Corynebacterium striatum

Corynebacterium striatum is a prokaryotic bacterium that is a member of the Corynebacterium genus. It is classified as non-diphtheritic. The bacterium is a gram-positive prokaryote that assumes a 'club-like' morphology, more formally known as a corynebacteria structure. It is non-lipophilic and undergoes aerobic respiration and is also a facultative anaerobe it is catalase negative and oxidase positive glucose and sucrose fermenter. It is generally found as a ubiquitous microorganism, and, as a commensal of humans, colonising the nasopharynx. It has recently been recognised as an emerging pathogen although the genus of Corynebacterium is not usually considered to be pathogenic. Particularly in the context of human disease Corynebacterium striatum is generally considered an opportunistic pathogenic, particularly in a nosocomial setting. It has been recorded to infect the skin, upper and lower respiratory tract and even disseminate resulting in septicaemia. Recent interest has been sparked in the microorganism as it is known to be resistant to and gaining resistances to many antibiotics. Corynebacterium striatum is a member of the genus Corynebacterium. Initially the species was described in 1901. Scientific papers dating back until approximately 1980 recount cases of commensal Corynebacterium striatum contaminating samples from sites of infections. A paper published in 1993 found that isolates of described Corynebacterium Stratum stored by the American Type Culture Collection and the National Collection of Type Cultures were in fact not that of Corynebacterium striatum, although the recorded sequences corresponded with other known isolates of the species. From this it was determined that at the time of isolation for storage, the incorrect bacteria was stored. Up until 1993 there had only been three documented cases of respiratory infections caused by the species. After this it was formally defined again in 1995. Coryneform bacteria had for a long time been described as commensals of humans, colonising the skin and mucous membranes without causing disease. More recently Corynebacterium striatum was found to in fact be the cause of infection and disease, given the opportunity. Early clinical testing of hospital patients found that infection generally only occurred in immunocompromised individuals or those that had some for of prosthetic device permanently or intermittently fitted. Not long after, researchers began to propose the notion that Corynebacterium striatum was the cause of disease even in patient that did not meet such criteria. Standardised methods of identification have been developed to improve the identification and isolation of Coronyforms. One such method is the API Coryne V2.0 system. API strips combine a series of small scale biochemical tests to distinguish key characteristics of bacterium, based on metabolic activity. The results are interpreted via standardised indicators and charts. This is a cost effective yet time consuming method of identification, taking approximately 16 hours, particularly in clinical settings. More modern identification techniques include genome sequencing - particularly 16S Ribosomal RNA (rRNA) Sequencing. This technique relies on computerised comparison of genome sequences between bacterium. The 16S rRNA sequence is highly conserved between bacterium, although will show slight variations and mutations between strains. Comparison of variations in the Corynebacterium genome allow for specific identification of the Corynebacterium Striatum. It must be noted that currently this is currently a relatively expensive method of identification - when compared to the API strip, although this is improving as technologies improve. The MALDI-TOF system is a clinically relevant method of detection that provides a rapid, 10 minute specific identification of bacteria. Both biochemical and molecular identification is accompanied by physical characterisation. Culturing the bacteria on blood cultures and gram staining to confirm morphology are integral additions to the process of identification. Corynebacterium striatum is a gram-positive bacterium, meaning they have a thin external peptidoglycan cell wall structure. They have been described as having an irregular pleomorphic shape, and are non-motile. Under a microscope they appearing as a hybrid of a bacillus and cocci morphology with a bulged pole attached to rod like end, more commonly described as a 'club-like' structure. They are broadly described as being 1.5-8.0 micrometers in length, but formal measurement of individual clinical isolates will vary upon observation. C. striatum colonies are able to be plated in vitro; when growing on Blood Agar the colonies will appear as small (1-2mm diameter) with a white, moist, and smooth appearance. It is otherwise called a diphtheroid or coryneform due to its close phylogenetic relationship with diphtheria causing bacterium Corynebacterium diphtheriae. Corynebacterium striatum can be differentiated from other Corynebacterium types based on its ability to ferment glucose and sucrose, and inability to ferment maltose. In comparison to other members of the genus Corynebacterium, it ferments sugars rapidly. Corynebacterium species are also known to ferment nitrates. It is also able to hydrolyse Tyrosine and Pyrazinamide. It does not metabolize urease, can hydrolyze esculin, and can also ferment mannitol and xylose. In a laboratory setting, it is best distinguished from other coronyforms through its fermentative activity. They are non-lipophilic preferring to persist