Indian Journal of Medical Microbiology Medknow Publications on behalf of Indian Association of Medical Microbiology ISSN: 0255-0857 EISSN: 1998-3646 Vol. 29, Num. 1, 2011, pp. 65-68

Indian Journal of Medical Microbiology, Vol. 29, No. 1, January-March, 2011, pp. 65-68

Case Report

Bacteremia due to Rhodococcus equi in an immunocompetent infant

P Devi, S Malhotra, A Chadha

Department of Microbiology, GMC, Amritsar 143 001, India

Correspondence Address: A Chadha, Department of Microbiology, GMC, Amritsar 143 001, India, docaarti2001@gmail.com

Date of Submission: 14-Jun-2010
Date of Acceptance: 26-Dec-2010

Code Number: mb11016

PMID: 21304200

DOI: 10.4103/0255-0857.76529

Abstract

Keywords: Bacteremia, immunocompetent host, rhodococcus equi

Introduction

Since the advent of acquired immunodeficiency syndrome (AIDS) epidemic, Rhodococcus equi has been emerging as an opportunistic pathogen, especially in immunocompromised patients. ^[1]

Primarily it causes zoonotic infections and is a rare opportunistic human pathogen causing pneumonia and pulmonary abscesses in the patients with lymphoreticular malignancies and solid organ transplants. ^[2] Almost all human infections have occurred in patients who have defects in cell mediated immunity (CMI) with or without histories of animal exposure. There have been a few case reports of R. equi infection in immunocompetent host although the course and the manifestations of the disease may differ from that seen in immunocompromised patients. ^[3] On blood agar colonies resemble those of klebsiella because of mucoid character and pink color (on prolonged incubation salmon pink color appears, especially at room temperature). ^[4]

Case Report

A 26-day-old male child was admitted in the pediatric ward with the history of an indurated, tender, erythematous swelling with no discharging pus on the ring finger of the left hand for the last 10 days [Figure - 1]. Patient was put on empirical antibiotic therapy using cefpodoxime and amoxicillin-clavalanic acid combination, but within few days newer swelling appeared in the preauricular and supraclavicular area.

No history of fever, cough, vomiting, breathlessness, or feeding difficulty was observed. Child was born preterm at 36 weeks by normal vaginal delivery conducted by a midwife (dai) at home. Child cried immediately after birth. He developed physiological jaundice for which he was admitted to the hospital for 10 days. Parents of the child had rural background and gave history of keeping cattle and horses.

On examination, the swelling on the finger was tender, erythematous, and indurated with no discharge. Laboratory findings showed Hb 15.4 g/dl, white blood cell count 29,600/cmm at the time of admission which increased to 40,000/cmm with 93% neutrophils which showed toxic granulations. Platelets were adequate. Urine for sugar and albumin was negative. Human immunodeficiency virus (HIV) serology was negative. Both the parents were also negative for HIV serology.

Blood sample was collected for bacteriological culture. A pure culture of salmon pink-colored mucoid colonies appeared on 5% sheep blood agar after 24 h of aerobic incubation at 37 ºC [Figure - 2]. It was thought to be Klebsiella spp. because of mucoid colonies, but as the colonies were salmon pink in color, gram′s staining was performed which showed gram-positive bacilli with occasional coccoid form [Figure - 3].

It was identified as R. equi based on the colony characters on nutrient agar and 5% sheep blood agar with typical salmon pink color and nonmotile, biochemical reaction were catalase positive, nitrate reduction positive, galactose positive but negative for oxidase and urease. No acid fast bacilli were seen on Ziehl-Neelsen staining done from the growth obtained.

Antimicrobial sensitivity was put up and it was found to be sensitive to amikacin and resistant to ampicillin, cephalexin, erythromycin, gentamycin, clindamycin, and gatifloxacin. Patient was put on inj. amikacin and responded well to the treatment and was discharged after 1 week.

Discussion

R. equi was first isolated in 1928 from the lungs of foals in Sweden. It had been isolated from a variety of land and water animals such as cattle, crocodile, and even wild animals. The organism is present in soil all over the world except in Antarctica, in fresh and sea water and in the intestine of blood-sucking arthropods. ^[4]

The role of R. equi as a human pathogen was not established until 1967, when the first case report was published of a 29-year-old man with plasma cell hepatitis who developed a cavitary pulmonary lesion after cleaning animal pens at a stockyard. ^[5] Only 12 additional cases were reported by Lipsky et al. ^[6] However with the AIDS epidemic, this number has greatly increased. Since then hundreds of cases of human infection with R. equi have been reported. ^[4]

Necrotizing lobar pneumonia is the commonest form of infection caused by R. equi. Extrapulmonary infection may include wound infection, subcutaneous abscesses, brain abscess, meningitis, pericarditis, osteomyletis, cervical adenopathy, endopthalmitis, lymphangitis, and mastoiditis. ^[1]

There is a possibility that our patient could have acquired the organism from the contaminated soil by direct inoculation as it was a case of home delivery by a midwife (Dai) who do not take proper aseptic precautions while conducting delivery and cutting the umbilical cord.

Usually, no history is elicited in many cases. Delay in diagnosis often results because of insidious onset of disease, clinical similarity to mycobacterium and fungal infection and the indistinguishable morphology of R. equi from normal diphtheroids of respiratory flora. ^[7]

Infection in immunocompetent patients is extremely rare-only 19 cases in immunocompetent hosts have been reported. Localized infection represents nearly 50% of reported cases. Pulmonary infections account for only 42% of infections in immunocompetent hosts. The mortality rate among immunocompetent patients is approximately 11%, compared with rates of 50-55% among HIV-infected patients and 20-25% among non-HIV-infected immunocompromised patients. ^[3]

The organism has generally shown in vitro susceptibility to erythromycin, rifampicin, vancomycin, fluoroquinolones, aminoglycosides and imipenem/cilastatin and resistance to penicillins, although this can vary in specific geographic areas or from the previous antibiotic therapy. This organism inhibits macrophage phagosome-lysosome fusion and survives intracellularly. There is no consensus on the optimal duration and regimen of antibiotic treatment, combination antimicrobial therapy using bactericidal and intracellularly active agents should be considered. ^[8] A carbapenem and a glycopeptide, such as meropenem and vancomycin, are good choices. ^[9] The use of combination therapy may decrease the risk of developing resistance during therapy, which has been described with penicillin and other β-lactam antibiotics. The combination of macrolides and rifampicin can also be considered.^[10] After initial improvement, the patient can be treated with an oral regimen that could include combination of quinolones, tetracycline, macrolides, and rifampicin. The optimal duration of treatment is unknown.

Conclusions

R. equi which is a opportunistic pathogen in immunocompromised persons is also causing infections in immunocompetent patients. Although the organism is easily cultured from specimens, it is difficult to treat. Moreover it may be misdiagnosed as a contaminant usually diphtheroids. Increased awareness among clinicians and microbiologists would aid in timely diagnosis of this potentially curable infection which may otherwise prove to be fatal.

References

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