microbiology – bacteria summary (updated)
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8/3/2019 Microbiology – bacteria summary (updated)
http://slidepdf.com/reader/full/microbiology-bacteria-summary-updated 1/26
Microbiology –bacteria summary
Gram +‘ve
8/3/2019 Microbiology – bacteria summary (updated)
http://slidepdf.com/reader/full/microbiology-bacteria-summary-updated 2/26
Cocci – aerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Staphylococcus Aureus
(coagulase+’ve)
AnerobicNon-sporingNon-motileNon-capsulate /limited capsuleformationCatalse +’ve
Appear as“bunches of grapes”
Enterotoxins- food poisoning- heat stable-Toxic shock syndrome toxin (TSST-1)
Epidermolytic toxins- type A&B- cause blistering disease
cytotoxin →alpha toxin- pore formation- proinflammatory
protein A- disrupts opsonization- binds IgG in Fc region(bind Ig with irregular orientation todisrupt opsonization)Causes infection of sites of loweredresistance →damaged skin / mucousmembrane
Enterotoxin & TSST-1 = superantigens- activate T lymphocytes- release cytokines (TNF)
coagulase & bound coagulase (clumpingfactor)
Nuclease
Haemolysans
leukocidins
Nose of 30% of healthypeople
Skin, glands and mucousmembranes
Colonization:- nares, axilla, vagina,
pharynx
Skin infection
Osteomyelitis
Food poisoning
Inherentlysensitive tomanyantimicrobialagents
90% resistantto:
penicillin G(benzylpenicillin)
resitance via:β -lactamase(penicillinase)
antibiotics:- must use β -lactamaseresistantpenicillins- cloxacillin
- flucloxacillin
MRSA(Methicillin-resistant Staph.aureus)∴ usevancomycin
epidermidis
Coagulase–‘ve
Normal flora of
cutaneousorgan system
Adhesion to biomaterials
- adhesion to silastic catheter bycapsular polysaccharide adhesion- forms biofilms →via extracellular slimesubstance
Major cause of
foreign bodyinfection
resitance via:
β -lactamase
- vancomycin
8/3/2019 Microbiology – bacteria summary (updated)
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Streptococcus Pyogenes(pus forming)
aka →groupAstreptococcus→GAS(Lancefieldgrouping)
β -
haemolysin
Facultativeanaerobe:- makes ATP bynormal aerobicrespiration- ferments inabsence of O2
Non-sporingNon-motilecapsulatedCatalase –‘ve
M proteins- prevent opsonization by C3b- B cells can produce anti-M protein Ab →Ab also damages cardiac muscles∴ rheumatic fever
Toxins- superantigens →do not requireprocessing by APC- bind directly to T cell MHC II(nonspecificly)∴ huge cytokine release
- rapid onset- pyrogenic- toxic onset syndrome∴”super bug” / “flesh eating bacteria”
capsule-hyaluronic acid- antiphagocytic
haemolysins→streptolysins O & S- lyse: eryhtrocytes, leucocytes, platelets
- β -haemolysis
hyalournidase
- degrades hyaluronic acid of groundsubstance
streptokinase- fibrinolysis ∴↑ spreading
DNAaseslocalized infections
suppurative infections(pus forming)
Pharyngitis
Skin infections
Rheumaticfever- type 2hypersensitivity
acuteglomerulonepgritis- immunecomplexdeposition inglmoeruli
Penicillin stilleffective forGoup Astreptococcal
antibiotics:- penicillin G &V
Specific M-proteinvaccines beingtested
typing:- β -haemolysis+’ve =pathogenic→clear zonearound colonyin blood agar- α -haemolysis= mostlycommensals →green for
oxidation byhydrogenperoxide (notactualhaemolysis)
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Pneumoniae(pneumococcus)
α -haemolysin
optochinsensitive
Pneumonia
Meningitis inchildren andadults
Typing:- α -haemolysis
Viridians(green)
α -haemolysin
optochinresistant
Commensals
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Cocci – anaerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Peptostreptococcus
AnaerobicNon-sporing
Normal flora of skin, oral cavity,colon,genitourinarytract
1. Abscesses:- brain- lung
2. Aspirationpneumonia
3. Gingivitis +other periodontaldiseases
Bacilli – aerobicGenus Species Description Virulence factors &
Pathogenesis
Epidemiology Diseases Treatment
Listeria Monocytogenes
Intracellularpathogen
Found in environment and animals
Contaminates food
Humans = local carriers
Adults:- asymptomaticGIT carrier- influenza like
antibiotics:- penicillin →Prolongedampicillin
β -lactamaseinhibitor:- clavulanic acid
Resistant:- cephalosporins(intrinsically)
8/3/2019 Microbiology – bacteria summary (updated)
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8/3/2019 Microbiology – bacteria summary (updated)
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Bacilli – anaerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Clostridium Tetani Anaerobicsporing
Toxins:tetanospasmin- neurotoxin →very leathal- blocks neurotransmitter release for 3-4 days
enzymes:- oxygen-labile haemolysin (tetanolysin)Spread:
1. ascending tetanus wound to trunk →viapheripheral nerves
2. Descending →Haematogenous→via lymp =lock jay
Found in soil &animal feces
spores enter deeptissue with lowoxygen tension
1. Tetanus- vascillatingspasms- respiratory arrest- death if dose ishigh
Diagnosis:- smear fromlesion
Immunization:- active → tetanustoxoid (neutralizeunbound toxin)
- passive →immunoglobulins
Supportive:- mechanicalventilation- muscle relaxants
- sedation- nutrition
antibiotics:- metronidazole(kills vegetative
bacteria)- penicillin G & VBotulium anaerobic
Sporing Toxins:1. neurotoxins- 7 forms (A-G)- invasion of peripheral nerves →blocks releaseof Ach ∴ flaccid paralysis →ocular andrespiratory muscles- blurred vision- trouble swallowing
Highly resistantspores
Found in feces,blood, food
Vaccine:- toxoid vaccinehelps clearunbound toxin → if given immediatelyBUT questionableefficacy
Antibiotics:- penicillin
supportive care
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Perfringens Anaerobicsporing
Toxins:exotoxins- deep tissue necrosis- gas production causing crepitus
1. Clostridialmyonecrosis→gas gangrene- complications →shock,haemolysis, renalfailure, metabolicacidosis, coma
2. Enteric infection
-food poisoning- enteritis necrosis
- neutropenicenterocolitis
3. Soft tissueinfections- polymicrobialinfection- crepitantcellulitis- suppurativemyositis
- Extensivedebridement- possibleamputation
antibiotics:- penicillin G & V
sometimeshyperbaric O2
Difficile Anaerobicsporing
Toxins:- Enterotoxin- cytotoxin
Antibiotics kills many GIT flora other thandifficile∴ multiplies and produces toxins
complications:- hypoproteinaemia-toxic colonic perforation- peritonitis
Part of normal GITflora in manyindividuals
1. Antibiotic-associateddiarrhoea +pseudomembranous colitis
watery →blooddiarrhoea 4-9 dayspost antibiotics
Discontinueantibiotic
supportive:- rehydrate
avoid anti-motilitydrugs
antibiotics:- metronidazole- vancomycin (if severe)
Propionibacterium
Normal flora of theskin
Opportunisticinfections:- prosthetic devices- CNS shunts
8/3/2019 Microbiology – bacteria summary (updated)
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Bifidobacterium
Questionable pathogenic potential - Predisposingcondition- dental extraction
Eubacterium Female genital tract- ICUD(contraceptive)
Predisposingcondition
Chronicperiodontaldisease
Actinomycetes Israelii Actinomycosis- chronic,granulomatousinfective disease- multipleabscesses, sinustracts, fistulae →erupt to thesurface →drainpus containingsulphur granules
Antibiotics:long coursepenicillin
8/3/2019 Microbiology – bacteria summary (updated)
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Gram –‘ve
8/3/2019 Microbiology – bacteria summary (updated)
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Cocci - aerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Neisseria
(describedby Neisser)
meningitidis Obligate humanpathogens
Diplococci(axis of pairparallel →sideby side)
Oval cocci to“bean shaped”
Found insideneutrophils(polymorphonuclear pus cells)
Capsule(determinesserogroup)
Immune evasion via capsule
Bacteremia
Antibodies and complementare essential for host immuneresponse
Carriers in:nasopharynxoropharynx
Increased incidence inwinter
Spread by kissing
Spread via respiratorydroplets
Meningococcalmeningitis
Danger of majorout break-endemic &epidemicsituations
2/3 of casesunder age of 5
Vaccine preventable(based on capsuleserogroups)- last 3 years-immunityprophylaxis- herd immunity →vaccinate populationgroups to avoid
outbreakscatch early → treatearly- chemoprophylaxis- if danger of outbreak treatmentshould begin beforedefinite diagnosis- notifiable
Antibiotics:- penicillin G & V
8/3/2019 Microbiology – bacteria summary (updated)
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gonococcus Non-capsule Pili(phase variation)
Antibiotics:- penicillin G & V
Cocci – anaerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Veillonella often contaminates skin
commensal of:- mouth, upper RT, GIT,vagina
1. Osteomyelitis
2. Periodontitis
1. antibiotics
2. Surgery- incision,drainage,debridement,removal of foreignbodies
3. Improvecirculation→oxygen
8/3/2019 Microbiology – bacteria summary (updated)
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8/3/2019 Microbiology – bacteria summary (updated)
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Bacilli – aerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Enterobacteria
Escherichia
Coli ?
strains
Aerobic(use / fermentcarbohydrates)
GITcommensals ?
Found in: soil,plants water
EPEC
enteropathogenic
Adherent bacteria
Adheres to gut wall(upper intestine)
- loss of microvilli ∴↓water &electrolyte absorption
Common in tropics- bad hygiene
Infantile diarrhoea- mild fever, malaise,vomiting- large amount of mucous
in stool →no blood
Supportive- replacement of water & electrolytes
avoid exposure toinfecting agent- “boil it, peel it, orleave it”
no antibiotictreatmentrecommended- diarrhoea normallyself-limiting
in VTEC- antibiotics
associated withdevelopment of HUS
antimicrobialprophylaxis→notadvised →development of resistance
ETEC
Enterotoxogenic
Toxins 1. fimbriae →adherence toepithelial membrane of smallintestine
2. enterotoxins- heat stable and heat labile- hyper secretion of fluids andelectrolytes in to lumen
Tropical and subtropicalclimates
Contaminated food andwater
Poor sanitation
Diarrhoea in adults andinfants
traveler’s diarrhoea
Major cause of death inchildren <5
rapid onsetno blood1-5 days
EIEC
enteroinvasive
Invasive bacteria
Direct penetration, invasionand destruction of intestinalmucosa
Food borne
Out breaks in schoolsand hospitals for thementally handicapped
Dysentery
- scanty stool with pus,mucous, blood
Fever, abdominal cramps,malaise
VTEC
Verocytotoxiogenic
(aka→enterohaemorragic)
Toxins
Cytotoxins- VT1- VT2
Out breaks- nursing homes- day care centres
food- hamburger meat,cooked meat- unpasteurized milk
Severe in old and young
hemorrhagic:- diarrhoea- colitis- uremic syndrome(HUS)→ ↓platelets, hemolyticanaemia, renal failure
no leukocytes in stoolFever, abdominal cramps
EAggEC
entero-aggregative
Adherent bacteria
Adheres to mucosal surface of intestine
Rare in industrializedcountry
Chronic diarrhoea(malnourished children)
Colonized but notpathogenic
8/3/2019 Microbiology – bacteria summary (updated)
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Shigella Dysenteriae(serogroup A)
Closely relatedto Escherichia
Non-motilenon-capsulate
Invasive bacteria:Superficial invasion of the gut
Toxin:Shiga Toxin- destroys epithelial cells- necrosis- neurotoxic- meningism(triad of nuchal rigidity [stiff neck], photophobia,headache)- coma
Transmission:- human to human- low infective dose →10 viable bacteria
4 F’s:FingersFaecesFliesFood
No animal reservoir
Most common in children
Dysentery:- Bloody diarrhoea
Bacteraemia = rare
β -lactamaseinhibitor:- clavulanic acid
Vibrio Cholerae ToxinEnterotoxin
Non-invasive
Outbreaks / epidemics
Contaminated water
Watery diarrhoea(20-30 liters/day)
Rapid onsetHypovolemic shockMetabolic acidosis
Cyanoticsunken eyes and cheeksPoor skin tugor
Detection:- fresh fecal sample→1-2hours- rectal swab
vaccine:- given to groups inhigh risk areas
Dukoral:- 85-90% efficiency- all ages- for 4-6 months
Parahaemolyticus
Acquired from food- mainly raw seafood
Dysentery-like picture
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Salmonella Enterica
typhiNon-typhi
Aerobicnon-sporingrods(coccobacillus)motile
Enter macrophages??
1. primary bacteraemicphase:Invades ileal mucosa →multiplies in mesentericlymphoid tissue→enters blood via thoracicduct→ liver, gall bladder, spleen,kidneys and bone marrowbecome infected
2. Second (heavier)bacteraemic phase:7-10 day incubation period →conincides with fever
3. Further infection of GITfrom gall bladder →Preyer’spatches and lymphoid tissueinvolved → inflammatoryresponse → typhoid ulcers
Transmission:- human to human
Fever:- enteric fever- typhoid fever(if causative agent istyphi)
long termasymptomatic carriers:- chronic excretion- biliary →necrotizingcholecystitis- urinary tact- dangerous for foodhandlers to be carriers
Diarrhoea
found in:- CSF- Stool, urine, blood
Detection:Blood cultures →ESBL-producing salmonella
Vaccine:- live attenuated Ty21a →approved for travelers
β -lactamaseinhibitor:- clavulanic acid
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Bacilli – anaerobicGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
BacteroidesPorphyromonasPrevotella
Fusobacterium
Fragilis Normal flora:– oral cavity, GIT, vagina
1. abscessformation
2. Periodontal
disease- Vincent’sangina →acutenecrotizingulcerativegingervitis
3. postaspirationpleuro-pulmonarydisease
4. Genital tract
infections
1. antibiotics
2. Surgery- incision,
drainage,debridement,removal of foreignbodies
3. Improvecirculation→oxygen
8/3/2019 Microbiology – bacteria summary (updated)
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Rods (coccobacilli)Genus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Nosocomial infections
Pseudomonas Aeruginosa Rods(coccobacilli)
Nonenterobactericacea
Non-fastidious(simplenutritionalneeds)
Ubiquitous innature
opportunistic,nosocomialpathogens
Obligateaerobiccapsulate
(mucoidpolysaccharide)glucoseoxidizer
4-42˚C
Toxins:- exotoxins A- lipopolysaccharide
Enzymes:- protease- phospholipase C
Invasins:- elastase- hemolysins- cytotoxin- pyocyanin
Adhesins:- pili- alginate capsule-biofilm
Genetic attributes:- transduction, conjugation,
antimicrobial resistanceOpportunistic pathogen
Can infect almost all tissue
Systemic infections incompromised patients can be50% fatality rate
Survives in:- hydrotherapy baths- hot tubs- swimming pools
Can infect alltissues
oppertunisitcpathogen- systemicinfection incompromised
host → 50%fatality rate
Resistance:- high [] of salts andanti-septics
antibiotics:- piperacillin(ureidopenicillins) +tazobactam
(β -lactamaseinhibitors)
8/3/2019 Microbiology – bacteria summary (updated)
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Acinetobacter
akinetos =“unable tomove”
Bactrim = “rod”
Baumannii AerobicNon-motile
20-30˚C
- Attachment- persistence on surfaces- secretion of enzymes andtoxins
Enters via:- open wounds- catheters- breathing tubes- Fomites- contaminated parentralsolutions
pathogen amongstwounded soldiers
moist and dry conditions
normal flora of oropharynxof some hosts
colonizes:- skin, wounds, GIT, resp.tact
Resistance:- resistant toall availabledrugs fortherapy
Stenotrophomonas
stenos =“narrow”trophos = “whofeeds”
monas = “ aunit”
Maltophilia
malt + philos=“friend of malt”
Low virulenceOpportunistic pathogen
rarely a true pathogen on itsown
Colonizes fluids in hospitalsettings
1. Nosocomialpneumonia
2. Present inmany cysticfibrosispatients
Resistance:
- β lactams-aminoglycosides- inherent tocarbapenems
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BacilliGenus Species Description Virulence factors &
PathogenesisEpidemiology Diseases Treatment
Fastidious
Pasturella Multocida Fastidious Colonizes mucousmembranes, upper resp.tract and GIT of mammalsand birds
Transmission:- bites and scratches
1. Localized infectionfrom scratch
2. resp. tract infection
3. Systemic disease(life threatening)- meningitis- bacteremia
Antibiotics:- penicillin
Legionella pneumophilia Ubiquitous
Transmission:- inhalation of aerosols
1. Legionnaire’s disease=febrile disease(associated with fever)+ pneumonia +extrapulmonaryinvolvement
2. Pontiac fever =without pulmonaryinvolvement
3. Asymptomaticinfection
Antibiotics:- quinolones(ciprofloxacin,ofloxacin)- macrolides
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Haemophilus Influenzae Capsulate(serotype B)non-motileCatalase +’veoxidase +’ve
Fastidious
Can be bacilli to coccobacilli→pleomorphic
Obligate human parasite
Capsule:- 6 serotypes- serotype B most common
enzymes:- IgA proteases
10% of upper respiratorytract flora
Growth = 5-10% CO2
Transmission:- repertory drops
entrance:- mucous membranes
Systemic:(encapsulated strains)- acute epiglottis- laryngotrachealinfection- cellulitis / arthritis- pneumonia- septicemia- conjunctivitis
local:(unencasulated – non
typable)- otitis media-sinusitis- pneumonia- bronchitis
Lab cultures:Requires- X factor →haemin/haematin(blood)
- V factor →NAD(nicotinamide-adeninedinucleotide)→ from S.aureus
β -lactamase inhibitor:
- clavulanic acid
adjunctive medication:- steroids
Resistance:- ampicillin (penicillin)vaccine:- HiB →serotype B
HACEK group
HaemophilusActinobacillus
CardiobateriumEikenellaKingella
aphrophilusactionomycet
em-comitanshominiscorrodenskingae
Fastidious Found in human oralcavity
1. endocarditis- long duration of symptoms→ largevegetations with
potential to embolise
2. Skin and soft tissueinfections
3. Eye →keratitis,corneal ulcers
Antibiotics:- penicillin
8/3/2019 Microbiology – bacteria summary (updated)
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Diarrhoeal pathogens
1. Ingestion of preformed toxins
- Clostridium botulinum- Clostridium perfringens
- Staphylococcus aureus- Bacillus cereus
Clinical:- Usually watery diarrhoea (water + electrolytes)
2. Toxins produced in the gut
- Vibrio cholerae- ETEC- Clostridium difficile
- Aeromonas sp.
Clinical:- Usually watery diarrhoea- Bacteria &/ toxins found in stool
3. Invasive bacteria
- salmonella- shigella- VTEC (aka →EHEC)- EIEC- Yersinia enterocolitica- Vibrio parahaemolyticus- Clostridium difficile
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Clinical:- dysentery / inflammatory diarrhoea- leukocytes (pus) & erythrocytes (blood) usually found in stool
4. adherent bacteria
- EPEC- EAEC
Clinical:- mucous diarrhoea
nosocomial infectionInfection Predisposing factorsCatheter-associated bacteruria Indwelling urinary catheterIntravenous line infection Central intravenous catheterUrosepsis Urinary tract instrumentation
Primary bacteremia Arterial monitoring devicesPseudobacteremia Contamination of blood during collection / processing of blood culture
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Anaerobic infection- Ubiquitous in nature and commensals of GIT- Weak pathogens ??- Produce toxins- Cause polymicrobial infections
Clinical:
- foul smelling discharge / odour- abscesses, necrotic tissue, gangrene- large quantity of gas production in tissue→creptitus (crackling & popping sounds/sensation under skin/joints)- black discolouration of tissue- sulphur granules- blood in exudate
situation suggestive:- bite wound infected- previous antimicrobial therapy- gram stained tissue yields organisms but no growth on culture
treatment- antimicrobial therapy- surgery → incision, drainage, debridement, removal of foreign bodies- improve circulation →oxygen