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.
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.
Staphylococcus aureus can only cause disease when the cells reach a certain population size. Explain how...
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