Chapter 4 - Bacteria Flashcards
What % of cardiac output reaches the skin?
4%
Which classes of antibiotics better penetrate fibrotic tissue?
Fluoroquinolones, lincosamides, chloramphenicol
Name two underlying conditions that can be associated with bullous impetigo in adult dogs?
Hyperadrenocorticism, hypothyroidism, diabetes mellitus, other debilitating disease
With a tuberculoid response to mycobacterial infection, do you see caseous necrosis with few bacteria or solid sheets of foamy macrophages with numerous bacteria?
Tuberculoid = caseous necrosis with few bacteria Lepromatous = solid sheets of foamy macrophages with numerous bacteria
Which domestic animals can be affected by Yersinia pestis?
Rodents and cats > dogs (other domestic animals are resistant)
Which bacteria are in the tuberculosis complex group?
M. bovis, M. tuberculosis, M. microti
Which of the TB complex group are cats most susceptible to?
M. microti and M. bovis (M. tuberculosis is rare in cats)
Which breeds of dog are most often affected by canine leproid granuloma?
Boxers, SBTs, Foxhounds, Dobermans (and other short coated dogs)
What can be seen on cytology of canine leproid granuloma?
Variable numbers of medium length acid-fast bacilli, either intracellularly (within macrophages or giant cells) or extracellularly
Which mycobacteria are associated with feline leprosy syndrome?
M. lepraemurium, M. visibile, M. sp. strain Tarwin and a novel species found in New Zealand and the East coast of Australia
Name the rapidly growing / atypical mycobacteria?
M. fortuitum group including M. fortuitum, M. perigrinum, and the third biovariant complex
M. chelonae/abscessus group including M. chelonae and M. abscessus
M. smegmatis group including M. smegmatis sensu stricto, M. goodii, M. wolinskyi
A variety of other species, including M. phlei and M. thermoresistibile
How readily are organisms found on histopathology of rapidly growing / atypical mycobacterial infections?
Organisms are characteristically rare and difficult to find but are usually located in small clumps within the clear vacuoles.
Which breeds of dog and cat may have a genetic predisposition to non-tuberculoid, slow growing mycobacterial infection?
Miniature schnauzers, Basset Hounds, Somali, Abyssinian, Siamese
What is the difference between lepromatous leprosy and tuberculoid leprosy?
In lepromatous leprosy, there is nodular-to diffuse dermal to subcutaneous granulomatous inflammation without necrosis and with large numbers of intracellular acid-fast bacilli.
In tuberculoid leprosy, there are dermal to subcutaneous granulomas with central caseous necrosis surrounded by a zone of lymphocytes. Few to moderate numbers of acid-fast bacilli are generally limited to the areas of necrosis.
Staph. pseud. carriage is most often found at which body site?
SP found on sampling of buccal mucosa (upper lip) most commonly
>64% sensitive at this site
> 90% if include nares and two additional sites
Which are the most widespread MRSP strain types?
ST45, ST68, ST71
Which are the (up to now) known exfoliative toxins of S. pseudintermedius?
SIET
SPETA
EXPA
EXPB
Which S. pseud. toxin is known to digest canine desmoglein-1? In which disease this is reported?
EXPA, EXPB (previously reported as EXI)
Ιmpetigo
Mycobacterium spp. have been classified as belonging to the Mycobacterium tuberculosis complex, non-tuberculous mycobacteria (NTM) including rapid- and slow-growing species, and lepromatous mycobacteria/feline leprosy syndrome. Name the rapidly growing, non-tuberculoid mycobacteria?
Mycobacterium fortuitum, Mycobacterium abscessus, and Mycobacterium smegmatis
What type of mycobacteria are the Mycobacterium avium complex (MAC)?
Slow-growing, non-tuberculoid mycobacteria
What are the clinical signs of feline leprosy syndrome?
It is primarily a cutaneous disease presenting as alopecic or ulcerated, non-painful and freely mobile single or multiple nodules, often on the head, limbs and occasionally trunk. Rare cases affect the tongue, lips, nose or conjunctivae. Regional lymphadenopathy can occur. Systemic disease is rare, but can be progressive and aggressive.
What does MALDI-TOF stand for?
Matrix-assisted laser desorption ionisation - time of flight mass spectrometry
Urine culture in dogs with inactive urine sediments can be positive in 3.4-6% of samples; is growth associated with proteinuria?
No statistically significant difference was noted between the low and high protein groups. Prior studies have also failed to show correlation between increased UPC and bacteriuria.
What is biofilm?
A biofilm is an aggregate of microorganisms that adhere to each other on a living or non-living surface, and are embedded within a self-produced matrix of extracellular polymeric substances (EPSs), including exopolysaccharides, proteins, metabolites and extracellular DNA (eDNA).
What are the mechanisms of biofilm-mediated resistance?
- Prevention of antibiotic penetration
- Altered microenvironment inducing slow growth of biofilm cells
- Induction of an adaptive stress response
- Persister cell differentiation (phenotypic variants that are not genetically resistant to antibiotics but are tolerant to high concentrations of antibiotics)
What is quorum sensing?
Quorum sensing is a mechanism that allows bacteria to control gene expression in a cell density-dependent manner
What is the mechanism of action of S. aureus alpha toxin?
It activates metalloproteinase domain-containing 10 ADAM10; cleaves E-cadherin; breaks adherens junction and compromises actin cytoskeleton
Which Staphylococcal toxins act as superantigenic toxins?
Enterotoxins (staphylococcal enterotoxin C in SP)
TSST-1 (toxic shock syndrome toxin-1)
How do superantigens work?
- activate T cells in a nonspecific manner
- results in excessive immune response with polyclonal T cell activation and massive cytokine release
- bind to MHC II outside the classical antigen binding region
What are the mechanisms that S.aureus uses to avoid elimination by neutrophils?
- Inhibition of neutrophil extravasation from the bloodstream into tissues, neutrophil activation, chemotaxis
- Inhibition of phagocytosis by aggregation, protective surface structures, biofilm formation
- Inhibition of opsonization
- Inhibition of neutrophil killing mechanism
- Direct elimination of neutrophils by cytolytic toxins or triggering apoptosis
Which cells can Staphylococci survive in?
Neutrophils
Endo-/Epi-thelial cells
Osteoblasts
(escape endosomes and replicate - avoid immune recognition and antimicrobials)
What is the role of Staphylococcal fibronectin?
Proteins anchored to peptidoglycan responsible for attaching to extracellular matrices - cell invasion
(target for slide agglutination testing)
What is the role of Staphylococcal protein A?
Cell-wall associated protein interacting with host IgG, IgA, IgE and platelets - attenuates opsonophagocytosis and modulates platelet aggregation
Sensitises B cells and binds TNF-1
Which gene codes for staphylococcal protein A?
spa
Staphylococcal capsule formation has what advantage?
Increased resistance to opsonophagocytosis (complement still binds to cell wall surface but complement receptors can’t see it).
What are staphylococcal CHIPS?
Chemotaxis inhibitory protein of S. aureus
small secreted protein that represses neutrophil and monocyte chemotaxis induced by activated complement (C5a) and N-formyl peptide (but not chemotaxis mediated by IL-8)
Staphylococcal cytotoxins lyse which cells?
PMN leukocytes
Monocytes
Erythrocytes
What is alpha-haemolysin?
Staphylococcal cytotoxin that forms pores in the cytoplasmic membrane of RBCs, mononuclear WBCs, platelets, endo-/epithelial cells leading to cell lysis
Causes beta (complete) haemolysis on blood agar
What is beta-haemolysin?
Staphylococcal cytotoxin - sphingomyelase that degrades and weakens RBC membranes
Causes alpha (partial) haemolysis on blood agar
Name a staphylococcal leukotoxin
Panton-Valentine leukocidin (PVL)
- associated with severe skin infections
- LUK-1 gene in SP
- acts on PMN leukocytes in SP
What do the icaA/icaD genes in Staphylococci encode for?
Polysaccharide intercellular adhesion (PIA) - biofilm
What are the main types of resistance mechanisms in bacteria?
- Efflux – FQs, aminoglycosides, tetracyclines, beta-lactams, macrolides
- Immunity and bypass (bacteria become able to produce an alternative form of a protein that has a low affinity for the antimicrobial) – tetracyclines, trimethoprim, sulfonamides, vancomycin
- Target modifications – FQs, rifamycins, vancomycin, penicillins, macrolides, amoinoglycosides
- Inactivating enzymes – beta-lactams, aminoglycosides, macrolides, rifamycins
Which antibiotics target 50S inhibitors in protein synthesis?
Erythromycin (macrolides)
Chloramphenicol
Clindamycin
Lincomycin
Which antibiotics target 30S inhibitors in protein synthesis?
Tetracyclines
Streptomycin
Gentamicin
Amikacin
Which antibiotics target DNA-directed RNA polymerase?
Rifampin
Which antibiotics target folic acid metabolism?
Trimethoprim
Sulfonamides
Which antibiotics target DNA gyrase?
FQs
How do beta-lactamases inactive penicillin type antibiotics?
They hydrolyse the beta-lactam ring
Which gene encodes for beta-lactamase?
blaZ - typically resides on a large transposon on a plasmid
Both transglycosylation (attaching repeating units to the peptidoglycan strand) and transpeptidation (cross linking of repeating units) are carried out by which protein?
Penicillin-binding proteins
Transpeptidation is the specific target of β-lactams
Why is PBP2a resistant to beta-lactams?
The active-site serine of PBP2a is less accessible to β-lactams than with susceptible PBPs because of its location in a narrow extended cleft
Which gene encodes PBP2a and on which element?
mecA
Staphylococcal chromosome cassette (SCCmec)
What is the role of ‘J’ (junk) regions of SCCmec?
J regions are now commonly referred to as joining regions because they can encode important functions such as resistance to additional antibiotics and to heavy metals
What mediates excision and integration of SCCmec?
ccr-encoded recombinases located on SCCmec
FQs bind to DNA gyrase - what is it also known as? - and which other enzyme?
Topoisomerase II (DNA gyrase)
Topoisomerase IV
What is the primary target for FQs in G-ve and G+ve bacteria in veterinary species?
G-ve = DNA gyrase G+ve = Topoisomerase IV
FQ resistance occurs via two pathways; mutation of the target Topoisomerase II and IV or which other mechanism?
Efflux pumps
Tetracycline resistance in Staph.
tet (K) and tet(L) genes lead to which type of resistance mechanism?
Efflux pumps
No resistance to minocylcine
Tetracycline resistance in Staph.
tet(M) gene leads to which type of resistance mechanism?
Ribosome-protective protein (tet(M) most common in SP)
Resistant to minocycline
What are the intrinsic mechanisms of antibiotic resistance in Pseudomonas aeruginosa?
- Restricted outer membrane permeability (extremely restricted; about 12- to 100-fold lower than that of E. coli)
- Efflux pump systems
- Production of antibiotic-inactivating enzymes
(β-lactamases and aminoglycoside-modifying enzymes)
What is the mechanism of action of polymixins?
They bind to the lipopolysaccharides (LPS) on the outer membrane of Gram negative bacteria, leading to increased cell membrane permeability and enhanced antibiotic uptake.
Antibiotic resistance genes can be carried on which elements?
Plasmids, transposons, integrons and prophages
The main mechanisms of horizontal gene transfer involve which processes?
Conjugation, transformation and transduction
Which resistance gene confers resistance to all three types of macrolide antibiotic?
erm (mostly erm(B) in SP)
Modifies target site on ribosomes
What is the mechanism of action of rifampicin and the resistance gene?
Inhibits bacterial RNA polymerase
rpoB chromosomal mutation
What is the D-test?
Disk testing using erythromycin and clindamycin disks 15mm apart - with inducible resistance you see a flattening of the zone of inhibition nearest the erythromycin disk (‘D’ shape)
Which antibiotics can be used to test for meticillin resistance?
Oxacillin
Cefoxitin
Salt media can be used to select for which bacteria?
Staphylococci
Which element is a limiting factor for bacterial growth in tissue?
Iron (can be released by cell necrosis and utilised by the bacteria)
Conjugation is a method of horizontal gene transfer that is used most often by G+ve or G-ve bacteria?
Gram -ve
Which type of antibiotics are the only antimicrobials that act on ribosomes and cause cell death?
Aminoglycosides (e.g. gentamicin, amikacin, neomycin)
Rapid growing mycobacteria are more like pyogenic organisms and give rise to what type of inflammation?
Pyogranulomatous
With sinuses that drain watery pus
Slow growing mycobacteria may take 2-3 months to culture and produce what type of inflammation?
Granulomatous
Nodules to tumour like masses
Disseminated M. avium infection is seen in which breeds of cat associated with an inherited immune defect?
Abyssinian and Somali
When should you suspect rapidly growing mycobacteria?
- Non-healing wounds
- Atypical cat bite wounds
- “pepper pot” draining tracts
- Thickening or hardening of subcutis
- As a differential for Nocardia infection
Aspirates of purulent debris from intact lesions of suspected mycobacterial infection is most likely to yield a diagnosis through which test?
Culture - inoculate media immediately e.g. BACTEC system
Hard to find on cytology
Using intact lesion minimises growth of contaminants that could out compete
M. smegmatis isolates in Australia typically respond to which antibiotics?
Doxycycline and pradofloxacin
Clarithromycin unreliable for most M. smegmatis strains
M. fortuitum in the USA typically responds to which antibiotics?
Clarithromycin and pradofloxacin
Which antibiotics can be used in refractory cases of mycobacterial infection?
Clofamizine or linezolid
Should consider surgical treatment too
Which mycobacteria does rifampicin not treat?
Rapidly growing mycobacteria - intrinsic resistance
In bullous impetigo, an exfoliatin toxin-producing Staph. pseud. causes cleavage of which desmosomal protein?
Desmoglein-1
According to WAVD guidelines, which three Staphs are of primary importance in small animals?
Staphylococcus pseudintermedius, S. schleiferi (including the coagulase-negative variant) and S. aureus
Should you ask for complete speciation of all types of Staph and an antibiogram?
Yes - regardless of coag +ve or -ve
According to WAVD guidelines, a restriction-of-use policy should apply to which types of antibiotics?
- Glycopeptides (vancomycin, teicoplanin, telavancin)
- Linezolid (oxazolidinon)
- Anti-MRSA cephalosporins
Does strain typing of MRSP impact on patient- or clinic-level management?
Rarely
Used to investigate outbreaks
Are MRS susceptible to commonly used disinfectants?
Yes
When do you call MRS multi-drug resistant?
When it expresses co-resistance to at least two additional antimicrobial classes
Call it extensively drug resistant (XDR) if the strain is non-susceptible to all but two or fewer antimicrobial classes
True or false; feline nasal carriage of staphylococci is consistent with that carried by the humans in their households
True
The mouth and which other body site are nearly equal in sensitivity for identifying longitudinal colonization in dogs?
Perineum
How does coagulase factor help Staph evade the immune system?
It promotes formation of a fibrin clot scaffold for tissue invasion, is associated with abscess formation and protects staphylococcal micro-colonies (in vitro) against neutrophils
Name three major mechanisms/types of Staph virulence factors
- Biofilm formation
- Expression of adhesins by which the bacterium binds to cells and extracellular matrix
- Production of toxins (which may include cytolytic, exfoliative, enterotoxigenic and super-antigenic toxins)
- Expression of factors which assist in evasion of the host’s immune response
What are the subspecies of the coagulase variable S. schleiferi?
- S. schleiferi subsp. coagulans (coagulase-positive)
- S. schleiferi subsp. schleiferi (coagulase-negative)
Recent genotypic and epidemiological studies have shown that these two biotypes are not genotypically distinct enough to be considered true sub-species, nor do they differ in their pathogenic effects
Which CoNS (other than S. schleiferi schleiferi) have been isolated from skin and soft tissue infections in dogs and cats?
S. lugdunensis
S. haemolyticus
S. epidermidis
True or false; coagulase-negative S. schleiferi should generally be considered pathogenic when isolated from inflamed tissue or a pyogenic fluid
True
Name risk factors associated with transmission of MRSA within the community (people):
Crowded living conditions, shared bathing facilities and participation in contact sports
In dogs, both coag +ve and coag -ve S. schleiferi skin and ear infections have been statistically associated with which risk factors?
Prior antimicrobial use or recurrent pyoderma
How common is isolation of S. schleiferi from pyogenic infections of cats?
Very rare