Pathogenic Bacteria to Human PDF

# Pathogenic Bacteria to Human ## Staphylococci - Gram positive cocci, widely distributed in nature - 3 Species of Medical Importance - *Staph. aureus* (Most important) - *Staph. epidermidis* - *Staph. saprophyticus* - *Staph. aureus* is differentiated from others by being coagulase po...

# Pathogenic Bacteria to Human ## Staphylococci - Gram positive cocci, widely distributed in nature - 3 Species of Medical Importance - *Staph. aureus* (Most important) - *Staph. epidermidis* - *Staph. saprophyticus* - *Staph. aureus* is differentiated from others by being coagulase positive, mannitol positive and by causing haemolysis of blood agar. - They are considered to be potentially pathogenic - All Staphylococci are catalase positive which differentiates them from Streptococci that are catalase negative - Staphylococci species produce intracellular pigments (endopigment) that are responsible for the coloration of the organisms ## Infections Caused by Staphylococci - Causes acute toxic food poisoning - Causes the toxic shock syndrome (TSS) - *Staph. epidermidis* - Non-pigmented, non-haemolytic colonies - Most infections are hospital acquired - *Staph. saprophyticus* - Colonies may be white or yellow, non-haemolytic - It causes urinary tract infections ## Streptococci - Gram positive cocci arranged in chains of variable length, widely distributed in nature, non-sporing - An important character for identification of streptococci is the type of haemolysis they produce on blood agar. - Beta haemolytic streptococci produce complete haemolysis with a clear zone around the colonies due to the haemolysin they produce e.g. Strept. pyogenes. - Alpha haemolytic streptococci produce greenish discolouration of blood agar due to production of H₂O₂ that changes haemoglobin to met-haemoglobin e.g. Streptococci viridans and Strept. pneumoniae. ## Diseases Caused by Strept. pyogenes - Cause sore throat, scarlet fever, toxic shock syndrome ## Strept. viridans - They form part of the normal flora of the mouth and throat - Few species are pathogenic (e.g. Strept. mutans, Strept. sanguis, Strept. mitior) causing dental caries, bacteraemia and subacute bacterial endocarditis. ## Streptococcus pneumoniae - **Pneumococci** - Members of the normal flora of the upper respiratory tract - Causes lobar pneumonia and its complications e.g. sinusitis, meningitis - Gram positive cocci arranged in pairs - Alpha haemolysis or greenish discolouration similar to Strept. viridans - Quellung test ## Neisseria - Found in the mouth, throat, pharynx and vagina - Two members, N. meningitidis and N. gonorrhoeae are important pathogens - Gram negative cocci arranged in pairs, oxidase positive - N. gonorrhoeae and N. meningitidis are fastidious and require enriched media for growth - N. meningitidis causes acute epidemic cerebrospinal meningitis - N. gonorrhoeae causes gonorrhoea in adult males, vulvo-vaginitis in young girls - It is a venereal disease i.e. transmitted by sexual intercourse. ## Corynebacterium - C. diphtheriae produces a powerful exotoxin that causes diphtheria in humans - Gram positive rods - Occur as normal flora on the skin and mucous membranes - Non-toxigenic strains are non-pathogenic ## Mycobacterium - Genus Mycobacterium comprises the 'acid-fast bacilli', which are difficult to stain. - They cannot be stained by simple stains due to their high lipid content - Stained by Ziehl-Neelsen stain, they appear as thin pink rods arranged singly or in small groups. - Grow on egg-enriched media such as Lowenstein-Jensen (L-J) medium. - M. tuberculosis and M. bovis are the cause of human tuberculosis - M. tuberculosis infects by the respiratory route through ingestion of infected milk. - M. bovis infects by the oral route through ingestion of infected milk - They grow very slowly, no growth appears before 2-4 weeks incubation at 37°C ## Tuberculin or PPD skin test (Mantoux Test) - This is a delayed hypersensitivity reaction used for diagnosis of tuberculosis. ## Mycobacterium Leprae - M. Leprae causes leprosy in man, which affects mainly the mucous membrane of the nose, skin and nerve fibres. - Leprosy bacillus has not been successfully cultivated on any medium - Lepromin test ## Enterobacteria - Gram negative bacilli found in the colon of humans and other animals, many as part of the normal flora - Family Enterobacteriaceae includes many genera - Pathogenic genera are Shigella, Salmonella, Yersinia and some strains of Escherichia. - Opportunistic pathogens are Klebsiella, Enterobacter, Serratia, Citrobacter, Proteus and Escherichia. - According to their effect on lactose the Enterobacteriaceae are divided to: - Lactose fermenters - Include the genera Escherichia, Klebsiella, Citrobacter and Enterobacter - Lactose non-fermenters - Include the genera Salmonella, Shigella, Yersinia and Proteus. ## Escherichia coli - Normal inhabitants of the intestines of man and animals - E. coli strains causing urinary tract infections produce haemolysis on blood agar - Gram negative bacilli, grow on simple media - Produce rose-pink colonies on MacConkey's medium due to lactose fermentation ## Diseases Caused by E. coli - Commonest cause of urinary tract infections - Cause wound infection, appendicitis, bacteraemia and endotoxic shock - Enteropathogenic E. coli (EPEC) cause gastroenteritis in children - Enterotoxigenic E. coli (ETEC), enteroinvasive (EIEC) and enterohaemorrhagic E. coli (EHEC) O157:H7 cause diarrhoea in all ages. ## Diseases Caused by Klebsiella - K. pneumoniae causes lobar pneumonia in man - Causes urinary tract infection - K. rhinoscleromatis causes rhinoscleroma which is a granulomatous lesion in the nose and throat. - K. oxytoca causes hospital acquired infections ## Salmonella - Gram negative bacilli, non-capsulated - S. Typhi, S. Paratyphi A, B and C cause enteric fever - S. Typhimurium, S. Enteretidis and others cause Salmonella food poisoning or enterocolitis - S. Choleraesuis cause septicaemia with metastatic abscesses - Widal test ## Shigella - Gram negative bacilli, non-capsulated - Members of the genus Shigella cause bacillary dysentery - Manifestations are abdominal pain, fever, diarrhoea with pus, blood and mucous in stools - Infection leads to local ulcers in the intestine ## Proteus - Gram negative bacilli, non-capsulated - Proteus organisms are found in stools of man and animals - Cause wound infection, urinary tract infection and septicaemia (potentially life-threatening infection in which large amounts of bacteria are present in the blood). - Two important species are Pr. mirabilis and Pr. vulgaris ## Pseudomonas - Gram negative bacilli, non-sporing - P. aeruginosa is the commonest human pathogen of the Pseudomonas group - Causes urinary tract infection, wound infection, corneal ulcers in contact lens users, pneumonia and sepsis with ecthyma gangrenosum in the skin - Causes osteomylitis and endocarditis in intravenous drug users ## Vibrios, Campylobacter & Helicobacter - Vibrio cholerae are Gram negative bacilli cause cholera like disease - Campylobacter are small Gram negative rods, C. jejuni causes 95% of campylobacter enterocolitis especially in children - Helicobacter pylori causes gastritis and peptic ulcers - Infection with H. pylori is a risk factor for gastric cancer ## Haemophilus - Gram negative small cocco-bacilli - H. Influenzae is found in normal throats - Capsulated strains cause meningitis and epiglottitis in children - Also causes respiratory disease complications (bronchitis, pneumonia, sinusitis) in patients having viral influenza. ## Clostridium - Gram positive bacilli - Most of the species are found in the intestine of man and animals - C. tetani causes tetanus in man and animals - C. perfringens causes gas gangrene (gas in tissues in gangrene) - C. botulinum causes food poisoning - C. difficile causes enterocolitis