The prfA gene ofListeria monocytogenes encodes a protein that activates transcription of the listeriolysin gene (lisA). In order to explore the role of the prfA gene product in the pathogenesis of listerial infection, we constructed a site-directed insertion mutation in prfA by the chromosomal integration of a novel suicide vector containing a portion of the prfA coding region. This mutation not only transcriptionally silenced the listeriolysin (lisA) gene but also abrogated production of specific RNA transcripts corresponding to the phosphatOdylfiititol-specific phospholipase C (pic) and metalloprotease (mpl) genes, two further virulence gene products expressed only by pathogenic Listeria strains. The strain was also found to be avirulent when tested in a mouse model of listerial infection. The concomitant loss of multiple characteristics such as production of LisA, Pic, Mpl, and loss of virulence in a mouse infection model is the result of a mutation in a single gene and demonstrates that the prfA gene product is a positive regulator of multiple virulence determinants in L.monocytogenes.

It is known that volatile fatty acids can inhibit growth of species of the family Enterobacteriaceae in vitro. However, whether these volatile fatty acids affect bacterial populations in the ceca of chickens is unknown. Therefore, a study was conducted to investigate if changes in volatile fatty acids in ceca of broiler chickens during growth affect bacterial populations. Results showed that members of the Enterobacteriaceae and enterococci are present in large numbers in 3-day-old broilers and start to decrease when broilers grow older. Lactobacilli are present in large numbers as well in 3-day-old broilers, but they remain stable during the growth of broilers. Acetate, butyrate, and propionate increase from undetectable levels in 1-day-old broilers to high concentrations in 15-day-old broilers, after which they stabilize. Significant negative correlations could be calculated between numbers of Enterobacteriaceae and concentrations of undissociated acetate, propionate, and butyrate. Furthermore, pure cultures of Enterobacteriaceae isolated from the ceca were grown in the presence of volatile fatty acids. Growth rates and maximal optical density decreased when these strains grew in the presence of increasing volatile fatty acid concentrations. It is concluded that volatile fatty acids are responsible for the reduction in numbers of Enterobacteriaceae in the ceca of broiler chickens during growth.

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Investigations of two chicken processing plants in The Netherlands have shown that large contamination with Campylobacter jejuni can exist on birds, equipment, hands of processing-line workers and in air samples from the processing facility. This contamination appeared only to be of intestinal origin. Intestinal contents of birds to be processed contained up to 107 C. jejuni per gram. Contamination of birds was reduced during scalding at 58°C, but this reduction was not always observed at 51.8°C. The number of C. jejuni on carcasses increased during defeathering and evisceration. Large numbers of C. jejuni were washed off the carcasses when a spinchiller was used. When air-cooling was employed, C. jejuni in some instances died off, probably due to drying. End-products from these chicken processing plants contained C. jejuni in 50% of carcasses and 75% of livers.

Aerolysin from Aeromonas sobria AB3 was isolated and purified. The pure toxin formed sodium dodecyl sulfate-insoluble oligomers in a lipidic environment. The addition of aerolysin to the aqueous phase bathing lipid bilayer membranes resulted in the formation of ion-permeable channels which had a single-channel conductance of about 70 pS in 0.1 M KCl. This defines the toxin as a channel-forming component similar to other toxins but without any indication for an association-dissociation reaction, since the channels had a long lifetime at low voltages. At voltages higher than 50 mV, the aerolysin channel switched into a closed state with a low residual conductance. The single-channel conductance was a linear function of the total aqueous conductance, which suggested that the toxin oligomers formed aqueous channels with an estimated minimal diameter of about 0.7 nm. The aerolysin pores were found to be slightly anion selective. The pore-forming properties of aerolysin were compared with those of alpha-toxin of Staphylococcus aureus. Both aerolysin and alpha-toxin share secondary structure features, must oligomerize to form pores in lipid bilayer membranes, and form channels with similar properties.

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The presence of antibodies to staphylococcal enterotoxins (enterotoxins A through F) in sera of healthy subjects (n = 567) and in sera of patients with toxic shock syndrome (n = 20) was determined. Furthermore, production of enterotoxins by Staphylococcus aureus isolated from humans was investigated. In 46, 86, 78, 41, 20, and 91% of the sera of healthy subjects, antibodies were found against enterotoxins A, B, C, D, E, and F, respectively. The high percentage of sera with antibodies against enterotoxin F correlated with the relatively high frequency of enterotoxin F-producing S. aureus isolated from humans (one-third of the isolates produced enterotoxin F). In patients with toxic shock syndrome, antibodies against enterotoxin F were not present or were present only at very low levels. An increase of antibodies after onset of the disease was observed in two of eight patients investigated. From the results, it can be concluded that only those humans who show low levels of antibodies are susceptible to toxic shock syndrome.

Four synthetic oligonucleotides encoding different parts of the Clostridium perfringens enterotoxin gene were used to test the enterotoxigenicity of C. perfringens strains isolated from confirmed outbreaks of food poisoning. Of the 245 strains isolated from food and feces originating from 186 separate outbreaks, 145 (59%) gave hybridization reactions with each of the four DNA probes used, while 104 strains did not hybridize with any of the probes. There was no correlation between serotype and the presence of the enterotoxin gene, although the C. perfiringens enterotoxin gene was rarely detected among nontypable strains (17%). Results show that DNA hybridization is a suitable method for the identification of C. perfringens strains which have the potential to produce enterotoxin.