Ampicillin-resistant strains

Several of the compounds synthesized showed antibacterial activity against E. coli (MTCC 41), S. aureus (MTCC 1144) and the ampicillin-resistant strain Pseudomonas putida (MTCC 1072) (Table 10). 

Mechanism of Action. The drug gets destroyed readily by stomaeh acid (HCl) and, therefore, it is only aetive when adminstered either by IM or IV. It has been observed that the P-laetamase susceptibility of this drug is not absolute by virtue of the fact that P-lactamase producing ampicillin-resistant strains of N-gonorrhoeae and H. influenzae are found to be susceptible to it. 

Typhoid fever and similar salmonellal infections are usually considered the prime indications for the use of chloramphenicol. It is also employed in acute infections due to Heamophilus influenzae, including meningitis attributed to ampicillin-resistant strains. It also find its enormous applications in topical infections of eye and skin. It has also been used to eradicate vibrios from patients with cholera. It is employed for rickettsial infections like typhus and Rocky Mountain spottedfever. 

Bacterial resistance to antibiotics has been recognized since the first drugs were introduced for clinical use. The sulphonamides were introduced in 1935 and approximately 10 years later 20% of clinical isolates of Neisseria gonorrhoeae had become resistant. Similar increases in sulphonamide resistance were found in streptococci, coliforms and other bacteria. Penicillin was first used in 1941, when less than 1 % of Staphylococcus aureus strains were resistant to its action. By 1947,3 8% of hospital strains had acquired resistance and currently over 90% of Staph, aureus isolates are resistant to penicillin. Increasing resistance to antibiotics is a consequence of selective pressure, but the actual incidence of resistance varies between different bacterial species. For example, ampicillin resistance inEscherichia coli, presumably under similar selective pressure as Staph, aureus with penicillin, has remained at a level of 30-40% for mai years with a slow rate of increase. Streptococcus pyogenes, another major pathogen, has remained susceptible to penicillin since its introduction, with no reports of resistance in the scientific literature. Equally, it is well recognized that certain bacteria are unaffected by specific antibiotics. In other words, these bacteria have always been antibiotic-resistant. 

Resistance to ampicillin for strains carrying pKMIOl and resistance to tetracycline for strains carrying pAQl ... 

TMP-SMX is also used in the treatment of infection caused by ampicillin-resistant Shigella spp. and for antibiotic-resistant Salmonella spp.. The combination is also effective for covering the carrier state of Salmonella typhi, the agent of typhoid fever, and other Salmonella spp.. Successful treatment of traveler s diarrhea due to susceptible E. coli is another advantage of the use of this combination. The combination is not indicated in the therapy of enterohemorrhagic E. coli strains such as 0157 H7 because of the risk of developing hemolytic-uremic syndrome associated with the release of the cytotoxic enterotoxin by the drugs. 

ScFv into the culture media. Escherichia coli strain XLl/Blue was transformed with pEScFv 2G42D7 plasmid, and plasmid DNA was obtained by alkaline lysis (57) from the ampicillin-resistant line. 

Pneumococcal isolates with a minimal inhibitory concentration for penicillin G of greater than 2 pg/mL are highly resistant. Such strains are not killed by the concentrations of penicillin G or ampicillin that can be achieved in the cerebrospinal fluid. Nafcillin would be of value in a purulent meningitis suspected to be due to staphylococci but has minimal activity against penicillin-resistant pneumococci. Cefotaxime and ceftriaxone (not listed) are the most active cephalosporins against penicillin-resistant pneumococci, and the addition of vancomycin or rifampin is recommended in the case of highly resistant strains. As mentioned above, cefopera-zone does not readily cross the blood-brain barrier. The answer is (C). 

The presence of diphtheroid-like gram-positive rods in the cerebrospinal fluid smear of an 82-year-old patient is indicative of the presence of Listeria monocytogenes. In addition to their role as a potential causative agent in neonatal meningitis, listeria infections are more common in elderly patients and in those who have been treated with immunosuppressive agents. Treatment consists of ampicillin with or without gentamicin. Resistant strains are rare. The answer is (A). 

Fig. 6. Fraction of ampicillin-resistant clones of E. coli MG 1655 (circles) and a chemostat-selected descendant (squares) from serial batch cultivations in ampicillin-free minimal medium. Both strains harbor the expression vector pCSS4-p for periplasmic production of the recombinant a-amylase of B. stearothermophilus. Reproduced with permission from Weikert etal. [137]...

Soon after the penicillins were introduced into practice, penicillin-resistant strains of bacteria began to appear and have since proliferated. One approach to combating resistant strains is to synthesize newer, more effective penicillins, such as ampicillin, methicillin, and amoxicillin. Another approach is to search for more effective )8-lactam antibiotics. At the present time, the most effective are the cephalosporins, the first of which was isolated from the fungus Cephalosporium acremonium. These antibiotics have an even broader spectrum of antibacterial activity than penicillins and are effective against many penicillin-resistant bacteria, although resistance to cephalosporins is becoming widespread. 

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