If immunity to pertussis in parents is maintained or boosted, 35%-55% of infant cases could be prevented. Furthermore, we found that, 1-3 years after vaccination with whole-cell or acellular vaccine, a significant percentage of children are again susceptible for typical pertussis. In the long term, pertussis vaccines and vaccination strategies should be improved to provide longer protection and prevent transmission.

The polymerase chain reaction (PCR) amplification technique was investigated as a tool for direct detection of Listeria monocytogenes in soft cheeses. Different sets of oligonucleotide primers were used, and parts of the L. monocytogenes Dth 18-gene could be amplified specifically when either a plasmid vector carrying the cloned gene or chromosomal DNA was used a template. The detection limit for L. monocytogenes in dilutions of pure cultures was between 1 and 10 colony-forming units. In extracts from soft cheeses containing L. monocytogenes DNA, the amplification was strongly inhibited. This inhibition could be reduced by an additional purification step. Despite this the detection limit showed a large variation, depending on the brand of cheese used. In some cheeses 10(3) cfu/0.5g could be visualized whereas in others the presence of 10(8) cfu/0.5 g did not yield a detectable quantity of amplified product.

Despite more than 50 years of vaccination, pertussis is still an endemic disease, with regular epidemic outbreaks. With the exception of Poland, European countries have replaced whole-cell vaccines (WCVs) by acellular vaccines (ACVs) in the 1990s. Worldwide, antigenic divergence in vaccine antigens has been found between vaccine strains and circulating strains. In this work, 466 Bordetella pertussis isolates collected in the period 1998–2012 from 13 European countries were characterised by multi-locus antigen sequence typing (MAST) of the pertussis toxin promoter (ptxP) and of the genes coding for proteins used in the ACVs: pertussis toxin (Ptx), pertactin (Prn), type 2 fimbriae (Fim2) and type 3 fimbriae (Fim3). Isolates were further characterised by fimbrial serotyping, multi-locus variable-number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE). The results showed a very similar B. pertussis population for 12 countries using ACVs, while Poland, which uses a WCV, was quite distinct, suggesting that ACVs and WCVs select for different B. pertussis populations. This study forms a baseline for future studies on the effect of vaccination programmes on B. pertussis populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s10096-014-2297-2) contains supplementary material, which is available to authorized users.

Pathogen adaptation has been proposed to contribute to the resurgence of pertussis. A striking recent example is the emergence of isolates deficient in the vaccine component pertactin (Prn). This study explores the emergence of such Prn-deficient isolates in six European countries. During 2007 to 2009, 0/83 isolates from the Netherlands, 0/18 from the United Kingdom, 0/17 Finland, 0/23 Denmark, 4/99 Sweden and 5/20 from Norway of the isolates collected were Prn-deficient. In the Netherlands and Sweden, respectively 4/146 and 1/8 were observed in a later period (2010-12). The Prn-deficient isolates were genetically diverse and different mutations were found to inactivate the prn gene. These are indications that Prn-deficiency is subject to positive selective pressure. We hypothesise that the switch from whole cell to acellular pertussis vaccines has affected the balance between 'costs and benefits' of Prn production by Bordetella pertussis to the extent that isolates that do not produce Prn are able to expand. The absence of Prn-deficient isolates in some countries may point to ways to prevent or delay the spread of Prn-deficient strains. In order to substantiate this hypothesis, trends in the European B. pertussis population should be monitored continuously.

Staphylococcus aureus growth and enterotoxin production in relation to a, (0.99-0.87), pH (4.0-7.0) and temperature (8-30°C) was determined in Brain-heart-infusion broth with respectively NaCl and sucrose as humectants. Growth of S. aureus was not observed at a, 0.85, at pH 4.3 or at 8°C. At 12'C no growth occurred at a, 0.90 or at a, 0.93 in combination with pH < 5.5. At a, 0.96 no growth occurred at pH Q 4.9. Production of staphylococcal enterotoxin type A (SEA) occurred under nearly all conditions allowing growth. Production of SEB appears to be determined by a,; at a, 0.96 SEB was produced at all temperatures allowing growth, while at a, 0.93 SEB was hardly produced. Production of SEC and SEF was affected both by a, and temperaure. Production of these toxins was rarely observed at a, 0.93. No SEC and SEF were produced at 12°C. Extrapolation of these findings to food is discussed.

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The significance of non-culturable forms of Campylobacter spp., especially with regard to the epidemiology of this organism in poultry flocks, was explored. Two different experiments were conducted to produce non-culturable Campylobacter spp. and test their ability to colonize the animal gut. In the first experiment a mixture of 28 different strains of Campylobacter spp. from various sources was inoculated in both sterilized surface water and potassium phosphate buffer and stored at 4 degrees C. After Campylobacter spp. were no longer detectable by culture in the microcosms, the mixtures of non-culturable cells were used to challenge both chicks and mice. Recovery of non-culturable Campylobacter spp. from the animals was not successful at 4 weeks after administration. In the second experiment the survival of six individual strains of Campylobacter spp. in sterilized surface water at 4 degrees C was studied and the resulting non-culturable cells were used to challenge chicks. None of the campylobacter strains could be recovered from the chicks at 2 weeks after administration. We conclude that occurrence of non-culturable forms of Campylobacter spp. capable of colonizing chicks is not a common phenomenon and that non-culturable forms of Campylobacter spp. are likely to be insignificant for importantly to the epidemiology of the organism in Dutch broiler flocks.

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