Gram Positive Bacteria Flashcards
where are Staphylococcus found in humans?
Found all over the skin
Form part of the human microbiota – normal flora
how is staphylococcus transmitted?
Transmitted by direct contact, via fomites and medical instruments
OPPORTUNISTIC pathogens
Cause minor to life threatening diseases
Staphylococcus genus
Genus is:
Gram positive
Facultatively anaerobic prokaryote
Staphylococcus shape
Spherical cells-clustered like grapes- due to cell division occuring in successively different planes and daughter cells remain attached
Staphle - greek for bunch of grapes
Kokkos - berry
Staphylococcus tolerance
Salt tolerant – sweat
Tolerant to desiccation, radiation and 60 deg C-survival on environmental surfaces
Desiccation - the removal of moisture from something
Survive in dust
Produce catalase
Can different between straph and streph. As one produces catalase to neutralise
2 staphylococcus species commonly associated with disease in humans
Staphylococcus aureus -more virulent
Staphylococcus epidermidis (collective term for many species) -part of normal flora of human skin-opportunistic pathogen
Common ‘staph’ infections occur when physical barriers breached.
Physical barriers breached, by IV drip, surgery,
Staphylococcus aureus defences against phagocytosis x3
Protein A coated – binds IgG stems and inhibits complement cascade (triggered by ab mol bound to ag)
Bound coagulase on surface – forms fibrin clots – hides bacteria
Slime/capsules – polysaccharide – inhibit chemotaxis and endocytosis by leukocytes and facilitates attachment (to entry points, IV drips, catheters)
Staphylococcus epidermidis
Relies almost exclusively on slime
Opportunistic – attach to urinary catheters, intravascular catheters – form biofilms
enzymes produced by Staphylococcus aureus x5
Coagulase – fibrin threads
Hyaluronidase – breaks down hyaluronic acid – major matrix component of cells
Staphylokinase – dissolves fibrin threads
Lipases – digest lipids- allows growth on skin and in cutaneous oil glands
β lactamase – 90%
Staphylococcus toxins
Cytolytic toxins – coded by genes and disrupt cytoplasmic membranes of cells including leukocytes.
Exfoliative toxin – dissolve intercellular bridge proteins causing skin sloughing
Enterotoxins – cause vomiting associated with Staphylococcal food poisoning
disease caused by staphylococcus toxins
Toxic shock syndrome toxin - fever, rash, low bp and loss of skin (tampons)
Noninvasive Staphylococcus aureus infection
food poisoning
Cutaneous Staphylococcus aureus infection
localised pyogenic lesions, e.g. SSS, impetigo
Folliculitis Staphylococcus aureus infection
hair follicle infection with progressive stages
furuncle or boil - extension of hf to surrounding tissue
carbuncle – coalesce of furuncle – deep tissue infection – fever/chills(2nd line)
Bacteremia caused by Staphylococcus aureus infections
systemic blood infection, septic
Endocarditis caused by Staphylococcus aureus infections
life-threatening inflammation of the inner lining of your heart’s chambers and valves(endocardium).
Resulting after bacteremia circulating through heart
other systemic diseases caused by Staphylococcus aureus infections
Pneumonia and empyema
Osteomyelitis caused by Staphylococcus aureus infections
infection of bone after bad bone breakage, breaks the skin
Other important groups of gram positive bacteria x7
Streptococci – lead to scarlet fever Bacillus - aerobic spore producers Clostridium Listeria Corynebacteria Mycobacteria Propionibacteria
Streptococci morphology
cocci
0.5-1.2um in diameter
Found in pairs and chains
characterics of streptococci
Gram positive cocci
Catalase negative
Facultatively anaerobic
Differentiation between gram positive cocci
Serology – reactions of antibodies to specific bacterial antigens
Haemolysis
Cell arrangement
Physiological – biochemical tests
Haemolysis differentiation
Alpha – Strep.pneumoniae & viridans streptococci
Beta – mainly Lancefield groups – Strep.pyogenes, Strep.agalactiae
Gamma – non haemolytic - Enterococci
Lancefield grouping
Serological classification scheme Based on the bacteria’s antigens Developed 1938 – Rebecca Lancefield Groups – A to H & K to V More significant human pathogens are in Lancefield groups A, B, C, D, F & G
Group A Streptococcus
AKA – GAS & S.pyogenes
1-2mm white colonies
Large zone of beta haemolysis on Blood agar at 24hrs
Bacitracin sensitive
Pathogenic species often capsulated
Pathogenesis of Group A Streptococcus
Evasion of phagocytosis
Protein M
membrane protein – destabilises complement interfering with opsonisation & lysis
Hyaluronic acid capsule
camouflage – ignored by WBCs
streptolysins
membrane bound proteins
lyse RBCs, WBCs & platelets
Interfere with oxygen-carrying capacity of blood, immunity & blood clotting
After being phagocytized – release streptolysins into phagocyte cytoplasm – causes lysosomes to be released = lyses of phagocyte & release of bacteria
Streptokinases
break down blood clots-facilitates rapid spread through infected & damaged tissue
4 distinct deoxyribonucleases
depolymerise DNA released from dead cells in abscesses – reduces firmness of pus & facilitates spread
C5a peptidase
breaks down C5a complement protein – acts as chemotactic factor – decreases movement of WBCs into infection site
Hyaluronidase
breaks down hyaluronic acid- facilitating spread through tissues
Toxins of Group A Streptococcus
Secretion of 3 distinct pyrogenic toxins-stimulate macrophage and T helper lymphocytes to release cytokines – stimulate fever, rash & shock – aka erythrogenic toxins
Toxin genes – carried on temperate phages = only lysogenised bacteria secrete
Epidemiology of Group A Streptococcus
Frequently infect pharynx or skin – resulting abscesses temporary – last only until specific immune responses occur against M proteins & streptolysins
GAS cause disease when competing microbiota depleted – large numbers gain rapid foothold before antibodies formed or patient immunocompromised
Following colonisation can invade deeper tissues & organs through barrier breaks
Spread is via respiratory droplets – especially in crowded conditions
Significance as pathogen declined since advent of antibiotics
GAS diseases x7
Pharyngitis Scarlet fever Pyoderma & Erysypelas Streptococcal Toxic Shock Syndrome Necrotizing fasciitis Rheumatic fever Glomerulonephritis - kidneys
GAS disease diagnosis
In the laboratory – Gram +ve cocci in pairs or short chains in cutaneous specimens
BA or BANA – haemolytic – Lancefield group A
ASOT - Anti-streptolysin O (ASO or ASLO) is the antibody made against streptolysin O, an immunogenic, oxygen-labile streptococcal hemolytic exotoxin produced by most strains of group A
Treatment for GAS
Penicillin
Erythromycin or Cephalexin for Penicillin allergic patients
Aggressive removal of non viable tissue in NF
Underlying infection arrested only in immune response resulting in RF & GN
Antibodies against M proteins confers long term protection but changes with strain
Group B streptococcus
S.agalactiae Bacitracin resistant Produces capsules – but targeted by antibodies – does not confer protection Predilection for newborns Produce proteases & haemolysins
Epidemiology of GBS
Normally colonise lower GI tract, genital & urinary tract
Maternal antibodies normally protects newborn
<1 week old – early onset infection
.1 week to 3 months –late onset infection
Mortality can >50%
Disease presentation of GBS
Mostly associated with
> Neonatal bacteremia, meningitis & pneumonia
Occurs 3/1000 newborns
Mortality reduced to 5% -rapid diagnosis & supportive care
25% permanent neurological damage – blindness, deafness or mental retardation
Diagnosis
Similar to GAS + B/C
treatment
Penicillin drug of choice
+ Streptomycin as some GBS can tolerate Pen x10 concentration
CDC recommend prophylaxis to newborns whose mums colonised with GBS
Immunisation
other Beta Haemolytic Streptococci x2
Group C – S.equisimilis (horses) – pharyngitis
Group F/G – S.anginosus – purulent abscesses
Penicillin effective against both
Viridans streptococci
Lack group specific carbohydrates
Normally inhabit mouth, pharynx, GI tract and urinary tract of humans
Viridans streptococci disease
Opportunistic – cause purulent abdominal infections & dental caries (dextran) – biofilm = dental plaque
Once in blood can cause meningitis & endocarditis
Streptococcus pneumoniae
Discovered 120 years ago – Louis Pasteur
Gram positive diplococcus
Disease caused
92% of pneumococci infect humans
classification
Alpha haemolytic
Dimpled colony due to death of older cells
Treatment
Sensitive to optochin
Pathogenicity
Normal flora of pharynx
Colonise – lungs, sinuses & middle ear
Virulence = polysaccharide capsule
Unencapsulated strains = avirulent
90 serotypes based on capsular antigen
Produce phosphorylecholine – stimulates cells receptors (lungs/meninges/blood vessels) to engulf & hide them
Could make its way to the brain, cause meningitis.
body defence against
Body limits migration into lungs – produces IgA – binds to organism – binds to mucous – swept away by ciliated epithelium
pathogens counteract
produce secretory IgA protease and pneumolysin binds to cholesterol in cytoplasmic membrane of ciliated epithelial cells & lysis cell
Epidemiology
Normal flora of pharynx in 75%
Cause lung infections
Typically highest in young & elderly – immune responses not fully active
annual vaccine is available
diseases caused
Pneumonia Sinusitis Otitis media Bacteremia Endocarditis Meningitis (mortality in children x20 other microorganisms)
treatment
Penicillin
1/3 now resistant – Cephalosporin, Erythromycin & Chloramphenicol
Vaccine – capsular material from 23 most common pneumococcal strains
Immunogenic – long lasting – except young, old & Aids patients
other gram positive bacteria
Enterococci Bacillus sp Listeria Corynebacteria Mycobacteria
Enterobacteriaceae
Gram negative
Enteric bacteria- members of intestinal microbiota of humans and animals
Ubiquitous in water, soil and decaying vegetation
Some are always pathogenic while others are opportunistic pathogens
Account for most nosocomial infections
morphology
Coccobacilli or bacilli – 1μm x 1.2-3μm
physiology
If motile – peritrichous flagella
Some have prominent capsule, others loose slime
All reduce nitrate to nitrite
Ferment glucose anaerobically – although grow better aerobically
All oxidase negative
differentiation
All have similar staining properties and microscopic appearance
Traditionally distinguished – biochemical tests, motility and colonial characteristics e.g MacConkey agar & Blood agar
Pathogenicity
Outer membrane lipopolysaccharide – 3 main antigenic components
a) core polysaccharide shared by all enteric bacteria-common antigen
b) O polysaccharide- various antigenic varieties among strains and species e.g. Salmonella sp
c) Lipid A
Virulence factors x7
Lipid A Capsules Fimbriae Exotoxins Iron binding compounds Haemolysins Type III secretion system
Opportunistic coliforms
E.coli Klebsiella sp Serratia sp Enterobacter sp Hafnai sp Citrobacter sp
Opportunistic noncoliform
Proteus sp
Morganella sp
Providencia sp
Edwardsiella sp
Truly pathogenic Enterobacteriaceae
Salmonella sp
Shigella sp
Yersinia sp
Escherichia coli taxonomy
Domain- Bacteria
Phylum- Proteobacteria
Class- Gammaproteobacteria
Order- Enterobacteriales
Family- Enterobacteriaceae
E.coli
Most common & important coliform
Has numerous O, H & K antigens used to identify particular strains
Some antigens e.g. O157 associated with virulence
Virulence plasmids – can be transferred
virulent e.coli
diseases caused by e.coli
UTI’s
Neonatal meningitis
Gastroenteritis- exotoxin called enterotoxin – bind proteins on intestinal tract cell lining – portion enters cell and triggers a series of chemical reactions - results in loss of electrolytes producing watery d & v – a common cause of paediatric infections on developing countries.
Severe to fatal hemorrhagic colitis
Vero toxin (VT), or Vero cytotoxin
The E coli strains associated with hemorrhagic colitis (enterohemorrhagic E coli, or EHEC) most notably O157:H7,
produce relatively large amounts of the bacteriophage-mediated Shiga-like toxin.
This toxin is called Vero toxin (VT), or Vero cytotoxin after its cytotoxic effect on cultured Vero cells.
Many strains of O157:H7 also produce a second cytotoxin (Shiga-like toxin 2, or Vero toxin 2), which is similar in effect but antigenically different.
Truly Pathogenic Enterobacteriaceae X3
Not considered members of normal microbiota of humans – almost always pathogenic due to their virulence factors
All 3 synthesize type III secretion systems
> Salmonella
> Shigella
> Yesinia
salmonella
Gram-negative facultatively anaerobic
predominantly motile by peritrichous flagella
over 2200 strains identified
all species are pathogenic to both humans and other animals
complex cycle of transmission
main reservoir of salmonella bacteria
intestinal tract of birds and animals
sewage, fertilisers and slurry
animal feeds
human carriers
foods that could be contaminated
meat and meat products milk and milk products eggs and egg products fish confectionery miscellaneous foods - dried yeast, frogs legs, marijuana, peanut butter
clinical features of Enteritis
diarrhoea, abdominal pain, mild fever, chills, nausea,
vomiting
incubation period of 5-72 hours, but occasionally up
to 7 days
lasts 2-5 days
infective dose varies from as little as 50 cells to 1,000,000 per gram of food
Enteric Fevers
some species can cause more serious infections eg. S. typhi and S. paratyphi.
Pathogenicity
Salmonellae adhere to the epithelial lining of the ileum by means of fimbriae followed by invasion and multiplication
Toxin production: endotoxin, 3 enterotoxins, cytotoxin
prevention
joint action by agriculture and food sectors of industry and also by the consumer control starts on the farm and continues through the food chain to the consumer
S.typhi infection through body
Humans sole hosts
Infection via ingestion of contaminated food or water
Bacteria pass through intestinal wall to bloodstream
Phagoscytised but not killed and carried to liver, spleen, bone marrow & gallbladder
Bacteria released from gallbladder to re-infect the intestines – resulting in gastroenteritis abdominal pain & recurring bacteremia
In some bacteria ulcerate and perforate intestinal wall causing peritonitis in abdominal cavity.
S.typhi symptoms
Patients have increasing symptoms of fever, headache, malaise, muscle pain & loss of appetite – lasts about a week
Shigella
Genus of Gram-negative, non-spore forming rod-shaped bacteria
closely related to Escherichia coli and Salmonella.
The causative agent of human shigellosis
Shigella cause disease in primates, but not in other mammals
Classification
Serogroup A: S. dysenteriae (12 serotypes)
Serogroup B: S. flexneri (6 serotypes)
Serogroup C: S. boydii(23 serotypes)
Serogroup D: S. sonnei (1 serotype)
S. flexneri
is the most frequently isolated species worldwide
accounts for 60% of cases in the developing world;
S. sonnei
causes 77% of cases in the developed world, compared to only 15% of cases in the developing world;
S. dysenteriae
is usually the cause of epidemics of dysentery, particularly in confined populations such as refugee camps.
shigella infection
Shigella infection is typically via ingestion (fecal–oral contamination); depending on age and condition of the host as few as ten bacterial cells can be enough to cause an infection.
disease presentation of shigella infection
Shigella causes dysentery that results in the destruction of the epithelial cells of the intestinal mucosa in the cecum and rectum.
Shiga toxin
Some strains produce enterotoxin & Shiga toxin, similar to the verotoxin of E. coli O157:H7.
Both Shiga toxin and verotoxin are associated with causing hemolytic uremic syndrome.
treatment
Replacing fluids & electrolytes
Oral antibiotics can be given to reduce the spread in close contacts – e.g.Ciprofloxacin & cephalosprins
Vaccine (live attenuated) being developed with some success against S. flexneri
Yersinia genus
Genus contains 3 notable species
Y. enterocolitica
Y. pseudotuberculosis
Y. pestis
pathogenesis
Normally pathogens of animals
All 3 contain virulence plasmids that code for adhesins & type III systems
Y. enterocolitica & Y. pseudotuberculosis (less severeform) are enteric pathogens acquired via consumption of contaminated food or water by animal faeces.
Y. enterocolitica occurs most often in young children.
symptoms
Common symptoms in children are fever, abdominal pain, and diarrhea, which is often bloody.
Symptoms typically develop 4 to 7 days after exposure and may last 1 to 3 weeks or longer.
In older children and adults, right-sided abdominal pain and fever may be the predominant symptoms, and may be confused with appendicitis due to inflammation of mesenteric lymph nodes
Yersinia pestis
Plague is an infectious disease of animals and humans caused by a bacterium named Yersinia pestis.
People usually get plague from being bitten by a rodent flea that is carrying the plague bacterium or by handling an infected animal.
fully treatable with antibiotics
Bubonic plague
painful swollen lymph nodes – bacteremia results in DIC, subcutaneous hemorrhaging & tissue death – ‘Black Death’
Pneumonic plague
pulmonary distress within a day – can spread person to person via aerosols & sputum
other gram negative bacteria
The Pasteurellaceae (oxidase pos) Haemophilus sp – require growth factors Bartonella Brucella Bordetella Burkholderia Pseudomonads
toxic forms of oxygen
highly reactive
because in the same way that oxygen is the final oxygen acceptor for aerobes, they are excellent oxidizing agents,
i.e. they steal electrons from other compounds
how oxygen cause damage
electron depleted compounds then steal electrons from other compounds
Resulting in a chain of vigorous oxidation
Causing irreparable damage to cells by oxidizing important compounds including proteins and lipids
Singlet oxygen (1O2)
Molecular oxygen – electrons boosted to a higher energy state – during aerobic metabolism
A very reactive oxidizing agent
Phagocytic cells – certain human white blood cells use it to oxidize pathogens
Superoxide radical (O2-)
Superoxide radicals form during incomplete reduction of O2 during electron transport in aerobes and during metabolism by anaerobes in the presence of oxygen
Aerobic organisms produce superoxide dismutase to detoxify them – lacking in anaerobes
Have active sites that contain metal ions e.g. Zn2+ and Fe2+
Combine 2 superoxide radicals and 2 protons to form hydrogen peroxide (H2O2) and oxygen
Peroxide anion (O22-)
Hydrogen peroxide produced during reactions catalysed by superoxide dismutase
Peroxide anion makes hydrogen peroxide an antimicrobial agent
Aerobes have either catalase or peroxidase to detoxify the peroxidase anion
Hydroxyl radical (OH)
Hydroxyl radicals result from ionizing radiation and from incomplete reduction of hydrogen peroxide
Most reactive of the 4
Due to catalase and peroxidase effect eliminated in aerobes
Facultative anaerobes
Can live in various oxygen concentrations
Can maintain life via fermentation or anaerobic respiration
Metabolic efficiency reduced in absence of oxygen
e.g. E.coli
Aerotolerant anaerobes
Do not use aerobic metabolism
Have some detoxifying enzymes
e.g. lactobacilli
Microaerophiles
Microaerophiles are damaged by the 21% concentration of atmospheric oxygen
Some organisms require oxygen levels of 2% to 10%
e.g. Helicobacter pylori – ulcer causing pathogen – concentration of oxygen in stomach 2-10%
Injecting Drug User (IDU) Infections
40% of IDU hospital admissions due to infections, 20% result in death
Intravenous, intra-muscular or subcutaneous injection
Minor bacterial infections usually result in local abscess formation
Severe illness if the injected material or paraphernalia, are contaminated with certain clostridial spores
Clostridia
Gram positive anaerobic spore-forming rods
pathogenic clostridia
C. perfringens C. septicum C. sordellii C. novyi C. histolyticum C. tetani C. botulinum C. difficile
distribution of clostridia
Widely distributed in soil and gut
Resistant to environmental conditions
Exist as exo-spores
Spores germinate when introduced into an oxygen-reduced environment
Pathogenic species may release powerful exotoxins
contamination of clostridia
Injuries as a result of warfare
Shrapnel wounds
Soil and faeces are the prime sources of clostridial spores
Practice of injecting substances into muscle tissue mimics the risk of infection associated with the trauma of warfare
IDU Outbreak, 2000
Cases of serious illness and deaths amongst IDUs recorded in parts of UK
60 IDUs in Scotland acquired a severe infection at or near an injection site
Spread rapidly
Extensive skin and muscle damage
Hypotension
Multi-organ failure
23 deaths
Association with a batch of heroin in circulation at the time and the practice of skin or muscle “popping”
clinical presentation of drug related infection
Soft tissue inflammation at injection site
> Abscess, Cellulitis, Fasciitis, Myositis
Local inflammatory reaction has varied
> Minimal pain and swelling at injection site
Severe local symptoms
> Extensive swelling, Pain, Oedema, Erythema with blackening/blistering at centre, Extensive necrosis, Necrotising fasciitis
infection of heroin injection
Veins become damaged after long periods of use, other areas of body may be used for injecting
> Groin area
> Behind the knees
> Neck
Bacterial contaminants of the injectate that survive can cause infections in users who inject by skin or muscle popping
Bacterial spores were suspected to be of potential importance in infections
C.novyi Type A
Widely distributed in soil
Examine anaerobic cultures after 24h incubation for small, flat, rough or rhizoidal, translucent, haemolytic colonies with a spreading edge
Exposure to air toxic to micro-colonies that haven’t begun sporulation
After 48-72h, colonies often coalesce to give a fine spreading growth
Gram-variable rods, some with sub-terminal spores
Unreactive in commercial anaerobe identification kits (API Anaerobe)
C.perfringens
Post-mortem contaminant
Large discrete colonies after 24h incubation
Flat and rough-edged, or smooth and domed
Non-haemolytic or with a narrow zone of complete haemolysis inside a larger zone of partial haemolysis
Straight-sided, gram variable rods, no spores
C.septicum
Grows rapidly
Thick, swarming growth, haemolytic
Gram variable rods, numerous sub-terminal spores
Most common source of isolates from blood cultures of patients with malignancies of the colon
C.botulinum
Proteolytic types A,B and F initially produce discrete rhizoidal colonies that spread and coalesce
Haemolysis is variable
Profuse sub-terminal and free spores, gram variable bacilli
Implicated in food-borne illnesses and cases of wound botulism
C.tetani
Uncommon in recent decades
Outbreak between July ‘03 and March ‘04, 22 cases in IDUs
Colonies may produce a fine swarming growth
Gram stain of overnight cultures can give readily over-decolorised long bacilli without spores
Classical ‘drumstick’ appearance of cells with terminal, round spores after further incubation
Treatment
Early surgical intervention
> Exploration, Drainage, Extensive debridement
Microbiological sampling
Patients presenting with compartment syndrome
> Urgent decompression
> Excision of surrounding oedematous tissues
Antimicrobial therapy
> Penicillin, Metronidazole, Clindamycin
