Microbiology Flashcards
What are commensals?
Presence, growth and multiplication of a microorganism on/in a host but without interaction between host and organism. Rarely cause disease, even in vulnerable individuals
• Staphylococcus epidermidis on the skin
• Lactobacillus in the gut
• Streptococcus salvarius oral microbiome
What are opportunistic pathogens?
Caused by microorganisms that are commonly found in the host’s environment or flora without causing harm, however infection may arise in individuals with compromised immunity. Exploit opportunities, causing infections when defenses are compromised
• S. aureus can cause infection if enters the bloodstream
• Candida albicans can cause thrush (common in antibiotics use)
• P. aeruginosa can cause serious infection (immunocompromised, CF)
Acute, subacute and chronic time periods
- acute(<4 weeks with rapid onset)influenza
- subacute(4-12 weeks, slower onset)endocarditis
- chronic(>12 weeks, long duration)tuberculosis
Transmission can occur by…
- direct or indirect contact
- respiratory route
- food or waterborne transmission
- fecal-oral route
- sexual
- vector
Evolved mechanisms for pathogens to damage host
Adhesion
Invasion
Colonisation
Immune evasion
Chain of reaction
How to break the chain of reaction
- Cleaning your hands frequently
- Staying up to date on your vaccines (including the flu)
- Covering coughs and sneezes and staying home when sick
- Following the rules for standard and contact isolation
- Using personal protective equipment correctly
- Cleaning and disinfecting the environment
- Sterilizing medical instruments and equipment
- Following safe injection practices
- Using antibiotics wisely to prevent antibiotic resistance
Stages of infection
- Incubation- Time interval betweeninitial contactwith an infectious agent and appearance of thefirst sign or symptomof disease
- Infectious period (communicability)- Timewhen aninfectious agent may be transferred directly or indirectlyperson to another person, animal to human, or infected person to animal (host is infectious to others)
- Latent Period- Periodbetween exposureand theonset of the infectious period, which may be shorter or longer than incubation period
Symbiotic relationship types
Colonisation vs infection
Colonisation
- Many opportunistic bacteria are part of the normal human flora
- Exist on skin or mucosa without causing harm
- May provide benefit to host
- Biofilm formation on plastics
Infection
- Invasion of the body by pathogens causing disease
What are the risk factors for a HCAI?
Health-care associated factors-
- Prolonged hospital admission
- Haemodialysis
- Immunosuppression
- Antibiotics within last 90 days
- Intensive care stay
- Prosthetic devices e.g. lines, catheter, ventilator
Patient factors-
- Extremes of age
- Immobility
- Chronic illness e.g. diabetes, COPD, obesity
- Pre-existing colonisation with bacteria e.g. MRSA, C. difficile
What are the common causative pathogens of HCAIs?
What are the routes of entry and source of pathogens?
Routes of entry-
Respiratory and urinary routes
- Main routes of entry for Gram negative bacteria
- Catheter associated UTI, hospital acquired pneumonia
Skin and soft tissue infections
- Gram positive bacteria
- Cannulas, pressure sores, surgical site infection
Source of pathogens-
Endogenous
- From patient’s own micro-flora
- Commonest
Exogenous
- Contaminated environment
- Cross-transmission from staff or other patients
Routes of infection
- Contact- hands, equipment, environment
- Air-borne
- Rarely- blood-borne
What are UTIs and LRTIs?
Where does sampling of pathogens take place?
What infections is reporting mandatory for?
- MSSA and MRSA blood stream infections
- C. difficile
- E.coli, Klebsiella and Pseudomonas blood stream infections
Communicable vs non-communicable diseases
How are communicable diseases managed?
Measures that are directed to the agent
- Sterilisation – complete removal of all forms of living/infectious agents
- Disinfection - a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects
- Antiseptics – disinfectants for use on skin
- Sanitisation - the cleaning and disinfection of an area or an item using heat or chemicals to reduce the number of microorganisms to safe levels.
- Proper treatment of infected individuals
Measures that are directed towards breaking transmission
- Isolation
- Decontaminating of fomites
- Promote handwashing
- Modify ventilation and air pressure
- Control vector population
- Environment: sanitation of water, food, proper sewage handling
Measures that are directed towards the reservoir
- Cases: Case finding, reporting to the local health authority in order to apply the appropriate control measures for contact and the environment, isolation (strict isolation or discharge/body fluid isolation) for the whole period of communicability and treatment, surveillance for the longest incubation period.
-
Carriers: Identification of carriers in the community, treatment and
exclusion from work till the organism is eliminated especially if food handlers or working with children. Its cost effectiveness depends on the proportion of carrier in the community as well as the sensitivity of their occupation. - Animal reservoir: Adequate animal husbandry, immunisation of animals (if vaccine is available), treatment of infected animals and killing if treatment is not feasible.
Measures that are directed towards protecting the portal of entry
- Using bed-nets
- Wearing masks and gowns to prevent entry of infected body secretions or droplets through skin or mucous membranes
- Covering skin and using insect repellents
Measures that are directed towards the host
- Health education
- Adequate personal hygiene
- Sound nutrition
- Immunisation
- Chemoprophylaxis
How are outbreaks managed in hospitals vs in the community
What leads to resistance?
• Increased use of antibiotics
• Prescriptions taken incorrectly
• Sold without medical supervision
• Prophylactic use before surgery
• Antibiotics used for viral infection
• Spread of resistant microbes in hospitals due to lack of hygiene
• Patients who do not complete course
• Antibiotics in animal feeds
What are the targets of different antibiotics resistance mechanisms?
How do cells acquire resistance?
What are examples of b-lactams
Penicillins (end in –cillin)
Benzylpenicillin, Phenoxymethylpenicillin, Amoxicillin, Ampicillin, Piperacillin, Carbenicillin, Ticarcillin,
Oxacillin, Flucloxacillin
Carbapenems (all end in –penem) used parenterally (via IV) can penetrate the BBB
Imipenem, Meropenem, Ertapenem
Cephalosporins (all start with Cef- or Ceph-)
1st Gen: Cephalexin, Cefazolin
2nd Gen: Cefotetan, Cefuroxime, Cefprozil, Cefoxitin
3rd Gen: Ceftriaxone, Cefotaxime, Cefixime, Cefdinir, Ceftazadime
4th Gen: Cefepime, Cefpirome
5th Gen: Ceftaroline
Monobactams
Aztreonam is the only approved
What is the mechanism of b-lactam resistance?
