Gram+ve bacteria.txt

• governs which antibiotic to give
• if both G+ and G- involved then give broad spectrum antibiotic

• 1. is it gram negative or positive
• 2. shape: round = cocci; rod = bacilli
• 3. arrangement: chains = strep; bunches = staph

• streptococci
• enterococci

• alpha haemolytic: SOME digestion of RBC, see some green which is residual Hb
• beta haemolytic: TOTAL

1. viridans: muttons, sanguine. they are normal flora or mouth and throat (URT flora)

• not in site of normal flora
• but potential for infection where mouth flora translocates: infective endocarditis (native valve) & aspiration pneumonia from mouth to airway

anaerobic organisms

• anaerobes
• 1% is E Coli

• 1. treat the alpha haemolytic strep which has gone from mouth to airway
• 2. empirically also treat anaerobic organism as they cover mucosal surfaces eg mouth so would also fall into airway

because the ENVRIONMENT is NOT ANAEROBIC

• PEPTIDOGLYCANS
• this is important binding site for B-lactam antibiotics eg penicillin

• 1. penicillin
• 2. gentamicin

• 1. metronidazole (for anaerobes)
• 2. penicillin eg amoxicillin for alpha streps

not

• G+ve cocci in pairs
• area of 'non staining' or halo around each of pairs

halo = capsule - thick polysaccharide capsule which does not take up gram stain

• its capsule! as it makes it anti-phagocytic
• phagocytes find it difficult to ingest a capsulated organism. goes to spleen for opsonisation by Ab and complement to coat organism - makes it more edible to neutrophil as on surface on neutrophil there are Ab and complement receptors

• opsonisation
• 1. complement
• 2. antibody coating

spleen

susceptible to overwhelming infection with capsular organisms especially pneumococcus (also meningococcus, haemophilus)

• 1. ask if had splenectomy
• 2. check spleen function
• 3. check for sickle cell

• pneumonia: lobar pneumonia, most important cause of CAP
• bacterial meningitis (outside of the neonatal period)

• protect with penicillin prophylaxis for life
• pneumococcal vaccine

• penicillin unless allergy or resistance. high dose benzyl-penicillin
• emerging resistance to penicillin amongst pneumonococcus then use cefuroxime (doesn't cross BBB)

• penicillin crosses the inflamed BBB very well
• use penicillin
• if suspect resistance eg spanish or american don't rely on penicillin so then give ceftriaxone (also penetrates BBB very well)

• grows on blood agar
• complete haemolysis of RBC on blood agar plate

• Lancefield grouping
• based on outer nature of the Ag carbohydrate around organism

• strep pyogenes
• wide range of infections

virus

GAS

• bacterial
• looks unwell
• fever
• severe pain in throat
• enlarged LN

• penicillin V (oral)
• not amoxicillin as could be glandular fever - EBV - causes RASH!

impetigo

bullous & non bullous - more common

• central crusting with surrounding redness
• impetigo is usually a dual infection: staph and strep. central crusting with pus is due to staph aureus
• peripheral erythema is due to GAStrep

• amoxicillin for GAS
• flucloxacillin for staph aureus

• 85% of staph worldwide make enzyme beta lactamase that destroys basic beta lactam molecule of penicillin V and amoxicillin
• flucloxacilin - structured in a way that is beta lactamase stable
• so if you see G+ve clusters = staph = only use fluclox

cellulitis

• 1. pain +++ around lesion
• 2. looks unwell - febrile toxic

• 1. mark cellulitis to see how fast spreading
• 2. bloods: FBC, CRP, blood cultures
• 3. swabs from anywhere
• 4. iv high dose ben pen & fluclox to cover staph that might inactivate penicillin

• extensive surgical debridement
• abx are only supplementary. wont work alone as blood vessels dead
• iv ben pen & clindamycin (acts on ribosome, switch off protein synthesis so toxin production stopped)

• 1. necrotising fasciitis
• 2. post partum sepsis (ascends and infects raw uterine bed, causes severe toxaemia and septicaemia) high mortality

• group C & G
• rare and less severe

• erysipelas: classic hard raised indurated lesion on face/limbs/ sub cut tissue. surrounding fluid filled blebs
• pyrogenic exotins

• swab throat or other lesion may get organism
• not just lesion as its caused by toxin of strep so might not see the actual GAS

penicillin

• scarlett fever
• erythrogenic toxin

• circumoral pallor
• fine reticular rash chest
• strawberry tongue

treat with penicillin, can give amoxicilin as no association between scarlet fever and EBV (amox is easier to swallow, better absorbed from stomach, only tds as opposed to penicillin qds)

toxic shock syndrome (nb originally assoc with staph but now we know also with strep too)

group A

• 1. rheumatic fever: cross reaction of Ab between strep Ag and cardiac tissue Ag (autoimmune)
• 2. post strep acute glomerulonephritis: immune complex (type 3) very big and settle on glomerular BM, attract complement and macrophages, neutrophils release potent tissue destroying enzymes so glomerular BM subjected to inflammatory reactions

sore throat causing streps

skin and subcut causing streps

• long term abx
• steroids

vagina (25-30% of women)

pregnant: UTI, most important cause of neonatal sepsis

antibiotic: penicillin

• to provide anti-microbial synergy
• penicillin attacks CELL WALL of strep
• through cell wall gentamicin HITS RIBOSOME AND STOPS PROTEIN SYNTHESIS to over kill the organism

• heart valve avascular
• vegetation avascular
• getting the antibiotic there depends on blood stream in heart by apposition to hit the organism
• need quick exponential killing so have to add gentamicin for synergy

• group F strep
• milleri group

colonises mucosal surfaces.

associated with internal organ abscess tooth, sinusitis, brain, splenic, liver form gut mucosa

• penicillin
• metronidazole: as anaerobe also sitting there

enterococci

• enterococcus faecalis
• enterococcus faecium

gut

• 1. cephalosporins wont work against enterococci
• 2. enterococci are LOW VIRULENCE, innocuous organisms that usually hang about, colonise diabetic ulcers, sacral sores

don't always need to treat unless some degree of immunocompromise (transplant, haem) then enterococi can cause ANYTHING from line infections, UTI, endocarditis, wound infection, septicaemia

• 1. find out if susceptible to amoxicillin - treatment of choice
• e. faecalis is SENSITIVE to amoxicillin
• BUT most of e.faecium is resistant to amoxicillin
• also give gentamicin
• if cant use amoxicillin or cephalosporins use vancomycin or teicopleinin for serious enterococcus that doesn't respond to amoxicillin

• VRE: vancomycin resistant enterococus
• then use the abx: linezolid

• staph produce beta lactamase so cant use normal penicillin or amoxicillin
• need to use beta lactamase stable penicillin

• coagulase positive eg staph aureus
• coagulase negative eg staph epidermidis

• add organism to plasma and cook it
• if there is coagulase it will form a clot and so if you see clot it is coag+ve which is staph aureus

• its loves moisture, warmth and salt so colonises sweaty areas
• skin: armpit, groin, hairline, nose

• abscess. hurt themselves
• pointy red lesion, if lance it PUS comes out
• little pus spots on skin
• likes to clog hair follicles, sebaceous cysts = folliculitis

staph aureus

• diabetes as neutrophils functionally not quite right
• prone to repeated, recurrent staph infections

furuncle

carbuncle

lactating breast abscess as baby is colonised with staph aureus in umbilicus or in the mouth. staph goes through duct and into substance of mammary gland

• lance it
• release pus
• treat with flucloxacillin

• 1. heart - endocarditis: new murmur, echo
• 2. bone esp vertebral bodies as distribution of blood supply is such that it is a common reservoir. vertebral osteomyelitis
• 3. psoas abscess - ask for bone and back pain
• 4. septicaemia
• 5. septic arthritis

staph aureus

• patchy decalcification
• periosteal elevation

• 1. toxic shock syndrome (TSST1). menstrual tampon use; non menstrual much commoner. the staph that has infected your wound carries the gene TSST1
• vomit, diarrhoea, rash - TSS. easily miss systemic effects of staph
• 2. scalded skin syndrome: babies. epidermylytic toxins - peel off skin. not life threatening if no secondary infection. treat iv flucloxacillin
• 3. food poisoning: some staph aureus have gene for enterotoxin. severe rapid onset vomiting. vomit rather than diarrhoea
• 4. PVL: pontoon valentine leukocidin: USA who played contact sport where mixture of sweat or share gear stained with sweat - toxin destroy leucocyte and cause severe necrotising skin and lung lesions, cause death.
• Rx: fluclox + clindamycin

• mild oral fluclox,
• severe iv fluclox + gent

• flucloxacillin resistant
• so need vancomycin, teicoplenin
• linezolid, rifampicin are other options

staph epidermidis

• central lines
• hickman lines
• plastic or metal - will get colonised with skin organisms
• prosthesis: knee joints, heart valves. so needs adequate prophylaxis, skin asepsis,

72 hours

slime, biofilm, glycocalyx trap the CNS. no abx can penetrate the glycocalyx so must remove line

• not flucloxacillin as skin commensals get acquired resistance to it
• so use vancomycin or teicopleinin +/- gentamicin