Mechanisms of beta-lactam resistance in Haemophilus influenzae

The Association between Transformation Ability and Antimicrobial Resistant Potential in Haemophilus influenzae

The prevalence of quinolone low-susceptible Haemophilus influenzae has increased in Japan. Low quinolone susceptibility is caused by point mutations in target genes; however, it can also be caused by horizontal gene transfer via natural transformation. In this study, we examined whether this horizontal gene transfer could be associated with resistance to not only quinolones but also other antimicrobial agents. Horizontal transfer ability was quantified using the experimental transfer assay method for low quinolone susceptibility. Further, the association between horizontal transfer ability and resistance to β-lactams, the first-choice drugs for H. influenzae infection, was investigated. The transformation efficiency of 50 clinical isolates varied widely, ranging from 102 to 106 colony forming unit (CFU) of the colonies obtained by horizontal transfer assay. Efficiency was associated with β-lactam resistance caused by ftsI mutations, indicating that strains with high horizontal transfer ability acquired quinolone low-susceptibility as well as β-lactam resistance more easily. Strains with high transformation efficiency increased the transcript level of comA, suggesting that enhanced com operon was associated with a high DNA uptake ability. Overall, this study revealed that the transformation ability of H. influenzae was associated with multiple antimicrobial resistance. Increase in the number of strains with high horizontal transformation ability has raised concerns regarding the rapid spread of antimicrobial-resistant H. influenzae.

Antibiotic susceptibility and genotypic characterization of Haemophilus influenzae strains isolated from nasopharyngeal specimens from children in day-care centers in eastern France

OBJECTIVE

To determine the overall carriage rate for Haemophilus influenzae in young children in day-care centers, the frequency of resistance to various classes of antibiotic, and the clonal relationship between isolates of the various resistant phenotypes.

METHODS

Nasopharyngeal (NP) specimens were obtained and cultured on chocolate agar with bacitracin. Antibiotic susceptibility testing and serotyping were performed for all isolates. The genetic polymorphism of ampicillin-susceptible and beta-lactamase-producing isolates was studied by pulsed-field gel electrophoresis using SmaI.

RESULTS

Of the 596 NP secretion cultures, 152 (25.5%) were positive for H. influenzae. Sixty-four (42.1%) isolates produced beta-lactamase and two (1.3%) were ampicillin resistant but did not produce beta-lactamase. We were unable to serotype 150 isolates; one isolate belonged to capsular serotype e and one to serotype f. Forty-six major DNA patterns were identified among 76 randomized isolates. beta-lactamase producing isolates more frequently showed EP than ampicillin-susceptible isolates P < 10(-4). The frequency of isolates with EP was significantly lower in day-care centers attended by less than 20 children than in those attended by more than 20 children (P = 0.020).

CONCLUSIONS

Resistance due to beta-lactamase production has disseminated in some day-care centers, mostly by person-to-person spread but also via the possible conjugal transfer of large plasmids between strains. The size of day-care centers may affect the risk of transmission.

Antibiotic resistance and prevalence of beta-lactamase in Haemophilus influenzae isolates-a surveillance study of patients with respiratory infection in Saudi Arabia

Haemophilus influenzae was isolated from patients with respiratory tract infections in five centers in Saudi Arabia. All of the 129 isolates tested by MIC agar dilution were fully susceptible to ceftazidime and ciprofloxacin but 13.2% were resistant to ampicillin, 7% to tetracycline, 5.4% to chloramphenicol, 3.9% to roxithromycin, and 1.6% to amoxicillin/clavulanic acid. Seventeen (13.2%) of all isolates produced TEM-1 type beta-lactamase, the majority (82%) characterized as biotype I or II with 4 (23.5%) encapsulated and belonging to serotype b. There was a clear distinction between the prevalence of beta-lactamase production in hospital patients (26.3% of 19 isolates) compared with community based patients (10.9% of 110 isolates). In addition, we report an increase in the prevalence of beta-lactamase negative, ampicillin intermediate strains (BLNAI) compared to previous studies in this defined geographical region. Changes in the frequency and nature of antimicrobial resistance in common respiratory pathogens confirms the need to maintain surveillance.

Emergence of drug resistance. Impact on bacterial meningitis

Antimicrobial resistance has emerged among the three major bacterial pathogens causing meningitis. Chloramphenicol resistance in the meningococcus recently has been described, and although intermediate penicillin resistance is common in some countries, the clinical importance of penicillin resistance in the meningococcus has yet to be established. Beta-lactamase-producing Haemophilus influenzae are relatively common, and chloramphenicol resistance is emerging. Third-generation cephalosporins are required to treat meningitis caused by these resistant strains. Pneumococcus resistance to penicillin and to chloramphenicol is widespread, and resistance to third-generation cephalosporins is found in many parts of the world. Correct management of these strains includes the addition of vancomycin or rifampin to therapy with third-generation cephalosporins.

Molecular epidemiology of ampicillin-resistant non-beta-lactamase-producing Haemophilus influenzae

Resistance to ampicillin without beta-lactamase production is not a frequent occurrence among Haemophilus influenzae strains. This kind of resistance is encountered in unencapsulated strains isolated from bronchial secretions and ear, nose, and throat specimens and is exceptional in H. influenzae type b. We studied 29 of these strains from various areas in France and 2 reference strains. Strains were compared by using ribotyping, arbitarily primed PCR with two primers, and pulsed-field gel electrophoresis. Each technique enabled the identification of 20 to 23 different patterns among the 31 strains. The combination of the different patterns for the strains obtained by the different techniques provided 27 distinct profiles. According to these results, it seems that the clonal propagation of these resistant strains does not occur.

Amoxicillin treatment of experimental acute otitis media caused by Haemophilus influenzae with non-beta-lactamase-mediated resistance to beta-lactams: aspects of virulence and treatment

Through alterations primarily in the penicillin-binding proteins, a non-beta-lactamase-mediated resistance to beta-lactams has evolved in Haemophilus influenzae. The virulence of these chromosomally changed strains has been questioned. To ascertain whether these alterations involve a reduction in virulence of H. influenzae and whether they could be advantageous for the bacterium during amoxicillin treatment of acute otitis media, a total of 70 Sprague-Dawley rats were challenged with a susceptible recipient strain or a genetically similar resistant transformant strain. Antibiotic therapy was started on day 3 after inoculation, and the animals were monitored by daily otomicroscopy and analysis of bacterial samples from middle ear effusions obtained on day 8, the last day of observation. The animals were also sacrificed on days 4 and 8 and after 2 months for morphological examination. Compared with the susceptible recipient strain, recovery from infections caused by the resistant transformant strain was delayed, and the late structural changes were more severe in the animals challenged with the latter strain. The results of the study indicate that chromosomal alterations mediating a relatively low level of resistance to beta-lactams may be advantageous for H. influenzae during antibiotic treatment of a local infection in the rat, and the alterations may occur without any significant loss of virulence.