Beneath the surface: a case report on nonencapsulated Streptococcus pneumoniae-associated invasive disease in an immunocompromised patient

Abstract

Background: Streptococcus pneumoniae, a prominent human pathogen linked to various systemic diseases, includes non-typeable pneumococci marked by the absence of a detectable capsule. However, the majority of invasive infections are attributed to encapsulated strains. This case report details the first documented instance of invasive disease caused by non-typeable S. pneumoniae in Argentina since 2017.

Case presentation: A 19-year-old woman presented with haemorrhagic injuries attributed to chronic oral mucosa irritation. Subsequent hospitalization revealed bone marrow aplasia, leading to antibiotic, antifungal, antiviral, and immunosuppressive treatments, culminating in her discharge. Two weeks later, she was readmitted with sepsis related to a respiratory focus, exhibiting a negative COVID-PCR test. After ten days, ICU admission revealed additional infections: positive COVID-PCR test, fungal sinusitis, and S. pneumoniae bacteremia. Targeted treatments led to improvement, and the patient was subsequently discharged.

S pneumoniae characterization: Verification of the capsule's absence utilized traditional methods such as the Quellung reaction, transmission electron microscopy, molecular assays, and Whole Genome Sequencing (WGS). The isolate, identified as ST18335, displayed genetic features and antibiotic resistance patterns, concordant between WGS and the agar dilution method. It demonstrated non-susceptibility to penicillin and cefotaxime, based on meningitis breakpoints, as well as meropenem and cotrimoxazole.

Conclusion: This case underscores the clinical significance of non-typeable S. pneumoniae, emphasizing the necessity for a comprehensive approach to identification and characterization. The findings contribute to ongoing discussions regarding the challenges posed by non-typeable strains in vaccine development, understanding clinical impacts, and addressing antibiotic resistance. As the pneumococcal epidemiological landscape evolves, this case serves as a valuable addition to the evolving knowledge surrounding non-typeable S. pneumoniae, highlighting the continued need for surveillance and research in infectious diseases.

Keywords: WGS; invasive pneumococcal disease; nonencapsulated Streptococcus pneumoniae; transmission electron microscopy.

Fig. 1.

(a) The Computerized Axial Tomography (CAT) scan exhibited a consolidation in the right maxillary sinus and notable thickening of the mucosa in both the left maxillary and sphenoid sinuses. (b) Microscopic examination of Bipolaris spp. microculture (lactophenol blue stain, 400×) and microculture on sabouraud agar.

Fig. 2.

(a) Quellung’s reaction: isolate 25 041, classified as NT-Spn, exhibited no reactivity in any of the anti-serum tests. In contrast, isolate 26 378, identified as S. pneumoniae serotype 3 (positive control), yielded a positive reaction with the specific anti-serum. (b) Gel electrophoresis of S. pneumoniae-specific PCR products targeting the 295 bp lytA gene. Lane 1: negative control; lane 2: isolate 25041 NT-Spn; lane 3: isolate 26 378 S. pneumoniae serotype 3. And 160 bp cpsA gene Lane 1: negative control; lane 2: isolate 25041 NT-Spn; lane 3: isolate 26 378 S. pneumoniae serotype 3. (c) Negative stain (phosphotungstic acid). On the left the Isolate 25041 NT-Spn demonstrates loss of the capsule compared with the image on the right, isolate 26 378 S. pneumoniae serotype 3, with the polysaccharide capsule surrounding the cell of the pneumococcal isolate.