A summary of pharmaceutical microbiology part 1 - bugs

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Presenter: Dr Kieran Hand
Date: 29/03/2010
Target Audience: All

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  • This presentation covers some basic principles of microbiology, common pathogens found in human infections and which antibiotics to use in common infections.
  • There are four main groups of bacteria. This is a major point to remember when selecting an antibiotic – what type of organism has been isolated or what type you expect at site of infection for empirical treatment.
  • Gram staining, although pioneered many years ago, remains as first step in identifying bacteria. Can quickly and easily get essential information to direct empirical treatment of potentially serious infections. Very useful for blood cultures.
  • This slide shows the structural differences between gram-positive and gram-negative cell walls. The gram-positive cell wall is thicker and the gram-negative wall has an outer membrane. These structural differences explain why some antibiotics are active against gram-positive and others against gram-negative as they have different targets within the bacterial cell.
  • Atypical bacteria and mycobacteria are unsuitable for gram staining as they either do not have a cell wall or it does not contain peptidoglycan. The name ‘atypical’ refers to the fact they cannot be gram-stained or cultivated using standard bacteriological media. Most bacteria can be identified in this way. With the exception of Chlamydia, these organisms are relatively rare in the UK.
  • This slide shows the four main types of organisms and examples within each group. They are grouped according to their shape and whether gram-positive or gram-negative. Anaerobic bacteria are distributed within 3 of the 4 groups.
  • Specific organisms tend to be found in specific areas of the body. This knowledge allows infections to be treated empirically if the site of infection is known. If the site of infection is unknown then a broad spectrum agent or a combination or two or more narrow spectrum agents may be required.
  • This slide shows the targets within bacterial cells for the various types of antibiotic.
  • Staph. aureus is a common skin commensal. Usually skin provides a protective barrier so organisms remain on the skin surface. Breakdown of this barrier can lead to infection of the skin and/or soft tissues. Less commonly other sites may become infected by Staph. aureus e.g. pneumonia, endocarditis, septicaemia, gastroenteritis. Resistant strains (MRSA) account for about 40% of cases in UK.
  • Other staphylococci may be found on skin or mucous membranes. Infections due to S. epidermidis are often resistant to flucloxacillin and other agents such as vancomycin may be required. S. saprophyticus is usually sensitive to most antibiotics routinely used for UTI e.g. trimethoprim, nitrofurantoin .
  • There are 3 commonly enconutered Streptococci species. Strep. Pneumoniae is major cause of otitis media in children and community acquired pneumonia. These infections are often preceded by a respiratory viral infection e.g. cold.
  • Group A Strep. is causative organism of ‘Strep. Throat’. This infection associated acute pharyngitis can lead to serious complications such as scarlet fever and rheumatic fever.
  • Group B Strep. is common cause of septicaemia in neonates. Prophylaxis is administered to mothers tested as positive for group B Strep. on vaginal swabs and may be administered to infants post-partum. Group B Strep. can also cause pneumonia and septicaemia in immunocompromised adults.
  • Atypical bacteria are obligate intracellular parasites – small cells with reduced genetic material unable to survive on their own. This is significant as poses problems getting an antimicrobial to the organism – needs to penetrate the host cell for activity. Mycoplasma may be caustive organism in community acquired pneumonia. Patients admitted to hospital treatment given dual empirical therapy including a macrolide to cover for possible mycoplasma infection.
  • Patients with Legionaires disease present with symptoms of severe pneumonia but may also have other symptoms such as diarrhoea, nausea, vomiting. Confirmation of diagnosis carried out by specialist laboratory so early empirical treatment including a macrolide is essential. Legionella can also cause Pontiac Fever – a mild influenza like illness which resolves without treatment in 2-3 days..
  • Pneumonia may also be caused by Chlamydia – less common than Strep. Pneumoniae. Chlamydia trachomatis is a genital infection transmitted by personal contact. Women with Chlamydia which is untreated can develop pelvic inflammatory disease. Repeated or chronic exposure can lead to sterility and ectopic pregnancy.
  • Gut coliforms are main cause of UTIs in women and major cause of diarrhoeal illness. Resistant strains of E. coli are increasing and UTIs may require to be treated with broader spectrum agents. Organisms such as Serratia are inherently resistant to many antimicrobials. Other gut coliforms less common cause of UTIs.
  • Haemophilus infections are common but introduction of Hib vaccine has reduced serious infections in children. Moraxella catarrhalis often isolated fro sputum samples in COPD exacerbation.
  • Epithelial lining usually acts as a barrier to Neisseria meningitidis but if barrier breached organisms can get into the bloodstream and meningococcemia can result. If the blood-brain barrier is crossed then meningitis can occur. Ceftriaxone or cefotaxime are used to treat meningitis. Neisseria gonnorrhoea is transmitted via sexual contact, or passage of a baby through an infected birth canal.
  • A summary of pharmaceutical microbiology part 1 - bugs

    1. 1. Bugs and drugs A summary of pharmaceutical microbiology
    2. 2. Part 1 <ul><li>Bugs </li></ul>
    3. 3. Four main groups of bacteria (according to sensitivity) <ul><li>Gram positive </li></ul><ul><li>Gram negative </li></ul><ul><li>Anaerobes </li></ul><ul><li>Atypical </li></ul>
    4. 4. Bacterial classification: Gram stain <ul><li>Gram +ve (blue/purple) </li></ul><ul><ul><ul><li>Thick peptidoglycan cell wall retains primary stain </li></ul></ul></ul><ul><li>Gram -ve (pink/red) </li></ul><ul><ul><ul><li>Thin peptidoglycan cell wall does not retain primary stain </li></ul></ul></ul>
    5. 5. Bacteria Structural Differences
    6. 6. Atypical bacteria & mycobacteria: Why no Gram stain? <ul><li>Atypical bacteria </li></ul><ul><ul><ul><li>Chlamydia </li></ul></ul></ul><ul><ul><ul><ul><li>Intracellular pathogen (hard to culture) </li></ul></ul></ul></ul><ul><ul><ul><li>Mycoplasma and Ureaplasma </li></ul></ul></ul><ul><ul><ul><ul><li>Small bacteria that lack a cell wall </li></ul></ul></ul></ul><ul><ul><ul><li>Legionella </li></ul></ul></ul><ul><ul><ul><ul><li>Gram –ve but concentrate intracellularly </li></ul></ul></ul></ul><ul><li>Mycobacteria </li></ul><ul><ul><ul><li>M. tuberculosis, M. avium complex, M. leprae </li></ul></ul></ul><ul><ul><ul><ul><li>Lipid-rich cell wall - NOT peptidoglycan </li></ul></ul></ul></ul>
    7. 7. <ul><li>Gram +ve Cocci (spherical) </li></ul><ul><li>Staphylococci </li></ul><ul><li>Streptococci </li></ul><ul><li>Enterococci </li></ul><ul><li>Peptococci/Peptostreptococci* </li></ul><ul><li>Gram -ve Cocci </li></ul><ul><li>Neisseria meningitidis </li></ul><ul><li>Neisseria gonorrhoea </li></ul><ul><li>Moraxella catarrhalis </li></ul><ul><li>Acinetobacter (coccobacillus) </li></ul><ul><li>Gram +ve Rods </li></ul><ul><li>Clostridia* </li></ul><ul><li>Corynebacteria (diphtheroids) </li></ul><ul><li>Listeria </li></ul><ul><li>Bacillus </li></ul><ul><li>*Anaerobes </li></ul><ul><li>Gram -ve Rods </li></ul><ul><li>Bacteroides* </li></ul><ul><li>Lactose-fermenting coliforms </li></ul><ul><li>E coli, Klebsiella, Enterobacter </li></ul><ul><li>Non lactose-fermenting coliforms </li></ul><ul><li>Proteus, Salmonella, Shigella </li></ul><ul><li>Pseudomonas </li></ul><ul><li>Haemophilus </li></ul><ul><li>Helicobacter, Campylobacter </li></ul><ul><li>Legionella </li></ul>
    8. 8. Generally Found…….. Aneorobes Mouth, teeth, throat, sinuses and lower bowel Abscesses Dental infections Peritonitis Appendicitis Gram positive Skin and mucous membranes Pneumonia Sinusitis Cellulitis Osteomyelitis Wound infection Line infection Atypicals Chest and genito-urinary Pneumonia Urethritis PID Gram negative Gastro-intestinal tract and genito-urinary UTI Peritonitis Biliary infection Pancreatitis PID
    9. 10. Staphylococci <ul><ul><li>S. Aureus (MSSA) </li></ul></ul><ul><ul><li>Normal skin and mucous membrane flora </li></ul></ul><ul><ul><li>Infected sweat/sebaceous glands, hair follicles e.g. sty, boils, furuncles, carbuncles </li></ul></ul><ul><ul><li>Superficial skin infections e.g. impetigo, </li></ul></ul><ul><ul><li>Deeper infections e.g. cellulitis, wound infections, osteomyelitis, septic arthritis </li></ul></ul><ul><ul><li>Treatment is usually with a β -lactamase stable penicillin such as flucloxacillin. </li></ul></ul>
    10. 11. Staphylococci cont. <ul><li>S. epidermidis </li></ul><ul><ul><li>Normal skin and nasal flora </li></ul></ul><ul><ul><li>Important cause of infected implants e.g. heart valves, catheters </li></ul></ul><ul><li>S. saprophyticus </li></ul><ul><ul><li>Normal vaginal flora </li></ul></ul><ul><ul><li>Frequent cause of cystitis in women </li></ul></ul>
    11. 12. Streptococci <ul><li>S. Pneumoniae (pneumococcus) </li></ul><ul><ul><li>Carried in the nasopharynx of many healthy individuals </li></ul></ul><ul><ul><li>Most common cause of pneumonia and otitis media </li></ul></ul><ul><ul><li>Can also be a cause of meningitis </li></ul></ul><ul><ul><li>Usually treated with penicillin or a macrolide. </li></ul></ul><ul><ul><li>Penicillin resistance is currently low in the UK but common in some parts of Europe and USA. </li></ul></ul>
    12. 13. Streptococci cont. <ul><li>S. pyogenes (Group A streptococcus) </li></ul><ul><ul><li>Carried in the nasopharynx of many healthy individuals. </li></ul></ul><ul><ul><li>Most common cause of sore throat, especially in children and teenagers. </li></ul></ul><ul><ul><li>Local skin infections e.g. impetigo, erysipelas </li></ul></ul><ul><ul><li>Deeper skin infections e.g. cellulitis, necrotising fasciitis. </li></ul></ul><ul><ul><li>Treatment is usually with a penicillin. </li></ul></ul>
    13. 14. Streptococci cont. <ul><li>S. agalactiae (Group B streptococcus) </li></ul><ul><ul><li>Carried in the vaginocervical tract, urethral mucous membrane in male carriers and the GI tract. </li></ul></ul><ul><ul><li>Causes meningitis and septicaemia in neonates. </li></ul></ul><ul><ul><li>Treatment is usually with a penicillin </li></ul></ul>
    14. 15. Atypicals <ul><li>Atypicals are intracellular parasites so antimicrobials need to penetrate the cell infected with the atypical organism for activity. </li></ul><ul><li>Mycoplasma pneumoniae </li></ul><ul><ul><li>Found within normal flora of the mouth and genitourinary tract. </li></ul></ul><ul><ul><li>Mainly causes pneumonia but also implicated in bronchitis, pharyngitis and otitis media. </li></ul></ul><ul><ul><li>Higher incidence in children and young adults </li></ul></ul><ul><ul><li>Treatment is usually with macrolide </li></ul></ul>
    15. 16. Atypicals cont. <ul><li>Legionella pneumophila </li></ul><ul><ul><li>Normal habitat is water and soil but can colonise air conditioning and water distribution systems. </li></ul></ul><ul><ul><li>Infection usually results from inhalation of aerosolised organisms. </li></ul></ul><ul><ul><li>Mainly causes “Legionaires disease” – severe pneumonia. </li></ul></ul><ul><ul><li>BTS recommend a fluoroquinolone alone or with a macrolide or rifampicin in severe cases. </li></ul></ul>
    16. 17. Atypicals cont. <ul><li>Chlamydia pneumoniae </li></ul><ul><ul><li>Transmitted by respiratory droplets. </li></ul></ul><ul><ul><li>Implicated in pharyngitis, laryngitis, bronchitis, pneumonia. </li></ul></ul><ul><ul><li>Treatment is usually with a macrolide </li></ul></ul><ul><ul><li>Chlamydia trachomatis </li></ul></ul><ul><ul><li>Cause of non-gonococcal urethritis. </li></ul></ul><ul><ul><li>Other infections include adult eye infections and conjunctivitis of the newborn. </li></ul></ul><ul><ul><li>Treatment is usually with azithromycin or doxycycline. </li></ul></ul>
    17. 18. Gram negative organisms – Gut “coliforms” <ul><li>Escherichia coli </li></ul><ul><ul><li>Part of the normal flora of the colon </li></ul></ul><ul><ul><li>GI infections caused by introduced strains that produce toxins resulting in diarrhoea. </li></ul></ul><ul><ul><li>Strain 0157 can cause serious complications including acute renal failure. </li></ul></ul><ul><ul><li>E. coli is most common cause of urinary tract infection especially in women. Usual treatment is trimethoprim. </li></ul></ul><ul><ul><li>Can also cause meningitis in neonates </li></ul></ul><ul><li>Enterobacter, Klebsiella, Serratia and Proteus: </li></ul><ul><ul><li>Normal inhabitants of the large bowel </li></ul></ul><ul><ul><li>Implicated in UTIs, abdominal infections and nosocomial infections particularly in the immunocompromised. </li></ul></ul>
    18. 19. Gram negative organisms - Chest <ul><li>Haemophilus species </li></ul><ul><ul><li>Part of the normal flora of the upper respiratory tract </li></ul></ul><ul><ul><li>Leading cause of meningitis especially in infants </li></ul></ul><ul><ul><li>Also implicated in pneumonia, otitis media, sinusitis and epiglottitis </li></ul></ul><ul><ul><li>Vaccine available (Hib) </li></ul></ul><ul><li>Moraxella catarrhalis </li></ul><ul><li>Common cause of infective exacerbation of COPD </li></ul>
    19. 20. Gram negative organisms cont. <ul><li>Neisseria meningitidis </li></ul><ul><ul><li>Carried in the nasopharynx of many healthy individuals. </li></ul></ul><ul><ul><li>Can cause meningitis. </li></ul></ul><ul><ul><li>Treatment is usually with a third generation cephalosporin </li></ul></ul><ul><li>Neisseria gonorrhoea </li></ul><ul><ul><li>Found in the human genital tract. </li></ul></ul><ul><ul><li>Infection can be asymptomatic </li></ul></ul><ul><ul><li>Causes gonorrhoea which can lead to pelvic inflammatory disease and infertility. </li></ul></ul><ul><ul><li>Can also cause conjunctivitis in the newborn and septic arthritis in adults </li></ul></ul><ul><ul><li>Resistance is an increasing problem. Treatment is with IV or IM ceftriaxone or oral cefixime (unlicensed use). </li></ul></ul>

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