Antimicrobial resistance and R factors in Salmonella isolated in California (1971-1972)

Antimicrobial Resistance in Salmonella in the United States from 1948 to 1995

We conducted a retrospective study of 2,149 clinicalSalmonellastrains to help document the historical emergence of antimicrobial resistance. There were significant increases in resistance to older drugs, including ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline, which were most common inSalmonella entericaserotype Typhimurium. An increase in multidrug resistance was observed for each decade since the 1950s. These data help show howSalmonellaevolved over the past 6 decades, after the introduction of new antimicrobial agents.

Incidence of plasmids in multiply-resistant Salmonella isolates from diarrhoeal patients in Hong Kong from 1973-82

Plasmids present in multiply-resistant salmonella strains including Salmonella typhimurium, S. johannesburg, S. wandsworth, S. derby, S. newport, S. london and S. choleraesuis causing diarrhoea in patients in Queen Mary Hospital in Hong Kong from 1973-82 were studied. In multiply-resistant S. typhimurium, plasmids belonging to groups FIme, H1 or H2 and plasmids encoding trimethoprim-resistance which were compatible with standard plasmids of testable incompatibility groups were detected. In S. johannesburg, both the ASTCKSu- and ASCKSu-resistant strains which were predominant in two consecutive periods of an outbreak were found to harbour the same plasmid which belonged to the incompatibility group FIme. S. wandsworth strains isolated from a hospital outbreak in 1980 harboured an identical R-plasmid belonging to group N. A few strains of the other salmonellae showing resistance to multiple antibiotics were found to harbour R-plasmids belonging to groups H1, H2 and FIme. The only salmonella of the enteric fever group resistant to ampicillin, chloramphenicol and trimethoprim was an S. paratyphi B strain. The resistances were encoded on a plasmid of an unknown incompatibility group. The occurrence and distribution of plasmids in these salmonellae isolated within the 10-year period are discussed.

A case of recurrent salmonella septicaemia in an infant

A 6-month-old girl was admitted with a febrile illness. Salmonella eastbourne was isolated from the stool and blood cultures. Septicaemia was treated with antibiotics but recurred twice on cessation of therapy. The only focus of infection found was the gut itself. Septicaemia did not recur following loss of the pathogen from the gut.

Molecular epidemiology of antibiotic resistance in salmonella from animals and human beings in the United States

We collected serotyped isolates of salmonella from reference laboratories in the United States, tested their susceptibility to antibiotics, and extracted plasmids from isolates that were resistant to a different combination of antibiotics from each of three serotypes. Restriction-endonuclease digestion showed that within each of the three groups, plasmid molecules from animal and human isolates were often identical or nearly identical. One serotype-plasmid combination appeared to be endemic in cattle in 20 states and infected 26 persons in two states. The human cases, which were not recognizably related except for their common plasmids, appeared to be clustered in time but geographically dispersed, like cases in previous outbreaks spread by food products. These findings suggest that resistance plasmids may be extensively shared between animal and human bacteria, and that spread of multiresistant strains of salmonella among animals and human beings, as observed in Britain, may have been undetected in the United States for lack of comparable surveillance.

Antimicrobial resistance among Salmonella isolates from hospitals in Rome

The susceptibility to antimicrobial agents of 569 salmonella isolated collected in 1977-8 from patients in hospitals in Rome was tested. Fifty-nine per cent of all isolates were resistant to one or more antimicrobials. Resistance was most common to sulphathiazole, tetracycline, streptomycin, whereas colistin, gentamicin, tobramycin, trimethoprim-sulphamethoxazole and nalidixic acid were the most active in vitro. Multiple resistance was most frequently found in strains of Salmonella wien and S. typhimurium (94% and 38% respectively). A significant change in the resistance pattern of S. wien was observed between 1977 and 1978, with a significant increase of susceptibility to some antimicrobials in 1978. Twenty-one R-plasmids transmissible to E. coli K12 were derived from 46 resistant strains of S. typhimurum.

Cefamandole treatment of Salmonella bacteremia

The efficacy of cefamandole in the treatment of 19 patients with salmonella bacteremia was evaluated. Although all of the salmonella strains isolated were highly susceptible to cefamandole in vitro, a therapeutic failure was observed in 7 (36.8%) of the 19 patients.

Antibiotic resistance and R-plasmids in food chain Salmonella: evidence of plasmid relatedness

A large number of strains (1,783) belonging to 15 Salmonella serovars isolated, in Canada, from the three major links of the human food chain were screened for multiple antibiotic resistance and the presence of R-plasmids. Multiresistant strains occurred among animal feed, livestock, and human isolates at frequencies of 4, 22, and 14%, respectively. Conjugation analysis revealed that 58% of the isolates from feeds, 87% of those from livestock, and 89% of the human strains carried all or part of their resistance determinants extrachromosomally on R-plasmids. Conjugative plasmids representing nine different incompatibility groups were detected, with the Inc I alpha group being predominant. Within the limits of the parameters measured, certain of these plasmids show a degree of relatedness suggestive of a common ancestry.

Incidence of resistance to ampicillin, chloramphenicol, kanamycin and tetracycline among Salmonella species isolated in the Netherlands in 1972, 1973 and 1974

The resistance of Salmonellae to drugs has been studied in the Netherlands since 1958. In 1972, 1973, and 1974 respectively, 14241, 13086, and 22927 strains were tested for resistance to ampicillin, chloramphenicol, kanamycin and tetracycline. From 1973 all strains were also tested for resistance to trimethoprim. In the period covered, the yearly incidence of resistance to at least one of the above drugs ranged from 39.2% to 45.6% of all strains obtained from various sources (humans, animals, animal products, sewage, etc.). A new finding in the period 1972 to 1974 was that many multiply resistant strains emerged in S. typhimurium and in S. dublin isolated from calves and cattle. In 1974, 64.4% of all strains of S. typhimurium from these animals appeared to be resistant to ampicillin, tetracycline, chloramphenicol and kanamycin, and 25.5% of those of S. dublin were found to be resistant to chloramphenicol and tetracycline. Of all strains of Salmonellae examined in 1973 and 1974 respectively, 0.15% and 0.22% were resistant to trimethoprim, the main component of the twin-drug cotrimoxazol. Of the 142 strains of S. typhi isolated in 1972 to 1974 two were resistant to tetracycline only, and one was resistant to all four antibiotics. The others had a normal susceptibility pattern.

In vitro antibiotic susceptibility of salmonellae

In vitro antibiotic susceptibilities were determined for 101 strains of salmonellae. Resistance to chloramphenicol and ampicillin was low. Cefamandole was active against the majority of strains and deserves further evaluation.

Drug resistance and R plasmids in Salmonella typhi isolated in Korea

A total of 949 strains of Salmonella typhi isolated in Korea from 1968 to 1975 were tested for drug resistance and distribution of R plasmids. Resistance was mostly restricted to streptomycin (SM) and sulfisomidine (SA), singly or in combination, at a low degree. A small number of strains (1.5%) were resistant to four or more drugs: chloramphenicol (CM), tetracycline (TC), SM, SA, ampicillin (AP), and kanamycin (KM). No strain was resistant to nalidixic acid or to a 1:20 mixture of trimethoprim and sulfamethoxazole. Nor was there any strain singly resistant to CM, TC, AP, or KM. Transfer experiments of multiple-drug resistance to Escherichia coli ML1410 showed that all the strains resistant to four or more drugs carried R plasmids, whereas those weakly resistant to three or less drugs did not. The quadruply resistant strains carried one R plasmid determining CM, TC, SM, and SA resistance, and sextuply resistant ones carried two plasmids, one determining CM, TC, SM, and SA resistance and the other determining AP and KM resistance. One strain carrying a plasmid determining AP and KM resistance was also found. The transfer frequency of CM, TC, SM, and SA resistance was much higher than that of AP and KM resistance. The resistance of S. typhi was more efficiently transferred to E. coli at 25 degrees C than at 37 degrees C.

Microbial development of drug resistance: mechanisms and clinical significance

Bacteria have demonstrated a disconcerting ability to develop resistance to antimicrobial agents nearly as quickly as new compounds become available. During the past two decades the molecular bases of several types of resistance have been elucidated. Mechanisms of resistance include the transference of genetic material either through conjugation (involving direct contact between microorganisms), or indirectly through transduction (involving bacteriophages). In addition to this "infectious" drug resistance, genetic mutations which permit the utilization of new metabolic pathways, and the production of enzymes which can inactivate the antimicrobic have been described. One particularly complex problem has been the ability of many Enterobacteriaceae to develop resistance to multiple antimicrobials simultaneously. The possible effect of such an occurrence is illustrated by the recent epidemic of multiply resistant Salmonella typhi in Mexico. Because the typhoid bacilli shared an identical resistance pattern to an epidemic Shigella dysenteriae type 1 the in vivo interspecies transmission of resistance has been postulated. Understanding the various mechanisms of resistance development should allow more rational use of antimicrobial agents.

Salmonella typhimurium resistant to silver nitrate, chloramphenicol, and ampicillin

A strain of Salmonella typhimurium appeared sequentially in three patients in a burn unit, and epidemiological study suggested the occurrence of person-to-person spread. This organism was responsible for both colonisation and invasive infection in these patients whose burn surfaces were receiving topical treatment with 0.5% silver nitrate (AgNO3) solution. The antibiotic and metal ionsusceptibility pattern of this strain of S. typhimurium was unique and disturbing: resistant to silver nitrate, mercuric chloride, ampicillin, chloramphenicol, tetracycline, streptomycin, and sulphonamides. This pattern of multiple resistances could be transferred by invitro mating experiments to sensitive recipient strains of Escherichia coli and S. typhimurium. Further transfer of these resistances could be consumated between different strains of E. coli. A survey of other salmonella strains isolated from patients in this hospital without thermal burns did not reveal this pattern of resistance. Also, strains of S. typhimurium, isolated elsewhere and showing simultaneous resistance to both ampicillin and chloramphenicol, were not resistant to AgNO3 in vitro. The very real danger of this strain of S. typhimurium in burn units stems from its resistance to the two most effective antibiotics (ampicillin and chloramphenicol) available for systemic therapy; and this threat may be compounded through the selection effected by the widespread topical use of AgNO3 solutions and sulphonamide preparations on burned surfaces.