Citrobacter species and Serratia species

C. freundii, C. Koseri (Citrobacter malonaticus), and C. amalonaticus are the most common Citrobacter species isolated from nosocomial infections, such as neonatal septicaemia and pneumonia (Brenner et al., 1999).

C. freundii was first identified in 1932, since then it has been reported to cause a variety of infections in aged, immunocompromised, and debilitated patients. With the use of broad-spectrum antibiotics, C. freundii has become increasingly resistant to antimicrobial agents (Wang et al., 2000).

Small, motile, Gram-negative bacilli conforming to the definition of the enterobacteria. It is customary to place in a third group, serratia, the rapidly gelatin-liquefying organisms that form a red pigment, together with the more numerous unpigmented strains that have similar biochemical characters (Bascomb and her colleagues, 1971).

Serratia species has been identified as an important opportunistic pathogen agent in nosocomial infections (Ulatowska, 2000).

Analysis of the resistance states of S. marcescens with mathematical kinetic models that highly resistant bacteria are approximately tenfold less permeable to Cefotaxime and other β-lactams than bacteria with lower resistance and cells of sensitive strains of S. marcescens (Ball et al., 1977).

Of all Serratia species, S. marcescens is the most resistant to antibiotics, antiseptics, and metal ions but S. plymuthica is the least resistant to antimicrobials (Grimont P. and Grimont F., 1984).
S. marcescens is resistant to a variety of antibiotics including ampicillin, cephalosporins (first and second generations) and although aminoglycosides have good activity against it, resistant strains have also been reported (Coria and Ortiz., 1994).

Gram-negative bacilli including Klebsiella, Citrobacter, Serratia, Enterobcter, Proteus species and P. aeruginosa may cause hospital-wide
problem because of their ability to acquire resistance to antibiotics. Multiple
antibiotic-resistant Gram negative bacilli are more wide spread in the hospital environment as a result of broad-spectrum antibiotic usage and advanced invasive techniques (Damani, 1997).

Imipenem and ciprofloxacin was found to be the best antibiotics for treatment of Serratia infection (Yu et al., 1998).