Haemophilus aegyptius
1. Classification
a. Higher order taxa Bacteria, Proteobacteria, Gamma Proteobacteria, Pasteurellales, Pasteurellacease, Haemophilus [1]
b. Species Haemophilus Influenzae [1]
2. Description and significance
Haemophilus influenzae biogroup aegyptius is a Gram-negative bacterium with an elongated rod shape [2]. H. aegyptius is normally found living in human epithelial cell linings [1], where it exhibits colonization and adherence to epithelial cells with large clusters of elongated chains of cells [2]. As a biogroup, H. influenzae biogroup aegyptius has traits that differ from Haemophilus influenzae (H. influenzae), including the severity of virulence and lack of genes that encode for a polysaccharide capsule [3] in H. influenzae biogroup aegyptius. For over a century since its first discovery, H. influenzae biogroup aegyptius had only been known to cause conjunctivitis. However, in 1995, the HaeBPF strain of H. influenzae biogroup aegyptius [3] was identified in patients with Brazilian Purpuric Fever (BPF) [4]. BPF has symptoms that are similar to that of meningococcal sepsis, which include an infection that results in high fever, vomiting, abdominal pain, and hemorrhagic skin lesions [5]. Researchers have spent over two decades learning about the transformation of H. influenzae biogroup aegyptius from causing mild conjunctivitis to deadly BPF. However, much is still unknown about the organism’s virulence factors [6]. Because of this, studies have been focused on understanding the mechanism of pathogenesis and developing preventative measures and treatments for BPF.
3. Genome structure
The Haemophilus influenzae biogroup aegyptius genome, or F3031 genome, contains 77% shared sequences with other H. influenzae genomes [4]. The Hae accessory genome sequences were delineated and 163 protein-coding genes were characterized as adhesins and fimbrial operons [3]. The Haemophilus influenzae biogroup aegyptius genome includes 3031 plasmids, and sequences coding for pilin proteins [6].
Unique genes sequences to the genome of H. influenzae biogroup aegyptius are: the bpf001 and bpf002 genes, which are associated with Brazilian Purpuric Fever (BPF) [4], and the Haemophilus adhesin A gene (HadA) [7]. bpf001 and bpf002 code for proteins that enhance epithelial cell entry, correlating with cell invasion of human respiratory epithelial cells during the pathogenesis of BPF [4]. The HadA gene codes for an adhesion protein that is associated with adherence to extracellular matrix proteins of human cells during the onset of BPF [7].
There has been evidence of exchange of the Las gene between H. influenzae biogroup aegyptius and Neisseria meningitidis, a bacterium that causes brain and spinal cord inflammation [5].
4. Cell structure
Unique to the H. influenzae biogroup aegyptius’s cell structure is an oliogomeric coiled-coil adhesion (Oca) adhesion called HadA (Haemophilus adhesion A), an adhesion protein. HadA allows bacterial aggregation when present in liquid culture, possibly through intrinsic hydrophilic properties and promotion of bacterial attachment to and invasion of host cells [7]. These phenotypic properties of HadA are associated with cell invasion in the pathogenesis of Brazilian Purpuric Fever (BPF).
During interaction with epithelial cells, H. influenzae biogroup aegyptius exhibits colonization and adherence to epithelial cells with large clusters of elongated chains of bacterial cells. This clustering of H. influenzae biogroup aegyptius is unlike H. influenzae, which organizes by an even distribution as individual coccobacilli on epithelial cells [2].
5. Metabolic processes
Haemophilus influenzae biogroup aegyptius has metabolic characteristics similar to H. influenzae in metabolizing sugars. H. influenzae metabolizes fructose using phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) [8]. When there is a scarcity in available fructose, H. influenzae transports and metabolizes fucose using fuculokinase, which is coded by an operon unique to H. influenzae [9].
A notable difference of H. influenzae biogroup aegyptius, compared to other H. influenzae strains, is its inability to ferment xylose and its inability to produce indole [9]. Inability to produce indole is an implication that H. influenzae biogroup aegyptius lacks the enzyme tryptophanase [9], which is present in other H. influenza strains. H. influenzae biogroup aegyptius also exhibits urease activity, but lacks ornithine decarboxylase activity [2].
6. Ecology
H. influenzae biogroup aegyptius is normally found as an inhabitant of human epithelial cell linings [10] such as the oropharynx [1] and the epithelial layer of the eyes, where it presents as conjunctivitis [4]. The manifestation of H. influenzae biogroup aegyptius has been identified as the disease-causing agent of BPF [11] in children and adults.
7. Pathology
Haemophilus influenzae biogroup aegyptius has been most commonly linked to cases of acute conjunctivitis and Brazilian Purpuric Fever (BPF) [6]. A particular strain of H. influenzae biogroup aegyptius known as Hae causes conjunctivitis. Conjunctivitis is a disease more commonly known as “pink eye” that induces inflammation in the eye [3]. The strain of Haemophilus influenzae biogroup aegyptius that is linked to BPF is known as HaeBPF.
The first outbreak of BPF occurred in Sao Paulo State, Brazil in 1984 [3] followed by several hundred cases that occurred sporadically. The outbreaks were occurring mainly in small towns [3] in Brazil including Presidente Prudente, Fartura, Sao Jose do Rio Preto, Serrana, Guatapara, and Promissao [1]. Three other cases that were reported: two in Australia [4] and one in United States, specifically in Connecticut [11].
HaeBPF was first identified and characterized during the second outbreak of BPF that occurred in 1995 [3]. The onset of BPF uniquely occurs in individuals that previously contracted pus-containing conjunctivitis that was eventually resolved [3]. However, these individuals later develop bacteremia, the presence of bacteria in the blood, when H. influenzae biogroup aegyptius enters the bloodstream [12]. This disease predominantly affects infants and young children under the age of 10, producing symptoms such as high fever, abdominal pain and vomiting, skin lesions, and vascular collapse, from which can lead to death [6]. On the cellular level, BPF is characterized by cytotoxicity in endothelial cells caused by H. influenzae biogroup aegyptius [13].
The mechanism through which Haemophilus influenzae biogroup aegyptius infects and causes disease has not been well defined. Adhesins for binding and other BPF-specific outer membrane proteins have been identified, but their roles in virulence and pathogenicity are not clear [3].
Although the BPF strain of Haemophilus influenzae biogroup aegyptius is generally pathogenic and can lead to serious symptoms, studies have indicated that older children and adults who were exposed to the bacteria were able to develop serum bactericidal antibodies against BPF strains [14]. As a result, they experienced no particular symptoms. Also, there was evidence of immunity from BPF through high levels of antibodies in children who had conjunctivitis caused by the BPF strain of Haemophilus influenzae biogroup aegyptius but did not develop BPF [14].
There is currently no established treatment for Brazilian Purpuric Fever; however, Haemophilus influenzae biogroup aegyptius is sensitive to antibiotics such as ampicillin and chloramphenicol [6], and research suggests that early antimicrobial treatment may improve chances of survival [15].
8. Epidemiology
In Brazil, around 90% of individuals who developed Brazilian Purpuric Fever did so after recovering from conjunctivitis [6]. Case control studies have been performed in three towns in Brazil-- Promissao, Londrina, and Serrana-- to investigate the relatedness between the two diseases. These studies found an association between conjunctivitis and BPF [6]. Other case control studies were carried out to determine risk factors for BPF. Day care attendance appeared to be a significant risk factor for BPF [6].
8. Current Research
Current research focuses on how H. influenzae biogroup aegyptius emerged as a virulent strain, causing Brazilian Purpuric Fever (BPF). Since horizontal transfer of virulence genes between Haemophilus influenzae and Neisseria meningitidis has been noted in the past, the genome sequences of H. influenzae biogroup aegyptius and N. meningitidis [5] were compared. A genetic sequence unique to N. meningitides, NMB0418, was identified in the genome of a H. influenzae biogroup aegyptius strain associated with BPF [5]. When cells that contained an antibiotic interacted with a H. influenzae biogroup aegyptius strain that expressed the NMB0418 sequence, the antibiotic-containing cells had a higher inflammatory response than when they were exposed to the N. meningitidis strain [5]. This indicated that there might be other genetic sequences that influence the expression of an inflammatory response during the onset of BPF.
9. References
[1] Brenner D. J., Mayer L. W., Carlone G.M., Harrison L. H., Bibb W.F., Brandileone M.C., Sottnek F. O., Irino K., Reeves M.W., Swenson J.M., et al. (1988). Biochemical, g[netic, and epidemiologic characterization of Haemophilus influenzae biogroup aegyptius (Haemophilus aegyptius) strains associated with Brazilian purpuric fever. Journal of Clinical Microbiology, 26. 1524-1534
[2] Kilian, M., Poulsen, K. and Lomholt, H. (2002). Evolution of the paralogous hap and igagenes in Haemophilus influenzae: evidence for a conserved hap pseudogene associated with microcolony formation in the recently diverged Haemophilus aegyptius and H. influenzae biogroup aegyptius. Molecular Microbiology, 46: 1367–1380. Web. 6 Oct. 2016.
[3] Strouts, F.R. Power, P. , Croucher, N.J., Corton, N. Tonder A. V., Quail, M.A., … Bentley, S.D. (2012). Lineage-specific virulence determinants of Haemophilus influenzae Biogroup aegyptius. Emerging Infectious Diseases, 18(3): 449-457. Web. 19 Sept. 2016.
[4] Li, Mingh-Shi, Jayne Farrant L., Pauld Langford R. and J. Kroll Simon (2003). Identification and Characterization of Genomic Loci Unique to the Brazilian Purpuric Fever Clonal Group of H. Influenzae Biogroup Aegyptius: Functionality Explored using Meningococcal Homology. Molecular Microbiology, 47(4): 1101-111. Web. 19 Sept. 2016.
[5] Cury, G. C. G., Pereira, R. F. C., de Hollanda, L. M., & Lancellotti, M. (2014). Inflammatory response of Haemophilus influenzae biotype aegyptius causing Brazilian Purpuric Fever. Brazilian Journal of Microbiology, 45(4): 1449–1454. Web. 20 Sept. 2016.
[6] Harrison, L.H., Da Silva, G.A., Pittman, M., Fleming, D.W., Vranjac, A., Broome, C.V., and the Brazilian Purpuric Fever Study Group (1989). Epidemiology and Clinical Spectrum of Brazilian Purpuric Fever. Journal of Clinical Microbiology, 27(4): 599-604. Web. 20 Oct. 2016.
[7] Serruto, D. , Spadafina, T. , Scarselli, M. , Comanducci, S.B.M. , Höhle, S. , Kilian, M. , Veiga, E. , Cossart, P. , Oggioni M.R. , Savino, S. , Ferlenghi I. , Taddei, A.R. , Rappuoli, R. , Pizza, M. , Masignani, V. , and Arico, B (2009). HadA is an atypical new multifunctional trimeric coiled-coil adhesin of Haemophilus influenzae biogroup aegyptius, which promotes entry into host. Cellular Microbiology, 11(7): 1044-1063. Web. 21 Sept. 2016.
[8] Macfadyen, L. P., Dorocicz, I. R., Reizer, J., Saier Jr, M. H. and Redfield, R. J. (1996), Regulation of competence development and sugar utilization in Haemophilus influenzae Rd by a phosphoenolpyruvate:fructose phosphotransferase system. Molecular Microbiology, 21: 941–952. doi:10.1046/j.1365-2958.1996.441420.x. Web. 19 Sept. 2016.
[9] Norskov-Lauritsen, N. (2014, April). Classification, Identification, and Clinical Significance of Haemophilus and Aggregatibacter Species with Host Specificity for Humans. Clinical Microbiology Reviews, 27(2), 214-240. doi:10.1128/cmr.00103-13. Web. 19 Sept. 2016.
[10] Farley, M. M., Whitney, A. M., Spellman, P., Quinn, F. D., Weyant, R. S., Mayer, L., & Stephens, D. S. (1992). Analysis of the Attachment and Invasion of Human Epithelial Cells by Haemophilus influenzae Biogroup Aegyptius. Journal of Infectious Diseases, 165(Supplement 1). doi:10.1093/infdis/165-supplement_1-s111. Web. 19 Sept. 2016.
[11] Smoot, L. M., Franke, D. D., McGillivary, G., & Actis, L. A. (2002). Genomic Analysis of the F3031 Brazilian Purpuric Fever Clone of Haemophilus Influenzae Biogroup Aegyptius by PCR-Based Subtractive Hybridization. Infection and Immunity, 70 (9): 2694-2699. Web. 21 Sept. 2016.
[12] Rubin, L.G., Gloster, E.S., Carlone, G.M., and the Brazilian Purpuric Fever Study Group (1989). An Infant Rat Model of Bacteremia with Brazilian Purpuric Fever Isolates of Hemophilus influenzae Biogroup Aegyptius. The Journal of Infectious Diseases, 160(3): 476-482. Web. 20 Oct. 2016.
[13] Weyant, R.S., Quinn, F.D., Utt, E. A., Worley, M., George, V. G., Candal, F. J., & Ades, E. W. (1994). Human Microvascular Endothelial Cell Toxicity Caused by Brazilian Purpuric Fever-Associated Strains of Haemophilus influenzae Biogroup Aegyptius. J infect Dis., 169 (2): 430-433. Web. 6 Oct. 2016.
[14] Rubin, L.G., Peters, V.B., Ferez, M.C.C. (1993). Bactericidal Activity of Human Sera against a Brazilian Purpuric Fever (BPF) Strain of Haemophilus influenzae Biogroup aegyptius Correlates with Age-Related Occurrence of BPF. The Journal of Infectious Diseases, 167(5): 1262-1264. Web. 20 Oct. 2016.
[15] Perkins BA, Silva GA, Tondella MLC, et al. Confirmation of Brazilian purpuric fever in a new region of Brazil and evaluation of oral rifampin to eradicate conjunctival carriage of Haemophilus aegyptius (Abstract). In: Proceedings of the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1990:277. Web. 20 Oct. 2016.
Edited by Helen Guan, Lena Huang, Sophie Lee, and Jessica Perez, students of Jennifer Talbot for BI 311 General Microbiology, 2016, Boston University
