Comparison of disk diffusion and agar dilution methods for erythromycin and ciprofloxacin susceptibility testing of Campylobacter jejuni subsp. jejuni

Antimicrobial Resistance of Human Campylobacter Species Infections in Saskatchewan, Canada (1999-2006): A Historical Provincial Collection of All Reported Cases

To describe a historical baseline of antimicrobial resistance (AMR) profiles for human clinical Campylobacter species isolates obtained by laboratory surveillance in the province of Saskatchewan from 1999 to 2006; to determine if there were differences in resistance between Campylobacter jejuni and Campylobacter coli; and to determine if there were changes in the annual resistance levels in the two species. One thousand three hundred seventy-eight Campylobacter isolates were subjected to antimicrobial susceptibility testing using the E-test method. Annual resistance levels in C. jejuni and C. coli were compared using logistic regression models. One thousand two hundred (87.1%) isolates were C. jejuni and 129 (9.4%) were C. coli. Resistance in C. jejuni isolates included ciprofloxacin (CIP: 9.4%), erythromycin (ERY: 0.5%), and tetracycline (33.3%). CIP resistance in C. jejuni was higher in 1999 (15.5%, odds ratio [OR] = 3.96, p = 0.01), 2000 (12.7%, OR = 3.10, p = 0.01), 2005 (10.2%, OR = 2.47, p = 0.05), and 2006 (13.0%, OR = 3.22, p = 0.01) compared with 2004 (4.4%). C. coli had significantly higher CIP resistance (15.5%, OR = 1.78, p = 0.03), ERY resistance (13.2%, OR = 60.12, p < 0.01), multidrug resistance (2.3%, OR = 36.29, p < 0.01), and CIP-ERY resistance (3.1%, OR = 50.23, p < 0.01) compared with C. jejuni. This represents the first and most current report of AMR of the collective human Campylobacter isolates from a province in Canada and provides a baseline against which current and future resistance patterns can be compared. Fluoroquinolone resistance in C. jejuni isolates fluctuated from 1999 to 2006, including an increased prevalence in 2005-2006, while macrolide/lincosamide resistance remained very low. Human clinical C. jejuni isolates from Saskatchewan demonstrated resistance to multiple antimicrobials but had significantly less fluoroquinolone and macrolide resistance than C. coli isolates.

Heterogeneity of Campylobacter species isolated from serial stool specimens of Egyptian children using pulsed field gel electrophoresis

BACKGROUND

The genus Campylobacter spp. is a common cause of human acute bacterial enteritis and travellers' diarrhoea worldwide.

OBJECTIVE

To determine whether multiple serial isolations of Campylobacter spp., when obtained from a single child, represented the same or a different organism.

METHODS

In a birth cohort study conducted in Egypt, numerous children showed serial isolations of Campylobacter spp. Of these, 13 children were selected from different households based on the successive isolation of six or more Campylobacter isolates from stool samples.

RESULTS

Eighty isolates were recovered and identified as either Campylobacter coli (n = 25) or Campylobacter jejuni (n = 55). Pulsed-field gel electrophoresis (PFGE) revealed the presence of 38 unique C. jejuni and 24 C. coli profiles at a similarity level of ≥ 90%. Although no serially-identical isolates were detected in six children, others demonstrated at least one identical couple of isolates; all identified serially between one to six weeks. Two children demonstrated > 80% similar couples of isolates that appeared seven months apart. PFGE could be a useful tool for differentiating reinfection, relapse and convalescent excretion phases.

CONCLUSION

Our data suggest that Campylobacter infection in children is a complex process; children are exposed to multiple species in endemic environments and strains of the same bacterium appear to be shed serially between one to six weeks after the first exposure. Isolates that persisted for longer periods were relatively less similar, as shown from the results of this study.

Antimicrobial resistance in campylobacter: susceptibility testing methods and resistance trends

Most Campylobacter infections are self-limiting but antimicrobial treatment (e.g., macrolides, fluoroquinolones) is necessary in severe or prolonged cases. Susceptibility testing continues to play a critical role in guiding therapy and epidemiological monitoring of resistance. The methods of choice for Campylobacter recommended by the Clinical and Laboratory Standards Institute (CLSI) are agar dilution and broth microdilution, while a disk diffusion method was recently standardized by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Macrolides, quinolones, and tetracyclines are among the common antimicrobials recommended for testing. Molecular determination of Campylobacter resistance via DNA sequencing or PCR-based methods has been performed. High levels of resistance to tetracycline and ciprofloxacin are frequently reported by many national surveillance programs, but resistance to erythromycin and gentamicin in Campylobacter jejuni remains low. Nonetheless, variations in susceptibility observed over time underscore the need for continued public health monitoring of Campylobacter resistance from humans, animals, and food.

An examination of the medicinal potential of Scaevola spinescens: Toxicity, antibacterial, and antiviral activities

Background:

Scaevola spinescens is an endemic Australian native plant with a history of use as a medicinal agent by indigenous Australians. Yet the medicinal bioactivities of this plant are poorly studied.

Materials and Methods:

S. spinescens solvent extracts were tested for antimicrobial activity, antiviral activity and toxicity in vitro.

Results:

All extracts displayed antibacterial activity in the disc diffusion assay. The methanol extract proved to have the broadest specificity, inhibiting the growth of 7 of the 14 bacteria tested (50%). The water, ethyl acetate, chloroform, and hexane extracts inhibited the growth of 6 (42.9%), 5 (35.7%), 5 (35.7%), and 4 (28.6%) of the 14 bacteria tested, respectively. S. spinescens methanolic extracts were equally effective against Gram-positive (50%) and Gram-negative bacteria (50%). All other extracts were more effective at inhibiting the growth of Gram-negative bacteria. All extracts also displayed antiviral activity in the MS2 plaque reduction assay with the methanol, water, ethyl acetate, chloroform, and hexane extracts inhibiting 95.2 ± 1.8%, 72.3 ± 6.3%, 82.6 ± 4.5%, 100 ± 0% and 47.7 ± 12.9% of plaque formation, respectively. All S. spinescens extracts were nontoxic in the Artemia fransiscana bioassay with no significant increase in mortality induced by any extract at 24 and 48 h. The only increase in mortality was seen for the water extract at 72 h, although even this extract displayed low toxicity, inducing only 41.7 ± 23.3% mortality.

Conclusions:

The lack of toxicity of the S. spinescens extracts and their inhibitory bioactivity against bacteria and viruses validate the Australian Aboriginal usage of S. spinescens and indicates its medicinal potential.

Bioactivity of Syzygium jambos methanolic extracts: Antibacterial activity and toxicity

Methanol extracts from S. jambos leaves were tested for antimicrobial activity and toxicity. S. jambos leaf extract inhibited the growth of 4 of the 14 bacteria tested (29%). Both gram-positive and gram-negative bacterial growths were inhibited by S. jambos leaf extract, although gram-positive bacteria appeared more susceptible. Two of the 10 gram-negative bacteria (20%) and 2 of the 4 gram-positive bacteria (50%) tested had their growths inhibited by the extract. The leaf extract also proved to be toxic in the Artemia franciscana bioassay, with a 48-h LC₅₀ of 387.9 ± 38.8 µg/mL, making it slightly more toxic than Mevinphos (505.3± 37.7 µg/mL) and approximately 5-fold less toxic than potassium dichromate (80.4 ± 4.3 µg/mL). Whilst potassium dichromate's LC₅₀ remained constant across the 72-hour test period (24-h LC₅₀, 86.3 ± 5.1; 72-h LC₅₀, 77.9 ± 4.9), the extract and Mevinphos LC₅₀ values decreased by 72 hours (87.0 ± 11.3 µg/mL and 103.9 ± 12.8 µg/mL, respectively), indicating their similar levels of toxicity in the assay.

Inaccuracy of the disk diffusion method compared with the agar dilution method for susceptibility testing of Campylobacter spp

The agar dilution method has been standardized by the CLSI for the susceptibility testing of Campylobacter species, and according to these standards, the disk diffusion method should be used only in screening for macrolide and ciprofloxacin resistance. Nevertheless, the disk diffusion test is currently widely used, since it is easy to perform in clinical microbiology laboratories. In this study, the disk diffusion method was compared to the agar dilution method by analyzing the in vitro activities of seven antimicrobial agents against 174 Campylobacter strains collected in Finland between 2003 and 2008. Recommendations of the CLSI were followed using Mueller-Hinton agar plates with 5% of sheep blood. For each strain, the disk diffusion tests were performed two to four times. Of the 33 erythromycin-resistant strains (MIC, ≥16 μg/ml), 24 (73%) constantly showed a 6-mm erythromycin inhibition zone (i.e., no inhibition), while for seven strains the inhibition zone varied from 6 to 44 mm in repeated measurements. Among the 141 erythromycin-susceptible strains (MIC, <16 μg/ml), erythromycin inhibition zones varied between 6 and 61 mm. Of the 87 ciprofloxacin-resistant strains, 47 (54%) showed 6-mm inhibition zones, while 40 strains showed inhibition zones between 6 and 60 mm. Significant differences between the repetitions were observed in the disk diffusion for all antimicrobial agents and all strains except for the macrolide-resistant strains regarding the macrolides. For 17 (10%) strains, the variation in repeated measurements was substantial. These results show that the disk diffusion method may not be a reliable tool for the susceptibility testing of Campylobacter spp. Further studies are needed to assess whether the disk diffusion test could be improved or whether all susceptibilities of campylobacters should be tested using an MIC-based method.

Antimicrobial susceptibilities of multidrug-resistant Campylobacter jejuni and C. coli strains: in vitro activities of 20 antimicrobial agents

There is a paucity of information regarding antimicrobial agents that are suitable to treat severe infections caused by multidrug-resistant Campylobacter spp. Our aim was to identify agents that are potentially effective against multiresistant Campylobacter strains. The in vitro activities of 20 antimicrobial agents against 238 Campylobacter strains were analyzed by determining MICs by the agar plate dilution method or the Etest. These strains were selected from 1,808 Campylobacter isolates collected from Finnish patients between 2003 and 2005 and screened for macrolide susceptibility by using the disk diffusion test. The 238 strains consisted of 183 strains with erythromycin inhibition zone diameters of < or =23 mm and 55 strains with inhibition zone diameters of >23 mm. Of the 238 Campylobacter strains, 19 were resistant to erythromycin by MIC determinations (MIC > or = 16 microg/ml). Given that the resistant strains were identified among the collection of 1,808 isolates, the frequency of erythromycin resistance was 1.1%. All erythromycin-resistant strains were multidrug resistant, with 18 (94.7%) of them being resistant to ciprofloxacin (MIC > or = 4 microg/ml). The percentages of resistance to tetracycline and amoxicillin-clavulanic acid (co-amoxiclav) were 73.7% and 31.6%, respectively. All macrolide-resistant strains were susceptible to imipenem, meropenem, and tigecycline. Ten (52.6%) multiresistant strains were identified as being Campylobacter jejuni strains, and 9 (47.4%) were identified as being C. coli strains. These data demonstrate that the incidence of macrolide resistance was low but that the macrolide-resistant Campylobacter strains were uniformly multidrug resistant. In addition to the carbapenems, tigecycline was also highly effective against these multidrug-resistant Campylobacter strains in vitro. Its efficacy for the treatment of human campylobacteriosis should be evaluated in clinical trials.

Comparison of disk diffusion and agar dilution methods for erythromycin, ciprofloxacin, and tetracycline susceptibility testing of Campylobacter coli and for tetracycline susceptibility testing of Campylobacter jejuni subsp. jejuni

With disk diffusion, the following zone diameters are suggested to be resistant and susceptible breakpoints, respectively: for susceptibility testing of Campylobacter coli, no inhibition zone and 15 mm or more for erythromycin, and 20 mm or less and 25 mm or more for ciprofloxacin, in the absence or presence of an inhibition zone around the nalidixic acid disk; and for susceptibility testing of C. coli and Campylobacter jejuni, 20 mm or less and 26 mm or more for tetracycline.