Question

Staphylococcus aureus can only cause disease when the cells reach a certain population size. Explain how S. aureus senses its cell density and activates gene expression. Based on this knowledge, discuss how antibacterial drugs can be designed to disrupt virulence and why these drugs have potential advantages over antibiotics to treat S. aureus infection.

Answer 1

Q.1 Staphylococcus aureus can only cause disease when the cells reach a certain population size. Explain how S. aureus senses its cell density and activates gene expression. Based on this knowledge, discuss how antibacterial drugs can be designed to disrupt virulence and why these drugs have potential advantages over antibiotics to treat S. aureus infection.

Ans 1During the late 1950s and early 1960s, Staphylococcus aureus caused considerable morbidity and mortality as a nosocomial, or hospital-acquired, pathogen. Since then, penicillinase-resistant, semisynthetic penicillins have proved to be successful antimicrobial agents in the treatment of staphylococcal infections. Unfortunately methicillinresistant S. aureus (MRSA) strains have recently emerged as a major nosocomial problem. One way in which staphylococci become resistant is through acquisition of a chromosomal gene (mecA) that encodes an alternate target protein which is not inactivated by methicillin. The majority of the strains are resistant to several of the most commonly used antimicrobial agents, including macrolides, aminoglycosides, and the beta-lactam antibiotics, including the latest generation of cephalosporins. Serious infections by methicillin resistant strains have been most often successfully treated with an older, potentially toxic antibiotic, vancomycin. However, strains of Enterococcus and Staphylococcus recently have become resistant to vancomycin. Recently methicillin-resistant S. epidermidis strains also have emerged as a nosocomial problem, especially in individuals with prosthetic heart valves or in people who have undergone other forms of cardiac surgery. Resistance to methicillin also may extend to the cephalosporin antibiotics. Difficulties in performing in vitro tests that adequately recognize cephalosporin resistance of these strains continue to exist. Serious infections due to methicillin-resistant S. epidermidis have been successfully treated with combination therapy, including vancomycin plus rifampin or an aminoglycoside.  S aureus coagulates (clots) the fibrinogen in plasma. The clot protects the pathogen from phagocytosis and isolates it from other host defenses.it is Located on cell wall  Immunoglobulin G (IgG) binds to protein A by its Fc end, thereby preventing complement from interacting with bound IgG. Staphylococcus aureus cannot colonize the gut, they pass through the body without producing any more exotoxin; thus, this type of bacterial disease is self-limiting.The quinolones also are active against gram-positive bacteria
such as Staphylococcus aureus, Streptococcus pyogenes, and Mycobacterium tuberculosis. Currently they are used in treating urinary tract infections, sexually transmitted diseases caused by Neisseria and Chlamydia, gastrointestinal infections, respiratory tract infections, skin infections, and osteomyelitis.Vancomycin-resistant strains of Enterococcus have become widespread and recently a few cases of resistant Staphylococcus aureus have appeared.During subsequent years, the emergence of methicillin-resistant Staphylococcus aureus (MRSA) increased from 2% in 1975, to 14% in 1987, and to over 40% in 1999; similar patterns are emerging for penicillin-resistant Streptococcus pneumoniae. S. aureus with intermediate resistance to vancomycin began to appear in 1997 and the CDC believes that glycopeptide-resistant S. aureus infections are inevitable.The space environment also challenges the growth of microorganisms. Increased antimicrobial resistance has been noted among E. coli and Staphylococcus aureus bacteria in space, and fungal overgrowths can be a problem
because of changes in humidity and pockets of increased condensation aboard spacecraft and space stations.Most Staphylococcus aureus strains cause a staphylococcal enteritis related to the synthesis of extracellular toxins. These are heat-resistant proteins, and heating will not usually render the food safe. The effects of the toxins are quickly felt, with disease symptoms occurring within 2 to 6 hours. The main reservoir of S. aureus is the human nasal cavity. Frequently S. aureus is transmitted to a person’s hands and then is introduced into food during preparation. Growth and enterotoxin production usually occur when contaminated foods are held at room temperature for several hours.Toxic shock syndrome also cause by S.aureus.