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Laboratory investigations may be carried out on living patients; this procedure goes by the special name "Clinical Pathology". Clinical Pathology includes clinical histopathology, clinical biochemistry, clinical haematology and clinical microbiology.

Melan-A / MART-1 is a recently identified new melanocytic differentiation marker, which is recognised as an antigen on melanoma cells by cytotoxic T-lymphocytes.

It is relevant to pathologists as a novel diagnostic marker, since two antibodies (A 103 and M2_7C10) have become available to study Melan-A expression or archival material (Busam KJ and Jungblueth AA 2000). It is of interest for clinicians as a potential immunotherapeutic agent. Both antibodies are useful in the differential diagnosis of melanocytic tumours, especially metastatic tumours since they are more sensitive than HMB-45 (Jungbluth AA et al 1998)

Melanoma-associated antigens (MRA) recognised by cytotoxic T-lymphocytes belong to three main groups; tumour-associated testis-specific antigens (e.g. MAGE, BAGE and GAGE): melanocytic differentiation antigens (e.g. tyrosine, Melan-A) and mutated or aberrantly expressed molecules (e.g. CDK4, MUM 1, beta-catenin) (Castelli C et al 2000).

In melanocytic lesions, the Melan-A staining pattern is similar to S100, but seems to be more specific. In desmoplastic melanomas, however, the variable Melan-1 staining further requires detailed histological examination and the use of the S100 reaction (Orosz Z 1999). Both antibodies (A103 and M2-C10) are also of diagnostic value in recognition of perivascular epitheloid cell tumours (angiolipoma, lymphangioleiomyomatosis and clear cell tumours). Since A103 has the unique property of staining many steroid hormone-producing cells, this antibody is also useful for the recognition of tumours derived from these cells, such as adrenocortical carcinomas (Jungbluth AA 1998). These antibodies can detect Melan-A antigen in formalin-fixed, paraffin-embedded tissues. Thus antibodies (A 103 and M2-C 10) are likely to be included in the routine diagnostic armamentarium of histopathological laboratories in the near future.

The distinction between non-tuberculous mycobacterial lymphadenitis (NTM) and other causes of cervical lymphadenitis is important, as different entities call for different treatments. Despite modern diagnostic techniques for NTM infections their prompt and accurate diagnosis is still difficult.

Authors (Kraus M et al 1999) assessed the value of different histological features in diagnosing clinically suggestive NTM cervical lymphadenitis in cases of granulomatous cervical lymphadenitis.

A rapid and accurate diagnostic procedure for NTM lymphadenitis is not yet available. Therefore in the presence of a suggestive clinical picture of NTM lymphadenitis, Kraus M et al propose four histological features: 1) presence of microabscesses, 2) ill-defined granulomas, 3) noncaseating granulomas and 4) a small number of giant cells. These features were found with significant statistical difference when comparison was made between the NTM group and the tuberculous group.

Classification of renal cell carcinoma (RCC) into specific subtypes has traditionally been based on cytomorphologic features. However recent advances in our understanding of the genetics of RCC have provided fresh impetus towards a combined morphologic and genetic classification of these tumours. Genetic alterations transmitted during cell division are fundamentally involved not only in neoplastic transformation but also in determining the morphologic appearance of RCC (Kovacs G. 1993). Thus conventional RCC composed of clear and /or granular cells is characterised by chromosome 3 short arm deletion while carcinomas with predominant papillary pattern manifest trisomy of chromosome 7and 17, along with loss of Y chromosome. A study was carried out by Iqbal M A (1999) to determine the efficiency of fluorescent in situ hybridization (FISH) technique in characterising various subtypes of RCC based on the presence of specific chromosome abnormalities found in each RCC subtype.

FISH was performed on touch imprint smears from eight renal cell carcinomas histologically confirmed by established criteria.

In the four tumours with histological features of chromophobe renal cell carcinoma (ChRCC), inter phase FISH was performed using centrometric probes for chromosomes 1,2,6,10,12,17,21. All four ChRCC tumours showed one FISH signal corresponding to one copy number for each of these chromosomes. ChRCC is characterised by a compact growth pattern of large tumour cells, having a translucent and reticular cytoplasm and distinct cell borders. Two papillary RCC included in this study showed tristomy 7 and 17, and loss of chromosome Y using corresponding chromosome centrometric probes. Similarly two clear cell RCC showed 3p21.3 signal.

The inter phase FISH technique performed on touch imprint smears was found to be a relatively simple, rapid and reliable method for detecting chromosome abnormalities which are specific for various subtypes of RCC.

The technique known as fluorescent in situ hybridisation or FISH, relies on the unique ability of a portion of single-stranded DNA, known as a probe, to anneal or hybridise with its complimentary target sequence where ever it is located in the genome. The probe is conjugated with a fluorescent label allowing it to be visualised under ultraviolet light.

Different types of chromosome-specific probes can be used. Some are specific for the centromere of a particular chromosome. Alternatively probes can be prepared from a whole chromosome. FISH has a particular advantage in that it can be applied during inter phase.

Extramammary Pagets disease (EPD) most commonly occurs on the female external genetalia and rarely in the perianal, male external genetalia, axilla, and external auditory canal (Chanda JJ 1985). Perianal Pagets disease accounts for approximately 20% of EPD cases.

Perianal Pagets disease is a heterogenous entity. The high frequency of associated underlying malignancies and resultant poor clinical outcomes highlight the importance of an aggressive search for a second malignancy. In some cases, perianal Pagets disease merely represents a cutaneous manifestation of an underlying rectal adenocarcinoma secondarily affecting the skin.

Extramammary Pagents disease (EPD) typically presents in elderly patients as a pruritic red or white, crusted patch in the same distribution as apocrine glands. The clinical and microscopic appearances of EPD are virtually identical to that of mammary Pagets disease (MPD). Despite their similarities, MPD and EPD differ with respect to histogenesis, staining characteristics, and relative frequencies of underlying malignancies. EPD is considered as an in situ adenocarcinoma arising within the epidermis of the skin in most cases, while MPD represents a cutaneous manifestation of an underlying mammary carcinoma in all cases. EPD may also represent direct extension of an underlying carcinoma of skin appendages, gastrointestinal or genitourinary track. Other cases represent synchronous or metachronous carcinomas, one arising in the skin and another arising in the internal organs.

In contrast to MPD, the Pagets cells of EPD are characterised by strong cytoplasmic PAS, mucicarmine and Alcian blue positivity, indicating the presence of mucoolysaccharides, which accounts for their clear, vacuolated cytoplasm. EPD is CEA-positive in 93 100% of cases, while MPD is frequently negative for CEA, PAS, mucin and Alcian blue stains (Battles OE, Page DL et al 1997). Since both MPD and EPD are S-100 protein-negative, this characteristic is useful in distinguishing Pagets disease and pagetoid Bowens disease from in situ melanoma.

Insulin-like growth factor (IGF) I and II are involved in the regulation of proliferation, differentiation and metabolism of numerous cell systems. Insulin-like growth factor binding proteins (IGFBPs) comprise a family of six homologous proteins that bind IGF-I and IGF-2 with high affinity and specificity.

The actim PROM test (Medix Biochemia OY AB Finland) is a rapid dipstic test based on detection of insulin-like growth factor binding protein-1 (IGFBP -1) in a vaginal fluid sample. As membranes rupture, amniotic fluid escapes into the vagina. IGFBP-1 is present in amniotic fluid at a very high concentration - there is 100-1000 times more IGFBP-1 in amniotic fluid than in maternal serum. On the other hand no IGFBP-1 is present in urine or seminal plasma that may contaminate a vaginal sample. Detection of IGFBP-1 in a vaginal sample is therefore an accurate indication of presence of amniotic fluid as a consequence of membrane rupture.

The test is based on immunochromatography and involves two monoclonal antibodies to human IGFBP-1. A specimen of vaginal secretion is taken with a dacron swab during speculum examination and extracted with specimen extraction solution. The presence of IGFBP-1 in the solution is detected by using a dipstic.

Presenters at American Association of Clinical Chemistrys (AACCs) Lab 2002 conference, held in New York City in March 2000, identified trends that labs will either see continuing into the future or will see emerging in the next few years. Heres what they said labs should expect:

• More movement toward total automation in the lab and smaller laboratory systems.
• More consolidation of testing, with haematology, chemistry, and immunochemistry on a single platform.
• Customised patient therapy, leading to more sophisticated programmes in therapeutic drug monitoring.
• Greater reliance on informatics and imaging software.
• Non-invasing testing for analytes such as bilrubin, glucose, haemoglobin and complete blood counts (CBCs).
• More ex situ testing, i.e. hair, breath, saliva, and tear testing .
• "Smart" computer systems on analysers that will, for example, automatically page physicians with the test result.
• More plasma and whole-blood testing.
• Test ordering through web browsers.
• Patients ordering their own tests.
• The digital virtual laboratory, which is validated and managed centrally, but does its testing in a multitude of places - Lab-0n-a-chip technology coming in its own.

West Nile virus (WNV) belongs to the genus Flavivirus. The virus presents with a nondescript febrile illness associated with rash, arthritis, lymphadenopathy and meningoencephalitis. Infections are reported in Asia, Africa and Europe. In 1999, West Nile Virus was described for the first time in the United States in New York.

At present, diagnosis of infection with WNV is based on serology, virus isolation and identification, or molecular analysis of brain materials in a few reference laboratories. These methods of diagnosing WNV take 3 to 4 days.

Recently Briese T, Glass W G, Lipkin W I (2000) established a sensitive and specific real-time PCR method for detection of West Nile Virus.

Real-time PCR is a method whereby the presence of a target sequence is detected by continuous measurements of a fluorescent dye label generated during the course of amplification. This test can detect minute amounts of WNV genetic material in samples of CSF from infected patients. This procedure, which can be conducted in a standard microbiological laboratory, allows clinicians to make a diagnosis within 5 hours of receiving the sample. This rapid diagnostic method is expected to allow physicians to offer early intervention with antiviral therapy to patients who test positive for WNV.

Epstein-Barr virus (EBV), a DNA virus, is a B-lymphotropic herpesvirus and is the most common cause of infectious mononucleosis. EBV is one of the most successful viruses, infecting over 90% of humans and persisting for the lifetime of the person (Cohen J 2000).

Replication of EBV in B lymphocytes and the resulting lymphoproliferation usually inhibited natural killer (NK) and T-cell responses, but in patients who have congenital or acquired cellular immune deficiencies, fatal disseminated infection or B-cell lymphomas can occur.

Central nervous system (CNS) complications of EBV infection include aseptic meningitis, encephalitis and Guillain-Barre syndrome. Rare complications include splenic rupture, thrombocytopenia, agranulocytosis, haemolytic anaemia, orchitis, myocarditis and haemophagocytic syndrome.

Haemophagocytic syndrome, which is also called Histiocytosis, is associated with exaggerated activity and proliferation of macrophages or histiocytes. Many infections can induce this disease including viruses. Different viruses can be responsible, but EVB is the leading cause among them, especially in children. The liver, as many other organs in the body including the spleen, lymph nodes and even the retina can be influenced by a significant degree of Haemophagocytosis. Ganciclover can be of great help in eradicating the virus and treating the disease, provided that it is given for a long enough period (Ali H, et al 2000).

EBV causes several other distinct disorders including the X-linked lymphoproliferational syndrome (also known as Duncan syndrome). This syndrome is an inherited condition of males who are unable to control infection with EBV. These patients die of infectious mononucleosis or of malignant lymphoma, post-transplantation lymphoproliferative disorders, Burkitt lymphoma, nasopharyngeal carcinoma and undifferentiated B-cell lymphomas of the CNS. EBV virus is capable of immortalization of B cells. This can result in neoplasia.

In most cases of Hodgkin lymphoma, Hodgkin cells can be shown to have EBV incorporated in their genome. It is likely that the transforming effects of EBV, incompletely handled by primitive lymphoid cells are responsible for many cases of Hodgkin lymphoma.

EBV was found to be associated with non-Hodgkins lymphoma and oral hairy leukoplakia in patients with AIDS. EBV DNA has been detected in lymphoid interstitial pneumonitis (LIP). LIP occurs primarily in children infected with HIV.

EBV-associated lymphoproliferative disorders result in a number of complex syndromes associated with immunosuppression, including HIV infection, and occur in approximately 2% of graft recipients. The highest incidence occurs after heart transplantation.

The chronic fatigue syndrome is not related to EBV infection. A small group of patients with recurring or persistent syndromes have abnormal serologic test results for EBV, as well as for other viruses.

EBV may play an indirect role in activating the underlying process of multiple sclerosis (MS) according to data from (Wandinger KP et al 2000). Authors also note that exacerbations are significantly reduced in MS patients treated with acyclovir.

Isolation of EBV from oropharyngeal secretions is possible, but the virus isolation does not necessarily indicate acute infection. Therefore, diagnosis depends on serologic testing. Nonspecific tests for heterophil antibody, including Paul Bunnel test and slide agglutination reaction are most commonly available. The results of these tests are often negative in infants and children younger than 4 years of age with EBV infection, but they identify approximately 90% of cases (proven by EBV-specific serology) in older children and adults. An absolute increase in atypical lymphocytes in second week of illness with infectious mononucleosis is a characteristic but not a specific finding.

Multiple specific serologic tests for EBV are available in diagnostic virology laboratories. The most commonly performed test is for antibody against the viral capsid antigen (VCA). Since IgG antibody against the VCA occurs in high titres early after onset of infection, testing of acute and convalescent serum samples for ant-VCA may not be useful for establishing the presence of infection. Testing for IgM ant-VCA antibody and for antibodies against early antigen (EA) is useful for identifying recent infections. Since serum antibody against EBV nuclear antigen (EBNA) is not present until several weeks to months after onset of infection, a positive anti-EBNA antibody test excludes acute infection. Serologic tests for EBV are particularly useful for evaluating patients who have heterophil-negative infectious mononucleosis.

The human papillomavirus (HPV) has been clearly established as the primary cause of cervical cancer in nearly all cases (Walboomers JJM et al 1999). Thus it should not be surprising that testing for HPV should have a role in measures aimed at control of this disease. The ultimate goal must be eradication of HPV by vaccination, but a more immediate prospect is the detection and monitoring of the virus as a part of the screening and the diagnostic process. Testing for HPV could have three potential roles: triage of patients with atypical squamous cells of undetermined significance (ASCUS) and low-grade cervical smear; surveillance of high-grade cervical intraepithelial neoplasia and localised (micro) invasive disease after treatment; and primary screening - either alone or in combination with cyrology (Cuzick J 2000).

A recent study conducted by the Imperial Cancer Research Fund demonstrated that testing of HPV is a more accurate method of detecting cervical cancer than the Pap smear (Cuzick J et al 1999).

The study evaluated the role of HPV testing as an adjunct to cytology in women aged 35 or over, and investigated a total of 2988 women recruited from 40 medical practices. The researchers propose that a combined screening test offers the possibility of greater protection and / or longer screening intervals, which could reduce the overall cost of the screening program.

A DNA-based test for HPV, manufactured by the company Digene, is reported to up to 90 to 95% of high-grade cervical cancer. The Pap smear, on the other hand, may miss 20-30% of cervical cancers and their premalignant lesions. Studies in progress should progress whether or not supplementing Pap smear with HPV testing. This not only prevents women with treatable disease being missed, but also allows smears to be done less frequently, thereby reducing the cost of screening. However, many women carry HPV without ever developing cervical cancer, and there is a danger that a screening test based on HPV test alone could cause undue anxiety for the participant.

In recent years, there has been a rapid progress in HPV, vaccine research, and animal models indicate that the development of both preventive and treatment vaccine are possible.

During 1999 three reports described a new form of encephalitis in a pig farm and abattoir workers in Malaysia and Singapore which was found to be caused by a novel paramyxovirus given the name Nipah virus (NV). Between February and June 99 a total of 110 patients were admitted to the University of Malaya Medical Centre with suspected NV infection which was proved in 94, 91 of whom had encephalitis. The mean age of patients with NV infection was 37 (13-68), 82% were male and 93% had occupational exposure to pigs or their carcasses (Goh KG et al 2000).

CSF white cell counts and protein levels were usually elevated. Thirty patients died, then fifty recovered completely, and 14 had persisting neurological damage.

NV causes severe encephalitis with prominent brain stem involvement. Case fatality in this hospital was 32%, and 22% of survivors were neurological impaired.

Rift Valley Fever (RVF) is a disease that primarily affects animals, but occasionally causes disease in humans. RVF affects livestock including cattle, buffalo, sheep and goat. It is named after a trough stretching 4000 miles from Jordan through eastern Africa to Mozambique.

The incubation period ranges from 2 to10 days. In most cases, RVF is a self-limited febrile illness. Occasionally, haemorrhagic fever with chock and icterus, encephalitis or retinitis develops.

RVF occurs throughout sub-Saharan Africa, and has caused epidemics in Egypt in 1977 and 1993 to 1996. In late 1997, after exceptionally heavy rains, an epidemic resulted in the deaths of at least 300 people and large number of animals in remote parts of Kenya and Somalia. In September 2000, RVF was for the first time reported outside of the African continent. Cases were confirmed in Saudi Arabia and Yemen.

This virgin-soil epidemic in the Arabian Peninsula raises the threat of expansion into other parts of Asia and Europe. Thus it appears that RVF is an emerging infectious disease (WHO Fact sheet 207,2000).

RVF virus is a member of the phlebovirus genus, one of the five genera in the family of Bunyaviridae. It is a single-stranded RNA virus. It is an arthropod-borne virus and is transmitted from domestic livestock to humans mainly by the Aedes and Culex mosquitoes. It can also be transmitted by aerosol and by direct contact with infected fresh animal carcasses.

In laboratory animals Ribavirin has shown promise in the treatment of RVF. There are effective vaccines to treat animals. As far as the human vaccine, there is one. It is produced by the U S Army. At present it is only used for researchers and veterinarians going to the infected areas.

Ebola virus infection is found in Africa transmitted to humans from primates from the putative rodent reservoir host. The virus causes an acute haemorrhagic disease with high fever, bleeding, toxicity, and shock; the mortality is high. Infection can be transmitted by close contact, especially in the hospital environment.

Scientists at the National Institutes of Health (NIH) have identified a protein that appears to be the key to the uncontrollable bleeding that is a hallmark of Ebola virus infection.

The investigators found that one of the Ebola viruss seven gene products, a glycoprotein (GP) that extends out from the surface of the virus, is apparently responsible for the viruss toxic effects. In studies of isolated blood vessels, GP caused the vessels to become leaky because of massive loss of the endothelial cells that line them. However, GP from a monkey strain of Ebola virus that does not cause illness in humans destroyed only monkey blood vessels, not human ones.

Further studies revealed that a specific region of the GP is responsible for its toxic effects. When the investigators tested synthetic forms of GP lacking this region, the protein no longer ravaged blood vessels.

Whipples disease is characterised by infiltration of intestine and other tissues by foam cells, full of Pas positive, diastase-resistant bodies. They contain large numbers of bacilli known as Whipples bacilli.

Whipples bacillus was uncultured until last year, but a molecular genetic approach has been used to identify the organism, comparing its genetic makeup with other bacilli. By this method the bacillus has been classified with actinomycetes bacillus and is named as Tropheryma whippelli.

Now workers in France have grown the bacillus. They obtained aortic valve tissue and vegetations removed surgically from a patient in Canada. Histologically specimens showed the evidence of Whipples disease. A bacterium was cultured by inoculation in human fibroblast cell line (HEL) and subcultures were established (Raoult D et al 2000). The patients serum contained antibodies against the bacillus and so did the sera of other patients of Whipples disease, but not those of controls. Antibodies were raised by injecting mice with the organism and these were used for immunohistochemical detection of the organism in the patients aortic valve tissue. RNA analysis of the cultured bacilli showed sequences identical with those previously recognised in the Tropheryma whippelii the Whipples bacillus is a gram-positive organism.

The clinical features of the Whipples disease include fever, weight loss, diarrhoea, lymphadopathy and polyarthritis. Some patients may develop myocarditis, pericarditis, endocarditis and some have central nervous system involvement. The cultivation of the Whipples bacillus may make it possible to develop a serological test for diagnosis of the disease (Swartz MN 2000). The Whipples bacillus is infectious, but not contagious and responds very slowly to antibiotics.

Chlamydia pneumoniae is a species of Chiamydia that is antigenically, and morphologically distinct from other Chlamydia species. In addition to acute respiratory tract disease, some investigators have associated C pneumoniae with atherosclerotic cardiovascular disease. This association is based on the increased frequency of serum antibodies in the patients compared with controls, the detection of antigen or DNA in atheromatous plaques, and the production of arterial lesions in experimentally infected animals. Small human trials, demonstrated that treatment high-risk patients with microlides decrease the risk of subsequent cardiovascular events. Large, prospective randomized trials are underway to further explore this association and to determine whether the treatment is beneficial (Hammerschlag MR 2000). Workers in Denmark (Lindholt JS 1999) have related evidence of C pneumoniae infection to progression of small abdominal aortic aneurysms.

Other investigators have associated C pneumoniae with asthma, Alzehiemer disease, multiple sclerosis, Kawasaki disease and otitis media but the evidence supporting any of these associations is limited.

Drug-resistant tuberculosis (TB) was first observed in 1948, subsequent to the first trial of streptomycin for TB treatment. Ever since then, drug-resistant TB has been recognised to occur as a result of sub-optimal treatment. In recent survey of 35 countries, 12.6% of M tuberculosis isolates were resistant to at least one drug, and 2.2% were resistant to both the primary drugs used to treat TB isozniazid and rifampicin. Further almost 80% in Philippines in one community-based study of M tuberculosis resistant to at least one drug at the beginning of therapy.

The recent battle against TB has been characterised by a rise in the number of cases of infection with multidrug-resistant Mycobacterium tuberculosis (MDR-TB) as the result of poorly run tuberculosis programs.

Globally, available data on the incidence and prevalence of drug-resistant TB is meagre. The acquisition of resistance to anti-tuberculous drugs has compromised treatment and control of programs. As a part of the resurgence of TB, a number of large dramatic hospital-acquired outbreaks of highly multi-drug-resistant (MDR) strains of M tuberculosis, referred to as the W strain, have occurred in institutional settings such as hospitals and correctional facilities in New York (Salmon N, Parman DC 1999).

Recent data suggest that the highly resistant strains may be derived from the ancestral susceptible W strain that is predominant in many parts of Asia. Although a number of these outbreaks were associated with very high mortality, they were brought under control by enhanced recognition of TB cases, the routine use of expedited susceptibility testing infection control programs and DOT.

MDR-TB is caused by a strain of M tuberculosis that is resistant to two or more antituberculosis drugs. Many investigations require that the strain be resistant to two or more first-line antituberculous medications, or at least resistant to isoniazid and rifampicin.

A drug-resistant isolate can be further categorized as exhibiting either primary or secondary resistance. In primary resistance the patient from whom the isolate is obtained has never received that specific anti-TB drug. In secondary resistance, the patient has previously been treated for TB with a specific drug or drugs, to which the isolate is resistant.

Resistance mechanisms appear to be encoded on genes. The mechanisms for resistance to different classes of drugs do not appear to be linked genetically. The observation accounts for the efficiency of combination chemotherapy in TB.

A significant factor contributing to the spread of MDR-TB has been a delay in obtaining laboratory confirmation of infection and data on drug susceptibility, which in turn has led to delays implementing proper therapy and infection control procedure.

In view of delays in results using the old systems of culture and susceptibility, myobacteriology laboratories have undergone substantial improvement in the past few years. The Center for Disease Control (CDC) in the USA has recommended changes in equipment, fluorescent staining of specimens for acid-fast bacilli, broth-based radiometrics, the BACTEC methods for culture and susceptibility studies, and molecular genetic probe or newer biochemical techniques (BACTET C- NAP or liquid chromatography) for identification.

The BACTEC system has decreased the interval from submission of specimens to reporting to the results to physicians take approximately 3 weeks. Drug susceptibility testing requires an additional 7 days.

Polymerase chain reaction (PCR) and Southern hybridization are helpful in the rapid diagnosis of mycobacterial infection. New molecular methods for rapid susceptibility testing are now available.

M tuberculosis can be type by an internationally standardized restriction fragment polymorphism (RFLP) method (Pickering LK 2000).

Treatment for MDR-TB is guided by susceptibility tests and the pattern of an epidemic strain.

The American Thoracic Society and CDC Tuberculosis Statement Committees recommend the use of four-drug daily regimens (isoniazid, rifampicin, pyrazinamide, ethambutol or streptomycin) for one or two months, with subsequent administration of appropriate drugs to complete the course of therapy in areas endemic for MDR-TB. Directly observed therapy (DOT) is critical to cure cases of drug resistant tuberculosis and to prevent the emergence of further resistance (Pilhew J A 1998).

Mycobacterium ulcerans belongs to the MOTT (Mycobactria Other Than Tuberculosis bacilli) group of bacilli. It has several unusual features. It grows at a restricted range of temperature from 240C to 310C, is biochemically unreactive, and has a marked tendency to clump, especially in fibrous bundles. It is one of the few mycobactria that is able to produce lethal disease in mice.

Mycobacterium ulcerans causes cutaneous infections in persons living in tropical countries (Africa, Australia, Asia and South America). Infection follows percutaneous inoculation and presents as a painless erythematous nodule, most frequently on leg, which undergoes central necrosis and ulceration. The lesion, often called a Buruli ulcer after the region in Uganda where most cases are reported, has a characteristic undermined edge, gradually expands, and may result in expansive soft tissue destruction with secondary bacterial infection. The lesion may heal slowly over 6-9 months or may continue to spread, leading to deformities and contractures (Scherpbier R, Asiedu K 2000).

Histologically, there is central necrosis, originating in the interlobular septa of the subcutaneous fat, which is surrounded by granulation tissue with giant cell; but there is no typical caseation necrosis or tubercles. Acid-fast bacilli can always be demonstrated in tissue sections of the lesion.

The treatment of the choice is simple excision of the early lesion; when ulceration has developed, wide excision and skin grafting are necessary. Local heat therapy, hyperbaric oxygen, and chemotherapy with rifampicin and trimethoprim-sulfamethoxazole have been shown to be of some value.

Escherichia coli ( E. coli) strains of biological significance to humans can be broadly classified on the basis of both genetic and clinical criteria into 3 major groups: commensal strains, intestinal pathogenic (enteric or diarrhoeagenic) strains, and extraintestinal pathogenic strains.

Commensal strains of E.coli: typically lack the specialized virulence traits that are present in intestinal and extraintestinal pathogenic strains.

In contrast to commensal strains, intestinal pathogenic strains of E. coli are rarely encountered in the fecal flora of healthy hosts and, instead, appear to essentially obligate pathogens, causing gastroenteritis or colitis when ingestion in sufficient quantities by a naïve host. Six distinct pathogenic categories (pathotypes) of intestinal pathogenic strains of E. coli are currently recognised: enterotoxigenic (ETEC) Shign-toxin producing/ enterohaemorrhagic (STEC/EHEC), enteropathogenic (EPEC), enteroinvasive (EIEC), enteroaggregative (EAEC) and diffusely adherent (DAEC). Despite their ability to cause enteric disease, these strains are mostly incapable of causing disease outside the intestinal tract.

Extraintestinal infections (EIs) due to E.coli are common in all age groups and can involve almost any organ or anatomical site. Current understanding of the pathogenesis of EIs due to E.coli is derived almost entirely from analysis of isolates from UTI s, bacteraemia, and neonatal meningitis. As a group these strains are epidemiologically and phylogenetically distant from both the commonsal and intestinal pathogenic strains; thus they have been classified as extraintestinal strains of E. coli. In the past, the ability of strains to asymptomatically colonize the human intestinal tract caused considerable uncertainty about whether the strains actually were pathogens or merely opportunistic commonsal strains.

This question has been largely resolved in favour of the "pathogens" hypothesis. Unlike most commonsal E. coli strains, EI isolates typically are derived from phylogenic group B2 or D and possess genes for various combinations of adhesins (e.g. P and S fimbriae), iron-acquisition systems (e.g. aerobactin) and toxins (e.g. haemolysin), which collectively are now regarded as extraintestinal virulence factors. Animal model experiments have confirmed the enhanced virulence of EI isolates, compared with that of commonsal strains, and the contribution of extraintestinal; virulence factor to pathogenicity (Picard B et al 1999). Genes for multiple virulence factors often are present together on large blocks of chromosomal DNA, termed "pathogenicially-associated islands" (PAIs), which are analogous to (but distinct from) the diarrhoea-associated PAIs that are present in many intestinal pathogenic E.coli.

By analogy to the acronyms currently used for various intestinal pathogenic E.coli types Russo and Johnson (2000) propose the acronym "EXPEC" (extraintestinal pathogenic E.coli) as a new inclusive designation for certain strains of E.coli that cause extraintestinal infections (EIs). Operationally, a clinical isolate of E.coli would be defined as an ExPEC strain if it possesses recognized extraintestinal virulence factors or if it demonstrated enhanced virulence in an appropriate animal model of EI (Russo TA, Johnson JR 2000).

Each pathotype of E Coli strains has a distinct set of somatic (O) and flagellar (H) antigens. Some clinical syndromes are associated with different O and H antigens e.g. E.coli O157:H7. Haemolytic uraemic syndrome is the most important complication of infection by verotoxin producing E.coli O157:H 7.

Distinguishing pathogenic E. coli from strains that are a part of the normal stool flora is not possible by usual clinical microbiologic procedures. E.coli O157:H7 is an exception: it can be screened by using Mac Conkey agar with sorbitol substitute by lactose. Most E.coli rapidly ferment sorbitol, but O157:H7 strains do not.

Methicillin-resistant S aureus (MRSA) accounts for one quarter of hospital-acquired S aureus infection. Screening for MRSA from routine swab samples, can now be performed more easily, using a new growth medium, Oxacillin Resistance Screening Agar Base (ORSB) (OXOID Ltd). It is a selective medium, which produces intense blue colonies of presumptive MRSA against a clear background for easier detection. Based on traditional Mannitol Salts Agar, the medium has been optimised for growth of low numbers of MRSA and incorporates aniline blue as an indicator dye to detect mannitol fementation produced by this organism. The addition of ORSAS selective supplement continuing oxacillin and polymyxin B to the agar base inhibits the growth of methicillin sensitive Staphylococcus aureus and other halophilic micro-organisms such as proteus spp.

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