Medical Microbiology and Infection

Immunization (Medical Microbiology and Infection)

Immunization Vaccination has virtually eradicated many infectious diseases (e.g. polio and diphtheria) and has made smallpox extinct. Immunization may be achieved passively, by administration of an immu-noglobulin preparation, or actively, by vaccination. Passive immunization Immunoglobulin, prepared from pooled plasma, may provide short-term protection against infections, such as measles, if given after exposure. This is used […]

Emerging infections

The incidence of an infection varies with changes in pathogen virulence and in the immunity of the host population. Many infectious diseases have a characteristic pattern. For example, meningococcal infection in the ‘meningitis belt’ of Africa is endemic (cases occur all of the time), but the incidence of the disease will sometimes rise to 1000 […]

Staphylococcus (Bacteriology) (Medical Microbiology and Infection)

Staphylococci are part of the normal flora and important human pathogens. There are more than 26 species but only a few are pathogenic. Staphylococcus aureus is the most invasive species, which can be differentiated from other species by its possession of the enzyme coagulase. Staphylococcus aureus Asymptomatic carriage of S. aureus is found in up […]

Streptococcal infections (Bacteriology)

The main characteristics of streptococci include the following. • They are Gram-positive cocci arranged in pairs and chains. • They are fastidious facultative anaerobes. • They require rich blood-containing media. • They may be cultured from the site of infection (throat, wound, etc.) or in blood cultures. • Colonies are distinguished by haemolysis: complete (β) […]

Streptococcus pneumoniae, other Gram-positive cocci and the alpha-haemolytic streptococci (Bacteriology) (Medical Microbiology and Infection)

Streptococcus pneumoniae Streptococcus pneumoniae (or pneumococcus) is a Gram-positive coccus seen in pairs, which is typically α-haemolytic, but can be variable. Pathogenesis Streptococcus pneumoniae has a polysaccharide capsule that protects it from phagocytosis. There are over 90 highly antigenic capsular serotypes and antibodies to specific types are protective. Pathogenicity features include: • pro-inflammatory cell wall […]

Listeria, Bacillus, Corynebacterium and environmental mycobacteria (Bacteriology) (Medical Microbiology and Infection)

Listeria Listeria are important Gram-positive organisms that can grow at low temperatures (4-10 °C); Listeria monocytogenes is associated with human disease. Epidemiology Listeria spp. are found in soil or animal faeces and can contaminate foodstuffs. Infection follows consumption of contaminated food; inadequately pasteurized foods and contaminated foods stored in the fridge are at risk. Clinical […]

Diphtheria, tetanus and pertussis (Bacteriology) (Medical Microbiology and Infection)

These three organisms are from widely differing taxonomic groups but are linked by being important diseases of childhood that are mediated by toxins and can be prevented by childhood immunization. Corynebacterium diphtheriae Pathogenesis Diphtheria is caused by Corynebacterium diphtheriae that contain a bacteriophage encoding diphtheria toxin. The toxin kills cells by interrupting protein synthesis, acting […]

Pathogenic mycobacteria (Bacteriology) (Medical Microbiology and Infection)

Mycobacteria possess a lipid-rich cell wall that retains some dyes, resisting decolourization with acid (hence they are known as acid-fast). There are more than 50 species; although most are environmental organisms that rarely cause human infection. Mycobacterium tuberculosis Epidemiology and pathogenesis Tuberculosis is spread from person to person by the airborne route. In childhood, the […]

Clostridium (Bacteriology) (Medical Microbiology and Infection)

Clostridium spp. are anaerobic spore-forming organisms that are able to survive well in the environment. Their normal habitats are soil, water and the intestinal tract of humans and animals. Only a few of the 80 species are human pathogens. Toxin production is the main pathogenicity mechanism. Clostridium difficile Pseudomembranous colitis, an acute inflammatory diarrhoeal disease, […]

Non-sporing anaerobic infections (Bacteriology)

Non-sporing anaerobes form the major part of the normal human bacterial flora, outnumbering all other organisms in the gut by a factor of 103. They are also found in the genital tract, oropharynx and skin. Anaerobic sepsis Pathogenesis • Infection with non-sporing anaerobes is usually endogenous. • Normal flora may escape into a sterile site […]