The evaluation of serotype distribution and antibiogram results of haemophilus influenzae isolates from intensive care units of Akdeniz University Faculty of Medicine Hospital

Haemophilus influenzae is a non-motile, non-spore forming, gram-negative bacterium that can cause life-threatening invasive and systemic infections. Encapsulated strains of this bacterium have multiple serotypes. Haemophilus influenzae type b (Hib) serotype, one of the encapsulated strains, is responsible for life-threatening invasive infections such as pneumonia, meningitis, bacteremia, and epiglottitis in children under five years of age. After the Hib vaccine was introduced into the routine childhood vaccination program in our country in 2007, changes in the distribution of circulating serotypes were observed, along with an increase in the incidence of non-typeable Haemophilus influenzae (NTHi) strains. In this study, we aimed to determine the serotype distribution, antibiotic susceptibility results, β-lactamase activity, and factors affecting mortality in Haemophilus influenzae isolates from patients in the intensive care units of Akdeniz University Hospital's Microbiology Laboratory. Serotype distribution was investigated using molecular methods (PCR). The PCR results showed that NTHi was the most prevalent serotype, accounting for 60.9%. Among encapsulated strains, Haemophilus influenzae type a was detected at 12.6%, type b at 4.6%, type c at 10.3%, type d at 2.3%, type e at 5.7%, and type f at 3.4%. Antibiotic susceptibility tests were conducted according to the guidelines of the European Committee on Antimicrobial Susceptibility Testing (EUCAST-V14.0). The results of these tests showed the highest resistance to azithromycin (80.9%), followed by ampicillin resistance at 57.6%. βlactamase activity, determined by the nitrocefin test, revealed a β-lactamase positivity rate of 11.8%. The proportion of β-lactamase-negative ampicillin-resistant (BLNAR) strains was found to be 45.8%. To examine the factors affecting mortality, we evaluated the demographic data of patients, the site from which the pathogen was isolated, and laboratory results from whole blood and serum samples (complete blood count, C-reactive protein level, serum creatinine level, and glomerular filtration rate). Leukocyte count, neutrophil count, creatinine, and glomerular filtration rate were statistically significantly associated with mortality. The data from our study were consistent with the literature, showing that the most common serotype in Haemophilus influenzae infections was NTHi and that the distribution of other encapsulated strains could show geographical variation. Moreover, due to the increasing production of β-lactamases and the rise of BLNAR strains worldwide, the use of ampicillin in empirical treatment should be avoided. In conclusion, our study contributes to the literature by identifying the serotype distribution, antibiotic susceptibility profile, and factors affecting mortality in Haemophilus influenzae infections in our region, highlighting the need for a review of empirical treatment approaches.