Blalock-Taussig Shunt Blockage Caused by Small Colony Variants of Enterococcus faecalis.

Abstract

To the Editors: Small colony variants (SCVs) constitute a subpopulation of nutrient-demanding bacteria that grow slower than the wild type. Selection pressure exerted by environmental factors, such as antimicrobial agents.1,2 SCVs of Enterococcus sp. are less frequent. We report the first case of Blalock–Taussig shunt (BTS) blockage caused by SCVs of Enterococcus faecalis. A 1-year-old boy diagnosed with tetralogy of Fallot underwent left BTS surgery and closure of patent ductus arteriosus 10 months before presentation. On postoperative day 11, a catheter-related bloodstream infection (CRBSI) was caused by E. faecalis. The peripherally inserted central catheter was removed. Echocardiography revealed the absence of verrucae, and the modified Duke criteria were not definite. Ampicillin was administered for 2 weeks; 4 months postcompletion of this therapy, the left BTS was occluded, and a right BTS surgery was performed with the left BTS remaining in place. Although he underwent this surgery for endocardial repair, the left BTS was only removed during the operation, as pus was found in the occluded left BTS during the intraoperative manipulation. No bacteria were detected in the pus using Gram staining, but vancomycin was administered for suspected shunt infection. After 2 days of culture, colonies of approximately 0.2–1 mm and 2–3 mm diameters were observed on the blood agar medium maintained in an aerobic environment and the Brucella HK agar (Kyokuto, Inc. Tokyo, Japan) medium maintained in an anaerobic environment, respectively (Fig. 1). Although biochemical analysis indicated Enterococcus spp., identification and drug sensitivity test performed using Micro Scan Walkaway 40 plus (Beckman Coulter, Inc. CA) indicated poor growth after 24 hours of incubation. Matrix-assisted laser desorption/ionization–time-of-flight analysis indicated the presence of E. faecalis; hence, the antimicrobial was changed to ampicillin, which was administered for 4 weeks to control the mediastinitis. He was discharged without sequelae and had no recurrence of bacteremia for over a year.FIGURE 1.: Bacterial colonies cultured using blood agar and Brucella HK agar media.SCVs originated due to stresses, such as perioperative exposure to antimicrobials used to treat E. faecalis bacteremia. In addition, the short duration of antimicrobial therapy used to treat CRBSI may be another reason. Enterococcus spp. bacteremia is considerably associated with the occurrence of infectious endocarditis (IE) caused by a prosthetic valve; hence, echocardiography is recommended.3 In this case, antimicrobials were administered for 2 weeks. However, 4–6 weeks of antimicrobial therapy may be appropriate for treating IE. SCVs, with a typical phenotype of low virulence and long-term persistence, adapt to the intracellular environment more efficiently than the wild type. We have listed previously reported cases of SCVs of Enterococcus spp. (Table Supplemental Digital Content 1, https://links.lww.com/INF/E930,); half of which were IE, including two cases of IE related to prosthetic valves, which may be attributed to the fact that SCVs tend to form biofilms, leading to infection in prostheses.4 Moreover, Enterococcus spp. have higher probability of forming biofilms than other bacteria. E. faecalis is particularly more prone to biofilm formation than E. faecium.5 This case indicates that SCVs of E. faecalis may survive for a long period, especially in case of artifact infection.