Susceptibility of Streptococcus Suis to Penicillin

Abstract

Infections caused by Streptococcus suis are widespread in most countries where the swine industry is important. 3,5,9,10,17 This microorganism is also associated with various infections of ruminants 8 and humans. 1 Thus far, 23 capsular types have been characterized 6 and all of them have been isolated in North America. 7 Commonly, S. suis infections in swine are controlled by feed medication with penicillin at periods of highest risk, e.g., weaning. 3 Treatment of individual cases has to be undertaken early in the course of the disease to be successful. 3 Penicillin has been the treatment of choice, although some human cases have been difficult to treat using usual dosages of this antibiotic. 12,16,19 Penicillin-resistant isolates have been reported. In these studies, only isolates belonging to capsular types 1-8 were tested using the agar-disk diffusion method of Kirby-Bauer, and the percentage of resistance varied from 5 to 13%. 10,14,15 The main objective of this study was to determine the minimal inhibitory concentrations (MICs) of penicillin for representative strains of all known capsular types of S. suis. Because the blood supplement for the media in different laboratories may have varied, sheep blood and bovine blood were used to study the effect of different media on bacterial sensitivity to penicillin.Reference strains representing each of the 23 capsular types and 99 field isolates (22 capsular types) of S. suis recovered from diseased pigs were used to test for sensitivity to penicillin. The MIC was determined by an agar dilution method using a standard powder of postassium penicillin. a Concentrations of penicillin from 0.03 to 32.0 µg/ml were tested. The following control strains were used throughout the study: Staphylococcus aureus ATCC 29213 and ATCC 25923, Enterococcus faecalis ATCC 29212, and Streptococcus pneumoniae ATCC 35088.Susceptibility of the isolates and control strains was determined in nonsupplemented Mueller-Hinton medium agar b and in Mueller-Hinton medium agar supplemented either with 5% defibrinated sheep blood or 5% bovine blood. Logphase inocula were prepared by incubation of strains in Mueller-Hinton broth b at 37 C for 5 hours. The turbidity was then adjusted to a 0.5 McFarland nephelometer standard. An inoculum of 10 4 colony-forming units (CFU) per spot was applied to agar with a modified Steers replicator. c A control plate without penicillin was inoculated at the end of the procedure to make sure that all strains of S. suis can grow on this medium agar. The plates were incubated overnight at 37 C. The MIC was defined as the lowest concentration of the antibiotic at which there was no visible growth.

Antimicrobial Resistance Patterns and Plasmid Profiles of Streptococcus Suis Isolates

“…9,20,25 Most porcine S. suis isolates from Quebec were clindamycin, erythromycin, and tetracycline resistant, which is in accordance with data from Ontario. 20 Isolates from western Canada were less resistant to clindamycin and erythromycin than were those from Quebec.…”

“…However, penicillin-resistant beta-lactamase-negative isolates have recently been detected. 9 Resistance to other antimicrobial agents normally effective against gram-positive organisms, such as erythromycin, streptomycin, and tetracycline, has also been reported. 20,25 are associated with the ability to confer antimicrobial resistance among bacteria.…”

“…Streptococcus suis strains belonging to other capsular types and that are resistant to penicillin and are beta-lactamase negative have previously been reported. 9 As has been previously suggested, 9 antimicrobial susceptibility testing should be carried out on S.…”

Concentração inibitória mínima (CIM) de oito antimicrobianos frente isolados de Streptococcus suis

“…Porém, a introdução de animais contaminados nos plantéis, também pode levar ao aparecimento da doença em suínos recém desmamados ou em fase de crescimento. 3 Taxas de mortalidade mais altas ocorrem geralmente em rebanhos de terminação que compram e alojam leitões de diferentes origens e em rebanhos infectados pela primeira vez. 4 Infecções associadas à presença de S. suis são identificadas em várias espécies animais, tais como: ruminantes, eqüinos, aves e homem.…”

Identification of the Gene Encoding a 38-Kilodalton Immunogenic and Protective Antigen of Streptococcus suis

“…Strains of other serotypes, such as serotypes 1/2, 7, 9, and 14, can also cause disease. Attempts to control the infection are hindered by a lack of thorough knowledge of the virulence factors and protective antigens of the bacterium, the existence of multiple serotypes with diverse genetic makeups, and the evolution of multidrug-resistant strains (3,6,13,24).…”