Susceptibility and Genetic Relatedness of InvasiveHaemophilus influenzaeType b in Italy

Abstract

Haemophilus influenzae type b (Hib) still causes a large portion of meningitis in children less than 5 year old in Italy because vaccination against this agent has not been fully implemented in the country. We have studied 78 Hib strains and 4 nontypable H. influenzae (NTHi) isolated from the cerebrospinal fluid of subjects with meningitis for susceptibility to ampicillin, chloramphenicol, and ceftriaxone. The macrorestriction profiles of chromosomal DNA obtained by pulsed-field gel electrophoresis (PFGE) following digestion with SmaI and ApaI were also determined. All strains except one were equally susceptible to the antibiotics tested. One Hib strain, the only beta-lactamase producer, showed an intermediate susceptibility to ampicillin (MIC = 2 microg/ml), while maintaining full susceptibility to chloramphenicol and ceftriaxone. The analysis of the PFGE patterns showed that most of the Hib isolates, including the beta-lactamase-positive Hib strain, belonged to the same clone or to closely related subclones. For three PCR-confirmed NTHi isolates, we obtained completely different PFGE profiles. In conclusion, resistance to ampicillin still appears to be a rare finding in Hib strains causing meningitis in Italy; moreover, PFGE showed that the population structure of invasive Hib is essentially clonal.

Characteristics of Haemophilus influenzae Type b Responsible for Meningitis in Poland from 1997 to 2004

“…Additionally, the most common PFGE type, A, characterized more than 95% of the Hib isolates, and the most common PFGE subtype, A1, was also the most prevalent among isolates responsible for invasive disease in Italy and the Czech Republic and among isolates causing lower respiratory tract infections in Poland (28,32). Thus, the results of this study support the evidence that the genetic structure of encapsulated H. influenzae is clonal.…”

“…In the light of the above data, the percentage of ␤-lactamase producers among Polish meningitis isolates is not very high, although it is three times higher than found among H. influenzae isolates responsible for lower respiratory tract infections in Poland (28). The observation that antibiotic resistance is more prevalent in encapsulated isolates, responsible for the majority of meningitis cases, than in nontypeable H. influenzae was also revealed by other authors (4,10,32). The results of some studies showed that there is also an increasing number of H. influenzae isolates resistant to chloramphenicol (e.g., Bangladesh, 21.5%; Paraguay, 20%; Cuba, 44%) and an increasing number of isolates resistant simultaneously to both mentioned antibiotics (2,26,31).…”

“…They constituted from 26.7% (in 1998) to 61.0% (in 2003) of notified cases, with an average of 40.1% (22). For comparison, the study also included representatives of Hib isolates of the most prevalent pulsed-field gel electrophoresis (PFGE) types responsible for invasive disease in Italy and the Czech Republic (28,32). All isolates were identified to the species level based on standard procedures (14).…”

“…The relatedness among encapsulated isolates was evaluated by restriction fragment length polymorphism of SmaI-digested chromosomal DNA following PFGE, using a method described previously by Tarasi et al (32). The isolates were classified into PFGE types according to the interpretive criteria proposed by Tenover et al (33).…”

Use of automated riboprinter and pulsed-field gel electrophoresis for epidemiological studies of invasive Haemophilus influenzae in Taiwan

“…Thus, they suggested that the population structure of capsulate H. in¯uenzae is basically clonal and that most infections are caused by a small number of clonal genotypes. The results obtained in the present study support the previous ®ndings [21,22]. Different riboprinter patterns were obtained for non-type b and non-typable H. in¯uenzae isolates.…”