Medical Microbiology week 6-11

Pasturella multocida

What is the most common organism associated with cat bite?

Group A strep, Staph. aureus, anaerobes

Apart from capnophilic gncb, what other organisms can be isolated from bite wounds?

Penicillin, Flucloxacillin and Metronidazole

How do we treat bite wounds?

Bartonella henselae. Regional lymphadeopathy that can be confused with non-Hodgkins lymphoma. Can cause an eye disease where there is ulceration on the sclera.

What organism causes Cat-scratch disease, what are the symptoms, what are the features of the disease?

Dermatophytosis

What is the medical name used to describe Tinea?

Microsporum canis

What is the main fungus associated with Tinea barbae and Tinea capitus?

Through worming of dogs to kill the adult egg-producing worms.

How has hydatid disease been controlled?

Diagnosis in humans is through finding space-occupying cysts in places like the liver, lungs and brains. These must be removed entire to avoid anaphylaxis in humans to hydatid sand. There are no eggs excreted in human faeces.

How is it diagnosed in humans?

Contracted from swimming and ingesting faecally contaminated water. Contamination of swimming pools is common and difficult to destroy as cysts are chlorine resistant.

How is cryptosporidium normally contracted?

Laboratory diagnosis is through acid-fast staining of faecal smear.

How is cryptosporidium diagnosed in the laboratory?

Causes CNS disease n the immunocompromised and congenital defects in the developing foetus of pregnant women.

What disease does Toxoplasmosis cause?

Diagnosis is through a TORCH antibody screen as it may not be diagnosed until birth and then there are a number of other microbes that can can also cause congenital defects.

how is Toxoplasmosis diagnosed?

Hendra virus infection

What new infection was diagnosed in Queensland that was passed from horses to humans?

Bats are the natural reservoir

What is the natural reservoir for Hendra Virus infection?

Rabies

What bat virus causes one of the most feared infections?

With passive transfer of rabies antibodies (immunoglobulin) and vaccine

How are victims of possible rabies transmission treated?

HUS (haemolytic uremic syndrome) following infection with a strain harbouring the shiga toxin gene. The main symptom is bloody diarrhoea.

What is the most severe form of disease caused by an E. coli strain?

Culture and test the E. coli strains by PCR for the shiga toxin gene. Assays for the toxin in stool also performed.

How do we diagnose disease with EHEC?

Atypical pneumonia caused by intracellular microbes such as Chlamydiophila psittaci or viruses. These elicit a lymphocyte response rather than pus. Cough is unproductive, chest Xray changes are diffuse.

How is atypical pneumonia different from acute bacterial pneumonia such as lobar pneumonia and bronchopneumonia?

beta-lactam antibiotics should not be used, as mycoplasma and like chlamydiophila do not have peptidoglycan. Some other causes also are difficult to treat (legionella) and thus may best be treated with azithromycin. Viral causes of atypical pneumonia will not respond to antibiotics and will need anti-virals instead.

What treatments are inappropriate for atypical pneumonia and why?

Disease caused by spiral shaped organisms, carried by rats. Can also infect animals of production. It is spread by contact with the infected animal's urine. Causes serious illness, promptly treat with penicillin to avoid long-term illness as it can localise in the CNS.

What is leptospirosis?

Brucellosis is a disease caused by a gncb and presents as a fever.

What is brucellosis?

thus blood cultures are usually collected.

How is Brucellosis diagnosed in the laboratory?

Carried by animals and excreted in their urine, milk and birth products. Humans infected through direct contact with animals or by eating or drinking infected milk or products such as unpasteurised soft cheese

How is Brucellosis spread?

Bush walkers from areas where the infected ticks may be on pastures, occupational groups like farmers, veterinarians, abattoir workers.

Who is at most risk of Q-fever infection?

Q-fever is a bacterial infection caused by the pathogen Coxiella burnetii. It can be transmitted to humans through inhalation of contaminated particles from infected animals or their products. Symptoms include high fever, severe headache, muscle pain, and fatigue.

What is q-fever?

Animal infection occurs in endemic regions. Sickened animals may die quickly and a veterinarian will make a diagnostic blood smear from the ear of the animal and stain to look for the characteristic bacilli in the blood. Swabs are usually received in the laboratory in cases of subjected cutaneous anthrax. Non-haemolytic colonies should be investigated however specimens and their cultures should be handled inside the biohazard cabinet.

How is anthrax diagnosed in animals and humans?

The lesion may start off as a spreading cellulitic area that blackens in the centre (called an eschar). Vesicles may form in the cellulitic area around the central blackened area. There will be notable swelling around the lesion early in the infection.

What are the clinical diagnostic signs of cutaneous anthrax?

When an animal dies of anthrax spores will be left behind that will start a future infection

Why does anthrax cause sporadic disease in some agricultural areas?

Hypochlorite is inactivated by organic material so all organic material must be disposed of before disinfection is attempted

Hypochlorite is sporocidal but what are the limitations?

Symptoms of legionellosis include severe respiratory symptoms, atypical pneumonia (with a diffuse chest X-ray pattern), and diarrhoea in approximately 50% of cases.

What are the symptoms of legionellosis?

Those exposed to aerosols from poor HVAC systems, immunocompromised, elderly, middle-aged smokers, and sporadic environmental cases.

which groups of patients are most at risk from legionellosis?

A urinary antigen test

What useful quick test can be performed in suspect legionellosis?

global warming and increased precipitation there is more risk of sporadic infection from the environment

Why are cases of legionellosis on the rise?

Monthly check cooling tower bacterial levels and regularly flush old plumbing with hot water to eliminate Legionella biofilm

What should hospitals do to ensure they reduce the incidence of legionellosis?

1. The organism is intracellular and difficult to see on Gram stain

2. The organism does not grow on HBA, it needs cysteine and grows best on agar also with charcoal that is buffered.

Why did it take so long to discover the agent of legionellosis?

It grows inside amoeba and is released from amoeba after it lyses the cell. It can also stay inside alive when the amoeba becomes a cyst when conditions dry out.

What is the natural life cycle of legionella?

They both phagocytose bacteria and then attempt to digest them

What do amoebae and macrophages have in common?

respiratory panel PCR

What is the best test for legionellosis?

Azithromycin of a respiratory fluoroquinolone like moxifloxacin

What is the treatment of choice for legionellosis?

Beta-lactam antibiotics and the cephalosporins have poor penetration into macrophages

What group of antibiotics should not be used for legionellosis?

Reduce the risk and growth of legionella

What is the key to legionella control?

Fermentation of glucose and Oxidase

What important tests are used to traditionally group gram negative rods?

Melioidosis

What does the organism Burkholderia pseudommallei cause?

In humans exposed to contaminated mud in the tropics such as northern Australia and Asia

Where is melioidosis traditionally found?

A patient may have a flu-like illness, septicaemia and abscesses

How does melioidosis present when it causes severe illness?

BSL-3 used and open cultures in the Class II biohazard cabinet.

What special precautions are taken with melioidosis cultures?

The gram-negative, safety pin appearance, culture may develop a pink colour after 48 hours, colony may have a crinkly surface

How is the microscopy and culture described for melioidosis?

susceptible to Augmentin

What useful test can help identify melioidosis?

fatality rate of 90%, only dropping to around 40% with appropriate quick treatment. Requires several months of treatment to prevent relapse

Why is melioidosis a terrible disease?

chemiluminescent molecules instead of enzyme-linked antibodies used

What are chemiluminescent assays?

offer higher sensitivity than ELISA

Why have chemiluminescent assays replaced ELISA in many settings?

Seroprevalence for both influenza and COVID-19 viruses is determined through haemagglutination inhibition assays, where the presence of antibodies in a patient's serum prevents virus-induced haemagglutination.

What two important viruses are seroprevalence determined through haemagglutination inhibition assays?

Perform serology on acute and convalescent sera and look for a rise in antibody titre

Some patients may have antibodies or may take time to form antibodies. What paired test is performed to overcome this limitation?

Immunofluorescence is used to detect antigens directly in samples, detecting viruses in tissues. It also detects antibodies, panel of different types of influenza antibodies

When is immunofluorescence used? Give two examples, one for antigen and one for antibody detection

microparticles

What does chemiluminescence use as the solid phase compared to ELISA?

minimal human intervention, high throughput, and cost-efficiency

What are the advantages of using track systems for modern serological testing?

need for specialist maintenance when they break down, the requirement for scientific monitoring to troubleshoot result patterns, and the unique behaviour of antibodies

What are the disadvantages of using track systems for modern serological testing?

Measurement of uncertainty quantifies the potential error due to run variation and is typically calculated using the mean and standard deviation

What is measurement of uncertainty?

In serology, values are assigned rather than measured as absolute values because they depend on the binding affinity of antibodies, which can vary significantly between individuals

Why is measure of uncertainty different for biochemistry compared to serology?

Type A measures inert substances measured as SI units. Type B analytes measure a functional activity and thus varies with the type of analyte, not traceable to SI units, given values that will vary with the assay

What are Type A analytes compared to Type B analytes?

good separation between those that do have antibodies from those that do not have antibodies for the disease

What would be the characteristics of a good serological assay?

The Western blot assay for HIV. Shows the number of different antigens and how different patients react differently to that antigen e.g. no one patient will react the same to any one virus.

What serological test gives a great example of the heterogeneity of the measurand?

Repeatability

measured over short period with one operator

Reproducibility

measured over longer periods with different operators

Accuracy

proximity of the results to the true value

Precision

scatter of individual values about the mean

Specificity

ability to correctly identify only the true analyte

Sensitivity

ability to detect an analyte if it is present

So no positives are missed. The trade-off may be that there is lowered specificity. However that can be covered by a confirmatory test.

Explain why high sensitivity testing is important in HIV screening? What is the trade-off?

The distance between the cut off and the negative results and the positive results. Ideally 15 or more SD away

What is the delta value in reference to serological testing?

It is based on statistics and positive and negative predictive values which are calculated from the prevalence.

What is the rational for 2/3 HIV screening tests negative to report a negative result?

Test for proviral DNA is performed on the white blood cells from a neonates blood, difficult to get blood from neonate, maternal transfer of antibodies

Explain how HIV testing is performed in neonates and the reasons why

Now we must look for pro-viral DNA because of early treatment strategies or that some patients may take prophylactic antivirals, you cannot rely on patients seroconverting as historically

Why has the HIV case definition changed?

It come down to dose. However if you give someone a litre of blood and there are very low levels of HIV, then the chances of transmission rise with the increased exposure to the volume of blood given.

Why does the undetectable=untransmissible not hold for blood screening of HIV in donatable blood products?

Antibody seroconversion has been lowered due to effective preventative and treatment strategies. Less antibodies in blood, there are less antibodies present to react with the antigens in Western Blot. This means that the sensitivity becomes too low

Why has Western blot become less useful as a confirmatory test in Australia?

Neutralisation assay where you remove the positivity with specific antibodies. If it remains positive after the neutralisation assay, then this would be a false positive.

In a patient who has a HepBsAg test positive and no risk factors, how could the test be confirmed?

For monitoring the treatment of syphilis as they will fall with successful treatment

These days, treponemal tests are used for screening and -non-treponemal for confirmation. When are non-treponemal tests useful on their own?

Malassazeia furfur

pityriasis versicolor, spaghetti and meatballs, yeast is lipophilic, grows is hair follicles

Trichosporon Beigelii

Micro: Irregular shaped conidia

Macro: white powdery obverse, cream reverse

Microsporum Canis

Micro: dotted conidia, hooked macroconidia

Macro: white-yellow obverse, white yellow reverse

Microsporum Gypseum

Micro: ovoid blastoconidia, thin cell walled macroconidia

Macro: beige buff obverse, beige-yellow (occasionally red) reverse

Paraphyton Cookei

Micro: thick cell walled macroconidia

Macro: white-yellow-beige obverse, deep purplish red reverse

Epidermophyton floccosum

Micro: thick cell walled macroconidia in clusters, no microconidia

Macro: white-beige-buff with radical furrows and folded centre obverse, white-yellow-beige reverse

Trichophyton rubrum

Micro: absent-numerous macroconidia in clusters, rare-numerous microconidia

Macro: cream pink obverse, wine red reverse

Trichophyton Interdigitale

Micro: tear drop shaped microconidia along hyphae, rare macroconidia

Macro: white-cream-tan powdery texture obverse, creamy yellow with red-brown centre reverse

Trichophyton tonsurans

Micro: variable sized thin walled macroconidia, spiral hyphae, spherical microconidia

Macro: white-yellow-brown obverse, cream-tan-brown reverse

Trichophyton violaceum

Micro: numerous chlamydospores, bizarre branching

Macro: violet with white overgrowth obverse, white-buff-lavender-purple reverse

Candida Albicans - candidosis

Chromogenic Agar: turquoise green colour, yeast cells with no capsules in wet prep

colour on chromogenic agar, metabolic profile

How to identify candida

Cladophialphora carrioni - chromoblastomycosis

Micro: shield cells detached from conidida, branching blastoconidia connected to each other

Macro: olive-black obverse, olive black reverse

phialophora verrucosa - chromoblastomycosis

Micro: phial flask shaped phialospores, phialoconidia clustered at phialide tips

Macro: olive-green-black obverse, olive-green-black reverse

Scedosporium boydii - eumycetoma

Micro: oval conidia attached to thin annelides like roots

Macro: white-wooly obverse, green-grey reverse

Eumycetoma

Presentation

Cryptococcus

Systemic mycosis, india ink shows halo surrounding yeast cell, use latex agglutination for test

Aspergillus Fumigatus - Aspergillosis

micro: flask shaped vesicle (Bulbing branch) and spherical conidia, apex oriented phialides

macro: blue-green obverse, white gold reverse

Aspergillus niger - Aspergillosis

Micro: globose/circular vesicle, globose conidia
Macro: whitw with black centres obverse, white yellow with furrows reverse

Aspergillus flavus

Micro: radiate sun like conidial head
Macro: yellow-green powdery obverse, gold-green reverse

Rhizopus microsporus - zygomycosis

Micro: spherical sporangium, ovoid conidia
Macro: white becoming grey-brown floccose obverse, white reverse

Rhizopus arrhizus - zygomycosis

Micro: mushroom like columella, spherical sporangium (bubble) containing circular spores
Macro: grey-white cottony obverse, white reverse