Biological differences between FIM2 and FIM3 fimbriae of Bordetella pertussis: not just the serotype

Resurgence of Bordetella pertussis, including one macrolide-resistant isolate, France, 2024

As other European countries, France is experiencing a resurgence of pertussis in 2024. Between 1 January and 31 May 2024, 5,616 (24.9%) positive Bordetella pertussis qPCR tests were identified, following a 3-year period of almost null incidence. Of 67 cultured and whole genome sequenced B. pertussis isolates, 66 produced pertactin and 56 produced FIM2, in contrast to pre-COVID-19 years. One isolate of genotype Bp-AgST4 was resistant to macrolides. Pertussis resurgence may favour isolates that produce FIM2 and pertactin.

fim3-24/ptxP-3 genotype is associated to whooping cough outbreak in Brazilian Midwest: The selection of Bordetella pertussis strains driven by vaccine immunization

Whopping cough (or Pertussis) is an acute infectious respiratory disease caused by Bordetella pertussis bacteria. The disease is highly transmissible and can be fatal in children under two years old. Since the introduction of vaccine immunization in 1940, Pertussis incidence decreased worldwide. In Brazil, the immunization was introduced in 1977 using the whole cell (wP) vaccine. Despite the high vaccination coverage, an unexpected increase in the number of observed Pertussis cases was observed in 2012. In this year, 2257 cases were reported exceeding the average incidence rate of <1000 cases per year until 2010. This outbreak reached a peak level in 2014 and ended in 2018 according to the Brazilian National Surveillance System (SINAN). To understand the relationship between the outbreak and the vaccination, bacterial isolates (n = 136) from the Brazilian Midwest region obtained during the outbreak were submitted to genotyping of two vaccine loci: ptxP and fim3. Most of isolates (102) were obtained from nursing children (29 days to 2 years old). Genotyping of 94 isolates revealed that fim3-24/ptxP-3 was the most prevalent genotype (68%) associated with the outbreak peak. Two additional genotypes were also observed: fim3-1/ptxP-3 (15%) and fim3-3/ptxP-3 (17%). Conversely, the fim3-1/ptxP-2 genotype, which is harbored by the strain used in the wP vaccine (Bp137), was not observed. These results showed that B. pertussis circulating strains in the outbreak analyzed were different from the strain used for Pertussis immunization in Brazil. These observations provide insights that could be used to target vaccination programs to prevent future whooping cough outbreaks in Brazil.

Bordetella pertussis isolates in Finland after acellular vaccination: serotype change and biofilm formation

OBJECTIVES

In Finland, whole cell pertussis vaccine (wP) was introduced in 1952 and was replaced by acellular pertussis vaccine (aP) without fimbrial (FIM) antigen in 2005. We aimed to analyse the changes in serotypes of circulating Bordetella pertussis before and after acellular vaccination and to explore the relationship between biofilm formation and serotype diversity after the introduction of aP vaccine.

METHODS

Serotyping of 1399 B. pertussis isolates collected at the Finnish National Reference Laboratory for Pertussis and Diphtheria in Turku, Finland, from 1974 to 2023 was performed by slide agglutination or indirect ELISA. Of 278 isolates collected after 2005, 53 were selected, genotyped for fim3 and fim2 alleles, and tested for biofilm formation. The selection criteria included maintaining a relatively equal distribution of isolates per time interval, ensuring approximately a 50:50 ratio of FIM2 (N = 26) and FIM3 (N = 27) serotypes. The reference strain Tohama I was used as a control.

RESULTS

During the wP era, the majority of circulating B. pertussis exhibited the FIM2 serotype. However, FIM3 strains have appeared since 1999 and become prevalent. After the implementation of aP vaccines, the distribution of serotypes has exhibited substantial variability. FIM3 isolates displayed an enhanced biofilm formation compared to FIM2 isolates (Geometric mean value (95% CI): 0.90 (0.79-1.03) vs. 0.75 (0.65-0.85); p < 0.05). Of the 27 FIM3 isolates, 8 harboured fim3-1 and 19 fim3-2 alleles. FIM3 isolates with fim3-2 allele were significantly associated with increased biofilm formation when compared to those with fim3-1 (1.07 (0.96-1.19) vs. 0.61 (0.52-0.72); p < 0.0001).

CONCLUSION

Following the implementation of aP vaccines, the distribution of serotypes in Finland has exhibited substantial variability. FIM3 isolates with the fim3-2 allele displayed an enhanced biofilm formation capability compared to FIM2 isolates.

Differences in Biofilm Formation of Listeria monocytogenes and Their Effects on Virulence and Drug Resistance of Different Strains

Listeria monocytogenes is recognized as one of the primary pathogens responsible for foodborne illnesses. The ability of L. monocytogenes to form biofilms notably increases its resistance to antibiotics such as ampicillin and tetracycline, making it exceedingly difficult to eradicate. Residual bacteria within the processing environment can contaminate food products, thereby posing a significant risk to public health. In this study, we used crystal violet staining to assess the biofilm-forming capacity of seven L. monocytogenes strains and identified ATCC 19112 as the strain with the most potent biofilm-forming. Subsequent fluorescence microscopy observations revealed that the biofilm-forming capacity was markedly enhanced after two days of culture. Then, we investigated into the factors contributing to biofilm formation and demonstrated that strains with more robust extracellular polymer secretion and self-agglutination capabilities exhibited a more pronounced ability to form biofilms. No significant correlation was found between surface hydrophobicity and biofilm formation capability. In addition, we found that after biofilm formation, the adhesion and invasion of cells were enhanced and drug resistance increased. Therefore, we hypothesized that the formation of biofilm makes L. monocytogenes more virulent and more difficult to remove by antibiotics. Lastly, utilizing RT-PCR, we detected the expression levels of genes associated with biofilm formation, including those involved in quorum sensing (QS), flagellar synthesis, and extracellular polymer production. These genes were significantly upregulated after biofilm formation. These findings underscore the critical relationship between extracellular polymers, self-agglutination abilities, and biofilm formation. In conclusion, the establishment of biofilms not only enhances L. monocytogenes' capacity for cell invasion and adhesion but also significantly increases its resistance to drugs, presenting a substantial threat to food safety.