Cross-reaction of spontaneous capsule-deficient Haemophilus influenzae type b mutants with type-specific antisera

Secondary Structural Transformation of Bovine Lactoferricin Affects Its Antibacterial Activity

Lactoferricin (Lfcin) is a potent antibacterial peptide derived from lactoferrin by pepsin hydrolysis. It was hypothesized that structural transformation of Lfcin could affect its antibacterial function through forming and breaking of intramolecular disulfide bond. To prove this hypothesis, bovine Lfcin (bLfcin) and its two derivatives, bLfcin with a disulfide bond (bLfcin DB) and bLfcin with a mutation C36G (bLfcin C36G), were synthesized, purified, and identified. The circular dichroism (CD) spectra of the peptides were detected in solutions with different ionic and hydrophobic strength. Then, the secondary structure contents of the peptides were calculated on the basis of the CD spectra. The antibacterial activity of the peptides against Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 14028, Shigella flexneri ATCC 12022, and Staphylococcus aureus ATCC 25923 was evaluated. The results showed that bLfcin and bLfcin C36G had similar percentages of secondary structure in water, while bLfcin and bLfcin DB had similar ratios of secondary structure under less hydrophobic conditions. The synthetic peptides exhibited antibacterial activity against all the tested bacteria, except for S. aureus ATCC 25923. bLfcin demonstrated higher antibacterial activity compared with its derivatives. The results suggested that bLfcin could transform its structure under alterative ionic strengths and hydrophobic conditions, and the transformation of structures was beneficial to enhancing the antibacterial function.

Determination of capsulation status in Haemophilus influenzae by multiplex polymerase chain reaction

Since the introduction of Haemophilus influenzae type b conjugate vaccines, there have been concerns regarding the emergence of invasive non-type b strains. Serotyping of H. influenzae with commercially available reagents is subjective. Definitive characterization of the capsulation status can be performed by polymerase chain reaction (PCR) amplification of capsular genes. However, PCR amplification of the conserved export locus in the 2 known phylogenic lines of type b strains and detection of serotype conferring genes in each of the 6 serotypes require multiple assays. To rapidly screen multiple isolates, we devised a multiplex method using 15 primers, which produced a serotype-specific, distinct pattern of amplicons with reference-encapsulated H. influenzae. We applied this technique to a panel of 35 clinical isolates that had been serotyped as type a, c, d, e, or f by slide agglutination; 15 strains lacked capsular genes. Conversely, of 69 invasive isolates that were not serotypeable, all but 11 contained capsule genes. We conclude that this technique will be useful in screening recently isolated H. influenzae for capsulation status.

Nontypeable Haemophilus influenzae strains with the capsule-associated insertion element IS1016 may mimic encapsulated strains

With the elimination of Haemophilus influenzae type b through vaccination, it has been suggested that other types of H. influenzae strains might acquire virulence traits and emerge as important pathogens. The gene sequence IS1016 has been associated with an increased capacity to cause severe infections. It is usually present in encapsulated strains but is sometimes harbored by nontypeable H. influenzae strains. To explore this further, 118 H. influenzae isolates, collected from both patients and healthy carriers, were investigated with PCR with reference to this gene sequence. Isolates positive for the insertion element were bio- and serotyped. The presence of hmw genes for adherence, the genetic profile, and the ability to form biofilm in vitro were investigated. A total of 15 isolates were IS1016-positive, whereof 12 were nontypeable. All 12 nontypeable isolates were obtained from healthy carriers, and 92% of the isolates were biotype I. They cross-reacted to some extent with type-specific antisera or exhibited a restricted genetic diversity like encapsulated strains. Furthermore, they lacked hmw-genes, and their ability to form biofilms was comparable with a capsule-deficient type b strain. Although this subset of strains mimicked traits usually exhibited by encapsulated strains, the isolation frequency did not seem to have been affected by vaccination.

Evaluation of methodology for serotyping invasive and nasopharyngeal isolates of Haemophilus influenzae in the ongoing surveillance in Brazil

To assess the magnitude of discrepant results obtained by routine Haemophilus influenzae serotyping, 258 isolates, collected by the epidemiological surveillance system in Brazil from individuals with invasive diseases or carriage, were evaluated by two slide agglutination (SlAg) methods: SlAg method 1, by which strains were initially screened with a serotype b-specific antiserum, and SlAg method 2, by which strains were tested against all serotype-specific antisera in parallel. Investigators comparing results of the two SlAg methods with those obtained by capsule type-specific PCR were blinded to the method used. The serotype prevalence rates found by the three methods were significantly different, involving discrepancies mainly between serotype b and noncapsulated (NC) isolates. For invasive isolates (n = 131), the overall agreement rate between SlAg method 1 or 2 and PCR was 68.0 or 88.3%, respectively, whereas for colonizing isolates (n = 127) the corresponding rate was 46.5 or 94.2%, respectively. SlAg method 2 improved the ascertainment of serotypes over that obtained with SlAg method 1, demonstrating good correlation with PCR. Use of the polyvalent antiserum as a screening reagent for SlAg for invasive and colonizing isolates showed poor discriminatory power, with a sensitivity of 65.8% and a specificity of 91.7%. We stress the importance of using a well-standardized SlAg methodology and suggest that reference laboratories should utilize PCR routinely to confirm SlAg results and to check all nonspecific SlAg reactions and apparent NC isolates by SlAg in order to provide reliable data on the prevalence of H. influenzae serotypes in the H. influenzae type b vaccine era.

Haemophilus influenzae: then and now

Haemophilus influenzae has long been recognised as a major cause of serious infection and mortality in children less than 5 years old. Prior to the introduction of Haemophilus influenzae type b (Hib) immunisation, the incidence of a child suffering an invasive Haemophilus infection was 20-50/100,000 in industrialised countries and up to ten times higher in developing regions. The introduction of a Hib vaccine programme results in a rapid and dramatic decline in the incidence of Hib infection in the susceptible childhood population. For example, within two years of the introduction of routine Hib vaccination of infants in the UK, the risk of serious Hib infection had fallen from 1:600 to 1:30,000 by 5 years of age. Many other European countries have introduced, or are in the process of introducing, a routine Hib immunisation programme. Because the epidemiology of Haemophilus influenzae infection is changing so dramatically, it is opportune to review Haemophilus influenzae as it was perceived in the pre-vaccine era (the past) and during vaccine implementation (the present), and how its role may change in the post-vaccination era (the future). This review will summarise the historical landmarks that have led to our present-day understanding of Haemophilus influenzae pathogenicity, the concerns about antibiotic resistance, the features of the host immune response to Haemophilus influenzae, and the introduction of the Hib vaccine. Furthermore, the possible importance of this organism in the future will be discussed.

PCR for capsular typing of Haemophilus influenzae

A PCR method for the unequivocal assignment of Haemophilus influenzae capsular type (types a to f) was developed. PCR primers were designed from capsule type-specific DNA sequences cloned from the capsular gene cluster of each of the six capsular types. PCR product was amplified only from the capsular type for which the primers were designed. Product was confirmed by using either an internal oligonucleotide or restriction endonuclease digestion. A total of 172 H. influenzae strains of known capsular type (determined genetically) comprising all capsular types and noncapsulate strains were tested by PCR capsular typing. In all cases the PCR capsular type corresponded to the capsular genotype determined by restriction fragment length polymorphism analysis of the cap region. When used in conjunction with PCR primers derived from the capsular gene bexA, capsulate, noncapsulate, and capsule-deficient type b mutant strains could be differentiated. PCR capsular typing overcomes the problems of cross-reaction and autoagglutination associated with the serotyping of H. influenzae strains. The rapid and unequivocal capsular typing method that is described will be particularly important for typing invasive H. influenzae strains isolated from recipients of H. influenzae type b vaccine.