Core Microbiology Pathology Flashcards
Why do Certain Bacteria Cause Particular Infections?
3 Factors:
Host factors (Immune system and devices)
Opportunity (Exposure and Normal flora)
Bacterial Factors ( Virulence, Resistance, Environmental survival)
Where are E.coli & UTIS found what happens?
Part most peoples NORMAL bowel flora.
•Colonise urethral meatus & surrounding area e.g. perineum.
•Females- short urethra.
•Use pili to adhere to uroepithelial cells/ urinary catheter materials triggers host inflamm response (infec).
•Can develop resistance to antibiotics that treat UTIs.
Where are S.aureus &; Skin Infecs found, what happens?
- In NASAL CARRIAGE in 50% people.
- Can adhere to damaged skin e.g. eczma, surgical wound, burn etc.
- Makes exoenzymes &; toxins damage tissues &a provoke host inflamm response (pus formation by WBCs).
What is Staphylococcus aureus? What does it cause?
- Gram +ve coccus.
- Primary pathogen.
- 30-50% carry in nose.
- Causes skin/ soft tissue infecs- commonest; of surgical site infecs.
- Can get into blood stream.
- Bacteraemia/ septicaemia.
- Osteomyelitis/ septic arthritis.
- Endocarditis
- Pneumonia
- UTI
- Meningitis
What is Staphylococcus epidermidis? What does it cause?
- Opportunistic pathogen.
- SKIN commensal.
- Most people carry it on skin as part of normal flora.
- Is a ‘coagulase –ve staphylococci’ (coagulase lab test).
- Causes infec in association with ‘foreign bodies’ which it sticks to e.g. intravascular catheters, Prosthetic joints, prosthetic cardiac valves.
- Adheres to plastics/ metals using glycocalyx (slime), forming biofilms.
- Causes inflamm response.
- Over time joint loosens rocks pain.
What is Streptococcus pyogenes? What does it cause?
•‘Group A Strep’.
•Strawberry tongue
•In chains (not clump- see pic )
•Commonest cause of bacterial sore throat (pustular appearance of tonsils).
•Also causes;
o Scarlet Fever
o Necrotising fasciitis (‘flesh eating bug’)
o Other SSTIs (skin & soft tissue infecs)
o Invasive infecs, such as pneumonia
o Puerperal sepsis (lower genital tracts of females that’ve just delivered)
• Also associated with 2ndry immunological presentations e.g. glomerulonephritis.
What is Streptococcus pneumoniae? What does it cause?
- Commonest cause of bacterial pneumonia & bacterial meningitis (except in neonates).
- Also causes resp tract infeccs & other childhood infecs e.g. otitis media.
What is Streptococcus agalacitae? What does it cause?
- ‘Group B strep’.
* Commonest cause of meningitis & sepsis in neonates (babies under 3 mnths).
What is the Streptococcus milleri complex ?
- 3 closely related species of pus-forming streptococci.
- Normal flora in bowel & upper resp tract.
- Trigger pus formation
- Associated with abscesses; dental, lung, liver, brain & others.
What is Viridans streptococci?
- Collective name for a number of species of α-haemolytic streptococci that inhabit the upper respiratory tract e.g. S. oralis, S. mitis
- Can invade mucosal surfaces into the bloodstream = infec damaged heart valves.
- Classic cause of sub-acute bacterial endocarditis (sub acute as present over couple of weeks e.g. with tiredness etc)
What is Streptococcus gallolyticus?
- Formerly known as Streptococcus bovis
- A type of α- haemolytic streptococcus that forms part of bowel flora
- Bacteraemia with this organism can be associated with colonic malignancies (lower GI malignancies)
What is Listeria monocytogenes?
- Gram +ve bacillus.
- Rare but signinf cause of sepsis & meningitis in pregnancy, neonates & immunosuppressed patients.
- Zoonosis (can be transmitted to humans from animals), able to grow at low temps.
- Associated with consuming cheese from unpasteurised milk &; other foodstuffs
What is Corynebacterium species ?
- Gram positive bacilli
- A number of species are commensals of skin &upper respiratory tract
- Occasional opportunistic infecs associated with devices & trauma
- Corynebacterium diphtheria- classic cause of diphtheria
- Rarely seen now in UK because of immunisation
What is Propionibacterium acnes?
- Gram positive bacillus
- Associated with acne
- Can also cause device-associated & post-procedural infections
What is Enterobacteriaceae (‘coliforms’) ?
- A collective terms for diff gram –ve bacilli species found in bowel flora.
- Gram –ve stain pink & bacilli more sausage shaped.
- Common species; Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae
What is E.Coli?
- Commonest cause of UTI & bacteraemia (sources include urinary (e.g. catheters), biliary (e.g. gallstones) & intra-abdominal)
- Cause of nosocomial (originate in hospital) infecs e.g. line infections, pneumonia, wound infections
- Certain toxigenic strains (e.g. O157) associated with severe diarrhoea & haemolytic uraemic syndrome (HUS)
- Growing resistance to antibiotics
What is Pseudomonas aeruginosa?
- Multi-resistant gram negative bacillus
- Opportunistic pathogen (can’t cause infec in healthy, needs immunosuppression)
- Can cause resp infecs, UTIs, soft-tissue and other infecs in vulnerable patients
- Often produces characteristic green pigment
What is Neisseria meniingitidis?
- Gram –ve diplococcus
- Causes meningococcal sepsis and/or meningitis
- Classic presentation- purpuric non-blanching rash (sepsis)- can do glass test to help i.d. rash
- Reduction in cases after vaccine intro
What is Neisseria gonorrhoeae?
- Gram –ve diplococcus
- Causes gonorrhoea
- Ophthalmia neonatum (in babies whose mother has gonorrhoea).
- Rarely causes invasive infecs (e.g. septic arthritis) 2ndry to primary sexually transmitted infec
What is Haemophilius influenzae?
- Gram negative bacillus
- Part of normal respiratory tract flora
- Can cause resp tract infecs (e.g. pneumonia, infective exacerbations of COPD)
- Capsulated types (e.g. type b) associated with meningitis & epiglottitis (can obstruct airway).
- Only type b infecs prevented by HIb vaccine
What are anaerobes?
• Grow in absence of oxygen.
• CLOSTRIDIUM species- many are spore-forming;
o C. difficile – antibiotic-associated diarrhoea/colitis
o C. perfringens – classical cause of gas gangrene
o C. tetani – cause of tetanus
o C. botulinum – cause of botulism
• Bacteroides species, Fusobacterium species, Prevotella species and many others
• Often part of polybacterial infecs (with other organisms) e.g. dental infecs, lung abscesses, colonic abscesses, post-trauma skin/soft tissue infecs
What is Mycobacterium species?
- Often referred to as ‘Acid Fast Bacilli’ (AFBs)
- Do NOT stain using conventional gram staining (has slightly diff cell wall)
- Mycobacterium tuberculosis – cause of TB
- Other Mycobacterium species sometimes called ‘Atypical Mycobacteria’ &; cause resp infecs in those with chronic lung disease or opportunistic infecs in immuno-compromised patients e.g. AIDS, transplant patients, etc
What are Bacteria without a conventional cell wall
- Not going to stain with gram stain.
- Chlamydia species
- C. trachomatis – commonest cause of STI
- Mycoplasma species
- M. pneumoniae – common cause of resp tract infecs
What is Spirochaetes? What does it cause?
• Treponema pallidum- causes syphilis
• Other species of spirochaetes that can cause important infecs:
oLeptospirosis (in contaminated water/ rats).
oLyme Disease (tic bites you reactive skin lesions).
Which are gram –ve? • A] Streptococcus pneumoniae • B] Mycobacterium tuberculosis • C] Escherichia coli • D] Listeria monocytogenes • E] Neisseria gonorrhoeae • F] Mycoplasma pneumoniae
C & E,
A] Streptococcus pneumoniae (streptococcus is actually +ve)
• B] Mycobacterium tuberculosis (this can’t stain)
Which bacteria is a common cause of skin infection? • A] Klebsiella pneumoniae • B] Streptococcus pneumoniae • C] Haemophilus pneumoniae • D] Neisseria meningitidis • E] Staphylococcus aureus • F] Clostridium difficile
Staphylococcus aureus
Which of the following is the most common sexually transmitted infec? • A] Chlamydia trachomatis • B] Treponema pallidum • C] Corynebacterium diphtheriae • D] Staphylococcus aureus • E] Neisseria gonorrhoeae • F] Viridans streptococci
Chlamydia trachomatis
Which of the following can cause meningitis? • A] Neisseria meningitidis • B] Streptococcus pneumoniae • C] Listeria monocytogenes • D] Streptococcus agalactiae • E] Haemophilus influenzae • F] Staphylococcus aureus
All of them A] Neisseria meningitidis B] Streptococcus pneumoniae C] Listeria monocytogenes D] Streptococcus agalactiae E] Haemophilus influenzae F] Staphylococcus aureus
How do you define the ‘reference range’?
- Way to set up reference range.
- Take normal patients, then can set a normal distribution- reference range roughly -2 standard deviations to +2SDs.
- So certain patients results outside reference range; would be false +ves (so potentially abnormal).
- But reference range not fixed boundaries, are a guide- interpret them in light of patient.
Which factors affect Factors which Affect Reference Ranges?
• Age
• Gender
• Diet
• Pregnancy
•Time of month (menstruation hormones change), day (e.g. cortisol changes), yr (e.g. vit D)
•Weight (e.g. can dilute yourself with water)
•Stimulus (e.g. if given glucose can change reference range)
Need to bear these in mind when interpreting results!!!
What is Diurnal Rhythm of Cortisol?
- Usually only allowed to measure cortisol at 9am or 12pm- are stable.
- During day reference range widens.
- E.g. if stressed cortisol gone up, or gone for a run.
What is the Glucose Tolerance Test?
- E.g. give 75grams of glucose; if fasting increases in a specific range, if diabetic glucose will shoot up.
- Depends on stimulus & what you expect to happen after given stim.
16 yr old boy to hospital in deep coma. Exam; severely dehydrated & has deep sighing respiration.
- What are the two most likely diagnoses?
- What extra information would you like to obtain?
- What tests are needed and why?
- What test(s) would you wish to use to follow-up the patient?
16 yr old boy to hospital in deep coma. Exam; severely dehydrated &; has deep sighing respiration.
- What are the two most likely diagnoses? Diabetes, Salicylate over dose (e.g. in aspirin)
- What extra information would you like to obtain? Previous history - wt loss, polyuria etc.
- What tests are needed and why? Glucose, Gases, U&E, Salicylate, pH (if acidotic)
- What test(s) would you wish to use to follow-up the patient? HbA1c
What is Protein Glycosylation ?
Protein + Glucose —-> Advanced Glycosylated Endproducts (AGE)
• Non-enzymatic process
• Rate of formation proportional to;
– a) glucose concentration
– b) time
• May explain long-term complications of diabetes
• Scientific basis of commonly used monitoring tests
What is HbA1c?
- HbA1c is a stable glycosylated haemoglobin
* Its % concentration indicates cumulative glucose exposure.
What is fungi?
•Separate kingdom of organisms- are eukaryotic microorganisms.
•Single celled to macroscopic (yeasts & hyphae).
•Various growth forms- mainly hyphal or yeast.
•Glucan- chitin cell wall.
•Reproduce sexually and/or asexually, spore formation.
•Lifestyle;
o Saprophytes (decaying organic matter)
o Plant pathogens
o Animal pathogens (small n.o. compared to bacteria, viruses, protozoa)
What are the different types of fungal disease?
Superficial infection- Affects skin, hair, nails &mucocutaneous tissue.
• Dermatophytes
• Candidia
Subcutaneous infection- Affects subcutaneous tissue, usually following traumatic implant).
Systemic infection- Affects deep-seated organs.
• Aspergillus
• Candida
What are Dermatophytes ?
- Keratinophilic fungi- cause of disease in skin, hair & nail.
- 3 genera: Trichophyton, Microsporum, Epidermophyton.
- Slow growing moulds.
- Originate in soil (geophilic), other animals (zoophilic) or confined to humans (anthropophilic).
What is Tinea pedis? What else is it known as?
Dermatophyte Infections of Foot skin
Athletes foot
•Athletes foot- more common than onychomycosis, common in males, younger adults &sportsmen
- Uni- or bilateral
- Itching, flaking, fissuring of skin.
- Little inflamm- fungi adapted to not cause host response, so can survive.
- Interdigital: toeweb skin wet & macerated.
- Plantar: soles of feet dry & scaly, if skin of whole foot affected ‘Moccasin foot’.
- Hyperhidrosis, 2ndry to infection may increase severity.
- 2ndry to bacterial infec.
- May spread to infect toe nails.
- Trypical causes: Trichophyton rubrum
What is Tinea unguium? What else is it known as?
Dermatophyte Infections of Nail (toe or finger) (onychomycosis)
Fungal nail disease
Fungal nail infec- common in general adult pop (5-25% rate), increasing incidence in elderly.
• Thickening, discolouring, dystrophy of nail 4 main types;
1. Lateral/ distal subungual (getiing in on top & sides of nail)
2. Superficial white (on top of nail)- usually in immunocompromised
3. Proximal
4. Total nail dystrophy (usually affects whole nail)
• Typical causes: Trichophyton rubrum & ; T. interdigitale.
What is Tinea cruris? What else is it known as?
Dermatophyte Infections of Groin area skin
Jock itch
- More prevalent in men.
- Itching, scaling, erythematous plaques with distinct edges.
- Satellite lesions sometimes present.
- May extend to buttocks, back & lower abdomen.
- Typical cause: T.rubrum
What is Tinea corporis? What else is it known as?
Dermatophyte Infections of Limbs and torso skin generally
Tinea corporis
- Circular, single or multiple erythematous plaques.
- May extend from e.g. scalp or groin.
- Invasion of follicle ‘Majocci’s granuloma’ (more intense disease).
- Typical cause: wide range of dermatophytes, anthropophilic or zoophilic
What is Tinea capitis? What else is it known as?
Dermatophyte Infections of Scalp skin and hair
Scalp ringworm
•Scalp ringworm- most common among prepubertal children (US survey- tinea capitis in 6.6% children). Tinea capitis more common in deprived areas & black children (rates up to 41%), global prevalence 200 million cases
• Ranges in presentation depending on organs involved; from slight inflamm, scaly patches, with alopecia, balck dots, grey patches to severe inflamm.
• Kerion celsi: boggy, inflamed lesions,hair loss, usually from zoophilic dermatophytes (from animals).
• Favus: presence of cup shaped crusts or scutula.
•These diseases associated with hair invasion:
o Endothrix, spores inside hair shaft (lead to black dots)
o Exothrix, spores outside hair shaft
o Favic, hyphae only in hair shaft (favus)
How do you treat tinea capitis ?
Treat ALL tinea capitis cases with SYSTEMIC antifungals; Griseofulvin, terbinafine. Topical therapy will NOT be curative (role in reducing spread).
What is Candidia ?
•Large genus of yeast.
•Colonises GI tract mucosal surfaces in healthy people.
•Cause of superficial mucosal (oral &; vaginal) disease ‘thrush’, also occasionally skin disease & keratitis.
•Cause of systemic disease when in circ, system, can infect almost any organ in body.
• Caused by range of Candidia species;
o Candida albicans
o Candida glabrata
o Candida parapsilosis
o Candida krusei
What are Superficial Candida Infections- Oral Mucosa- the different types?
• Acute pseudo-membranous; o White plaques in mouth o Low CD4 count (<200 cells/ul) o Younger patients o Asthma with steroid inhalers (dampens down mouths mucosal immunity) • Chronic atrophic o Older patients o Erythema • Angular cheilitis • Chronic hypoplastic o Oral leukoplakia o Lesions may undergo malignant transformation
What is the epidemiology of Oral candidosis ?
- See it in HIV/AIDS- sometimes even if on Anti-retroviral therapy, T-cell immunity important to prevent mucosal candidosis.
- Antibiotic use- supress normal bacteria flora, less competition for yeasts.
- Patients with head & neck cancer- radiotherapy & chemo affect immune responses & salivary secretions.
- General debilitation in hospitalised patients- increases colonisation &; risk of oral disease.
What is Candida vulvovaginitis ?
- Affects 70-80% women at least once during child-bearing years.
- Pruritis, burning sensation, +/- discharge.
- Vaginal epithelium inflamm, may extend to labia majora.
- Often more florid infecs during pregnancy (becomes worse)
- 10% women- recurrent vulvovaginal candidosis (probably relates to subtle immune defect).
- Diagnosis: +ve culture in symptomatic patients (from swab).
What is the Diagnosis & Treatment of Superficial Candidosis?
- Diagnosis: culture with i.d. & antifungal sensitivity testing where appropriate.
- Treatment; usually oral azoles, fluconazole highly effective resistance in normally sensitive species (e.g. Candida albicans) or naturally resistant species (Candida krusei) can be a prob.
