24 Chapter 2 Table 1. Different beta- lactamase families with possible original species, number of variants and expected phenotype ( ↑↑ = strongly increased MIC, ↑ = moderately increased MIC, ↓ = low MIC) 3,4 AmpC betalactamase family Probably from chromosome of species Genetic similarity chromosomal gene Number of variants Phenotype 1 blaCMY -2 family Citrobacter freundii 96% n =171 Third-generation cephalosporins ↑↑, cephamycins (blaCMY -13 inducible) 2 blaDHA family Morganella morgagnii 99% n =29 Third-generation cephalosporins ↑, cephamycins (inducible) 3 blaACC family Hafnia alvei 99% n = 7 Third-generation cephalosporins ↑, cephamycins 4 blaACT /MIR family Enterobacter cloacal complex 98-99% n = 83 (blaACT ), n = 22 (blaMIR ) Third-generation cephalosporins ↑, cephamycins (blaACT inducible) 5 blaFOX family Aeromonas caviae 99% n=16 Third-generation cephalosporins ↓, cephamycins ↑↑ 6 blaMOX/CMY-1 family Aeromonas hydrophila 80-82% n=14 (blaMOX), n=6 (blaCMY-1) Third-generation cephalosporins ↑, cephamycins In certain species within the group 1 Enterobacterales, e.g., E. coli and Shigella spp, the production of AmpC beta-lactamase is not only encoded on plasmids, but can also be mediated by hyperexpression of a chromosome-encoded ampC gene (campC) (Jacoby 2009; Tracz et al. 2007). Normally, campC is only expressed at a low level in E. coli, but mutations in the promoter/attenuator region of the campC gene lead to hyperproduction of the chromosome-encoded AmpC beta-lactamase. The presence of these “chromosomal AmpC hyperproducers” complicates the detection of pampC genes in E. coli when
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