Antibiotic resistance in Haemophilus influenzae: mechanisms, clinical importance and consequences for therapy

Membranome-based identification of amino acid substitution in Haemophilus influenzae multidrug efflux pump HmrM for reduced chloramphenicol susceptibility

A decreased chloramphenicol susceptibility in Haemophilus influenzae is commonly caused by the activity of chloramphenicol acetyltransferases (CATs). However, the involvement of membrane proteins in chloramphenicol susceptibility in H. influenzae remains unclear. In this study, chloramphenicol susceptibility testing, whole-genome sequencing, and analyses of membrane-related genes were performed in 51 H. influenzae isolates. Functional complementation assays and structure-based protein analyses were conducted to assess the effect of proteins with sequence substitutions on the minimum inhibitory concentration (MIC) of chloramphenicol in CAT-negative H. influenzae isolates. Six isolates were resistant to chloramphenicol and positive for type A-2 CATs. Of these isolates, A3256 had a similar level of CAT activity but a higher chloramphenicol MIC relative to the other resistant isolates; it also had 163 specific variations in 58 membrane genes. Regarding the CAT-negative isolates, logistic regression and receiver operator characteristic curve analyses revealed that 48T > G (Asn16Lys), 85 C > T (Leu29Phe), and 88 C > A (Leu30Ile) in HI_0898 (emrA), and 86T > G (Phe29Cys) and 141T > A (Ser47Arg) in HI_1177 (artM) were associated with enhanced chloramphenicol susceptibility, whereas 997G > A (Val333Ile) in HI_1612 (hmrM) was associated with reduced chloramphenicol susceptibility. Furthermore, the chloramphenicol MIC was lower in the CAT-negative isolates with EmrA-Leu29Phe/Leu30Ile or ArtM-Ser47Arg substitution and higher in those with HmrM-Val333Ile substitution, relative to their counterparts. The Val333Ile substitution was associated with enhanced HmrM protein stability and flexibility and increased chloramphenicol MICs in CAT-negative H. influenzae isolates. In conclusion, the substitution in H. influenzae multidrug efflux pump HmrM associated with reduced chloramphenicol susceptibility was characterised.

Molecular characterization of cefepime and aztreonam nonsusceptibility in Haemophilus influenzae

BACKGROUND

Cefepime and aztreonam are highly efficacious against H. influenzae, and resistant strains are rare. In this study, we isolated cefepime- and aztreonam-nonsusceptible H. influenzae strains and addressed the molecular basis of their resistance to cefepime and aztreonam.

METHODS

Two hundred and 28 specimens containing H. influenzae were screened, of which 32 isolates were enrolled and applied to antimicrobial susceptibility testing and whole-genome sequencing. Genetic variations that were detected in all nonsusceptible isolates with statistical significance by Fisher's exact tests were identified as cefepime or aztreonam nonsusceptibility related. Functional complementation assays were conducted to assess the in vitro effects of proteins with sequence substitutions on drug susceptibility.

RESULTS

Three H. influenzae isolates were nonsusceptible to cefepime, one of which was also nonsusceptible to aztreonam. Genes encoding TEM, SHV and CTX-M extended-spectrum β-lactamases were not detected in the cefepime- and aztreonam-nonsusceptible isolates. Five genetic variations in four genes and 10 genetic variations in five genes were associated with cefepime and aztreonam nonsusceptibility, respectively. Phylogenetic analyses revealed that changes in FtsI were correlated strongly with the MIC of cefepime and moderately with aztreonam. FtsI Thr532Ser-Tyr557His cosubstitution linked to cefepime nonsusceptibility and Asn305Lys-Ser385Asn-Glu416Asp cosubstitution to aztreonam nonsusceptibility. Functional complementation assays revealed that these cosubstitutions increased MICs of cefepime and aztreonam in susceptible H. influenzae isolates, respectively.

CONCLUSIONS

Genetic variations relevant to resistant phenotypes of cefepime and aztreonam nonsusceptibility in H. influenzae were identified. Moreover, the effects of FtsI cosubstitutions on increasing MICs of cefepime and aztreonam in H. influenzae were demonstrated.

Diversity of beta-lactam resistance-conferring amino acid substitutions in penicillin-binding protein 3 of Haemophilus influenzae

The sequences of the ftsI gene, encoding the transpeptidase domain of penicillin binding protein (PBP) 3A and/or PBP 3B, which are involved in septal peptidoglycan synthesis, were determined for 108 clinical strains of Haemophilus influenzae with reduced susceptibility to beta-lactam antibiotics with or without beta-lactamase production and were compared to those of the ampicillin-susceptible Rd strain and ampicillin-susceptible clinical isolates. The sequences have 18 different mutation patterns and were classified into two groups on the basis of amino acid substitutions deduced from the nucleotide sequences located between bp 960 and 1618 of the ftsI gene. In group I strains (n = 7), His-517 was substituted for Arg-517. In group II strains (n = 101), Lys-526 was substituted for Asn-526. In subgroup IIa (n = 5; H. influenzae ATCC 49247), the only observed substitution was Lys-526 for Asn-526; in subgroup IIb (n = 56), Val-502 was substituted for Ala-502 (n = 13), along with several other substitutions: Asn-350 for Asp-350 (n = 15), Asn-350 for Asp-350 and Glu-490 for Gly-490 (n = 14), and Asn-350 for Asp-350 and Ser-437 for Ala-437 (n = 5). In subgroup IIc (n = 25), Thr-502 was substituted for Ala-502. In subgroup IId, Val-449 was substituted for Ile-449 (n = 15). The MICs of beta-lactam antibiotics for the 108 strains were to 8 to 16 times the MICs for susceptible strains. The strains, isolated from both adults and children, were analyzed for genetic relationship by pulsed-field gel electrophoresis and by determination of ftsI sequence phylogeny. Both analyses revealed the lack of clonality and the heterogeneity of the strains, but some clusters suggest the spread and/or persistence of a limited number of strains of the same pulsotype and pattern of amino acid substitutions. Reduced susceptibility to beta-lactam, brought about by mutations of the ftsI gene, is becoming a frequent phenomenon, affecting both strains that produce beta-lactamase and those that do not. The level of resistance remains low but opens the way to greater resistance in the future.

Acute exacerbations of chronic bronchitis: a pharmacoeconomic review of antibacterial use

Chronic bronchitis is a common problem affecting a large proportion of the adult population. People with chronic bronchitis are subject to recurrent attacks of bronchial inflammation called acute exacerbations of chronic bronchitis (AECBs). In patients with AECBs, symptoms may worsen due to a bacterial infection; the exacerbation is then known as an acute bacterial exacerbation of chronic bronchitis (ABECB). ABECBs are thought to be controllable through the use of antibacterial agents. In this paper we review current evidence on the cost of chronic bronchitis and AECBs, the cost effectiveness of antibacterials in the management of ABECB, and the factors that may affect the cost-effectiveness of antibacterials in the management of ABECB. We find that the number of economic evaluations conducted in this area is small. Of the few economic evaluations that have been conducted there has been only one prospective economic evaluation based on a clinical trial. The remainder are simple decision analysis-based modelling studies or retrospective database studies. Our principle findings are as follows: a key factor affecting the cost-effective use of antibacterials in the management of ABECB is the definitive diagnosis of the condition. Unfortunately, diagnosing a bacterial cause of an AECB is difficult, which presents problems in ensuring that antibacterials are not prescribed unnecessarily;current evidence suggests but does not prove that use of more effective but more costly first-line antibacterials may be relatively cost effective and may minimise overall expenditure by reducing the high costs associated with treatment failure;chronic bronchitis and AECB have a significant and negative physical and psychological effect on health-related quality of life. In conclusion, the small number of economic evaluations conducted in this area, coupled with the nature of the design of these studies, precludes a definitive statement recommending which specific antibacterial should be preferred on cost-effectiveness grounds for the management of ABECB. On the basis of our findings we suggest some topics for further research.

Antimicrobial susceptibility of nasopharyngeal isolates of Haemophilus influenzae from healthy children in day-care centres: results of multicentre study in Russia

Resistance of Haemophilus influenzae from clinical isolates can be predicted on the basis of results of antimicrobial susceptibility of nasopharyngeal isolates. The carriage rate and the antimicrobial susceptibility of H. influenzae isolated in healthy children attending day-care centres in Moscow, Smolensk and Yartsevo was studied. The susceptibility of ampicillin, amoxycillin/clavulanate, cefaclor, erythromycin, roxithromycin, clarithromycin and trimethoprim-sulphamethoxazole were determined by the E-test. The mean carriage rate of H. influenzae was 44%. Resistance of H. influenzae to ampicillin was 2.3%, to amoxycillin/clavulanate 0.7%, to cefaclor 0.7%, to clarithromycin 18.7% and to trimethoprim-sulphamethoxazole 21%. These included strains that showed intermediate-resistance. The antimicrobial resistance profiles varied in different centres. The clinical use of trimethoprim-sulphamethoxazole should be restricted because of the high resistance of H. influenzae to antifolate compounds.

A 1994-95 survey of Haemophilus influenzae susceptibility to ten orally administered agents. A 187 clinical laboratory center sample in the United States

During August, 1994 to April, 1995, a total of 2278 clinical isolates of Haemophilus influenzae were obtained from 187 clinical laboratories in the United States (U.S.). The vast majority of these isolates (75%) were from respiratory sites, and the remaining organisms were from blood, ear, eye, and spinal fluid sources. The overall rate of beta-lactamase production and ampicillin resistance was 36%. The antimicrobial susceptibility of isolates was determined by reference broth microdilution testing against ten orally administered agents. MIC values were compared according to 12 geographical regions, inpatient or outpatient status, gender, and eight age groupings. Modest and occasionally significant differences were observed: 1) greater numbers of beta-lactamase-producing strains among outpatients, in males, in the mid-Atlantic region, and in children < or = 12 years of age; 2) lower prevalence of beta-lactamase-producing isolates in the Southeast and Pacific regions; 3) cefaclor, cefprozil, and loracarbef activity was lowest among the younger children (< or = six years); and 4) macrolide in vitro efficacy was lowest in patients > 50 years of age and in three eastern regions. Overall, more than 99% of the strains were susceptible to amoxicillin/clavulanic acid, cefixime, and cefpodoxime (e.g., widest potential clinical use). Susceptibilities using National Committee for Clinical Laboratory Standards (NCCLS) breakpoint criteria for the other agents were: 96.6% to cefuroxime, 86.5% to loracarbef, 84.0% to clarithromycin, 81.8% to cefaclor, and 80.7% to cefprozil. Non-beta-lactamase mechanisms of resistance to ampicillin were rare (0.2%) or episodic and were attributed to altered penicillin-binding proteins. Although there is an increased prevalence of beta-lactamase production among H. influenzae isolates compared to prior years, four beta-lactams remain highly active (> 95% susceptibility) against contemporary strains of H. influenzae. Other monitored compounds seem to have declined in spectrum and surveillance trials for resistance among H. influenzae isolates should continue in an effort to identify trends in the U.S.

Bacterial meningitis: mechanisms of disease and therapy

Bacterial meningitis continues to be a serious infectious disease with a high morbidity and mortality in young children. Early recognition and initiation of adequate treatment are the major determinants for a good outcome. Recent advances in our understanding of the host inflammatory response by cytokines may result in the use of new therapeutic strategies. Such modulation of the inflammatory response may reduce the incidence of sequelae and death. The use of steroids as adjunctive therapy in children with bacterial meningitis probably has beneficial effects although the available data are still controversial. Additionally, studies in experimental meningitis models indicate that non-steroidal anti-inflammatory drugs and monoclonal antibodies against bacterial products, cytokines and CD18 on leucocytes reduce the extent of the meningeal inflammation. Human studies to evaluate the efficacy of these immune modulators are expected to start soon. However, prevention of bacterial meningitis by conjugate vaccines against Streptococcus pneumoniae and Neisseria meningitidis will be the most promising development in the next decade.

Antibiotic susceptibility of 206 Haemophilus influenzae isolates collected from children in central Italy

Susceptibility of 206 H. influenzae isolates was evaluated by disk diffusion method for 11 antimicrobial agents. No isolates were found to be resistant to third-generation cephalosporins, amoxicillin+clavulanic acid, gentamicin and ciprofloxacin. Four untypable isolates (1.9%) were beta-lactamase producing ampicillin-resistant; one of these was also resistant to chloramphenicol. The rate of resistance against rifampin was 0.5 percent.