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  • Writer's pictureNalaka de Silva

Microbiology in ENT

Updated: Jun 29, 2019

General Outline

Best to think of Microbiology and treatment as follows. First, know the main groups of bacteria with their virulence factors and features. Then understand the mechanism of action of Antibiotics. Marry the 2 to understand which bacteria is countered with what antibiotic.

1) Bacteria in ENT

a) G stein and Features

b) Main to know Types and subtypes of importance

c) Virulence factors and what ENT manifestations do they cause.

2) Main types of antibiotics

a) cell wall inhibitors

b) stops protein synthesis,

c) nucleic acid

d) metabolism

3) Then what antibiotic to use for what (combine 1 and 2)



G+ves :

Streps and Staphs

G -ves :

HI, Moraxella C

Obligate Aerobes:


Obligate Anaerobes :

Bacteriodes, petostrep, Clostridium types, Fusobacterium

Without a capsule-:




Features G+ve diplococcus-or chains , facultative anaerobe

Types: 2 maintypes on haemolysis

1)Alpha H is Strep Pneumoniae

Causes - Pneumonia, Acute Sinusitis, AOM/ mastoiditis, meningitis

2) beta Haemolytic (groups A-F)

Group A is the most common Strep Pyogenes

Has exotoxins, supra AG can cause toxic shock (shock in the absence of culture)

Causes: Tonsillitis, Erysepelus, Impetigo, Neck Fasciitis, parotitis-lymph adenitis Mastoiditis also RF and post step GN


G+ve cocci in clumps, facultative anaerobe

2 main types: Coagulase - Promotes activation of thrombin

Cogulase - ve are usually commensals as Staph Epi (commensal)

Cogulalase +ve are pathogenic mostly Staph Aureus

causes: Skin infections ie cellulitis, furuncle, Otitis externa

Sinus: chronic sinusitis

Middle Ear: CSOM, Mastoiditis

Parotitis, lymph adentitis

Toxic Shock Sy

Haemophilus influenzae

G-ve coco bacillus, facultative anaerobe, produces B lactamase

Can be Typable or Non

Typable: most important is HI B

Causes Epiglottis in kids rare now

Non Typable

AOM/mastoiditis, Sinus, URTI,

Moraxella catarrhalis

Gram negative diplococcus which is a common respiratory pathogen in humans

Nasopharyngeal colonisation in 1-5% of adults, 30-100% of infants

Clinical manifestations

Otitis media

Lower respiratory tract infections

COPD, elderly, nosocomial



Some of these are +ve some -ve main importance is that they are anaerobic. This will help determine the choice of antibiotic

ie Pep Strep is G+ve ve anaerobe: can cause tonsillitis, dental infections

i.e. Fusobacterium NF: G-ve bacilli (AGNB) Deep neck infections with JV thrombosis, Parotitis, CSOM, mastoiditis



Motile gram negative aerobic bacillus which is ubiquitous in the environment and an opportunistic pathogen

CSOM, OE, Mastoiditis, Skull base OM


Consider Antibiotics- 4 main types

A) Acts on the cell wall

B) Acts on Protein synthesis

C) Acts on the nuclear nucleic acid synthesis

D) affects metabolism

A On cell wall (beta lactums and Non beta lactums)


Beta lactums:

penicillins (Penicillin G, Amoxyl, Flucox)

Cefs. (1st, 2nd, 3rd)


and Monobactums

Non beta lactums:



penicillin G: for most streps, not staph, some good anaerobic activity

Amoxyl: Variable for strep , not staph, HI and anaerobes (better 90 mg /kg per day) (not for staph). All of this is increased with clay acid.

Flucox (good for staph, not for strep anaerobes)

Tazocillin: broad inc Pseudomonas

Cephs: 1st gen ceph +ves low anaerobes , 2n both +ves and -ves and some anaerobes, 3rd mostly -ves, 4th Gen alls and inc pusedomaonas

penums broad spectrum G+ves, -ves, anaerobes and pseudomonas

B Protein synthesis





C DNA synthesis ie Quinolones

mostly Cipro

good for strep, staph, HI and pseudomonas, G-ve No anaerobic cover


A Pharyngo-tonsilitis

Streps, N gono, N mengid,

1st line -PO penicillin, IV ceph

less likely

Corynebact dip, anaerobes


If recurrence after penicillin consider shielding by beta lactamase producers and try amox/clav)

Clinical Q2


As Above

Penicillin still 1st line and has sufficient anaerobic cover as well

Clinica Q 3

Deep neck abscess

Mostly anaerobes, Group A Strep,

staph, Fusobacterium

Must give broad spectrum until sensitivity, hence pipera/tazo, Imipenem is reaosnable.

Alternately Cef and Met (combination)

Parotitis/ lymph adenitis

SA, GABHS, G-ve bacilli, Anaerobes Amoxyl/Clav, 1st Gen Ceph/met


Acute OM

S pneu, Hi, M cat - High dose amoxl po

(If no response Augmentin rarely needed)

Acute, Chronic Mastoiditis

S. pneu, S pyo, S. aureus, HI, Pseudo

Enterobacter, AGNB, Peptostrep

Augmentin, if Pseudo: Pip/tazo, Imipenem


Pseudo, S. aureus, AGNB, Peptostrep -Augmentin, clinda,

Acute Sinusitis

S pneu, H. i, M cat, S pyo, S. aureus -

1st line Augmentin,


2nd gen ceph, clinda, doxy, macro


Group A is the most common Strep Pyogenes

Has exotoxins, supra AG can cause toxic shock (shock in the absence of culture)

Treatment: Penicillin (+/- Flucox)

Nasal Furuncle


Flucox, 1st Gen Ceph if allergic Clindamycin

Other Cases....

Cervical lymph adenitis

Mostly viral, SA, GABHS,

-Augmentin, Clindamycin

Dental origin serious infection

Anaerobes, Fusobacteria, Treponemes

Penicillin +Metronidazole or Amox/clav

if allergic: clindamycin

Descending Mediastinitis

Polymicrobial with Anaerobes esp F. necrophorum

meropenem or cephalosporin + metronidazole

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