Pharyngeal Colonization Dynamics of Haemophilus influenzae and Haemophilus haemolyticus in Healthy Adult Carriers

Abstract

Haemophilus influenzae is an important cause of respiratory infections, including acute otitis media, sinusitis, and chronic bronchitis, which are preceded by asymptomatic H. influenzae colonization of the human pharynx. The aim of this study was to describe the dynamics of pharyngeal colonization by H. influenzae and an intimately related species, Haemophilus haemolyticus, in healthy adults. Throat specimens from four healthy adult carriers were screened for Haemophilus species; 860 isolates were identified as H. influenzae or H. haemolyticus based on the porphyrin test and on dependence on hemin and NAD for growth. Based on tests for hemolysis, for the presence of the 7F3 epitope of the P6 protein, and for the presence of iga in 412 of the isolates, 346 (84%) were H. influenzae, 47 (11%) were H. haemolyticus, 18 (4%) were nonhemolytic H. haemolyticus, and 1 was a variant strain. Carriers A and B were predominantly colonized with nontypeable H. influenzae, carrier C predominantly with b ؊ H. influenzae mutants, and carrier D with H. haemolyticus. A total of 358 H. influenzae and H. haemolyticus isolates were genotyped by pulsed-field gel electrophoresis (PFGE) following SmaI or EagI digestion of their DNA, and the carriers displayed the following: carrier A had 11 unique PFGE genotypes, carrier B had 15, carrier C had 7, and carrier D had 10. Thus, adult H. influenzae and H. haemolyticus carriers are colonized with multiple unique genotypes, the colonizing strains exhibit genetic diversity, and we observed day-to-day and week-to-week variability of the genotypes. These results appear to reflect both evolutionary processes that occur among H. influenzae isolates during asymptomatic pharyngeal carriage and sample-to-sample collection bias from a large, variable population of colonizing bacteria.Haemophilus species constitute approximately 10% of the total bacterial flora in the human upper respiratory tract (27). Haemophilus influenzae is an opportunistic pathogen in humans that asymptomatically colonizes the pharyngeal mucosa and occasionally the genital mucosa. The rate of carriage of H. influenzae increases from infancy (about 20% in the first year of life) to early childhood (Ͼ50% in children 5 to 6 years old), and H. influenzae is recoverable from the upper airways of 20 to 80% of healthy children (2,15,22,32).Colonization of the human respiratory mucosal surface represents a dynamic process in which bacteria are acquired, replaced, and reacquired many times in a lifetime. Past studies have demonstrated that H. influenzae colonization of the pharynx is characterized by rapid bacterial turnover (9, 12, 50, 58) and carriage of multiple strains at any one time (18,37,43,52,58). Previous studies have demonstrated a 62% week-to-week turnover rate of H. influenzae isolated from healthy children attending day care; 37 to 43% of throat cultures contained two or more genetically distinct strains (range, zero to five) (14,56).In addition to living as a commensal in the respiratory tract, H. influenzae may also cause s...

Nasal colonization by four potential respiratory bacteria in healthy children attending kindergarten or elementary school in Seoul, Korea

“…In the human URT, bacterial colonization is a dynamic process in which bacteria are acquired, eliminated and reacquired many times during a human life and can be influenced by various factors such as host age, immune status, exposure to antibiotics, smoking and overcrowded living conditions (Marchisio et al, 2001;García-Rodríguez & Fresnadillo Martínez, 2002;Chen et al, 2007;Mukundan et al, 2007).…”

Difficult identification ofHaemophilus influenzae, a typical cause of upper respiratory tract infections, in the microbiological diagnostic routine

“…Biochemical assays have been shown to lack reliability [6,17,[20][21][22][23][24][25][26][27][28]. Complex multiplex PCR-approaches [38] or sequence-based approaches [5] are hardly realistic for the routine setting because such procedures are both expensive and demanding regarding hands-on time of technical laboratory assistants.…”

“…The saprophytic colonizer H. parainfl uenzae is no typical cause of local infections of the upper respiratory tract and has been described as a potential cause of infectious endocarditis in few incidences [15]. Most available studies deny a relevant clinical importance of H. haemolyticus [5,16,17], although recent investigations suggest etiological relevance at least at some occasions [18].…”

“…Unfortunately, H. haemolyticus does not show this phenomenon on sheep blood agar, which is most frequently used in microbiological routine diagnostics, considerably reducing the practical relevance. Furthermore, also nonhemolytically growing H. haemolyticus isolates have been observed [6,17] and even primarily hemolytic H. haemolyticus isolates can lose this phenotype during passage [25]. Accordingly, the discriminative power of α-hemolysis should not be overestimated and H. haemolyticus isolates will usually be misidentified as H. influenzae under routine conditions by a large proportion of diagnostic laboratories.…”

“…Between 4% and 27% of throat culture strains that were initially identifi ed as H. infl uenzae turned out to be H. haemolyticus by confi rmatory testing in recent studies [5,17,44]. In sputum of COPD patients, up to 39.5% H. haemolyticus isolates were observed, at least if no association with acute exacerbations was guaranteed [5,45].…”