De kan vara konstitutiva eller inducerbara, och de kan vara kromosomalt medierade eller plasmidmedierade. Betalaktamaspositiva stammar klassas som R mot penicilliner. Enterococcus faecalis kan i undantagsfall, oftast med samtidig aminoglykosidresistens, bilda betalaktamas av samma typ som Staphylococcus aureus. They are present in many different bacterial species. They are constitutively or inducibly produced, and they are mediated by genes of chromosomal origin or carried on plasmids.
Various methods are available for detection of betalactamase activity.
The most specific of these and also the most commonly used is the nitrocefin test. This test is based on the use of a chromogenic cephalosporin, which is yellow when intact but changes colour to red when its betalactam bond is hydrolysed by a bacterial betalactamase. Nitrocefin can be used in solution or as paper disks. The colour change is often rapid and can be read within 30 minutes. Alternative methods are the so called cloverleaf test , the acidometric method and the iodometric method.