First Case of Staphylococci Carrying Linezolid Resistance Genes from Laryngological Infections in Poland

Linezolid is currently used to treat infections caused by multidrug-resistant Gram-positive cocci. Both linezolid-resistant S. aureus (LRSA) and coagulase-negative staphylococci (CoNS) strains have been collected worldwide. Two isolates carrying linezolid resistance genes were recovered from laryngological patients and characterized by determining their antimicrobial resistance patterns and using molecular methods such as spa typing, MLST, SCCmec typing, detection of virulence genes and ica operon expression, and analysis of antimicrobial resistance determinants. Both isolates were multidrug resistant, including resistance to methicillin. The S. aureus strain was identified as ST-398/t4474/SCCmec IVe, harboring adhesin, hemolysin genes, and the ica operon. The S. haemolyticus strain was identified as ST-42/mecA-positive and harbored hemolysin genes. Linezolid resistance in S. aureus strain was associated with the mutations in the ribosomal proteins L3 and L4, and in S. haemolyticus, resistance was associated with the presence of cfr gene. Moreover, S. aureus strain harbored optrA and poxtA genes. We identified the first case of staphylococci carrying linezolid resistance genes from patients with chronic sinusitis in Poland. Since both S. aureus and CoNS are the most common etiological factors in laryngological infections, monitoring of such infections combined with surveillance and infection prevention programs is important to decrease the number of linezolid-resistant staphylococcal strains.

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Staphylococci among Wild European Rabbits from the Azores: A Potential Zoonotic Issue?

Journal of Food Protection ◽

10.4315/0362-028x.jfp-19-423 ◽

2020 ◽

Vol 83 (7) ◽

pp. 1110-1114 ◽

Cited By ~ 1

Author(s):

MARGARIDA SOUSA ◽

VANESSA SILVA ◽

ADRIANA SILVA ◽

NUNO SILVA ◽

JESSICA RIBEIRO ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Resistance Genes ◽

Meca Gene ◽

Diffusion Method ◽

Coagulase Negative Staphylococci ◽

Spa Typing ◽

Disk Diffusion Method ◽

Genetic Lineages ◽

Antimicrobial Resistance Genes ◽

European Rabbits

ABSTRACT The prevalence and diversity of Staphylococcus species from wild European rabbits (Oryctolagus cuniculus) in the Azores were investigated, and the antibiotic resistance phenotype and genotype of the isolates were determined. Nasal samples from 77 wild European rabbits from São Jorge and São Miguel islands in Azores were examined. Antibiotic susceptibility of the isolates was determined using the Kirby-Bauer disk diffusion method, and the presence of antimicrobial resistance genes and virulence factors was determined by PCR. The genetic lineages of S. aureus isolates were characterized by spa typing and multilocus sequence typing. A total of 49 staphylococci were obtained from 35 of the 77 wild rabbits. Both coagulase-positive (8.2%) and coagulase-negative (91.8%) staphylococci were detected: 4 S. aureus, 17 S. fleurettii, 13 S. sciuri, 7 S. xylosus, 4 S. epidermidis, and 1 each of S. simulans, S. saprophyticus, S. succinus, and S. equorum. The four S. aureus isolates showed methicillin susceptibility and were characterized as spa type t272/CC121, Panton-Valentine leukocidin negative, and hlB positive. Most of the coagulase-negative staphylococci showed resistance to fusidic acid and beta-lactams, and multidrug resistance was identified especially among S. epidermidis isolates. The mecA gene was detected in 20 isolates of the species S. fleurettii and S. epidermidis, associated with the blaZ gene in one S. epidermidis isolate. Five antimicrobial resistance genes were detected in one S. epidermidis isolate (mecA,dfrA,dfrG,aac6′-aph2′′, and ant4). Our results highlight that wild rabbits are reservoirs or “temporary hosts” of Staphylococcus species with zoonotic potential, some of them carrying relevant antimicrobial resistances. HIGHLIGHTS

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Antimicrobial resistance in coagulase-negative staphylococci isolated from subclinical mastitis in Ettawa Crossbred goat (PE) in Yogyakarta, Indonesia

Biodiversitas Journal of Biological Diversity ◽

10.13057/biodiv/d220650 ◽

2021 ◽

Vol 22 (6) ◽

Author(s):

Widodo Suwito ◽

WIDAGDO SRI NUGROHO ◽

AGNESIA ENDANG TRI HASTUTI WAHYUNI ◽

BAMBANG SUMIARTO

Keyword(s):

Antimicrobial Resistance ◽

Susceptibility Testing ◽

Clinical Laboratory ◽

Subclinical Mastitis ◽

Multidrug Resistant ◽

Resistance Rate ◽

Diffusion Method ◽

Disc Diffusion Method ◽

Coagulase Negative Staphylococci ◽

Resistance Patterns

Abstract. Suwito W, Nugroho WS, Wahyuni AETH, Sumiarto B. 2021. Antimicrobial resistance in coagulase-negative staphylococci isolated from subclinical mastitis in Ettawa Crossbred goat (PE) in Yogyakarta, Indonesia. Biodiversitas 22: 3418-3422. Subclinical mastitis (SCM) in Ettawa Crossbred Goat (PE) is most frequently caused by staphylococci with a significant reduction in milk yield. The aim of this study is to determine antimicrobial resistance patterns of coagulase-negative staphylococci (CoNS) from PE goat SCM. A total of 36 CoNS isolates originating from PE goat SCM were collected in semisolid tube use in this study. All CoNS isolates were further examined for antimicrobial susceptibility testing by the Kirby-Bauer disc diffusion method. Antibiotic susceptibility of CoNS isolated samples according to Clinical Laboratory Standards Institute (CLSI). The CoNS isolates showed the highest resistance rate against sulfamethoxazole (65%), ampicillin (55.56%), penicillin (45%), cefoxitin (33.33%), erythromycin (25%), oxytetracycline (20%), tetracycline (15%), gentamicin and neomycin (11.11%), while oxacillin was sensitive. The highest of multiple antimicrobials resistance observed 15% in ampicillin, penicillin and tetracycline, then 5-10% in ampicillin, penicillin, erythromycin, tetracycline and oxytetracycline. The majority of CoNS in this study were resistant to sulfamethoxazole and then, followed by ampicillin, penicillin, cefoxitin, erythromycin, oxytetracycline, tetracycline, gentamicin and neomycin. In addition, most isolates were penicillin-resistant and multidrug-resistant (MDR).

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Molecular Typing and Antimicrobial Susceptibility Profile of Staphylococcus aureus Isolates Recovered from Bovine Mastitis and Nasal Samples

10.20944/preprints202009.0115.v1 ◽

2020 ◽

Author(s):

Renata P. Santos ◽

Fernando N. Souza ◽

Ana Claudia C. Oliveira ◽

Antônio F. de Souza Filho ◽

Juliana Aizawa ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Antimicrobial Susceptibility ◽

Protein A ◽

Bovine Mastitis ◽

Multidrug Resistant ◽

Aureus Strain ◽

Staphylococcal Protein A ◽

Spa Typing ◽

Antimicrobial Susceptibility Profile ◽

High Level

In the present study, we aimed to determine the antimicrobial resistance and genetic structure of a population of S. aureus recovered from transient and persistent intramammary infections and nares/muzzles. We investigated the antimicrobial resistance of 189 S. aureus strains using a broad antimicrobial susceptibility profile. Furthermore, 107 S. aureus isolates were strain-typed using staphylococcal protein-A (spa) typing. Here, a great proportion of strains exhibited multidrug resistance to antimicrobials, including resistance to critically important antimicrobials, although no methicillin-resistant S. aureus strains were found. Our study did not strengthen the idea that extramammary niches (i.e., nares/muzzles) are an important source for S. aureus. A discrepancy in the antimicrobial resistance between S. aureus strains isolated from nasal/muzzles and milk samples was observed. Furthermore, S. aureus isolates from transient and persistent IMIs did not differ by spa typing, suggesting that the persistence of bovine IMIs was determined by cow factors. Thus, the high level of multidrug-resistant S. aureus found in the two herds studied together with the predominance of a well udder-adapted S. aureus strain may contribute to the history of the high prevalence of mastitis caused by S. aureus, leading to great animal and public health concerns.

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The Emergence of Linezolid-resistant Staphylococcus Epidermidis in the COVID-19 Hospitalized Intubated Patients in North Khorasan, Iran

10.21203/rs.3.rs-1033554/v1 ◽

2021 ◽

Author(s):

Amir Azimian ◽

Mahsa Khosrojerdi ◽

Hamed GhasemZadeh-Moghadam ◽

Hasan NamdarAhmad-Abad ◽

Seyed Ahmad Hashemi

Keyword(s):

Antimicrobial Resistance ◽

Staphylococcus Epidermidis ◽

Viral Infections ◽

Underlying Disease ◽

Resistance Pattern ◽

Bacterial Strains ◽

Coagulase Negative Staphylococci ◽

Linezolid Resistance ◽

Resistance Patterns ◽

Phenotypic Methods

Abstract BackgroundIn the COVID-19 pandemic from 2019 to date, we confront secondary bacterial and viral infections in SARS-CoV2 infected patients, especially hospitalized patients. Coagulase-negative staphylococci, are commensals of the human body and can lead to infections in immunocompromised patients. The antimicrobial resistance is increasingly reported in coagulase-negative staphylococci, especially in Staphylococcus epidermidis. One of the most critical problems is resistance to linezolid in S. epidermidis, observed in Europe since 2014. The aim of this study was to evaluation of bacterial Co-infections and determination of antimicrobial resistance pattern of co-infection isolated strains in North Khorasan, Iran, in the last six-month period. MethodsAfter microbiological evaluation of pulmonary samples of hospitalized intubated patients with signs of bacterial pneumonia, we found co-infection in 11 of 185 patients with S. epidermidis, S. aureus, and Acinetobacter baumani, respectively. Interestingly seven of nine S. epidermidis isolates were linezolid resistant. For identification of the isolates at the species level, we used phenotypic methods and also the Polymerase Chain Reaction (PCR) for the atlE gene. Selected isolates were characterized by determining their antimicrobial resistance patterns and using molecular methods including SCCmec typing, detection of ica, mecA, vanA, and cfr genes. ResultsAll isolates were resistant to methicillin, and Seven isolates were resistant to linezolid. It should be noted that all nine isolates were positive for the ica gene. Nine of 11 isolated have belonged to the SCCmec I, and two belonged to the SCCmec IV. It should be noted that all patients had the underlying disease and six patients died.ConclusionThe increasing linezolid resistance in bacterial strains becomes a real threat for patients, and monitoring such infections combined with surveillance and infection prevention programs is very important to decrease the number of linezolid-resistant staphylococcal strains.

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Diversities of antimicrobial resistance patterns across Staphylococcus aureus and Coagulase-Negative Staphylococci isolated from dairy herbs in Jiangsu province, China

10.21203/rs.3.rs-80176/v1 ◽

2020 ◽

Author(s):

Weijie Jin ◽

Weidong Lin ◽

Qing Feng ◽

Dashuai Zhang ◽

Juan Yang ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Subclinical Mastitis ◽

Jiangsu Province ◽

The Other ◽

Multiple Drug ◽

Drug Resistant ◽

Coagulase Negative Staphylococci ◽

Resistance Patterns

Abstract Background As mastitis major causing agents, Coagulase-Negative Staphylococci (CNS) and Staphylococcus aureus (SA), are important and their connections are special and worth comparing. The overall aim of this study is to investigate antimicrobial resistance patterns of CNS and SA. Understanding the special characters of staphylococci is essential for finding the precise strategies or directions against them. Results Staphylococci (47.63%) were the commonest pathogens in subclinical mastitis in Jiangsu province. 73.34% and 45.78% of CNS respectively were extensively drug-resistant (XDR) strains and multiple drug-resistant (MDR) strains, mainly resisting penicillin (77.78%) and ceftazidime (55.95%); for SA, 62.52% of them were MDR strains and resistant to penicillin (94.05%) and norfloxacin (58.33%). Notably, 4 CNS were pandrug-resistant (PDR) strains. According to the chi-square test results, we summary and find that SA was more resistant to quinolones (ciprofloxacin, levofloxacin, and norfloxacin) and co-trimoxazole antibiotics than CNS, significantly; on the other hand, CNS were significantly more resistant to lincomycins (clindamycin), macrolides (including erythromycin and clarithromycin), tetracycline, and nitrofurantoin antibiotics than SA,, in total. Resistance genes were detected more frequently in CNS than SA; nearly a third of CNS resit penicillin by β-lactamase coded by blaZ and CNS resist tetracycline mainly by protein pump mechanism. For SA, blaZ was detected out 27.2%, and the other five resistance genes were rare to be found. Conclusion Responding to antibiotics interfering with metabolisms of nucleotide, SA might be more resistant than CNS; while CNS strains are more likely to become mutations to survive under the stress of antibiotics interfering with protein synthesis. These might provide the advantages for CNS to represent like a reservoir of resistance genes for other staphylococci as the previous researches’ assumption.

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Distribution and Clonal Diversity of Staphylococcus aureus and Other Staphylococci in Surface Waters: Detection of ST425-t742 and ST130-t843 mecC-Positive MRSA Strains

Antibiotics ◽

10.3390/antibiotics10111416 ◽

2021 ◽

Vol 10 (11) ◽

pp. 1416

Author(s):

Vanessa Silva ◽

Eugénia Ferreira ◽

Vera Manageiro ◽

Lígia Reis ◽

María Teresa Tejedor-Junco ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Multidrug Resistance ◽

Antimicrobial Resistance ◽

Virulence Factors ◽

Resistance Genes ◽

Surface Waters ◽

Water Samples ◽

Coagulase Negative Staphylococci ◽

Spa Typing ◽

Antimicrobial Resistance Genes

Natural aquatic environments represent one of the most important vehicles of bacterial dissemination. Therefore, we aimed to isolate staphylococci from surface waters and to investigate the presence of antimicrobial resistance genes and virulence factors as well as the genetic lineages of all Staphylococcus aureus isolates. Staphylococci were recovered from water samples collected from 78 surface waters, including rivers, streams, irrigation ditches, dams, lakes, and fountains. The presence of antimicrobial resistance genes and virulence factors was investigated by PCR. Multilocus sequence typing and spa-typing were performed in all S. aureus isolates. From the 78 water samples, 33 S. aureus, one S. pseudintermedius, and 51 coagulase-negative staphylococci (CoNS) were identified. Among the S. aureus isolates, four MRSA were identified, and all harbored the mecC gene. Fourteen S. aureus were susceptible to all antimicrobials tested and the remaining showed resistance to penicillin, erythromycin and/or tetracycline encoded by the blaZ, ermT, msr(A/B), tetL, and vgaA genes. Regarding the clonal lineages, one mecC-MRSA isolate belonged to spa-type t843 and sequence type (ST) 130 and the other three to t742 and ST425. The remaining S. aureus were ascribed 14 spa-types and 17 sequence types. Eleven species of CoNS were isolated: S. sciuri, S. lentus, S. xylosus, S. epidermidis, S. cohnii spp. urealyticus, S. vitulinus, S. caprae, S. carnosus spp. Carnosus, S. equorum, S. simulans, and S. succinus. Thirteen CoNS isolates had a multidrug resistance profile and carried the following genes: mecA, msr(A/B), mph(C), aph(3′)-IIIa, aac(6′)-Ie–aph(2′’)-Ia, dfrA, fusB, catpC221, and tetK. A high diversity of staphylococci was isolated from surface waters including mecCMRSA strains and isolates presenting multidrug-resistance profiles. Studies on the prevalence of antibiotic-resistant staphylococci in surface waters are still very scarce but extremely important to estimate the contribution of the aquatic environment in the spread of these bacteria.

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Antimicrobial Resistance and Presence of Class 1 Integrons Among Different Serotypes of Salmonella spp. Recovered From Children with Diarrhea in Tehran, Iran

Infectious Disorders - Drug Targets ◽

10.2174/1871526519666190130171020 ◽

2020 ◽

Vol 20 (2) ◽

pp. 160-166

Author(s):

Seyedeh Hanieh Eshaghi Zadeh ◽

Hossein Fahimi ◽

Fatemeh Fardsanei ◽

Mohammad Mehdi Soltan Dallal

Keyword(s):

Antibiotic Resistance ◽

Antimicrobial Resistance ◽

Multidrug Resistant ◽

Salmonella Spp ◽

Class 1 Integron ◽

Class 1 Integrons ◽

Food Borne ◽

Class 1 ◽

Resistance Patterns ◽

C 30

Background: Salmonellosis is a major food-borne disease worldwide. The increasing prevalence of antimicrobial resistance among food-borne pathogens such as Salmonella spp. is concerning. Objective: The main objective of this study is to identify class 1 integron genes and to determine antibiotic resistance patterns among Salmonella isolates from children with diarrhea. Methods: A total of 30 Salmonella isolates were recovered from children with diarrhea. The isolates were characterized for antimicrobial susceptibility and screened for the presence of class 1 integron genes (i.e. intI1, sulI1, and qacEΔ1). Results: The most prevalent serotype was Enteritidis 36.7%, followed by Paratyphi C (30%), and Typhimurium (16.7%). The highest rates of antibiotic resistance were obtained for nalidixic acid (53.3%), followed by streptomycin (40%), and tetracycline (36.7%). Regarding class 1 integrons, 36.7%, 26.7%, and 33.3% of the isolates carried intI1, SulI, and qacEΔ1, respectively, most of which (81.8%) were multidrug-resistant (MDR). Statistical analysis revealed that the presence of class 1 integron was significantly associated with resistance to streptomycin and tetracycline (p = 0.042). However, there was no association between class 1 integron and other antibiotics used in this study (p > 0.05). Conclusion: The high frequency of integron class 1 gene in MDR Salmonella strains indicates that these mobile genetic elements are versatile among different Salmonella serotypes, and associated with reduced susceptibility to many antimicrobials.

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Detection of extended spectrum beta-lactamase genes in Pseudomonas aeruginosa isolated from patients in rural Eastern Cape Province, South Africa

Scientific Reports ◽

10.1038/s41598-021-86570-y ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Mojisola C. Hosu ◽

Sandeep D. Vasaikar ◽

Grace E. Okuthe ◽

Teke Apalata

Keyword(s):

Pseudomonas Aeruginosa ◽

Antimicrobial Resistance ◽

Multidrug Resistant ◽

High Rate ◽

Infection Prevention And Control ◽

Beta Lactamase ◽

Eastern Cape ◽

Extended Spectrum Beta Lactamase ◽

Extended Spectrum ◽

Resistance Patterns

AbstractThe proliferation of extended spectrum beta-lactamase (ESBL) producing Pseudomonas aeruginosa represent a major public health threat. In this study, we evaluated the antimicrobial resistance patterns of P. aeruginosa strains and characterized the ESBLs and Metallo- β-lactamases (MBL) produced. Strains of P. aeruginosa cultured from patients who attended Nelson Mandela Academic Hospital and other clinics in the four district municipalities of the Eastern Cape between August 2017 and May 2019 were identified; antimicrobial susceptibility testing was carried out against thirteen clinically relevant antibiotics using the BioMérieux VITEK 2 and confirmed by Beckman autoSCAN-4 System. Real-time PCR was done using Roche Light Cycler 2.0 to detect the presence of ESBLs; blaSHV, blaTEM and blaCTX-M genes; and MBLs; blaIMP, blaVIM. Strains of P. aeruginosa demonstrated resistance to wide-ranging clinically relevant antibiotics including piperacillin (64.2%), followed by aztreonam (57.8%), cefepime (51.5%), ceftazidime (51.0%), piperacillin/tazobactam (50.5%), and imipenem (46.6%). A total of 75 (36.8%) multidrug-resistant (MDR) strains were observed of the total pool of isolates. The blaTEM, blaSHV and blaCTX-M was detected in 79.3%, 69.5% and 31.7% isolates (n = 82), respectively. The blaIMP was detected in 1.25% while no blaVIM was detected in any of the strains tested. The study showed a high rate of MDR P. aeruginosa in our setting. The vast majority of these resistant strains carried blaTEM and blaSHV genes. Continuous monitoring of antimicrobial resistance and strict compliance towards infection prevention and control practices are the best defence against spread of MDR P. aeruginosa.

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Serotype distribution, antimicrobial susceptibility, antimicrobial resistance genes and virulence genes of Salmonella isolated from a pig slaughterhouse in Yangzhou, China

AMB Express ◽

10.1186/s13568-019-0936-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Quan Li ◽

Jian Yin ◽

Zheng Li ◽

Zewei Li ◽

Yuanzhao Du ◽

...

Keyword(s):

Public Health ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Antimicrobial Susceptibility ◽

Virulence Genes ◽

Multidrug Resistant ◽

Resistance Rate ◽

Economic Losses ◽

Production Chain ◽

Antimicrobial Resistance Genes

AbstractSalmonella is an important food-borne pathogen associated with public health and high economic losses. To investigate the prevalence and the characteristics of Salmonella in a pig slaughterhouse in Yangzhou, a total of 80 Salmonella isolates were isolated from 459 (17.43%) samples in 2016–2017. S. Derby (35/80, 43.75%) was the most prevalent, followed by S. Rissen (16/80, 20.00%) and S. Newlands (11/80, 13.75%). The highest rates of susceptibility were observed to cefoxitin (80/80, 100.0%) and amikacin (80/80, 100.0%), followed by aztreonam (79/80, 98.75%) and nitrofurantoin (79/80, 98.75%). The highest resistance rate was detected for tetracycline (65/80, 81.25%), followed by ampicillin (60/80, 75.00%), bactrim (55/80, 68.75%), and sulfisoxazole (54/80, 67.50%). Overall, 91.25% (73/80) of the isolates were resistant to at least one antibiotic, while 71.25% (57/80) of the isolate strains were multidrug resistant in the antimicrobial susceptibility tested. In addition, 86.36% (19/22) of the 22 antimicrobial resistance genes in the isolates were identified. Our data indicated that the resistance to certain antimicrobials was significantly associated, in part, with antimicrobial resistance genes. Furthermore, 81.25% (65/80) isolates harbored the virulence gene of mogA, of which 2 Salmonella Typhimurium isolates carried the mogA, spvB and spvC virulence genes at the same time. The results showed that swine products in the slaughterhouse were contaminated with multidrug resistant Salmonella commonly, especially some isolates carry the spv virulence genes. The virulence genes might facilitate the dissemination of the resistance genes to consumers along the production chain, suggesting the importance of controlling Salmonella during slaughter for public health.

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Comparison of Prevalence, Antimicrobial Resistance, and Occurrence of Multidrug-Resistant Salmonella in Antimicrobial-Free and Conventional Pig Production

Journal of Food Protection ◽

10.4315/0362-028x-69.4.743 ◽

2006 ◽

Vol 69 (4) ◽

pp. 743-748 ◽

Cited By ~ 39

Author(s):

WONDWOSSEN A. GEBREYES ◽

SIDDHARTHA THAKUR ◽

W. E. MORGAN MORROW

Keyword(s):

Antimicrobial Resistance ◽

Production Systems ◽

Multidrug Resistant ◽

Resistance Pattern ◽

Swine Production ◽

Significant Difference ◽

Conventional Farms ◽

Resistance Patterns ◽

Conventional Systems ◽

On Farm

Conventional swine production evolved to routinely use antimicrobials, and common occurrence of antimicrobial-resistant Salmonella has been reported. There is a paucity of information on the antimicrobial resistance of Salmonella in swine production in the absence of antimicrobial selective pressure. Therefore, we compared the prevalence and antimicrobial resistance of Salmonella isolated from antimicrobial-free and conventional production systems. A total of 889 pigs and 743 carcasses were sampled in the study. Salmonella prevalence was significantly higher among the antimicrobial-free systems (15.2%) than the conventional systems (4.2%) (odds ratio [OR] = 4.23; P < 0.05). Antimicrobial resistance was detected against 10 of the 12 antimicrobials tested. The highest frequency of resistance was found against tetracycline (80%), followed by streptomycin (43.4%) and sulfamethoxazole (36%). Frequency of resistance to most classes of antimicrobials (except tetracycline) was significantly higher among conventional farms than antimicrobial-free farms, with ORs ranging from 2.84 for chloramphenicol to 23.22 for kanamycin at the on-farm level. A total of 28 antimicrobial resistance patterns were detected. A resistance pattern with streptomycin, sulfamethoxazole, and tetracycline (n = 130) was the most common multidrug resistance pattern. There was no significant difference in the proportion of isolates with this pattern between the conventional (19.5%) and the antimicrobial-free systems (18%) (OR = 1.8; P > 0.05). A pentaresistance pattern with ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline was strongly associated with antimicrobial-free groups (OR = 5.4; P = 0.01). While showing the higher likelihood of finding antimicrobial resistance among conventional herds, this study also implies that specific multidrug-resistant strains may occur on antimicrobial-free farms. A longitudinal study with a representative sample size is needed to reach more conclusive results of the associations detected in this study.

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