For this reason, it is considered a "respiratory fluoroquinolone" along with more recently developed fluoroquinolones such as moxifloxacin and gemifloxacin. It is less active than ciprofloxacin against Gram-negative bacteria, especially "Pseudomonas aeruginosa", and lacks the anti-methicillin-resistant "Staphylococcus aureus" (MRSA) activity of moxifloxacin and gemifloxacin. Levofloxacin has shown moderate activity against anaerobes, and is about twice as potent as ofloxacin against "Mycobacterium tuberculosis" and other mycobacteria, including "Mycobacterium avium" complex. Its spectrum of activity includes most strains of bacterial pathogens responsible for respiratory, urinary tract, gastrointestinal, and abdominal infections, including Gram negative ("Escherichia coli"," Haemophilus influenzae", "Klebsiella pneumoniae", "Legionella pneumophila", "Moraxella catarrhalis", "Proteus mirabilis", and "Pseudomonas aeruginosa"), Gram positive (methicillin-sensitive but not methicillin-resistant "Staphylococcus aureus", "Streptococcus pneumoniae", "Staphylococcus epidermidis", "Enterococcus faecalis", and "Streptococcus pyogenes"), and atypical bacterial pathogens ("Chlamydophila pneumoniae" and "Mycoplasma pneumoniae"). Compared to earlier antibiotics of the fluoroquinoline class such as ciprofloxacin, levofloxacin exhibits greater activity towards Gram-positive bacteria but lesser activity toward Gram-negative bacteria, especially "Pseudomonas aeruginosa". Resistance to fluoroquinolones is common in "staphylococcus" and "pseudomonas". Resistance occurs in multiple ways. One mechanism is by an alteration in topoisomerase IV enzyme. A double mutant form of S. "pneumoniae" Gyr A + Par C bearing Ser-81-->Phe and Ser-79-->Phe mutations were eight to sixteen times less responsive to ciprofloxacin. Package inserts mention that levofloxacin is to be avoided in patients with a known hypersensitivity to levofloxacin or other quinolone drugs.