Bacterial resistance to fluoroquinolones: lessons to be learned

Marbofloxacin combined with heavy rare-earth ions makes better candidates for veterinary drugs: crystal structure and bio-activity studies

Marbofloxacin (MB) is a newly developed fluoroquinolone antibiotic used especially as a veterinary drug. It may be regarded as the improved version of enrofloxacin owing to its antibacterial activity, enhanced bioavailability, and pharmacokinetic-pharmacodynamic (PK-PD) properties. In this study, nine heavy rare-earth ions (Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were selected in light of their potential antibacterial activity and satisfactory biosafety to afford the corresponding rare-earth metal complexes of MB: the MB-Ln series. Their chemical structures and coordination patterns were characterized using IR spectroscopy, HRMS, TGA, and X-ray single-crystal diffraction analysis. Our results confirmed that all the MB-Ln complexes yielded the coincident coordination modes with four MB ligands coordinating to the Ln(III) center. In vitro antibacterial screening on five typical bacteria strains revealed that the MB-Ln complexes exhibited antibacterial activities comparable with MB, as indicated by the MIC/MBC values, in which Escherichia coli and Salmonella typhi were the most sensitive ones to MB-Ln. Furthermore, the MB-Ln complexes were found to be much less toxic in vivo than MB, as suggested by the evaluated LD50 (50% lethal dose) values. All the MB-Ln series complexes fell in the LD50 range of 5000-15 000 mg kg-1, while the LD50 value of MB was only 1294 mg kg-1. Furthermore, MB-Lu, as the selected representative of MB-Ln, could effectively inhibit the activity of DNA gyrase, the same as MB, suggesting the primary antibacterial mechanism of the MB-Ln series. The results demonstrated the good prospects and potential of metal-based veterinary drugs with better drug performance.

Prospective Implementation of a Point-of-Care PCR-Based Detection Method to Guide Antibiotic Use Prior to Prostate Biopsy Compared to Targeted Prophylaxis and Physician Choice

OBJECTIVE

To perform pilot testing regarding implementation of a point-of-care qPCR-based test (EST200) targeting bacterial clonal groups representing the majority of sepsis-causing Escherichia coli before prostate biopsy to determine antibiotic selection.

MATERIALS AND METHODS

After IRB approval, we obtained rectal swabs to compare real-time qPCR analysis on a Rotor-Gene Q instrument (Qiagen, Hilden, Germany) to standard culture on ciprofloxacin infused (10mg/L) MacConkey agar and susceptibility testing. Techniques are compared by an area under the receiver operative curve (AUC).

RESULTS

A total of 140 men participated in the study, 102 prebiopsy cultures were utilized to guide prophylaxis. We did not meet our accrual for the randomized portion of the clinical study, yet we did randomized 38 men without prebiopsy cultures to physician choice of antibiotic versus PCR-based approach. Regarding predicting Fluoroquinolone Resistant (FQR) at biopsy, prebiopsy cultures had an AUC of 0.91 (95%CI 0.84-1.00, P > .001) and polymerase chain reaction (PCR) had an AUC of 0.71 (95%CI 0.58-0.84, P = .005) (AUC comparison; Z = 2.31, P = .02). PCR correctly identified 4 of 5 FQR specimens. The PCR test attained an AUC of 0.79 (95%CI 0.56-1.00, P = .044) for detection of total FQR on the day of the biopsy. Risk-based techniques may overcompensate with additional antibiotics (21% versus 0%, P = .10).

CONCLUSION

EST200 is a rapid PCR-based microbial detection system that has moderate ability to detect total FQR at the time of biopsy. Our study is underpowered, yet provide opportunities to improve the point of care PCR method, such as table tope testing in less than 20 minutes and include additional antibacterial resistant genes.

Relationships among ciprofloxacin, gatifloxacin, levofloxacin, and norfloxacin MICs for fluoroquinolone-resistant Escherichia coli clinical isolates

Fluoroquinolones are some of the most prescribed antibiotics in the United States. Previously, we and others showed that the fluoroquinolones exhibit a class effect with regard to the CLSI-established breakpoints for resistance, such that decreased susceptibility (i.e., an increased MIC) to one fluoroquinolone means a simultaneously decreased susceptibility to all. For defined strains, however, clear differences exist in the pharmacodynamic properties of each fluoroquinolone and the extent to which resistance-associated genotypes affect the MICs of each fluoroquinolone. In a pilot study of 920 clinical Escherichia coli isolates, we uncovered tremendous variation in norfloxacin MICs. The MICs for all of the fluoroquinolone-resistant isolates exceeded the resistance breakpoint, reaching 1,000 microg/ml. Approximately 25% of the isolates (n = 214), representing the full range of resistant norfloxacin MICs, were selected for the simultaneous determinations of ciprofloxacin, gatifloxacin, levofloxacin, and norfloxacin MICs. We found that (i) great MIC variation existed for all four fluoroquinolones, (ii) the ciprofloxacin and levofloxacin MICs of >90% of the fluoroquinolone-resistant isolates were higher than the resistance breakpoints, (iii) ciprofloxacin and levofloxacin MICs were distributed into two distinct groups, (iv) the MICs of two drug pairs (ciprofloxacin and norfloxacin by Kendall's Tau-b test and gatifloxacin and levofloxacin by paired t test) were similar with statistical significance but were different from each other, and (v) approximately 2% of isolates had unprecedented fluoroquinolone MIC relationships. Thus, although the fluoroquinolones can be considered equivalent with regard to clinical susceptibility or resistance, fluoroquinolone MICs differ dramatically for fluoroquinolone-resistant clinical isolates, likely because of differences in drug structure.

Synthesis and antibacterial activity of N-(5-benzylthio-1,3,4-thiadiazol-2-yl) and N-(5-benzylsulfonyl-1,3,4-thiadiazol-2-yl)piperazinyl quinolone derivatives

A series of N-(5-benzylthio-1,3,4-thiadiazol-2-yl) and N-(5-benzylsulfonyl-1,3,4-thiadiazol-2-yl) derivatives of piperazinyl quinolones was synthesized and evaluated for antibacterial activity against Gram-positive and Gram-negative microorganisms. Some of these derivatives exhibit high activity against Gram-positive bacteria; Staphylococcus aureus and Staphylococcus epidermidis, comparable or more potent than their parent N-piperazinyl quinolones norfloxacin and ciprofloxacin as reference drugs. The SAR of this series indicates that both the structure of the benzyl unit and the S or SO(2) linker dramatically impact antibacterial activity.

Serum bactericidal activity of gemifloxacin versus clarithromycin against Streptococcus pneumoniae with different susceptibility to quinolones

The objective of this study was to determine serum bactericidal titers (SBT, the highest dilution of serum showing no growth) and the serum bactericidal activity (SBA, i.e. duration of SBT greater than 1:2) as well as the serum bactericidal rate of gemifloxacin and clarithromycin after single doses in healthy male volunteers against Streptococcus pneumoniae. Strains tested had various degrees of susceptibility to penicillin as well as different susceptibility to quinolones due to a different QRDR mutation pattern (parC, gyrA). Serum samples from volunteers (n = 12) who had received a single oral dose of either 320 mg gemifloxacin or 500 mg clarithromycin in an open-label crossover study were obtained over a 24-hour period. SBA was determined, using the microdilution method. SBA of wildtype strains for gemifloxacin ranged from 8.9 to 15.4 h (mean 12.6 h). For gemifloxacin, 2 strains with solitary gyrA mutation had an SBA from 4.5 to 4.7 h (median 4.5 h). One of the 2 strains with a single QRDR mutation in parC displayed an SBA of 4.5 h, comparable to the gyrA mutation strains, whereas the second strain had a nearly twice as long SBA of 8.9 h. Two strains with two mutations (parC and gyrA) did not display any SBA. For clarithromycin, the duration of SBA ranged from 11.3 to 15.5 h (mean 13.6 h) for 6 of the 12 strains with an MIC < or = 0.06 mg/L (no SBA was found for the remaining strains, with an MIC of 0.25 mg/L or higher). In conclusion, a correlation between individual serum concentrations and SBA was found for both antibiotics.

The current management strategies for community-acquired urinary tract infection

Acute uncomplicated UTI is one of the most common problems for which young women seek medical attention and accounts for considerable morbidity and health care costs. Acute cystitis or pyelonephritis in the adult patient should be considered uncomplicated if the patient is not pregnant or elderly, if there has been no recent instrumentation or antimicrobial treatment, and if there are no known functional or anatomic abnormalities of the genitourinary tract. Most of these infections are caused by E. coli, which are susceptible to many oral antimicrobials, although resistance is increasing to some of the commonly used agents, especially TMP-SMX. In women with risk factors for infection with resistant bacteria, or in the setting of a high prevalence of TMP-SMX-resistant uropathogens, a case can be made for using a fluoroquinolone or nitrofurantoin. Use of nitrofurantoin for the empiric treatment of mild cystitis is supportable from a public health perspective in an attempt to decrease uropathogen resistance because it does not share cross-resistance with more commonly prescribed antimicrobials. Beta-lactams and fosfomycin should be considered second-line agents for empiric treatment of cystitis. Acute pyelonephritis in an otherwise healthy woman may be considered an uncomplicated infection. Fluoroquinolone regimens are superior to TMP-SMX for empiric therapy because of the relatively high prevalence of TMP-SMX resistance among uropathogens causing pyelonephritis. TMP-SMX, effective for patients with mild to moderate disease, is an appropriate drug if the uropathogen is known to be susceptible. It is reasonable to use a 7- to 10-day oral fluoroquinolone regimen for outpatient management of mild to moderate pyelonephritis in the setting of a susceptible causative pathogen and rapid clinical response to therapy. Most women with acute uncomplicated pyelonephritis are now managed safely and effectively as outpatients. Acute uncomplicated cystitis or pyelonephritis in healthy adult men is very uncommon but is generally caused by the same spectrum of uropathogens with the same antimicrobial susceptibility profile as that seen in women. The choice of antimicrobials is similar to that recommended for cystitis in women except that nitrofurantoin is not considered a good choice. Treatment duration should generally be longer than that recommended for women.

Bactericidal activities of BMS-284756, a novel Des-F(6)-quinolone, against Staphylococcus aureus strains with topoisomerase mutations

The antistaphylococcal activities of BMS-284756 (T-3811ME), levofloxacin, moxifloxacin, and ciprofloxacin were compared against wild-type and grlA and grlA/gyrA mutant strains of Staphylococcus aureus. BMS-284756 was the most active quinolone tested, with MICs and minimal bactericidal concentrations against S. aureus wild-type strain MT5, grlA mutant MT5224c4, and grlA/gyrA mutant EN8 of 0.03 and 0.06, 0.125 and 0.125, and 4 and 4 microg/ml, respectively. In the time-kill studies, BMS-284756 and levofloxacin exhibited rapid killing against all strains. Ciprofloxacin, however, was not bactericidal for the double mutant, EN8. BMS-284756 and levofloxacin were bactericidal (3 log(10) decrease in CFU/ml) against the MT5 and MT5224c4 strains at two and four times the MIC within 2 to 4 h. Against EN8, BMS-284756 was bactericidal within 4 h at two and four times the MIC, and levofloxacin achieved similar results within 4 to 6 h. Both the wild-type strain MT5 and grlA mutant MT5224c4 should be considered susceptible to both BMS-284756 and levofloxacin, and both quinolones are predicted to have clinical efficacy. The in vivo efficacy of BMS-284756, levofloxacin, and moxifloxacin against S. aureus strain ISP794 and its single mutant 2C6(1)-1 directly reflected the in vitro activity: increased MICs correlated with decreased in vivo efficacy. The 50% protective doses of BMS-284756 against wild-type and mutant strains were 2.2 and 1.6 mg/kg of body weight/day, respectively, compared to the levofloxacin values of 16 and 71 mg/kg/day and moxifloxacin values of 4.7 and 61.6 mg/kg/day. BMS-284756 was more potent than levofloxacin and equipotent with moxifloxacin against ISP794 both in vitro and in vivo, while BMS-284756 was more potent than levofloxacin and moxifloxacin against 2C6(1)-1.

Mechanism of action of and resistance to quinolones

A topoisomerase was identified as the bacterial target site for quinolone action in the late 1970s. Since that time, further study identified two bacterial topoisomerases, DNA gyrase and topoisomerase IV, as sites of antibacterial activity DNA gyrase appears to be the primary quinolone target for gram-negative bacteria. Topoisomerase IV appears to be the preferential target in gram-positive organisms, but this varies with the drug. Three mechanisms of resistance against quinolones are mutations of topoisomerases, decreased membrane permeability, and active drug efflux. Although these mechanisms occur singly, several resistance factors are often required to produce clinically applicable increases in minimum inhibitory concentrations. Appropriate drug selection and dosage and prudent human and veterinary interventions are important factors in controlling the emergence of resistance.

Molecular surveillance of European quinolone-resistant clinical isolates of Pseudomonas aeruginosa and Acinetobacter spp. using automated ribotyping

Nosocomial isolates of Pseudomonas aeruginosa and Acinetobacter spp. exhibit high rates of resistance to antibiotics and are often multidrug resistant. In a previous study (D. Milatovic, A. Fluit, S. Brisse, J. Verhoef, and F. J. Schmitz, Antimicrob. Agents Chemother. 44:1102-1107, 2000), isolates of these species that were resistant to sitafloxacin, a new advanced-generation fluoroquinolone with a high potency and a broad spectrum of antimicrobial activity, were found in high proportion in 23 European hospitals. Here, we investigate the clonal diversity of the 155 P. aeruginosa and 145 Acinetobacter spp. sitafloxacin-resistant isolates from that study by automated ribotyping. Numerous ribogroups (sets of isolates with indistinguishable ribotypes) were found among isolates of P. aeruginosa (n = 34) and Acinetobacter spp. (n = 16), but the majority of the isolates belonged to a limited number of major ribogroups. Sitafloxacin-resistant isolates (MICs > 2 mg/liter, used as a provisional breakpoint) showed increased concomitant resistance to piperacillin, piperacillin-tazobactam, ceftriaxone, ceftazidime, amikacin, gentamicin, and imipenem. The major ribogroups were repeatedly found in isolates from several European hospitals; these isolates showed higher levels of resistance to gentamicin and imipenem, and some of them appeared to correspond to previously described multidrug-resistant international clones of P. aeruginosa (serotype O:12) and Acinetobacter baumannii (clones I and II). Automated ribotyping, when used in combination with more discriminatory typing methods, may be a convenient library typing system for monitoring future epidemiological dynamics of geographically widespread multidrug-resistant bacterial clones.

Quinolone generations: natural history or natural selection?

The quinolones have evolved from antibacterial agents with a limited spectrum of predominantly anti-gram-negative antimicrobial activity and a restricted number of indications to a class of widely used oral (and, in some cases, intravenous) antibiotics with extensive indications for infections caused by many bacterial pathogens in most body tissues and fluids. This evolutionary pattern has arisen through the development of new core and side-chain structures, with associated improvements in activity, pharmacokinetics and tolerability, and through the selection of molecules that remain useful and well tolerated. This review describes the progress of the quinolones from the first to the third (IIIa and IIIb) generations. Special attention is given to gemifloxacin, currently the most developmentally advanced third-generation quinolone, which has enhanced in vitro gram-positive antimicrobial activity and no troublesome adverse drug reactions. Preliminary data indicate that gemifloxacin should prove to be an important addition to the fluoroquinolone class. Further clinical trial data are awaited with interest.

Selection of resistant variants of respiratory pathogens by quinolones

Quinolones are widely used in the treatment of respiratory tract infections. However, some disquiet has been expressed over using quinolones for community-acquired pneumonia since their activity is generally rather poor against Streptococcus pneumoniae. In addition, it is known that resistant variants emerge at a fairly high frequency during exposure of Enterobacteriaceae to quinolones; if this also occurred during quinolone treatment of community-acquired pneumonia it could lead to an increased risk of clinical failure. We therefore determined the selection rate of quinolone-resistant variants for six strains of S. pneumoniae, Haemophilus influenzae and Moraxella catarrhalis with nalidixic acid (except for S. pneumoniae), ciprofloxacin, ofloxacin and levofloxacin. We were only able to select resistant variants at low frequency from two of the six strains of S. pneumoniae with ciprofloxacin: no resistant variants were selected by either ofloxacin or levofloxacin. Variants of H. influenzae and M. catarrhalis with decreased susceptibility to quinolones were produced both with more strains and with a greater frequency; however, these variants still remained susceptible according to the NCCLS guidelines. Our study suggests that resistant variants of S. pneumoniae are relatively unlikely to occur in individuals treated with fluoroquinolones especially if they are given quinolones with enhanced anti-gram-positive activity compared to ciprofloxacin.

Infections caused by Escherichia coli resistant to norfloxacin in hospitalized cirrhotic patients

Selective intestinal decontamination with norfloxacin is useful to prevent bacterial infections in several groups of cirrhotic patients at high risk of infection. However, the emergence of infections caused by Escherichia coli resistant to quinolones has recently been observed in cirrhotic patients undergoing prophylactic norfloxacin. Our aim is to determine the characteristics of the infections caused by E. coli resistant to norfloxacin in hospitalized cirrhotic patients. One hundred and six infections caused by E. coli in 99 hospitalized cirrhotic patients were analyzed and distributed into two groups: group I (n = 67), infections caused by E. coli sensitive to norfloxacin, and group II (n = 39), infections caused by E. coli resistant to norfloxacin. The clinical and analytical characteristics at diagnosis of the infection were similar in both groups. Previous prophylaxis with norfloxacin was more frequent in group II (15/67, 22.4% vs. 32/39, 82%, P <.0001), as a result of a higher number of patients submitted to continuous long-term prophylaxis in this group, whereas previous short-term prophylaxis was similar in both groups. Infections were more frequently nosocomial-acquired in group II than in group I (17/67, 25.3% vs. 20/39, 51.2%, P =.01). The type of infections was similar in both groups: urinary tract infections 38 in group I and 24 in group II, spontaneous bacterial peritonitis 8 and 2, spontaneous bacteremia 4 and 4, and bacterascites 1 and 0, respectively (pNS). Mortality during hospitalization was similar in the two groups (4/67, 5.9% vs. 5/39, 12.8%, pNS). None of the E. coli resistant to norfloxacin were also resistant to cefotaxime and only one of them was resistant to amoxicillin-clavulanic acid. Prophylaxis with norfloxacin, usually continuous long-term prophylaxis, favors the development of infections caused by norfloxacin-resistant E. coli. Long-term antibiotic prophylaxis should therefore be restricted to highly selected groups of cirrhotic patients at high-risk of infection. Infections caused by E. coli resistant to norfloxacin show a severity similar to those caused by sensitive E. coli. No significant associated resistance between norfloxacin and the antibiotics most frequently used in the treatment of bacterial infections in cirrhotic patients has been observed.

Pharmacokinetic profiles of high-dose intravenous ciprofloxacin in severe sepsis. The Baragwanath Ciprofloxacin Study Group

The pharmacokinetics of 400 mg of ciprofloxacin given intravenously (i.v.) every 8 h (q8h) in severely septic adults was documented in a multidisciplinary, tertiary referral intensive care unit (ICU). Sixteen evaluable patients (three pharmacokinetic profiles) without renal dysfunction and with severe sepsis were studied. Ciprofloxacin at a dosage of 400 mg given i.v. q8h was administered over 1 h. Plasma samples for assay (high-pressure liquid chromatography) were taken at timed intervals (preinfusion, at the end of infusion, and at 1, 2, 3, 5, and 7 h postinfusion) for first-dose kinetics (day 0 [D0]), D2, and between D6 and D8. All pharmacokinetic variables were calculated by noncompartmental methods. Standard intensive care was provided. Peak ciprofloxacin concentrations were as follows: D0, 6. 01 +/- 1.93 mg/liter; D2, 6.68 +/- 2.01 mg/liter; and D6 to D8 6.45 +/- 1.54 mg/liter. Trough levels were as follows: D0, 0.6 +/- 0.5 mg/liter; D2, 0.7 +/- 0.4 mg/liter; and D6 to D8 0.6 +/- 0.4 mg/liter. The areas under the concentration curves (8 h) were as follows: D0, 13.3 +/- 3.8 mg . h/liter; D2, 16.8 +/- 5.4 mg . h/liter; and D6 to D8, 15.5 +/- 4.7 mg . h/liter. No drug-related serious adverse events occurred. For 17 of 18 patients enrolled in the study, the causative organisms were susceptible to ciprofloxacin. One patient developed renal failure (non-drug related) after the administration of three doses of ciprofloxacin. One patient was infected with ciprofloxacin-resistant organisms on enrollment. Nine of 16 evaluable patients had clinical cures, and 8 had bacteriological cures. One patient developed a ciprofloxacin-resistant superinfection. In two patients the clinical course was indeterminate. Two bacteriological failures occurred. We conclude that in critically ill adults ciprofloxacin at a dosage of 400 mg given i.v. q8h is safe. Its pharmacokinetic profile provides bactericidal activity against most organisms encountered in an ICU. Except for some initial accumulation on D2, no further accumulation occurred in patients without renal failure. Ciprofloxacin should be administered i.v. at a dosage of 400 mg q8h for severe sepsis.

How common is prostatitis? A national survey of physician visits

PURPOSE

We used a national data base to explore the epidemiology of physician visits for genitourinary symptoms or a diagnosis of prostatitis.

MATERIALS AND METHODS

We analyzed 58,955 visits by men 18 years old or older to office based physicians of all specialties, as included in the National Ambulatory Medical Care Surveys from 1990 to 1994. Physicians selected by random sampling completed visit forms that included information on patient reasons for visits and physician diagnoses.

RESULTS

From 1990 to 1994, 5% of all ambulatory visits by men 18 years old or older included genitourinary symptoms as a reason for the visit. In almost 2 million visits annually prostatitis was listed as a diagnosis, including 0.7 million by men 18 to 50 years old and 0.9 million by those older than 50 years. Of the prostatitis visits 46 and 47% were to urologists and primary care physicians, respectively. A prostatitis diagnosis was assigned at 8 and 1% of all urologist and primary care physician visits, respectively. The odds of a prostatitis diagnosis were 13-fold greater at visits to urologists compared with visits to primary care physicians, and approximately 2-fold greater in the south than in the northeast. Surprisingly, compared with men 66 years old or older, prostatitis was more commonly diagnosed in men 36 to 65 than men 18 to 35 years old. When a prostatitis diagnosis was given, antimicrobial use was likely to be reported 45% of the time for men with and 27% for those without genitourinary symptoms. Visits to primary care physicians were more often associated with antimicrobial use than visits to urologists.

CONCLUSIONS

Genitourinary symptoms are a frequent reason for office visits by younger and older men, and prostatitis is a common diagnosis. Despite a report that less than 10% of prostatitis cases are bacterial, a much higher proportion of men in whom prostatitis is diagnosed receive antimicrobials.