Gram positive bacilli bacteraemia

Publication: 22/07/2014  
Next review: 09/01/2026  
Clinical Guideline
ID: 3908 
Approved By: Trust Clinical Guidelines Group 
Copyright© Leeds Teaching Hospitals NHS Trust 2023  


This Clinical Guideline is intended for use by healthcare professionals within Leeds unless otherwise stated.
For healthcare professionals in other trusts, please ensure that you consult relevant local and national guidance.

Department of Microbiology Bacteraemia guideline

Bacteraemia with Gram Positive Bacilli

Quick reference guide:

This document provides guidelines for doctors on the management of patients with confirmed bacteraemia with Gram positive bacilli (GPB).  This document is supplementary to, and should be used in conjunction with, the antimicrobial guidelines.

Back to top

Gram stain: Gram negative Cocci & coccobacilli


The aim of this guideline is to:

  • Provide education to junior microbiology registrars
  • Support communication of Gram stain results from microbiologists to ward doctors
  • Support ward doctors in treating and investigating bacteraemic patients

Back to top


The blood culture process: Timings of culture, identification, susceptibility tests and clinical liaison.
How to use this guideline: This guideline should be used to help in the management of patients with a confirmed bacteraemia. The guideline should be used to support interaction with specialist advice e.g.  Microbiology.

Back to top

Bacteriological differential diagnosis (Gram guideline only)

Common causes of bacteraemia with a Gram Positive Bacilli (GPB)

  • Corynebacterium species.
  • Propionibacterium species e.g. Propionibacterium acnes

Uncommon causes of bacteraemia with a GPB

  • Bacillus species e.g. Bacillus anthracis
  • Clostridium species e.g. Clostridium perfingens
  • Listeria monocytogenes

Rare causes of bacteraemia with GPB.

  • Erysipelothrix rhusiopathiae
  • Rhodococcus equi
  • Mycobacterium species
  • Lactobacillus species
  • Nocardia species.


Table 1: Gram Positive Bacilli causing bacteraemias, their appearance on the Gram stain and atmospheric growth requirements. 




Corynebacterium species

 GPBs that are slightly curved with tapered or clubbed ends; may occur singly or in pairs, forming a ‘‘Chinese letters’’ pattern.

Given the appearance of Corynebacterium diptheriae is the same as other Corynebacteria, they are commonly referred to as “diptheroids” when their species name is not known.

Aerobe/facultative anaerobe

Propionibacterium species

Gram positive pleomorphic bacilli with branching (short ‘‘Y’’ forms),


Bacillus species

Gram positive, large spore forming bacillus that forms chains.

Aerobe/facultative anaerobe

Listeria monocytogenes

Regular GPB with rounded ends in short chains or sometimes in pairs or short plump coccobacilli 
non-spore forming, non-acid fast.

Aerobe/facultative anaerobe

Clostridium species

Spore bearing, large GPB with slightly rounded ends


Erysipelothrix rhusiopathiae

Non-spore forming GPB

Aerobe/facultative anaerobe

Rhodococcus equi

Aerobic, non-spore forming, coccobacillus


Gardnerella vaginale

Pleomorphic, non-sporing, Gram variable rod

Aerobe/facultative anaerobe

Lactobacillus species

Long Gram positive rods

Aerobe/facultative anaerobe

Nocardia species

 Filamentous, beaded GPB with some Acid & alcohol fast bacilli (AAFB)


Mycobacterium species

Beaded, filamentous, acid and alcohol fast Gram positive  bacilli


Back to top

Clinical differential diagnosis

There is a wide differential diagnosis for the source of GPBs in blood cultures. A full systems review is recommended to identify the source of GPBs in blood. The differential diagnosis includes:

  • Prosthetic material associated infection (e.g. central venous catheter, pacemaker)
  • Intra-abdominal infection
  • Skin and soft tissue infection e.g. gas gangrene/necrotising fasciitis
  • Meningitis/Encephalitis/Cerebritis
  • Endocarditis 
  • Mycobacterial infection
  • Contamination: Diptheroids, Propionibacterium species and Bacillus species are common contaminants isolated from blood culture bottles.  Repeat negative blood cultures whilst off antibiotics can confirm a diagnosis of contamination.

Back to top

Technical issues

Additional laboratory tests available:
Bacteraemia with rapidly growing atypical mycobacteria should be considered in immunocompromised patients due to suppressed host immunity and resistance factors. An Acid and Alcohol Fast Bacilli (AAFB) stain should be performed in these patients when GPB is isolated from the blood cultures.

Streptococcus spp can be confused with GPB. Please ensure you review species identification which is normally available within 24 hours of the Gram stain result. 

Back to top

Antimicrobial treatment

Antimicrobial therapy can often be improved with knowledge of the Gram stain result. An antibiotic may be started, stopped, or have its dose changed.

  • Antibiotic therapy should always be reviewed the day after the Gram result as bacterial growth will have allowed further speciation of the bacteria, and sensitivity tests to be completed.

History of the following are important to determine appropriate antimicrobial therapy

  • Any prostheses on patient
  • Immunosuppressed/immunocompromised
  • Any indwelling ling term vascular access devices on patient
  • source of infection
  • Allergy status and nature of allergy

Gram positive bacilli bacteraemias often represent contamination of the skin. The first clinical decision that is required in the management of a GPB bacteraemia is if the result is likely to represent infection or contamination. It can be reasonable to assume a GPB bacteraemia represents contamination if all the other clinical syndromes in Table 2 have been excluded, and the patient can be confirmed to have no prosthetic material e.g. central venous access or cardiac valve. Where there is uncertainty blood cultures should be repeated. If multiple blood cultures isolate a GPB, then it is likely the GPB are clinically significant and will require appropriate antimicrobial management.

The table below outlines some of the common organisms associated with each of the clinical syndromes. Please be aware that Gram positive bacilli can present in unusual ways, and that this list is by no means exhaustive

Table 2: Clinical diagnoses and treatment associated with Gram Positive Bacilli bacteraemias. 

Clinical diagnosis

Likely bacterial aetiological agent

Empirical antimicrobial therapy (click on the link)

Prosthetic joint infection

Corynebacterium species Propionibacterium species

Discuss with microbiology

Prosthetic cardiac material (e.g.  cardiac valve, pacemaker)

Corynebacterium speciese.g. C. jeikeium
Propionibacterium species

Discuss with microbiology

Infections of central venous catheters

Corynebacterium species Propionibacterium acnes
Atypical  Mycobacterium

Link Send, paired cultures (Link to paired BC SOP)

Meningitis /Cerebritis/Encepahilitis

Listeria monocytogenes

See guideline

Gas gangrene/Necrotising fasciitis

Clostridia perfringens

See guideline

Intra-abdominal infection

Anaerobe including Clostridia spp

See guideline

Skin & soft tissue infection

Bacillus anthracis

See guideline


Corynebacterium species Propionibacterium species

No antibiotics indicated.
Consider repeat blood cultures.
Consider discussion with microbiology

Back to top

Supplementary Investigations

Consider further investigations as appropriate to source of infection, please see relevant guidelines.

Notification to the local health protection unit is required for Anthrax, Botulism, Diphtheria and Listeriosis.

Back to top


Record: 3908
Clinical condition:


Target patient group:
Target professional group(s): Pharmacists
Secondary Care Doctors
Adapted from:

Evidence base

Back to top

Approved By

Trust Clinical Guidelines Group

Document history

LHP version 1.0

Related information

Not supplied

Equity and Diversity

The Leeds Teaching Hospitals NHS Trust is committed to ensuring that the way that we provide services and the way we recruit and treat staff reflects individual needs, promotes equality and does not discriminate unfairly against any particular individual or group.