Bacterial infections Medical Assignment Help

Gram-positive cocci

Staphylococci are aerobic, facultatively anaerobic,  rampositive cocci. They contain a number of cellular antigens and produce enzymes such as coagulase as well as toxins such as enterotoxin. Their ogenicity correlates most closely with the production of the oagulase enzymes. Three pathogenic species are recognized. Staph. aureus is coagulase positive and Staph. epidermidis and Staph. saprophyticus are coagulase negative. Staphylococci are part of the normal micro flora of the human skin, the upper respiratory tract, especially the nasopharynx, and the intestinal tract. Twenty-five per cent of the population are permanent carriers of Staph. au reus.

Immunization schedule recommended in the UK and developing countries (WHO).

Immunization schedule recommended in the UK and developing countries (WHO).

Approximately 20% of all human staphylococcal infections are autogenous. Transmission is most frequently by direct contact with an infected individual but may be airborne or via fomites. Several predisposing host factors have been identified.

The organism can cause a wide clinical spectrum of diseases. These are usually localized, but infection may spread, resulting in bacteraemia or metastatic infection. shows a list of conditions due to Staph. aureus; a few of these will be considered below.


Acute osteomyelitis is almost always due to staphylococcal infection. It occurs predominantly in males between the ages of 3 and 12 years, usually affecting the lower limbs. A history of trauma is often present. The diaphysis is initially involved, with subsequent spread of the infection to the periosteum and the subcutaneous tissues. Signs of inflammation are present. The child is usually irritable and febrile. There is leucocytosis and blood cultures
are positive in about 75% of patients.Osteomyelitis involving the vertebrae occurs in adultsover 50 years of age. The onset is insidious, with pain; often there are no other features of infection.
Radiographs are usually normal in the first week after onset in both varieties of osteomyelitis.

Host factors that increase susceptibility to staphylococcal infections (predominantly Staphylococcus aureus).

Host factors that increase susceptibility to
staphylococcal infections (predominantly Staphylococcus

Food poisoning

his results from ingestion of food contaminated with preformed heat-stable enterotoxins A, B, C, D and E in varying combinations. Staph. aureus accounts for approximately 5% of all food poisoning in the UK. Contamination is usually from an infected individual. Foods such as canned foods, processed meats, milk and cheese favour the growth of Staph. aureus. The illness is manifest within 6 hours of ingestion of contaminated foods and affects close to 100% of individuals who have eaten such foods. In contrast to food poisoning due to other organisms, staphylococcal food poisoning is characterized by the presence of persistent vomiting. Fever, when present, is usually below 38°C. Abdominal discomfort, diarrhoea or dysentery may be present. No specific reatment is necessary as the illness is short-lived (12- 24 hours); however, supportive treatment with fluids and electrolytes is occasionally indicated. Acute staphylococcal enterocolitis This presents as a more severe fulminant clinical syndrome, typically following broad-spectrum antibiotics. Pseudomembranes may be seen at sigmoidoscopy.

Clinical conditions produced by Staphylococcus aureus.

Clinical conditions produced by Staphylococcus

Toxic shock syndrome

Staphylococci that produce the toxic shock syndrome toxin-I (TSST-l) are responsible for this syndrome. TSS is seen most frequently in menstruating women below the age of 30 years who use high absorbancy polyacrylatecontaining tampons. However, it can occur in other situations including the use of female barrier contraceptive and men and children are not exempt. It is characterized by the abrupt onset of fever, a diffuse macular erythema, vomiting, diarrhoea, severe myalgia and shock. Blood cultures are negative and anti-TSST-l antibodies are present in low concentrations in serum. Treatment is supportive. Antibiotics are usually given, although the syndrome is produced by the exotoxin. Mortality is about 10%.

Scalded skin syndrome

Scalded skin syndrome is caused by staphylococci which elaborate the toxin exfoliatin. It is seen in children under 5 years of age and is characterized by a painful macular skin rash followed by bullae and generalized shedding of  the epidermis.

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