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Forstner P, Laireiter CM, Friedl S, Steinmetz I, Dichtl K. Bacitracin agar vs. oleandomycin disk supplemented chocolate agar for the recovery of Haemophilus influenzae in diagnostic samples: A prospective comparison. Diagn Microbiol Infect Dis 2024; 109:116203. [PMID: 38422664 DOI: 10.1016/j.diagmicrobio.2024.116203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Revised: 01/30/2024] [Accepted: 01/30/2024] [Indexed: 03/02/2024]
Abstract
Haemophilus influenzae is an important pathogen able to cause various forms of respiratory and invasive disease. To provide high sensitivity for detection, culture media must inhibit growth of residential flora from the respiratory tract. This study aimed to identify and compare the diagnostic and economic advantages of using bacitracin containing selective agar (SEL) or oleandomycin disk supplemented chocolate agar (CHOC). Growth and semi-quantitative abundance of H. influenzae and growth suppression of residential flora was prospectively assessed in a 28-week period. H. influenzae was identified in 164 (5 %) of all included samples: CHOC and SEL, CHOC only, and SEL only were positive in 95, 24, and 45 cases. Diagnostic superiority of SEL was primarily attributable to the results of throat swabs. However, on average, € 200 had to be spent for the detection of each additional isolate that was recovered only because of additional incubation on SEL.
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Affiliation(s)
- Patrick Forstner
- Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria
| | - Christina Maria Laireiter
- Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria
| | - Simone Friedl
- Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria
| | - Ivo Steinmetz
- Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria
| | - Karl Dichtl
- Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria.
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Lee H, Edgar RJ, Lichtenstein IJ, Velarde JJ, Korotkova N, Wessels MR. Streptococcus pyogenes can support or inhibit growth of Haemophilus influenzae by supplying or restricting extracellular NAD+. PLoS One 2022; 17:e0270697. [PMID: 36170255 PMCID: PMC9518897 DOI: 10.1371/journal.pone.0270697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 06/15/2022] [Indexed: 11/19/2022] Open
Abstract
Nicotinamide adenine dinucleotide (NAD+) is an essential co-factor for cellular metabolism and serves as a substrate in enzymatic processes. NAD+ is produced by de novo synthesis or salvage pathways in nearly all bacterial species. Haemophilus influenzae lacks the capacity for de novo synthesis, so it is dependent on import of NAD+ from the external environment or salvage biosynthetic pathways for recycling of NAD+ precursors and breakdown products. However, the actual sources of NAD+ utilized by H. influenzae in the respiratory tract are not well defined. In this study, we found that a variety of bacteria, including species found in the upper airway of humans, released NAD+ that was readily detectable in extracellular culture fluid, and which supported growth of H. influenzae in vitro. By contrast, certain strains of Streptococcus pyogenes (group A streptococcus or GAS) inhibited growth of H. influenzae in vitro by secreting NAD+-glycohydrolase (NADase), which degraded extracellular NAD+. Conversely, GAS strains that lacked enzymatically active NADase released extracellular NAD+, which could support H. influenzae growth. Our results suggest that many bacterial species, including normal flora of the upper airway, release NAD+ into the environment. GAS is distinctive in its ability to both release and degrade NAD+. Thus, colonization of the airway with H. influenzae may be promoted or restricted by co-colonization with GAS in a strain-specific manner that depends, respectively, on release of NAD+ or secretion of active NADase. We suggest that, in addition to its role as a cytotoxin for host cells, NADase may serve a separate function by restricting growth of H. influenzae in the human respiratory tract.
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Affiliation(s)
- Hyunju Lee
- Division of Infectious Diseases, Boston Children’s Hospital, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Pediatrics, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seoul, Korea
| | - Rebecca J. Edgar
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
| | - Ian J. Lichtenstein
- Division of Infectious Diseases, Boston Children’s Hospital, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jorge J. Velarde
- Division of Infectious Diseases, Boston Children’s Hospital, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Natalia Korotkova
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, United States of America
- Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky, Lexington, Kentucky, United States of America
| | - Michael R. Wessels
- Division of Infectious Diseases, Boston Children’s Hospital, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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Gupta V, Shekhawat SS, Kulshreshtha NM, Gupta AB. A systematic review on chlorine tolerance among bacteria and standardization of their assessment protocol in wastewater. WATER SCIENCE AND TECHNOLOGY : A JOURNAL OF THE INTERNATIONAL ASSOCIATION ON WATER POLLUTION RESEARCH 2022; 86:261-291. [PMID: 35906907 DOI: 10.2166/wst.2022.206] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria surviving after chlorination pose serious public health and environmental problems. This review critically assesses the mechanism of chlorine disinfection as described by various researchers; factors affecting chlorination efficacy; and the re-growth potential of microbial contaminations in treated wastewater post chlorination to arrive at meaningful doses for ensuring health safety. Literature analysis shows procedural inconsistencies in the assessment of chlorine tolerant bacteria, making it extremely difficult to compare the tolerance characteristics of different reported tolerant bacteria. A comparison of logarithmic reduction after chlorination and the concentration-time values for prominent pathogens led to the generation of a standard protocol for the assessment of chlorine tolerance. The factors that need to be critically monitored include applied chlorine doses, contact time, determination of chlorine demands of the medium, and the consideration of bacterial counts immediately after chlorination and in post chlorinated samples (regrowth). The protocol devised here appropriately assesses the chlorine-tolerant bacteria and urges the scientific community to report the regrowth characteristics as well. This would increase the confidence in data interpretation that can provide a better understanding of chlorine tolerance in bacteria and aid in formulating strategies for effective chlorination.
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Affiliation(s)
- Vinayak Gupta
- Alumnus, Department of Civil and Environmental Engineering, National University of Singapore, Singapore; School of Environment and Society, Tokyo Institute of Technology, Tokyo, Japan
| | - Sandeep Singh Shekhawat
- Department of Civil Engineering, Malaviya National Institute of Technology, Jaipur, India E-mail: ; School of Life and Basic Sciences, SIILAS Campus, Jaipur National University Jaipur, India
| | - Niha Mohan Kulshreshtha
- Department of Civil Engineering, Malaviya National Institute of Technology, Jaipur, India E-mail:
| | - Akhilendra Bhushan Gupta
- Department of Civil Engineering, Malaviya National Institute of Technology, Jaipur, India E-mail:
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Shin CH, Lim C, Kim TS, Choi EH, Cho TJ, Choi IH, Yoo WJ. Effective and Rapid Microbial Identification in Pediatric Osteoarticular Infections Using Blood Culture Bottles. J Bone Joint Surg Am 2020; 102:1792-1798. [PMID: 33086346 DOI: 10.2106/jbjs.20.00219] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND The detection and identification of pathogenic microorganisms are essential for the treatment of osteoarticular infection. However, obtaining a sufficient amount of specimen from pediatric patients is often difficult. Herein, we aimed to demonstrate the effectiveness of the blood culture bottle (BCB) system in pediatric osteoarticular infections. We hypothesized that our BCB culture method is superior to the conventional swab and tissue culture methods in terms of required specimen size, incubation time, and microbial identification rate. METHODS We analyzed the prospectively collected data of pediatric patients who underwent surgical treatment for osteoarticular infections between August 2016 and October 2019. Four needles were dipped in the infected fluid or tissue during the surgical procedure as soon as the infected area was exposed and were used to inoculate 2 aerobic pediatric BCBs and 2 anaerobic general BCBs. We also collected 2 conventional swab samples and 2 tissue samples from the identical area. The microbial identification rate and the time required for identification were compared between BCB, swab, and tissue cultures. RESULTS Forty patients constituted the study group; 13 patients had osteomyelitis, 17 patients had septic arthritis, and 10 patients had both. Of these 40 patients, the microbial identification rate was higher with BCB cultures (27 [68%]) than with swab cultures (18 [45%]; p = 0.004) or tissue cultures (15 [38%]; p < 0.001). Nine samples (9 patients [23%]) were only positive in the BCB culture. Positive microbial growth was not detected with conventional culture methods when microorganisms did not grow on the BCB culture. Compared with swab culture (4.3 ± 1.1 days; p < 0.001) or tissue culture (4.4 ± 1.1 days; p < 0.001), the BCB culture reduced the time required for microbial identification (3.5 ± 0.9 days). CONCLUSIONS In pediatric osteoarticular infections, the BCB culture system improved the microbial identification rate, reduced the time to identification, and permitted a smaller-volume specimen, compared with traditional culture systems. LEVEL OF EVIDENCE Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.
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Affiliation(s)
- Chang Ho Shin
- Divisions of Pediatric Orthopaedics (C.H.S., T.-J.C., I.H.C., and W.J.Y.), and Pediatrics (E.H.C.), Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - Chaemoon Lim
- Department of Orthopaedic Surgery, Jeju National University Hospital, Jeju, Republic of Korea
| | - Taek Soo Kim
- Department of Laboratory Medicine, Seoul National University Hospital, Seoul, Republic of Korea
| | - Eun Hwa Choi
- Divisions of Pediatric Orthopaedics (C.H.S., T.-J.C., I.H.C., and W.J.Y.), and Pediatrics (E.H.C.), Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - Tae-Joon Cho
- Divisions of Pediatric Orthopaedics (C.H.S., T.-J.C., I.H.C., and W.J.Y.), and Pediatrics (E.H.C.), Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - In Ho Choi
- Divisions of Pediatric Orthopaedics (C.H.S., T.-J.C., I.H.C., and W.J.Y.), and Pediatrics (E.H.C.), Seoul National University Children's Hospital, Seoul, Republic of Korea
| | - Won Joon Yoo
- Divisions of Pediatric Orthopaedics (C.H.S., T.-J.C., I.H.C., and W.J.Y.), and Pediatrics (E.H.C.), Seoul National University Children's Hospital, Seoul, Republic of Korea
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Whitby PW, VanWagoner TM, Seale TW, Morton DJ, Stull TL. Comparison of transcription of the Haemophilus influenzae iron/heme modulon genes in vitro and in vivo in the chinchilla middle ear. BMC Genomics 2013; 14:925. [PMID: 24373462 PMCID: PMC3879429 DOI: 10.1186/1471-2164-14-925] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 12/17/2013] [Indexed: 08/30/2023] Open
Abstract
Background Haemophilus influenzae is a significant cause of childhood otitis media, and also has an absolute growth requirement for heme. Recent microarray studies using three H. influenzae isolates were used to propose a putative core of genes responsive to iron and heme levels. Included in the core modulon were thirty seven genes that are preferentially expressed under iron/heme limitation, most of which are directly involved with iron and or heme acquisition. In this report, the core iron/heme modulon was further refined following microarray analysis of two additional nontypeable H. influenzae isolates from patients with otitis media. The transcriptional status of the genes comprising the refined iron/heme core modulon was then assessed in vivo, in a chinchilla model of otitis media. These in vivo experiments were performed to address the hypothesis that iron and heme regulated genes are both highly expressed in vivo and important, during clinical infection. Results Microarray analysis of two additional H. influenzae strains resulted in the definition of a core of iron/heme responsive genes. This core consisted of 35 genes maximally expressed under heme restriction and a further 20 genes maximally expressed in heme replete conditions. In vivo studies were performed with two nontypeable H. influenzae strains, 86-028NP and HI1722. The majority of operons identified as members of the core modulon by microarray were also actively upregulated in the chinchilla ear during otitis media. In 86-028NP, 70% of the operons were significantly upregulated while in HI1722 100% of the operons were upregulated in samples recovered from the chinchilla middle ear. Conclusion This study elucidates a conserved core of H. influenzae genes the transcription of which is altered by the availability of iron and heme in the growth environment, and further assesses transcription of these genes in vivo. Elucidation of this modulon allows for identification of genes with unrecognized roles in iron/heme acquisition or homeostasis and/or potential roles in virulence. Defining these core genes is also of potential importance in identifying targets for therapeutic and vaccine designs since products of these genes are likely to be preferentially expressed during growth in iron/heme restricted sites of the human body.
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Affiliation(s)
- Paul W Whitby
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City 73104, OK, USA.
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Morton DJ, Turman EJ, Hensley PD, VanWagoner TM, Seale TW, Whitby PW, Stull TL. Identification of a siderophore utilization locus in nontypeable Haemophilus influenzae. BMC Microbiol 2010; 10:113. [PMID: 20398325 PMCID: PMC2859871 DOI: 10.1186/1471-2180-10-113] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 04/15/2010] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Haemophilus influenzae has an absolute aerobic growth requirement for either heme, or iron in the presence of protoporphyrin IX. Both iron and heme in the mammalian host are strictly limited in their availability to invading microorganisms. Many bacterial species overcome iron limitation in their environment by the synthesis and secretion of small iron binding molecules termed siderophores, which bind iron and deliver it into the bacterial cell via specific siderophore receptor proteins on the bacterial cell surface. There are currently no reports of siderophore production or utilization by H. influenzae. RESULTS Comparative genomics revealed a putative four gene operon in the recently sequenced nontypeable H. influenzae strain R2846 that encodes predicted proteins exhibiting significant identity at the amino acid level to proteins involved in the utilization of the siderophore ferrichrome in other bacterial species. No siderophore biosynthesis genes were identified in the R2846 genome. Both comparative genomics and a PCR based analysis identified several additional H. influenzae strains possessing this operon. In growth curve assays strains containing the genes were able to utilize ferrichrome as an iron source. H. influenzae strains lacking the operon were unable to obtain iron from ferrichrome. An insertional mutation in one gene of the operon abrogated the ability of strains to utilize ferrichrome. In addition transcription of genes in the identified operon were repressible by high iron/heme levels in the growth media. CONCLUSIONS We have identified an iron/heme-repressible siderophore utilization locus present in several nontypeable H. influenzae strains. The same strains do not possess genes encoding proteins associated with siderophore synthesis. The siderophore utilization locus may enable the utilization of siderophores produced by other microorganisms in the polymicrobial environmental niche of the human nasopharynx colonized by H. influenzae. This is the first report of siderophore utilization by H. influenzae.
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Affiliation(s)
- Daniel J Morton
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Elizabeth J Turman
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Patrick D Hensley
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Timothy M VanWagoner
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
- Department of Biology, Oklahoma Christian University, Oklahoma City, OK 73136, USA
| | - Thomas W Seale
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Paul W Whitby
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Terrence L Stull
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
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Whitby PW, Seale TW, Morton DJ, VanWagoner TM, Stull TL. Characterization of the Haemophilus influenzae tehB gene and its role in virulence. MICROBIOLOGY-SGM 2010; 156:1188-1200. [PMID: 20075041 DOI: 10.1099/mic.0.036400-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The Haemophilus influenzae ORF designated HI1275 in the Rd KW20 genomic sequence encodes a putative S-adenosyl methyltransferase with significant similarity to tellurite-resistance determinants (tehB) in other species. While the H. influenzae tehB can complement an Escherichia coli tehB mutation, thus restoring tellurite resistance, its role in H. influenzae is unknown. In a previous study defining the iron and haem modulon of H. influenzae, we showed that transcription of this gene in H. influenzae Rd KW20 increases during growth in iron- and haem-restricted media. Since iron and haem uptake genes, and other known virulence factors, constitute the majority of the iron- and haem-regulated gene set, we postulated that tehB may play a role in nutrient acquisition and/or the virulence of H. influenzae. A tehB mutant was constructed in the H. influenzae type b strain 10810 and was evaluated for growth defects in various supplemented media, as well as for its ability to cause infection in rat models of infection. Deletion of tehB leads to an increase in sensitivity both to tellurite and to the oxidizing agents cumene hydroperoxide, tert-butyl hydroperoxide and hydrogen peroxide. The tehB mutant additionally showed a significantly reduced ability to utilize free haem as well as several haem-containing moieties including haem-human serum albumin, haemoglobin and haemoglobin-haptoglobin. Examination of the regulation kinetics indicated that transcription of tehB was independent of both tellurite exposure and oxidative stress. Paired comparisons of the tehB mutant and the wild-type H. influenzae strain 10810 showed that tehB is required for wild-type levels of infection in rat models of H. influenzae invasive disease. To our knowledge this is the first report of a role for tehB in virulence in any bacterial species. These data demonstrate that H. influenzae tehB plays a role in both resistance to oxidative damage and haem uptake/utilization, protects H. influenzae from tellurite exposure, and is important for virulence of this organism in an animal model of invasive disease.
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Affiliation(s)
- Paul W Whitby
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Thomas W Seale
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Daniel J Morton
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Timothy M VanWagoner
- Department of Biology, Oklahoma Christian University, Oklahoma City, OK 73136, USA
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Terrence L Stull
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
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Morton DJ, Seale TW, Bakaletz LO, Jurcisek JA, Smith A, VanWagoner TM, Whitby PW, Stull TL. The heme-binding protein (HbpA) of Haemophilus influenzae as a virulence determinant. Int J Med Microbiol 2009; 299:479-88. [PMID: 19451029 PMCID: PMC2749905 DOI: 10.1016/j.ijmm.2009.03.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 03/09/2009] [Accepted: 03/27/2009] [Indexed: 01/29/2023] Open
Abstract
Haemophilus influenzae has an absolute growth requirement for heme and the heme-binding lipoprotein (HbpA) and has been implicated in the utilization of this essential nutrient. We constructed an insertional mutation of hbpA in a type b and a nontypeable H. influenzae strain. In the type b strain, the hbpA mutant was impaired in utilization of heme complexed to either hemopexin or to albumin and in the utilization of low levels of heme but not in the utilization of heme at high levels or of hemoglobin or hemoglobin-haptoglobin complexes. In contrast, the hbpA mutant derivative of the nontypeable strain was impaired in utilization of all tested heme sources. We further examined the impact of the hbpA mutation in animal models of H. influenzae disease. The hbpA mutant of the nontypeable strain was indistinguishable from the wild-type strain in the chinchilla model of otitis media. The hbpA mutant derivative of the type b strain caused bacteremia as well as the wild-type strain in 5-day old infant rats. However, in 30-day old rats the hbpA caused significantly lower rates of bacteremia than the wild-type strain indicating a role for hbpA and heme acquisition in virulence in this model of H. influenzae disease. In conclusion, HbpA is important for heme utilization by multiple H. influenzae strains and is a virulence determinant in a model of H. influenzae invasive disease.
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Affiliation(s)
- Daniel J Morton
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
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Whitby PW, Seale TW, VanWagoner TM, Morton DJ, Stull TL. The iron/heme regulated genes of Haemophilus influenzae: comparative transcriptional profiling as a tool to define the species core modulon. BMC Genomics 2009; 10:6. [PMID: 19128474 PMCID: PMC2627913 DOI: 10.1186/1471-2164-10-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 01/07/2009] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Haemophilus influenzae requires heme for aerobic growth and possesses multiple mechanisms to obtain this essential nutrient. Although an understanding of the heme acquisition mechanisms of H. influenzae is emerging, significant gaps in our knowledge remain. Unresolved issues include the identities of all genes exhibiting altered transcription in response to iron and heme availability, the fraction of such genes functioning in iron/heme acquisition, and the heterogeneity of this gene set among clinical isolates. Previously we utilized H. influenzae strain Rd KW20 to demonstrate the utility of transcriptional profiling in defining the genes exhibiting altered transcription in response to environmental iron and heme levels. The current study expands upon those observations by determining the iron/heme modulons of two clinical isolates, the type b isolate 10810 and the nontypeable isolate R2866. These data are used to begin to define the core iron/heme modulon of the species. RESULTS Microarray studies were performed to compare gene expression on transition from iron/heme-restricted to iron/heme-replete conditions for each isolate. Of 1820 ORFs on the array corresponding to R2866 genes, 363 were significantly differentially expressed: 233 were maximally transcribed under iron/heme-replete conditions and 130 under iron/heme-restricted conditions. Of the 1883 ORFs representing genes of strain 10810, 353 were significantly differentially transcribed: 150 were preferentially transcribed under iron/heme-replete conditions and 203 under iron/heme-restricted conditions. Comparison of the data sets indicated that 163 genes exhibited similar regulation in both isolates and that 74 of these exhibited similar patterns of regulation in Rd KW20. These comprise the putative core iron/heme modulon. CONCLUSION This study provides evidence for a conserved core of H. influenzae genes the transcription of which is altered by the availability of iron and/or heme in the growth environment. Elucidation of this modulon provides a means to identify genes with unrecognized roles in iron/heme acquisition or homeostasis, unanticipated responsiveness to environmental levels of the micronutrients or potential roles in virulence. Defining these core genes is also of potential importance in identifying targets for therapeutic and vaccine designs since products of these genes are likely to be preferentially expressed during growth in iron/heme restricted sites of the human body.
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Affiliation(s)
- Paul W Whitby
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Thomas W Seale
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Timothy M VanWagoner
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
- Department of Biology, Oklahoma Christian University, Oklahoma City, OK 73136, USA
| | - Daniel J Morton
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Terrence L Stull
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
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