Abstract

 Background: Despite Israel's vaccination rate of 95%, pertussis incidence has peaked at 37/100, 000 (2007). Antigenic divergence between clinical isolates and vaccine strains may lead to the circulation of Bordetella pertussis (Bp) strains that are antigenically distinct from vaccine strains, thereby possibly contributing to the increasing numbers of pertussis cases in western countries. To date, there has been no attempt to identify the strain specific clone(s) of circulating Bp in Israel.

Objective: To employ Pulsed-Field Gel Electrophoresis (PFGE) to evaluate the polymorphism of the circulating Bp strains in Israel during a period of high disease activity.

Methods: We analyzed 82 isolates of Bp collected during high incidence rate years, 2007-2008 using PFGE.  The SpeI restriction enzyme was utilized.

Results: Four strains of Bp were found, named A, B, C and D.  Types A and B were the most common, are closely related and constitute 95% of the isolates. Notably, Strains A and B are identical to the 2010 European strains referenced at the Pasteur Institute (Paris), FR4803 (PFGE group IVβ) and FR4736 (PFGE group IVα), respectively. The most common Israeli strain, A, has the same PFGE cluster of the dominant European BpSR11 strain (PFGE group IVβ) identified in the 1999-2004 EUpertstrain II project (Hallander, 2007). Strain clonal expansion may represent an adaptive response to high vaccination coverage.

Conclusion: The dominant European PFGE cluster (PFGE group IVβ) was  also predominant in Israel, 2007-2008. International pertussis strains monitoring among highly vaccinated population should be pursued to track Bp polymorphism.

 

Introduction

 

v In recent years, despite widespread vaccination, Bordetella pertussis (Bp) has become increasingly prevalent. vAntigenic divergence between pertussis clinical isolates and vaccine strains may lead to the circulation of pertussis strains that are antigenically distinct     from vaccine strains. vPulsed field gel electrophoresis (PFGE) is the most discriminatory typing method for studying the Bp population. vIn Europe, Hallander et al identified a predominant pertussis strain with a distinct PFGE profile (BpSR11, PFGE cluster IVβ). v To date, there has been no attempt to identify the strain specific clone(s) of circulating Bp in Israel.  

Aim of the study

 

v to employ PFGE to evaluate the polymorphism of the circulating Bp strains in Israel during a period of high disease activity and to compare them with        select European strains.  

Methods

 

vAll culture and polymerase chain reaction (PCR) - positive samples for Bp (n=82) sent to Bnai Zion Medical Center's referral Clinical Microbiology      Laboratory in Haifa, Israel between 2007-2008 were included in the study (2007, n=37; 2008, n=45). vCultures, real time PCR (n=51) and conventional semi-nested PCR (n=31) were performed. vPFGE was performed in the Clinical Microbiology Laboratory at Rambam Medical Center, Haifa, Israel. v The SpeI restriction enzyme was utilized.  Results   vStrains A and B, A and C, B and C, and A and D differed by one or two DNA segment and as such represent closely related B. pertussis strains caused by changes occurring as a result of a single genetic event (i.e., point mutation, deletion or insertion of DNA) (Figure 1). v Strains A and B are identical to the 2010 Pasteur Institute referenced European strains, FR4803 (PFGE group IVβ) and FR4736 (PFGE group IVα), respectively, yet differ from the BP134 (PFGE group III), B902 (PFGE group IVα) and FR287 (PFGE group V) strains described by Mooi et al. (Figure 1).  vThe most common Israeli strain (A), has the same PFGE cluster of the dominant European BpSR11 strain (PFGE group IVβ) identified in the    

      1999 to 2004 EU Pertstrain II project  

vBpSR11 strains have been shown to carry the ptxP3 allele which is associated with increased pertussis toxin production (Mooi 2009).

 

Conclusions

 

vPFGE restriction profiles representing four circulating B. pertussis strains were identified in Israel, a country with high compliance to immunization. vStrains A and B were found to be closely related and predominant during this high pertussis activity period. vThe dominant European PFGE cluster (PFGE group IVβ) in 1999-2004 was also predominant in Israel, 2007-2008. vBpSR11 strains have been shown to carry the ptxP3 allele which is associated with increased pertussis toxin production (Mooi 2009). vInternational pertussis strain monitoring among highly vaccinated population should be pursued to track B. pertussis polymorphism.

Part of Session

Bacterial infections