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Case Thirty-Three: An Unexpected Cause of a Bloodstream Infection.

EDITOR'S NOTE: BEFORE reading the Case Follow-up and Discussion below, study the Case Description on page 8 of this issue, and formulate your own answers to the questions posed.

Case Discussion

MALDI-ToF MS (Vitek MS, bioMerieux, Leone, France) identified the organism as Paenibacillus glucanolyticus with 99 percent confidence, but the identification was part of the unclaimed database. Sequencing of the 16S ribosomal RNA gene confirmed the isolate identification as Paenibacillus glucanolyticus, with 99.57 percent sequence homology to a reference sequence.

Once Paenibacillus was identified, the patient's central line was removed, and antimicrobial therapy was adjusted based on the isolate's susceptibility (Table 2).

Antimicrobial susceptibility testing was performed using the E-test method (bioMerieux, Leone, France) with blood Mueller Hinton agar at 35[degrees]C for 24 hours (Figure 2).


Until 1993, Paenibacillus spp. were classified under group 3 of the Bacillus family with closest relation to Bacillus subtilis due to similarities in structure and function of flagellar genes. Recently, variation found in 16S rRNA sequences resulted in the reclassification of this group into a new family, Paenibacillaceae. Paenibacillus, which means "almost Bacillus" in Latin, were found to exhibit large differences in G+C content, displaying between 39 to 59 mol%. All organisms grouped under this classification share at least 89% homogeneity in rRNA composition, as well as similarities in flagellar arrangement and pigmentation on nutrient agar. According to the International Journal of Systematic Bacteriology, 238 species comprise Paenibacillus, though additional phylogenetic reclassification may be necessary.

Epidemiology and Transmission

Paenibacillus can be found in a multitude of environmental sources, including soil, water and insect larvae. Initial isolates were discovered during agricultural research looking for ways to decrease the use of pesticides while developing cultivation techniques that would increase agricultural productivity. Paenibacillus spp. have been shown to increase the biological availability of phosphorous and nitrogen in soil, and induce systematic resistance, a mechanism used to protect plants against pathogenic bacteria, fungi, nematodes and viruses.

Recently, several species of Paenibacillus have exhibited production of two classes of bacteriocins, active against Gram-positive bacteria, and polymyxins, active against both Gram-positive and -negative bacteria. These biologically active molecules might prove useful in the treatment of multi-resistant bacteria such as Pseudomonas and Acinetobacter spp.

Paenibacillus species are also known to infect insects. Paenibacillus larvae is the cause of American foulbrood in honeybees. Paenibacillus spores may survive for years in honey from infected bees. This has been problematic in human medicine considering methadone, a drug used to assist with opioid dependence, is sometimes mixed with syrup or honey to discourage abuse by injection. In several cases, injected methadone mixed with residual honey and contaminated with Paenibacillus spores has caused bacteremia.

Isolation of Paenibacillus species from humans may represent acquisition from the environment. Paenibacillus has also been reported in gut flora. Human-to-human transmission has not been reported.

Clinical Significance

When isolated from humans, Paenibacillus is often classified as a contaminant and considered clinically irrelevant; however, when associated with disease, they appear to be limited to infections in immunocompromised and elderly patients. Clinically relevant isolates have been reported from blood, cerebrospinal fluid, pleural fluid, wounds and other sources. (5)

Paenibacillus spp. have the ability to form biofilms, increasing the likelihood for growth and survival in unfavorable conditions. This enables them to grow without difficulty on medical devices and hard surfaces, such as pacemakers and microsurgical clipping devices. Ferrand et al. described a case of P. glucanolyticus as the source of endocarditis in a 65-year-old woman with type 2 diabetes following implantation of a pacemaker.

A number of other Paenibacillus species have been implicated in human infection. Paenibacillus alvei was isolated from a preterm infant with sepsis and meningoencephalitits. Paenibacillus turicensis was isolated from a bone infection in a 65-year-old man with cardiovascular disease following a motorcycle accident in Laos. Paenibacillus residui was isolated from an infected breast implant in a 54-year old woman with breast cancer. These cases (and other published reports) illustrate the pathogenic potential of a wide range of Paenibacillus species.

Laboratory Identification

Paenibacillus are large, facultatively anaerobic, Gram-positive bacilli. Most isolates appear flat, opaque and smooth on routine media, though some species--including P. glucanolyticus--also have the ability to swarm. Paenibacillus can also stain as Gram-variable or Gram-negative, which can cause delays in identification and appropriate treatment. It is spore forming, contributing to variability in staining and difficulties in identification. The endospores provide resistance to extreme temperatures and the action of a number of disinfectants, allowing survival on a surface.

There are minimal phenotypic differences between Bacillus and Paenibacillus spp., so identification of Paenibacillus based on biochemical and physical characteristics is not recommended. MALDI-ToF is likely to be an accurate identification method; however, there are limitations to the databases of the two FDA-cleared MALDI-ToF systems. Many species are only identifiable through the use of supplemental testing. 16S rRNA amplification and sequencing is more successful in the speciation of Paenibacillus. When this methodology is used, CLSI guidelines set specific requirements for genus and species identity scores of 97% and 99%, respectively.


Isolates of Paenibacillus have been reported with a variety of antimicrobial resistance patterns. Research has shown P. glucanolyticus to be unique from most other species of this genus in that it is commonly resistant to penicillin due to beta-lactamase production. Many other antimicrobials, including erythromycin, trimethoprimsulfamethoxazole, gentamicin, tobramycin and vancomycin, generally display low minimum inhibitory concentrations. CLSI guidelines for Bacillus species are commonly used to determine antimicrobial breakpoints, as there are no such standard guidelines for Paenibacillus at this time.


Clinical microbiology laboratories should be familiar with Paenibacillus species, as they may occur as a contaminant or a pathogen in a variety of specimen types. Advances in technology used for bacterial identification better equip laboratories to identify these and other environmental organisms traditionally considered contaminants. Careful clinical correlation is typically necessary to determine the significance of these isolates.

Article 461: 1 Clock Hour

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1. Which of the following is not a characteristic of Paenibacillus species?

A. Endospore forming

B. Gram-positive rod

C. Dry, white colonies on Blood agar

D. Unable to grow on Macconkey agar

2. Paenibacillus species can be found in which of the following?

A. Soil

B. Water

C. Honey

D. All of the above

3. Paenibacillus bacteremia has been associated with the intravenous use of which drug?

A. Vancomycin

B. Methadone

C. Heroin

D. Warfarin

4. Paenibacillus was historically thought to belong to what genus of bacteria?

A. Enterobacter

B. Bacillus

C. Cutibacterium (formerly known as


D. Corynebacterium

5. Which of the following is the most reliable method to differentiate Paenibacillus species from other bacteria?

A. Biochemical testing


C. Gram stain

D. 16S rRNA sequencing

6. Which of the following increases the risk of bacteremia due to opportunistic environmental organisms?

A. Central venous lines

B. Paper cuts

C. Suppressed immune system

D. A and C

7. The infection in this case study may have persisted despite appropriate antimicrobial therapy due to a blood clot preventing medication from reaching the bacteria.

A. True

B. False

8. All Paenibacillus species have the same antimicrobial resistance patterns and are resistant to penicillin.

A. True

B. False

9. Elevated AST and ALT are enzymes associated primarily with the function of which organ?

A. Pancreas

B. Kidney

C. Liver

D. Spleen

10. Elevated BUN levels typically indicated decreased function of which organ?

A. Pancreas

B. Kidney

C. Liver

D. Spleen


(1) Celandroni, F., Salvetti, S., Gueye, S. A., Mazzantini, D., Lupetti, A., Senesi, S., & Ghelardi, E. (2016, March 31). Identification and pathogenic potential of clinical Bacillus and Paenibacillus isolates. Plos One, 11(3). doi:10.1371/journal.pone.0152831

(2) DeLeon, S. D., & Welliver, R. C. (2016, March). Paeni bacillus alvei sepsis in a neonate. The Pediatric Infectious Disease Journal (35)3. doi:10.1097/ INF.0000000000001003

(3) Ferrand, J., Hadou, T., Selton-Suty, C., Goehringer, F., Sadoul, N., Alauzet, C., & Lozniewski, A. (2013, October). Cardiac device-related endocarditis caused by Paenibacillus glucanolyticus. Journal of Clinical Microbiology, 51(10), 3439-3442. doi:10.1128/jcm.00864-13

(4) Govindasamy, V., Senthilkumar, M., Magheshwaran, V., Kumar, U., Bose, P., Sharma, V., & Annapurna, K. (2010). Bacillus and Paenibacillus spp.: potential PGPR for sustainable agriculture. Plant Growth and Health Promoting Bacteria Microbiology Monographs, 333-364. doi:10.1007/978-3-642-13612-2_15

(5) Grady, E. N., Macdonald, J., Liu, L., Richman, A., & Yuan, Z. (2016, December 1). Current knowledge and perspectives of Paenibacillus: A review. Microbial Cell Factories, 15(1):203. doi:10.1186/s12934-016-0603-7

(6) Kobayashi, K., Kanesaki, Y., & Yoshikawa, H. (2016, October 20). Genetic analysis of collective motility of Paenibacillus sp. NAIST15-1. PLOS Genetics, 12(10). doi:10.1371/journal.pgen.1006387

(7) Marchese, A., Barbieri, R., Pesce, M., Franchelli, S., & De Maria, A. (2016, August) Breast implant infection due to Paenibacillus residui in a cancer patient. Clinical Microbiology and Infection, 22(8), 743-744.. doi: 10.1016/j.cmi.2016.05.012

(8) Mei, Q.-X., Huang, C.-L., Luo, S.-Z., Zhang, X.-M., Zeng, Y., & Lua, Y.-Y. (2018, June). Characterization of the duodenal bacterial microbiota in patients with pancreatic head cancer vs. healthy controls. Pancreatology, 18(4). doi: 10.1016/j.pan.2018.03.005

(9) MM18-Interpretive criteria for identification of bacteria and fungi by targeted DNA sequencing (2nd ed). CLSI guideline MM18. Wayne, PA: Clinical and Laboratory Standards Institute.

(10) Parte, A. (n.d.). Genus Paenibacillus. Retrieved from

(11) Sant'Anna, F. H., Ambrosini, A., De Souza, R., De Carvalho Fernandes, G., Bach, E., Balsanelli, E., ... Passaglia, L. M. (2017). Reclassification of Paenibacillus riograndensis as a genomovar of Paenibacillus sonchi: Genome-based metrics improve bacterial taxonomic classification. Frontiers in Microbiology, 8(1849). doi:10.3389/fmicb.2017.01849

(12) Tidjani Alou, M., Rathored, J., Nguyen, T. T., Andrieu, C., Couderc, C., Brah, S., Diallo, B. A., Fournier, P. E., Raoult, D., ... Dubourg, G. (2016). Paenibacillusphocaensis sp. nov., isolated from the gut microbiota of a healthy infant. New Microbes and New Infections, 16: 13-24. doi:10.1016/j.nmni.2016.12.001

By Ariela Topper, Martina Beckman, Dr. Eleanor A. Powell, and Dr. Joel E. Mortensen

Ariela Topper, MT(ASCP), and Martina Beckman, MT(ASCP), MHA, are technologists in the Diagnostic Infectious Diseases Testing Laboratory, Eleanor Powell, PhD, is a visiting Scientist in the Diagnostic Infectious Diseases Testing Laboratory, Joel Mortensen, PhD, is the Director of the Diagnostic Infectious Diseases Testing Laboratory, Department of Pathology and Laboratory Medicine, Cincinnati Children's Hospital

Caption: Figure 2. Antimicrobial susceptibility testing on blood Mueller Hinton agar
Table 2. Antimicrobial Minimum Inhibitory
Concentration by E-test

Antimicrobial         Patient          CLSI
Agent           MIC ([micro]g/mL)   Breakpoints
                                      S      R

Ciprofloxin            0.19          <1      >4
Clindamycin            >256          <0.5    >4
Penicillin             >32           <0.12   >0.25
Meropenem               2            <4      >16
Vancomycin             1.5           <4
Gentamycin             1.0           <4      >16
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Title Annotation:Article 461: 1 Clock Hour
Author:Topper, Ariela; Beckman, Martina; Powell, Eleanor A.; Mortensen, Joel E.
Publication:Journal of Continuing Education Topics & Issues
Date:Jan 1, 2019
Previous Article:How Important is Integrity in the Workplace?

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