1. Klebsiella oxytoca and K1 enzyme
(indole positive)
Chromosomal
R/ ampicillin
Mutational hyperproduction
R/ cephalosporins
Less susceptible to clavulanic acid than ESBL
No key hole
Key hole not obvious

2. A Klebsiella oxytoca with basal K1 b-lactamase resistant to ampicillin and susceptible to Augmentin, cephalexin and cefotaxime.

3. A hyperproducer Klebsiella oxytoca with a high level of mutational K1 b-lactamase shows resistance to Augmentin, cephalexin and cefotaxime.

4. Another hyperproducer Klebsiella oxytoca with a high level of mutational K1 b-lactamase. Note the tiny "keyhole" between cefotaxime (CTX 5) and Augmentin (AMC 60) and the small inhibitory zone around cephalexin (CL100). The tiny "keyhole“ is a “bonus” as most strains with high K1 activity simply show resistance to Augmentin, cephalexin and cefotaxime.

5. A hyperproducer Klebsiella oxytoca with a low level of mutational K1 b-lactamase. Note the slight synergy between Augmentin (AMC 60) and the cephalosporin discs cephalexin (CL100) and cefotaxime (CTX 5).

6. A Klebsiella oxytoca with an ESBL
A Klebsiella oxytoca with an ESBL. It’s likely that the isolate only has basal K1 b-lactamase (large zone around AMC 60).

7. Klebsiella oxytoca hyperproducer of K1
Reporting
Klebsiella oxytoca hyperproducer of K1
Not ESBL (plasmid mediated)
As per Table 4
R/ ampicillin, cephalexin, cefotaxime…..