Multidrug resistant Salmonella

A total of 326 salmonella strains was isolated and studied from suspected enteric fever cases in Mumbai (Bombay) during a 2 year period from May 1992 to July 1994. These were identified using standard biochemical and serological tests. Bacteriophage typing, antibiotic sensitivity and conjugation experiments were also carried out. S. typhi was the most common serotype accounting for 75.46% of the strains. Among S. typhi strains 87% were biotype I and 13% were biotype II. 9.5% strains were of S. paratyphi A, 5.52% of S. typhimurium, 4.60% of S. worthington, 4.30% of S. havana and 0.62% of S. enteritidis. The commonest bacteriophage type of S. typhi was E1, and of S. paratyphi A type 1, whereas 88.88% strains of S. typhimurium were untypable. Most of the strains were multidrug resistant including commonly used antibiotics such as chloramphemicol, ampicillin, and cotrimaxazole. Quinolone derivatives such as Ciprofloxacin were found to be the most effective drugs. In the conjugation experiments there was direct transfer of resistance pattern and enbloc transfer of resistance was observed in most strains. Salmonella typhi is still the most commonly encountered species. There is an alarming increase in multidrug resistance.     

Molecular and epidemiological study of Salmonella clinical isolates

A survey of Salmonella infections was carried out over a 1-year period in the rural community covered by the Hospital Reina Sofía (Tudela, Spain). The 255 strains that were collected were studied by serotyping, antimicrobial resistance, and plasmid profile analysis. The predominant serotype was S. enteritidis (85.90%), followed by S. typhimurium (7.06%) and S. virchow (2.36%). Only 7.84% of the strains were resistant to antimicrobial agents. The most common resistance was to beta-lactam antibiotics. This resistance was due to the presence of one of two types of beta-lactamases, TEM-1 or TEM-2. Resistance to kanamycin was associated with the synthesis of a 3'-O-phosphotransferase. The resistance to streptomycin and chloramphenicol was either not enzymatic or was due to a 3"-O-phosphotransferase and a chloramphenicol acetyltransferase, respectively. Analysis of total plasmid DNA content revealed the presence of plasmids in 96.08% of the isolates. According to their plasmid profile, the strains could be classified into different groups. The three main groups, which accounted for 50.19, 20.78, and 4.70% of the isolates, respectively, corresponded to the antimicrobial-susceptible S. enteritidis serotype. These results suggested that plasmid profile analysis in conjunction with antimicrobial resistance determination can be useful for subtyping resistant Salmonella isolates.     

Class 1 integrons and Salmonella genomic island 1 among Salmonella enterica isolated from poultry and swine

Two hundred eleven Salmonella enterica strains representing 35 serotypes isolated from healthy poultry (n=103) and swine (n=108) were used in this study. The occurrence and characteristics of class 1 integrons were investigated. Salmonella genomic islands (SGIs) and the horizontal transfer of integrons were assessed. One hundred eighty-six isolates (88%) were resistant to at least one antimicrobial and 140 isolates (66%) were multidrug resistant. The intI1 gene was present in 54 isolates (25.6%), of which 33 (15.6%) carried gene cassettes with sizes ranging from 0.7 to 2.3 kb. Sequence analysis revealed 11 distinct integron profiles in which resistance genes bla(PSE-1), dfrA1, dfrA12, aadA2, aadA4a, and silB were present. The gene cassette array dfrA12-aadA2 was the most prevalent among the isolates whereas most integrons were located on conjugative plasmids. SGI1 variants (SGI1-A and -F) were present in nine isolates belonging to serovars Albany, Emek, Kedougou, and Kingston.     

Characterization and localization of drug resistance determinants in multidrug-resistant, integron-carrying Salmonella enterica serotype Typhimurium strains

The genetic background of the antimicrobial resistance of 10 selected multiresistant Salmonella serotype Typhimurium (S. Typhimurium) strains (including the emerging monophasic variant [4,5,12:i:- ]) was investigated. All strains shared class 1 integrons (with seven types of variable regions) and belonged to different lineages (L1-L6) according to their phage types, DNA polymorphisms by XbaI-pulsed-field gel electrophoresis (PFGE), integrons, and/or resistance patterns. The strains were screened for the presence and localization (chromosomal or plasmid) of 32 DNA sequences representing integron-, Tn21-like transposon-, resistance-, and virulence-plasmid genes. Strains belonging to lineage L1 (definitive phage type DT104) carried the 90-kb Salmonella virulence plasmid together with the complete or partial chromosomally located Salmonella Genomic Island 1 (SGI1). All strains belonging to the other five lineages carried their resistance determinants on various resistance plasmids. Two of these strains showed complex plasmid profiles, which included a 95 kb virulence plasmid together with two or four resistance plasmids. Two strains carried a resistance plasmid that lacked the virulence-plasmid-encoding sequences. The remaining two strains carried two different hybrid virulence-resistance plasmids. Twenty-three of the DNA sequences could be assigned to distinct XbaI genomic restriction patterns (PFGE profiles). In this way, the influence of the resistance and virulence plasmids on the PFGE profiles was determined, and several groups of resistance genes could be identified. The data obtained represent a useful epidemiological tool for tracing the emergence and distribution of multiresistant S. Typhimurium worldwide.     

Molecular characterization of multidrug-resistant Salmonella enterica subsp. enterica serovar Typhimurium isolates from swine

As part of a longitudinal study of antimicrobial resistance among salmonellae isolated from swine, we studied 484 Salmonella enterica subsp. enterica serovar Typhimurium (including serovar Typhimurium var. Copenhagen) isolates. We found two common pentaresistant phenotypes. The first was resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (the AmCmStSuTe phenotype; 36.2% of all isolates), mainly of the definitive type 104 (DT104) phage type (180 of 187 isolates). The second was resistance to ampicillin, kanamycin, streptomycin, sulfamethoxazole, and tetracycline (the AmKmStSuTe phenotype; 44.6% of all isolates), most commonly of the DT193 phage type (77 of 165 isolates), which represents an unusual resistance pattern for DT193 isolates. We analyzed 64 representative isolates by amplified fragment length polymorphism (AFLP) analysis, which revealed DNA fingerprint similarities that correlated with both resistance patterns and phage types. To investigate the genetic basis for resistance among DT193 isolates, we characterized three AmKmStSuTe pentaresistant strains and one hexaresistant strain, which also expressed resistance to gentamicin (Gm phenotype), all of which had similar DNA fingerprints and all of which were collected during the same sampling. We found that the genes encoding the pentaresistance pattern were different from those from isolates of the DT104 phage type. We also found that all strains encoded all of their resistance genes on plasmids, unlike the chromosomally encoded genes of DT104 isolates, which could be transferred to Escherichia coli via conjugation, but that the plasmid compositions varied among the isolates. Two strains (strains UT08 and UT12) had a single, identical plasmid carrying bla(TEM) (which encodes ampicillin resistance), aphA1-Iab (which encodes kanamycin resistance), strA and strB (which encode streptomycin resistance), class B tetA (which encodes tetracycline resistance), and an unidentified sulfamethoxazole resistance allele. The third pentaresistant strain (strain UT20) was capable of transferring by conjugation two distinct resistance patterns, AmKmStSuTe and KmStSuTe, but the genes were carried on plasmids with slightly different restriction patterns (differing by a single band of 15 kb). The hexaresistant strain (strain UT30) had the same plasmid as strains UT08 and UT12, but it also carried a second plasmid that conferred the AmKmStSuGm phenotype. The second plasmid harbored the gentamicin resistance methylase (grm), which has not previously been reported in food-borne pathogenic bacteria. It also carried the sul1 gene for sulfamethoxazole resistance and a 1-kb class I integron bearing aadA for streptomycin resistance. We also characterized isolates of the DT104 phage type. We found a number of isolates that expressed resistance only to streptomycin and sulfamethoxazole (the StSu phenotype; 8.3% of serovar Typhimurium var. Copenhagen strains) but that had AFLP DNA fingerprints similar or identical to those of strains with genes encoding the typical AmCmStSuTe pentaresistance phenotype of DT104. These atypical StSu DT104 isolates were predominantly cultured from environmental samples and were found to carry only one class I integron of 1.0 kb, in contrast to the typical two integrons (InC and InD) of 1.0 and 1.2 kb, respectively, of the pentaresistant DT104 isolates. Our findings show the widespread existence of multidrug-resistant Salmonella strains and the diversity of multidrug resistance among epidemiologically related strains. The presence of resistance genes on conjugative plasmids and duplicate genes on multiple plasmids could have implications for the spread of resistance factors and for the stability of multidrug resistance among Salmonella serovar Typhimurium isolates.     

Immunogenicity of Living and Heat-Killed Salmonella pullorum Vaccines

Specific pathogen-free CD-1 and C57Bl mice were infected in a hind footpad with 5 x 10(4) viable Salmonella enteritidis cells or 10(7) viable S. pullorum cells. The resulting bacterial growth within the footpad, the draining lymph nodes, and the liver and spleen was followed for 14 days. Mice vaccinated with live S. enteritidis rapidly developed an effective antibacterial resistance to both intravenous and intragastric challenge with S. enteritidis SM(R). The viable inoculum of S. pullorum was rapidly eliminated from the normal mouse tissues and failed to induce a detectable anti-Salmonella resistance to parenteral or oral challenge with S. enteritidis. Heat-killed saline suspensions (200 mug, dry wt) of S. enteritidis or S. pullorum were unable to induce an effective antimicrobial resistance against a subsequent virulent Salmonella challenge. However, when the organisms were suspended in Freund complete adjuvant, both vaccines induced an antibacterial resistance to intravenous and intragastric challenge. Reduction of the antigenic dose from 200 to 40 mug did not greatly affect the protective value of the two killed vaccines against an intravenous challenge, but the level of protection observed with two 40-mug doses of S. pullorum was considerably reduced when the animals were infected intragastrically, suggesting that some quantitative differences existed between the sensitizing antigenic contents of the two test organisms.     

Molecular analysis of ampicillin-resistant sporadic Salmonella typhi and Salmonella paratyphi B clinical isolates

Objective: To study the mechanisms of antibiotic resistance in Salmonella typhi and Salmonella paratyphi B clinical isolates, and the clonality of resistant strains.
Method: Antibiotic susceptibility was tested by disk-agar diffusion. Conjugation experiments and plasmid analysis by agarose gel electrophoresis after Eco RI digestion were followed by hybridization to a digoxigenin-labeled TEM-type β-lactamase probe. DNA fingerprints were obtained by pulsed-field gel electrophoresis of Xba I-digested chromosomal DNA.
Results: Three S. typhi isolates (7% of the isolates studied), of which one was ampicillin resistant and the other two multiresistant (ampicillin, chloramphenicol, tetracycline, sulfamethoxazole/trimethoprim and streptomycin), and two ampicillin-resistant S. paratyphi B isolates (25% of the isolates studied) were further evaluated. A 34-MDa conjugative plasmid, previously isolated from Salmonella enteritidis , conferred ampicillin resistance. A 100-MDa conjugative plasmid encoded resistance to chloramphenicol, tetracycline and sulfamethoxazole/trimethoprim, as well as ampicillin. Chromosomal fingerprinting revealed two distinct resistant strains for each serovar which were different from a matched set of sensitive S. typhi strains.
Conclusions: Two conjugative, TEM-type β-lactamase-encoding plasmids conferred ampicillin resistance to S. typhi and S. paratyphi B. The 34-MDa plasmid was identical to that previously characterized from S. enteritidis , while the 100-MDa plasmid also encoded resistance to chloramphenicol, tetracycline and sulfamethoxazole/trimethoprim. Resistant isolates did not belong to a single clone but rather represented distinct strains.     

Multidrug resistance in Salmonella enterica serotype Typhimurium from humans in France (1993 to 2003)

The aim of this study was to determine the distribution of the antimicrobial resistance phenotypes (R types), the phage types and XbaI-pulsed-field gel electrophoresis (PFGE) types, the genes coding for resistance to beta-lactams and to quinolones, and the class 1 integrons among a representative sample of Salmonella enterica serotype Typhimurium isolates collected from humans in 2002 through the French National Reference Center for Salmonella (NRC-Salm) network. The trends in the evolution of antimicrobial resistance of serotype Typhimurium were reviewed by using NRC-Salm data from 1993, 1997, 2000, and 2003. In 2002, 3,998 isolates of serotype Typhimurium were registered at the NRC-Salm among 11,775 serotyped S. enterica isolates (34%). The most common multiple antibiotic resistance pattern was resistance to amoxicillin, chloramphenicol, streptomycin and spectinomycin, sulfonamides, and tetracycline (ACSSpSuTe R type), with 156 isolates (48.8%). One isolate resistant to extended-spectrum cephalosporins due to the production of TEM-52 extended-spectrum beta-lactamase was detected (0.3%), and one multidrug-resistant isolate was highly resistant to ciprofloxacin (MIC > 32 mg/liter). We found that 57.2% of the isolates tested belonged to the DT104 clone. The main resistance pattern of DT104 isolates was R type ACSSpSuTe (83.2%). However, evolutionary changes have occurred within DT104, involving both loss (variants of Salmonella genomic island 1) and acquisition of genes for drug resistance to trimethoprim or to quinolones. PFGE profile X1 was the most prevalent (74.5%) among DT104 isolates, indicating the need to use a more discriminatory subtyping method for such isolates. Global data from the NRC-Salm suggested that DT104 was the main cause of multidrug resistance in serotype Typhimurium from humans from at least 1997 to 2003, with a roughly stable prevalence during this period.     

Genetic control of resistance to Salmonella typhimurium infection in high and low antibody responder mice.

Mice selected by Biozzi for high and low responses to sheep erythrocytes were investigated for resistance to subcutaneous Salmonella typhimurium infection. The resistance was measured by LD50 values, viable bacterial counts in liver and spleen at 10 days, and the kinetics of infection over 4 weeks. High responder mice were susceptible to S. typhimurium injected subcutaneously (LD50 less than 10) and low line resistant (LD50 3 x 10(6)). Control of natural resistance to S. typhimurium in inbred mice is primarily by a single gene. Ity, on chromosome 1. Results with hybrid generations of Biozzi mice with either BALB/c (sensitive) or CBA (resistant) inbred mice indicated additional genetic control of resistance in Biozzi mice. Analysis of resistance data of backcrosses of (high x low)F1 with either parental strain showed this genetic control to be at least one other gene in the Biozzi mice, not linked to Ity. The antibody responses in the hybrid generations and inbred and Biozzi parental strains were tested by haemagglutination assays and ELISA. After specific stimulation of the mice there was an inverse relationship between resistance to S. typhimurium and antibody levels.     

Characterization of Salmonella enterica serotype newport isolated from humans and food animals

Salmonella enterica serotype Newport isolates resistant to at least nine antimicrobials (including extended-spectrum cephalosporins), known as serotype Newport MDR-AmpC isolates, have been rapidly emerging as pathogens in both animals and humans throughout the United States. Resistance to extended-spectrum cephalosporins is associated with clinical failures, including death, in patients with systemic infections. In this study, 87 Salmonella serotype Newport strains were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing and examined for the presence of class 1 integrons and bla(CMY) genes. Thirty-five PFGE patterns were observed with XbaI, and three of these patterns were indistinguishable among isolates from humans and animals. Fifty-three (60%) Salmonella serotype Newport isolates were identified as serotype Newport MDR-AmpC, including 16 (53%) of 30 human isolates, 27 (93%) of 29 cattle isolates, 7 (70%) of 10 swine isolates, and 3 (30%) of 10 chicken isolates. However, 28 (32%) Salmonella serotype Newport isolates were susceptible to all 16 antimicrobials tested. The bla(CMY) gene was present in all serotype Newport MDR-AmpC isolates. Furthermore, the plasmid-mediated bla(CMY) gene was transferable via conjugation to an Escherichia coli strain. The transconjugant showed the MDR-AmpC resistance profile. Thirty-five (40%) of the isolates possessed class 1 integrons. Sequence analyses of the integrons showed that they contained aadA, which confers resistance to streptomycin, or aadA and dhfr, which confer resistance to trimethoprim-sulfamethoxazole. One integron from a swine isolate contained the sat-1 gene, which encodes resistance to streptothricin, an antimicrobial agent that has never been approved for use in the United States. In conclusion, Salmonella serotype Newport MDR-AmpC was commonly identified among Salmonella serotype Newport isolates recovered from humans and food animals. These findings support the possibility of transmission of this organism to humans through the food chain.     

Antimicrobial resistance of Salmonella serotypes isolated from slaughter-age pigs and environmental samples

The aim of this study was to determine the antimicrobial resistance patterns of Salmonella strains isolated from slaughter-age pigs and environmental samples collected at modern swine raising facilities in Brazil. Seventeen isolates of six serotypes of Salmonella enterica subsp. enterica were isolated out of 1,026 collected samples: Salmonella Typhimurium (1), Salmonella Agona (5), Salmonella Sandiego (5), Salmonella Rissen (1), Salmonella Senftenberg (4), and Salmonella Javiana (1). Resistance patterns were determined to extended-spectrum penicillin (ampicillin), broad-spectrum cephalosporins (cefotaxime and ceftriaxone), aminoglycosides (streptomycin, neomycin, gentamicin, amikacin, and tobramycin), narrow-spectrum quinolone (nalidixic acid), broad-spectrum quinolone (ciprofloxacin and norfloxacin), tetracycline, trimethoprim, and chloramphenicol. Antimicrobial resistance patterns varied among serotypes, but isolates from a single serotype consistently showed the same resistance profile. All isolates were resistant to tetracycline, streptomycin, and nalidixic acid. One isolate, Salmonella Rissen, was also resistant to cefotaxime and tobramycin. All serotypes were susceptible to ceftriaxone, norfloxacin, ciprofloxacin, ampicillin, gentamicin, and chloramphenicol. The high resistance to tetracycline and streptomycin may be linked to their common use as therapeutic drugs on the tested farms. No relation was seen between nalidixic acid and fluoroquinolone resistance.     

Salmonella types and antibiotic susceptibility: a six months survey

A total of 51 Salmonella strains were isolated during the six month period of May 1998 till October 1998. Of these, 41 (80.3%) were Salmonella typhi, 5 (9.8%) Salmonella pararyphi A,2 (3.9%) Salmonella worthington and 1 (1.9%) Salmonella senftenberg. The prevalent phage and biotype of Salmonella typhi was E1 (75%) and type 1 (90.2%) respectively. The commonest pattern of multiple drug resistance in Salmonella typhi was ACCoT and 92.5% of these belonged to phage E1. Out of the five Salmonella paratyphi A, one belonged to phage type 1 and the others were untypable. Similarly both the strains of Salmonella typhimurium were untypable. Thus the predominant isolate was Salmonella typhi and the commonest phage and biotype were E1 and biotype1 respectively.     

Antimicrobial resistance of Salmonella enterica serovar Heidelberg isolated from poultry in Alberta

Salmonella enterica serovar Heidelberg is one of the top three serovars implicated in human infections in Canada. In 2003, the Canadian Integrated Program for Antimicrobial Resistance Surveillance reported antimicrobial resistance (AMR) in S. Heidelberg in Canada. The study objective was to investigate the AMR of S. Heidelberg isolated from poultry in Alberta. We examined 951 S. Heidelberg poultry isolates obtained during 1996 to 2010 and tested against 18 antibiotics using the Sensititre AVIAN1F system. Temporal resistance patterns were analysed using single-level logistic regression models. Continuous variables were included in the multivariable models. Multivariable models were built and variables and interactions were included in these final models. Data were analysed using Stata 11 Intercooled. Ceftiofur resistance ranged annually from 0 to 10.5% and gentamicin resistance ranged annually from 0 to 33.3%; no isolates were enrofloxacin resistant. Resistance to amoxicillin (annual range 0 to 42.6%) varied significantly by time and interaction with commodity type. Meat turkey S. Heidelberg isolates had higher ceftiofur resistance compared with chickens: layers plus layer breeders (odds ratio = 22.6, P < 0.01) and broiler breeders (odds ratio = 9.1, P < 0.01). Gentamicin resistance decreased significantly over the study period (odds ratio = 0.72 per year, P < 0.01). Tetracycline (TET) resistance changed significantly over time (annual range 0 to 39.6%), interacting with poultry commodity type. Meat turkey isolate TET resistance, higher overall than that of chicken, increased throughout the study. All turkey breeder isolates were resistant to TET. In conclusion, this study provides AMR data for S. Heidelberg isolates from the Alberta poultry industry and demonstrated significant trends in resistance, both temporal and between poultry commodities.     

Cell-Mediated Resistance Induced with Immunogenic Preparations of Salmonella typhimurium

Peritoneal cells obtained from mice immunized 15 or 30 days previously with (i) 0.1 LD(50) of attenuated Salmonella typhimurium (RIA), (ii) 20 mug (dry weight) of heat-killed Salmonella (SR-11), (iii) 20 mug (dry weight) of immunogenic ribosomal subfractions, or (iv) 20 mug of ribonucleic acid (RNA) subfractions were passively transferred to normal unimmunized mice. The ability of the recipient animals to inhibit or retard the multiplication of virulent challenge S. typhimurium 5 days post-infection was determined by pathogen counts on the carcasses. Peritoneal cells from donors immunized with the RIA, ribosomal, or RNA preparations (i) conferred maximal resistance to challenge 10 to 15 days after cell transfer and demonstrable resistance throughout the 45-day assay period, (ii) conferred resistance to infection when 10(5), 10(3), or 10(2) peritoneal cells were injected subcutaneously but not with fewer than 10(5) cells administered intraperitoneally, and (iii) rendered recipients capable of acting as donors of peritoneal cells that conferred demonstrable resistance on normal recipients. Recipients of peritoneal cells obtained from donors immunized with heat-killed bacteria were unable to (i) significantly inhibit bacterial proliferation at 10 days post-transfer, (ii) resist infection by a challenge inoculum greater than 50 LD(50), and (iii) secondarily confer resistance on normal animals through the passive transfer of cells or serum.     

Characterization of antimicrobial resistance of recent Salmonella enterica serovar Gallinarum isolates from chickens in South Korea

Salmonella enterica serovar Gallinarum isolates (n=105) from chickens in South Korea between 2002 and 2007 were tested for antimicrobial susceptibility by determining minimum inhibitory concentrations of 16 antimicrobials, and their predominant resistance profiles were genetically characterized. Most isolates (99/105; 94.3%) were resistant to nalidixic acid and resistant/intermediately resistant to fluoroquinolones, and 63.8% (67/105) of the isolates were resistant to three or more antimicrobials. Forty-two quinolone-resistant isolates, of which the quinolone resistance-determining regions of the gyrA genes were sequenced, contained a substitution of a Ser to a Phe or Tyr at position 83 (71.4%), or a substitution of an Asp to an Asn, Gly, or Tyr at position 87 (28.6%). Fifty-seven sulphamethoxazole-resistant isolates were tested for the presence of class 1 integrons by polymerase chain reaction, and their resistance gene cassettes were analysed by sequencing. Three different class 1 integrons containing the resistance-gene insert aadA (52.6%; n=30), aadB (12.3%; n=7), or aadB-aadA (12.3%; n=7) were identified. Most isolates harbouring the integron containing aadB-aadA displayed resistance to all three aminoglycosides tested and also showed increased resistance to fluoroquinolones. These findings suggest that fluoroquinolone resistance may be epidemiologically linked to multiple aminoglycoside resistance.     

Salmonella bloodstream infection in Ghanaian children

Objective: To examine the frequency of community-acquired salmonella bloodstream infection in Ghanaian children and the occurrence of antibiotic resistance in salmonellae.
Methods: The study comprised 472 patients with a blood culture obtained within 48 h of admission to the pediatric department of Korle Bu Teaching Hospital in Accra, Ghana, over a 3-month period. All Salmonella isolates from blood cultures were speciated and antibiotic susceptibility tests were performed. Clinical data of children with salmonella bloodstream infection were compared to those of controls. Two control groups were identified: all children enrolled in the study without salmonella bloodstream infection (group 1), and those with bloodstream infection due to other organisms (group 2).
Results: A pathogen was isolated from 111 children (23.5%), and salmonellae were among the most common isolates ( n =24; 21.6%). Among Salmonella strains, S. enteritidis ( n =14;59%) predominated over S. typhi ( n =6;25%). Resistance to several antibiotics was only found in S. enteritidis isolates ( n =8;57%). Children with salmonella bloodstream infection presented more often than controls with severe anemia, jaundice, abdominal pain and distension as well as hepatomegaly and splenomegaly. They were also hospitalized for a significantly longer period, but the case-fatality rate was similar.
Conclusions: Salmonella bloodstream infection, especially due to non-typhoidal strains, is a potential health problem for Ghanaian children and may be complicated by resistance to the commonly available antibiotics.     

High level ciprofloxacin resistance in Salmonella enterica isolated from blood

PURPOSE: Over the last few years, resistance to ciprofloxacin in Salmonella enterica has become a global concern. The present study was undertaken to find out the susceptibility pattern of Salmonella enterica isolates in our hospital. METHODS: Blood cultures were done using BacT/ALERT 3D system. The antimicrobial susceptibility testing was carried out by the Kirby-Bauer disc diffusion method using CLSI breakpoints. Minimum inhibitory concentration was determined for ciprofloxacin-resistant strains using E-test and Vitek-1 automated system. RESULTS: A total of 25,953 samples of blood culture yielded 431 Salmonella enterica serotype Typhi and 198 serotype Paratyphi A isolates. Twenty-two isolates of serotype Typhi were resistant to ciprofloxacin, while two isolates of Typhi and two Paratyphi A were intermediately susceptible to ciprofloxacin. Ciprofloxacin resistance is 5.6% (24 isolates) among Salmonella enterica serotype Typhi. Ampicillin, chloramphenicol and co-trimoxazole resistance in Salmonella enterica serotype Typhi appears to have decreased to 14.9% (64/431) in comparison to the 27% (55/205) during 2003. All isolates were sensitive to ceftriaxone. CONCLUSIONS: Ciprofloxacin can no longer be considered as the drug of choice in treating Salmonella infections. While first-line antimicrobials may still have a role to play in the treatment of enteric fever, ceftriaxone remains the sole defence against ciprofloxacin-resistant Salmonella infections.     

Intraperitoneal infection with Salmonella abortusovis is partially controlled by a gene closely linked with the Ity gene.

The aim of the present study was to determine whether the Ity gene, which controls the resistance to S. typhimurium infection in mice, also governs the resistance to S. abortusovis, a serotype specific for goat and sheep. During either i.v. or i.p. infection, BALB/c mice (Itys) were not able to control the growth of S. abortusovis and eventually died from infection. In contrast CBA (Ityr) or (C.CB)F1 (Ityr/s) mice were able to control the growth of these bacteria. Using congenic C.D2 Ityr mice, we found that the gene controlling resistance to S. abortusovis was tightly linked to the Ity gene on chromosome 1. Furthermore, in the spleen and the liver of backcross BALB/c x (CBA x BALB/c) mice, the S. abortusovis resistance phenotype cosegregated with the two alleles of the Len-1 gene, a gene tightly linked to the Ity gene. By contrast, in these backcross mice, the level of infection of the peritoneal cavity, the site of inoculation, did not correlated with the Len-1 phenotype of the animal. These results provide evidence that after i.p. inoculation the control of S. abortusovis growth in the spleen and the liver is controlled by the Ity gene, but also suggest that additional gene(s) regulate the number of bacteria at the site of inoculation.     

Diagnostic accuracy of class 1 integron PCR method in detection of antibiotic resistance in Salmonella isolates from swine production systems

The diagnostic accuracy of an integron PCR method (Int-PCR) for detecting class 1 integrons (1,000, 1,200, and 1,600 bp) in the identification of antibiotic-resistant Salmonella strains was evaluated using 730 Salmonella isolates from pen floor samples collected from four swine production systems in Illinois. Three integron groupings were detected: 1,000 bp only, 1,600 bp only, and both 1,000 and 1,200 bp. The presence of any of the three class 1 integron groupings was associated with four-drug resistance (streptomycin, spectinomycin, sulfisoxazole, and tetracycline [St Spc Su Tet]). In addition, the presence of both the 1,000- and 1,200-bp integrons added resistance to ampicillin (Amp) and chloramphenicol (Cm), and the 1,600-bp integron added resistance to gentamicin (Gen) and kanamycin (Kan). DNA sequencing of integrons confirmed the presence of the aminoglycoside adenyl transferase (aadA) gene, conferring St Spc resistance in the 1,000-bp integron; the beta-lactamase gene, conferring Amp resistance in the 1,200-bp integron; and the aadA and aadB genes, conferring St Spc Gen Kan resistance in the 1,600-bp integron. The 1,600-bp integron appears to have the 1,000-bp intergron as its core, with additional genetic material conferring additional antibiotic resistance. The diagnostic accuracy of Int-PCR in detecting resistance to individual antibiotics was limited by the presence of phenotypic resistance in isolates without integrons. However, Int-PCR had high diagnostic accuracy (sensitivity and specificity) in detecting multidrug resistance: 0.98 and 0.92, respectively, for St Spc Su Tet; 0.95 and 1.0 for Amp Cm St Spc Su Tet; and 1.0 and 0.99 for Gen Kan St Spc Su Tet. Thus, Int-PCR can be valuable in epidemiological surveys as a screening tool for the detection of multidrug-resistant Salmonella strains.     

Association between cyclohexane resistance in Salmonella of different serovars and increased resistance to multiple antibiotics, disinfectants and dyes

A panel of 388 salmonellas of animal and human origin, comprising 35 serotypes, was tested for resistance to cyclohexane and to a range of antibiotics, disinfectants and dyes. Cyclohexane resistance was detected in 41 isolates (10.6%): these comprised members of the serovars Binza (1 of 15), Dublin (1 of 24), Enteritidis (1 of 61), Fischerkietz (4 of 5), Livingstone (9 of 11), Montevideo (1 of 32), Newport (4 of 23), Saint-paul (1 of 3), Senftenberg (10 of 24) and Typhimurium (9 of 93). Most (39 of 41) of the cyclohexane-resistant isolates were from poultry. Statistical analysis showed that the cyclohexane-resistant strains were significantly more resistant than the cyclohexane-susceptible strains to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, nalidixic acid, tetracycline, trimethoprim, cetrimide and triclosan. The multiresistance patterns seen were typical of those caused by efflux pumps, such as AcrAB. The emergence of such resistance may play an important role in the overall antibiotic resistance picture of Salmonella, with particular effect on ciprofloxacin.