Question

How do bacteria become resistant to beta lactams?

Answer 1

Some can produce an enzyme called beta lactamase that breaks down beta-lactam antibiotics.
Some efflux pump is also important

Explanation:

The way that beta-lactam antibiotics work is that they bind to to the enzyme that forms cell wall. (called D,D-transpeptidase). Beta-lactamase have a similar structure D,D-transpeptidase which allows it to bind to beta-lactam. But unlike D,D-transpeptidase, it can also break down the beta lactam.

Beta-lactamase relies mainly on the following amino acid residues to function:-
1) Lys73 OR Glu166 (unsure) - activate -CONH- group inside beta-lactam structure
2) Ser70 - nucleophilic attack on carbonyl group inside beta-lactam structure. The Serine - Lysine configuration is frequently referred to as Ser-X-X-Lys
3) possible - Ser130, Lys234 - protonation of nitrogen group inside beta-lactam structure

There are a variety of antibiotics. Other mechanism for other antibiotic resistance is through the use of protein pump called efflux pump.

CmeDEF-based efflux pump is associated with resistance to antibiotics like ampicillin (which is also a beta-lactam).

Although antibiotics are the most clinically important substrates of efflux systems, it is probable that most efflux pumps have other natural physiological functions. Examples include:

• The E. coli AcrAB efflux system, which has a physiologic role of pumping out bile acids and fatty acids to lower their toxicity.
• The MexXY component of the MexXY-OprM multidrug efflux system of P. aeruginosa is inducible by antibiotics that target ribosomes via the PA5471 gene product

Also read
https://www.quora.com/How-did-certain-bacteria-become-resistant-to-certain-antibiotics/answer/Stuart-Rawson

The importance of efflux pumps in bacterial antibiotic resistance M. A. Webber and L. J. V. Piddock http://jac.oxfordjournals.org/content/51/1/9.full.pdf+html

Evidence for Multiple-Antibiotic Resistance in Campylobacter jejuni Not Mediated by CmeB or CmeF Lilian Pumbwe,1 Luke P. Randall,2 Martin J. Woodward,2 and Laura J. V. Piddock http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1068584/pdf/0475-04.pdf

Interaction of CmeABC and CmeDEF in conferring antimicrobial resistance and maintaining cell viability in Campylobacter jejuni Masato Akiba†, Jun Lin‡, Yi-Wen Barton and Qijing Zhang http://jac.oxfordjournals.org/content/57/1/52.full.pdf