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RECENT ADVANCES IN MEDICAL MICROBIOLOGY - LABORATORY ASPECTS

Dr Martin Parry, Senior Lecturer in Biomedical Sciences at the University of Westminster (UK), introduced himself as someone who has worked in routine diagnostic laboratories years ago and who has now moved on to teaching. The talk was held in a hall filled with laboratory personnel composed of the consultant pathologist, pathologists, consultant virology, principals, seniors and medical laboratory technicians.

In his introduction to the topic, Dr Parry presented some selective examples of agents which had come into the limelight only recently in the field of microbiology as shown in the table below:

Field

Agents

Remarks

Microbiology

Campylo-bacter

Commonest cause of gastro-enteritis in UK

 

Vibrio cholerae

O 139

Serotyping of this agent has only been done for 5 years

 

Escherichia

Coli O157

Increasing importance

Parasitology

Pneumocys-tis carnii

Protozoal parasite

 

Crypto parvum

High profile in UK

 

Cyclospora cayetanesis

 
 

Microspori-dia

 

Virology

HCV, HDV, HEV, HGV

Transfusion-transmitted virus a.k.a "non A-non B" hepatitis virus

Mycology

Cryptoco-cus neoformans

2 variants:

neoformans gatii

Opportunists associated with immuno-compromised patients e.g HIV and transplants

 

Candida dublinien-sis

Candida lusitaniae

Immuno-compromised patients

Often resistant to antifungal drugs

4 4 4 talk for the month of May

 

Dr Parry pointed out that two most important agents that have mobilised scientists are:

The former being well known to the audience present, Dr Parry prefered to elaborate more on the "recently" discovered bacterium, which can survive in the acid environment of the stomach, namely Helicobacter pylori. This bacterium is diagnosed mostly by serological tests and has been described as:

About the emerging infections, the speaker could not omit to talk about Creutzfeldt-Jacob's disease more commonly known as the "mad-cow" disease. These days, many epidemiologists are monitoring this disease closely because of the fear of an epidemic which could strike anywhere. Much research has been carried out and the new variants or strains are looked into; and it has been found out that this infective agent can be transmitted like a bacterium or a virus. The point of interest is that it has no nucleic acid and is hence called a prion.

A rare finding though, in Britain these days is for the Haemophilus influenzae. This is so because the population at risk has been vaccinated. However, other pathogens are still important namely Neisseria meningitidis type c. The latter was responsible for small outbreaks last year among the student population. For this pathogen too, population at risk has been vaccinated.

In order to come up with trends in microbiology, Dr Parry looked at some of his student's projects and he found out that the major areas of interest are:

Also to establish the trend in the London routine laboratories, the following factors emerged during the survey:

  1. Money - we don't have many! (for purchase of equipment)
  2. Workload - we have too much!
  3. Staff - we don't have enough!
  4. Molecular biology
  5. Automation

In view of the above, Dr Parry elaborated more on molecular biology and automation saying that the other factors being pretty much the same everywhere in the world. So, in these two areas; major progress is expected for diagnostic purposes in the future. Also molecular biology has been used extensively for the study of the Mycobacterium species responsible for tuberculosis.

Hence, molecular techniques can help in the detection of resistant genes. Such studies are carried out at the St Thomas Hospital and it is anticipated that a Multidrug-Resistant Mycobacterium tuberculosis (MRTB) outbreak can occur in the future because of the increasing number of cases. Most of these are from incoming passengers from developing countries and are not as is believed, related to the number of people suffering from HIV. To illustrate this, Dr Parry used the case of a Zimbabwean nurse who went to UK for a training course and who was suffering from tuberculosis. What was even more alarming was the fact that she was working in a paediatric ward at the Wycombe General Hospital.

In the field of parasitology, molecular techniques are used in the detection and speciation of Plasmodium. In the future, routine laboratories will use polymerase chain reaction for the diagnosis of malaria. Also it can be used to differentiate between Entamoeba histolytica and Entamoeba dispar as they have identical cysts. Here, Elisa-based tests may also be used.

As for mycology, it is used for the investigation of Aspergillus species in leukaemic patients. This particular fungus is difficult to isolate. Hence the difficulty to develop techniques for its detection.

In Britain, the cut down in staff has led to the introduction of automated systems in the microbiology laboratory. One such system is BACTEC (Becton Dickinson) which is used extensively in laboratories. This apparatus auto-incubates and signals positive blood cultures. When it "flags" a positive culture, the laboratory technician will be called upon to conduct such an expert technique as a Gram stain. It is a non-invasive culturing system and can incubate up to 240 vials at once. The use of ultra-sensitive fluorescence system monitors the blood cultures so as to provide the earliest possible detection. On one hand, another model of this system has a range of antibiotics in the bottles of blood cultures, for Mycobacterium tuberculosis sensitivity testing is indicated by growth or no growth. On the other hand, other types of automated systems such as VITEK (Biomérieux) can identify and perform sensitivity testing of isolates. Such a facility needs to be developed for the detection of resistant organisms such as Methicillin-Resistant Staphylococcus aureus (MRSA), Vancomycin-resistant enterococci (VRE) and fastidious bacteria. Also more automated systems are being developed such as VITEK 2, which has multi-probes.

This is to say that progress in technology will never stop and all this new technology has left the technicians to their dreams while they were thinking at the increasing workload year by year.