Antibiotic – intrinsic resistance

Enterobacterales & Aeromonas

Enterobacterales and Aeromonas are intrinsically resistant to benzylpenicillin, glycopeptides, lipoglycopeptides, fusidic acid, macrolides (Except Azithromycin, effective for typhoid/paratyphoid fever and erythromycin for travellers’ diarrhoea), lincosamides, streptogramins, rifampicin, and oxazolidinones.

Bacteria	Beta-lactams	Non-beta-lactams
Klebsiella pneumonia complex, Klebsiella oxytoca Roultella sp. Citrobacter koseri, Citrobacter amalonaticus	Amoxicillin, Ticarcillin
Klebsiella aerogenes, Enterobacter cloacae complex Citrobacter freundii Hafnia alvei	Amoxicillin, Coamoxiclav, 1st generation cephalosporins Cefoxitin
Serratia marcescens	Amoxicillin, Coamoxiclav, 1st and 2nd generation cephalosporin	Tetracycline, doxycycline (not minocycline or tigecycline) Colistin, Nitrofurantoin

Bacteria	Beta-lactams	Non beta-lactams
Proteus mirabilis		Tetracycline, Tigecycline Colistin, Nitrofurantoin
Proteus vulgaris	Amoxicillin 1st generation cephalosporins, cefuroxime	Tetracycline, Tigecycline Colistin, Nitrofurantoin
Providencia stuartii, P rettgeri	Amoxicillin, Coamoxiclav 1st generation cephalosporin	Tetracycline Colistin, Nitrofurantoin
Morganella morganii	Amoxicillin, Coamoxiclav 1st generation cephalosporin	Tetracycline Colistin, Nitrofurantoin

Bacteria	Beta-lactams	Non-beta-lactams
Yersinia enterocolitica	Amoxicillin, Coamoxiclav, 1st generation cephalosporins 2nd generation – cefoxitin (but not cefuroxime)
Yersinia pseudotuberculosis		Colistin
Aeromonas hydrophila Aeromonas caviae	Amoxicillin, coamoxiclav, Cefoxitin

Non-fermentative gram-negative bacteria

Generally intrinsically resistant to benzylpenicillin, first- and second-generation cephalosporins, glycopeptides, lipoglycopeptides, fusidic acid, macrolides, lincosamides, streptogramins, rifampicin and oxazolidinones.

Bacteria	Beta-lactam	Non-beta-lactam
Acinetobacter baumannii, Acinetobacter pittii, Acinetobacter nosocomialis	Amoxicillin, Coamoxiclav Ceftriaxone, Cefotaxime, Ertapenem, Aztreonam	Trimethoprim, Fosfomycin, Tetracycline, Doxycycline (Not Minocycline/Tigecycline)
Pseudomonas aeruginosa	Amoxicillin, Coamoxiclav Ceftriaxone, Cefotaxime, Ertapenem	Trimethoprim Chloramphenicol Tetracycline group, Tigecycline Kanamycin, Neomycin
Burkholderia cepacia complex	Amoxicillin, Coamoxiclav Ticar-clavulinic acid, Pip-tazobactam, Ceftriaxone, Cefotaxime, Ertapenem, Aztreonam	Trimethoprim, Chloramphenicol, Ciprofloxacin, Fosfomycin, Colistin Aminoglycoside
Stenotrophomonas maltophilia	Amoxicillin, Coamoxiclav Pip-tazobactam, Ceftriaxone, Cefotaxime, Ertapenem, Meropenem, Aztreonam	Aminoglycoside, Trimethoprim (cotrimoxazole), Fosfomycin, Tetracycline (Not doxycycline, minocycline, tigecycline)

Bacteria	Beta-lactams	Non-beta-lactams
Achromobacter xylosoxidans	Amoxicillin, Ceftriaxone, Cefotaxime, Ertapenem
Ochrobactrum anthropi	Amoxicillin, Coamoxiclav Ticar-clavulinic acid, Pip-tazobactam, Ceftriaxone, Cefotaxime, Ceftazidime, Cefepime Ertapenem , Aztreonam
Elizabethkingia meningoseptica	Amoxicillin, Coamoxiclav Ticar-clavulinic acid, Ceftriaxone, Cefotaxime, Ceftazidime, Cefepime Ertapenem , Aztreonam Meropenem	Colistin

Other gram negatives

All of them are intrinsically resistant to glycopeptides, lipoglycopeptides, lincosamides, and oxazolidinones. Additionally…

Bacteria	Antibiotic
Haemophilus influenzae	Fusidic acid, Streptogramins
Moraxella catarrhalis	Trimethoprim
Neisseria spp	Trimethoprim
Campylobacter jejuni, Campylobacter coli	Fusidic acid, Streptogramins, Trimethoprim
Campylobacter fetus	Fusidic acid, Streptogramins, Trimethoprim, nalidixic acid

Gram-positive bacteria

Gram-positive bacteria are also intrinsically resistant to aztreonam, temocillin, polymyxin B/colistin and nalidixic acid.

Bacteria	Beta-lactams	Aminoglycoside, MLSB	Others
Staphylococcus saprophyticus	Ceftazidime		Fosfomycin Novobiocin
Staph cohnii, Staph xylosus	Ceftazidime		Novobiocin
Staph capitis	Ceftazidime		Fosfomycin
Staph aureus, other CoNs	Ceftazidime
Streptococcus	Ceftazidime	Aminoglycoside (low-level resistance*)
Enterococcus faecalis	Cephalosporins	Aminoglycoside (low-level resistance*) Macrolides, clindamycin Quinupristin-dalfopristin	Fusidic acid, Sulfonamide
Enterococcus gallinarum, Enterococcus casseliflavus	Cephalosporins	Aminoglycoside (low-level resistance*) Macrolides, clindamycin Quinupristin-dalfopristin	Fusidic acid, Sulfonamide, Vancomycin
Enterococcus faecium	Cephalosporins	Aminoglycosides (low-level resistance+AAC(6’)-I**) Macrolide	Fusidic acid Sulfonamide
Corynebacterium spp.			Fosfomycin
Listeria	Cephalosporins
Leuconostoc spp., Pediococcus spp. Lactobacillus spp. (L. casei, L. casei var. rhamnosus)			Vancomycin Teicoplanin

* Low-level resistance – Synergy can be achieved with penicillin or vancomycin unless high-level resistance is present (need testing)
** Low-level resistance + AAC(6’)-I enzyme – the synergy is only seen in gent, amikacin and streptomycin.

Anaerobes

Anaerobes are intrinsically resistant to aztreonam, aminoglycosides, polymyxin B/colistin and nalidixic acid.

Additionally,

Clostridium ramosum & Clostridium innocuum are resistant to vancomycin.

Reference:

https://www.eucast.org/expert_rules_and_intrinsic_resistance/

https://www.eucast.org/fileadmin/src/media/PDFs/EUCAST_files/Expert_Rules/2020/Intrinsic_Resistance_and_Unusual_Phenotypes_Tables_v3.2_20200225.pdf