Example Bacterial Pathogens Flashcards
ILOs
By the end of this lecture you should …
- Be able to describe an example of a Gram negative pathogen
- Be able to describe an example of a Gram positive pathogen
- Understand the concept of zoonoses and emerging infections
Spread and control of infection
Clinical infection can be either be endogenous or exogenous
Endogenous: Staphylococcus aureus
Exogenous: Clostridium spp.
Spread and control of infection
- Social and environmental factors
- Health education
- Food safety
- Vector control Chemoprophylaxis
- Outbreak investigation
Gram negative pathogens
Gram negative pathogens: Neisseria meningitidis – beta proteobacteria
- Carriage in the nasopharynx in 10-15% of the population
- 2.Epidemics occur every 10-12 years
- Meningitidis belt in Africa where rates of infection can be 1 in 100
- Classified by serogroup – reactivity to a bacterial polysaccharide capsule
Neisseria meningitidis – beta proteobacteria
- Carriage is facilitated by downregulation or loss of capsule expression, as this sterically inhibits adherence and biofilm formation.
- However, survival in the bloodstream and in epithelial cells is enhanced by capsule expression
- There are 12 serogroups of N. meningitidis that have been identified, 6 of which (A, B, C, W, X and Y) can cause epidemics.
Neisseria meningitidis – beta proteobacteria
- Several vaccines are available to control the disease: a meningococcal A conjugate vaccine, C conjugate vaccines, tetravalent A, C, Y and W conjugate vaccines and meningococcal polysaccharide vaccines.
- As of January 2015, over 217 million persons have received meningococcal A conjugate vaccine in 15 countries of the African belt
- Before 2010 and the mass immunization campaign, Group A meningococcus accounted for an estimated 80–85% of all cases in the meningitis belt, with epidemics occurring at intervals of 7– 14 years. Since then, the proportion of the A serogroup has declined dramatically.
Gram positive pathogens: Diphtheria (Corynebacterium diphtheriae)
- Disease reports from 4th century B.C.
- Corynebacterium diphtheriae
- Gram positive, immotile rod
- Colonises upper respiratory tract
- Route of infection: Airborne droplet
- Person to person: coughs, sneezes etc
Diptheria
- Corynebacterium diphtheriae establishes in throat, upper respiratory tract
- Produces exotoxin
- Kills surrounding host cells
- Toxin spreads systemically
- Principally affects: Heart and Lungs
- Main cause of mortality
Diptheria
- Classic AB toxin - the main virulence factor
- Controlled by immunisation (DTaB)
- All babies are offered vaccination against diphtheria as part of the 5-in-1 vaccine that is given when they’re two, three and four months old. The 5-in-1 vaccine, is also known as the DTaP/IPV/Hib vaccine
Emerging infections
- Although the existence of pathogens has been recognised for centuries, the first comprehensive list of human pathogen species was not published until 2001 (Taylor, Latham, and Woolhouse 2001).
- Emerging infections are infections that are rapidly increasing in incidence and/or geographic range.
- While many pathogens periodically infect humans, few become adept at transmitting or propagating themselves. Human activity, however, is making this transition increasingly easy by creating efficient pathways for pathogen transmission around the globe. “We know what is responsible for emerging infections, and should be able to prevent them,”
Emerging infections
There are several possible reasons for a pathogen to appear in the list of “new” species.
- Both the pathogen and the disease it causes did not occur before 1980.
- The disease was already recognised but the pathogen was not identified as the etiological agent before 1980.
- The pathogen was already recognised but had not been associated with human disease before 1980.
- Neither the pathogen nor the disease it causes were recognised or reported before 1980, but they did occur.
- What was considered to be a single pathogen before 1980 was subsequently recognised as comprising two or more species.
Emerging infections
Not all bad news!
The process of disease emergence can be divided into two steps
(1) Introduction - where these “Andromeda-like” infections come from
(2) Establishment and dissemination - which is much harder for most of these agents to achieve.
The basic lesson there is that many may be called, but few are chosen
Zoonotic diseases
- Relatively few human pathogens are known solely as human pathogens.
- Many more pathogens—over 800 species—are capable of infecting animal hosts other than humans.
- The escalated need for food production to meet present and future demand has led to the intrusion of agriculture into previously untouched areas of the native
- environment.
- The impact of climate change has resulted in disturbances in ecosystems and a re-distribution of disease reservoirs and vectors.
- Increased globalisation and travel has increased the chance, extent and spread at which disease transmission occurs.
Zoonotic diseases - animal to human
Many zoonotic agents cause little or no signs of disease in their natural hosts, such as wild birds and bats, but transmission hosts might present with disease symptoms ranging from moderate (for example, pigs infected with avian influenza virus) to severe (for example, horses infected with Hendra virus). The terminal or spill over host can present with severe symptoms and high mortality rates (for example, in the case of humans infected with H5N1 influenza)
In figures: Streptococcus suis
- S. suis has been reported to have spread over 30 countries
- 1,600 human cases, some of which were fatal
- 35 serotypes bases on capsular antigen
- Two big outbreaks of human SS2 endemics which occurred in China, in 1998 and 2005
- Chinese epidemic SS2 strain 05ZYH33 - 2096309bp
Streptococcus suis
Massive variability in genomic content between serogroup 2 strains
- The Chinese serogroup 2 strain 05ZYH33 has a pathogenicity island (PAI89K)
- Contains a system similar to a Type 4 secretion system which is thought to stimulate the host immune reaction observed with streptococcal toxic shock-like syndrome (STSLS)
