active immunization of animals can also reduce probability of human infections and economic losses (leptospirosis, rabies). In special cases it is advised to perform eradication programmes to get pathogenic-free domestic animals (brucellosis, bovine tuberculosis, salmonellosis, campylobacteriosis). Permanent surveillance is obligatory to recognize changing nature of pathogens, alteration of epidemiological situation and to identify areas for further research. Continuous education of population in general and special teaching of risky groups are very important for an effective prevention.

Differentiation of Listeria and Streptococcus strains.

Colonial morphology of non-beta haemolytic Listeria strains is frequently similar to that of non-haemolytic streptococci. Biochemical characteristics, motility, haemolysis on ox blood agar, growth on Clauberg, selective streptococcus (Si) and Mitis-Salivarius agar medium, CAMP test, serological behaviour of 16 Listeria strains were studied and the results were compared with the properties of Streptococcus strains. Microscopic morphology, motility and catalase activity are useful for distinguishing these strains. To avoid a false diagnosis, latex-agglutination should be supplemented with the above tests.

Model examination of selective media for isolation of Listeria strains.

During the Tenth International Symposium on Listeriosis (Pécs, Hungary, 1988) the Working Party on Culture Media of IUMS-ICFMH suggested comparative examination of nine enrichment broths and nine solid selective media. On the basis of this proposal the following media were studied: LiCl-phenylethanol-moxalactam agar (LPM), polymyxin-acriflavine-LiCl-ceftazidime-aesculin-mannitol agar (PALCAM) No. 1 (home made) and No. 2 (Merck), acriflavine-ceftazidime agar (AC), Oxford agar, tripaflavine-nalidixic acid serum agar (TNSA) and Forray's agar. The study was performed as described in "Testing methods for use in quality assurance of culture media". Oxford agar proved to be the best medium. LPM, AC and Forray's agars were somewhat more inhibitory than Oxford medium. In productivity TNSA and PALCAM media were weakest but the latter one was more selective. When 43 sausage samples were enriched in UVM broths and subcultured on the above mentioned media the number of positive samples was the same on Oxford, LPM, AC and TNSA agars but it was lower on PALCAM agar No. 1. When 103 milk samples were subcultured on TNSA and PALCAM agar No. 2, the number of positive samples was the same.

Specificity of antipyrogenic immunity.

The specificity of antipyrogenic immunity as well as the structural differences of the Enterobacteria responsible for pyrogenicity have been studied. Strains S. minnesota Re 595 and S. typhimurium SL 1102 as well as glycolipids obtained from them, further E. coli 083 and E. coli F 576 as well as the LPS extracted from them were used in the experiments. In conformity with the results of chemical analysis it was found that the method reflected exactly the antigenicity of the receptors responsible for pyrogenicity. Alterations of the antipyrogenic immunity may indicate that the structure of the single endotoxins responsible for pyrogenicity are different in antigenicity.

What is the diagnostic value of beta-D-glucuronidase (BDG) activity of bacteria using Fluorocult ECD agar for their cultivation?

A total of 1510 strains from 15 genera of Gram-negative and Gram-positive bacteria were studied. More than 94% of 327 Escherichia coli strains showed beta-D-glucuronidase (BDG) activity. Seventeen serotypes from 170 E. coli O serogroup representatives were negative. Relationship between the existence of BDG positive and negative E. coli strains in the same serogroup or serotype has not been observed. The rate of BDG positivity was 42% among Salmonella arizonae strains and 42.2% among Shigella strains. Only one Citrobacter strain out of the 971 strains belonging to Citrobacter, Edwardsiella, Enterobacter, Hafnia, Klebsiella, Proteus, Serratia, Yersinia, Pseudomonas, Aeromonas, Vibrio and Listeria was BDG positive. A screening method based on only BDG activity is not sufficient for the primary diagnosis of E. coli.

beta-D-glucuronidase (BDG) activity of gram-negative bacteria.

BDG is an inducible enzyme that is encoded by the uidA gene in Escherichia coli. Genetic sequences of this gene are present in most if not all E. coli strains regardless of the BDG phenotype. Expression of BDG activity can be influenced by lactose-induced catabolite repression or genetic mutations. Salmonella, Shigella and Yersinia strains frequently exhibit positive BDG reaction. BDG activity of strains belonging to genus Edwardsiella, Serratia, Yersinia, Vibrio, Erwinia, Alcaligenes, Acinetobacter, Moraxella, Plesiomonas, Achromobacter, Flavobacterium, Chromobacterium and Pasteurella awaits examination.

Alteration of phage- and biotypes of Listeria strains.

Ethyl-methyl-sulphonate mutants of Listeria monocytogenes might be different from the parent strain in phage type and in splitting of lactose, maltose, melezitose, sucrose and trehalose. Differences were observed in repeated control studies in phage type and carbohydrate-decomposition of 550 Listeria strains isolated from a variety of sources (patients, healthy and dead animals). It has been concluded that certain carbohydrate tests are unsuitable for distinguishing biotypes of Listeria. An improvement of the evaluation of phage typing results is recommended.

Computer analysis of some bacteriological, biological and physiochemical parameters of the coastal water of Lake Balaton.

Some 61 coastal water samples were taken at four definite points of Balaton Lake. Seventeen parameters of each sample characterizing the quality of the water were studied by means of multiple correlation and regression analysis, one-way variance analysis and by factor analysis with the help of BMD computer program. Uni- and multilateral relationships could be observed among the single parameters. On the basis of the results of factor analysis six factors--phytoplankton system, anthropogenic effect, own bacterial system of the lake, nitrogen circulation, hydrocarbonate and reactive phosphate system and NH+4 circulation--could be separated. Significant qualitative differences could be found along the longitudinal axis of Balaton. It could be also demonstrated that the water of the lake in its present condition is suitable for the proliferation of bacteria. Further and deeper examinations are necessary for a better understanding of the biochemical and biological processes.

Further data on the characters of Listeria strains.

The composition of a minimal medium suitable for the demands of modern genetical work is described. The nutritional requirements of some 15 strains of L. monocytogenes were studied on this medium. DL-6,8-thioctic acid was not essential. The organisms also grew without thiamine but for a convenient colony size this vitamin had to be used. The presence of Fe++, Mg++, and Ca++ ions as well as a low redox potential supplied by thioglycollate was necessary. There was some difference in the amino acid requirements of the strains. The most common demand was for leucine, iso-leucine, valine, and cysteine. The serotype, agglutinability, hemolytic effect, virulence, and nutritional requirements of the Listeria were compared. It seems that these properties are not consistently linked. Two 'EMS' mutants were also studied. The arginine, glutamine, and methionine metabolism of the auxotrophic mutant 025/4/4 was damaged and its virulence was lost. Data connected with the virulence markers of Listeria are discussed.