Department of Microbiology Bacteraemia guideline

Bacteraemia with Gram Positive Bacilli

Quick reference guide:

• Aim
• Background
• Bacteriological differential diagnosis
• Clinical differential diagnosis
• Technical issues
• Antimicrobial treatment
• Supplementary Investigations

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.

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Gram stain: Gram negative Cocci & coccobacilli

Aim

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

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Background

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.

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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.

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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.

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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. 

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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

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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.

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