Haemophilus Haemophilus spp. are fastidious Gram-negative coccobacilli that colonize mucosal surfaces. H. influenzae and H. ducreyi are the main pathogenic species. Haemophilus Influenzae Haemophilus influenzae expresses an antiphagocytic polysaccharide capsule…
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…
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…
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…
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…
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…
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…
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…
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,…
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…
