MM 4.1 Gram negative rods 1 - Enterobacteriaceae 2021 PDF

Module 4.1 Gram negative rods 1 The Enterobacteriaceae Dr Liam O’Connor Gram negative rods 1 – the Enterobacteriaceae Classification of Gram negative rods 1 Enterobacteriaceae Escherichia Citrobacter Edwardsiella Enterobacter Klebsiella Morganella Proteus Providencia Serratia Salmonella Shigel...

Module 4.1 Gram negative rods 1 The Enterobacteriaceae Dr Liam O’Connor Gram negative rods 1 – the Enterobacteriaceae Classification of Gram negative rods 1 Enterobacteriaceae Escherichia Citrobacter Edwardsiella Enterobacter Klebsiella Morganella Proteus Providencia Serratia Salmonella Shigella Yersinia Gram negative rods This module will focus on the above genera in the Family Enterobacteriaceae Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae This is a very large group. Its members share the following properties: 1. They ferment glucose 2. They are negative in the oxidase test 3. The are nitrate positive Don’t be concerned about these, except for the oxidase test. This is a rapid laboratory test that can be used to distinguish these bacteria from many other Gram negative rods. The Enterobacteriaceae are divided into “tribes” and then into genera; you will need to learn the important diseases produced by members of this group. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – disease associations The important diseases produced by Enterobacteriaceae can be considered under the following headings, and this is the most useful way to learn the important members of this group: 1. Urinary tract infections 2. Antibiotic resistant nosocomial infections 3. Diarrhoeal illness 4. Typhoid fever 5. Plague These will be briefly discussed. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 1. Urinary tract infections Urinary tract infections (UTIs) consist of bladder infections (cystitis) or kidney infections (pyelonephritis). In most cases, these result from bacteria of bowel origin gaining access to the distal urethra and ascending the urinary tract. Many of the Enterobacteriaceae are commensals of the human bowel, and for this reason members of this group are the most common causes of UTIs. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 1. Urinary tract infections The precise causes of UTIs will vary according to the “clinical setting”, particularly patient’s age and gender and where the infection was acquired, ie. in the community or in hospital (nosocomial). Particular strains of Escherichia coli cause most UTIs. These strains are called uropathogenic because they possess virulence factors which enable them to colonise the urethra and survive in the urinary tract. Proteus mirabilis is the second most common cause of UTIs in the community. What is the most common cause of UTIs in young sexually active females? (Clue: It is not a Gram negative rod). In the hospital setting, a broader range of bacteria cause UTIs. (See later section). Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections Within several days of being admitted to a hospital, a patient becomes colonised by the hospital’s resident bacteria, many of which are Enterobacteriaceae or members of other Gram negative groups. In general, these bacteria are very resistant to antibiotics. The intensive use of antibiotics within hospitals has applied an evolutionary selective pressure to the bacteria that reside in hospitals, selecting out those that are resistant. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections Many patients in hospital are very susceptible to infections because: • they are elderly, ill, debilitated or post operative • their immune systems are compromised for these reasons or because they have cancer or are on immunosuppressive drugs • things are done to their bodies which interfere with aspects of their innate immunity, including the use of foreign devices, eg: - intravenous catheters – breach the skin - endotracheal tubes – bypass the defences of the upper airways - urinary catheters – bypass the defences of the urinary tract - surgery, with or without foreign devices left in place, breaches the skin and exposes normally sterile body sites Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections The combination of: • antibiotic resistant bacteria • patients with increased susceptibility to infection makes hospital a very dangerous place to be. Nosocomial infections are a significant cause of death and a major public health problem. The problem is combatted by: • stringent infection control practices such as hand washing • antibiotic stewardship – judicious, controlled use of antibiotics • minimising factors which make patients prone to infections Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections Enterobacteriaceae which are not as commonly encountered in the community are frequently involved in nosocomial infections. The genera involved include: • Enterobacter • Serratia • Klebsiella • Proteus • Morganella • Providencia • even Escherichia coli, but much more resistant strains than those usually found in the community. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections The types of nosocomial infections caused by hospital Enterobacteriaceae include: • Pneumonia – often associated with mechanical ventilator use • UTI – often associated with catheterisation of the urethra and bladder • Bloodstream infections – often associated with intravenous cannulas • Surgical wound infections • Orthopaedic infections – particularly of prosthetic joints, pins & plates Remember that bacteria other than Enterobacteriaceae are also causes of nosocomial infections. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 2. Antibiotic resistant nosocomial infections This elderly man is in the Intensive Care Unit following a large bowel resection for bowel cancer. He has a tracheostomy and endotracheal tube, several intravenous cannulas, a urethral catheter draining his bladder and a surgical wound with several drains. His recovery from surgery may be compromised because he is very susceptible to bacterial infections. Many kinds of bacteria can potentially put him at risk, including members of the Enterobacteriaceae which in the hospital setting may be very resistant to antibiotics. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 3. Diarrhoeal illness Several members of this group may cause infection of the bowel resulting in different diarrhoeal syndromes. Some strains of Escherichia coli with virulence factors which make them “diarrhoeagenic”: EHEC: Enterohaemorrhagic E. coli (also called STEC: Shigatoxin producing E. coli) EPEC: EIEC: ETEC: EaggEC: Enteropathogenic E. coli Enteroinvasive E. coli Enterotoxigenic E. coli Enteroaggregative E. coli As the names suggest, these strains produce diarrhoea by different mechanisms, and the appearance of the faeces may give a clue as to the cause. ETEC is the commonest cause of “travellers’ diarrhoea”. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 3. Diarrhoeal illness Several members of this group may cause infection of the bowel resulting in different diarrhoeal syndromes. Yersinia enterocolitica, which also infects the lymph nodes within the mesentery, producing a pain which can mimic appendicitis. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 3. Diarrhoeal illness Several members of this group may cause infection of the bowel resulting in different diarrhoeal syndromes. Classification within the genus Salmonella is very complex. There are only two species in this genus, S. enterica and S. bongori. However, they can be distinguished by antigenic differences in outer membrane components & given serotype names. It is easiest to think of them as: • typhoidal serotypes (see later) • non-typhoidal serotypes those which cause self-limiting diarrhoea Many of the >2000 different serotypes within the genus Salmonella. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 3. Diarrhoeal illness Several members of this group may cause infection of the bowel resulting in different diarrhoeal syndromes. The species in the genus Shigella are causes of bacillary dysentery, in which the faeces contain blood and pus due to the inflammatory process in the bowel wall. Species from the genus Shigella, which invade the bowel wall causing an inflammatory diarrhoea Red blood cells White blood cells (pus) Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 3. Diarrhoeal illness Several members of this group may cause infection of the bowel resulting in different diarrhoeal syndromes. Some strains of Escherichia coli with virulence factors which make them “diarrhoeagenic”: EHEC: EPEC: EIEC: ETEC: EaggEC: Enterohaemorrhagic E. coli Enteropathogenic E. coli Enteroinvasive E. coli Enterotoxigenic E. coli Enteroaggregative E. coli Species from the genus Shigella, which invade the bowel wall causing an inflammatory diarrhoea Yersinia enterocolitica, which also infects the lymph nodes within the mesentery, producing a pain which can mimic appendicitis. Many of the >2000 different serotypes within the genus Salmonella. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 4. Typhoid fever Several serotypes of Salmonella may invade the bowel wall to produce a serious systemic disease called typhoid fever (or the similar paratyphoid fever). The disease is also called enteric fever. These serotypes are: • Salmonella Typhi • Salmonella Paratyphi The bacteria in this disease may be found in the bloodstream and in lymphoreticular tissue. It is a systemic disease rather than a diarrhoeal disease. Gram negative rods 1 – the Enterobacteriaceae The Enterobacteriaceae – 5. Plague During the Middle Ages, a diseases termed the Black Death killed 1/3 of Europe’s population. Excavations in Europe’s cities still uncover mass graves (“plague pits”) from that time. East Smithfield, London Gloucester