Microbial Histochemistry

False gram negatives can be due to - [blank_start]Dead bacteria[blank_end] and [blank_start]Technical[blank_end] faults such as [blank_start]tissue processing[blank_end] and over [blank_start]differentiation[blank_end]

Quality control for Grams include - [blank_start]Fibrin[blank_end], [blank_start]elastic fibres[blank_end] and [blank_start]paneth cell granules[blank_end] for Gram positives, and [blank_start]Neutrophils[blank_end] and [blank_start]epithelial cells[blank_end] for Gram Negatives.

Histopathological features of Mycobacteria includes [blank_start]Langhan's giant cell[blank_end] for Tuberculosis. Mycobacteria are considered [blank_start]Gram positive[blank_end], but most are [blank_start]Gram Neutral[blank_end]. They can be identified by using the [blank_start]Ziehl Neelsen[blank_end] stain

Mycobacterium and Nocardia have unusual [blank_start]cell walls[blank_end] that are waxy and nearly [blank_start]impermeable[blank_end] due to the presence of [blank_start]mycolic acid[blank_end]

[blank_start]M. Tuberculosis[blank_end] is resistant to acid-alcohol, whilst [blank_start]M. Leprae[blank_end] is resistant to acid. M. Tuberculosis is stained by the [blank_start]classic Ziehl Neelsen[blank_end] whilst M. Leprae stains with the [blank_start]Fite stain[blank_end]

Filamentous bacteria with a beaded and branching morphology includes [blank_start]Actinomycetes[blank_end] and [blank_start]Nocardia[blank_end]. They are both Gram positive, however, [blank_start]Actinomycetes[blank_end] are Fite negative, whilst [blank_start]Nocardia[blank_end] is Fite positive.

Ziehl Neelsen controls include [blank_start]Red blood cells[blank_end] and [blank_start]Russell Bodies[blank_end].

Helicobacter Pylori is able to survive in the stomach because it produces pH neutralising Ammonia

Helicobacter Pylori can cause [blank_start]gastritis[blank_end], [blank_start]ulcers[blank_end], [blank_start]carcinoma[blank_end] and [blank_start]lymphoma[blank_end].

Staining of Helicobacter Pylori includes [blank_start]Warthin Starry[blank_end], which is a difficult silver stain to do. [blank_start]Immunohistochemistry[blank_end], and [blank_start]Acridine orange[blank_end] (usually has dark background).

Increased incidence of mycoses can be due to [blank_start]immunosuppression[blank_end] (due to HIV disease and [blank_start]organ transplantation[blank_end]). Histopathology is important to diagnose fungi because [blank_start]microbiologic culture[blank_end] may nit be available for several days or weeks, and some [blank_start]fungi[blank_end] may not culture.

Some fungi like [blank_start]aspergilli[blank_end] and [blank_start]zygomycetes[blank_end] stain well on H&E. [blank_start]Pigmented fungi[blank_end] are easy to see, whilst many [blank_start]yeasts[blank_end] stain poorly.

Morphologies of fungi includes [blank_start]round[blank_end] for [blank_start]yeasts[blank_end] like [blank_start]Candida[blank_end], and [blank_start]hyphae[blank_end] for [blank_start]Molds[blank_end].

Fungi stains like [blank_start]PAS[blank_end] is pseudofungi positive. It is quick and easy to do, but [blank_start]old fungi[blank_end] and Nocardia and [blank_start]Actinomyces[blank_end] does not stain well.

[blank_start]Methenamine Silver (GMS)[blank_end] is high contrast with minimal background, stains both [blank_start]degenerative[blank_end] and non-viable [blank_start]fungal[blank_end] elements. [blank_start]Calcific bodies[blank_end] are unsustained, and [blank_start]Pseudo-fungi[blank_end] do not stain.

Pseudo-fungi look like fungi on H&E and [blank_start]PAS[blank_end]. Fibrin, [blank_start]collagen[blank_end], exogenous fibres and bacteria. PAS positive but [blank_start]GMS[blank_end] negative. Sometimes can be Perls and Von Kossa [blank_start]positive[blank_end].

Pseudo-fungi includes Hamazaki-Wesenberg bodies that look like [blank_start]yeast[blank_end], and Gamna-Gandy bodies and small branching [blank_start]blood vessels[blank_end] that look like [blank_start]fungal hyphae[blank_end].

[blank_start]Aspergillus[blank_end] are the most common [blank_start]invasive[blank_end] mould infection. They produce [blank_start]oxalic acid[blank_end] and Use the Yasue's silver nitrate-rubeanic acid method.

[blank_start]Cryptococcus[blank_end] neoformans use Alcian blue and Mucicarmine for mucopolysaccharide rich capsule. Masson Fontana for [blank_start]melanin[blank_end]-like substance in capsule [blank_start]deficient[blank_end] form.

Histoplasma capsulatum are tiny, intracellular [blank_start]yeasts[blank_end] observed within [blank_start]Histiocytes[blank_end]. [blank_start]GMS[blank_end] differentiates Histoplasma capsulatum ([blank_start]positive[blank_end]) from Leishmania and toxoplasma (both [blank_start]negative[blank_end]).

In Ziehl Neelsen, acid fast bacteria stains [blank_start]pink[blank_end], whilst non acid-fast stains [blank_start]blue[blank_end]

Pneumocystis carinii are invisible with both H&E and [blank_start]PAS[blank_end]. But are best shown with [blank_start]GMS[blank_end] and STB

In order to compare true fungi and pseudo-fungi, we must confirm a positive [blank_start]PAS[blank_end] with a [blank_start]positive[blank_end] classical GMS (using chromic acid oxidation). [blank_start]Weak GMS positivity[blank_end] of pseudo-fungi might be caused by [blank_start]overstaining[blank_end] sectionsin the methenamine silver solution. Compare with surrounding [blank_start]collagen[blank_end]. In some cases, [blank_start]metal[blank_end] staining can be useful.

Hemozoin is a [blank_start]pigment[blank_end] formed due to a parasite's inability to [blank_start]catabolise[blank_end] [blank_start]heme[blank_end]. This is usually [blank_start]golden-brown[blank_end] and found in [blank_start]Malarial[blank_end] parasites.

Apart from electron microscopy and assuming good specific [blank_start]antobody[blank_end] is available, [blank_start]Immunohistochemistry[blank_end] is best for demonstrating viruses such as [blank_start]CMV[blank_end] and BK virus.