Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species (Part 6) doc

Diphtheria and Other Infections Caused by Corynebacteria and Related Species Part 6 Microbiology and Laboratory Diagnosis These organisms are non-acid-fast, catalase-positive, aerobic

Chapter 131 Diphtheria and Other Infections Caused by

Corynebacteria and Related Species

(Part 6)

Microbiology and Laboratory Diagnosis

These organisms are non-acid-fast, catalase-positive, aerobic or facultatively anaerobic bacilli Their colonial morphologies vary widely; some species are small and α-hemolytic (similar to lactobacilli), whereas others form large white colonies (similar to yeasts) Many nondiphtherial coryneforms require special medium (e.g., Löffler's, Tinsdale's, or telluride medium) for growth

Epidemiology

Humans are the natural reservoirs for several nondiphtherial coryneforms,

including C xerosis, C pseudodiphtheriticum, C striatum, C minutissimum, C

jeikeium, C urealyticum, and A haemolyticum Animal reservoirs are responsible

for carriage of A pyogenes, C ulcerans, and C pseudotuberculosis Soil is the natural reservoir for R equi

C pseudodiphtheriticum is part of the normal flora of the human pharynx

and skin C xerosis is found on the skin, nasopharynx, and conjunctiva; C auris

in the external auditory canal; and C striatum in the anterior nares and on the skin

C jeikeium and C urealyticum are found in the axilla, groin, and perineum,

particularly in hospitalized patients C ulcerans and C pseudotuberculosis

infections have been associated with the consumption of raw milk from infected cattle

Specific Nondiphtherial Coryneforms

C ulcerans

This organism causes a diphtheria like illness and produces both diphtheria

toxin and a dermonecrotic toxin C ulcerans is a commensal in horses and cattle

and has been isolated from cow's milk The organism causes exudative pharyngitis, primarily during summer months, in rural areas, and among

individuals exposed to cattle In contrast to diphtheria, C ulcerans infection is

considered a zoonosis, and person-to-person transmission has not been firmly established Nevertheless, treatment with antitoxin and antibiotics should be

initiated when respiratory C ulcerans is identified, and a contact investigation

(including throat cultures to determine the need for antimicrobial prophylaxis and vaccination with the appropriate diphtheria toxoid–containing vaccine for unimmunized human contacts) should be conducted The organism grows on

Löffler's, Tinsdale's, and telluride media as well as blood agar In addition to

exudative pharyngitis, cutaneous disease due to C ulcerans has been reported

C ulcerans is susceptible to a wide panel of antibiotics Erythromycin and

macrolides appear to be the first-line agents

C pseudotuberculosis (ovis)

Infections caused by C pseudotuberculosis are rare and are reported almost

exclusively from Australia C pseudotuberculosis causes suppurative

granulomatous lymphadenitis and an eosinophilic pneumonia syndrome among individuals who handle horses, cattle, goats, and deer or who drink unpasteurized milk The organism is an important veterinary pathogen, causing suppurative lymphadenitis, abscesses, and pneumonia, but is rarely a human pathogen Successful treatment with erythromycin or tetracycline has been reported, with surgery also performed when indicated

C jeikeium (Group JK)

After a 1976 survey of diseases caused by nondiphtherial corynebacteria, CDC Group JK was recognized as an important opportunistic pathogen among neutropenic patients and later emerged in HIV-infected patients as an AIDS-associated opportunistic infection This led to the organism's reclassification as a

separate species, C jeikeium The predominant syndrome associated with C

jeikeium is sepsis, which can occur in conjunction with pneumonia, endocarditis,

meningitis, osteomyelitis, or epidural abscess Risk factors for C jeikeium

infection include hematologic malignancy, neutropenia from comorbid conditions, prolonged hospitalization, exposure to multiple antibiotics, and skin disruption

There is evidence that C jeikeium is part of the normal flora of the inguinal,

axillary, genital, and perirectal areas in hospitalized patients

Broad-spectrum antimicrobial therapy appears to select for colonization

Originally described in the United States, C jeikeium has also been reported in

Europe The gram-positive coccobacilli, which slightly resemble streptococci,

grow as small, gray to white, glistening, nonhemolytic colonies on blood agar C

jeikeium lacks urease and nitrate reductase and does not ferment most

carbohydrates It is resistant to most antibiotics tested except for vancomycin Effective therapy involves removal of the source of infection, be it a catheter, a

prosthetic joint, or a prosthetic valve There have been efforts to prevent C

jeikeium infection by use of antibacterial soap in the care of high risk patients in

intensive care settings

C urealyticum (Group D2)

Identified as a urease-positive nondiphtherial Corynebacterium in 1972, C

urealyticum is an opportunistic cause of sepsis and urinary tract infection This

organism appears to be the etiologic agent of a severe urinary tract syndrome

known as alkaline-encrusted cystitis: a chronic inflammatory bladder infection

associated with deposition of ammonium magnesium phosphate on the surface and

walls of ulcerating lesions in the bladder In addition, C urealyticum has been

associated with pneumonia, peritonitis, endocarditis, osteomyelitis, and wound

infection It is similar to C jeikeium in its resistance to most antibiotics except

vancomycin, which has been used successfully in the treatment of severe infections

C minutissimum

Erythrasma is a cutaneous infection producing reddish-brown, macular,

scaly, pruritic intertriginous patches The dermatologic presentation under the

Wood's lamp is of coral-red fluorescence C minutissimum appears to be a

common cause of erythrasma, although there is evidence for a polymicrobial etiology in certain settings In addition, this fluorescent microbe has been associated with bacteremia in patients with hematologic malignancy Erythrasma responds to topical erythromycin, clarithromycin, clindamycin, or fusidic acid, although more severe infections may require oral macrolide therapy