Increasing bacterial resistance in pediatric acute conjunctivitis (1997-1998)

We sought to determine the current level of resistance in Haemophilus influenzae and Streptococcus pneumoniae, the primary pathogens of pediatric conjunctivitis. Between January 1997 and March 1998, we prospectively cultured acute conjunctivitis in 250 ambulatory pediatric patients from rural Kentucky whose average age was 24.3 months. In those 250 cases, 106 H. influenzae (42% of the total) and 75 S. pneumoniae (30% of the total) pathogens were isolated, with no growth or no pathogen resulting in 79 cases (32% of the total). Beta-lactamase was detected in 60 (69%) of 87 tested strains of H. influenzae. Among 65 isolates of S. pneumoniae tested for penicillin susceptibility, 44 (68%) were susceptible, 17 (26%) were resistant, and 4 (6%) were intermediate. Conjunctivitis with acute otitis media was observed in 97 patients (39%), and H. influenzae was recovered in 57% of these 97 cases. As for in vitro activity, ciprofloxacin, ofloxacin, and tetracycline were the most active; and gentamicin, tobramycin, polymyxin B-trimethoprim, and polymyxin B-neomycin were intermediately active. Sulfamethoxazole possessed no activity against either pathogen. Beta-lactamase production was detected in 69% of H. influenzae strains, which still remains the primary causative pathogen of both conjunctivitis and conjunctivitis-otitis syndrome. Penicillin-nonsusceptible S. pneumoniae was observed in 32% of 65 patients with S. pneumoniae conjunctivitis, with most strains being penicillin resistant.     

Emergence of fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli in subjects from Finland.

The in vitro susceptibilities of 102 human campylobacter strains isolated between 1978 and 1980 and 100 strains isolated in 1990 to ciprofloxacin, norfloxacin, erythromycin, gentamicin, and doxycycline were examined. The biotypes and heat-stable serotypes of the strains as well as antimicrobial treatments and travel history of the campylobacter-positive patients were also studied. The results indicated that susceptibility to erythromycin, gentamicin, and doxycycline has remained the same during the past 10 years. No gentamicin-resistant strains were found. Resistance to erythromycin was 3% in both groups of strains. However, the number of norfloxacin-resistant strains increased from 4 to 11% in the follow-up period, and ciprofloxacin-resistant strains, which had not occurred 10 years ago, composed 9% of the strains isolated in 1990. Thus, the increase of fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli has been significant in Finland in the past 10 years.     

Trends in fluoroquinolone resistance of Mycobacterium tuberculosis complex in a Taiwanese medical centre: 1995-2003

OBJECTIVES: Fluoroquinolones are being used more frequently for the treatment of multidrug-resistant (MDR) strains of Mycobacterium tuberculosis complex (MTB). This study was designed to determine the frequency of the emergence of fluoroquinolone-resistant strains in Taiwan and to assess whether this might be due to use of fluoroquinolones for treatment of patients with MDR or because of increased use of fluoroquinolones in the community for treatment of other infections. We also sought to determine whether there might be clonal spread of fluoroquinolone resistance. METHODS: A total of 3497 clinical isolates of M. tuberculosis complex were obtained during 1995-2003, of which 141 were selected. They consisted of 62 isolates fully susceptible to four first-line drugs, 33 isolates resistant to rifampicin and isoniazid (MDR), and 46 isolates with a variety of any drug resistant patterns other than MDR (combination group). The MICs were determined for ciprofloxacin, ofloxacin and levofloxacin. RESULTS: An increase in the MIC90 and rates of resistance to ciprofloxacin, ofloxacin and levofloxacin were noted only in the MDR group. The rates were higher among strains isolated between 1998-2003 compared with those obtained between 1995-1997 (rate of resistance, 20% versus 7.7%; MIC > or = 4 mg/L versus 1-2 mg/L). Among the 10 fluoroquinolone-resistant isolates, five (50%) possessed mutations other than S95T in the gyrA gene. No gyrB mutation was found in any of the clinical isolates. Conclusions: These findings suggest that fluoroquinolone resistance is the result of treatment of patients with MDR strains rather than from use in the general community in Taiwan. The emergence of fluoroquinolone resistance among MDR strains reinforces the need for routine fluoroquinolone susceptibility testing whenever these drugs might be used.     

Rare serotypes of salmonella circulating in Kazakhstan

The serotypic picture of rare-type salmonellas, isolated in the South region of Kazakhstan, was studied. The circulation of 31 serotypes of 17 groups was established. The circulation of serotypes 0:13, 0:38, 0:44 serogroups, was found among people (patients and bacterium-carriers). Serotypes 0:28, 0:42, 0:62, 0:66 serogroups, were isolated only from the environment. The combined circulation (patients, bacterium-carriers, environment) was registered for seroviruses 0:14, 0:35 and serogroups 0:58. The obtained data suggested that separate rare salmonella types area tied to ecology.     

Trends in antimicrobial resistance, phage types and integrons among Salmonella serotypes from pigs, 1997-2000

OBJECTIVES: The objectives of this study were to determine antimicrobial resistance and to identify phage types and class 1 integrons among non-typhoidal Salmonella isolates from 24 pig farms in North Carolina collected between 1997 and 2000. METHODS: A total of 1314 isolates of 30 serotypes from pig faecal samples were collected and analysed over a 3 year period. The isolates were characterized using antimicrobial susceptibility testing, phage typing, PCR and DNA sequencing for class 1 integrons. RESULTS: A high frequency of resistance to antimicrobial agents including tetracycline (85%), ampicillin (47%), co-amoxiclav (23%) and chloramphenicol (21%) was detected. Two multidrug resistance patterns were common in Typhimurium (including variant Copenhagen): isolates with co-amoxiclav, ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline (R-type AxACSSuT) [36%] and isolates with ampicillin, kanamycin, streptomycin, sulfamethoxazole and tetracycline (R-type AKSSuT) [45%] resistance patterns. Definitive Type 104 (DT104) was the most common (34%) among eight phage types identified. AKSSuT was found among non-DT104 phage types, particularly DT21 and DT193. Class 1 integrons were detected among various serotypes including Typhimurium, Derby, Muenchen, Worthington, Bere and Muenster. aadA was the most common resistance gene insert, and the oxa30 beta-lactamase resistance gene was also identified among serovar Muenchen. CONCLUSIONS: In this study, two most important multidrug resistance patterns (AxACSSuT and AKSSuT) and phage types of public health significance (DT104 and DT193) constituted two-thirds of the serotype Typhimurium isolates. The findings imply that pigs raised in the commercial production system may pose a risk in serving as reservoirs of resistant Salmonella.     

Changing patterns of fluoroquinolone resistance among Bacteroides fragilis group organisms over a 6-year period (1997-2002)

The evolution of susceptibility to the newer fluoroquinolones, moxifloxacin and trovafloxacin, of Bacteroides fragilis group organisms isolated in our hospital from 1997 to 2002 was studied. A total of 927 strains were included in the study. Trovafloxacin was more active than moxifloxacin against the various species of the group. During the study period, an increase in resistance to both quinolones was observed. Rates of resistance to moxifloxacin at a breakpoint of 8 microg/mL remained stable at around 6% during the period 1997-1998 and increased to 11.4% in 2000 and to 16.5% in 2001-2002 (P<0.005). Resistance to trovafloxacin rose significantly from 0.6% in 1998 to 6.8% in 1999 (P<0.05) and did not change appreciably over the last 3 years studied. This study confirms the increasing resistance of B. fragilis group organisms to trovafloxacin and moxifloxacin and emphasizes the need to perform periodic antimicrobial susceptibility tests to guide the selection of appropriate antimicrobial therapy.     

Molecular characterization of increasing fluoroquinolone resistance in Streptococcus pneumoniae isolates in Canada, 1997 to 2005

Molecular characterization of fluoroquinolone-resistant Streptococcus pneumoniae in Canada was conducted from 1997 to 2005. Over the course of the study, 205 ciprofloxacin-resistant isolates were evaluated for ParC and GyrA quinolone resistance-determining region (QRDR) substitutions, substitutions in the full genes of ParC, ParE, and GyrA, reserpine sensitivity, and serotype and by pulsed-field gel electrophoresis. Rates of ciprofloxacin resistance of S. pneumoniae increased significantly, from less than 1% in 1997 to 4.2% in 2005. Ciprofloxacin resistance was greatest in people >64 years of age and least in those <16 years of age. Significant increases were also noted in rates of resistance to gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin, to the current rates of 1.6%, 1.0%, 1.1%, and 1.0%, respectively. The most common genotype observed consisted of QRDR substitutions in GyrA (Ser81Phe) and ParC (Ser79Phe). Substitutions outside the QRDR of GyrA, ParC, and ParE were not associated with fluoroquinolone resistance in this study. Overall, 21% of isolates were reserpine-sensitive and were thus assumed to be efflux positive. The ciprofloxacin-resistant isolates belonged to 35 different serotypes, but 10 (19F, 11A, 23F, 6B, 22F, 12F, 6A, 14, 9V, and 19A) accounted for 72% of all isolates. The majority of the isolates were found to be genetically unrelated by pulsed-field gel electrophoresis. Within the observed clusters, there was considerable genetic heterogeneity with regard to fluoroquinolone resistance mechanisms and serotypes. Continued surveillance and molecular analysis of fluoroquinolone-resistant S. pneumoniae in Canada are essential for appropriate empirical treatment of infections and early detection of novel resistance mechanisms.     

Multidrug resistance in Campylobacter jejuni strains collected from Finnish patients during 1995-2000

OBJECTIVES: The resistance of Campylobacter jejuni to fluoroquinolones is increasing globally. This study was performed to delineate those antimicrobial agents that are effective in vitro against ciprofloxacin-resistant C. jejuni isolates and potentially suitable for the treatment of severe disease when fluoroquinolone resistance or multidrug resistance is known or suspected. METHODS: During 1995-2000 we collected 376 C. jejuni strains, of which 354 were of foreign origin from multiple countries and 22 were of domestic origin. The MICs of 12 antimicrobial agents against the isolates were determined. RESULTS: Of the 376 strains, 174 (46%) were resistant to ciprofloxacin. Among other antimicrobials, resistance was most common to tetracycline (46%) and ampicillin (17%). Of the ciprofloxacin-resistant strains, 68% and 25%, respectively, were resistant to tetracycline and ampicillin, and 3% were resistant to erythromycin, gentamicin or clindamycin. One (0.6%) ciprofloxacin-resistant isolate was resistant to co-amoxiclav and none was resistant to imipenem. Resistance to three or more antimicrobial groups was detected in 22% of the isolates. Multidrug resistance was significantly associated with ciprofloxacin resistance (33% versus 12%; P<0.01). Eight (2%) strains were resistant to macrolides, of which 75% were also resistant to ciprofloxacin, but none was resistant to co-amoxiclav or imipenem. CONCLUSIONS: Macrolides still appear to be the first-choice alternative for suspected C. jejuni enteritis, if antimicrobial treatment is needed. The in vitro susceptibilities suggest that clinical trials to treat enteritis caused by multidrug-resistant C. jejuni with co-amoxiclav, and life-threatening infections with a carbapenem, may be valuable.     

Antimicrobial resistance of invasive pneumococci in Finland in 1999-2000

The resistance patterns and macrolide resistance mechanisms of 910 Finnish invasive pneumococci isolated during 1999 and 2000 were studied. Macrolide resistance was detected in 6.9% of isolates. Penicillin resistance was detected in 1.5% of isolates, and penicillin intermediate resistance was detected in 4.0% of isolates. Active macrolide efflux, mediated by the mef(A) gene, was the most common macrolide resistance mechanism. Four macrolide-resistant isolates had mutations in rRNA or ribosomal protein L22.     

Salmonella typhimurium gyrA mutations associated with fluoroquinolone resistance.

Spontaneous quinolone-resistant mutants obtained from Salmonella typhimurium Su694 were screened for mutations by direct DNA sequencing of an amplified PCR gyrA fragment. Substitutions Ser-83-->Phe (Ser83Phe), Ser83Tyr, Asp87Tyr, and Asp87Asn and double mutation Ala67Pro-Gly81Ser, which resulted in decreased sensitivities to ciprofloxacin, enoxacin, pefloxacin, norfloxacin, ofloxacin, and nalidixic acid, were found. The levels of resistance to quinolones for each mutant were determined.     

Emergence of fluoroquinolone resistance in Bacteroides fragilis accompanied by resistance to beta-lactam antibiotics.

The in vitro susceptibilities of a group of 93 isolates of Bacteroides fragilis collected from 1983 to 1984 to six fluoroquinolones were compared with those of a group of 93 isolates collected from 1986 to 1987. The recently collected strains were less susceptible than the older strains to all of the agents tested. Norfloxacin-resistant (MIC, greater than 100 micrograms/ml) strains were less susceptible to cefoxitin and piperacillin than norfloxacin-susceptible strains.     

Fluoroquinolone resistance in Streptococcus pneumoniae in United States since 1994-1995

The in vitro activities of ciprofloxacin, levofloxacin, gatifloxacin, and moxifloxacin against a large collection of clinical isolates of Streptococcus pneumoniae (n = 4,650) obtained over a 5-year period, 1994-1995 through 1999-2000, were assessed as part of a longitudinal multicenter U.S. surveillance study of antimicrobial resistance. Three sampling periods were used during this investigation, the winter seasons of 1994-1995, 1997-1998, and 1999-2000; and 1,523, 1,596 and 1,531 isolates were collected during these three periods, respectively. The overall rank order of activity of the four fluoroquinolones examined in this study was moxifloxacin > gatifloxacin > levofloxacin = ciprofloxacin, in which moxifloxacin (MIC at which 90% of isolates are inhibited [MIC(90)], 0.25 microg/ml; modal MIC, 0.12 microg/ml) was twofold more active than gatifloxacin (MIC(90), 0.5 microg/ml; modal MIC, 0.25 microg/ml), which in turn was fourfold more active than either levofloxacin (MIC(90), 1 microg/ml; modal MIC, 1 microg/ml) or ciprofloxacin (MIC(90), 2 microg/ml; modal MIC, 1 microg/ml). Changes in the in vitro activities of fluoroquinolones against S. pneumoniae strains in the United States over the 5-year period of the survey were assessed by comparing the MIC frequency distributions of the study drugs against the isolates obtained during the three sampling periods encompassing this investigation. These comparisons revealed no evidence of changes in the in vitro activities of the fluoroquinolones. In addition, the percentages of isolates in the three sampling periods for which MICs were above the resistance breakpoints were compared. Low percentages of resistant strains were detected, and there was no evidence of resistance rate changes over time. For example, by use of a ciprofloxacin MIC of > or = 4 microg/ml to define resistance, the proportions of isolates from the three sampling periods for which MICs were at or above this breakpoint were 1.2, 1.6, and 1.4%, respectively. A total of 164 unique isolates (n = 58 from 1994-1995, 65 from 1997-1998, and 42 from 1999-2000) were examined for evidence of mutations in the quinolone resistance-determining regions (QRDRs) of the parC and the gyrA genes. Forty-nine isolates harbored at least one mutation in the QRDRs of one or both genes (1994-1995, n = 15; 1997-1998, n = 19; 1999-2000, n = 15). Among the 4,650 isolates of S. pneumoniae examined in the study, we estimated that 0.3% had mutations in both the parC and gyrA loci. The majority of mutations (67.3% of the mutations in 49 isolates with mutations) were amino acid substitutions in the parC locus only. Four isolates had a mutation in the gyrA locus only, and 12 isolates had mutations in both genes (8.2 and 24.5% of isolates with mutations, respectively). There was no significant difference in the number of isolates with parC and/or gyrA mutations detected during each study period. Finally, because of the magnitude of the study, we had reasonably large numbers of pneumococcal isolates with genotypically defined mechanisms of fluoroquinolone resistance and were thus able to determine the effects of specific resistance mutations on the activities of different fluoroquinolones. In general, isolates with mutations in parC only were resistant to ciprofloxacin but remained susceptible to levofloxacin, gatifloxacin, and moxifloxacin, whereas isolates with mutations in gyrA only and isolates with mutations in both parC and gyrA were resistant to all four fluoroquinolones tested.     

Fitness costs of fluoroquinolone resistance in Streptococcus pneumoniae

The fitness cost of the genes responsible for resistance to fluoroquinolones in clinical isolates of Streptococcus pneumoniae were estimated in vitro in a common genetic background. Naturally occurring parC, parE, and gyrA loci containing mutations in the quinolone-resistance-determining regions were introduced by transformation into S. pneumoniae strain R6 individually and in combinations. The fitness of these transformants was estimated by pairwise competition experiments with a common R6 strain. On average, single par and gyr mutants responsible for low-level MIC resistance (first-step resistance) impose a fitness burden of approximately 8%. Some of these mutants engender no measurable cost, while one, a parE mutant, reduces the fitness of these bacteria by more than 40%. Most interestingly, the addition of the second par or gyr mutations required for clinically significant, high-MIC fluoroquinolone resistance does not increase the fitness burden imposed by these single genes and can even reduce it. We discuss the implications of these results for the epidemiology of fluoroquinolone resistance and the evolution of acquired resistance in treated patients.     

Mechanisms of fluoroquinolone resistance in genetically related strains of Staphylococcus aureus.

Fluoroquinolone resistance in Staphylococcus aureus results from amino acid substitutions at particular locations in the DNA gyrase A and B subunits as well as in the topoisomerase IV A subunit and from NorA-mediated efflux. More than one resistance mechanism may be present in a single strain. Fluoroquinolone-resistant derivatives of SA-1199, a methicillin-susceptible S. aureus strain, were selected in vivo or in vitro, and their mechanisms of fluoroquinolone resistance were identified. We found that many of the resistance mechanisms described above can develop in derivatives of a single parent strain, either singly or in combination, and can arise in a single step. Variances in MICs for strains with the same apparent resistance mechanisms likely are due to the presence of new or undetected but established means of fluoroquinolone resistance. NorA-mediated resistance can occur in the apparent absence of topoisomerase mutations and in some strains may be the result of a promoter region mutation causing increased expression of norA. However, increased expression of norA can occur independently of this mutation, suggesting that a regulatory locus for this gene exists elsewhere on the chromosome.     

First characterization of fluoroquinolone resistance in Streptococcus suis

We have identified and sequenced the genes encoding the quinolone-resistance determining region (QRDR) of ParC and GyrA in fluoroquinolone-susceptible and -resistant Streptococcus suis clinical isolates. Resistance is the consequence of single point mutations in the QRDRs of ParC and GyrA and is not due to clonal spread of resistant strains or horizontal gene transfer with other bacteria.