Corynebacterium pseudodiphtheriticum: an easily missed respiratory pathogen in HIV-infected patients

Exudative pharyngitis and Corynebacterium pseudodiphtheriticum: A case report and review of the literature

Corynebacterium pseudodiphtheriticum is an established member of the normal flora of the respiratory tract. This organism is an emerging cause of respiratory tract infection, as well as infection of the skin and skin structures, urinary tract and other sterile sites. The syndrome of C. pseudodiphtheriticum exudative pharyngitis is a diagnostic challenge of particular relevance in recent times as this organism can be confused with Corynebacterium diphtheriae in the clinical setting and in the laboratory. We report a case of exudative pharyngitis, possibly due to C. pseudodiphtheriticum, in a 14-month old, incompletely vaccinated, human immunodeficiency virus (HIV)-positive infant and review the role of this organism in terms of its microbiological profile and identification, disease spectrum and antimicrobial susceptibility pattern.

Infection and colonization by Corynebacterium pseudodiphtheriticum: a 9-year observational study in a university central hospital

Despite constituting part of the human commensal flora, Corynebacterium pseudodiphtheriticum has been recognized as a potentially infectious agent, most frequently in immunocompromised patients or individuals with other morbidity factors, but significant association to comorbid states remains unproven. This study's purpose was to assess clinical significance, risk factors for infection and antimicrobial susceptibility of C. pseudodiphtheriticum isolates. A retrospective observational study was conducted. Relevance of isolation was determined by clinical, laboratory, and imaging criteria. Forty-nine isolates occurred in 47 episodes. Colonization was assumed in 12% and infection in 78%, of which 51% were nosocomial. Patients with infection were older, with male predominance; both age and gender were statistically significant (p < 0.05) between infection and colonization groups. Although dyslipidemia (58%), arterial hypertension (58%), invasive procedures (56%), and chronic lung disease (50%) were prevalent in the infection group, no comorbidity was a significant risk factor for infection compared with colonization. Charlson comorbidity index showed no statistically difference between groups. Mortality rate was 14% in infection. Respiratory samples were the main isolation product; all tested strains were susceptible to amoxicillin/clavulanate and vancomycin. Resistant strains were observed for clindamycin (77%) and erythromycin (48%). C. pseudodiphtheriticum isolation was associated with infection in most cases. Despite the high prevalence of comorbidities and invasive procedures, no factors other than age and gender were significantly associated with infection. Although C. pseudodiphtheriticum may constitute a contaminant or colonizer in clinical samples, positive cultures in patients with signs and symptoms consistent with infection should not be neglected.

Corynebacteria as a cause of pulmonary infection: a case series and literature review

Background

In most cases of community-acquired pneumonia (CAP), an etiologic agent is not determined; the most common report from the microbiological evaluation of sputum cites “normal respiratory flora.” Non-diphtheria Corynebacterium spp., a component of this flora, is commonly viewed as a contaminant, but it may be the cause of pneumonia and the frequency with which it causes CAP may be underestimated.

Case presentations

This report present 3 cases of CAP in which Corynebacterium spp. was clearly the predominant isolate; identification was confirmed by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry. Two cases were caused by C. propinquum and one by C. striatum. Two patients had a tracheostomy and one was on hemodialysis. Patients who received an appropriate antibiotic responded well.

Conclusion

When identified as the predominant isolate in sputum from a patient with CAP, Corynebacterium spp. should be considered as a potential cause of the infection. In cases with patients who have compromised airway clearance or who are immunocompromised, microaspiration may be responsible. While some Corynebacterium spp. are suspectible to antibiotics usually prescribed for CAP, others are susceptible only to vancomycin or aminoglycosides. Vancomycin is thus the appropriate empiric antibiotic, pending speciation and susceptibility test results. The number of reported cases with result of antibiotic susceptibility testing, however, remains limited, and further investigation is needed. Non-diphtheria Corynebacterium spp. represent a noteworthy clinical cause of pneumonia. Identification by Gram stain and as a predominant organism on culture demands careful consideration for management.

Clinical relevance of Corynebacterium pseudodiphtheriticum in lower respiratory tract specimens

BACKGROUND

Corynebacterium pseudodiphtheriticum may be present as commensal flora of the respiratory tract and therefore it may be difficult to assess clinical relevance when it is cultured from lower respiratory tract specimens. Our objective was to determine the clinical relevance of C. pseudodiphtheriticum as a lower respiratory tract pathogen and to define patients at risk of developing lower respiratory tract infections caused by C. pseudodiphtheriticum.

METHODS

We retrospectively identified all lower respiratory tract cultures positive for C. pseudodiphtheriticum over a 10-year period and assessed clinical relevance by predefined criteria.

RESULTS

Clinical relevance was likely or possible in 86% of patients. Pre-existent comorbidity was present in 86% of patients, mostly underlying cardiac or pulmonary disease. All isolates were susceptible to amoxicillin.

CONCLUSION

C. pseudodiphtheriticum should be considered a clinically relevant pathogen when cultured from the lower respiratory tract in symptomatic patients.

Recognition of Corynebacterium pseudodiphtheriticum by Toll-like receptors and up-regulation of antimicrobial peptides in human corneal epithelial cells

Bacterial keratitis is a major cause of corneal ulcers in developing and industrialized nations. In this study, we examined the host innate immune responses to Corynebacterium pseudodiphtheriticum, often overlooked as commensal, in human corneal epithelial cells. The expressions of innate immune mediators were determined by quantitative PCR from corneal ulcers of patients and immortalized human corneal epithelial cells (HCEC). We have found an elevated expression of Toll like receptors (TLRs) along with IL-6 and IL-1β from both ulcers and epithelial cells infected with C. pseudodiphtheriticum. Activation of NF-κB and MAPK signaling pathways were also observed in HCEC in response to C. pseudodiphtheriticum. In addition, we found a significant increase in the expression of antimicrobial peptides S100A8, S100A9 and human β-defensin 1 from both corneal ulcers and HCEC.

Nasal microenvironments and interspecific interactions influence nasal microbiota complexity and S. aureus carriage

The indigenous microbiota of the nasal cavity plays important roles in human health and disease. Patterns of spatial variation in microbiota composition may help explain Staphylococcus aureus colonization and reveal interspecies and species-host interactions. To assess the biogeography of the nasal microbiota, we sampled healthy subjects, representing both S. aureus carriers and noncarriers at three nasal sites (anterior naris, middle meatus, and sphenoethmoidal recess). Phylogenetic compositional and sparse linear discriminant analyses revealed communities that differed according to site epithelium type and S. aureus culture-based carriage status. Corynebacterium accolens and C. pseudodiphtheriticum were identified as the most important microbial community determinants of S. aureus carriage, and competitive interactions were only evident at sites with ciliated pseudostratified columnar epithelium. In vitro cocultivation experiments provided supporting evidence of interactions among these species. These results highlight spatial variation in nasal microbial communities and differences in community composition between S. aureus carriers and noncarriers.

Non-diphtheriae Corynebacterium species: an emerging respiratory pathogen

The purpose of the study was to describe the microbiological and clinical features of ten cases of lower respiratory tract infection due to Corynebacterium striatum, Corynebacterium propinquum and Corynebacterium pseudodiphtheriticum. Respiratory samples were recovered from hospitalised patients who were diagnosed of pneumonia and exacerbations of chronic respiratory infections. The samples were Gram-stained and seeded on conventional bacterial growing media. Bacteria were identified by matrix-assisted linear desorption/ionisation-time-of-flight mass spectrometry (MALDI-TOF MS). Antibiotic susceptibility was tested by the disk diffusion method. All patients presented an acute respiratory onset, most of them in the context of an underlying disease and/or immunosuppression. In all patients, the microscopical examination of Gram-stained respiratory samples showed numerous polymorphonuclear cells and Gram-positive bacilli, suggestive of the Corynebacterium morphotype. A pure culture growth of Corynebacterium was obtained in the majority (72 %) of samples. The conclusions are that non-diphtheriae Corynebacterium species are an emerging cause of respiratory infection among patients with chronic respiratory disease and/or immunosuppression, and cannot always be considered as mere colonisers. The microorganism's predominance in Gram-stained purulent respiratory samples together with abundant growth in the culture is the key for the microbiological diagnosis.

Microbiological investigation and clinical significance of Corynebacterium spp. in respiratory specimens

The purpose of this retrospective study was to evaluate the pathogenic role of Corynebacterium species in lower respiratory tract infections as well as their routine laboratory investigation. From April 2007 to August 2009, 27 clinical isolates were significantly recovered from respiratory specimens of 27 different patients clinically suspected of having lower respiratory tract infections. The average age of patients was 65 years, while 22 (81%) patients presented at least 1 predisposing condition. Of the 27 patients, 15 (56%) were classified as infected according to Centers for Disease Control and Prevention/National Healthcare Safety Network criteria, with 93% of infections being hospital acquired. All isolates were accurately identified to the species level using molecular methods (i.e., 17 Corynebacterium pseudodiphtheriticum, 7 Corynebacterium striatum, and 3 Corynebacterium accolens), whereas phenotypic methods remained frequently unreliable for identifying C. striatum and C. accolens strains. All tested isolates were susceptible to amoxicillin, imipenem, vancomycin, linezolid, and tigecycline, whereas most of them were resistant to erythromycin.

Outbreak of Corynebacterium pseudodiphtheriticum infection in cystic fibrosis patients, France

An increasing body of evidence indicates that nondiphtheria corynebacteria may be responsible for respiratory tract infections. We report an outbreak of Corynebacterium pseudodiphtheriticum infection in children with cystic fibrosis (CF). To identify 18 C. pseudodiphtheriticum strains isolated from 13 French children with CF, we used molecular methods (partial rpoB gene sequencing) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Clinical symptoms were exhibited by 10 children (76.9%), including cough, rhinitis, and lung exacerbations. The results of MALDI-TOF identification matched perfectly with those obtained from molecular identification. Retrospective analysis of sputum specimens by using specific real-time PCR showed that approximately 20% of children with CF were colonized with these bacteria, whereas children who did not have CF had negative test results. Our study reemphasizes the conclusion that correctly identifying bacteria at the species level facilitates detection of an outbreak of new or emerging infections in humans.

[Two cases of Corynebacterium pseudodiphtheriticum respiratory tract infection]

Corynebacterium pseudodiphtheriticum, one cause of respiratory tract infection, is rarely considered as a pathogen because it is among normal bacterial flora colonizing the oral cavity. We report two cases of C. pseudodiphtheriticum causing respiratory tract infection--an exacerbation of chronic obstructive pulmonary disease and pneumonia--, both in the presence of underlying respiratory disease. Both required antibiotics after first-line chemotherapy failed. Isolates were susceptible to beta-lactams. Gram-staining of respiratory tract specimens is important in diagnosing this infection and determining appropriate antimicrobial use.

Cutaneous infection caused by Corynebacterium pseudodiphtheriticum: a microbiological report

We report here a rare case of cutaneous infection due to Corynebacterium pseudodiphtheriticum. The patient presented to the clinical laboratory with a skin ulcer on his left leg. Gram-stained preparation of the purulent secretion revealed the presence of numerous rod-shaped Gram-positive organisms in the absence of any other species. The organism was grown in pure culture on sheep blood agar and was further identified as C. pseudodiphtheriticum using a commercial identification system (API-Coryne, BioMérieux, France). The infection was successfully treated with ciprofloxacin. This case emphasizes the importance of the clinical microbiology laboratory in correctly identifying Gram-positive organisms obtained in pure culture from skin ulcers.

Expression of a functional single-chain antibody via Corynebacterium pseudodiphtheriticum

Antibody-based therapeutics are effective against conditions ranging from acute infections to malignancy. They may prove crucial in combating bioterrorism and responding to drug-resistant and emerging pathogens. At present the cost of producing therapeutic monoclonal antibodies is between $1,000 to $6,000 per gram. The need to administer antibodies parenterally at frequent intervals further drives the cost of this treatment. Here we present an antibody delivery system, termed paratransgenesis, with the potential to overcome these limitations. The paratransgenic approach involves genetically transforming a commensal or symbiont bacterium to express foreign molecules that target pathogens. We describe transformation of Corynebacterium pseudodiptheriticum, a commensal bacterium found in the human respiratory tract, to express a murine single-chain antibody binding progesterone. The antibody was functional and bound specifically to progesterone in a concentration-dependent manner. This marker antibody system is the precursor to development of expression systems producing recombinant humanized single-chain antibodies. Studies are in progress evaluating fitness, transgene stablility, and pathogenecity of the genetically engineered C. pseudodiptheriticum. We anticipate developing a repertoire of expressed molecules targeting infectious agents and surface epitopes of pulmonary mass lesions. If expression systems for anti-pathogen molecules in C. pseudodiptheriticum and other respiratory commensal bacteria can be optimized, these bacteria have the potential for a range of therapeutic and prophylactic applications.

Corynebacterium afermentans Lung Abscess and Empyema in a Patient with Human Immunodeficiency Virus Infection

Necrotizing pleuropulmonary infection in a patient with acquired immunodeficiency syndrome developed due to Corynebacterium afermentans subspecies lipophilum. Long-term combination antibiotic therapy was successful in eradicating the infection without surgery.

Antimicrobial therapy of infections with aerobic Gram-positive rods

This review presents data on in vitro susceptibilities of aerobically growing Gram-positive rods and in vivo activities of antibiotics used against Gram-positive rods. While in some instances susceptibility and efficacy are predictable (e.g. penicillin vs. Listeria and microaerophilic coryneforms, or metronidazole vs. Gardnerella) susceptibility testing by dilution techniques seems necessary for many Gram-positive rods as long as they are deemed clinically relevant.