Bacteriology Flashcards
what domain of life are bacteria?
prokaryotes
unique features of bacteria (differences from eukaryotes)
- rigid cell walls containing a peptidoglycan layer,
- nucleus is not bound by a nuclear membrane, is usually singular and circular
- do not have an nucleolus, mitochondria, endoplasmic reticulum, or Golgi apparatus
- multiply by binary fission
- exhibit considerable morphologic diversity but
are usually <5μm
cocci
circles
staphylococci
clumps/clusters of cocci
streptococci
chains of cocci
cell capsule
- Amorphous, gelatinous materials lying outside the cell wall (= “goop”)
- Most commonly carbohydrates, but some are polypeptides (= “sticky goop”)
- Very variable (antigenically diverse)
- Importance: anti-phagocytic, may help with adherence and prolong survival
cell wall
- ~20% of total dry weight of bacteria
- gives bacteria their shape and rigid structure!
- differs in structure & chemical composition between different bacteria; which influences their pathogenicity and staining characteristics:
- –Gram Positive
- –Gram Negative
- –Acid Fast
- –“Others”
gram stain process
- fixation (heat)
- crystal violet
- iodine treatment (binds to crytal violet to form complex)
- decolorization (alcohol)
- counter stain safranin
is antimicrobial therapy most effective as narrow or broad spectrum?
narrow
gram positive bacteria
- simpler structure cf gram negative
- thicker more uniform cell wall
- predominantly composed of peptidoglycan & teichoic acid
- the peptidoglycan dessicates on decolourization (gram stain) making it less permeable to dye complex
- thicker wall also more resistant to mechanical damage
- peptidoglycan is a target for some antibiotics and also lysozyme
gram negative bacteria
- more complex cf gram positive
Outer membrane (OM) which has:
* Lipopolysaccharide (LPS) MAJOR virulence factor - Porins
- periplasmic space containing smaller amount ofpeptidoglycan
- due to its structure, the OM excludes hydrophilic molecules and renders gram negative bacteria resistant to some detergents
acid fast bacteria
- cell envelope contains additional molecules:
- Mycolic Acid
- Glycolipids and Fatty Acids
- Polypeptides
makes them very hard to stain (so special stain – Acid
Fast)
also allows them to:
* Survive in the environment
* Survive inside cells!!!!
* target for other antibiotics
flagella
confer motility
fimbriae (pili)
important for adherence
spores
important for long term survival and physical resistance
biofilms
- bacteria exist as planktonic (free) or sessile (attached)
- biofims are sessile and created by some bacteria when
a bacterial population becomes adherent to each other and/or a surface, and it then enclosed within a biopolymer matrix - Inside the biofilm the bacteria can act as an “organism”
through “quorum sensing” - Biofilms help in the pathogenesis of bacterial infections by:
- –aid colonization
- –avoid phagocytosis
- –avoid antibiotics
how do bacteria divide?
binary fission
how do bacteria divide?
binary fission
what influences bacterial growth/replication?
- Genetics (type of bacteria)
- Nutritional factors (nutrient media)
- Chemical, physical and environmental factors
bacterial growth on an agar plate
on an agar plate a single colony is a clonal expansion of a single bacterium
Small colonies = slow growing
Big colonies = fast growing
the number of colonies is directly related to the number of bacteria you put on there!!!
optimal pH is neutral to alkaline
optimal tonicity is isotonic to hypotonic
temperature effect on bacterial growth
- Optimal temperature for growth = 98.6°F (body temp)
- But most can grow 68-113°F
- Some pathogenic bacteria grow outside this range
strict/obligate aerobes
require O2 for growth
strict/obligate anaerobes
killed by O2
Facultative anaerobes
can grow in O2 or without
microaerophiles
Require reduced O2 (< than the 20% in air); some also like ↑ CO2)
Where do strict anaerobic bacteria live in the body?
- GI tract (lumen)
- mouth (between teeth and gums)
- urogenital tract (vagina)
bacterial genome
haploid circular chromosome (double stranded)
plasmids
* small circular DNA which can autonomously replicate
bacteriophages
viruses that infect bacteria
integrate into bacterial genome
recombination of DNA
transduction: phage mediated transfer
conjugation: plasmid transfer
transformation: uptake of naked DNA
host
any organism that supports the survival and growth of microorganisms (parasites, bacteria, viruses, etc.)
saprophyte
- organisms that live on dead or decaying organic matter (environment)
- usually not parasites of animals but can occasionally live in/on animals & cause disease
parasite
- a general term that denotes an organism that lives on or within another living organism and derives sustenance
- the parasite does not necessarily harm the host, but has the ability to given the right circumstances
it should also be noted that the distinction between saprophyte and parasite is not complete; some microorganisms can live as either a saprophyte or a parasite e.g., Clostridia may live in the soil as well as the intestine
commensal parasite
- an organism that lives in/on the host without causing disease
- most of the bacteria that normally live in the intestine, on the skin, and on mucous membranes are commensals
pathogen
- Parasitic and saprophytic bacteria which have the potential to cause disease
- Pathogens don’t always cause disease, but become pathogenic under conditions where host animals, or their tissues, allow invasion and disease production
- can either live on the host as part of the normal flora i.e., be present on MOST of the animals in a population
- Or they can live in only a proportion of animals in a population (= carrier state)
carriers/carrier state
- Animals with a specific bacterial pathogens present in “fewer” animals within a population are called “carriers”
- These pathogens may be causing subclinical disease, or no clinical disease at all, but still shed the pathogen
streptococcus zooepidemicus
most common pathogen of horses
normal flora
opportunistic
Where is the normal flora on the skin?
all over skin
more in folds, crevaces
mostly gr +
where is normal flora on the ear?
ear flap
vertical canal (fewer than ear flap)
horzontal canal (fewer than vertical canal)
sterile after tympanic membrane
Where is normal flora bacteria on the udder?
in the streak canal
cistern is sterile
where is normal flora on the eye?
conjunctiva (few due to tears)
very few on cornea
inside eye is sterile
where is normal flora in the respiratory tract?
normal flora is rostral to the larynx
caudal to larynx is sterile
mix of gr - and gr +
where is normal flora in the urinary tract?
distal urethra
bladder is sterile
gr- and gr+
where is normal flora in the genital tract?
distal vagina
past cervix is sterile
gr+ and gr-
pathogenicity vs virulence
- the capacity of a bacteria to produce disease in a host is pathogenicity (e.g., S. aureus is a pathogenic bacteria)
- variation in this capacity is referred to in terms of virulence (i.e., highly versus weakly virulent)
- virulence may vary between bacteria genera, species, or strains and also depend on site of infection (e.g., some strains of E. coli are only virulent in the intestine)
Obligate (true) pathogens
bacteria that must cause disease in order to be transmitted from one host to another AND must also infect a host in order to survive; they can’t survive outside the host
opportunistic pathogens
more common than obligate/true pathogens
bacteria that are normal flora or saprophytes, but can cause disease when something changes in the host animal that allows them to invade and cause disease
predisposing factors to opportunistic pathogens
- tissue damage causing impairment of hosts defense mechanisms
- damage to innate defense mechanisms
- introduction of microorganisms to body sites where they are not normally found
- distrubance of normal flora
infectivity
- capacity of the organism to become established in the tissues of the host
- involves the ability to penetrate the tissues, survive the host’s defences, and multiply/disseminate within the host
innate predisposing factors
- breed/species
- age
- sex
external predisposing factors
- diet/nutrition
- temperature
- overcrowding
- transportation
- change in food
- weaning
internal host stressors/predisposing factors
- anything causing tissue damage (direct trauma, circulatory distrubance)
- anything that changes host response (endocrine changes, immunosuppressive organisms/drugs)
what type of bacteria found on the skin?
gr +
staphylococci
(staph pseuodintermedius in dogs)
what bacteria usually causes skin/ear infections in dogs?
staph pseuodintermedius
gr + cocci
sources of bacteria that cause infection
- Normal Flora (opportunistic infections)
- Animals Incubating Disease
- Animals with Overt Disease
- Carrier Animals (subclinical infections or recovered)
- Fomites (inanimate objects in environment that are contaminated with pathogens)
- environment (saprophytes)
transmission routes of bacteria
- Inhalation
- Ingestion
- Inoculation (e.g., wounds, bites, etc)
- Transplacental
- Via genital tract
- Via umbilicus
key things a bacteria needs to do to cause disease
- attach and colonize
- gain access to body
- evade innate defense
- cause damage
virulence factors for adhesion
Fimbriae(Pili) and Adhesions Factors (Attach)
* present on some bacteria (particularly gram negative)
* assist adhesion to a cell surface through a specific interaction with cell surface receptors
* weaker adhesion by physico-chemical attractions
* allow bacteria to attach and colonize body sites
virulence factors for invasion
- Bacteria can actively or passively enter a host
- Passive entry through damaged or compromised tissues (e.g. S. aureus)
- Active entry via intact epithelium using specific molecules including exotoxins (e.g., Leptospira)
virulence factors for survival inside tissue
Anti-phagocytic Molecules (evasion)
* Capsule, slime layer, biofilms, M protein etc
* Protect the bacteria from ingestion and killing by phagocytic cells (one of the main innate/primary defense mechanisms)
* body gets around this by using antibodies but this takes ~2 weeks
Iron Sequestration
* bacteria must have iron to survive inside a host
* most** iron in hosts are bound to lactoferrin/transferrin**
* but many pathogenic bacteria have siderophores that remove iron from these molecules
* others lyse RBCs and get iron from hemoglobin
Survival in Protected Sites
* as a general rule, extracellular bacteria are cleared with development of antibody
* but some may survive longer in protected sites e.g., Leptospira in renal tubules
Intracellular Survival
* SOME (not all) bacteria can survive inside cells
* Facultative Intracellular Parasites
* Can live outside or inside cells
* Some of the major pathogens (e.g., S. aureus, Salmonella, Brucella etc.)
* Obligate Intracellular Parasites
* Must live inside cells whilst in animal host
* Less common and often “other” bacteria (Rickettsia, Chlamydophila)
