What type of bacteria do first generation cephalosporins target primarily?

First generation cephalosporins are primarily effective against Gram-positive bacteria. This class of antibiotics, which includes drugs such as cephalexin and cefazolin, demonstrates strong activity against streptococci and staphylococci, which are notable examples of Gram-positive organisms.

The structure of the first generation cephalosporins provides them with better penetration and binding to the penicillin-binding proteins (PBPs) found in Gram-positive bacteria, leading to effective bactericidal action.

While first generation cephalosporins can have some activity against certain types of Gram-negative bacteria, their primary strength lies in combating Gram-positive infections. Other classes of antibiotics are typically used to target anaerobic bacteria or mycobacterial infections, making first generation cephalosporins less suitable for those specific types of bacteria.