The incidence and epidemiology of beta-lactam resistance in Haemophilus influenzae

Molecular characterization of multidrug-resistant non-typeable Haemophilus influenzae with high-level resistance to cefuroxime, levofloxacin, and trimethoprim-sulfamethoxazole

BACKGROUND

Non-typeable Haemophilus influenzae (NTHi) has become the major cause of invasive H. influenzae diseases in the post-H. influenzae type b vaccine era. The emergence of multidrug-resistant (MDR) NTHi is a growing public health problem. Herein, we investigated the molecular basis of MDR in NTHi. The isolated NTHi were subjected to antimicrobial susceptibility testing for 12 agents. Whole genome and plasmid sequencing were conducted and analyzed to identify significant genetic variations and plasmid-encoded genes conferred antibiotic resistance.

RESULTS

Thirteen (50%) MDR NTHi isolates were obtained; of these, 92.3% were non-susceptible to ampicillin, 30.8% to amoxicillin-clavulanate, 61.5% to cefuroxime, 61.5% to ciprofloxacin/levofloxacin, 92.3% to trimethoprim-sulfamethoxazole, 30.8% to tetracycline, and 7.7% to azithromycin. Eight ampicillin-resistant isolates were β-lactamase positive; of these, 6 carried bla_TEM-1 and 2 carried bla_ROB-1, whereas 4 were β-lactamase negative. Genetic variations in mrdA, mepA, and pbpG were correlated with amoxicillin-clavulanate non-susceptibility, whereas variations in ftsI and lpoA conferred cefuroxime resistance. Five variations in gyrA, 2 in gyrB, 3 in parC, 1 in parE, and 1 in the parC-parE intergenic region were associated with levofloxacin/ciprofloxacin non-susceptibility. Among these genes, 8 variations were linked to high-level levofloxacin resistance. Six variations in folA were associated with trimethoprim-sulfamethoxazole resistance. Plasmid-bearing tet(B) and mef(A) genes were responsible for tetracycline and azithromycin resistance in 4 and 1 MDR isolates, respectively.

CONCLUSIONS

This study clarified the molecular epidemiology of MDR in NTHi. This can benefit the monitoring of drug resistance trends in NTHi and the adequate medical management of patients with NTHi infection.

Phenotypic and molecular characterization of nosocomial K. pneumoniae isolates by ribotyping

PURPOSE

To characterize clinical isolates of Klebsiella pneumoniae by phenotypic and genotypic methods.

MATERIAL/METHODS

Over a 12-month period, 52 isolates of K. pneumoniae were isolated. Of these 52 isolates, 7 were isolated over a period of 21 days from a suspected outbreak in the Neonatal Intensive Care Unit (NICU) and 45 from sporadic cases occurring in different wards of hospital were analysed.

RESULTS

The prevalence of K. pneumoniae isolates was 4% (52/1295). Quinolones, aztreonam and amikacin showed the greatest efficacy showing >85% sensitivity. Of the 52 isolates of K. pneumoniae, 8 (15.4%) isolates were positive for ESBL-production. Among the ESBL-producing K. pneumoniae, two out of 8 (25%) and 6 out of 8 (75%) were positive for (bla)SHV and (bla)CTX-M genes respectively. Ribotyping identified 30 distinct ribogroups among 52 isolates evaluated. Seven NICU outbreak isolates were divided into 2 ribotypes, as many as 6 belonged to one ribotype while one isolate which was isolated a week later was of a different ribotype, indicating the termination of the outbreak in the NICU. The outbreak in the NICU thus, was shown to have been caused by a single clone.

CONCLUSIONS

A high discriminatory power, ease of interpretation coupled with excellent reproducibility and stability make ribotyping a very useful technique for investigating the molecular epidemiology of nosocomial infections caused by K. pneumoniae. A regular surveillance of hospital associated infections including monitoring antibiotic sensitivity pattern of K. pneumoniae, ESBL-production and molecular characterization is mandatory to control the spread of multidrug-resistant and ESBL-producing K. pneumoniae and for epidemiological purposes especially in outbreak situations.

Phenotypic and molecular characterization of beta-lactam resistance and capsular typing of colonizing Haemophilus influenzae strains isolated from neutropenic patients in Tunisia

OBJECTIVE

The aim of this study was to determine the overall percentage of beta-lactams susceptibility, beta-lactamase production, penicillin binding protein (PBP) modification and serotypes of colonizing Haemophilus influenzae strains.

DESIGN

A total of 50 isolates of colonized H. influenzae, isolated from neutropenic patients. The prevalence of beta-lactams resistance and beta-lactamase production were recorded for each strains using E-test strips and chromogenic cephalosporin test, then were determined their resistance genes (bla(TEM) and bla(ROB)) by PCR as well as their capsular types by standard slide agglutination serotyping (SAST) and capsular genes amplification.

RESULTS

Thirty-two percent of the 50 strains were amoxicillin resistant, among these, 20% were resistant by beta-lactamase production, and they produced all type TEM beta-lactamase. Four percent of the isolates had PBP modification and three strains (6%) associated the two resistance mechanisms. Slide agglutination serotyping showed that 95.8% of the strains were unencapsulated, and 4.1% were of serogroup b. The result was confirmed by PCR capsular typing.

CONCLUSION

By the light of these results, our findings suggest that it becomes important to follow the evolution of the resistance background of our strains, and that the majority of colonizing H. influenzae strains isolated in our center are unencapsulated.

Genetic characteristics and clonal dissemination of beta-lactamase-negative ampicillin-resistant Haemophilus influenzae strains isolated from the upper respiratory tract of patients in Japan

We evaluated the recent prevalence of antimicrobial-resistant Haemophilus influenzae isolated from the upper respiratory tracts (URT) of patients in Japan. Mutations in the ftsI gene, which encodes penicillin binding protein 3 (PBP3), and the clonal dissemination of the resistant strains were also investigated. A total of 264 H. influenzae isolates were collected from patients with URT infections. According to the criteria of the Clinical and Laboratory Standards Institute for the susceptibility of H. influenzae to ampicillin (AMP), the isolates were distributed as follows: 161 (61.0%) susceptible strains (MIC < or = 1 microg/ml), 37 (14.0%) intermediately resistant strains (MIC = 2 microg/ml), and 66 (25.0%) resistant strains (MIC > or = 4 microg/ml). According to PCR-based genotyping, 172 (65.1%) of the isolates had mutations in the ftsI gene and were negative for the beta-lactamase (bla) gene. These 172 isolates were thus defined as genetically beta-lactamase-negative ampicillin-resistant (gBLNAR) strains. The ftsI mutant group included 98 (37.1%) strains with group I/II mutations in the variable mutated region (group I/II gBLNAR) and 74 (28.0%) strains with group III mutations in the highly mutated region (group III gBLNAR). Eighty-seven (33.0%) of the isolates were genetically beta-lactamase-negative ampicillin-susceptible (gBLNAS) strains. The group III gBLNAR strains showed resistance to beta-lactams. Only five strains (1.9%) were positive for a bla gene encoding TEM-type beta-lactamase. The three clusters consisting of 16 strains found among the 61 BLNAR strains (MIC > or = 4 microg/ml and without the bla gene) showed identical or closely related DNA restriction fragment patterns. Those isolates were frequently identified among strains with a MIC to AMP of 16 microg/ml. The current study demonstrates the apparent dissemination and spread of a resistant clone of H. influenzae among medical centers in Japan. The gBLNAR strains show a remarkable prevalence among H. influenzae isolates, with the prevalence increasing with time. This fact should be taken into account when treating URT infections.

Antimicrobial resistance in Haemophilus influenzae

Haemophilus influenzae is a major community-acquired pathogen causing significant morbidity and mortality worldwide. Meningitis and bacteremia due to type b strains occur in areas where the protein-conjugated type b vaccine is not in use, whereas nontypeable strains are major causes of otitis media, sinusitis, acute exacerbations of chronic bronchitis, and pneumonia. Antibiotic resistance in this organism is more diverse and widespread than is commonly appreciated. Intrinsic efflux resistance mechanisms limit the activity of the macrolides, azalides, and ketolides. beta-Lactamase production is highly prevalent worldwide and is associated with resistance to ampicillin and amoxicillin. Strains with alterations in penicillin binding proteins, particularly PBP3 (beta-lactamase negative ampicillin resistant and beta-lactamase positive amoxicillin-clavulanate resistant), are increasing in prevalence, particularly in Japan, with increasing resistance to ampicillin, amoxicillin, amoxicillin-clavulanate, and many cephalosporins, limiting the efficacy of expanded-spectrum cephalosporins against meningitis and of many oral cephalosporins against other diseases. Most strains remain susceptible to the carbapenems, which are not affected by penicillin binding protein changes, and the quinolones. The activity of many oral agents is limited by pharmacokinetics achieved with administration by this route, and the susceptibility of isolates based on pharmacokinetic and pharmacodynamic parameters is reviewed.

Diversity of ampicillin resistance genes and antimicrobial susceptibility patterns in Haemophilus influenzae strains isolated in Korea

By Etest determination of the susceptibilities of 229 Haemophilus influenzae strains isolated in Korea to 10 antibiotics, the isolates were found to be antibiotic nonsusceptible in the following order: ampicillin (58.1%), trimethoprim-sulfamethoxazole (52%), cefaclor (41.1%), clarithromycin (25.8%), chloramphenicol (14.0%), amoxicillin-clavulanic acid (13.5%), meropenem (11.7%), cefixime (10.9%), cefuroxime (9.2%), and levofloxacin (1.3%). The prevalences of each resistance class were 23.6% for beta-lactamase-negative ampicillin-susceptible (BLNAS) strains; 37.6% for strains with the TEM-1 type beta-lactamase gene; 1.3% for strains with the ROB-1 type beta-lactamase gene; 29.3% for the beta-lactamase-negative ampicillin-resistant (BLNAR) strains with a mutation in the ftsI gene, which encodes PBP 3; and 8.3% for beta-lactamase-positive amoxicillin-clavulanate-resistant (BLPACR) strains, which showed both resistance mechanisms (i.e., a beta-lactamase gene and a mutation in the ftsI gene). The MIC50s of all beta-lactams, including cephem and meropenem agents, for the BLNAR strains were two to three times higher than those for the BLNAS strains. This study confirms that the prevalence of BLNAR and BLPACR strains is relatively high and for the first time confirms the presence of H. influenzae strains carrying blaROB-1 in Korea. Even though mutations in another gene(s) might be involved in beta-lactam resistance, these results suggest that mutations in the ftsI gene are important for the development of resistance to beta-lactams in H. influenzae strains in Korea.

Antimicrobial resistance among invasive Haemophilus influenzae strains: results of a Brazilian study carried out from 1996 through 2000

A total of 1712 strains of Haemophilus influenzae isolated from patients with invasive diseases were obtained from ten Brazilian states from 1996 to 2000. beta-Lactamase production was assessed and the minimum inhibitory concentrations (MIC) of ampicillin, chloramphenicol, ceftriaxone and rifampin were determined using a method for broth microdilution of Haemophilus test medium. The prevalence of strains producing beta-lactamase ranged from 6.6 to 57.7%, with an overall prevalence of 18.4%. High frequency of beta-lactamase-mediated ampicillin resistance was observed in Distrito Federal (25%), São Paulo (21.7%) and Paraná (18.5%). Of the 1712 strains analyzed, none was beta-lactamase negative, ampicillin resistant. A total of 16.8% of the strains were resistant to chloramphenicol, and 13.8% of these also presented resistance to ampicillin, and only 3.0% were resistant to chloramphenicol alone. All strains were susceptible to ceftriaxone and rifampin and the MIC90 were 0.015 micro g/ml and 0.25 micro g/ml, respectively. Ceftriaxone is the drug of choice for empirical treatment of bacterial meningitis in pediatric patients who have not been screened for drug susceptibility. The emergence of drug resistance is a serious challenge for the management of invasive H. influenzae disease, which emphasizes the fundamental role of laboratory-based surveillance for antimicrobial resistance.

Haemophilus influenzae resistance in Latin America: systematic review of surveillance data

Haemophilus influenzae is a relevant cause of morbidity and mortality among children under 5 years of age in the developing world. In Latin America, H. influenzae type b (Hib) conjugate vaccine and surveillance of H. influenzae antimicrobial susceptibility have been implemented in recent years. We have undertaken a systematic review and a pooled analysis on H. influenzae antimicrobial resistance, including reports of 15 Latin America countries over a 10-year period (1990-2000). We have found that 450 (21.4%) of 2,100 invasive isolates were beta-lactamase producers compared to 145 (14.5%) of 998 isolates of noninvasive isolates (p < 0.05). Ampicillin resistance was detected among 783 (21.9%) of 3,577 invasive isolates compared to 111 (17.2%) of 646 noninvasive strains (p < 0.05). In contrast, 568 (41.9%) of 1,355 noninvasive strains were trimethoprim-sulfamethoxazole (TMP-SMX) resistance against 241 (26.9%) of 897 invasive ones (p < 0.05). Therefore, TMP-SMX resistance was more common in nonsterile fluids than in sterile fluids. Over time, rates of beta-lactamase-producing strains were stable in Brazil and Mexico, whereas rates of TMP-SMX resistance were increasing in Brazil. It is predictable that following the Hib immunization, Latin America countries will be faced with increased nontypeable H. influenzae infection. Although standing by the nontypeable H. influenzae vaccine, in this novel epidemiological scenario of post-Hib vaccination in Latin America settings there is a need to improve H. influenzae resistance monitoring to guide clinicians to choose efficacious antimicrobial therapy.

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.

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.

Antimicrobial resistance patterns of Haemophilus influenzae isolated from patients with meningitis in São Paulo, Brazil

From 1989 to 1995, a total of 391 Haemophilus influenzae isolates were recovered from the cerebrospinal fluid (CSF) of hospitalized patients in São Paulo, Brazil. The majority of strains were isolated from infants aged less than 5 years. Strains belonging to biotype I (64.7%), biotype II (34.5%) and biotype IV (0.76%) were detected. Ninety-nine percent of these strains were serotype b. Minimal inhibitory concentration (MIC) was determined for ampicillin, chloramphenicol and ceftriaxone. The ss-lactamase assay was performed for all strains. The rate of ss-lactamase producer strains ranged from 10 to 21.4% during a period of 7 years, with an overall rate of 13.8%. Of the 391 strains analyzed, none was ss-lactamase negative ampicillin resistant (BLNAR). A total of 9.7% of strains showed resistance to both ampicillin and chloramphenicol; however, 4% of them were resistant to ampicillin only and 2% to chloramphenicol. All strains were susceptible to ceftriaxone and the MIC90 was 0.007 microg/ml, suggesting that ceftriaxone could be an option for the treatment of bacterial meningitis in pediatric patients who have not been screened for drug sensitivity.

Antimicrobial susceptibility of Haemophilus influenzae in the respiratory tracts of patients with cystic fibrosis

We analyzed the antimicrobial susceptibilities of Haemophilus influenzae isolates from 157 sputum specimens prospectively collected from 39 cystic fibrosis (CF) patients during a 2-year study. These isolates were characterized by random amplified polymorphic DNA analysis and major outer membrane protein (MOMP) analysis to identify H. influenzae strains and MOMP variants and to assess their persistence in the respiratory tract. Among the 247 H. influenzae isolates, 16 (6.5%) produced beta-lactamase. The 231 beta-lactamase-negative isolates represented 85 H. influenzae strains, 61 MOMP variants derived from 27 of these strains, and 85 persistent isolates identical to strains or MOMP variants. All beta-lactamase-negative isolates were tested for susceptibility to ampicillin, amoxicillin-clavulanic acid, cefuroxime, cefotaxime, cefaclor, imipenem, tetracycline, and trimethoprim-sulfamethoxazole by disk diffusion testing. Eleven (13%) H. influenzae strains, 18 (30%) MOMP variants, and 30 (35%) persistent isolates were resistant to one or more of the antibiotics tested. Antimicrobial susceptibility was decreased among MOMP variants and persistent isolates compared to nonpersistent H. influenzae strains, and changes in susceptibility occurred irrespective of MOMP variation. We conclude that the decreased antimicrobial susceptibility of H. influenzae during persistence contributes to the poor eradication of H. influenzae from the respiratory tracts of CF patients.