Serotypes and antimicrobial susceptibility in clinical isolates of Haemophilus influenzae from Korean children in prevaccination era

Characterization of Ceftriaxone-Resistant Haemophilus influenzae Among Korean Children

BACKGROUND

Haemophilus influenzae is a frequently encountered pathogen responsible for respiratory tract infections in children. Following the detection of ceftriaxone-resistant H. influenzae at our institution, we aimed to investigate the resistance mechanisms of ceftriaxone in H. influenzae, with a particular focus on alterations in penicillin-binding protein 3 (PBP3) and β-lactamase production.

METHODS

Among H. influenzae isolates collected at Asan Medical Center Children's Hospital from March 2014 to April 2019, ceftriaxone-resistant strains by the disk-diffusion test were included. Ceftriaxone minimum inhibitory concentrations (MICs) were determined using the E-test according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. The presence of β-lactamase was assessed through cefinase test and TEM-1/ROB-1 polymerase chain reaction (PCR). PBP3 alterations were explored via ftsI gene sequencing.

RESULTS

Out of the 68 collected strains, 21 exhibited resistance to ceftriaxone in disk diffusion tests. Two strains were excluded due to failed subculture. Among 19 ceftriaxone-resistant H. influenzae isolates, eighteen were non-typeable H. influenzae, and twelve were positive for TEM-1 PCR. Isolates were classified into groups II (harboring only N526K, n = 3), III (N526K+S385T, n = 2), III+ (S385T+L389F+N526K, n = 11), and III-like+ (S385T+L389F+R517H, n = 3) according to the PBP3 alteration pattern. With a median ceftriaxone MIC of 0.190 mg/L (range, 0.008-0.750), the median ceftriaxone MIC was the highest in group III-like+ (0.250 mg/L), followed by groups III+ (0.190 mg/L), III (0.158 mg/L), and II (0.012 mg/L). All three strains belonging to group II, which did not harbor the S385T substitution, had ceftriaxone MICs of ≤ 0.125 mg/L.

CONCLUSION

The emergence of ceftriaxone-resistant H. influenzae with ceftriaxone MIC values of up to 0.75 mg/L was observed even in children in South Korea, with most associated with S385T and L389F substitutions. The N526K mutation alone does not significantly impact ceftriaxone resistance. Further large-scale studies are essential to investigate changes in antibiotic resistance patterns and factors influencing antibiotic resistance in H. influenzae isolated from pediatric patients in Korea.

Increasing Prevalence of Group III Penicillin-Binding Protein 3 Mutations Conferring High-Level Resistance to Beta-Lactams Among Nontypeable Haemophilus influenzae Isolates from Children in Korea

This study investigated the roles of β-lactamase and penicillin-binding protein 3 (PBP3) alterations in the development of recent antimicrobial resistance in nontypeable Haemophilus influenzae (NTHi) isolated from Korean children. Nasopharyngeal NTHi isolates from children at a tertiary children's hospital were tested for antimicrobial susceptibility using E-test. β-lactamase production was screened by the paper disc test, and polymerase chain reaction amplification of bla_TEM and bla_ROB-1 was performed. The ftsI gene was amplified to identify PBP3 alteration. Of the 53 NTHi isolates, 69.8% were ampicillin nonsusceptible. The nonsusceptibility rates for cefaclor were 81.1%, cefpodoxime 69.8%, and amoxicillin/clavulanate 32.1%. About 60.3% and 32.1% of the isolates were genetically β-lactamase-nonproducing ampicillin-resistant (gBLNAR) and genetically β-lactamase-producing amoxicillin/clavulanate-resistant (gBLPACR) strains, respectively. Group III amino acid substitutions comprised 65.6% of the gBLNAR strains and 70.6% of the gBLPACR strains. MIC₅₀ for amoxicillin/clavulanate, cefaclor, cefuroxime, cefpodoxime, and cefixime were more than 2-80 times higher in the gBLNAR and gBLPACR strains compared with gBLPAR strains. Group III gBLNAR strains had significantly higher ampicillin, amoxicillin/clavulanate, cefpodoxime, and cefixime minimum inhibitory concentrations than group II strains. Group III gBLNAR and gBLPACR NTHi strains are highly prevalent in Korea, raising the alarm about increasing β-lactam resistance in NTHi.

Prevention ofHaemophilus influenzaetype b disease: past success and future challenges

Haemophilus influenzae type b (Hib) is responsible for significant morbidity and mortality worldwide, particularly in children under 5 years of age. In countries where the Hib conjugate vaccine is not routinely used, Hib is a leading cause of childhood pneumonia and meningitis. Routine use of the Hib conjugate vaccines has resulted in a remarkable decline in Hib disease in developed and developing countries. However, Hib conjugate vaccines are not routinely available in most developing countries, many of which have high burdens of Hib disease. This review outlines the pathogenesis and epidemiology of Hib disease, and the various options for prevention.

Haemophilus influenzae serotype a as a cause of serious invasive infections

Haemophilus influenzae, particularly H influenzae serotype b (Hib), is an important pathogen that causes serious diseases like meningitis and septicaemia. Since the introduction of Hib conjugate vaccines in the 1990s, the epidemiology of invasive H influenzae disease has changed substantially, with most infections now caused by non-Hib strains. We discuss the importance of H influenzae serotype a (Hia) as a cause of serious morbidity and mortality and its global epidemiology, clinical presentation, microbiology, immunology, prevention, and control. Much like Hib, the capsule of Hia is an important virulence factor contributing to the development of invasive disease. Molecular typing of Hia has identified distinct clonal groups, with some linked to severe disease and high case-fatality rates. Similarities between Hia and Hib capsules, their clinical presentation, and immunology of infection suggest that a bivalent Hia-Hib capsular polysaccharide-protein conjugate vaccine could offer protection against these two important serotypes of H influenzae.

Antibiotic resistance and molecular epidemiology of the beta-lactamase-producing Haemophilus influenzae isolated in Chongqing, China

This study aimed to determine the antibiotic resistance and molecular epidemiology of Haemophilus influenzae isolated from children with acute respiratory infection in Chongqing, China. To this end, 1967 H. influenzae isolates from 2006 to 2009 were analysed regarding β-lactamase production and antibiotic resistance. Ninety-nine β-lactamase-producing H. influenzae isolates from 2010 were analysed for antibiotic resistance and promoter regions of bla(TEM) (-1) . β-lactamase production was found in 35.8% (705/1967) of the strains. All ninety-nine β-lactamase-producing strains from 2010 were of the TEM-1 type as determined by PCR but did not produce the predicted 1075 bp product. According to PCR-SSCP and DNA sequencing, the promoter regions of bla(TEM) (-1) were categorized into 6 genotypes as SSCP1 (Pdel), SSCP2 (Pa/Pb), SSCP3 (P4), SSCP4 (Prpt.b), SSCP5 (2Prpt) and SSCP6 (P3.b). The Pdel, Pa/Pb and Prpt.b were common promoters of bla(TEM) (-1) for H. influenzae isolated from children in Chongqing. Strains with Prpt.b were more resistant to ampicillin (AMP) than strains with Pdel, Pa/Pb and P4 (p < 0.05). Therefore, bla(TEM-1) β-lactamase is the main mechanism for resistance of H. influenzae to ampicillin in Chongqing. Furthermore, the Prpt.b promoters may be related to the high resistance of H. influenzae to AMP.

Serotype distribution and beta-lactam resistance in Haemophilus influenzae isolated from patients with respiratory infections in Korea

Haemophilus influenzae is a frequent causative bacterial pathogen of respiratory tract infections. Resistance to beta-lactam antibiotics has been a significant clinical problem in treatment for H. influenzae respiratory infections. This study describes the serotype, antibiotic resistance and distribution of TEM-1 or ROB-1 beta-lactamase in H. influenzae isolates from local private hospitals from 2002 to 2004. Among the 100 H. influenzae respiratory isolates, only 7% were identified as serotypes a, b, e, and f, with the remaining 93% being nontypeable. Resistance to ampicillin, cefaclor, and tetracycline was 57%, 46%, and 16%, respectively. All strains were susceptible to azithromycin and ciprofloxacin, whereas amoxicillin/clavulanate, cefotaxime, and imipenem exhibited reduced susceptibilities of 99%, 99%, and 91%, respectively. All 57 ampicillin-resistant strains (minimum inhibitory concentration, MIC>or=4 microg/ml) were beta-lactamase-positive and possessed the TEM-1 type beta-lactamase. One beta-lactamase-positive amoxicillin/clavulanate-resistant isolate that was resistant to ampicillin (MIC>128 microg/ml) had the TEM-1 type beta-lactamase and not susceptible to cefaclor and cefotaxime. Analysis of penicillin binding protein 3 revealed six residues (Asp-350, Met-377, Ala-502, Asn-526, Val-547, and Asn-569) that were substituted by Asn, Ile, Val, Lys, Ile, and Ser, respectively.

PCR-based capsular serotype determination of Haemophilus influenzae strains recovered from Japanese paediatric patients with invasive infection

The serotypes of 53 isolates of Haemophilus influenzae from children with invasive infections were determined by a conventional slide agglutination test (SAT) and a recently proposed PCR-based method for serotyping H. influenzae. The PCR assay identified 47 (88.7%) type b isolates, one (1.9%) type e isolate and five (9.4%) non-typeable isolates. The only discrepancy between the methods was an isolate that was non-typeable by SAT, but was identified as serotype e by PCR. Of 41 isolates from patients with meningitis, 39 (95.1%) were type b. Of the five non-typeable isolates, three (60%) were from the blood of patients with septicaemic pneumonia and two (40%) were from the cerebrospinal fluid of patients with meningitis. None of the non-typeable isolates appeared to be a capsule-deficient mutant of an encapsulated H. influenzae strain. Overall, the study confirmed the usefulness of this PCR method for the serotyping of invasive H. influenzae isolates.