The Brief Case: A case of bloodstream infection with Corynebacterium kroppenstedtii in an infant

CASE

A 4-month-old male presented to the emergency department for multiple febrile episodes over the course of the prior 5 weeks. He was born at 37 weeks and had many medical events since birth including multiple thrombotic events, central nervous system bleeds, pulmonary insufficiency and hemorrhage, and ileal atresia leading to resection and short gut. He was totally parenteral nutrition (TPN) dependent with a G tube. He had 5+ documented recurrent episodes of fever at the time of presentation with no etiology found. Respiratory viral panels performed during these episodes were negative with the exception of a single panel positive for rhinovirus/enterovirus. A previous hospitalization at an outside facility 4 weeks prior was associated with cellulitis surrounding the G tube site and was treated with unknown antibiotics. There had been no additional erythema or tenderness since then. The patient presented to an outside emergency department 1 week prior to the current admission for a home fever of 102°F and was discharged 2 days later with no antibiotics. Prior fevers were often resolved within a day and were accompanied by a rise in C-reactive protein and white blood cells.

Upon admission, blood (Becton Dickinson Plus Aerobic and Lytic Anaerobic) 73383 and urine cultures were obtained as well as a nasopharyngeal swab for respiratory virus testing. All tests had negative results. Two days after admission, a fungal blood culture (Becton Dickinson Myco/F Lytic) was obtained to rule out Malassezia furfur as the mother had noted there was drainage at the TPN site after each fever episode. Routine blood culture bottles were placed in the Bactec FX system. No antibiotic treatment was given during this admission, and the patient was discharged 4 days later.

Two days after receipt into the laboratory, the Myco/F blood culture bottle turned positive with Gram-positive bacilli observed on Gram stain (Fig. 1A). At this point, the finding was noted to most likely be a contaminant, although it was noted that Gram-positive bacilli can cause line infections.

Fig 1.

(A) Direct Gram stain of positive Myco/F lytic blood culture bottle demonstrating Gram-positive bacilli (100× magnification). (B) Culture growth of small colonies on chocolate agar after 48 hours of incubation. (C) Culture growth of small colonies on colistin-nalidixic agar (CNA) after 48 hours of incubation.

Colony growth was observed on both chocolate agar and CNA (Fig. 1B) with better growth on CNA, suggesting that the organism is lipophilic. This is also consistent with the fact that the organism only grew in the Myco/F blood culture bottle which is enriched with additional lipids compared with regular blood culture bottles. Colonies were very small and appeared after 48 hours of growth at 37°C temperature. The organism was identified as Corynebacterium kroppenstedtii by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (VITEK MS). Subsequent routine blood cultures (n = 2) were negative; however, additional fungal blood cultures collected the following day and following week grew C. kroppenstedtii. Because of this finding, it was determined that C. kroppenstedtii was likely colonizing the patient’s TPN site and the lines were replaced. The organism was sent to a referral laboratory for antimicrobial susceptibility testing with the susceptibility pattern shown in Table 1.

TABLE 1.

MICs of Corynebacterium kroppenstedtii isolated from blood culture

Antibiotic	MIC (mcg/mL)	Interpretation
Penicillin	1	Intermediate
Ceftriaxone	2	Intermediate
Meropenem	<0.25	Susceptible
Vancomycin	<1	Susceptible

The child received 14 days of vancomycin treatment and has had no recurrent episodes since.

DISCUSSION

Corynebacterium kroppenstedtii belongs to the genus Corynebacterium and was first isolated from a sputum sample from an elderly woman with pulmonary disease in 1998 (1). This strain is different from many other corynebacteria due to its lack of typical mycolic acids included in the cell envelope. It was originally cultured on horse blood agar at 37°C and identified by 16S gene sequence analysis. Colonies are non-pigmented, non-hemolytic, small, and smooth appearing. It is catalase positive and facultatively anaerobic. C. kroppenstedtii most closely resembles Corynebacterium amycolatum and Turicella otitidis in its lack of mycolic acids. It is a Gram-positive, non-acid fast, non-motile, non-spore-forming diphtheroid. In a Gram stain, the arrangement of Corynebacterium is frequently observed in V-shaped forms and palisades. The phylum Actinobacteria where this organism belongs is composed of Gram-positive bacteria that are distinguished with a high G + C content in their genomic DNA. Within the phylum, there is a large amount of diversity in terms of colony morphology, physiology, and metabolism.

Although it was first isolated from a sputum sample, C. kroppenstedtii has been most frequently associated with breast abscesses and granulomatous mastitis, an inflammatory breast disease generally affecting women of child bearing age, often a few years after giving birth (2). In a 2016 review, there were 42 published cases of clinical infections worldwide with documented C. kroppenstedtii, 41 of which were isolated from female patients. Thirty-seven of the isolates were isolated from breast isolates, although there was also a lung biopsy, blood culture, and a prosthetic heart valve as well (3). To our knowledge, this is the first case of C. kroppenstedtii recovered in an infant. We wondered if the mother had any history of mastitis and whether she was breastfeeding the child. It was noted that the child was not breastfeeding due to a complicated medical history and was receiving TPN.

C. kroppenstedtii is considered lipophilic as noted by the observation that colonies grew poorly on sheep blood agar and grew better on the same medium supplemented with 1% Tween 80 (4). This would also explain why in this case, it did not grow in routine blood culture bottles but instead grew in the Myco/F blood bottle, which is a 7H9 Middlebrook Broth Base with additional lipids including 0.10% glycerol and 0.0025% Tween 80 present to support the growth of mycobacteria, yeast, and fungi for recovery (5). It has been suggested that this lipophilic characteristic is supported by the loss of a fatty acid synthase gene which is also observed in other Corynebacterium relatives as well as Corynebacterium jeikeium, Corynebacterium urealyticum, Corynebacterium bovis, and Corynebacterium resistens (6).(7)

While traditional biochemical approaches such as the API Coryne had difficulty resolving C. kroppenstedtii from other species (Add PMID 12409436), C. kroppenstedtii can be readily identified in the clinical laboratory through the use of MALDI-TOF MS. C. kroppenstedtii is in the FDA-cleared database of the Bruker Biotyper and is present but not claimed by the FDA in the VITEK MS knowledgebase v 3.2. 16S rRNA sequencing has also been used to successfully identify C. kroppenstedtii. A direct PCR technique using a broad range of 16S rRNA primers and sequencing was used to identify C. kroppenstedtii in a case of prosthetic valve endocarditis in a middle-aged male patient (8). Since many clinical labs may not work up and report corynebacteria to the species level from a fungal blood culture, it is important to consider patient risk factors and recurrence of the issue when considering whether the organism warrants further identification. As C. kroppenstedtii is a relatively uncommon pathogen, it is important to consider identifying and reporting it to the species level in certain specimen types, like a breast abscess, if it is grown in culture.

The most common antibiotic treatments used for C. kroppenstedtii infections are doxycycline, amoxicillin, ciprofloxacin, and cefuroxime. However, antibiotics are not always prescribed for the treatment of granulomatous mastitis as there is insufficient data to the support dosage and duration of treatment for this specific bacterium in this clinical setting. Granulomatous mastitis is instead often treated with steroids (9). Information on antimicrobial susceptibility of C. kroppenstedtii is limited to case series and case reports. Antimicrobial susceptibility testing should be considered in patients with risk factors limiting their potential antibiotic treatments and if they have previously been on prolonged antibiotic treatment. Resistance has not been described for vancomycin or linezolid, but resistance has been reported for many other commonly used antimicrobials (10, 11). Resistance is thought to be driven by acquisition of a plasmid containing common antimicrobial resistance genes such as erm (X), tet (W), aphA1-IAB, and sul1 as well as mutations of target genes such as gyrA. Further study is needed to determine if C. kroppenstedtii is prone to developing high-level daptomycin resistance as seen in other corynebacteria (12).

SELF-ASSESSMENT QUESTIONS

1. What characteristic of Corynebacterium kroppenstedtii makes it hard to recover in routine blood cultures?

   1. Gram positive

   2. High G + C content in genomic DNA

   3. Lipophilic

   4. Mycolic acids in cell envelope

2. What is the most common type of infection associated with Corynebacterium kroppenstedtii?

   1. Pulmonary disease

   2. Breast abscesses

   3. Bloodstream infection

   4. Endocarditis

3. Which antibiotic is Corynebacterium kroppenstedtii is predictably susceptible to?

   1. Ciprofloxacin

   2. Clindamycin

   3. Linezolid

   4. Trimethoprim-Sulfamethoxazole

ANSWERS TO SELF-ASSESSMENT QUESTIONS

1. What characteristic of Corynebacterium kroppenstedtii makes it hard to recover in routine blood cultures?

   1. Gram positive

   2. High G + C content in genomic DNA

   3. Lipophilic

   4. Mycolic acids in cell envelope

Answer: c. While C. kroppenstedtii is Gram positive and has a high G + C content in genomic DNA, it lacks mycolic acids in its cell envelope which is why it requires additional lipids to grow, making it hard to recover in routine blood culture bottles.

1. What is the most common type of infection associated with Corynebacterium kroppenstedtii?

   1. Pulmonary disease

   2. Breast abscesses

   3. Bloodstream infection

   4. Endocarditis

Answer: b. C. kroppenstedtii has been known to cause all of the infections listed, but it most commonly is associated with breast abscesses.

1. Which antibiotic is Corynebacterium kroppenstedtii is predictably susceptible to?

   1. Ciprofloxacin

   2. Clindamycin

   3. Linezolid

   4. Trimethoprim-Sulfamethoxazole

Answer: c. Resistance has been reported to all of the above agents except linezolid. In larger case series, only about 50% of isolates is susceptible to trimethoprim-sulfamethoxazole, 70% to ciprofloxacin, and 90% to clindamycin.

TAKE-HOME POINTS.

• Corynebacterium kroppenstedtii is a Gram-positive bacteria that lacks typical mycolic acids in its cell envelope, meaning it requires additional lipids to grow in vitro.

• Corynebacterium kroppenstedtii is most commonly associated with breast abscess infections.

• Corynebacterium kroppenstedtii may be under-recovered in blood cultures due to a lack of lipids in the growth medium.