Gram Negative bacteria Flashcards
What does the Ziehl- Neelson Stain show?
Acid-fast bacteria, stains red, bacteria have mycolic acid in cell wall
Describe Gram Negative Bacteria
Thin layer of peptidoglycan Outer lipid membrane (dissolved by ethanol) Counterstain applied (safarin) – pink/red
What are Lipopolysaccharides/ lipoglycans/ endotoxins?
- a conserved lipid portion (lipid A) inserted into the cell wall, responsible for much of the toxic activity
- a conserved core polysaccharide
- the highly variable O-polysaccharide, responsible for the serological diversity which is a feature of organisms such as salmonellae and shigellae
What immune stimuli is affected by LPS?
LPS activates immune mechanisms causing fever and vascular collapse (shock) – e.g. E. coli, N. meningitidis
activates almost every immune mechanism as well as the clotting pathway
What are the growth requirements for different bacteria?
Anaerobic- grows with oxygen
Aerobic- grows in oxygen
Facultative- either in or without oxygen
Microaerophilic- grows in the presence of oxygen at lower concentrations than that of air
Name examples of Gram-Negative Cocci
Neisseria meningitidis
Neisseria gonorrhoeae
Moraxella catharralis
Describe Neisseria meningitidis
- 10% of population carries back of their throat/nose (nasopharynx) without causing any illness = commensal
- Transmitted by inhaling respiratory secretions/ direct contact (kissing). Close and prolonged contact
- Six meningococcal capsular groups (A, B, C, W, X and Y), distinguished by their polysaccharide capsule, cause almost all invasive infections in humans . An effective vaccine is available for most meningococcal groups
What are the symptoms of Neisseria meningitidis?
rash usually starts as small, red pinpricks before spreading quickly and turning into red or purple blotches
Non-blanching rash
What diseases can Neisseria meningitidis cause?
- Can cause severe and sometimes fatal disease - meningitis (inflammation of the meninges) bacteraemia (blood) and pneumonia.
Describe Neisseria gonorrhoeae
Causal agent of gonorrhoea
Transmission: Sexual contact/ Mother to infant (perinatally)
Management includes screening for other sexually transmitted infections, contact tracing of sexual partners.
Concerns of drug-resistance – prevention is better than cure.
What are the clinical manifestations of Neisseria gonorrhoeae?
- Localised; urethritis, cervicitis, pharyngitis, rectal infection, conjunctivitis
- Pelvic inflammatory disease
- Perihepatiis (Fitz-Hugh Curtis Syndrome, also seen in C. trachomatis)
- Disseminated infection – e.g. septic arthritis
- Conjunctivitis (Ophthalmia Neonatorum)
Describe Moraxella catarrhalis
Common commensal of the human upper respiratory tract (esp. infants)
More than 90% of M. catarrhalis produce β-lactamase and are, thus, resistant to amoxicillin
What are the clinical manifestations of Moraxella catarrhalis?
Opportunistic pathogen, altered flora – commensal becomes pathogen
Children /infants - otitis media
Adults - lower respiratory tract infection (LRTI) in chronic obstructive pulmonary disease (COPD)
Describe a gram-film of Moraxella catarrhalis
Gram-film of expectorated sputum from an adult experiencing an exacerbation of COPD caused by M. catarrhalis
Abundance of neutrophils and gram-negative diplococci
What is the largest family of Gram-Negative Bacilli?
Enterobacteriaceae (facultative anaerobe)
What are the characteristics of Enterobacteriaceae coliforms?
Sugar fermenters, non-spore forming, motile by polar flagella, fimbriae for adhesion
Principal habitat: Lower gastrointestinal tract of humans and animals/ Environment (e.g. soil and water)
From in out- Cytoplasm/ Cytoplasmic membrane/ Periplasmic space/ Peptidoglycan layer/ Outer membrane/ Flagellar/ Fimbriae
What bacteria are in the family?
Escherichia coli (E.coli) Salmonella spp Shigella spp Campylobacter spp Klebsiella spp Pseudomonas aeruginosa
What are the clinical manifestations of Escherichia coli (E.coli)?
- Diarrhoeal illness - Pathogenic phenotypes including Shiga toxin producing E. coli (STEC) e.g. E coli 0157:H7 – Haemolytic Uraemia Syndrome (HUS) - do note require antibiotics
- Urinary tract infection (ascending infection)
- Bacteraemia
- Intra-abdominal and biliary tract infection
- Neonatal meningitis
- Hospital acquired infections
What are the types of UTI?
Bacterial infection is usually acquired by the ascending route from the urethra to the bladder
Lower urinary tract infection (bladder and urethra)
Upper UTI (ascending to ureter/kidneys) – pyelonethritis, renal abscess.
Prostatitis (form ascending or haematogenous infection)
What are the different pathotypes of E. Coli that are diarrhoea associated?
enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), shiga-toxin-producing E. coli (STEC) also called enterohaemorrhagic E. coli (EHEC) or verocytotoxin-producing E. coli (VTEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC) diffusely aggregative E. coli (DAEC).
What are Enteropathogenic E. coli?
They are attaching and effacing pathogens that form distinct lesions on the surfaces of intestinal epithelial cells in the small intestine. Virulence factors allow bacterial attachment to epithelial cells of the small intestine, leading to disruption of the microvillus (an ‘attaching–effacing’ mechanism of action leading to diarrhoea
Describe Salmonella spp
Can colonize a wide range of hosts and all
the major livestock species poultry, cattle, and pigs
Invade intestinal tissues, producing an enterotoxin (Stn) causing an inflammatory reaction and diarrhoea.
Carrier state; excreted in stool and can persist in gallbladder (food handlers!)
What are the clinical manifestations of Salmonella spp?
– Gastroenteritis (non-typhoidal Salmonella)
– Typhoid fever (S. Typhi and various S. Paratyphi ); Indian subcontinent, Africa, South America, South and South East Asia)
– Bacteraemia
Describe Shigella spp
Human reservoir only
Found in unclean water and contaminated food , person to person (sexual transmission)
Can survive transit through stomach (less susceptible to acid) - infective dose is small 10-200 organisms
Major health threat in developing countries where sanitation conditions are poor
What are the clinical manifestations of Shigella spp?
Causes dysentery (bloody low volume diarrhoea, abdominal pain, fever). Very rarely invasive
What are the different types of Shigella spp?
UK: Shigella flexneri Shigella sonnei Travel: Shigella dysenteriae (stx) Shigella boydii
Describe Campylobacter spp
Microaerophilic – grows in the presence of oxygen at lower concentrations than are present in atmosphere (air) (i.e. <21% O2; typically 2–10% O2)
GI tract of mammals including livestock and pets such as dogs and cats (zoonotic).
People often get C. jejuni and C. coli from:
raw or undercooked meat, especially poultry - unpasteurised milk, untreated water
What are the clinical manifestations of Campylobacter spp?
Campylobacter causes food poisoning (usually self-limiting - C. jejuni and C. Coli)
C. fetus (septic absorption sheep and cattle) – severe infection in neonates, immunocompromised, extra-intestinal disease
Describe Klebsiella spp
second largest in Enterobacteriaceae
Important in hospitals
Antibiotic resistance (Difficult to treat)
Infection Control (to prevent transmission)
What are the clinical manifestations of Klebsiella?
UTI
Liver abscess
Bacteraemia
Pneumonia
What are they hypervirulent characteristics of Klebsiella pneumoniae?
Pyogenic liver abscess, necrotising fasciitis, myositis
Diabetics and healthy people, hyper capsular serotype, community acquired infection, Taiwan Korea and SE Asia, infrequent antibiotic resistance
Describe Pseudomonas aeruginosa
Grows aerobically
Ubiquitous microorganism - found widely in nature, in soil and water. Has few nutritional requirements
Opportunistic human pathogen
Innate resistance to many antibiotics
Produces extra-cellular pigments (e.g. pyocyanin) blue/green grape like odour
What are the clinical manifestations of Pseudomonas aeruginosa?
Respiratory (e.g. cystic fibrosis (CF))
Burns
Nosocomial (hospital acquired) pathogen (e.g. environmental cross contamination)
Extensive colonisation and biofilm , mucoud forms (e.g. diabetic wounds, CF lungs).
