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Library of Congress Cataloging-in-Publication Data
Names: Weston, Debbie, author. | Burgess, Alison, 1963- , author. | Roberts,
Sue, 1955- , author.
Title: Infection prevention and control at a glance / Debbie Weston, Alison
Burgess, Sue Roberts.
Other titles: At a glance series (Oxford, England)
Description: Chichester, West Sussex: John Wiley and Sons, Ltd,
2017. | Series: At a glance series | Includes bibliographical references and index.
Identifiers: LCCN 2016012192 (print) | LCCN 2016013004 (ebook)
ISBN 9781118973554 (pbk.) | ISBN 9781118973547 (pdf) | ISBN 9781118973523 (epub)
Subjects: | MESH: Cross Infection—nursing | Cross Infection—prevention &
control | Infection Control | Handbooks
Classification: LCC RC112 (print) | LCC RC112 (ebook) | NLM WY 49
DDC 616.9/04231—dc23
LC record available at http://lccn.loc.gov/2016012192
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
Cover image: © Getty/Science Photo Library – MOREDU
The idea for this book emerged from the recognition that whilst there are a number of excellent infection prevention and control textbooks available, the concise ‘at a glance’ format is unique and there was therefore a gap in the market for presenting infection prevention and control (IP&C) in this way.
The book has been written by three Senior Infection Prevention and Control Clinical Nurse Specialists with a wealth of experience, still working in a clinical setting, who are alert to and understand the difficulties of clinical staff adhering to infection prevention principles, with many other competing priorities. With this in mind, the concise nature of this book is aimed at a wide range of healthcare professionals, from student nurses embarking on their first exploration of microbiology and the principles of infection prevention and control, to more experienced healthcare professionals working in a high-pressure environment who may have limited time on their hands, find it hard to read the guidance and policies in depth, and simply require a quick revision of the pertinent points.
The book, consisting of 45 short chapters (all of which are based on the most up-to-date guidance), takes the reader on a journey, initially introducing basic microbiology and the body’s immune response before moving on to the practical management of patients with infections caused by specific microorganisms (including current highly resistant microorganisms). Each chapter outlines the characteristics of specific microorganisms, method of diagnosis and the key points of patient management, as well as the pathogenesis of infection where appropriate. Student nurses may find it useful to refer to an anatomy and physiology textbook where appropriate, particularly where aspects of the pathogenesis of infection are described.
The book is not intended to be read from cover to cover in one sitting, although the understanding of the reader may be enhanced if the basic microbiology chapters are read first. Rather, each chapter is written as a separate entity, which can be read on its own or in combination with chapters that are linked. On completion of the book, the reader should have an excellent knowledge of basic microbiology and immunology, which underpins the principles of infection prevention and control, and feel more confident regarding their own management of patients with infections. Hopefully, the book will encourage the reader to want to expand their knowledge still further.
We very much hope that you enjoy reading this book in whichever way is suitable for you.
Bold type is used in the text for emphasis of important terms and points. Terms that appear and are defined in the Glossary are in colour.
Debbie, Ali and Sue
Ali and Sue would like to thank Debbie for all her support and encouragement in the development of this book.
The authors would like to thank their families for their support in the creation of this book, along with grateful thanks to Karen Moore and the team at Wiley for their invaluable support and guidance. Ali would like to acknowledge Clive Burgess, who drew several of the original drawings, Eric Grafman from the CDC, who assisted her with obtaining images for some of the chapters, and her colleagues at Public Health England. Sue would like to thank Tina Dunstall for her assistance, and also East Kent Hospitals University NHS Foundation Trust for permission to reproduce some of the figures. Debbie would like to thank Sue and Ali for their hard work, support and commitment.
A healthcare associated infection (HCAI) can be defined as ‘an infection occurring in a patient during the process of care in a hospital or other healthcare facility, which was not present or incubating at the time of admission. This includes infections acquired in the hospital but appearing after discharge and also occupational infections among staff of the facility’ (WHO, 2011). Figure 1.1, Boxes 1 and 2, describes individual patient and other risk factors for the development of HCAIs; Box 3 lists the top six HCAIs.
HCAIs are significant harm events and healthcare staff have to be aware of their implications, not just from an individual patient perspective (patients can, and do, die from infections that they did not come into hospital with, or contracted as a result of hospital or other healthcare intervention), but also in the wider context. It is important to have a high awareness of the possibility of HCAI in both patients and healthcare staff to ensure early and rapid diagnosis resulting in effective treatment and containment of infection.
The introduction of national reduction, and local ‘stretch’, targets for MRSA bloodstream infections (see Chapter 43) and Clostridium difficile (see Chapter 31) , has kept these organisms at the top of the Department of Health agenda and in the media spotlight since 2004. These targets have largely been successful.
The focus has been on the implementation of evidence-based best practice and adherence to sound infection prevention and control practice, supported by a large number of Department of Health / NHS England / Public Health England drives, initiatives and legislation. MRSA and C. difficile, however, are just the tip of the iceberg, as the nature of infections and infectious diseases is constantly evolving. At the time of writing, the greatest ‘infection control’ threat that the NHS is facing is not from pandemic influenza (see Chapter 41) or another outbreak of Ebola virus disease (see Chapter 33) but from multi-drug resistant Gram-negative bacteria (see Chapter 29), which presents a global public health threat and, perhaps, the beginning of a world without antibiotics. The application of, and compliance with, infection prevention and control as part of everyday practice is going to become more crucial to patient care than ever, given the risk of patients dying from infections that previously could have been treated.
Figure 1.1, Box 4, lists the ‘alert organisms’ that are commonly implicated in HCAIs, as they can cause cross-infection and outbreaks in healthcare settings. There are also a number of ‘alert conditions’ that have wider public healthcare implications (see Figure 1.1, Box 5).
While HCAIs are, on the majority of occasions, acquired as a result of cross-infection arising from exposure to other colonised or infected patients or staff, they can arise endogenously from the patient’s own resident microbial population, particularly where invasive devices (see Chapters 20 and 30) are inappropriately managed. Communicable diseases (see Chapter 2) acquired in healthcare settings through exposure to other patients, relatives or healthcare staff, can also be considered to be healthcare associated.
The Code of Practice on the prevention and control of infections and related guidance (DH, 2015) came into being in 2008 as part of the Health and Social Care Act, which established the Care Quality Commission (CQC) (http://cqc.org.uk).The Health and Social Care Act 2008 and its regulations are law, and must be complied with.
Since April 2009, NHS Trusts have been legally required to register with the Care Quality Commission (CQC) under the Health and Social Care Act, 2008, and as a legal requirement of their registration must protect patients, workers and others who may be at risk of a healthcare associated infection. This has since extended to encompass other NHS bodies, independent healthcare and social care providers, primary dental care and independent sector ambulance providers and primary medical care providers.
In relation to HCAI, the CQC will monitor compliance with the statutory requirements of registration and will judge whether the requirement is met with reference to the Code of Practice. In cases of failure to comply with the registration requirements, the CQC has a range of enforcement powers that it can use to respond to breaches and which are proportionate to the risk of infection. It may draw the breach to the registered provider’s attention and give the provider an opportunity to put it right within a reasonable period of time. In extreme cases the CQC has the power to cancel registration.
Table 1.1 lists the 10 Compliance Criteria of the Code of Practice.
Infection prevention and control is an integral part of an effective risk management and patient safety programme and as such must be embedded in every aspect of patient care in every conceivable patient / healthcare setting by all healthcare staff. It is important to note that Registered Nurses and Midwives are bound by the Nursing and Midwifery Council (NMC) Professional Standards of practice and behaviour for Nurses and Midwives (The Code) (NMC, 2015), and medical staff registered with the General Medical Council (GMC) and licensed to practise medicine have to abide by the GMC’s Good Practice Guidance (2013) (http://www.gmc-uk.org/guidance/good_medical_practice.asp).
Good management and organisation are crucial to establishing high standards of infection control. All healthcare providers must ensure that they have systems in place that address:
All staff are responsible for the care that they give, and are accountable or answerable to someone for their actions. They also have a duty of care, which is a legal obligation to ensure that patients in their care come to no harm as a consequence of any act or omission by the healthcare worker. The Infection Prevention and Control Team (IP&CT) are required to hold staff to account and to challenge poor practice and non-compliance (compliance essentially means acting in accordance with agreed standards or guidelines). Therefore it is essential that staff understand that they are responsible for their practice in relation to IP&C, and for protecting the patients in their care as far it is practically and reasonably possible from HCAIs, and that they are answerable to someone if they are non-compliant. For example, failure to record the visual infusion phlebitis (VIP) scores for two days on a patient with a peripheral cannula in situ (see Chapter 20) leading to a bloodstream infection (BSI – bacteraemia or septicaemia; see Chapter 25) could be viewed as negligent, meaning that harm has been caused to the patient through careless omission (as opposed to a deliberate act), and that the duty of care has been breached.
Holding staff to account however is not about apportioning blame. It is about encouraging responsibility, ownership and engagement, and the IP&CT and healthcare staff working together to reduce, prevent, control and manage HCAIs and the risk to patients. IP&C is an integral component of patient centred care, and all aspects of IP&C clinical practice must be viewed as being as important as all other aspects of patient care, not as add-ons.
Staff must have the competency or ability to undertake tasks or clinical interventions; part of this ability means possessing the necessary knowledge and skills. To undertake clinical activities / interventions without the appropriate knowledge or skills or training places patients and healthcare workers at risk. Staff must also be aware that if there are omissions or gaps in a patient’s paperwork in relation to the documentation of IP&C interventions, the legal interpretation is that care was not given.
Avoidable HCAIs are essentially those where poor clinical practice and non-compliance with IP&C can be evidenced / demonstrated. Any successful reduction in HCAIs requires a zero tolerance approach by all healthcare staff with regard to poor infection control practice, non-compliance with policies, protocols and evidence-based best practice recommendations, and avoidable infections.
All NHS provider bodies registered with the Care Quality Commission (CQC) have to comply with the new Statutory Duty of Candour as a requirement of their registration.
The Duty of Candour is legal duty on hospital, community and mental health Trusts to inform and apologise to patients if there have been mistakes in their care that have led to significant harm. It is therefore applicable to all healthcare professionals in all settings who have a professional responsibility to be honest with patients when things go wrong. This includes reporting incidents and near misses, being open and honest with patients / clients and their carers, and apologising. With regard to applying the Duty of Candour in relation to HCAIs, the onus is on the medical team responsible for the patient’s care, not the IP&CT.
The Code of Practice on the prevention and control of infections and related guidance (DH, 2015), part of the Health and Social Care 2008, requires healthcare organisations to have, or have access to, ‘an appropriate mix of both nursing and consultant medical expertise (with specialist training in infection prevention and cleanliness)’. The IP&CT are the nursing and medical experts responsible for providing the organisation within which they work with evidence-based best practice advice on all aspects of infection prevention and control, and are the only specialist nursing and medical team with responsibility for patients, staff, the public and the environment. The IP&CT are the authors of the Infection Prevention and Control Annual Report, which is presented to the Trust Board of Directors and describes the activities undertaken by the IP&CT during that year in relation to the prevention and control of healthcare associated infections (HCAIs). Activities undertaken by the IP&CT are described in Figure 1.2, and are all focused on ensuring that the organisation is compliant with the Code of Practice.
The risk of HCAIs is generally considered to be greater to patients within an acute healthcare setting (i.e. NHS Trusts) given the types of interventions / invasive procedures that patients typically undergo, and other HCAI risk factors (see Figure 1.1, Boxes 1 and 2), although, in theory, infections / outbreaks should be easier to prevent and manage given that the hospital environment is more ‘controlled’.
There are some patient/client groups in whom the prevention and control of infection poses particular challenges, such as those who are confused and wandering, and/or have reduced mental capacity, or disabilities.
Staff education and training in the application of standard precautions (see Figure 1.1, Box 6) is paramount, and staff may need to be creative in how they actually apply or practice IP&C. When caring for elderly, confused and wandering patients who are colonised or who have an infection for example (and this is just as applicable to an acute care setting), there will need to be an increased focus on patient / client hand hygiene (i.e. by using patient hand hygiene ‘wet wipes’), and additional / enhanced cleaning of the environment, particularly frequent ‘touch points’ (areas that the patients’ / clients’ hands are most likely to come into contact with) and communal areas such as toilets and bathrooms.
NICE (2012) and the DH/HPA (2013) have published specific guidance for the prevention and control of infection in community care, and the HPA/DH have also published specific guidance for staff working in prisons and places of detention (HPA/DH, 2011).
Communicable diseases are contagious or infectious diseases spread by pathogenic microorganisms that can be transmitted from one person to another and that generally have significant public health implications for the wider community and global public health. In 2002, the Chief Medical Officer published Getting Ahead of the Curve (DH, 2002) which emphasised the inevitability of the global emergence of, and subsequent threat from, new infectious diseases, given that 30 such diseases had emerged since the 1970s. Among these diseases were Ebola (see Chapter 33), HIV and HCV (see Chapter 26) and Legionnaires’ disease (see Chapter 37). Ebola and HIV, along with severe acute respiratory syndrome (SARS) which first emerged in China in 2003 (caused by a novel coronavirus), and Middle East respiratory syndrome coronavirus (MERS-CoV) which was first identified in Saudi Arabia in 2012, are known or strongly suspected to have originated in animals (zoonotic infections). Some communicable diseases are particularly associated with children, such as measles, mumps and rubella (Chapter 38), whooping cough (pertussis) (Chapter 27), varicella (Chapter 45) and meningococcal disease (Chapter 39).
In England, Public Health England (PHE) is an external agency sponsored by the Department of Health (DH) whose overarching aim is to protect and improve the nation's health and wellbeing and reduce health inequalities. One of its key roles is the provision of specialist advice in relation to outbreaks and incidences of infectious diseases, including preparedness planning and local and national responses to infectious disease threats (www.gov.uk/government/organisations/public-health-england). (See www.healthscotland.com, www.publichealthwales.wales.nhs.uk and www.publichealth.ie for public health arrangements in Wales, Scotland and Ireland.) The Centers for Disease Control and Prevention (CDC) is the public health agency in America (www.cdc.gov). The World Health Organization (WHO) is the directing and coordinating authority on international health within the United Nations system.
Under the Health Protection (Notification) Regulations (2010), there are 32 notifiable infectious diseases (www.gov.uk/guidance/notifiable-diseases-and-causative-organisms-how-to-report) and 60 notifiable bacteria and viruses (see Figures 2.1 and 2.2).
The doctor looking after the patient (hospital or GP) has a statutory duty (legal requirement) to notify the ‘Proper Officer’ (the Consultant in Communicable Disease Control (CCDC) at the local Public Health England (PHE) Health Protection Team) if s/he suspects a single case of a notifiable infection; therefore notification must not be delayed until positive laboratory confirmation has been received. The main purpose of the notification system is that of surveillance in order to detect, as early as possible, potential outbreaks. Communicable disease surveillance has four key functions (Hawker et al, 2012). It:
Under the International Health Regulations (IHR) (part of a global agreement under the WHO constitution and adopted by all member states), communicable diseases are monitored by global surveillance, alert and response activities, and public health infrastructures are strengthened, or in some cases re-established, in order to ensure that emerging disease threats, whether ‘old’ or new, are identified early in order that a rapid public health response can be initiated (Heymann, 2015). There are four communicable diseases that are considered to have such significant public health implications that the emergence of just a single case poses a public health emergency of international concern and must be notified to the WHO (Heymann, 2015). These diseases are:
Figure 2.3 describes some essential key measures in the prevention of communicable diseases applicable to healthcare and other settings.
In order to understand the role of different microbes in causing infection, it is important to understand the way in which their genetic material and cellular components are organised. All organisms other than viruses (see Chapter 5) and prions are made up of cells (Mims et al, 2004a). There are two major divisions of cellular organisms, prokaryotes and eukaryotes, and many differences between the two. Bacteria are classed as prokaryotes whilst all other organisms (animals, plants, algae, fungi and protozoa) are classed as eukaryotes. Bacteria are all around us in huge numbers but only a few of them actually cause disease.
Figure 3.1 shows the structure of a bacterial cell. Bacteria are single-celled microorganisms, smaller and much less complex than eukaryote cells, with a much simpler internal structure. The main components of bacterial cells are as follows:
Capsules: Some bacteria have capsules, which lie outside the cell wall, made out of glycocalyx to protect them from white blood cells (see Chapter 4).
Flagella, fimbriae and pili: These are often present on the exterior of the cell (see Chapter 4).
Cell wall: The cell wall is located outside the plasma membrane and is made up of a rigid matrix of peptidoglycan, which gives the cell shape and provides a rigid structural support. The thickness of the cell wall varies and determines whether bacteria are classed as Gram-positive or Gram-negative. Gram-positive bacteria have a thick peptidoglycan wall (20–80 nm), with extensive cross-linking of amino acid chains, whereas Gram-negative bacteria have thinner cell walls (5–10 nm) with a much simpler cross-linking pattern (Mims et al, 2004b). As bacteria are colourless, the process of Gram staining in the laboratory is used to identify both the type of cell wall and whether a bacterium is round or rod-shaped (Gladwin and Trattler, 2006a). Gram-positive bacteria stain blue and Gram-negative bacteria stain red (see Chapter 9). NB: Some bacteria do not clearly fit into either category. Mycobacteria, which cause tuberculosis (see Chapter 44), whilst weakly Gram-positive, can be identified more efficiently in the laboratory using an acid-fast stain. Spirochaetes, whilst Gram-negative, are very tiny so better seen with a special microscope. Mycoplasma do not have a cell wall so are neither Gram-positive nor Gram-negative (Gladwin and Trattler, 2006a).
Cytoplasmic / plasma membrane: This forms the outer structure of the cell and provides a ‘selective’ barrier that allows certain substances and chemicals to move into and out of the cell (Betsy and Keogh, 2012a).
Cytoplasm: This contains water, enzymes, waste products, nutrients, proteins, carbohydrates and lipids, all of which are required for the cell’s metabolic functions. In addition, the cytoplasm contains the cell chromosomes and the DNA molecule (Weston, 2013).
Ribosomes: These synthesise polypeptides (proteins).
Mesosomes: These are folded areas of membrane thought to be involved in protein secretion, transport and chromosome separation during cell division and, in some bacteria, contain the enzymes for respiration (Wilson, 2006).
Inclusion bodies: These are areas within the cytoplasm used for the storage of lipids, nitrogen, phosphate, starch and sulphur (Betsy and Keogh, 2012a).
The main differences between prokaryote and eukaryote cells are discussed in more detail in Chapter 4.
Taxonomy or classification of organisms is a scientific way of classifying organisms based on common properties. The top layer of classification is the five kingdoms, of which bacteria is one (the four remaining kingdoms are Animalia (including eukaryotes), Fungi, Plantae and Protozoa). The kingdom of bacteria is further broken down into the genus of the bacteria, followed by the species, for example, Clostridium (genus) difficile (species).
There are four main shapes of bacteria (see Figure 3.2): cocci, which are spherical; bacilli, which are rod-shaped; spiral-shaped (or comma-shaped, ‘S’-shaped); and pleomorphic, which lack a distinct shape (Gladwin and Trattler, 2006a).
There are six classic Gram-positive bacteria that cause disease in humans, and almost every other organism is Gram-negative (Gladwin and Trattler, 2006a). The six Gram-positive bacteria are Streptococci (forming chains of cocci), and Staphylococci (forming clusters); two rods that produce spores, Bacillus and Clostridium; and finally two non-spore-forming rods – Corynebacterium and Listeria. Listeria is the only genus of Gram-positive bacteria that produces an endotoxin (see Chapter 4).
There is only one group of Gram-negative cocci- Neisseria, which is a diplococcus (coffee-bean shaped). There is one group of spiral-shaped organisms known as Spirochaetes, and the remaining Gram-negative bacteria are rod-shaped or pleomorphic (Gladwin and Trattler, 2006a).
Examples of some Gram-positive and Gram-negative bacteria are listed in Figures 3.3 and 3.4.
Nutrition: All pathogenic bacteria are heterotrophic, i.e. they obtain energy by oxidising preformed organic molecules (carbohydrates, lipids and proteins) from their environment (Mims et al, 2004b). Bacteria can also be distinguished by their preference of pH and temperature.
Growth and division: Bacteria rates of growth and division also vary significantly. For example Escherichia coli may divide every 20–30 minutes whereas Mycobacterium may only divide every 24 hours. Generally, though, growth and division are faster when the nutritional status of the surrounding environment is good (Mims et al, 2004b).
Bacteria have a number of different virulence factors to help them to evade the host’s immune system. These are discussed in detail in Chapter 4.
Bacteria have a number of virulence factors. These are usually very effective (although their effectiveness varies) in evading the host’s immune system. Whilst Gram-positive and Gram-negative bacteria share many of the same virulence factors, Gram-negative bacteria have several unique characteristics present in their cell wall structure that make them generally more pathogenic than Gram-positive bacteria (see Chapter 3), thereby causing a greater number of life-threatening diseases in humans. (see Figures 4.1–4.3)
Flagella, present in both Gram-positive and Gram-negative bacteria, assist bacteria in moving freely within their environment. Flagella are long protein filaments fixed to the basal body of the bacteria, extending from the cell membrane and several times the length of the bacterial cell. The basal body spins around, which has the effect of causing the bacterium to move in a coordinated manner either towards a chemical concentration or away from it by a process called chemotaxis (Gladwin and Trattler, 2006b). There are very different patterns of flagella distribution in bacteria, ranging from a single flagellum (monotrichous) to clusters/tufts of flagella (lophotrichous), and they move in different ways (Prescott et al, 2005a).
Pili (fimbriae) are straight filaments, shorter and more rigid than flagella. There are two types of pili: ‘sex’ pili, which attach to other bacteria (see Chapter 11), and ‘common’ pili which attach to host cells with adhesins (Mims et al, 2004b). Adhesins are specialised molecules or structures on the bacteria’s cell surface that bind to complementary receptor sites on the host cell surface (Prescott et al, 2005a).This is an important factor in causing disease. Escherichia coli and Campylobacter (see Chapter 28) use adhesins to bind to intestinal cells, and Bordetella pertussis (see Chapter 27) uses adhesins to bind to ciliated epithelial cells (Gladwin and Trattler, 2006b). Although pili are not generally thought to be involved in bacterial motility, they are required in the ‘twitching motility’ that occurs in some bacteria, for example in Pseudomonas aeruginosa, and Neisseria gonorrhoeae and some strains of E. coli (Prescott et al, 2005a). The presence of many pili may also help to prevent phagocytosis (see Chapter 6), reducing host resistance to bacterial infection (Mims et al, 2004b).
Capsules are protective walls made of glycocalyx that surround the outside of the cell membranes of both Gram- positive and Gram-negative bacteria. Bacterial cells may also be surrounded by a layer of slime, which is also made of glycocalyx but easily washed off (Prescott et al, 2005a). Capsules and slime increase the virulence of bacteria because the body’s immune system, in particular the macrophages and neutrophils, is unable to phagocytose these particular bacteria (Gladwin and Trattler, 2006b). Capsules are also able to resist desiccation and some bacteria glide through the slime to aid their mobility (Prescott et al, 2005a). Fortunately, certain antibodies are able to bind to capsules (opsonisation), and once the macrophages and neutrophils bind to the antibodies they are able to phagocytose the bacteria (Gladwin and Trattler, 2006b) (see Chapters 6 and 7).
The production of endospores is another way in which bacteria try to outwit the host’s immune system. Only two bacterial species, both Gram-positive rods, form spores; these are Bacillus and Clostridium. Endospores are metabolically dormant forms of bacteria that are resistant to heat (boiling), cold, drying and chemical agents. Spores (which have a protective coat of five layers) form when there is a shortage of nutrients and can lie dormant for years until the environment and availability of nutrition improve (Gladwin and Trattler, 2006b).
Some bacteria, called facultative intracellular organisms, are phagocytosed by the macrophages and neutrophils but survive within these cells unharmed because they are able to inhibit phagosome–lysosome fusion (see Chapter 6). Examples include Listeria monocytogenes, Salmonella typhi, Legionella and Mycobacterium tuberculosis (Gladwin and Trattler, 2006b) (see Chapters 37 and 44).
Exotoxins are proteins that are released by both Gram-positive and Gram-negative bacteria. All Gram-positive bacteria produce exotoxins (extracellularly), with the exception of Listeria monocytogenes, which produces endotoxin. Endotoxins, which are only present in Gram-negative bacteria (except for the Gram-positive Listeria monocytogenes) differ from exotoxins in that they are cell bound and form an integral part of the cell wall that is only released during cell lysis (Gladwin and Trattler, 2006b).
Exotoxins that act on the nerves are called neurotoxins, and exotoxins that act on the gastrointestinal tract and cause both infectious diarrhoea and food poisoning are called enterotoxins (Gladwin and Trattler, 2006b). Examples of bacteria that produce exotoxins can be found in Figure 4.4.
Endotoxins are particularly characteristic of Gram-negative bacteria and form part of the bacterial cell wall, which consists of lipopolysaccharide (LPS). LPS is composed of: a lipid portion (lipid A) inserted into the cell wall which is responsible for much of the toxic activity; a conserved core polysaccharide; and the highly variable O-polysaccharide (Mims et al, 2004b). Lipid A is extremely toxic to humans. When the host immune system lyses Gram-negative bacterial cells, lipid A is released into the bloodstream, often causing fever and vascular collapse (septic shock) (see Chapter 25), sometimes with fatal consequences (Gladwin and Trattler, 2006b). The most common example of endotoxin (or ‘septic’) shock is septicaemia caused by Gram-negative bacteria such as Escherichia coli or Neisseria meningitidis (see Chapter 39) (Mims et al, 2004c).
The cell membrane of Gram-negative bacteria is also able to block the entry of substances such as antibiotics to the inner parts of the cell, making it harder to treat Gram-negative infections (Gladwin and Trattler, 2006b) (see Chapter 11).
Some bacteria release enzymes that break down the tissues or intercellular substances of the host allowing the infection to spread freely. Examples of such enzymes are hyaluronidase, collagenase, DNase and streptokinase (Mims et al, 2004c) (see Chapter 36).
Plasmids are double-stranded DNA(deoxyribonucleic acid) molecules that often carry antimicrobial resistance genes and are easily transferred from one bacterial cell to another by a mechanism known as conjugation, thus facilitating growth of antimicrobial resistance (Prescott et al, 2005a) (see Chapter 11).