Antimicrobial resistance of Haemophilus influenzae isolated from the nasopharynx of Japanese children with acute otitis media

Non-typeable Haemophilus influenzae, an under-recognised pathogen

Non-typeable Haemophilus influenzae (NTHi) is a major cause of mucosal infections such as otitis media, sinusitis, conjunctivitis, and exacerbations of chronic obstructive pulmonary disease. In some regions, a strong causal relation links this pathogen with infections of the lower respiratory tract. In the past 20 years, a steady but constant increase has occurred in invasive NTHi worldwide, with perinatal infants, young children, and elderly people most at risk. Individuals with underlying comorbidities are most susceptible and infection is associated with high mortality. β-lactamase production is the predominant mechanism of resistance. However, the emergence and spread of β-lactamase-negative ampicillin-resistant strains in many regions of the world is of substantial concern, potentially necessitating changes to antibiotic treatment guidelines for community-acquired infections of the upper and lower respiratory tract and potentially increasing morbidity associated with invasive NTHi infections. Standardised surveillance protocols and typing methodologies to monitor this emerging pathogen should be implemented. International scientific organisations need to raise the profile of NTHi and to document the pathobiology of this microbe.

PCR screening for the N526K substitution in isolates of Haemophilus influenzae and Haemophilus haemolyticus

OBJECTIVES

Firstly, to evaluate the current PBP3-S primers of Hasegawa et al. (Microb Drug Resist 2003; 9: 39-46) and develop new primers for the amplification of N526 in isolates of Haemophilus haemolyticus. Secondly, to develop a new PCR assay for the detection (by amplification) of the N526K substitution, encoded by either the AAA or AAG single nucleotide polymorphism (SNP) at position 1576-1578 of the ftsI gene, in isolates of both Haemophilus influenzae and H. haemolyticus.

METHODS

A total of 50 H. influenzae and 50 H. haemolyticus isolates, comprising N526 and N526K genotypes, were used to evaluate the performance of SNP-based PCR primers for the detection of the β-lactamase-negative ampicillin resistance (BLNAR)-defining N526K substitution in H. influenzae and H. haemolyticus, using a real-time PCR platform.

RESULTS

The PBP3-S primers of Hasegawa et al. failed to amplify H. haemolyticus isolates, irrespective of their N526/N526K status, owing to an inability of the forward primer to bind the H. haemolyticus ftsI sequence, giving an overall sensitivity of 100% and a specificity of 40% when using all of the isolates. However, the PBP3-N526 and PBP3-N526K PCR primers designed in this study were 100% sensitive and specific, and 84% sensitive and 100% specific, respectively, for the detection of N526K-positive isolates.

CONCLUSIONS

Although antibiotic resistance surveillance studies on H. influenzae should include a definitive test for H. influenzae/H. haemolyticus identification, the new primers from this study will not only allow for PCR characterization of both H. influenzae and H. haemolyticus with respect to the N526K BLNAR substitutions, they will also stop incorrect characterization of susceptible H. haemolyticus isolates as low-BLNAR H. influenzae.

Diverse mutations in the ftsI gene in ampicillin-resistant Haemophilus influenzae isolates from pediatric patients with acute otitis media

To clarify molecular changes in beta-lactamase-nonproducing, ampicillin-resistant (BLNAR) Haemophilus influenzae, which is increasing in pediatric patients with acute otitis media (AOM) in Japan, we identified amino acid (aa) substitutions in penicillin-binding protein 3 for the BLNAR strains. Of 191 H. influenzae strains isolated from middle ear fluid of pediatric AOM patients between October 2005 and March 2008, BLNAR strains determined by PCR accounted for 49.2%. Of the BLNAR strains, 91.5% possessed 4 aa substitutions: Met377Ile, Ser385Thr, Leu389Phe, and either Asn526Lys or Arg517His. Additionally, the emergence of BLNAR strains possessing a new aa substitution of Val329Ala in the conserved aa motif of Ser327-Thr-Val-Lys, or Val511Ala adjacent to the conserved aa motif of Lys512-Thr-Gly, was noted. Transformation of the ftsI gene into the Rd reference strain (ATCC 51907) demonstrated that these two aa substitutions reduced susceptibility to amoxicillin more than to cephalosporins. Pulsed-field gel electrophoretic profiles of BLNAR strains were highly diverse. These results suggested that inadequate antibiotic use may increase BLNAR strains by selecting mutations in the ftsI gene and that such use may have favored the new aa substitutions.

Comparison of the efficacies of oral beta-lactams in selection of Haemophilus influenzae transformants with mutated ftsI genes

Horizontal transfer of the mutated ftsI gene from beta-lactamase-nonproducing ampicillin-resistant (BLNAR) Haemophilus influenzae to a susceptible strain was examined in vitro under selection with nine oral beta-lactams (ampicillin, amoxicillin, cefprozil, cefuroxime, cefpodoxime, cefdinir, cefcapene, cefditoren, and tebipenem). Compared to the penicillins and the carbapenem, the cephalosporins showed a wide selection window for the genetic transfer.

[Will we still have antibiotics tomorrow?]

Since the discovery of antibiotics, it has been generally believed that these antimicrobials are capable of curing almost all bacterial infections. More recently, the appearance of increasing resistance to antibiotics and the emergence of multiresistant microorganisms have given rise to growing concern among physicians, and that concern has now started to filter through to society in general. The problem is further aggravated by a situation that not many people are currently aware of, that is, the limited prospects for future development of new antibiotics in the short to medium term. Appropriate use of available antibiotics based on a thorough understanding of their in vivo activity and the emergence of new forms of administration, such as inhalers, may help to alleviate the problem.