Reading of a gram stain in diagnostic microbiology
READING OF A GRAM STAIN IN DIAGNOSTIC MICROBIOLOGY
The observation of the Gram stain continues to be primary skill among the Microbiologists, many times
performed by junior staff and the senior microbiologists scrutinize the results. However it is one of the
tests survived more than century of its discovery by Christian Gram in 1884. Minimal quality assurances
are recommended doing the staining with standard strains available for the both gram positive and gram
negative organism, Learnto define a direct smear.
Describe several ways that Gram stained direct smears are clinically useful. And educating the junior staff
to realise the importance of the tests, or else theyare done causally and discarded.
Understand examination of direct smears with respect to: control smears, macroscopic appearance, and
characteristics of appropriate microscopic fields.
Discuss the identification of common nonbacterial elements with respect to: purpose, size, shape,
differentiating characteristics, and Gram stain reaction. Many times the artefacts are interpreted as rare
type microbes by the over confident microbiologists
Identify the following types of bacteria found in Gram stained direct smears:
Gram-positive cocci, gram-negative cocci, gram-positive bacilli, gram-negative bacilli, gram negative
diplococci .Pleomorphism Discuss with staff procedure for reading Gram stained direct smears with respect to: principle, procedure,
and sources of error.
It is important the Microbiologists should be familiar to interpret the results of CSF and other important
specimens from body fluids and to be reported promptly. Provide the Clinician with Same-Day
Information Regarding Possible Pathogens, Information from Gram stained direct smears may help the
physician make a preliminary diagnosis when the Gram stain information is combination with clinical
Microbiologists should be familiar to report the following bacteria
Bacteria in Direct Smears
Special Considerations for Genital Smears
Significance of Specific Findings when the bacteria in the slide are gram-negative cocci.
The presence of intracellular gram-negative diplococci on a smear made from a purulent urethral
discharge from a male can be confirmatory of the diagnosis of Gonorrhoeal infection.
All the nonbacterial elements and artefacts’ should be read with caution and reported with wisdom
Nonbacterial Cells in Direct Smears Size and Appearance of Nonbacterial Cellular Elements on Gram
Stained Smear Match the Gram stain reaction for each of the following nonbacterial elements. Which of
the following cells are about the same size as red blood cells? What nonbacterial structures are present in
this microscopic field of a Gram-stained smear?
This Gram stain was prepared from a sputum specimen and is viewed under oil immersion (1000X).
Never forget to interpret the observation of sputum smear with culture reports; however my experience
proves it is difficult to interpret the Sputum and Wound specimen with precision and accuracy
Unless clearly associated with neutrophils or seen intracellular, the various organisms of normal flora
need not necessarily be reported individually. In we report the Normal fora, may be confusing and
misleading to the clinician who may interpret these organisms as potential pathogens simply because
“the laboratory reported it.” However, if any single morphotype (even one that is considered normal
flora) is closely associated with neutrophils, its presence should be reported, one should realise the
presence of Moraxella in sputum cultures with confluent growth in association with observation of many
If the laboratories’ interpretation is not consistent with the guidelines presented in the interpretation
should be reconsidered or consultation should be sought. Possibly over or under decolourization has
occurred. Al though these guidelines give objective criteria for interpreting the most commonly
encountered Gram stains, there will be exceptions. The quality of the reports and confidence in the
reports will improve if consultation with an-other technologist occurs before reporting such findings
Never forget the importance of Gram’s stain; it continues to be most rapid method in Diagnostic
Microbiology or even more than molecular diagnostic advances.
Dr.T.V.Rao MD Professor of Microbiology Freelancewriter.