Resistance of Salmonellae Isolated in 1962 to Chlortetracycline

Among 652 salmonellae examined, Salmonella typhimurium displayed a much higher incidence of resistance to chlortetracycline than did other serotypes. Among S. typhimurium cultures from man, the incidence of resistance (38%) increased markedly over that of cultures isolated 3 years previously (13.9%), whereas a similar increase was not noted among cultures from fowls. Resistance among cultures from animals other than fowls (72.5%) was due largely to the high incidence of resistance among cultures from bovine sources (93.7%).     

Thermal Resistance of Salmonellae Isolated from Dry Milk

Salmonella anatum, S. binza, S. cubana, S. meleagridis, S. newbrunswick, and S. tennessee isolated from dry milk, and S. senftenberg 775W were studied for heat resistance to determine whether these organisms would survive pasteurization as recommended by the 1965 Pasteurized Milk Ordinance of the U.S. Public Health Service. Thermal inactivation determinations were made on washed cells of the test microorganisms suspended in sterile whole milk. Excluding S. senftenberg, D values ranged from 3.6 to 5.7 sec at 62.8 C, from 1.1 to 1.8 sec at 65.6 C, and from 0.28 to 0.52 sec at 68.3 C. Corresponding values for S. senftenberg were 34.0, 10.0, 1.2, and 0.55 sec for respective exposure temperatures of 65.5, 68.3, 71.7, and 73.9 C. The present milk pasteurization processes as recommended by the Public Health Service will inactivate all seven strains of salmonellae studied, provided that the initial concentration does not exceed a calculated 3 × 10¹² salmonellae per ml of milk.     

Thermal Resistance of Salmonellae and Staphylococci in Foods

The heat-resistant Salmonella senftenberg 775W and two strains of Staphylococcus aureus were tested at temperatures up to 68.3 C (71.1 C for S. senftenberg) in four different media. From the survival data, decimal reduction times (D values) were calculated for each set of conditions, and decimal reduction time curves were constructed for each bacterial strain in each medium. Slopes of decimal reduction time curves (Z(D)) ranged from 4.52 to 6.38 C with a single exception. There was no statistical heterogeneity among the remaining values. Results were in close agreement with published results of similar studies conducted at somewhat lower temperatures and support the practice of using a slope value (Z(D)) of 5.56 C for establishing time-temperature relationships for food processing. It is recommended that such a decimal reduction time curve not be extrapolated to temperatures more than 5.56 C higher than those actually tested.     

Heat Resistance of Salmonellae in Concentrated Milk

The heat resistance of Escherichia coli, Salmonella typhimurium, and Salmonella alachua in milk solutions containing 10, 30, 42, and 51% (w/w) skim milk for total solids was determined. Increased milk-solids level effected a significant increase in the heat resistance of each organism. Although E. coli was more heat-resistant than both strains of Salmonella in 10% milk, the situation was reversed in 42 and 51% milk. Prior growth temperature was found to exert a profound effect on the heat resistance of S. typhimurium. Growth of S. typhimurium in 42% milk solids for 24 hr did not greatly enhance the thermal resistance of the organism when heated in a fresh 42% solids concentrate. Application of a partial vaccum during heating greatly diminished the decimal reduction times of S. typhimurium and E. coli and, in addition, virtually eliminated the protective effect of increased solids level.     

Co-Transduction of Plasmids Mediating Resistance to Tetracycline and Chloramphenicol in Staphylococcus aureus

Independent plasmids mediating resistance either to tetracycline (Tc) or chloramphenicol (Cm) were transduced successively into Staphylococcus aureus strain 8325. From this doubly resistant donor strain, Tc was co-transduced with a frequency of 40 to 50% when Cm was selected. Co-transduction of Cm was 5 to 10% with Tc selection. Plasmid elimination was infrequent and restricted to the Cm plasmid. A variant, doubly resistant strain gave 100% co-transduction of Tc and Cm and a high rate of joint elimination of both plasmid markers. Co-transduction of the plasmids from recombination-deficient donor strains was much reduced if the plasmids had been introduced separately into the donor strain, but occurred at the normal high rate if they had been introduced jointly. The plasmids were co-transformed at relatively low rates with closed circular deoxyribonucleic acid (DNA) from doubly resistant donors, but not with DNA from a mixed lysate of singly resistant strains. Our evidence favored a hypothesis of recombination-dependent, reversible linkage between the two plasmids as the basis for their co-transduction. Examination of plasmid DNA from the doubly resistant strains by ultracentrifugal and electron microscopic methods did not disclose any physical differences between singly and doubly resistant strains that might account for the observed co-transduction.     

Mechanism of Chloramphenicol Resistance in Staphylococcus epidermidis

The mechanism of chloramphenicol resistance in several multiple-resistant Staphylococcus epidermidis strains has been studied and shown to be due to the presence of the enzyme, chloramphenicol acetyltransferase. As with S. aureus, the inactivating enzyme in S. epidermidis appears to be the product of a structural gene on the chloramphenicol plasmid because resistance and enzyme activity are concurcurrently lost after growth in acridine orange or at elevated temperatures. The synthesis of chloramphenicol acetyltransferase in S. epidermidis has been compared with the function of a similar enzyme in chloramphenicol-resistant S. aureus with the conclusion that the kinetics of induction, products of the reaction, and general properties of the enzymes are identical. The chloramphenicol acetylating enzyme from S. epidermidis has been purified to a state of homogeneity and compared with the analogous purified S. aureus enzyme. Both purified preparations consist of native enzymes with molecular weights of 80,000, and evidence is presented that is consistent with their being made up of four identical subunits of 20,000 each. The two staphylococcal enzymes are identical with respect to pH optimum, apparent affinity (K_m) for chloramphenicol, heat denaturation, and immunological reactivity, but they differ in electrophoretic mobility, chromatographic behavior, substrate specificity, and sensitivity to inhibition by mercuric ion.     

Cytoplasmic Inheritance of Chloramphenicol Resistance in Tetrahymena

Chloramphenicol-resistant mutants of Tetrahymena pyriformis were obtained after mutagenesis with nitrosoguanidine at an estimated frequency of 10(-3) mutants per mutagenized cell. The mutants are still partially sensitive to chloramphenicol and have a lowered growth rate, compared to the wild type strain, in rich medium without chloramphenicol. The genetic analysis described here indicates that chloramphenicol resistance is inherited as a cytoplasmic determinant that is not exchanged during conjugation. This represents the first simple cytoplasmic genetic determinant described in this species. A number of arguments favor a mitochondrial localization for this genetic determinant. In addition to the possible utility of such mutants for studies of mitochondrial structure and function in Tetrahymena, analogous mutations might serve as cytoplasmic "tags" in other ciliate species where the results of selfing need to be distinguished from those of outcrossing.     

Relationship of the Frequency of Isolation of Salmonellae to Their Resistance to Drying and Freezing

The resistance of different Salmonella serotypes to drying and freezing has been shown to be related to their incidence in salmonellosis.     

Annual Report Of The Edward Grey Institute (May 1959 to April 1960)

First-year Cuckoos commence emigration at a lower body-weight than adults. The author suggests that foisting their offspring on other species may allow the adult Cuckoos to specialise on certain foods (viz hairy lepidopterous larvae), enabling themselves to depart early on migration.     

Tetracyclines and Tetracycline Resistance in Agricultural Soils: Microcosm and Field Studies

The influence of the use of antibiotics on the prevalence of resistance genes in the environment is still poorly understood. We studied the diversity of tetracycline and sulfonamide resistance genes as influenced by fertilization with pig manure in soil microcosms and at two field locations. Manure contained a high diversity of resistance genes, regardless of whether it stemmed from a farm operation with low or regular use of antibiotics. In the microcosm soils, the influence of fertilization with manure was clearly shown by an increase in the number of resistance genes in the soil after manuring. Spiking of the tetracycline compounds to the microcosms had only little additional impact on the diversity of resistance genes. Overall, the tetracycline resistance genes tet(T), tet(W), and tet(Z) were ubiquitous in soil and pig slurries, whereas tet(Y), tet(S), tet(C), tet(Q), and tet(H) were introduced to the microcosm soil by manuring. The diversity of tetracycline and sulfonamide [sul(1), sul(2), and sul(3)] resistance genes on a Swiss pasture was very high even before slurry amendment, although manure from intensive farming had not been applied in the previous years. The additional effect of manuring was small, with the tetracycline and sulfonamide resistance diversity staying at high levels for the complete growth season. At an agricultural field site in Germany, the diversity of tetracycline and sulfonamide resistance genes was considerably lower, possibly reflecting regional differences in gene diversity. This study shows that there is a considerable pool of resistance genes in soils. Although it is not possible to conclude whether this diversity is caused by the global spread of resistance genes after 50 years of tetracycline use or is due to the natural background in soil resistance genes, it highlights a role that environmental reservoirs might play in resistance gene capture.     

Drug Resistance of Staphylococci VI. Genetic Determinant for Chloramphenicol Resistance

Naturally occurring strains of staphylococci which are resistant to chloramphenicol (CM) inactivate this antibiotic. One of the inactivation products of CM showed the chromatographic behavior of 3-acetoxychloramphenicol. Induction of resistance occurred after prior exposure to subinhibitory concentrations of the antibiotic. The resistance of induced populations, as well as CM-inactivation ability, was decreased when they were grown in CM-free medium. The CM-inactivation property was transduced together with CM resistance. Transductional analysis and CM-resistance elimination experiments indicated that CM resistance in naturally occurring strains of staphylococci is mainly accounted for by inactivation of the drug.     

Relation of the Heat Resistance of Salmonellae to the Water Activity of the Environment

The effect of water activity (a_w) on the heat resistance of eight strains of Salmonella was studied. Heat resistance of the organisms increased as the a_w of the heating menstruum was reduced. Sucrose afforded the cells a greater degree of protection than did fructose, glycerol, and sorbitol. A direct correlation between a_w and heat resistance could not be established over the range of a_w levels tested in this study. There was variation among the strains of salmonellae in the magnitude of the increase in heat resistance as the a_w level was reduced. All strains of Salmonella tested showed a greater increase in heat resistance than S. senftenberg 775W as the environment became drier. Washed cells had D values 25 to 75% lower than unwashed cells. Prior growth of the organisms in media with a reduced a_w increased the heat resistance of the organisms when glycerol, but not when sucrose, was the controlling substance.     

Effect of Resistance to Chloramphenicol on Bacteriophage Sensitivity of Group A Streptococci

Several phage hosts of group A streptococci became resistant to lysis by bacteriophage as a consequence of having acquired the ability to grow in the presence of chloramphenicol. The phage was adsorbed to the streptococcal cell, and P(32)-labeling of the phage showed that the phage genome penetrated the chloramphenicol (CM)- resistant cells as it did the parent cells. However, artificial lysis of the infected CM-resistant cells with chloroform or enzymes revealed no intracellular mature phage particles. Lysates of infected CM-resistant cells contained no phage-related antigenic materials which possessed serum-blocking power, although they were readily detected in lysates of infected parent cells. The CM-resistant cells were not lysogenized by the phage. Only cells resistant to more than 10 mug/ml of chloramphenicol were resistant to phage, and this threshold effect was taken as an indication of at least two different loci of chloramphenicol resistance on the streptococcal genome. Strains resistant to high levels of other antibiotics, such as streptomycin and erythromycin, showed no resistance to lysis by phage. Evidence indicated that the mutant cells were deficient in an essential function associated with the phage genome.     

Serological Relationships of Salmonella A Bacteriophages Isolated from Salmonellae in Different Kauffmann- White Groups

Six different Salmonella group A phages from salmonellae in Kauffmann- White groups B, C(1), C(2), and D were examined serologically. Those phages which were specific for a particular somatic antigen were found to be serologically very similar. Antiserum against a phage with one specificity was able to neutralize a different phage with the same specificity but unable to neutralize, in the normal way, a phage with a different specificity. Phages mixed with heterologous phage antiserum responded with an "inhibition response" in which there appeared to be a neutralization of the phage infectivity for the first 10 min, followed by a reversal of the neutralization until, by 20 or 25 min, there was no apparent neutralization. This response was interpreted to indicate that the adsorption antigens, probably situated on the tail fibers, were different for phages with different specificities but sufficiently similar so that heterologous antibodies could react with the antigens; but the antigen-antibody complex was quickly disassociated, resulting in a modification of the antibody molecules but no change in the specificity sites of the antigen. A subgrouping of the Salmonella A phages based on their antigenic specificity is suggested.     

The Effect of Sugars and Polyols on the Heat Resistance of Salmonellae

S ummary . The heat resistance at 65° of 3 strains of salmonellae in solutions of sugars or polyols was enhanced as the concentration of the solutes increased. There was no linear relationship between heat resistance and water activity ( a_w ), but for all solutes except glycerol there was a linear relationship between log D ₆₅ and concentration (% w/w) of solute. Comparison of D ₆₅ at a particular a_w or percentage (w/w) solute concentration showed that the value decreased in the order: sucrose > glucose > sorbitol > fructose > glycerol. In glycerol, D ₆₅ values were always very much lower than in any other solute. With sucrose–glycerol or sucrose–glucose mixtures, heat resistance depended both on the total concentration (% w/w) of solutes present and also on the a_w of the solution.     

Geographical and Temporal Dissemination of Salmonellae Isolated from Domestic Animal Hosts in the Culiacan Valley,Mexico

The prevalence and diversity of salmonellae from domestic animal hosts were investigated in the Culiacan Valley, Mexico. A total of 240 farm animal feces (cows, chicken, and sheep) were evaluated for Salmonella spp. presence from July 2008 to June 2009. Salmonella enterica subsp. enterica strains were isolated from 76 samples (31.7%), and 20 serotypes were identified being Salmonella Oranienburg (25%), Salmonella Give (14%), Salmonella Saintpaul (12%), and Salmonella Minnesota (11%) the most frequent isolates. Twenty-four percent (18/76) of the isolates were resistant to ampicillin. Salmonella Oranienburg, Salmonella Minnesota, Salmonella Give, Salmonella Agona, Salmonella Weltevreden, and Salmonella Newport serotypes showed multiple pulsed-field electrophoresis patterns. Salmonella Oranienburg was the dominant serotype in the Culiacan Valley; however, no specific distribution patterns were detected in animal sources or sampling sites. The genetic diversity of salmonellae could be an evidence of the continuous animal exposition to the bacteria. Also, Salmonella adaptation in asymptomatic animals could be justified by the development of natural host immunity. This study provides novel information about Salmonella population distribution in domestic animals living at tropical areas. The presence of asymptomatic carriers may be critical to understand the routes of transmission of Salmonella in areas of high disease prevalence.     

Resistance to Antimicrobial Agents in Lactobacilli Isolated from Caper Fermentations

A collection of lactobacilli comprising species of Lactobacillus plantarum (43 isolates), Lactobacillus brevis (9 isolates) and Lactobacillus fermentum (6 isolates) obtained from spontaneous fermentations of capers (the fruits of Capparis spinosa) were investigated for resistance to antimicrobial agents. All isolates were resistant to vancomycin and teicoplanin (MIC > 16 μg/ml). Resistance to ciprofloxacin (MIC > 2 μg/ml) was detected in all isolates of L. brevis and L. fermentum as well as in most isolates of L. plantarum, whilst resistance to levofloxacin showed a much lower incidence. Among L. plantarum and L. brevis isolates, low levels of resistance to tetracycline and/or nitrofurantoin were detected. Higher resistance levels were also detected in some isolates. Resistance to penicillin and rifampicin were also detected among L. plantarum isolates. All isolates were sensitive to ampicillin, erythromycin, chloramphenicol, gentamicin, streptomycin, and quinupristin/dalfopristin.