Reduced Ciprofloxacin Susceptibility Research Articles

A mismatch amplification mutation assay for specific detection of ciprofloxacin-resistant Neisseria meningitidis

Meningococcal chemoprophylaxis for people in close contact with patients with invasive meningococcal disease (IMD) is necessary for preventing the spread of Neisseria meningitidis. Ciprofloxacin (CIP) is commonly used to treat IMD. However, CIP-resistant N. meningitidis isolates have rapidly evolved worldwide; therefore, rapid and accurate detection of CIP-resistant N. meningitidis is essential. We developed a mismatch amplification mutation assay for identifying gyrA substitutions T91I and D95Y, associated with reduced CIP susceptibility, using two primer sets to detect these variants. Comparison with gyrA sequencing data showed complete congruency. This method enables reliable detection of CIP-resistant N. meningitidis, thus leading to efficient management and control of IMD infections.

Expansion of Salmonella Typhi clonal lineages with ampicillin resistance and reduced ciprofloxacin susceptibility in Eastern China.

PurposeThis study was aimed to investigate the dynamics of antimicrobial resistance expansion among different lineages and isolates of S. Typhi.Materials and methodsThe S. Typhi isolates were collected from the patients clinically suspected of typhoid fever in Eastern China during 2005–2017. All isolates were tested retrospectively for susceptibility to eight antimicrobials and the genes related to quinolone and ampicillin resistance, including gyrA, ParC, qnrA, qnrB, qnrS, aac(6´)-Ib-cr, qepA and blaTEM. The isolates were subtyped by PFGE.ResultsOf 140 isolates, all were susceptible to ciprofloxacin, cefotaxime, chloramphenicol, and trimethoprim-sulfamethoxazole, 95 (68%) were nalidixic acid resistant, and 74 (53%) were ampicillin resistant. The resistance to ampicillin and nalidixic acid was first observed in 2006. Among the 95 nalidixic acid-resistant S. Typhi isolates, 62 possessed S83F mutation in gyrA and 25 possessed D87Y mutation. All ampicillin-resistant isolates harbored gene blaTEM-1. PFGE generated 47 distinguishable clonal lineages. Overall, 64% (89/140) belonged to seven prevalent lineages of clustering isolates. PFGE results illustrated the prevalence of nalidixic acid-resistant lineages increased steadily from 19% during 2005–2012 to 50% during 2013–2014, and thereafter to 74% during 2015–2017 and similar development of ampicillin-resistant lineages increased from 6% to 38%, and also to 39%.ConclusionThe present study indicated the clonal expansion of S. Typhi with ampicillin resistance and reduced ciprofloxacin susceptibility. The findings also suggested that the differential development of antimicrobial resistance to various antimicrobial agents in S. Typhi, showing the rapid increase in ampicillin resistance and reduced ciprofloxacin susceptibility, and the high susceptibility to other traditional antimicrobial agents.

The Emergence of Reduced Ciprofloxacin Susceptibility in Salmonella enterica Causing Bloodstream Infections in Rural Ghana.

Salmonella ranks among the leading causes of bloodstream infections in sub-Saharan Africa. Multidrug resistant typhoidal and nontyphoidal Salmonella (NTS) isolates have been previously identified in this region. However, resistance to ciprofloxacin has rarely been reported in West Africa. This study aims to assess susceptibility against ciprofloxacin in Salmonella causing invasive bloodstream infections among children in rural Ghana. From May 2007 until May 2012, children attending a rural district hospital in central Ghana were eligible for recruitment. Salmonella enterica isolated from blood cultures were assessed for ciprofloxacin susceptibility by Etest (susceptible minimum inhibitory concentration [MIC] ≤ 0.06 µg/mL). The gyrA, gyrB, parC, and parE genes were sequenced to identify mutations associated with changes in susceptibility to fluoroquinolones. Two hundred eighty-five Salmonella enterica isolates from 5211 blood cultures were most commonly identified as Salmonella enterica serovar Typhimurium (n = 129 [45%]), Salmonella enterica serovar Typhi (n = 89 [31%]), Salmonella enterica serovar Dublin (n = 20 [7%]), and Salmonella enterica serovar Enteritidis (n = 19 [7%]). All S. Typhi and S. Dublin were susceptible to ciprofloxacin. Reduced susceptibility (MIC >0.06 µg/mL) was found in 53% (10/19) of S. Enteritidis and in 2% (3/129) of S. Typhimurium isolates. Sequencing detected a single gyrB mutation (Glu466Asp) and a single gyrA mutation (Ser83Tyr) in all 3 S. Typhimurium isolates, while 9 of 10 S. Enteritidis harbored single gyrA mutations (Asp87Gly, Asp87Asn, or Asp87Tyr). No mutations were found in the parC and parE genes. Ciprofloxacin susceptibility in invasive NTS in rural Ghana is highly dependent on serotype. Although reduced ciprofloxacin susceptibility is low in S. Typhimurium, more than half of all S. Enteritidis isolates are affected. Healthcare practitioners in Ghana should be aware of potential treatment failure in patients with invasive S. Enteritidis infections.

Clonal relatedness and resistance patterns of Salmonella Corvallis from poultry carcasses in a Brazilian slaughterhouse.

Salmonella is a major cause of foodborne disease, and poultry products are important contributors to the transmission of this zoonotic pathogen. Although considered to be rare in most countries, Salmonella Corvallis has been reported in specific geographic areas isolated from both human and non-human sources. The aim of this study was to report the occurrence, the antimicrobial resistance profiles including the extended-spectrum beta-lactamase (ESBL) production, and the clonal relatedness of S. Corvallis strains. A total of 132 fragments of poultry carcasses from a slaughterhouse in São Paulo State, Brazil, were collected at different stages of the manufacturing process (post-bleeding, post-plucking, and post-chilling) and analyzed for the presence of Salmonella. Antimicrobial resistance was determined by disc diffusion method and Etest. Clonal relatedness was determined by pulsed-field gel electrophoresis (PFGE). Among the 272 Salmonella strains recovered, fourteen were S. Corvallis. Ten (71.4%) showed ESBL production and resistance to at least three antimicrobial agents. Nalidixic acid resistance and reduced ciprofloxacin susceptibility was verified in four (28.6%) strains. PFGE analyses showed that all the S. Corvallis strains belonged to the same pulsotype. This study identified genetically related S. Corvallis strains exhibiting ESBL production and reduced susceptibility to quinolone. The results suggest the need to improve the sanitary conditions in the slaughterhouse. Moreover, from a public health perspective, continuous surveillance on Salmonella is needed to control the dissemination of this important zoonotic pathogen and its resistance determinants.

Nalidixic Acid Susceptibility Test for Screening Salmonella Isolates of Reduced Susceptibility/Higher Minimum Inhibitory Concentration to Ciprofloxacin

Enteric fever is the major diagnosis among febrile patients in Nepal with yearly increase in nalidixic acid resistance and reduced ciprofloxacin susceptibility among Salmonella isolates. This study was carried out to evaluate the validity of nalidixic acid resistance as an indicator of reduced susceptibility of Salmonella isolates to ciprofloxacin. In this study, 999 blood specimens collected from suspected enteric fever patients visiting B&B Hospital were processed by standard microbiological techniques. Isolates were identified by biochemical tests and serotyping. Antibiotic susceptibility test was performed by Kirby Bauer disc diffusion method and CLSI recommended interpretive criteria. MIC of ciprofloxacin was determined by agar dilution method. Isolation rate of Salmonella species was 6.21%. Among 62 Salmonella isolates, 51 were S. typhi, 10 were S. paratyphi A and one isolate was S. paratyphi B. Only one isolate of S. typhi was multi-drug resistant. Resistance to ceftriaxone, cefixime and azithromycin was nil. On disc diffusion test, 55 isolates were resistant to nalidixic acid. Fifty-seven isolates were found to have increased (>0.125mg/ml) MIC of ciprofloxacin with the clinical and laboratory standards institute breakpoints. Nalidixic acid resistance showed a predictive value of 100% for ciprofloxacin resistance. Screening with nalidixic acid disc had a sensitivity of 100% and a specificity of 71.43% for the determination of decreased ciprofloxacin susceptibility. Before using ciprofloxacin for the treatment of enteric fever, appropriate identification of Salmonella isolates with reduced ciprofloxacin susceptibility is essential to limit the possible treatment failure and further development of highly resistant strains.DOI: http://dx.doi.org/njst.v15i2.12122Nepal Journal of Science and Technology Vol. 15, No.2 (2014) 97-104

Salmonella Alachua: causative agent of a foodborne disease outbreak

ObjectivesThe aim of this study is to report the occurrence of the first outbreak of food poisoning caused by Salmonella Alachua in Brazil, as well as the antimicrobial susceptibility and the genetic relatedness of Salmonella Alachua strains isolated from clinical and food samples. Material and methodsTo elucidate the outbreak, an epidemiological investigation was carried out, and two samples of common food were tested – mayonnaise salad and galinhada (a traditional Brazilian dish of chicken and rice) – according to the Compendium of methods for the microbiological examination of foods. Five stool samples were tested employing classic methods for the isolation and identification of enterobacteria. Strains of Salmonella were characterized for antibiotic susceptibility according to the Clinical and Laboratory Standards Institute guidelines (2013), and submitted to pulsed-field gel electrophoresis analysis, performed according to the Centers for Disease Control and Prevention PulseNet protocol. ResultsA total of 94 people were interviewed after ingesting the food, 66 of whom had become ill. A 60-year old female patient who was hospitalized in a serious condition, developed septic shock and died two days after consuming the food. The presence of Salmonella Alachua was confirmed in all the analyzed stool samples, and in the two types of food. The five strains showed higher than minimum inhibitory concentration values of nalidixic acid (≥256μg/mL) and reduced ciprofloxacin susceptibility (minimum inhibitory concentration=0.5μg/mL). The pulsed-field gel electrophoresis analysis revealed indistinguishable patterns in Salmonella Alachua strains isolated from clinical and food samples. ConclusionThe data presented herein confirm the foodborne disease outbreak. They also allowed for the identification of the source of infection, and suggest that products from poultry are potential reservoirs for this serotype, reinforcing the importance of warning consumers about the danger of possible contamination.

Prevalence and role of efflux pump activity in ciprofloxacin resistance in clinical isolates of Klebsiella pneumoniae

We investigated the prevalence and role of efflux pump activity and possible drug influx resistance in ciprofloxacin susceptibility amongst 26 distinct clinical isolates of Klebsiella pneumoniae of varying ciprofloxacin susceptibilities and known quinolone resistance-determining region (QRDR) genotypes. Cellular [(14)C]ciprofloxacin accumulation patterns and the amount of cell-associated [(14)C]ciprofloxacin of mid-logarithmic phase cells were determined before and after challenging with the efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Most isolates (24/26), and all with ciprofloxacin minimum inhibitory concentrations (MICs) >1µg/ml, had efflux activity that could extrude up to 90% of cell-associated [(14)C]ciprofloxacin; none had significant influx resistance. In isolates with no QRDR mutations, efflux alone reduced ciprofloxacin susceptibility. In isolates with QRDR mutations, the efflux activity varied: in one isolate with no efflux activity, the most common fluoroquinolone resistance-causing QRDR mutation did not bring about clinically significant ciprofloxacin resistance; isolates with multiple mutations had high MICs and, usually, high levels of efflux activity. Fluoroquinolone efflux activity is much more common in clinical isolates of K. pneumoniae than previously reported and it can contribute to decreased ciprofloxacin susceptibility.

Resistance to ampicillin, third-generation cephalosporins, ciprofloxacin, co-trimoxazole and azithromycin in clinical isolates of Salmonella enterica subsp. enterica from Germany: Real problem or sporadic circumstance?

The objective of this study was to determine the in vitro activity of ampicillin, third-generation cephalosporins, ciprofloxacin, co-trimoxazole and azithromycin against Salmonella enterica isolates. None of the isolates tested showed resistance to third-generation cephalosporins or azithromycin. The rates of resistance to ampicillin, co-trimoxazole and ciprofloxacin were 16.8%, 3.2% and 0.8%, respectively. Moreover, 7.2% of the isolates showed reduced ciprofloxacin susceptibility, but none of them harboured qnr genes. To conclude, our data show that resistance to fluoroquinolones and third-generation cephalosporins in clinical isolates found in Germany still represents a rare circumstance.

Analysis of mechanisms involved in reduced susceptibility to ciprofloxacin in Salmonella enterica serotypes Typhi and Paratyphi A isolates from travellers to Southeast Asia

Owing to multidrug resistance, quinolones and third-generation cephalosporins are currently used as key antibiotics to combat Salmonella organisms. Therapy failure due to reduced ciprofloxacin susceptibility has been reported in endemic areas, but also in imported disease. Different bacterial resistance mechanisms may result in reduced ciprofloxacin susceptibility. In this study, the presence and expression of different resistance mechanisms resulting in reduced minimum inhibitory concentrations (MICs) for ciprofloxacin were evaluated in 23 blood-culture-derived Salmonella enterica serotypes Typhi and Paratyphi A organisms from ill-returned travellers to Asia. The presence of mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene as well as an activated efflux pump and plasmid-mediated quinolone resistance genes was determined. Resistance selection during therapy and the clonal relatedness of all isolates were established. Efflux pump inhibition did not appear to affect the MICs of ciprofloxacin and activity of the efflux pump appeared to be specific for nalidixic acid. Repeated exposure of the isolates to ciprofloxacin did not result in a significant increase in the MICs for ciprofloxacin. Repetitive sequence-based polymerase chain reaction (rep-PCR) profiles identified five different genotypes, but no correlation with resistance was observed. However, a significant relation was found with geographic region; reduced ciprofloxacin susceptibility was only found in travellers returning from India and Pakistan. All isolates with reduced ciprofloxacin susceptibility had a mutation at position 83 in the QRDR region of the gyrA gene. Plasmid-mediated quinolone resistance was not found. These findings confirm that the reduced ciprofloxacin MIC in S. Typhi and S. Paratyphi A is solely due to an amino acid substitution in the QRDR ‘cluster’ of the gyrA gene.

Salmonella enterica serovar Typhi de sensibilité diminuée à la ciprofloxacine

The use of fluoroquinolone (FQ) as first line therapy for typhoid fever should be reconsidered because of the emergence of Salmonella Typhi and Paratyphi A strains with decreased susceptibility to FQ, mainly from Asia. Relapse can occur when ciprofloxacin MIC is over 0.12 mg/l, as illustrated by our case report. Azithromycin can be used successfully for patients infected with reduced ciprofloxacin susceptibility isolates. Literature review led us to suggest a new therapeutic strategy for uncomplicated typhoid fever, the antibiotic was chosen according to nalidixic acid susceptibility and ciprofloxacin MIC of the strain. High-dose intravenous ceftriaxone (4 g per day) is always efficient in first line therapy. Depending on FQ susceptibility testing results, it is relayed by oral therapy with a FQ (ciprofloxacin 500 mg bid for 7 days) if the isolate has maintained susceptibility, or azithromycin (1 g first day and 500 mg per day, 7 days) if the isolate is resistant to nalidixic acid or has a ciprofloxacin MIC superior to 0.12 mg/l.

Serogroup ANeisseria meningitidiswith Reduced Susceptibility to Ciprofloxacin

Serogroup A<i>Neisseria meningitidis</i>with Reduced Susceptibility to Ciprofloxacin

Serotype distribution and antimicrobial resistance of Salmonella enterica from patients with gastroenteritis in Crete, Greece

The aim of the present study was to determine the serotype distribution and the evolution of antimicrobial resistance among Salmonella enterica strains isolated from patients with diarrhea in Crete, Greece, during a 5-year period (2000-2004). Among the 401 S. enterica isolates recovered, serotype Enteritidis was the most prevalent (66.6%), followed by serotype Typhimurium (14.2%). The rates of resistance to ampicillin, amoxicillin-clavulanic acid, gentamicin, chloramphenicol, tetracycline, nalidixic acid and trimethoprim-sulfamethoxazole were 8.5, 7, 0.7, 5.4, 14.2, 2.7 and 2.7%, respectively. A marked decrease in resistance was observed during the study period. Resistance and multidrug resistance was most common in serotype Typhimurium. The extended-spectrum beta-lactamase production observed in one strain of S. enterica serotype Virchow and the reduced ciprofloxacin susceptibility detected in 2.7% of the isolates studied are causes of concern.

Reduction in fluoroquinolone susceptibility among non-typhoidal strains of Salmonella enterica isolated from Finnish patients

The proportion of Salmonella isolates with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, especially in South-east Asia. The present study was performed to evaluate the incidence of and changes in quinolone resistance in Salmonella isolates of either foreign or domestic origin in Finland. A total of 1004 Salmonella isolates collected from Finnish patients between 2000 and 2004 were analysed for ciprofloxacin susceptibility. Of these isolates, 504 were of domestic origin and 500 were of foreign origin, collected from travellers to 43 different countries. The Salmonella collection consisted of 89 different serotypes. All isolates belonged to non-typhoidal Salmonella enterica. Of all isolates, 3 (0.3%) were ciprofloxacin-resistant (MIC > or = 4 mg/L) and 214 (21.3%) exhibited reduced susceptibility to ciprofloxacin (MIC > or = 0.125-2 mg/L). The annual proportion of reduced susceptibility varied between 3 and 15% among the domestic Salmonella isolates (P = 0.123). Between 2000 and 2004, the annual proportion of reduced susceptibility increased significantly (from 23 to 39%; P = 0.001) among all foreign isolates as well as among those from Spain alone (from 4 to 73%; P < 0.001). Among the isolates from Thailand, reduced ciprofloxacin susceptibility remained at a constantly high level (52-66%) throughout the study. Our results show that reduced fluoroquinolone susceptibility in S. enterica is not restricted to South-east Asia alone but continues to grow rapidly in many parts of the world including countries of the European Union.

In vitro activities of 11 fluoroquinolones against 816 non-typhoidal strains of Salmonella enterica isolated from Finnish patients with special reference to reduced ciprofloxacin susceptibility

BackgroundThe number of Salmonella strains with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, threatening the value of this antimicrobial group in the treatment of severe salmonella infections.MethodsWe analyzed the in vitro activities of ciprofloxacin and 10 additional fluoroquinolones against 816 Salmonella strains collected from Finnish patients between 1995 and 2003. Special attention was focused on the efficacy of newer fluoroquinolones against the Salmonella strains with reduced ciprofloxacin susceptibility.ResultsThe isolates represented 119 different serotypes. Of all 816 Salmonella strains, 3 (0.4%) were resistant to ciprofloxacin (MIC ≥ 4 μg/ml), 232 (28.4%) showed reduced susceptibility to ciprofloxacin (MIC ≥ 0.125 – 2 μg/ml), and 581 (71.2%) were ciprofloxacin-susceptible. The MIC50 and MIC90 values of ciprofloxacin for these strains were 0.032 and 0.25 μg/ml, respectively, being lower than those of the other fluoroquinolone compounds presently on market in Finland (ofloxacin, norfloxacin, levofloxacin, and moxifloxacin). For two newer quinolones, clinafloxacin and sitafloxacin, the MIC50 and MIC90 values were lowest, both 0.016 and 0.064 μg/ml, respectively. Moreover, clinafloxacin and sitafloxacin exhibited the lowest MIC50 and MIC90 values, 0.064 and 0.125 μg/ml, against the 235 Salmonella strains with reduced susceptibility and strains fully resistant to ciprofloxacin.ConclusionAmong the registered fluoroquinolones in Finland, ciprofloxacin still appears to be the most effective drug for the treatment salmonella infections. Among the newer preparations, both clinafloxacin and sitafloxacin are promising based on in vitro studies, especially for strains showing reduced ciprofloxacin susceptibility. Their efficacy, however, has not been demonstrated in clinical investigations.

Trends in nalidixic acid resistance in nontyphoidal Salmonella isolated from 1999 to 2002: decreased susceptibility to 6 fluoroquinolones

We determined the resistance to nalidixic acid and 6 fluoroquinolones of 771 nontyphoidal Salmonella strains isolated from humans between 1999 and 2002. A total of 22 different serotypes were identified among the Salmonella isolates, the most common being Salmonella Enteritidis (79%) and Salmonella Derby (8%). Resistance to nalidixic acid increased from 38% in 1999 to 43% in 2002. This resistance was not homogeneous among the different serotypes, with the highest percentage of resistant isolates belonging to Salmonella Hadar (79%) followed by Salmonella Enteritidis (46%). Reduced ciprofloxacin susceptibility (minimal inhibitory concentrations [MICs] from 0.12 to 0.5 μg/mL) was observed in 300 (39%) Salmonella. In our study, the nalidixic acid-resistant strains had an MIC 90 at least 4-fold higher than the susceptible ones for all the fluoroquinolones tested, thus showing that resistance to nalidixic acid is an indicator of low-level resistance to all fluoroquinolones.

Salmonella as a Causative Organism of Various Infections in Patients with Sickle Cell Disease

Patients with sickle cell disease (SCD) are susceptible to a variety of bacterial infections, including infections caused by Salmonella species. We sought to identify the most common infections caused by Salmonella spp. in SCD patients at our hospital, and to determine their mortality rates and susceptibility to commonly used antimicrobial agents. We conducted a retrospective review of all Salmonella infections in SCD patients admitted to Qatif Central Hospital during the last 11 years. During the 11 years of the study, 331 episodes of Salmonella infection occurred in 319 patients. The incidence of Salmonella infection in SCD patients was 11.5% compared to only 0.65% in the general hospital population. The commonest sites of Salmonella infection were blood (42% of isolates), followed by gastrointestinal tract (23.5%) and the skeletal system (22.5%). Salmonella infection was commonly seen in patients less than 15 years of age. The case fatality rate in patients with Salmonella sepsis was 2.2% (3/139), but there were no deaths associated with other types of Salmonella infections. Ampicillin and cotrimoxazole resistance occurred in 29% and 24% of the isolates, respectively, but only 0.6% were resistant to ceftriaxone and 1.8% had intermediate resistance to ciprofloxacin. Salmonella is a common cause of sepsis and osteomyelitis in patients with SCD in our locality. Empirical antimicrobial therapy should cover the likely pathogens, including Salmonella species.

Influence of the decrease in ciprofloxacin susceptibility and the presence of human serum on the in vitro susceptibility of Streptococcus pneumoniae to five new quinolones.

Sixty recent Streptococcus pneumoniae isolates with different susceptibilities to ciprofloxacin (14 with MIC 0.5 mg/L, 10 with MIC 1 mg/L, eight with MIC 2 mg/L, 11 with MIC 4 mg/L and 17 with MIC > or =8 mg/L) were tested against five new quinolones using Todd-Hewitt broth with and without 80% serum. The final inoculum was 5 x 10(5) cfu/mL. Gemifloxacin and clinafloxacin exhibited the lowest MIC90 values and resistance rates (percentage above and defined breakpoint) with and without serum for strains with a ciprofloxacin MIC of > or =4 mg/L. Other quinolones tested were less active against strains with reduced ciprofloxacin susceptibility. The presence of serum did not affect susceptibility to moxifloxacin, but increased the resistance rates to other new quinolones for strains with high ciprofloxacin MICs.

Reduced fluoroquinolone susceptibility in Salmonella enterica serotypes in travelers returning from Southeast Asia.

During 1995 to 1999, we collected 1,210 Salmonella isolates; 629 were from Finnish travelers returning from abroad. These isolates were tested for susceptibility by determining MICs to ciprofloxacin, nalidixic acid, and seven additional antimicrobial agents. From 1995 to 1999, the annual proportion of reduced ciprofloxacin susceptibility (MIC > 0.125 microg/mL) among all travelers' isolates increased from 3.9% to 23.5% (p<0.001). The increasing trend was outstanding among the isolates from Southeast Asia; isolates from Thailand alone increased from 5.6% to 50.0% (p<0.001). The reduced fluoroquinolone susceptibility was nonclonal in character and significantly associated with multidrug resistance. A point mutation in the quinolone resistance-determining region of gyrA was present in all isolates with reduced susceptibility. These data provide further evidence for the rapid spread of multidrug-resistant pathogens from one continent to another.

Antibiotic resistance in Salmonella enterica subsp. enterica strains isolated in Poland from 1998 to 1999

A total of 326 Salmonella enterica subsp . enterica strains representing 29 serotypes, isolated from human stool specimens during 1998–1999 in sanitary-epidemiological units in Poland were tested for antibiotic susceptibility by a standard disk diffusion method. The antibiotics used were ampicillin, cefotaxime, chloramphenicol, tetracycline, streptomycin, gentamicin, kanamycin, nalidixic acid, ciprofloxacin, furazolidone, cotrimoxazole, sulphonamides and trimethoprim. In addition, 201 strains belonging to the five most commonly isolated serotypes ( S. Enteritidis, S. Typhimurium, S. Hadar, S. Infantis and S. Virchow) also had minimal inhibitory concentrations (MICs) determined for amoxycillin/clavulanic acid. Selected strains were screened for production of extended spectrum β-lactamases (ESBLs). There were 49.4% of Salmonella enterica subsp. enterica strains resistant to two or more antibiotics, with the highest prevalence of multiple resistant strains among serotypes Typhimurium, Hadar and Virchow. Resistance to ampicillin, streptomycin, tetracycline, nalidixic acid, furazolidone and sulphonamides occurred most frequently. Over 93% of S. Virchow strains were resistant to furazolidone. No strains resistant to ciprofloxacin by disk-diffusion method were detected but 31.3% of isolates of the 201 strains representing the five most common serotypes had reduced ciprofloxacin susceptibility (MICs ranging 0.125–0.5 mg/l). One strain ( S. Mbandaka) was resistant to cefotaxime and produced ESBL.

Detection of decreased fluoroquinolone susceptibility in Salmonellas and validation of nalidixic acid screening test.

We evaluated 1,010 Salmonella isolates classified as fluoroquinolone susceptible according to the National Committee for Clinical Laboratory Standards guidelines for susceptibility to nalidixic acid and three fluoroquinolones. These isolates were divided into two distinct subpopulations, with the great majority (n = 960) being fully ciprofloxacin susceptible and a minority (n = 50) exhibiting reduced ciprofloxacin susceptibility (MICs ranging between 0.125 and 0.5 microg/ml). The less ciprofloxacin-susceptible isolates were uniformly resistant to nalidixic acid, while only 12 (1.3%) of the fully susceptible isolates were nalidixic acid resistant. A similar association was observed between resistance to nalidixic acid and decreased susceptibility to ofloxacin or norfloxacin. A mutation of the gyrA gene could be demonstrated in all isolates for which the ciprofloxacin MICs were >/= 0.125 microg/ml and in 94% of the nalidixic acid-resistant isolates but in none of the nalidixic acid-susceptible isolates analyzed. Identification of nalidixic acid resistance by the disk diffusion method provided a sensitivity of 100% and a specificity of 87.3% as tools to screen for isolates for which the MICs of ciprofloxacin were >/= 0.125 microg/ml. We regard it as important that microbiology laboratories endeavor to recognize these less susceptible Salmonella strains, in order to reveal their clinical importance and to survey their epidemic spread.