When should a stool culture be ordered instead of empirical treatment?

Culture is ordered when the clinical picture is severe (bloody diarrhoea, fever, dehydration), when the patient is immunocompromised, when symptoms persist beyond a week, in outbreak settings, or when antimicrobial therapy is being considered and susceptibility data will guide agent selection.

Does a negative culture rule out bacterial infection?

No. Culture can be negative if the specimen was collected late, after antimicrobials were started, if transport was delayed, or if the pathogen is fastidious or not targeted by the laboratory's standard media. Clinical judgement and additional testing may be needed.

Why is antimicrobial susceptibility testing important?

Susceptibility testing identifies which antimicrobials are active against the recovered isolate, allowing practitioners to select an effective agent, avoid drugs likely to fail because of resistance, and de-escalate from empirical broad-spectrum therapy to a targeted regimen.

How should the stool specimen be collected?

Collect a fresh stool sample during acute diarrhoea into the sterile container provided, using the transport medium (Cary-Blair) to preserve organism viability. Avoid contamination with urine, water, or toilet chemicals, and ship or deliver the specimen to the laboratory promptly, refrigerating if delay is unavoidable.

Can antimicrobials be started before the specimen is collected?

Ideally collect the specimen before starting antimicrobials, as even short courses can suppress bacterial growth and yield false-negative results. If therapy has already begun, note it on the requisition so the laboratory and clinician can interpret the culture accordingly.

Why does the laboratory need to know about recent travel?

Travel history helps the laboratory select additional media or methods for pathogens endemic to the region visited (for example enterotoxigenic E. coli, Vibrio cholerae) and informs interpretation of the susceptibility pattern.

Are all positive cultures reportable to public health authorities?

Most isolates of Salmonella, Shigella, and certain other enteric pathogens are notifiable diseases; the laboratory will report confirmed cases to public health for surveillance and outbreak investigation. Practitioners should be aware of local reporting requirements.

How long do culture results take?

Results typically take 3–7 business days from specimen receipt at Doctor's Data. Preliminary results may be available earlier if a pathogen is detected, but final identification and susceptibility testing require full incubation and characterisation.

BML-INF-081infectious diseaseUSA

Bacteriology Culture/Sensitivities

The Bacteriology Culture/Sensitivities test identifies pathogenic enteric bacteria—Salmonella, Shigella, Campylobacter, pathogenic E. coli, Yersinia, Vibrio, Aeromonas—in stool and determines their antimicrobial susceptibility. It is the definitive diagnostic for bacterial gastroenteritis, guides targeted therapy, and supports public health surveillance and outbreak investigation.

Biomarkers

Stool

Sample

3–7 business days

Turnaround

Fasting

What is the Bacteriology Culture test?

The Bacteriology Culture/Sensitivities test identifies pathogenic bacteria in stool and determines their antimicrobial susceptibility profile. It is the definitive diagnostic method for bacterial gastroenteritis caused by recognised enteric pathogens, enabling species-level identification and guiding targeted antimicrobial therapy when treatment is indicated. Bacterial culture is ordered when the clinical picture — acute diarrhoea, fever, mucoid or bloody stools, recent travel, or foodborne exposure — suggests a bacterial aetiology. Because most acute diarrhoea is self-limited and viral or toxin-mediated, culture is reserved for patients with severe symptoms, immunocompromise, healthcare or outbreak settings, or when antimicrobial therapy is being considered. The test also serves a public health function: confirmed isolates of Salmonella, Shigella, and other notifiable pathogens trigger case investigation and contact tracing.

What does the Bacteriology Culture test measure?

Culture(Pathogenic Bacterial Isolates)

Range: No growth of Salmonella, Shigella, Campylobacter, Yersinia, pathogenic E. coli, Vibrio, or Aeromonas species; see laboratory-specific reporting criteria.Optimal: No growth of recognised enteric pathogens; culture is interpreted qualitatively rather than by a continuous reference interval.qualitative identification / CFU/g

The gastrointestinal tract harbours a complex microbial ecosystem in which commensal organisms outnumber pathogens many-fold. Traditional stool culture employs selective and differential media to isolate known enteric bacterial pathogens — Salmonella, Shigella, Campylobacter, pathogenic Escherichia coli (including enterohaemorrhagic, enterotoxigenic, and enteroinvasive pathotypes), Yersinia enterocolitica, Vibrio, and Aeromonas species — that are not part of the normal flora. Recovery depends on organism load, transport time, and prior antimicrobial exposure.

Detection of a pathogenic isolate confirms bacterial gastroenteritis, informs antimicrobial choice, and enables public health reporting. Negative culture does not exclude bacterial infection if the organism is fastidious, the specimen was delayed, or antimicrobials were started before collection. Culture sensitivities guide therapy when resistance is suspected and help tailor treatment in severe or persistent disease.

AST(Antimicrobial Susceptibility Testing)

Range: Isolate-specific; reported as susceptible (S), intermediate (I), or resistant (R) to each tested agent according to CLSI or EUCAST interpretive criteria.Optimal: Not applicable — AST is reported per isolate and interpreted in the clinical context; 'optimal' is susceptibility to first-line agents with minimal collateral resistance.susceptible/intermediate/resistant classification / minimum inhibitory concentration (µg/mL)

Susceptibility testing measures the in-vitro activity of antimicrobials against a recovered isolate, typically by disc diffusion or automated broth microdilution. Results are interpreted against breakpoints that predict clinical response and correlate with the pharmacodynamics of each drug and infection site. Testing panels are chosen according to the organism identified and local resistance epidemiology.

Susceptibility data allow practitioners to select an effective agent, de-escalate empirical broad-spectrum therapy, and avoid drugs likely to fail. For public health surveillance, resistance patterns inform empirical guidelines and track the emergence of multidrug-resistant strains.

Why is the Bacteriology Culture test ordered?

Investigation of acute bloody diarrhoea (dysentery) where bacterial pathogens such as Shigella, Campylobacter, or enterohaemorrhagic E. coli are suspected
Evaluation of persistent diarrhoea (>7 days) that has not responded to empirical therapy or when a bacterial cause is considered
Work-up of diarrhoea in immunocompromised patients (HIV, transplant recipients, chemotherapy), where bacterial pathogens may cause severe disease
Assessment of travellers returning with acute diarrhoea and fever, particularly from regions endemic for Salmonella, Shigella, Campylobacter, or enterotoxigenic E. coli
Outbreak investigation in healthcare facilities, food service, or community settings where bacterial foodborne or waterborne transmission is suspected
Pre-treatment culture and susceptibility testing when antimicrobials are being considered for severe or systemic bacterial gastroenteritis, guiding agent selection and duration
Public health surveillance and notifiable disease reporting for confirmed isolates of Salmonella, Shigella, and other regulated pathogens
Evaluation of healthcare-associated diarrhoea not attributable to Clostridioides difficile, where hospital-acquired bacterial pathogens may be present

Sample collection and turnaround

Sample type

Stool

Fasting required

Collection method

At-home collection kit

Turnaround

3–7 business days

Collection notes

Patient collects a fresh stool specimen into the provided sterile container with transport medium (typically Cary-Blair), avoiding contamination with urine, water, or toilet chemicals. Specimen should be collected during acute diarrhoea and ideally before antimicrobial therapy is started. Ship to Doctor's Data according to kit instructions; refrigerate if shipping is delayed beyond a few hours.

Specimen requirements

Approximately 1–2 grams of stool (pea-sized) in Cary-Blair or equivalent transport medium. Avoid preservatives or fixatives intended for parasite testing, which inhibit bacterial growth. Note recent antimicrobial use and travel history on the requisition to guide laboratory interpretation.

What can affect Bacteriology Culture results?

reducesPrior antimicrobial therapy

Even short courses of antimicrobials can suppress bacterial growth and yield false-negative cultures; ideally collect the specimen before starting therapy or note recent exposure for interpretation.

reducesDelayed specimen transport and improper storage

Enteric pathogens, particularly Shigella and Campylobacter, are labile; specimens should reach the laboratory within hours or be placed in Cary-Blair or other transport medium to preserve viability.

reducesCollection after symptom resolution

Pathogen shedding peaks during acute illness; specimens collected late in the course or after diarrhoea has resolved may miss the organism.

variablePresence of non-pathogenic flora

Heavy overgrowth of commensal organisms can obscure pathogens on culture plates; selective media mitigate this, but fastidious pathogens may still be missed.

reducesAntimicrobial or antiseptic contamination of the collection container

Residues of antiseptics, toilet cleaners, or urine in the container can inhibit bacterial growth; use a clean, dedicated collection vessel.

reducesPathogen load below the limit of detection

Culture sensitivity depends on organism density; low-level carriage or certain pathotypes (for example some enterotoxigenic E. coli) may not grow on standard media.

What do Bacteriology Culture results mean?

Elevated

Not applicable — bacteriology culture is qualitative. A positive result reports the identity of the pathogenic isolate (for example Salmonella enterica serovar, Campylobacter jejuni, Shigella species, or pathogenic E. coli) and its susceptibility pattern, confirming bacterial gastroenteritis and guiding antimicrobial selection when therapy is warranted.

Normal

No growth of Salmonella, Shigella, Campylobacter, Yersinia, pathogenic E. coli, Vibrio, or Aeromonas on the culture media tested. A negative culture does not exclude bacterial infection if the organism is fastidious, the specimen was delayed or collected after antimicrobials were started, or the pathogen is not targeted by the laboratory's standard panel.

Reduced

Not applicable — the relevant finding is presence or absence of a pathogen.

Note: Culture detects only the pathogens for which selective media are used; emerging or uncommon organisms may be missed. Susceptibility results are in-vitro predictions and must be interpreted with the infection site, severity, and pharmacokinetics of each agent. Many episodes of bacterial gastroenteritis are self-limited and do not require antimicrobials; treatment is reserved for severe, invasive, or high-risk cases. Positive cultures of notifiable organisms must be reported to public health authorities.

Frequently asked questions

A stool bacteriology culture targets recognised enteric pathogens: Salmonella, Shigella, Campylobacter, pathogenic Escherichia coli (including enterohaemorrhagic and enterotoxigenic strains), Yersinia enterocolitica, Vibrio, and Aeromonas species. It does not detect viruses, parasites, or Clostridioides difficile, which require separate tests.

How to access the Bacteriology Culture test

The Bacteriology Culture reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: October 7, 2026

Last reviewed: October 7, 2026

References:

Shane AL, et al. Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. (2017)
Riddle MS, et al. ACG clinical guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults. Am J Gastroenterol. (2016)
CLSI. Performance standards for antimicrobial susceptibility testing (M100). (2023)
EUCAST. Breakpoint tables for interpretation of MICs and zone diameters. (2023)
Scallan E, et al. Foodborne illness acquired in the United States — major pathogens. Emerg Infect Dis. (2011)

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.

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