Beta-lactam resistance in invasive and non-invasive Haemophilus influenzae isolates in Germany 10/2022-03/2023.

INTRODUCTION

Haemophilus influenzae (Hi) is a commensal pathogen of the respiratory epithelium. However, it can also cause a wide range of infections, from minor ear, nose and throat conditions to severe sepsis and meningitis. In this context, aminopenicillins, either alone or in combination with a beta-lactamase inhibitor, and third-generation cephalosporins are the preferred treatment options. Antibiotic resistance surveillance is important in providing a basis for recommendations on the empirical use of antibiotic agents.

OBJECTIVES

To analyse the dynamics of the susceptibility rates of invasive and non-invasive Hi isolates to aminopenicillins and third-generation cephalosporins, and to compare the molecular mechanisms of resistance. Furthermore, an analysis of the epidemiology of invasive and non-invasive infections in Germany was conducted.

METHODS

Non-invasive Hi isolates (n = 208) were collected from a sentinel network of diagnostic laboratories in a prospective multicentre prevalence study conducted by the Paul-Ehrlich Society in the period 10/2022-03/2023. Invasive isolates (n = 905) were collected at the NRZMHi at the same time period. Antimicrobial susceptibility testing was carried out using gradient agar diffusion (GAD) test. MICs were interpreted in accordance with EUCAST guidelines. β-lactamase production was tested using the Nitrocefin test. Sequencing of the ftsI gene, encoding penicillin binding protein 3 (PBP3) was performed to analyse the molecular mechanism of β-lactam resistance among all β-lactamase negative ampicillin resistant (BLNAR).

RESULTS

The results showed no significant differences in the proportions of β-lactamase negative ampicillin-susceptible (BLNAS, 79.3% vs. 77.5%), β-lactamase positive ampicillin-resistant (BLPAR, 13% vs. 15%) and BLNAR Hi (6.7% vs. 7.4%) in non-invasive and invasive isolates, respectively. Resistance to third-generation cephalosporins was rare in both non-invasive and invasive isolates (1.0% vs 1.3%). Most BLNAR exhibited PBP3 amino-acid substitutions of group II, most frequently IIb and IIa. Furthermore, 92% of isolates carrying group III PBP3 mutations (n = 12/13) exhibited increased MICs against cefotaxime (≥0.125 mg/l). The present study revealed that, compared to invasive encapsulated isolates (n = 104), NTHi (n = 801) exhibited a significantly higher propensity towards ampicillin resistance (p < 0.0001; Fisher's exact test). The vast majority of non-invasive isolates were also NTHi (204/208). All non-invasive ampicillin-resistant strains were NTHi (n = 42).

CONCLUSIONS

The findings generally indicated that resistance rates of invasive and non-invasive isolates were comparable. The molecular analysis revealed the presence of characteristic PBP3 mutations in BLNAR and cefotaxime-resistant isolates. Overall, the resistance rates to β-lactam antibiotics do not seem to have changed in Germany.