Antimicrobial resistance to Citrobacter spp. and Salmonella spp. isolated from goose eggs

Infections with bacteria of the genus Salmonella are responsible for a variety of acute and chronic diseases in poultry. Infected poultry flocks are also among the most important reservoirs of salmonellae that can be transmitted through the food chain to humans. Citrobacter belongs to the Enterobacteriaceae family which is closely related to Salmonella. The aim of this study was to examine goose eggs contaminated with Citrobacter spp. and Salmonella spp. and determine the drug resistance pattern of the isolated organisms. Two hundred and forty goose eggs were collected in Zabol region and were transferred to the microbiology laboratory of Zabol University. The egg shells were thoroughly disinfected and the interior contents of individual eggs were pooled into a sterile beaker in groups of four resulting in 60 samples overall. These samples were then incubated at 37°C for 24 h. Swab samples were prepared from the incubated contents and then subcultured on several solid media. Identification of the isolated bacteria was performed using standard bacteriological and biochemical procedures. Final confirmation of Salmonella in the isolates was by slide serum agglutination test. The isolation rates of Salmonella spp. from the egg samples were determined to be at least 3.75%. Disc diffusion tests on Muller–Hinton agar were used to determine the sensitivity to antibacterial agents. Ten antibiotics were studied: ampicillin, colistin, cephalexin, ciprofloxacin, chloramphenicol, gentamycin, furazolidone, nalidixic acid, norfloxacin and tetracycline. Both genera of the bacteria showed 100% susceptibility to ciprofloxacin and norfloxacin. Salmonella isolates showed the most resistance to tetracycline (100%), but Citrobacter isolates showed the most resistance to cephalexin and furazolidone (88.8%).     

The consequences of a sudden demographic change on the seroprevalence pattern,virulence genes,identification and characterisation of integron-mediated antibiotic resistance in the Salmonella enterica isolated from clinically diarrhoeic humans in Egypt

The present study was undertaken to identify and characterise integrons and integrated resistance gene cassettes among eight multidrug-resistant (MDR) Salmonella serovars isolated from humans in Egypt. Virulotyping by polymerase chain reaction (PCR) was used for the detection of the presence of virulence genes. Integron PCR was used to detect the presence of class 1 in the MDR strains. The associated individual resistance gene cassettes were identified using specific PCRs. The isolated serovars were Salmonella Grampian (C1; 2/5), Larose (C1; 1/5), Hato (B; 1/5) and Texas (B; 1/5). Among the Salmonella serovars, five Salmonella isolates showed the highest resistance to amoxicillin, ampicillin, chloramphenicol, lincomycin, gentamicin, nalidixic acid, streptomycin and trimethoprim (100 %), followed by neomycin, norfloxacin and tetracycline (80 %), while the lowest resistance was recorded to colistin sulphate and ciprofloxacin in percentages of 20 and 40 %, respectively. The invA, avrA, ssaQ, mgtC, siiD and sopB genes were detected in all isolates (100 %), while the spvC and gipA genes were totally (100 %) absent from all isolates. The remaining three virulence genes were diversely distributed as follows: the bcfC gene was detected in all isolates except Salmonella Hato (80 %); the sodC1 gene was detected only in Salmonella Grampian and Salmonella Texas (60 %); and the sopE1 gene was detected only in Salmonella Grampian, Hato and Texas (60 %). Class 1 integrons were detected in 90 % of the MDR isolates, comprising serovars Muenster, Florian, Noya, Grampian, Larose, Hato and Texas. Of the class 1 integron-positive isolates, 45 % harboured Salmonella genomic island 1 (SGI1) either right junction or right and left junction having an A-C-S-T phenotype. Of the class 1 integron-positive isolates, 44 % harboured integron gene cassette aadA2, while 11 % harboured the floR gene present in multidrug resistance flanked by two integrons of SGI1. The results of the present study indicate that class 1 integrons carrying gene cassettes conferring resistance mainly to aminoglycosides are widespread among the MDR Salmonella serovars isolated from humans in Egypt, indicating the important role of these genetic elements in the dissemination of multidrug resistance.     

In vitro and in vivo susceptibility of Salmonella spp. isolated from broiler chickens

Salmonellosis is the most important zoonotic disease, causing diarrhea and systemic infections. Due to poor management in antibiotic consumption, microbial resistance has increased in the treatment of zoonotic diseases. This study was conducted to evaluate the antimicrobial susceptibility of Salmonella spp. isolated from day-old broiler chickens which were referred to a private laboratory in Mazandaran—a province in the north of Iran—from 2008 to 2010. After harvesting the samples from the yolk sac, liver, and intestine of chickens, intestinal samples were transferred to selenite F and then incubated at 43 °C for 12–16 h. A loopful from selenite F and samples of liver and yolk sac were streaked on XLD and S.S agars. After incubation, the suspected colonies were inoculated into TSI agar for biochemical confirmation. The disk diffusion method on Muller Hinton agar was used to determine the susceptibility to antimicrobial agents. Because of the predominant use of enrofloxacin, sulfadiazine + trimethoprim, and flumequine for controlling Salmonella and Escherichia coli infections in the first week of broilers brooding in Iran, these three antibiotics were used in the in vivo study. From day 2 and continuing for 4 days, antibiotics were administrated in water, and after 10 days, samples from the liver, heart, and intestine were taken for isolation of Salmonella. In antimicrobial resistant tests, the most susceptible antibiotics were chloramphenicol, cefotaxime, and sulfadiazine + trimethoprim. The antimicrobial resistance to enrofloxacin, flumequine, colistin, and neomycin were 6.6, 11.6, 21.6, and 33.3 %, respectively. The results showed that 12 parties of broiler chickens were infected with paratyphoid salmonellae and the in vivo study showed that enrofloxacin and sulfadiazine + trimethoprim had the best and the weakest performance, respectively.     

Antibiotic sensitivity of E. coli and Salmonella isolated from different water sources in Kashmir, India

The objective of the present study was to determine the prevalence of Salmonella and Escherichia coli, the serotypes involved and the antibiogram of the various isolates obtained from different sources of water supply (streams, Dal Lake, tube wells and community supply water) in Kashmir, India, during the years 2009–2010. A total of 100 samples, 25 from each source, were taken for the present study. All samples were evaluated for the presence of Salmonella and E. coli, stereotyped and tested for antimicrobial susceptibility. A total of 60 isolates of E. coli and 12 isolates of Salmonella were obtained. The antimicrobial susceptibilities of different isolates of E. coli and Salmonella from different water sources were examined by disc diffusion method. The high in vitro sensitivity was shown by 100 % of E. coli isolates for ciprofloxacin, 95 % for amoxycillin/clavulanic acid, 93.33 % for each of cephotaxime and amikacin and 91.67 % for lavofloxacin and gentamicin. The isolates registered an intermediate response to rifampicin (85.00 %), lomefloxacin (83.33 %) and norfloxacin (83.33 %) and showed resistance to erythromycin (98.33 %). The isolates of Salmonella were 100 % sensitive for gentamicin, 91.67 % for each of cefixime, ciprofloxacin, amikacin and lavofloxacin; 83.33 % for each of cephotaxime and amoxycillin/clavulanic acid and showed resistance to erythromycin (100 %), nalidixic acid (100 %) and rifampicin (91.67 %). The isolates, however, showed an intermediate resistance to lomefloxacin (83.34 %) and norfloxacin (66.67). The high incidence of multi-drug-resistant strains of E. coli and Salmonella is due to injudicious use of antibiotics and exchange of antibiotic resistance among bacterial populations.     

Improved isolation of salmonellae from faeces using a semisolid rappaport-vassiliadis medium

A modified semisolid Rappaport-Vassiliadis (MSRV) enrichment medium was evaluated as an alternative to Rappaport-Vassiliadis (RV) broth for culture of salmonellae from faeces. Faeces from 1544 subjects were cultured using MSRV medium, selective agars, and RV and selenite F enrichment broths. Of the 183 strains ofSalmonella spp. isolated, 88 % were recovered on MSRV medium, whilst only 59 % were recovered using RV broth. When MSRV medium was combined with direct culture and selenite enrichment, 98.9 % of salmonellae were recovered. The MSRV culture was found to be easy to read, and in most cases confirmation of organisms asSalmonella spp. could be made 24 hours after receipt of the faecal specimen.     

In vitro antibacterial activity of norfloxacin compared with eight other antimicrobial agents

The antibacterial activity of norfloxacin, an organic acid structurally related to nalidixic acid, was compared with that of the oral cephalosporins cefaclor and cephalexin, and with that of nalidixic acid, cinoxacin, amikacin, ampicillin, trimethoprim alone and the combination of trimethoprim and sulfamethoxazole. Agar dilution studies were performed with a total of 398 clinical isolates of gram-negative bacteria, Norfloxacin was found to be the most active drug studied against each of the different groups of organisms tested. MIC₉₀ values for norfloxacin were as follows:Citrobacter spp., 2μg/ml;Enterobacter spp., 0.13μg/ml;Escherichia coli, 0.06μg/ml;Klebsiella spp., 0.13μg/ml;Proteus spp., 0.06μg/ml;Salmonella spp., 1μg/ml;Serratia spp., 0.13μg/ml; andPseudomonas spp., 2μg/ml. MIC₉₀ values for the other drugs were 4μg/ml or greater and many organisms were totally resistant to one or more of the other drugs (MIC > 128μg/ml). Cross resistance between norfloxacin and the related drugs nalidixic acid and cinoxacin was not observed.     

Drug resistance of Salmonella spp. isolated from pigeon eggs

Avian Salmonellae infections cause not only clinical disease in poultry but are also recognized as a source of food-borne disease transmission to humans. Domestic pigeons usually live in urban and rural areas in close proximity to human residential areas. Although their role in transmission of different infectious organisms is important from public health point of view, there are few reports available on Salmonella infections and their resistance to antibiotics in pigeon. In order to study pigeon egg contamination to the Salmonella spp. and the drug resistance pattern of the isolated organisms, pigeon egg shells were cleaned and disinfected with 96% ethanol. The contents of each egg was emptied into a sterile petri dish and incubated at 37°C for 24 h. Isolates were finally confirmed by PCR, using specific primers targeting the invA gene sequences from Salmonella spp. The results of this study showed that 5.7% of pigeon eggs had Salmonella spp. contamination. Disk diffusion test on Muller–Hinton agar was used to determine the sensitivity to antibacterial agents. Study of resistance to antimicrobial agents of isolated Salmonella spp. among the ten antibiotics showed a high frequency of sensitivity to ciprofloxacin, norfloxacin, gentamycin, and chloramphenicol (100%), and a high level of resistance to tetracycline (50%) was observed.     

Epidemic increase in Salmonella bloodstream infection in children, Bwamanda, the Democratic Republic of Congo

Salmonella enterica is the leading cause of bloodstream infection in children in sub-Saharan Africa, but few data are available from Central-Africa. We documented during the period November 2011 to May 2012 an epidemic increase in invasive Salmonella bloodstream infections in HGR Bwamanda, a referral hospital in Equateur Province, DR Congo. Salmonella spp. represented 90.4 % (103 out of 114) of clinically significant blood culture isolates and comprised Salmonella Typhimurium (54.4 %, 56 out of 103), Salmonella Enteritidis (28.2 %, 29 out of 103) and Salmonella Typhi (17.5 %, 18 out of 103), with Salmonella Enteritidis accounting for most of the increase. Most (82 out of 103, 79.6 %) isolates were obtained from children < 5 years old. Median ages of patients infected with Salmonella Typhimurium and Salmonella Enteritidis were 14 months (14 days to 64 years) and 19 months (3 months to 8 years) respectively. Clinical presentation was non-specific; the in-hospital case fatality rate was 11.1 %. More than two thirds (69.7 %, 53 out of 76) of children < 5 years for whom laboratory data were available had Plasmodium falciparum infection. Most (83/85, 97.6 %) non-typhoid Salmonella isolates as well as 6/18 (33.3 %) Salmonella Typhi isolates were multidrug resistant (i.e. resistant to the first-line oral antibiotics amoxicillin, trimethoprim-sulfamethoxazole and chloramphenicol), one (1.0 %) Salmonella Typhimurium had decreased ciprofloxacin susceptibility owing to a point mutation in the gyrA gene (Gly81Cys). Multilocus variable-number tandem-repeat (MLVA) analysis of the Salmonella Enteritidis isolates revealed closely related patterns comprising three major and four minor profiles, with differences limited to one out of five loci. These data show an epidemic increase in clonally related multidrug-resistant Salmonella bloodstream infection in children in DR Congo.     

mcr-1 is borne by highly diverse Escherichia coli isolates since 2004 in food-producing animals in Europe

Objectives

In November 2015, a plasmid-mediated colistin resistance, MCR-1, was described in animals, food and humans in China, and it was considered as a potential emerging threat to public health. Therefore, we screened for the mcr-1 gene a European collection of colistin-resistant Escherichia coli (n = 218) and Salmonella spp. (n = 74) isolated from diseased food-producing animals between 2004 and 2014 and characterized the mcr-1-positive clones.

A study of bacteriologic status of infertile ostrich (Struthio camelus) eggs

There are many obstacles which impede progress in the ostrich industry. Despite a century of commercial ostrich production, there has been little progress in scientific research which deals with management practices, health care, nutrition, or breeding. The fertility of ostrich eggs is poor in comparison with more conventional domesticated birds and is a major problem in the efficient production of ostriches under farming conditions. In order to study the bacterial populations of ostrich eggs that were determined infertile by candling, swab samples were prepared from the contents of 40 infertile eggs and inoculated into tryptic soy broth and selenite-F broths. The media was incubated at 37°C and then subcultured on solid media. The identification of the isolated colonies was performed using standard bacteriological and biochemical procedures. Microbiologic investigations showed bacterial isolation in 45% of the samples from infertile eggs including: Bacillus spp. (33.4%), Staphylococcus spp. (29.1%), Escherichia coli (12.5%), Proteus spp. (12.5%), Streptococcus spp. (8.3%), and Klebsiella spp. (4.2%).     

Evaluation of colistin susceptibility in multidrug-resistant clinical isolates from cystic fibrosis, France

The emergence of multidrug-resistant (MDR) bacteria in cystic fibrosis (CF) patients has led to the use of colistin drug and the emergence of colistin-resistant Gram-negative bacteria. The aim of this study was to compare the disk diffusion and Etest methods for colistin susceptibility testing on MDR bacteria associated with CF from Marseille, France. Forty-nine MDR clinical isolates (27 Stenotrophomonas maltophilia, 22 Achromobacter xylosoxidans) were used in this study. Disk diffusion and Etest assays were used to assess the reliability of these two techniques. For S. maltophilia, 25 out of 27 isolates had low minimum inhibitory concentrations (MICs, 0.125–0.75 mg/L), whereas two isolates displayed high MICs (32 mg/L). Similarly, 19 out of 22 A. xylosoxidans isolates had low MICs (0.75–3.0 mg/L), whereas three isolates had high MICs (32–256 mg/L). The diameters of zone inhibition with a 50-μg colistin disk displayed a good correlation with the MICs obtained by the Etest. Susceptible and resistant strains were eventually separated using a disk diffusion assay at a cut-off of ≤12 mm for a 50-μg disk. Colistin displayed excellent activity against S. maltophilia and A. xylosoxidans and the disk diffusion assay could be confidently used to determine the susceptibility to colistin for MDR Gram-negative bacteria in the context of CF.     

Mutant prevention concentration of colistin alone and in combination with rifampicin for multidrug-resistant <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis>

Colistin-susceptible isolates of Acinetobacter baumannii often contain subpopulations that are resistant to colistin. Monotherapy with colistin can lead to selective growth of these subpopulations and emergence of colistin-resistant strains. Our objectives were to explore the susceptibility pattern of colistin-resistant subpopulations and investigate if combining colistin with a second antibiotic could prevent their selective growth. Four colistin-susceptible clinical isolates of A. baumannii and one reference isolate were used. The mutant prevention concentration (MPC) of colistin, i.e. the concentration required to block growth of all single-step-mutant subpopulations, was determined by plating an inoculum of 10⁹ CFU on Mueller Hinton agar (MHA)-plates containing 2-fold dilutions of colistin (0.125–128 mg/L). Susceptibility testing of colistin-resistant subpopulations, obtained in the MPC assay, was performed with Etest. The MPC of colistin, in combination with rifampicin, was determined by plating an inoculum of 10⁹ CFU on MHA-plates containing colistin (0.125–128 mg/L) and fixed concentrations of rifampicin (1.1 mg/L or 4.4 mg/L). The colistin-resistant subpopulations demonstrated increased susceptibility to a number of agents compared to their main populations. These subpopulations were even susceptible to agents that normally are inactive against gram-negative bacteria and all had rifampicin MICs of?<?0.002 mg/L. The combination of colistin and rifampicin completely inhibited the growth of all colistin-resistant subpopulations and significantly lowered the MPC of colistin for A. baumannii. Combining colistin with rifampicin could be a way to prevent selective growth of colistin-resistant subpopulations of A. baumannii and possibly the emergence of colistin-resistant strains.     

Highly synergistic activity of melittin with imipenem and colistin in biofilm inhibition against multidrug-resistant strong biofilm producer strains of <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis>

The rapid increase of drug resistance and failure of available antibiotics to treat biofilm-associated infections is of great health concern. Accordingly, our study aimed to evaluate the synergistic antibacterial, biofilm inhibitory, and biofilm removal activities of melittin in combination with colistin, imipenem, and ciprofloxacin against multidrug-resistant (MDR) strong biofilm producer Acinetobacter baumannii isolates. The kinetics of biofilm formation were evaluated for the isolates for 144 h. Minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), minimum biofilm inhibitory concentrations (MBICs), and biofilm removal activities for melittin and combinations with antibiotics were determined. Inhibition of biofilm-associated protein (bap) expression by melittin was evaluated with real-time polymerase chain reaction (PCR). Field emission scanning electron microscopy (FE-SEM) was used to visualize the effect of synergism on the inhibition of biofilm production. The geometric means of the fractional inhibitory concentration index (FICi) for melittin–colistin, melittin–imipenem, and melittin–ciprofloxacin combinations were calculated as 0.31, 0.24, and 0.94, respectively. Comparing the geometric means of the removal activity for melittin, colistin, imipenem, and combinations of them in both 6 and 24 h showed a significant difference between the groups (p-value < 0.05). Exposure to melittin induced a statistically significant downregulation of bap mRNA levels in all isolates at sub-MIC doses. Analysis of the FE-SEM results demonstrated that the synergism of melittin–colistin at 0.125–0.25 μg inhibited biofilm formation completely. In conclusion, our findings indicate that melittin possesses considerable potential for use in combination with colistin and imipenem to treat infections caused by MDR strong biofilm producer A. baumannii isolates.     

Study on Salmonella contamination of traditionally produced edible poultry eggs

One of the important issues of food hygiene is Salmonella contamination of eggs that may cause food-borne infection and disease in humans. The aim of this study was to investigate Salmonella contamination of traditionally produced poultry eggs in Tehran. Contamination of eggs to other Enterobacteriaceae was also investigated. For this purpose, 200 eggs including 131 egg samples from chickens and 69 from quails, geese, and ducks (23 samples from each species) were investigated. After conventional isolation procedures, Salmonella contamination was detected in five chicken eggs. Serological tests revealed that all of the isolated genera belonged to D serogroup and multiplex PCR showed that all strains carried spv and sefA genes and also random sequence (specific for the genus Salmonella); therefore, all strains confirmed as Salmonella Enteritidis. Antimicrobial susceptibility test revealed sensitivity of all Salmonella isolates to florfenicol, ceftriaxone, trimethoprim–sulfamethoxazole, chloramfenicol, and oxytetracycline. In addition, except the quail eggs, 29 enteric bacteria were isolated from eggs including 21 Enterobacter spp., 4 Klebsiella spp., 3 Escherichia coli, and 1 Proteus spp. This study indicated that traditionally produced poultry eggs were highly contaminated by Enterobacteriaceae. Moreover, the chicken eggs were contaminated by Salmonella Enteritidis; therefore, non-commercial chicken eggs can be considered as an important threat for public health.     

Fluoroquinolone Susceptibility Testing of Salmonella enterica: Detection of Acquired Resistance and Selection of Zone Diameter Breakpoints for Levofloxacin and Ofloxacin

Fluoroquinolones (e.g., ciprofloxacin) have become a mainstay for treating severe Salmonella infections in adults. Fluoroquinolone resistance in Salmonella is mostly due to mutations in the topoisomerase genes, but plasmid-mediated quinolone resistance (PMQR) mechanisms have also been described. In 2012, the Clinical and Laboratory Standards Institute (CLSI) revised the ciprofloxacin interpretive criteria (breakpoints) for disk diffusion and MIC test methods for Salmonella. In 2013, the CLSI published MIC breakpoints for Salmonella to levofloxacin and ofloxacin, but breakpoints for assigning disk diffusion results to susceptible (S), intermediate (I), and resistant (R) categories are still needed. In this study, the MICs and inhibition zone diameters for nalidixic acid, ciprofloxacin, levofloxacin, and ofloxacin were determined for 100 clinical isolates of nontyphi Salmonella with or without resistance mechanisms. We confirmed that the new levofloxacin MIC breakpoints resulted in the highest category agreement (94%) when plotted against the ciprofloxacin MICs and that the new ofloxacin MIC breakpoints resulted in 92% category agreement between ofloxacin and ciprofloxacin. By applying the new MIC breakpoints in the MIC zone scattergrams for levofloxacin and ofloxacin, the following disk diffusion breakpoints generated the least number of errors: ≥28 mm (S), 19 to 27 mm (I), and ≤18 mm (R) for levofloxacin and ≥25 mm (S), 16 to 24 mm (I), and ≤15 mm (R) for ofloxacin. Neither the levofloxacin nor the ofloxacin disk yielded good separation of isolates with and without resistance mechanisms. Further studies will be needed to develop a disk diffusion assay that efficiently detects all isolates with acquired resistance to fluoroquinolones.     

Tetracycline use in the community may promote decreased susceptibility to quinolones in <Emphasis Type="Italic">Escherichia coli</Emphasis> isolates

We previously found that the hospital use of tetracyclines is associated with quinolone resistance in hospital isolates of Enterobacteriaceae. Tetracyclines are heavily used in the community. Our aim was to assess whether their use in the community favors quinolone resistance in community isolates of Escherichia coli. Monthly data of community antibiotics use and E. coli quinolone resistance in a 1.3 million inhabitant French area were obtained from 2009 to 2014, and were analyzed with autoregressive integrated moving average (ARIMA) models. Quinolone use decreased from 10.1% of the total antibiotic use in 2009 to 9.3% in 2014 (trend, ? 0.016; p-value < 0.0001), while tetracycline use increased from 16.5% in 2009 to 17.1% in 2014 (trend, 0.016; p < 0.0001). The mean (95% confidence interval) monthly proportions of isolates that were non-susceptible to nalidixic acid and ciprofloxacin were 14.8% (14.2%–15.5%) and 9.5% (8.8%–10.1%), respectively, with no significant temporal trend. After adjusting on quinolone use, tetracycline use in the preceding month was significantly associated with nalidixic acid non-susceptibility (estimate [SD], 0.01 [0.007]; p-value, 0.04), but not with ciprofloxacin non-susceptibility (estimate [SD], 0.01 [0.009]; p-value, 0.23). Tetracycline use in the community may promote quinolone non-susceptibility in E. coli. Decreasing both tetracycline and quinolone use may be necessary to fight against the worldwide growth of quinolone resistance.     

In vitro activity of daptomycin in combination with low-dose colistin against a diverse collection of Gram-negative bacterial pathogens

The activity of colistin in combination with daptomycin was assessed using 30 Gram-negative type strains and multidrug-resistant isolates with defined mechanisms of resistance. Daptomycin minimum inhibitory concentrations (MICs) were determined with and without sub-inhibitory concentrations of colistin. The activity of daptomycin was not affected with respect to Escherichia coli, Klebsiella pneumoniae or Pseudomonas aeruginosa. For colistin-susceptible Acinetobacter baumannii, sensitisation factors ranged from 8 to 128 (median 32), with the daptomycin MIC being reduced to the Clinical and Laboratory Standards Institute (CLSI) enterococci susceptibility breakpoint of 4 μg/ml for the ATCC 19606 type strain. A combination of daptomycin and colistin may be useful for the treatment of A. baumannii but not infections due to other Gram-negative species.     

Prevalence and antimicrobial resistance of Salmonella isolated from fish, shrimp, lobster, and crab in Iran

The objective of this study was to determine the Salmonella prevalence, the serotypes involved, and antimicrobial susceptibility patterns of Salmonella isolates recovered from fish, shrimp, lobster, and crab in Iran. A total of 384 samples of fish, shrimp, lobster, and crab were collected in three provinces along the Persian Gulf in the south coast of Iran. Samples were collected at the end of each month from September 2009 to May 2011. All samples were evaluated for the presence of Salmonella, stereotyped and tested for antimicrobial susceptibility. There was an overall Salmonella prevalence of 5%. Salmonella was isolated from a significantly larger number of fish (10.4%) than shrimp (1.8%; P?≤?0.05). No Salmonella was isolated from lobster and crab samples. Salmonella isolates recovered from fish and shrimp samples were of five different serotypes including Salmonella typhimurium, Salmonella enteritidis, Salmonel la typhi, Salmonella paratyphi B, and Salmonella newport. Susceptibilities of Salmonella isolates were determined for 12 antimicrobial drugs using the disk-diffusion method. Resistance to nalidixic acid was the most common finding (47.4%), followed by resistance to tetracycline (36.8%), streptomycin (15.8%), trimethoprim (15.8%), and ciprofloxacin (5.3%). To our best knowledge, this is the first study on prevalence of Salmonella in fish, shrimp, lobster, and crab and the first report on the isolation of Salmonella spp. from retail fish and shrimp in Iran.     

Plasmid-mediated quinolone resistance in typhoidal Salmonellae: A preliminary report from South India

Background: Fluoroquinolones are the drugs extensively employed for the treatment of Salmonella infections. Over the couple of decades that have elapsed since the introduction of fluoroquinolones, resistance to these agents by Enterobacteriaceae family members has become common and widespread. Although fluoroquinolone resistance is mediated by genomic DNA (deoxyribonucleic acid) as well as plasmid DNA, the plasmid-mediated quinolone resistance (PMQR) facilitates higher level resistance by interacting with genomic mechanism and is capable of horizontal spread. Materials and Methods: During a period of 1-year, 63 typhoidal Salmonellae were isolated from 14,050 blood cultures and one parietal wall abscess. 36 (56.25%) were Salmonella Typhi and 27 (42%) were Salmonella Paratyphi A. They were all screened for resistance by the disc diffusion method and their minimum inhibitory concentrations were determined using agar dilution, broth dilution and E-strip method. Ciprofloxacin resistant isolates were screened for PMQR determinants by polymerase chain reaction assay. Results: All the 63 isolates were resistant to nalidixic acid. Among the 36 S. Typhi isolates 20 were resistant to ciprofloxacin, of which 14 carried the plasmid gene qnrB and one carried the aac(6’)-Ib-cr gene. qnrA and qnrS genes were not detected. Ciprofloxacin resistance was not seen in any of the S. Paratyphi A isolates. Conclusion: The antibiotic sensitivity pattern of typhoidal Salmonellae shows an increasing trend of PMQR. The allele B of qnr gene was found to be the predominant cause of PMQR in this study.     

Cross-resistance of nalidixic acid resistantEnterobacteriaceae to new quinolones and other antimicrobials

One hundred urine isolates of Enterobacteriaceae screened for resistance to 30 g nalidixic acid by disc diffusion test were examined by MIC determination for in vitro susceptibility to nalidixic acid, ciprofloxacin, enoxacin, gentamicin, nitrofurantoin, trimethoprim, cephalexin and ceftazidime. Those resistant to nalidixic acid and also gentamicin or a cephalosporin were further examined to determine the mechanism of resistance. Compared to the total urine isolates of Enterobacteriaceae from the same time period, this population as a whole was less susceptible to all antimicrobials tested except gentamicin. Strains that exhibited multiple resistance had the conventional mechanisms of resistance to those antimicrobials. No multiply resistant strains had a permeability barrier due to outer membrane protein alterations causing cross-resistance to chemically unrelated classes of antimicrobials.