Streptomyces species: A friend or foe? the diagnostic dilemma of cutaneous and mucocutaneous infections

ABSTRACT

Mycetoma and various invasive forms of the disease are caused by etiological agents like Nocardia, Actinomycetes, and Streptomyces spp. Streptomyces spp. is notable for its production of antibiotics. However, it is also most commonly associated with actinomycetoma, especially Streptomyces somaliensis (S. somaliensis), Streptomyces griseus. (S. griseus), S. sudanensis, and S. viridis. We present a series of cases with varied clinical presentations ranging from cutaneous nodules to plunging ranula in which Streptomyces spp have been isolated in culture with further species-level identification using MALDI-TOF.

Introduction

The aerobic actinomycetes include the genera Nocardia, Actinomadura, and Streptomyces are widely known etiological agents responsible for various spectrum of manifestations including pulmonary, systemic, and cutaneous diseases that is mycetoma (swollen tumor-like subcutaneous lesions that yield granular pus through draining sinuses). Streptomyces species are filamentous Gram-positive bacteria that commonly inhabit the soil and are notable for producing antibiotics as secondary metabolites. These are present ubiquitously hence, when grown in a culture of samples collected from patients with chronic cutaneous and subcutaneous diseases are often misdiagnosed as environmental contaminants. It not only delays the diagnosis but also appropriate and timely treatment, thereby prolonging the morbidity. The spectrum of infection varies depending on the immune status of the individual. The most common infection caused by Streptomyces is actinomycetoma, an endemic disease associated with Streptomyces species, especially S. somaliensis, S. griseus, S. sudanensis, and S. viridis. In addition, Streptomyces is also rarely associated with invasive manifestations like bacteremia, brain abscesses, pulmonary infections, peritonitis, etc., especially with immunosuppression.[1] The primary care physicians are most likely the first to come across many such cases in their day-to-day practice. It is therefore of utmost need to not only to have adequate knowledge of the suspicion of this infection, appropriate methods of diagnosis, reporting as well as treatment. Herewith, presenting four cases in which Streptomyces species have been isolated.

Case 1

A 52-year-old diabetic female presented with discoloration and dryness of the nails with paronychia in one of the fingers [Figure 1a]. The initial KOH mount of the nail revealed thin filamentous structures [Figure 1b]. Growth of Streptomyces spp was observed in the culture on the Sabouraud Dextrose Agar (SDA) tube at 25°C as downy colonies later turned to chalky white almost after 15 days of aerobic incubation with no growth at 37°C [Figure 1c].

Figure 1.

(a) Case 1: Clinical presentation, (b) Direct KOH mount, (c) Culture on SDA

Case 2

A 43-year-old HIV-positive male presented with multiple cutaneous nodules on the upper limb, legs, and dorsal aspect of the feet and toes. The lesions were tender, and firm with few being ulcerated and no associated lymphadenopathy, with clinical suspicion of Sporotrichosis [Figure 2a]. Gram stain of the Skin biopsy showed abundant pus cells and epithelial cells along with the presence of Gram-positive bacilli [Figure 2b]. Growth of a white rough rugose colony with a greyish tinge was observed on SDA after 10 days of aerobic incubation at 25°C, which was identified as Streptomyces spp. with no growth at 37°C [Figure 2c]. Modified ZN stain revealed nonacid fast filamentous bacteria [Figure 2d].

Figure 2.

(a) Case 2: Clinical presentation, (b) Direct Gram stain showing pus cells and Gram-positive filamentous bacteria, (c) Culture on Blood Agar (BA), (d) Modified ZN Staining showing non-acid fast filamentous bacteria

Case 3

A 58-year-old male presented to the trauma and emergency department with complaints of difficulty in breathing. On examination, a plunging ranula was observed. The obstructive symptoms were because of a sudden increase in the size of the swelling in the last few months which had been present for almost 10 years. A biopsy of the swelling was sent for fungal culture. The gram stain showed the presence of gram-positive filamentous structures surrounded by epithelial cells [Figure 3a]. Dry translucent colonies with moist backgrounds were observed on SDA incubated at 37°C after 12 days with no growth at 25°C which was later identified as Streptomyces spp. [Figure 3b].

Figure 3.

(a) Case 3: Direct Gram stain showing gram-positive filamentous bacteria, (b) Culture on SDA

Case 4

A 68-year-old male presented to the Dermatology OPD with complaints of non-tender nodules over his lower back associated with bloody purulent discharge with grains for 1 month [Figure 4a]. The patient had similar history at the same site 4 years back for which he was treated with cotrimoxazole for 6 months. A wedge biopsy of the nodules was sent for histopathology and microbiology. In histopathology ulcerated epidermis with mixed inflammatory infiltrate collection like neutrophils, plasma cells, and histiocytes in the superficial and deep dermis was noted. Growth of a chalky white dry rough rugose colony with a greyish tinge was observed on SDA incubated at 37°C after 10 days without growth at 25°C which was later identified as Streptomyces spp. [Figure 4b].

Figure 4.

(a) Case 4: Clinical presentation, (b) Culture on BA

Materials and Methods

Samples were subjected to KOH mount initially along with the culture in Blood Agar, Lowenstein-Jensen Agar tube incubated at 37°C for 48 h and at least 4 weeks respectively, and SDA tubes, incubated at both 25°C and 37°C for at least 4 weeks. On Blood Agar and SDA colonies initially were observed to be slightly folded, and hard but later developed into a fine chalky, or powdery aerial mycelium. Further staining and Biochemical testing revealed these to be Gram-positive filamentous bacteria, nonacid fast on ZN staining with catalase production and urea hydrolysis. However, hydrolysis of Starch was inconclusive. All the Streptomyces species were identified by MALDI-TOF and the final identification was as follows:

CASE 1: Streptomyces albus

CASE 2: Streptomyces violaceoruber

CASE 3: Streptomyces thermoviolaceus

CASE 4: Streptomyces albus

Clinical and Laboratory Standards Institute (CLSI) M24 recommends testing of Cotrimoxazole which showed susceptibility in all the isolates.

Discussion

Streptomyces is a gram-positive filamentous bacteria belonging to the order Actinomycetales family Streptomycetaceae consisting of more than 500 species Its natural habitat is rhizospheric soil, marine and inland water, it occurs mainly as an environmental contaminant.[2] Streptomyces species are common etiological agents associated with actinomycetoma or mycetoma with a typical characteristic of tumefaction and draining sinuses that clinically presents as a chronic suppuration of the skin with involvement of the underlying bone and soft tissue. Disruption of mucosa facilitates the entry of the culprit environmental agents which is aggravated further by their collagenase activity to access deeper tissues.[1] The most common clinical presentation of streptomyces infection are the mycetomas with S. somaliensis being one of the principal etiologic agents of actinomycetoma in the United States, Mexico, South America, Africa, Malaysia and India.[3,4,5] Streptomyces species are rare causative agents of invasive infections like pneumonia, lung nodules, bacteremia, brain abscess, endocarditis of the prosthetic valve, arthritis, lymphadenitis, pericarditis and peritonitis, cervical lymphadenitis, intracranial mycetoma, keratitis, and otitis media.[4,5,6,7,8,9,10,11,12,13,14] The various Clinical manifestations are quoted in Table 1. The ubiquitous nature, as well as the low pathogenicity of Streptomyces spp results in most clinical isolates being labeled as contaminants or colonizers. However, in the study conducted by Gras E et al.,[15] it was observed that nearly fifty percent of the clinical samples that grew Streptomyces in culture were from patients with invasive infection. This result cannot be ignored thereby highlighting the importance of early and correct diagnosis. To determine the definitive diagnosis of Streptomyces spp as an etiological agent responsible for human infection, the requirement of either of the conditions is essential that is the presence of clinical manifestation, direct microscopic observation in infected tissue, single organism isolated from sterile sites or post exclusion of any other possible causes. In Case 1, repeated isolation from the same site, and direct demonstration from the sample makes it a definitive pathogen while in Case 2 and 3: Streptomyces spp. is the only organism isolated and the sample being a biopsy specimen is presumed to be sterile, thereby ruling out contamination. In the last case repeated isolation from the same site as well as the sample being tissue biopsy establishes Streptomyces spp as the definitive etiological agent of Actinomycetoma.

Table 1.

Streptomyces species identification in invasive infections with the clinical characteristics and epidemiological profile

Site of Infection	Age/Sex	Species	Method of identification	Co-morbidities	Outcome	Location, Year	Ref
Lung nodule	21/F	Streptomyces maritimus/Streptomyces olivaceus	Culture	Acute myeloid leukemia (AML)	Exitus of AML	Houston, USA, 2007	[6]
	23/F	Streptomyces albus	Culture	Systemic lupus erythematosus	Cure
Cutaneous lesions in cervical lesions	50/F	Streptomyces griseus	Culture	None	Cure	Chandigarh, India, 2012	[7]
Pneumonia	75/M	Streptomyces albireticuli	Culture + WGS	None	Cure	China, 2024	[8]
CVC related Bacteremia	51/F	Streptomyces humidus/Streptomyces pilosus	Culture	Metastatic breast cancer	Recovered after the removal of the CVC catheter	Houston, USA, 2007	[6]
	25/M	Streptomyces indigoferus/Streptomyces herbaricolor		Ewing sarcoma; neutropenia
	71/M	Streptomyces nobilis/Streptomyces parvulus		Metastatic cholangiocarcinoma
Bacteremia	80/F	Streptomyces thermovulgaris	Culture + 16S rRNA	Corticosteroid therapy	Exitus of bowel perforation	Utrecht, the Netherlands, 2004	[9]
Brain abscess	19/M	Streptomyces spp.	Culture	None	Cure	Atlanta, Georgia, USA, 2008	[10]
Cranial and epidural mycetoma	30/F	Streptomyces somaliensis	Immuno- diffusion & counter current immuno- diffusion tests	None	Sinus cleared but persistence of raised ICT	Riyadh, Saudi Arabia, 1987	[11]
Endocarditis	56/M	Streptomyces spp.	Culture	None	Cure	Riyadh, Saudi Arabia, 1995	[12]
Keratitis with corneal infiltrates	50/M	Streptomyces thermocarboxydus	Culture + 16S rRNA	None	Cure	Japan, 2013	[13]
Mastoid bone	62/F	Streptomyces cacaoi	Culture + 16S rRNA	Dyslipidemia	Cure	China, 2020	[14]

CVC=Central Venous Catheter, ICT=Intracranial Tension, WGS=Whole Genome Sequencing

Conclusion

Identification of Streptomyces species being the definitive causative agent of infection is challenging due to its low pathogenicity and ubiquitous nature. A stringent clinical and microbiological correlation is needed, such as clinical manifestations, repeated isolation of the organism from the sources, direct microscopic detection in infected tissue, and exclusion of any other possible cause.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.